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Wright CS, Lewis KJ, Semon K, Yi X, Reyes Fernandez PC, Rust K, Prideaux M, Schneider A, Pederson M, Deosthale P, Plotkin LI, Hum JM, Sankar U, Farach-Carson MC, Robling AG, Thompson WR. Deletion of the auxiliary α2δ1 voltage sensitive calcium channel subunit in osteocytes and late-stage osteoblasts impairs femur strength and load-induced bone formation in male mice. J Bone Miner Res 2024; 39:298-314. [PMID: 38477790 DOI: 10.1093/jbmr/zjae010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Revised: 12/03/2023] [Accepted: 12/27/2023] [Indexed: 03/14/2024]
Abstract
Osteocytes sense and respond to mechanical force by controlling the activity of other bone cells. However, the mechanisms by which osteocytes sense mechanical input and transmit biological signals remain unclear. Voltage-sensitive calcium channels (VSCCs) regulate calcium (Ca2+) influx in response to external stimuli. Inhibition or deletion of VSCCs impairs osteogenesis and skeletal responses to mechanical loading. VSCC activity is influenced by its auxiliary subunits, which bind the channel's α1 pore-forming subunit to alter intracellular Ca2+ concentrations. The α2δ1 auxiliary subunit associates with the pore-forming subunit via a glycosylphosphatidylinositol anchor and regulates the channel's calcium-gating kinetics. Knockdown of α2δ1 in osteocytes impairs responses to membrane stretch, and global deletion of α2δ1 in mice results in osteopenia and impaired skeletal responses to loading in vivo. Therefore, we hypothesized that the α2δ1 subunit functions as a mechanotransducer, and its deletion in osteocytes would impair skeletal development and load-induced bone formation. Mice (C57BL/6) with LoxP sequences flanking Cacna2d1, the gene encoding α2δ1, were crossed with mice expressing Cre under the control of the Dmp1 promoter (10 kb). Deletion of α2δ1 in osteocytes and late-stage osteoblasts decreased femoral bone quantity (P < .05) by DXA, reduced relative osteoid surface (P < .05), and altered osteoblast and osteocyte regulatory gene expression (P < .01). Cacna2d1f/f, Cre + male mice displayed decreased femoral strength and lower 10-wk cancellous bone in vivo micro-computed tomography measurements at the proximal tibia (P < .01) compared to controls, whereas Cacna2d1f/f, Cre + female mice showed impaired 20-wk cancellous and cortical bone ex vivo micro-computed tomography measurements (P < .05) vs controls. Deletion of α2δ1 in osteocytes and late-stage osteoblasts suppressed load-induced calcium signaling in vivo and decreased anabolic responses to mechanical loading in male mice, demonstrating decreased mechanosensitivity. Collectively, the α2δ1 auxiliary subunit is essential for the regulation of osteoid-formation, femur strength, and load-induced bone formation in male mice.
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Affiliation(s)
- Christian S Wright
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
| | - Karl J Lewis
- Department of Biomedical Engineering, Cornell University, Ithaca, NY 14850, United States
| | - Katelyn Semon
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
| | - Xin Yi
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
| | - Perla C Reyes Fernandez
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
| | - Katie Rust
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
| | - Matthew Prideaux
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
| | - Artur Schneider
- Department of Physiology, College of Osteopathic Medicine, Marian University, Indianapolis, IN 46202, United States
| | - Molly Pederson
- School of Science, Indiana University-Purdue University, Indianapolis, IN 46202, United States
| | - Padmini Deosthale
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
| | - Lilian I Plotkin
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
| | - Julia M Hum
- Department of Physiology, College of Osteopathic Medicine, Marian University, Indianapolis, IN 46202, United States
| | - Uma Sankar
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
| | - Mary C Farach-Carson
- Department of Diagnostic and Biomedical Sciences, School of Dentistry, University of Texas, Health Science Center, Houston, TX 78712, United States
| | - Alexander G Robling
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
| | - William R Thompson
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indianapolis, IN 46202, United States
- Department of Anatomy & Cell Biology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States
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Kelly MM, Sharma K, Wright CS, Yi X, Reyes Fernandez PC, Gegg AT, Gorrell TA, Noonan ML, Baghdady A, Sieger JA, Dolphin AC, Warden SJ, Deosthale P, Plotkin LI, Sankar U, Hum JM, Robling AG, Farach-Carson MC, Thompson WR. Loss of the auxiliary α 2δ 1 voltage-sensitive calcium channel subunit impairs bone formation and anabolic responses to mechanical loading. JBMR Plus 2024; 8:ziad008. [PMID: 38505532 PMCID: PMC10945727 DOI: 10.1093/jbmrpl/ziad008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Revised: 10/31/2023] [Accepted: 11/27/2023] [Indexed: 03/21/2024] Open
Abstract
Voltage-sensitive calcium channels (VSCCs) influence bone structure and function, including anabolic responses to mechanical loading. While the pore-forming (α1) subunit of VSCCs allows Ca2+ influx, auxiliary subunits regulate the biophysical properties of the pore. The α2δ1 subunit influences gating kinetics of the α1 pore and enables mechanically induced signaling in osteocytes; however, the skeletal function of α2δ1 in vivo remains unknown. In this work, we examined the skeletal consequences of deleting Cacna2d1, the gene encoding α2δ1. Dual-energy X-ray absorptiometry and microcomputed tomography imaging demonstrated that deletion of α2δ1 diminished bone mineral content and density in both male and female C57BL/6 mice. Structural differences manifested in both trabecular and cortical bone for males, while the absence of α2δ1 affected only cortical bone in female mice. Deletion of α2δ1 impaired skeletal mechanical properties in both sexes, as measured by three-point bending to failure. While no changes in osteoblast number or activity were found for either sex, male mice displayed a significant increase in osteoclast number, accompanied by increased eroded bone surface and upregulation of genes that regulate osteoclast differentiation. Deletion of α2δ1 also rendered the skeleton insensitive to exogenous mechanical loading in males. While previous work demonstrates that VSCCs are essential for anabolic responses to mechanical loading, the mechanism by which these channels sense and respond to force remained unclear. Our data demonstrate that the α2δ1 auxiliary VSCC subunit functions to maintain baseline bone mass and strength through regulation of osteoclast activity and also provides skeletal mechanotransduction in male mice. These data reveal a molecular player in our understanding of the mechanisms by which VSCCs influence skeletal adaptation.
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Affiliation(s)
- Madison M Kelly
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
| | - Karan Sharma
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
| | - Christian S Wright
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
| | - Xin Yi
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
| | - Perla C Reyes Fernandez
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
| | - Aaron T Gegg
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
| | - Taylor A Gorrell
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
| | - Megan L Noonan
- Department of Medical and Molecular Genetics, Indiana University, Indianapolis, IN 46202, United States
| | - Ahmed Baghdady
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
| | - Jacob A Sieger
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
| | - Annette C Dolphin
- Department of Neuroscience, Physiology and Pharmacology, University College of London, Gower Street, London WC1E 6BT, United Kingdom
| | - Stuart J Warden
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Melbourne Victoria 3086, DX 211319, Australia
| | - Padmini Deosthale
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy, Cell Biology, & Physiology, Indiana University, Indianapolis, IN 46202, United States
| | - Lilian I Plotkin
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy, Cell Biology, & Physiology, Indiana University, Indianapolis, IN 46202, United States
| | - Uma Sankar
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy, Cell Biology, & Physiology, Indiana University, Indianapolis, IN 46202, United States
| | - Julia M Hum
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
| | - Alexander G Robling
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy, Cell Biology, & Physiology, Indiana University, Indianapolis, IN 46202, United States
| | - Mary C Farach-Carson
- Department of Diagnostic & Biomedical Sciences, University of Texas Health Science Center at Houston School of Dentistry, Houston, TX 77054, United States
| | - William R Thompson
- Department of Physical Therapy, School of Health and Human Sciences, Indiana University, Indianapolis, IN 46202, United States
- College of Osteopathic Medicine, Marian University, Indianapolis, IN 46222, United States
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN 46202, United States
- Department of Anatomy, Cell Biology, & Physiology, Indiana University, Indianapolis, IN 46202, United States
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Nile M, Folwaczny M, Wichelhaus A, Baumert U, Janjic Rankovic M. Fluid flow shear stress and tissue remodeling-an orthodontic perspective: evidence synthesis and differential gene expression network analysis. Front Bioeng Biotechnol 2023; 11:1256825. [PMID: 37795174 PMCID: PMC10545883 DOI: 10.3389/fbioe.2023.1256825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Accepted: 08/28/2023] [Indexed: 10/06/2023] Open
Abstract
Introduction: This study aimed to identify and analyze in vitro studies investigating the biological effect of fluid-flow shear stress (FSS) on cells found in the periodontal ligament and bone tissue. Method: We followed the PRISMA guideline for systematic reviews. A PubMed search strategy was developed, studies were selected according to predefined eligibility criteria, and the risk of bias was assessed. Relevant data related to cell source, applied FSS, and locus-specific expression were extracted. Based on this evidence synthesis and, as an original part of this work, analysis of differential gene expression using over-representation and network-analysis was performed. Five relevant publicly available gene expression datasets were analyzed using gene set enrichment analysis (GSEA). Result: A total of 6,974 articles were identified. Titles and abstracts were screened, and 218 articles were selected for full-text assessment. Finally, 120 articles were included in this study. Sample size determination and statistical analysis related to methodological quality and the ethical statement item in reporting quality were most frequently identified as high risk of bias. The analyzed studies mostly used custom-made fluid-flow apparatuses (61.7%). FSS was most frequently applied for 0.5 h, 1 h, or 2 h, whereas FSS magnitudes ranged from 6 to 20 dyn/cm2 depending on cell type and flow profile. Fluid-flow frequencies of 1 Hz in human cells and 1 and 5 Hz in mouse cells were mostly applied. FSS upregulated genes/metabolites responsible for tissue formation (AKT1, alkaline phosphatase, BGLAP, BMP2, Ca2+, COL1A1, CTNNB1, GJA1, MAPK1/MAPK3, PDPN, RUNX2, SPP1, TNFRSF11B, VEGFA, WNT3A) and inflammation (nitric oxide, PGE-2, PGI-2, PTGS1, PTGS2). Protein-protein interaction networks were constructed and analyzed using over-representation analysis and GSEA to identify shared signaling pathways. Conclusion: To our knowledge, this is the first review giving a comprehensive overview and discussion of methodological technical details regarding fluid flow application in 2D cell culture in vitro experimental conditions. Therefore, it is not only providing valuable information about cellular molecular events and their quantitative and qualitative analysis, but also confirming the reproducibility of previously published results.
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Affiliation(s)
- Mustafa Nile
- Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU Munich, Munich, Germany
| | - Matthias Folwaczny
- Department of Conservative Dentistry and Periodontology, LMU University Hospital, LMU Munich, Munich, Germany
| | - Andrea Wichelhaus
- Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU Munich, Munich, Germany
| | - Uwe Baumert
- Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU Munich, Munich, Germany
| | - Mila Janjic Rankovic
- Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU Munich, Munich, Germany
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Assanah F, Grassie K, Anderson H, Xin X, Rowe D, Khan Y. Ultrasound-derived mechanical stimulation of cell-laden collagen hydrogels for bone repair. J Biomed Mater Res A 2023; 111:1200-1215. [PMID: 36728346 DOI: 10.1002/jbm.a.37508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 01/12/2023] [Accepted: 01/20/2023] [Indexed: 02/03/2023]
Abstract
Cell therapy is emerging as an effective treatment strategy for many diseases. Here we describe a novel approach to bone tissue repair that combines hydrogel-based cell therapy with low intensity pulsed ultrasound (LIPUS), an FDA approved treatment for fracture repair. Bone marrow-derived stromal cells (BMSCs) have been encapsulated in type I collagen hydrogels and mechanically stimulated using LIPUS-derived acoustic radiation force (ARF). We observed the expression and upward trend of load-sensitive, osteoblast-specific markers and determined that the extent of cell response is dependent on an optimal combination of both hydrogel stiffness and ARF intensity. Specifically, cells encapsulated in hydrogels of optimal stiffness respond at the onset of ultrasound by upregulating early bone-sensitive markers such as calcium, cyclooxygenase-2, and prostaglandin E2 , and later by supporting mineralized tissue formation after 21 days of culture. In vivo evaluation of a critical size calvarial defect in NOD scid gamma (NSG) mice indicated that the implantation of BMSC-laden hydrogels of optimal stiffness improved healing of calvarial defects after daily administration of ARF over 4 weeks. Collectively, these findings validate the efficacy of our system of localized cell delivery for treating bone defects where undifferentiated BMSCs are induced to the osteoblastic lineage. Further, in vivo healing may be enhanced via non-invasive transdermal mechanical stimulation of implanted cells using ARF.
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Affiliation(s)
- Fayekah Assanah
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
- Connecticut Convergence Institute for Translation in Regenerative Engineering, UCONN Health, Farmington, Connecticut, USA
| | - Kevin Grassie
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
- Connecticut Convergence Institute for Translation in Regenerative Engineering, UCONN Health, Farmington, Connecticut, USA
| | - Hanna Anderson
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
- Connecticut Convergence Institute for Translation in Regenerative Engineering, UCONN Health, Farmington, Connecticut, USA
| | - Xiaonan Xin
- Center for Regenerative Medicine and Skeletal Development, UCONN School of Dental Medicine, Farmington, Connecticut, USA
| | - David Rowe
- Center for Regenerative Medicine and Skeletal Development, UCONN School of Dental Medicine, Farmington, Connecticut, USA
| | - Yusuf Khan
- Department of Biomedical Engineering, University of Connecticut, Storrs, Connecticut, USA
- Connecticut Convergence Institute for Translation in Regenerative Engineering, UCONN Health, Farmington, Connecticut, USA
- Department of Orthopedic Surgery, UCONN Health, Farmington, Connecticut, USA
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Zhong W, Pathak JL, Liang Y, Zhytnik L, Pals G, Eekhoff EMW, Bravenboer N, Micha D. The intricate mechanism of PLS3 in bone homeostasis and disease. Front Endocrinol (Lausanne) 2023; 14:1168306. [PMID: 37484945 PMCID: PMC10361617 DOI: 10.3389/fendo.2023.1168306] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 06/19/2023] [Indexed: 07/25/2023] Open
Abstract
Since our discovery in 2013 that genetic defects in PLS3 lead to bone fragility, the mechanistic details of this process have remained obscure. It has been established that PLS3 variants cause syndromic and nonsyndromic osteoporosis as well as osteoarthritis. PLS3 codes for an actin-bundling protein with a broad pattern of expression. As such, it is puzzling how PLS3 specifically leads to bone-related disease presentation. Our review aims to summarize the current state of knowledge regarding the function of PLS3 in the predominant cell types in the bone tissue, the osteocytes, osteoblasts and osteoclasts. This is related to the role of PLS3 in regulating mechanotransduction, calcium regulation, vesicle trafficking, cell differentiation and mineralization as part of the complex bone pathology presented by PLS3 defects. Considering the consequences of PLS3 defects on multiple aspects of bone tissue metabolism, our review motivates the study of its mechanism in bone diseases which can potentially help in the design of suitable therapy.
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Affiliation(s)
- Wenchao Zhong
- Department of Human Genetics, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Department of Clinical Chemistry, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Amsterdam Movement Sciences, Tissue Function And Regeneration, Amsterdam, Netherlands
- Department of Temporomandibular Joint, Guangdong Engineering Research Center of Oral Restoration and Reconstruction, Guangzhou Key Laboratory of Basic and Applied Research of Oral Regenerative Medicine, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
| | - Janak L. Pathak
- Department of Temporomandibular Joint, Guangdong Engineering Research Center of Oral Restoration and Reconstruction, Guangzhou Key Laboratory of Basic and Applied Research of Oral Regenerative Medicine, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, Guangdong, China
| | - Yueting Liang
- Department of Radiation Oncology, Peking University Cancer Hospital & Institute, Beijing, China
- The Second Clinical College, Guangzhou Medical University, Guangzhou, China
| | - Lidiia Zhytnik
- Department of Human Genetics, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Amsterdam Movement Sciences, Tissue Function And Regeneration, Amsterdam, Netherlands
- Department of Traumatology and Orthopaedics, Institute of Clinical Medicine, The University of Tartu, Tartu, Estonia
| | - Gerard Pals
- Department of Human Genetics, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Amsterdam Movement Sciences, Tissue Function And Regeneration, Amsterdam, Netherlands
| | - Elisabeth M. W. Eekhoff
- Department Internal Medicine Section Endocrinology and Metabolism, Amsterdam UMC Location Vrije Universiteit Amsterdam, Rare Bone Disease Center, AMS, Amsterdam, Netherlands
- Amsterdam Reproduction and Development Research Institute, Amsterdam, Netherlands
| | - Nathalie Bravenboer
- Department of Clinical Chemistry, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Amsterdam Movement Sciences, Tissue Function And Regeneration, Amsterdam, Netherlands
| | - Dimitra Micha
- Department of Human Genetics, Amsterdam UMC Location Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- Amsterdam Movement Sciences, Tissue Function And Regeneration, Amsterdam, Netherlands
- Amsterdam Reproduction and Development Research Institute, Amsterdam, Netherlands
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6
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Zhao D, Wu J, Acosta FM, Xu H, Jiang JX. Connexin 43 hemichannels and prostaglandin E 2 release in anabolic function of the skeletal tissue to mechanical stimulation. Front Cell Dev Biol 2023; 11:1151838. [PMID: 37123401 PMCID: PMC10133519 DOI: 10.3389/fcell.2023.1151838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 04/05/2023] [Indexed: 05/02/2023] Open
Abstract
Bone adapts to changes in the physical environment by modulating remodeling through bone resorption and formation to maintain optimal bone mass. As the most abundant connexin subtype in bone tissue, connexin 43 (Cx43)-forming hemichannels are highly responsive to mechanical stimulation by permitting the exchange of small molecules (<1.2 kDa) between bone cells and the extracellular environment. Upon mechanical stimulation, Cx43 hemichannels facilitate the release of prostaglandins E2 (PGE2), a vital bone anabolic factor from osteocytes. Although most bone cells are involved in mechanosensing, osteocytes are the principal mechanosensitive cells, and PGE2 biosynthesis is greatly enhanced by mechanical stimulation. Mechanical stimulation-induced PGE2 released from osteocytic Cx43 hemichannels acts as autocrine effects that promote β-catenin nuclear accumulation, Cx43 expression, gap junction function, and protects osteocytes against glucocorticoid-induced osteoporosis in cultured osteocytes. In vivo, Cx43 hemichannels with PGE2 release promote bone formation and anabolism in response to mechanical loading. This review summarizes current in vitro and in vivo understanding of Cx43 hemichannels and extracellular PGE2 release, and their roles in bone function and mechanical responses. Cx43 hemichannels could be a significant potential new therapeutic target for treating bone loss and osteoporosis.
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Affiliation(s)
- Dezhi Zhao
- School of Medicine, Northwest University, Xi’an, China
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
- School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Jiawei Wu
- School of Medicine, Northwest University, Xi’an, China
| | - Francisca M. Acosta
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
| | - Huiyun Xu
- School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Jean X. Jiang
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, United States
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7
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Choi JUA, Kijas AW, Lauko J, Rowan AE. The Mechanosensory Role of Osteocytes and Implications for Bone Health and Disease States. Front Cell Dev Biol 2022; 9:770143. [PMID: 35265628 PMCID: PMC8900535 DOI: 10.3389/fcell.2021.770143] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 12/13/2021] [Indexed: 12/14/2022] Open
Abstract
Bone homeostasis is a dynamic equilibrium between bone-forming osteoblasts and bone-resorbing osteoclasts. This process is primarily controlled by the most abundant and mechanosensitive bone cells, osteocytes, that reside individually, within chambers of porous hydroxyapatite bone matrix. Recent studies have unveiled additional functional roles for osteocytes in directly contributing to local matrix regulation as well as systemic roles through endocrine functions by communicating with distant organs such as the kidney. Osteocyte function is governed largely by both biochemical signaling and the mechanical stimuli exerted on bone. Mechanical stimulation is required to maintain bone health whilst aging and reduced level of loading are known to result in bone loss. To date, both in vivo and in vitro approaches have been established to answer important questions such as the effect of mechanical stimuli, the mechanosensors involved, and the mechanosensitive signaling pathways in osteocytes. However, our understanding of osteocyte mechanotransduction has been limited due to the technical challenges of working with these cells since they are individually embedded within the hard hydroxyapatite bone matrix. This review highlights the current knowledge of the osteocyte functional role in maintaining bone health and the key regulatory pathways of these mechanosensitive cells. Finally, we elaborate on the current therapeutic opportunities offered by existing treatments and the potential for targeting osteocyte-directed signaling.
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Affiliation(s)
- Jung Un Ally Choi
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, Australia
| | - Amanda W Kijas
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, Australia
| | - Jan Lauko
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, Australia
| | - Alan E Rowan
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, Australia
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8
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Altered mechanotransduction in adolescent idiopathic scoliosis osteoblasts: an exploratory in vitro study. Sci Rep 2022; 12:1846. [PMID: 35115632 PMCID: PMC8813918 DOI: 10.1038/s41598-022-05918-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 01/14/2022] [Indexed: 11/16/2022] Open
Abstract
Adolescent idiopathic scoliosis (AIS) is the most prevalent pediatric spinal deformity. We previously demonstrated elongated cilia and an altered molecular mechanosensory response in AIS osteoblasts. The purpose of this exploratory study was to characterize the mechanosensory defect occurring in AIS osteoblasts. We found that cilia length dynamics in response to flow significantly differ in AIS osteoblasts compared to control cells. In addition, strain-induced rearrangement of actin filaments was compromised resulting in a failure of AIS osteoblasts to position or elongate in function of the bidirectional-applied flow. Contrary to control osteoblasts, fluid flow had an inhibitory effect on AIS cell migration. Moreover, flow induced an increase in secreted VEGF-A and PGE2 in control but not AIS cells. Collectively our data demonstrated that in addition to the observed primary cilium defects, there are cytoskeletal abnormalities correlated to impaired mechanotransduction in AIS. Thus, we propose that the AIS etiology could be a result of generalized defects in cellular mechanotransduction given that an adolescent growing spine is under constant stimulation for growth and bone remodeling in response to applied mechanical forces. Recognition of an altered mechanotransduction as part of the AIS pathomechanism must be considered in the conception and development of more effective bracing treatments.
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9
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Lewis KJ. Osteocyte calcium signaling - A potential translator of mechanical load to mechanobiology. Bone 2021; 153:116136. [PMID: 34339908 DOI: 10.1016/j.bone.2021.116136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 06/25/2021] [Accepted: 07/27/2021] [Indexed: 10/20/2022]
Abstract
Osteocytes are embedded dendritic bone cells; by virtue of their position in bone tissue, ability to coordinate bone building osteoblasts and resorbing osteoclasts, and sensitivity to tissue level mechanical loading, they serve as the resident bone mechanosensor. The mechanisms osteocytes use to change mechanical loading into biological signals that drive tissue level changes has been well studied over the last 30 years, however the ways loading parameters are encoded at the cellular level are still not fully understood. Calcium signaling is a first messenger signal exhibited by osteocytes in response to mechanical forces. A body of work interrogating the mechanisms of osteocyte calcium signaling exists and is presently expanding, presenting the opportunity to better understand the relationship between calcium signaling characteristics and tuned osteocyte responses to tissue level strain features (e.g. magnitude, duration, frequency). This review covers the history of osteocyte load induced calcium signaling and highlights potential cellular mechanisms used by osteocytes to turn details about loading parameters into biological events.
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Affiliation(s)
- Karl J Lewis
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, United States of America.
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10
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Moharrer Y, Boerckel JD. Tunnels in the rock: Dynamics of osteocyte morphogenesis. Bone 2021; 153:116104. [PMID: 34245936 PMCID: PMC8478866 DOI: 10.1016/j.bone.2021.116104] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Revised: 06/11/2021] [Accepted: 06/28/2021] [Indexed: 11/27/2022]
Abstract
Osteocytes are dynamic, bone matrix-remodeling cells that form an intricate network of interconnected projections through the bone matrix, called the lacunar-canalicular system. Osteocytes are the dominant mechanosensory cells in bone and their mechanosensory and mechanotransductive functions follow their morphological form. During osteocytogenesis and development of the osteocyte lacunar-canalicular network, osteocytes must dramatically remodel both their cytoskeleton and their extracellular matrix. In this review, we summarize our current understanding of the mechanisms that govern osteocyte differentiation, cytoskeletal morphogenesis, mechanotransduction, and matrix remodeling. We postulate that the physiologic activation of matrix remodeling in adult osteocytes, known as perilacunar/canalicular remodeling (PLR) represents a re-activation of the developmental program by which the osteocyte network is first established. While much of osteocyte biology remains unclear, new tools and approaches make the present moment a particularly fruitful and exciting time to study the development of these remarkable cells.
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Affiliation(s)
- Yasaman Moharrer
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, United States of America; Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Joel D Boerckel
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, United States of America; Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA, United States of America; Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, United States of America.
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11
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Effects of Extracellular Osteoanabolic Agents on the Endogenous Response of Osteoblastic Cells. Cells 2021; 10:cells10092383. [PMID: 34572032 PMCID: PMC8471159 DOI: 10.3390/cells10092383] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/31/2021] [Accepted: 09/07/2021] [Indexed: 12/27/2022] Open
Abstract
The complex multidimensional skeletal organization can adapt its structure in accordance with external contexts, demonstrating excellent self-renewal capacity. Thus, optimal extracellular environmental properties are critical for bone regeneration and inextricably linked to the mechanical and biological states of bone. It is interesting to note that the microstructure of bone depends not only on genetic determinants (which control the bone remodeling loop through autocrine and paracrine signals) but also, more importantly, on the continuous response of cells to external mechanical cues. In particular, bone cells sense mechanical signals such as shear, tensile, loading and vibration, and once activated, they react by regulating bone anabolism. Although several specific surrounding conditions needed for osteoblast cells to specifically augment bone formation have been empirically discovered, most of the underlying biomechanical cellular processes underneath remain largely unknown. Nevertheless, exogenous stimuli of endogenous osteogenesis can be applied to promote the mineral apposition rate, bone formation, bone mass and bone strength, as well as expediting fracture repair and bone regeneration. The following review summarizes the latest studies related to the proliferation and differentiation of osteoblastic cells, enhanced by mechanical forces or supplemental signaling factors (such as trace metals, nutraceuticals, vitamins and exosomes), providing a thorough overview of the exogenous osteogenic agents which can be exploited to modulate and influence the mechanically induced anabolism of bone. Furthermore, this review aims to discuss the emerging role of extracellular stimuli in skeletal metabolism as well as their potential roles and provide new perspectives for the treatment of bone disorders.
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12
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Gardinier JD. The Diminishing Returns of Mechanical Loading and Potential Mechanisms that Desensitize Osteocytes. Curr Osteoporos Rep 2021; 19:436-443. [PMID: 34216359 PMCID: PMC9306018 DOI: 10.1007/s11914-021-00693-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 05/27/2021] [Indexed: 11/30/2022]
Abstract
Adaptation to mechanical loading is critical to maintaining bone mass and offers therapeutic potential to preventing age-related bone loss and osteoporosis. However, increasing the duration of loading is met with "diminishing returns" as the anabolic response quickly becomes saturated. As a result, the anabolic response to daily activities and repetitive bouts of loading is limited by the underlying mechanisms that desensitize and render bone unresponsive at the cellular level. Osteocytes are the primary cells that respond to skeletal loading and facilitate the overall anabolic response. Although many of osteocytes' signaling mechanisms activated in response to loading are considered anabolic in nature, several of them can also render osteocytes insensitive to further stimuli and thereby creating a negative feedback loop that limits osteocytes' overall response. The purpose of this review is to examine the potential mechanisms that may contribute to the loss of mechanosensitivity. In particular, we examined the inactivation/desensitization of ion channels and signaling molecules along with the potential role of endocytosis and cytoskeletal reorganization. The significance in defining the negative feedback loop is the potential to identify unique targets for enabling osteocytes to maintain their sensitivity. In doing so, we can begin to cultivate new strategies that capitalize on the anabolic nature of daily activities that repeatedly load the skeleton.
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13
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Wright CS, Robling AG, Farach-Carson MC, Thompson WR. Skeletal Functions of Voltage Sensitive Calcium Channels. Curr Osteoporos Rep 2021; 19:206-221. [PMID: 33721180 PMCID: PMC8216424 DOI: 10.1007/s11914-020-00647-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 12/16/2020] [Indexed: 12/15/2022]
Abstract
Voltage-sensitive calcium channels (VSCCs) are ubiquitous multimeric protein complexes that are necessary for the regulation of numerous physiological processes. VSCCs regulate calcium influx and various intracellular processes including muscle contraction, neurotransmission, hormone secretion, and gene transcription, with function specificity defined by the channel's subunits and tissue location. The functions of VSCCs in bone are often overlooked since bone is not considered an electrically excitable tissue. However, skeletal homeostasis and adaptation relies heavily on VSCCs. Inhibition or deletion of VSCCs decreases osteogenesis, impairs skeletal structure, and impedes anabolic responses to mechanical loading. RECENT FINDINGS: While the functions of VSCCs in osteoclasts are less clear, VSCCs have distinct but complementary functions in osteoblasts and osteocytes. PURPOSE OF REVIEW: This review details the structure, function, and nomenclature of VSCCs, followed by a comprehensive description of the known functions of VSCCs in bone cells and their regulation of bone development, bone formation, and mechanotransduction.
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Affiliation(s)
- Christian S Wright
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN, 46202, USA
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN, 46202, USA
| | - Alexander G Robling
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN, 46202, USA
- Department of Anatomy & Cell Biology, Indiana University, Indianapolis, IN, 46202, USA
| | - Mary C Farach-Carson
- Department of Diagnostic & Biomedical Sciences, University of Texas Health Science Center at Houston School of Dentistry, Houston, TX, 77054, USA
| | - William R Thompson
- Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN, 46202, USA.
- Indiana Center for Musculoskeletal Health, Indiana University, Indianapolis, IN, 46202, USA.
- Department of Anatomy & Cell Biology, Indiana University, Indianapolis, IN, 46202, USA.
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14
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Abstract
PURPOSE OF REVIEW Skeletal adaptation to mechanical loading plays a critical role in bone growth and the maintenance of bone homeostasis. Osteocytes are postulated to serve as a hub orchestrating bone remodeling. The recent findings on the molecular mechanisms by which osteocytes sense mechanical loads and the downstream bone-forming factors are reviewed. RECENT FINDINGS Calcium channels have been implicated in mechanotransduction in bone cells for a long time. Efforts have been made to identify a specific calcium channel mediating the skeletal response to mechanical loads. Recent studies have revealed that Piezo1, a mechanosensitive ion channel, is critical for normal bone growth and is essential for the skeletal response to mechanical loading. Identification of mechanosensors and their downstream effectors in mechanosensing bone cells is essential for new strategies to modulate regenerative responses and develop therapies to treat the bone loss related to disuse or advanced age.
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Affiliation(s)
- Xuehua Li
- Department of Orthopaedic Surgery, Center for Musculoskeletal Disease Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
| | - Jacob Kordsmeier
- Department of Orthopaedic Surgery, Center for Musculoskeletal Disease Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA
| | - Jinhu Xiong
- Department of Orthopaedic Surgery, Center for Musculoskeletal Disease Research, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
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15
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El-Gazzar A, Högler W. Mechanisms of Bone Fragility: From Osteogenesis Imperfecta to Secondary Osteoporosis. Int J Mol Sci 2021; 22:ijms22020625. [PMID: 33435159 PMCID: PMC7826666 DOI: 10.3390/ijms22020625] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 01/07/2021] [Accepted: 01/07/2021] [Indexed: 12/13/2022] Open
Abstract
Bone material strength is determined by several factors, such as bone mass, matrix composition, mineralization, architecture and shape. From a clinical perspective, bone fragility is classified as primary (i.e., genetic and rare) or secondary (i.e., acquired and common) osteoporosis. Understanding the mechanism of rare genetic bone fragility disorders not only advances medical knowledge on rare diseases, it may open doors for drug development for more common disorders (i.e., postmenopausal osteoporosis). In this review, we highlight the main disease mechanisms underlying the development of human bone fragility associated with low bone mass known to date. The pathways we focus on are type I collagen processing, WNT-signaling, TGF-ß signaling, the RANKL-RANK system and the osteocyte mechanosensing pathway. We demonstrate how the discovery of most of these pathways has led to targeted, pathway-specific treatments.
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Affiliation(s)
| | - Wolfgang Högler
- Correspondence: ; Tel.: +43-(0)5-7680-84-22001; Fax: +43-(0)5-7680-84-22004
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16
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Qin L, Liu W, Cao H, Xiao G. Molecular mechanosensors in osteocytes. Bone Res 2020; 8:23. [PMID: 32550039 PMCID: PMC7280204 DOI: 10.1038/s41413-020-0099-y] [Citation(s) in RCA: 197] [Impact Index Per Article: 49.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Revised: 04/07/2020] [Accepted: 04/17/2020] [Indexed: 12/11/2022] Open
Abstract
Osteocytes, the most abundant and long-lived cells in bone, are the master regulators of bone remodeling. In addition to their functions in endocrine regulation and calcium and phosphate metabolism, osteocytes are the major responsive cells in force adaptation due to mechanical stimulation. Mechanically induced bone formation and adaptation, disuse-induced bone loss and skeletal fragility are mediated by osteocytes, which sense local mechanical cues and respond to these cues in both direct and indirect ways. The mechanotransduction process in osteocytes is a complex but exquisite regulatory process between cells and their environment, between neighboring cells, and between different functional mechanosensors in individual cells. Over the past two decades, great efforts have focused on finding various mechanosensors in osteocytes that transmit extracellular mechanical signals into osteocytes and regulate responsive gene expression. The osteocyte cytoskeleton, dendritic processes, Integrin-based focal adhesions, connexin-based intercellular junctions, primary cilium, ion channels, and extracellular matrix are the major mechanosensors in osteocytes reported so far with evidence from both in vitro and in vitro studies. This review aims to give a systematic introduction to osteocyte mechanobiology, provide details of osteocyte mechanosensors, and discuss the roles of osteocyte mechanosensitive signaling pathways in the regulation of bone homeostasis.
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Affiliation(s)
- Lei Qin
- Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment, and School of Medicine, Southern University of Science and Technology, Shenzhen, 518055 China
| | - Wen Liu
- Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment, and School of Medicine, Southern University of Science and Technology, Shenzhen, 518055 China
| | - Huiling Cao
- Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment, and School of Medicine, Southern University of Science and Technology, Shenzhen, 518055 China
| | - Guozhi Xiao
- Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research, Shenzhen Key Laboratory of Cell Microenvironment, and School of Medicine, Southern University of Science and Technology, Shenzhen, 518055 China
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17
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Yan Y, Wang L, Ge L, Pathak JL. Osteocyte-Mediated Translation of Mechanical Stimuli to Cellular Signaling and Its Role in Bone and Non-bone-Related Clinical Complications. Curr Osteoporos Rep 2020; 18:67-80. [PMID: 31953640 DOI: 10.1007/s11914-020-00564-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
PURPOSE OF REVIEW Osteocytes comprise > 95% of the cellular component in bone tissue and produce a wide range of cytokines and cellular signaling molecules in response to mechanical stimuli. In this review, we aimed to summarize the molecular mechanisms involved in the osteocyte-mediated translation of mechanical stimuli to cellular signaling, and discuss their role in skeletal (bone) diseases and extra-skeletal (non-bone) clinical complications. RECENT FINDINGS Two decades before, osteocytes were assumed as a dormant cells buried in bone matrix. In recent years, emerging evidences have shown that osteocytes are pivotal not only for bone homeostasis but also for vital organ functions such as muscle, kidney, and heart. Osteocyte mechanotransduction regulates osteoblast and osteoclast function and maintains bone homeostasis. Mechanical stimuli modulate the release of osteocyte-derived cytokines, signaling molecules, and extracellular cellular vesicles that regulate not only the surrounding bone cell function and bone homeostasis but also the distant organ function in a paracrine and endocrine fashion. Mechanical loading and unloading modulate the osteocytic release of NO, PGE2, and ATPs that regulates multiple cellular signaling such as Wnt/β-catenin, RANKL/OPG, BMPs, PTH, IGF1, VEGF, sclerostin, and others. Therefore, the in-depth study of the molecular mechanism of osteocyte mechanotransduction could unravel therapeutic targets for various bone and non-bone-related clinical complications such as osteoporosis, sarcopenia, and cancer metastasis to bone.
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Affiliation(s)
- Yongyong Yan
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, 510140, China
| | - Liping Wang
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, 510140, China
| | - Linhu Ge
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, 510140, China.
| | - Janak L Pathak
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, 510140, China.
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18
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Sun T, Yan Z, Cai J, Shao X, Wang D, Ding Y, Feng Y, Yang J, Luo E, Feng X, Jing D. Effects of mechanical vibration on cell morphology, proliferation, apoptosis, and cytokine expression/secretion in osteocyte-like MLO-Y4 cells exposed to high glucose. Cell Biol Int 2020; 44:216-228. [PMID: 31448865 DOI: 10.1002/cbin.11221] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Accepted: 08/22/2019] [Indexed: 01/24/2023]
Abstract
Diabetic patients exhibit significant bone deterioration. Our recent findings demonstrate that mechanical vibration is capable of resisting diabetic bone loss, whereas the relevant mechanism remains unclear. We herein examined the effects of mechanical vibration on the activities and functions of osteocytes (the most abundant and well-recognized mechanosensitive cells in the bone) exposed to high glucose (HG). The osteocytic MLO-Y4 cells were incubated with 50 mM HG for 24 h, and then stimulated with 1 h/day mechanical vibration (0.5 g, 45 Hz) for 3 days. We found that mechanical vibration significantly increased the proliferation and viability of MLO-Y4 cells under the HG environment via the MTT, BrdU, and Cell Viability Analyzer assays. The apoptosis detection showed that HG-induced apoptosis in MLO-Y4 cells was inhibited by mechanical vibration. Moreover, increased cellular area, microfilament density, and anisotropy in HG-incubated MLO-Y4 cells were observed after mechanical vibration via the F-actin fluorescence staining. The real-time polymerase chain reaction and western blotting results demonstrated that mechanical vibration significantly upregulated the gene and protein expression of Wnt3a, β-catenin, and osteoprotegerin (OPG) and decreased the sclerostin, DKK1, and receptor activator for nuclear factor-κB ligand (RANKL) expression in osteocytes exposed to HG. The enzyme-linked immunosorbent assay assays showed that mechanical vibration promoted the secretion of prostaglandin E2 and OPG, and inhibited the secretion of tumor necrosis factor-α and RANKL in the supernatant of HG-treated MLO-Y4 cells. Together, this study demonstrates that mechanical vibration improves osteocytic architecture and viability, and regulates cytokine expression and secretion in the HG environment, and implies the potential great contribution of the modulation of osteocytic activities in resisting diabetic osteopenia/osteoporosis by mechanical vibration.
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Affiliation(s)
- Tao Sun
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
| | - Zedong Yan
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
| | - Jing Cai
- Department of Diagnosis, College of Basic Medicine, Shaanxi University of Chinese Medicine, Xianyang, China
| | - Xi Shao
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
| | - Dan Wang
- Lab of Tissue Engineering, Faculty of Life Sciences, Northwest University, Xi'an, China
| | - Yuanjun Ding
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
| | - Ying Feng
- Department of Diagnosis, College of Basic Medicine, Shaanxi University of Chinese Medicine, Xianyang, China
| | - Jingyue Yang
- Department of Oncology of Xijing Hospital, Fourth Military Medical University, Xi'an, China
| | - Erping Luo
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
| | - Xue Feng
- Department of Cell Biology, School of Medicine, Northwest University, Xi'an, China
| | - Da Jing
- Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China
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19
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Pathak JL, Bravenboer N, Klein-Nulend J. The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases. Front Endocrinol (Lausanne) 2020; 11:405. [PMID: 32733380 PMCID: PMC7360678 DOI: 10.3389/fendo.2020.00405] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 05/20/2020] [Indexed: 01/18/2023] Open
Abstract
Osteocytes are the most abundant (~95%) cells in bone with the longest half-life (~25 years) in humans. In the past osteocytes have been regarded as vestigial cells in bone, since they are buried inside the tough bone matrix. However, during the last 30 years it has become clear that osteocytes are as important as bone forming osteoblasts and bone resorbing osteoclasts in maintaining bone homeostasis. The osteocyte cell body and dendritic processes reside in bone in a complex lacuno-canalicular system, which allows the direct networking of osteocytes to their neighboring osteocytes, osteoblasts, osteoclasts, bone marrow, blood vessels, and nerves. Mechanosensing of osteocytes translates the applied mechanical force on bone to cellular signaling and regulation of bone adaptation. The osteocyte lacuno-canalicular system is highly efficient in transferring external mechanical force on bone to the osteocyte cell body and dendritic processes via displacement of fluid in the lacuno-canalicular space. Osteocyte mechanotransduction regulates the formation and function of the osteoblasts and osteoclasts to maintain bone homeostasis. Osteocytes produce a variety of proteins and signaling molecules such as sclerostin, cathepsin K, Wnts, DKK1, DMP1, IGF1, and RANKL/OPG to regulate osteoblast and osteoclast activity. Various genetic abnormality-associated rare bone diseases are related to disrupted osteocyte functions, including sclerosteosis, van Buchem disease, hypophosphatemic rickets, and WNT1 and plastin3 mutation-related disorders. Meticulous studies during the last 15 years on disrupted osteocyte function in rare bone diseases guided for the development of various novel therapeutic agents to treat bone diseases. Studies on genetic, molecular, and cellular mechanisms of sclerosteosis and van Buchem disease revealed a role for sclerostin in bone homeostasis, which led to the development of the sclerostin antibody to treat osteoporosis and other bone degenerative diseases. The mechanism of many other rare bone diseases and the role of the osteocyte in the development of such conditions still needs to be investigated. In this review, we mainly discuss the knowledge obtained during the last 30 years on the role of the osteocyte in rare bone diseases. We speculate about future research directions to develop novel therapeutic drugs targeting osteocyte functions to treat both common and rare bone diseases.
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Affiliation(s)
- Janak L. Pathak
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, China
| | - Nathalie Bravenboer
- Department of Clinical Chemistry, Amsterdam University Medical Centers, Amsterdam Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Jenneke Klein-Nulend
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, China
- Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam, Amsterdam Movement Sciences, University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- *Correspondence: Jenneke Klein-Nulend
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20
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Yi Q, Liu H, Feng J, Wu Y, Sun W, Ou M, Tang L. Splicing factor-modulated generation of mechano growth factor regulates physiological processes in osteoblasts under mechanical stimuli. Cell Adh Migr 2019; 13:322-331. [PMID: 31680616 PMCID: PMC6844564 DOI: 10.1080/19336918.2019.1686103] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Mechanical stimuli influence various physiological processes in osteoblasts. We previously showed that mechano-growth factor (MGF), a splicing variant of insulin-like growth factor 1, is highly expressed in osteoblasts in response to mechanical stimuli. This study aims to explore the systemic functions of MGF in osteoblasts, and the mechanisms by which mechanical stress regulates the alternative splicing of Igf1 to generate MGF. We found that MGF promoted the proliferation and migration of osteoblasts, while it inhibited their differentiation via Erk1/2 pathway. Furthermore, cyclic stretching upregulated the expression of ASF/SF2, which in turn regulated the expression of MGF. Our findings indicate that mechanical stimuli influence the physiological responses of osteoblasts by increasing the expression of MGF, which is regulated by splicing factors.
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Affiliation(s)
- Qian Yi
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, China.,Department of Physiology, School of Basic Medical Sciences, Southwest Medical University, Luzhou, Sichuan, China
| | - Huan Liu
- Department of Orthopaedics, Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, Sichuan, China
| | - Jianguo Feng
- Department of Anesthesiology, The Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, China
| | - Yanjiao Wu
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, China
| | - Weichao Sun
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, China
| | - Mengting Ou
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, China
| | - Liling Tang
- Key Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing, China
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21
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Abstract
PURPOSE OF REVIEW Osteocytes are responsible for mechanosensing and mechanotransduction in bone and play a crucial role in bone homeostasis. They are embedded in a calcified collagenous matrix and connected with each other through the lacuno-canalicular network. Due to this specific native environment, it is a challenge to isolate primary osteocytes without losing their specific characteristics in vitro. This review summarizes the commonly used and recently established models to study the function of osteocytes in vitro. RECENT FINDINGS Osteocytes are mostly studied in monolayer culture, but recently, 3D models of osteocyte-like cells and primary osteocytes in vitro have been established as well. These models mimic the native environment of osteocytes and show superior osteocyte morphology and behavior, enabling the development of human disease models. Osteocyte-like cell lines as well as primary osteocytes isolated from bone are widely used to study the role of osteocytes in bone homeostasis. Both cells lines and primary cells are cultured in 2D-monolayer and 3D-models. The use of these models and their advantages and shortcomings are discussed in this review.
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Affiliation(s)
- Chen Zhang
- Department of Oral Cell Biology, Amsterdam Movement Sciences, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
- Department of Clinical Chemistry, Amsterdam Movement Sciences, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Astrid D Bakker
- Department of Oral Cell Biology, Amsterdam Movement Sciences, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Jenneke Klein-Nulend
- Department of Oral Cell Biology, Amsterdam Movement Sciences, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Nathalie Bravenboer
- Department of Clinical Chemistry, Amsterdam Movement Sciences, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
- Department of Internal Medicine, Division of Endocrinology and Center for Bone Quality, Leiden University Medical Center, Leiden, The Netherlands.
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22
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Deepak V, Kayastha P, McNamara LM. Estrogen deficiency attenuates fluid flow‐induced [Ca
2+
]
i
oscillations and mechanoresponsiveness of MLO‐Y4 osteocytes. FASEB J 2017; 31:3027-3039. [DOI: 10.1096/fj.201601280r] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 03/13/2017] [Indexed: 01/19/2023]
Affiliation(s)
- Vishwa Deepak
- Mechanobiology and Medical Device Research GroupBiomechanics Research CentreBiomedical EngineeringCollege of Engineering and InformaticsNational University of Ireland GalwayGalway Ireland
| | - Pushpalata Kayastha
- Mechanobiology and Medical Device Research GroupBiomechanics Research CentreBiomedical EngineeringCollege of Engineering and InformaticsNational University of Ireland GalwayGalway Ireland
| | - Laoise M. McNamara
- Mechanobiology and Medical Device Research GroupBiomechanics Research CentreBiomedical EngineeringCollege of Engineering and InformaticsNational University of Ireland GalwayGalway Ireland
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23
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Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids. Prostaglandins Other Lipid Mediat 2017; 132:59-68. [PMID: 28108282 DOI: 10.1016/j.prostaglandins.2017.01.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 12/22/2016] [Accepted: 01/10/2017] [Indexed: 12/29/2022]
Abstract
Hyperfiltration is a well-known risk factor in progressive loss of renal function in chronic kidney disease (CKD) secondary to various diseases. A reduced number of functional nephrons due to congenital or acquired cause(s) results in hyperfiltration in the remnant kidney. Hyperfiltration-associated increase in biomechanical forces, namely pressure-induced tensile stress and fluid flow-induced shear stress (FFSS) determine cellular injury and response. We believe the current treatment of CKD yields limited success because it largely attenuates pressure-induced tensile stress changes but not the effect of FFSS on podocytes. Studies on glomerular podocytes, tubular epithelial cells and bone osteocytes provide evidence for a significant role of COX-2 generated PGE2 and its receptors in response to tensile stress and FFSS. Preliminary observations show increased urinary PGE2 in children born with a solitary kidney. FFSS-induced COX2-PGE2-EP2 signaling provides an opportunity to identify targets and, for developing novel agents to complement currently available treatment.
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24
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Wittkowske C, Reilly GC, Lacroix D, Perrault CM. In Vitro Bone Cell Models: Impact of Fluid Shear Stress on Bone Formation. Front Bioeng Biotechnol 2016; 4:87. [PMID: 27896266 PMCID: PMC5108781 DOI: 10.3389/fbioe.2016.00087] [Citation(s) in RCA: 173] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2016] [Accepted: 10/25/2016] [Indexed: 01/06/2023] Open
Abstract
This review describes the role of bone cells and their surrounding matrix in maintaining bone strength through the process of bone remodeling. Subsequently, this work focusses on how bone formation is guided by mechanical forces and fluid shear stress in particular. It has been demonstrated that mechanical stimulation is an important regulator of bone metabolism. Shear stress generated by interstitial fluid flow in the lacunar-canalicular network influences maintenance and healing of bone tissue. Fluid flow is primarily caused by compressive loading of bone as a result of physical activity. Changes in loading, e.g., due to extended periods of bed rest or microgravity in space are associated with altered bone remodeling and formation in vivo. In vitro, it has been reported that bone cells respond to fluid shear stress by releasing osteogenic signaling factors, such as nitric oxide, and prostaglandins. This work focusses on the application of in vitro models to study the effects of fluid flow on bone cell signaling, collagen deposition, and matrix mineralization. Particular attention is given to in vitro set-ups, which allow long-term cell culture and the application of low fluid shear stress. In addition, this review explores what mechanisms influence the orientation of collagen fibers, which determine the anisotropic properties of bone. A better understanding of these mechanisms could facilitate the design of improved tissue-engineered bone implants or more effective bone disease models.
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Affiliation(s)
- Claudia Wittkowske
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - Gwendolen C Reilly
- INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK; Department of Material Science, University of Sheffield, Sheffield, UK
| | - Damien Lacroix
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - Cecile M Perrault
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
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Abstract
Mechanical loading is a potent anabolic regulator of bone mass, and the first line of defense for bone loss is weight-bearing exercise. Likewise, protected weight bearing is the first prescribed physical therapy following orthopedic reconstructive surgery. In both cases, enhancement of new bone formation is the goal. Our understanding of the physical cues, mechanisms of force sensation, and the subsequent cellular response will help identify novel physical and therapeutic treatments for age- and disuse-related bone loss, delayed- and nonunion fractures, and significant bony defects. This review highlights important new insights into the principles and mechanisms governing mechanical adaptation of the skeleton during homeostasis and repair and ends with a summary of clinical implications stemming from our current understanding of how bone adapts to biophysical force.
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Brown GN, Sattler RL, Guo XE. Experimental studies of bone mechanoadaptation: bridging in vitro and in vivo studies with multiscale systems. Interface Focus 2016; 6:20150071. [PMID: 26855756 DOI: 10.1098/rsfs.2015.0071] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Despite advancements in technology and science over the last century, the mechanisms underlying Wolff's law-bone structure adaptation in response to physical stimuli-remain poorly understood, limiting the ability to effectively treat and prevent skeletal diseases. A challenge to overcome in the study of the underlying mechanisms of this principle is the multiscale nature of mechanoadaptation. While there exist in silico systems that are capable of studying across these scales, experimental studies are typically limited to interpretation at a single dimension or time point. For instance, studies of single-cell responses to defined physical stimuli offer only a limited prediction of the whole bone response, while overlapping pathways or compensatory mechanisms complicate the ability to isolate critical targets in a whole animal model. Thus, there exists a need to develop experimental systems capable of bridging traditional experimental approaches and informing existing multiscale theoretical models. The purpose of this article is to review the process of mechanoadaptation and inherent challenges in studying its underlying mechanisms, discuss the limitations of traditional experimental systems in capturing the many facets of this process and highlight three multiscale experimental systems which bridge traditional approaches and cover relatively understudied time and length scales in bone adaptation.
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Affiliation(s)
- Genevieve N Brown
- Bone Bioengineering Laboratory, Department of Biomedical Engineering , Columbia University , New York, NY 10027 , USA
| | - Rachel L Sattler
- Bone Bioengineering Laboratory, Department of Biomedical Engineering , Columbia University , New York, NY 10027 , USA
| | - X Edward Guo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering , Columbia University , New York, NY 10027 , USA
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LIU Z, YAMAMOTO T, HASEGAWA T, HONGO H, TSUBOI K, TSUCHIYA E, HARAGUCHI M, ABE M, FREITAS PHLD, KUDO A, ODA K, LI M, AMIZUKA N. Immunolocalization of osteocyte-derived molecules during bone fracture healing of mouse ribs . Biomed Res 2016; 37:141-51. [DOI: 10.2220/biomedres.37.141] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Zhusheng LIU
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Tomomaya YAMAMOTO
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Tomoka HASEGAWA
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Hiromi HONGO
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Kanako TSUBOI
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Erika TSUCHIYA
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Mai HARAGUCHI
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | - Miki ABE
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
| | | | - Akira KUDO
- Department of Biological Information, Tokyo Institute of Technology
| | - Kimimitsu ODA
- Division of Biochemistry, Niigata University Graduate School of Medical and Dental Sciences
| | - Minqi LI
- Shandong Provincial Key Laboratory of Oral Biomedicine, The School of Stomatology, Shandong University
| | - Norio AMIZUKA
- Department of Developmental Biology of Hard Tissue Graduate School of Dental Medicine, Hokkaido University
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Sontam DM, Firth EC, Tsai P, Vickers MH, O'Sullivan JM. Different exercise modalities have distinct effects on the integrin-linked kinase (ILK) and Ca2+ signaling pathways in the male rat bone. Physiol Rep 2015; 3:3/10/e12568. [PMID: 26471755 PMCID: PMC4632950 DOI: 10.14814/phy2.12568] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Mechanical loading is essential to maintain optimal skeletal health. Despite the fact that early-life exercise has positive, long-lasting effects on the musculo-skeletal system, the response of the musculo-skeletal system to spontaneous low-impact exercise has been poorly studied. Previously, we identified subtle morphological changes in the femoral diaphysis of exercised animals compared to nonexercised controls. We hypothesized that significant changes in gene expression of cells should precede significant measurable phenotypic changes in the tissues of which they are part. Here, we employed RNA-Seq to analyse the transcriptome of the cortical bone from the femoral mid-diaphysis of prepubertal male Sprague-Dawley rats that were assigned to control (CON); bipedal stance (BPS); or wheel exercise (WEX) groups for 15 days. We identified 808 and 324 differentially expressed transcripts in the BPS and WEX animals respectively. While a number of transcripts change their levels in an exercise-specific manner, we identified 191 transcripts that were differentially expressed in both BPS and WEX. Importantly, we observed that the exercise mode had diametrically opposite effects on transcripts for multiple genes within the integrin-linked kinase (ILK) and Ca(2+) signaling pathways such that they were up-regulated in BPS and down-regulated in WEX. The findings are important for our understanding of possible ways in which different exercise regimens might affect bone when normal activities apply mechanical stimuli during postnatal growth and development.
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Affiliation(s)
- Dharani M Sontam
- The Liggins Institute, University of Auckland, Auckland, New Zealand Gravida: National Centre for Growth and Development, University of Auckland, Auckland, New Zealand
| | - Elwyn C Firth
- The Liggins Institute, University of Auckland, Auckland, New Zealand Gravida: National Centre for Growth and Development, University of Auckland, Auckland, New Zealand Department of Sport and Exercise Science, University of Auckland, Auckland, New Zealand
| | - Peter Tsai
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Mark H Vickers
- The Liggins Institute, University of Auckland, Auckland, New Zealand Gravida: National Centre for Growth and Development, University of Auckland, Auckland, New Zealand
| | - Justin M O'Sullivan
- The Liggins Institute, University of Auckland, Auckland, New Zealand Gravida: National Centre for Growth and Development, University of Auckland, Auckland, New Zealand
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Preclinical models for in vitro mechanical loading of bone-derived cells. BONEKEY REPORTS 2015; 4:728. [PMID: 26331007 DOI: 10.1038/bonekey.2015.97] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 05/29/2015] [Indexed: 02/06/2023]
Abstract
It is well established that bone responds to mechanical stimuli whereby physical forces are translated into chemical signals between cells, via mechanotransduction. It is difficult however to study the precise cellular and molecular responses using in vivo systems. In vitro loading models, which aim to replicate forces found within the bone microenvironment, make the underlying processes of mechanotransduction accessible to the researcher. Direct measurements in vivo and predictive modeling have been used to define these forces in normal physiological and pathological states. The types of mechanical stimuli present in the bone include vibration, fluid shear, substrate deformation and compressive loading, which can all be applied in vitro to monolayer and three-dimensional (3D) cultures. In monolayer, vibration can be readily applied to cultures via a low-magnitude, high-frequency loading rig. Fluid shear can be applied to cultures in multiwell plates via a simple rocking platform to engender gravitational fluid movement or via a pump to cells attached to a slide within a parallel-plate flow chamber, which may be micropatterned for use with osteocytes. Substrate strain can be applied via the vacuum-driven FlexCell system or via a four-point loading jig. 3D cultures better replicate the bone microenvironment and can also be subjected to the same forms of mechanical stimuli as monolayer, including vibration, fluid shear via perfusion flow, strain or compression. 3D cocultures that more closely replicate the bone microenvironment can be used to study the collective response of several cell types to loading. This technical review summarizes the methods for applying mechanical stimuli to bone cells in vitro.
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Lara-Castillo N, Kim-Weroha NA, Kamel MA, Javaheri B, Ellies DL, Krumlauf RE, Thiagarajan G, Johnson ML. In vivo mechanical loading rapidly activates β-catenin signaling in osteocytes through a prostaglandin mediated mechanism. Bone 2015; 76:58-66. [PMID: 25836764 PMCID: PMC4447591 DOI: 10.1016/j.bone.2015.03.019] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 01/27/2015] [Accepted: 03/02/2015] [Indexed: 12/25/2022]
Abstract
The response of the skeleton to loading appears to be mediated through the activation of the Wnt/β-catenin signaling pathway and osteocytes have long been postulated to be the primary mechanosensory cells in bone. To examine the kinetics of the mechanoresponse of bone and cell types involved in vivo, we performed forearm loading of 17-week-old female TOPGAL mice. β-catenin signaling was observed only in embedded osteocytes, not osteoblasts, at 1h post-loading, spreading to additional osteocytes and finally to cells on the bone surface by 24h. This early activation at 1h appeared to be independent of receptor (Lrp5/6) mediated activation as it occurred in the presence of the inhibitors sclerostin and/or Dkk1. The COX-2 inhibitor, Carprofen, blocked the activation of β-catenin signaling and decline in sclerostin positive osteocytes post-loading implying an important role for prostaglandin. In vitro, PI3K/Akt activation was shown to be required for β-catenin nuclear translocation downstream from prostaglandin in MLO-Y4 osteocyte-like cells supporting this mechanism. Downstream targets of β-catenin signaling, sclerostin and Dkk1, were also examined and found to be significantly downregulated in osteocytes in vivo at 24h post-loading. The pattern of initially activated osteocytes appeared random and in order to understand this heterogeneous expression, a novel finite element model of the strain field in the ulna was developed, which predicts highly variable local magnitudes of strain experienced by osteocytes. In summary, both in vivo and in vitro models show the rapid activation of β-catenin in response to load through the early release of prostaglandin and that strain fields in the bone are extremely heterogeneous resulting in heterogeneous activation of the β-catenin pathway in osteocytes in vivo.
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Affiliation(s)
- N Lara-Castillo
- UMKC School of Dentistry, Department of Oral and Craniofacial Sciences, Kansas City, MO 64108, USA
| | - N A Kim-Weroha
- UMKC School of Dentistry, Department of Oral and Craniofacial Sciences, Kansas City, MO 64108, USA
| | - M A Kamel
- UMKC School of Dentistry, Department of Oral and Craniofacial Sciences, Kansas City, MO 64108, USA
| | - B Javaheri
- The Royal Veterinary College, Royal College Street, London, NW1 0TU, UK
| | - D L Ellies
- OsteoGeneX Inc, Kansas City, KS 66103, USA
| | - R E Krumlauf
- UMKC School of Dentistry, Department of Oral and Craniofacial Sciences, Kansas City, MO 64108, USA; Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - G Thiagarajan
- UMKC School of Computing and Engineering, Kansas City, MO 64110, USA
| | - M L Johnson
- UMKC School of Dentistry, Department of Oral and Craniofacial Sciences, Kansas City, MO 64108, USA.
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Lee KL, Guevarra MD, Nguyen AM, Chua MC, Wang Y, Jacobs CR. The primary cilium functions as a mechanical and calcium signaling nexus. Cilia 2015; 4:7. [PMID: 26029358 PMCID: PMC4448211 DOI: 10.1186/s13630-015-0016-y] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Accepted: 04/28/2015] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND The primary cilium is an antenna-like, nonmotile structure that extends from the surface of most mammalian cell types and is critical for chemosensing and mechanosensing in a variety of tissues including cartilage, bone, and kidney. Flow-induced intracellular calcium ion (Ca(2+)) increases in kidney epithelia depend on primary cilia and primary cilium-localized Ca(2+)-permeable channels polycystin-2 (PC2) and transient receptor potential vanilloid 4 (TRPV4). While primary cilia have been implicated in osteocyte mechanotransduction, the molecular mechanism that mediates this process is not fully understood. We directed a fluorescence resonance energy transfer (FRET)-based Ca(2+) biosensor to the cilium by fusing the biosensor sequence to the sequence of the primary cilium-specific protein Arl13b. Using this tool, we investigated the role of several Ca(2+)-permeable channels that may mediate flow-induced Ca(2+) entry: PC2, TRPV4, and PIEZO1. RESULTS Here, we report the first measurements of Ca(2+) signaling within osteocyte primary cilia using a FRET-based biosensor fused to ARL13B. We show that fluid flow induces Ca(2+) increases in osteocyte primary cilia which depend on both intracellular Ca(2+) release and extracellular Ca(2+) entry. Using siRNA-mediated knockdowns, we demonstrate that TRPV4, but not PC2 or PIEZO1, mediates flow-induced ciliary Ca(2+) increases and loading-induced Cox-2 mRNA increases, an osteogenic response. CONCLUSIONS In this study, we show that the primary cilium forms a Ca(2+) microdomain dependent on Ca(2+) entry through TRPV4. These results demonstrate that the mechanism of mechanotransduction mediated by primary cilia varies in different tissue contexts. Additionally, we anticipate that this work is a starting point for more studies investigating the role of TRPV4 in mechanotransduction.
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Affiliation(s)
- Kristen L Lee
- />Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Ave, New York, NY 10027 USA
| | - Marie D Guevarra
- />Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Ave, New York, NY 10027 USA
| | - An M Nguyen
- />Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Ave, New York, NY 10027 USA
- />Jacobs Technion-Cornell Innovation Institute, Cornell Tech, New York, NY 10011 USA
| | - Mardonn C Chua
- />Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Ave, New York, NY 10027 USA
- />Department of Biotechnology, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
| | - Yingxiao Wang
- />Bioengineering Department, UC San Diego, La Jolla, CA 92093 USA
| | - Christopher R Jacobs
- />Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, MC 8904, 1210 Amsterdam Ave, New York, NY 10027 USA
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Diaz MF, Li N, Lee HJ, Adamo L, Evans SM, Willey HE, Arora N, Torisawa YS, Vickers DA, Morris SA, Naveiras O, Murthy SK, Ingber DE, Daley GQ, García-Cardeña G, Wenzel PL. Biomechanical forces promote blood development through prostaglandin E2 and the cAMP-PKA signaling axis. ACTA ACUST UNITED AC 2015; 212:665-80. [PMID: 25870199 PMCID: PMC4419354 DOI: 10.1084/jem.20142235] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 03/17/2015] [Indexed: 12/12/2022]
Abstract
Blood flow promotes emergence of definitive hematopoietic stem cells (HSCs) in the developing embryo, yet the signals generated by hemodynamic forces that influence hematopoietic potential remain poorly defined. Here we show that fluid shear stress endows long-term multilineage engraftment potential upon early hematopoietic tissues at embryonic day 9.5, an embryonic stage not previously described to harbor HSCs. Effects on hematopoiesis are mediated in part by a cascade downstream of wall shear stress that involves calcium efflux and stimulation of the prostaglandin E2 (PGE2)-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling axis. Blockade of the PGE2-cAMP-PKA pathway in the aorta-gonad-mesonephros (AGM) abolished enhancement in hematopoietic activity. Furthermore, Ncx1 heartbeat mutants, as well as static cultures of AGM, exhibit lower levels of expression of prostaglandin synthases and reduced phosphorylation of the cAMP response element-binding protein (CREB). Similar to flow-exposed cultures, transient treatment of AGM with the synthetic analogue 16,16-dimethyl-PGE2 stimulates more robust engraftment of adult recipients and greater lymphoid reconstitution. These data provide one mechanism by which biomechanical forces induced by blood flow modulate hematopoietic potential.
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Affiliation(s)
- Miguel F Diaz
- Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030
| | - Nan Li
- Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030
| | - Hyun Jung Lee
- Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030
| | - Luigi Adamo
- Center for Excellence in Vascular Biology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115
| | - Siobahn M Evans
- Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030
| | - Hannah E Willey
- Department of Bioengineering, Rice University, Houston, TX 77030
| | - Natasha Arora
- Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Yu-Suke Torisawa
- Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 Wyss Institute for Biologically Inspired Engineering at Harvard University and Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115 Wyss Institute for Biologically Inspired Engineering at Harvard University and Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115
| | - Dwayne A Vickers
- Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA 02115
| | - Samantha A Morris
- Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Olaia Naveiras
- Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Shashi K Murthy
- Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA 02115
| | - Donald E Ingber
- Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 Wyss Institute for Biologically Inspired Engineering at Harvard University and Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115 Wyss Institute for Biologically Inspired Engineering at Harvard University and Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115
| | - George Q Daley
- Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Manton Center for Orphan Disease Research, and Howard Hughes Medical Institute, Children's Hospital Boston and Dana-Farber Cancer Institute, Boston, MA 02115 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Guillermo García-Cardeña
- Center for Excellence in Vascular Biology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115 Harvard Stem Cell Institute and School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Pamela L Wenzel
- Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030 Program in Children's Regenerative Medicine, Department of Pediatric Surgery, Center for Stem Cell and Regenerative Medicine, The Brown Foundation Institute of Molecular Medicine, and Immunology Program, Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030
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Abstract
Bone fragility is a major health concern, as the increased risk of bone fractures has devastating outcomes in terms of mortality, decreased autonomy, and healthcare costs. Efforts made to address this problem have considerably increased our knowledge about the mechanisms that regulate bone formation and resorption. In particular, we now have a much better understanding of the cellular events that are triggered when bones are mechanically stimulated and how these events can lead to improvements in bone mass. Despite these findings at the molecular level, most exercise intervention studies reveal either no effects or only minor benefits of exercise programs in improving bone mineral density (BMD) in osteoporotic patients. Nevertheless, and despite that BMD is the gold standard for diagnosing osteoporosis, this measure is only able to provide insights regarding the quantity of bone tissue. In this article, we review the complex structure of bone tissue and highlight the concept that its mechanical strength stems from the interaction of several different features. We revisited the available data showing that bone mineralization degree, hydroxyapatite crystal size and heterogeneity, collagen properties, osteocyte density, trabecular and cortical microarchitecture, as well as whole bone geometry, are determinants of bone strength and that each one of these properties may independently contribute to the increased or decreased risk of fracture, even without meaningful changes in aBMD. Based on these findings, we emphasize that while osteoporosis (almost) always causes bone fragility, bone fragility is not always caused just by osteoporosis, as other important variables also play a major role in this etiology. Furthermore, the results of several studies showing compelling data that physical exercise has the potential to improve bone quality and to decrease fracture risk by influencing each one of these determinants are also reviewed. These findings have meaningful clinical repercussions as they emphasize the fact that, even without leading to improvements in BMD, exercise interventions in patients with osteoporosis may be beneficial by improving other determinants of bone strength.
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Uzer G, Pongkitwitoon S, Ian C, Thompson WR, Rubin J, Chan ME, Judex S. Gap junctional communication in osteocytes is amplified by low intensity vibrations in vitro. PLoS One 2014; 9:e90840. [PMID: 24614887 PMCID: PMC3948700 DOI: 10.1371/journal.pone.0090840] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 02/05/2014] [Indexed: 11/21/2022] Open
Abstract
The physical mechanism by which cells sense high-frequency mechanical signals of small magnitude is unknown. During exposure to vibrations, cell populations within a bone are subjected not only to acceleratory motions but also to fluid shear as a result of fluid-cell interactions. We explored displacements of the cell nucleus during exposure to vibrations with a finite element (FE) model and tested in vitro whether vibrations can affect osteocyte communication independent of fluid shear. Osteocyte like MLO-Y4 cells were subjected to vibrations at acceleration magnitudes of 0.15 g and 1 g and frequencies of 30 Hz and 100 Hz. Gap junctional intracellular communication (GJIC) in response to these four individual vibration regimes was investigated. The FE model demonstrated that vibration induced dynamic accelerations caused larger relative nuclear displacement than fluid shear. Across the four regimes, vibrations significantly increased GJIC between osteocytes by 25%. Enhanced GJIC was independent of vibration induced fluid shear; there were no differences in GJIC between the four different vibration regimes even though differences in fluid shear generated by the four regimes varied 23-fold. Vibration induced increases in GJIC were not associated with altered connexin 43 (Cx43) mRNA or protein levels, but were dependent on Akt activation. Combined, the in silico and in vitro experiments suggest that externally applied vibrations caused nuclear motions and that large differences in fluid shear did not influence nuclear motion (<1%) or GJIC, perhaps indicating that vibration induced nuclear motions may directly increase GJIC. Whether the increase in GJIC is instrumental in modulating anabolic and anti-catabolic processes associated with the application of vibrations remains to be determined.
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Affiliation(s)
- Gunes Uzer
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America
- Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Suphannee Pongkitwitoon
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America
| | - Cheng Ian
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America
| | - William R. Thompson
- Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Janet Rubin
- Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Meilin E. Chan
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America
| | - Stefan Judex
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America
- * E-mail:
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Jing D, Baik AD, Lu XL, Zhou B, Lai X, Wang L, Luo E, Guo XE. In situ intracellular calcium oscillations in osteocytes in intact mouse long bones under dynamic mechanical loading. FASEB J 2013; 28:1582-92. [PMID: 24347610 DOI: 10.1096/fj.13-237578] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Osteocytes have been hypothesized to be the major mechanosensors in bone. How in situ osteocytes respond to mechanical stimuli is still unclear because of technical difficulties. In vitro studies have shown that osteocytes exhibited unique calcium (Ca(2+)) oscillations to fluid shear. However, whether this mechanotransduction phenomenon holds for in situ osteocytes embedded within a mineralized bone matrix under dynamic loading remains unknown. Using a novel synchronized loading/imaging technique, we successfully visualized in real time and quantified Ca(2+) responses in osteocytes and bone surface cells in situ under controlled dynamic loading on intact mouse tibia. The resultant fluid-induced shear stress on the osteocyte in the lacunocanalicular system (LCS) was also quantified. Osteocytes, but not surface cells, displayed repetitive Ca(2+) spikes in response to dynamic loading, with spike frequency and magnitude dependent on load magnitude, tissue strain, and shear stress in the LCS. The Ca(2+) oscillations were significantly reduced by endoplasmic reticulum (ER) depletion and P2 purinergic receptor (P2R)/phospholipase C (PLC) inhibition. This study provides direct evidence that osteocytes respond to in situ mechanical loading by Ca(2+) oscillations, which are dependent on the P2R/PLC/inositol trisphosphate/ER pathway. This study develops a novel approach in skeletal mechanobiology and also advances our fundamental knowledge of bone mechanotransduction.
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Affiliation(s)
- Da Jing
- 1351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Ave., Columbia University, New York, NY 10027, USA.
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Kalajzic I, Matthews BG, Torreggiani E, Harris MA, Divieti Pajevic P, Harris SE. In vitro and in vivo approaches to study osteocyte biology. Bone 2013; 54:296-306. [PMID: 23072918 PMCID: PMC3566324 DOI: 10.1016/j.bone.2012.09.040] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 09/27/2012] [Accepted: 09/27/2012] [Indexed: 11/26/2022]
Abstract
Osteocytes, the most abundant cell population of the bone lineage, have been a major focus in the bone research field in recent years. This population of cells that resides within mineralized matrix is now thought to be the mechanosensory cell in bone and plays major roles in the regulation of bone formation and resorption. Studies of osteocytes had been impaired by their location, resulting in numerous attempts to isolate primary osteocytes and to generate cell lines representative of the osteocytic phenotype. Progress has been achieved in recent years by utilizing in vivo genetic technology and generation of osteocyte directed transgenic and gene deficiency mouse models. We will provide an overview of the current in vitro and in vivo models utilized to study osteocyte biology. We discuss generation of osteocyte-like cell lines and isolation of primary osteocytes and summarize studies that have utilized these cellular models to understand the functional role of osteocytes. Approaches that attempt to selectively identify and isolate osteocytes using fluorescent protein reporters driven by regulatory elements of genes that are highly expressed in osteocytes will be discussed. In addition, recent in vivo studies utilizing overexpression or conditional deletion of various genes using dentin matrix protein (Dmp1) directed Cre recombinase are outlined. In conclusion, evaluation of the benefits and deficiencies of currently used cell lines/genetic models in understanding osteocyte biology underlines the current progress in this field. The future efforts will be directed towards developing novel in vitro and in vivo models that would additionally facilitate in understanding the multiple roles of osteocytes.
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Affiliation(s)
- Ivo Kalajzic
- Department of Reconstructive Sciences, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
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Lu XL, Huo B, Park M, Guo XE. Calcium response in osteocytic networks under steady and oscillatory fluid flow. Bone 2012; 51:466-73. [PMID: 22750013 PMCID: PMC3412915 DOI: 10.1016/j.bone.2012.05.021] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 05/04/2012] [Accepted: 05/05/2012] [Indexed: 02/05/2023]
Abstract
The fluid flow in the lacunar-canalicular system of bone is an essential mechanical stimulation on the osteocyte networks. Due to the complexity of human physical activities, the fluid shear stress on osteocyte bodies and processes consists of both steady and oscillatory components. In this study, we investigated and compared the intracellular calcium ([Ca(2+)](i)) responses of osteocytic networks under steady and oscillatory fluid flows. An in vitro osteocytic network was built with MLO-Y4 osteocyte-like cells using micro-patterning techniques to simulate the in vivo orderly organization of osteocyte networks. Sinusoidal oscillating fluid flow or unidirectional steady flow was applied on the cell surface with 2Pa peak shear stress. It was found that the osteocytic networks were significantly more responsive to steady flow than to oscillatory flow. The osteocytes can release more calcium peaks with higher magnitudes at a faster speed under steady flow stimulation. The [Ca(2+)](i) signaling transients under the steady and oscillatory flows have significantly different spatiotemporal characters, but a similar responsive percentage of cells. Further signaling pathway studies using inhibitors showed that endoplasmic reticulum (ER) calcium store, extracellular calcium source, ATP, PGE(2) and NO related pathways play similar roles in the [Ca(2+)](i) signaling of osteocytes under either steady or oscillating flow. The spatiotemporal characteristics of [Ca(2+)](i) transients under oscillating fluid flow are affected more profoundly by pharmacological treatments than under the steady flow. Our findings support the hypothesis that the [Ca(2+)](i) responses of osteocytic networks are significantly dependent on the profiles of fluid flow.
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Affiliation(s)
- X. Lucas Lu
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY 10027
- Department of Mechanical Engineering, University of Delaware, Newark, DE 19716
| | - Bo Huo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY 10027
- Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, P. R. China
| | - Miri Park
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY 10027
- Department of Mechanical Engineering, University of Delaware, Newark, DE 19716
| | - X. Edward Guo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY 10027
- Address correspondence to: Professor X. Edward Guo, Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, 1210 Amsterdam Avenue, New York, NY 10027, Telephone: (212) 854-6196, Fax: (212) 854-8725,
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38
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Lu XL, Huo B, Chiang V, Guo XE. Osteocytic network is more responsive in calcium signaling than osteoblastic network under fluid flow. J Bone Miner Res 2012; 27:563-74. [PMID: 22113822 PMCID: PMC3343217 DOI: 10.1002/jbmr.1474] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Osteocytes, regarded as the mechanical sensor in bone, respond to mechanical stimulation by activating biochemical pathways and mediating the cellular activities of other bone cells. Little is known about how osteocytic networks respond to physiological mechanical stimuli. In this study, we compared the mechanical sensitivity of osteocytic and osteoblastic networks under physiological-related fluid shear stress (0.5 to 4 Pa). The intracellular calcium ([Ca(2+)](i)) responses in micropatterned in vitro osteoblastic or osteocytic networks were recorded and analyzed. Osteocytes in the network showed highly repetitive spikelike [Ca(2+)](i) peaks under fluid flow stimulation, which are dramatically different from those in the osteoblastic network. The number of responsive osteocytes in the network remained at a constant high percentage (>95%) regardless of the magnitude of shear stress, whereas the number of responsive osteoblasts in the network significantly depends on the strength of fluid flow. All spatiotemporal parameters of calcium signaling demonstrated that osteocytic networks are more sensitive and dynamic than osteoblastic networks, especially under low-level mechanical stimulations. Furthermore, pathway studies were performed to identify the molecular mechanisms responsible for the differences in [Ca(2+)](i) signaling between osteoblastic and osteocytic networks. The results suggested that the T-type voltage-gated calcium channels (VGCC) expressed on osteocytes may play an essential role in the unique kinetics of [Ca(2+)](i) signaling in osteocytic networks, whereas the L-type VGCC is critical for both types of cells to release multiple [Ca(2+)](i) peaks. The extracellular calcium source and intracellular calcium store in ER-, ATP-, PGE₂-, NO-, and caffeine-related pathways are found to play similar roles in the [Ca(2+)](i) signaling for both osteoblasts and osteocytes. The findings in this study proved that osteocytic networks possess unique characteristics in sensing and processing mechanical signals.
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Affiliation(s)
- X Lucas Lu
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA
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39
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Enhanced osteoclastic resorption and responsiveness to mechanical load in gap junction deficient bone. PLoS One 2011; 6:e23516. [PMID: 21897843 PMCID: PMC3163577 DOI: 10.1371/journal.pone.0023516] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 07/20/2011] [Indexed: 11/20/2022] Open
Abstract
Emerging evidence suggests that connexin mediated gap junctional intercellular communication contributes to many aspects of bone biology including bone development, maintenance of bone homeostasis and responsiveness of bone cells to diverse extracellular signals. Deletion of connexin 43, the predominant gap junction protein in bone, is embryonic lethal making it challenging to examine the role of connexin 43 in bone in vivo. However, transgenic murine models in which only osteocytes and osteoblasts are deficient in connexin 43, and which are fully viable, have recently been developed. Unfortunately, the bone phenotype of different connexin 43 deficient models has been variable. To address this issue, we used an osteocalcin driven Cre-lox system to create osteoblast and osteocyte specific connexin 43 deficient mice. These mice displayed bone loss as a result of increased bone resorption and osteoclastogenesis. The mechanism underlying this increased osteoclastogenesis included increases in the osteocytic, but not osteoblastic, RANKL/OPG ratio. Previous in vitro studies suggest that connexin 43 deficient bone cells are less responsive to biomechanical signals. Interestingly, and in contrast to in vitro studies, we found that connexin 43 deficient mice displayed an enhanced anabolic response to mechanical load. Our results suggest that transient inhibition of connexin 43 expression and gap junctional intercellular communication may prove a potentially powerful means of enhancing the anabolic response of bone to mechanical loading.
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40
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Sugawara Y, Ando R, Kamioka H, Ishihara Y, Honjo T, Kawanabe N, Kurosaka H, Takano-Yamamoto T, Yamashiro T. The three-dimensional morphometry and cell-cell communication of the osteocyte network in chick and mouse embryonic calvaria. Calcif Tissue Int 2011; 88:416-24. [PMID: 21340572 DOI: 10.1007/s00223-011-9471-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Accepted: 01/25/2011] [Indexed: 12/22/2022]
Abstract
The study of osteocytes has progressed in chicks. We examined whether chick osteocyte data can be applied to other species. We used mice for comparison because they are common clinical tools in biomedical research and useful for future study. We analyzed the three-dimensional (3D) osteocyte network and gap junctional intercellular communication (GJIC) in living embryonic calvaria for the anatomical features. Embryonic parietal bones were stained with fluorescently labeled phalloidin and observed using confocal laser scanning microscopy. GJIC between osteocytes in chick and mouse parietal bone was assessed using fluorescence recovery after photobleaching (FRAP). The values for one chick and mouse osteocyte, respectively, were calculated as follows: cell processes 1,131 ± 139 μm, 2,668 ± 596 μm; surface area 1,128 ± 358 μm(2), 2,654 ± 659 μm(2); and cell volume 455 ± 90 μm(3), 1,328 ± 210 μm(3). The density of 3D osteocyte processes in the bone matrix was not significantly different. FRAP analysis showed dye coupling among osteocytes in chick and mouse bone. The fluorescence intensity recovered to 49.0 ± 2.4% in chicks and 39.9 ± 2.4% in mice after 5 minutes. Fluorescence recovery was similar within 4 minutes. The difference in osteocyte size between the two species might have affected their functions. Osteocyte processes in the two species may sense similarly changes in the exterior environment. We successfully conducted morphological and functional analyses of the osteocyte network in chicks and mice. The size of the osteocytes in bone differed between the two species.
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Affiliation(s)
- Yasuyo Sugawara
- Department of Orthodontics and Dentofacial Orthopedics, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, 2-5-1 Shikata, Okayama-City, Okayama 700-8525, Japan.
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41
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Santos RCV, Rico MAP, Bartrons R, Pujol FV, Rosa JL, de Oliveira JR. The Transcriptional Activation of the Cyclooxygenase-2 Gene in Zymosan-Activated Macrophages is Dependent on NF-Kappa B, C/EBP, AP-1, and CRE Sites. Inflammation 2010; 34:653-8. [DOI: 10.1007/s10753-010-9275-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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42
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Srivastava T, McCarthy ET, Sharma R, Cudmore PA, Sharma M, Johnson ML, Bonewald LF. Prostaglandin E(2) is crucial in the response of podocytes to fluid flow shear stress. J Cell Commun Signal 2010; 4:79-90. [PMID: 20531983 PMCID: PMC2876242 DOI: 10.1007/s12079-010-0088-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Accepted: 03/05/2010] [Indexed: 12/11/2022] Open
Abstract
Podocytes play a key role in maintaining and modulating the filtration barrier of the glomerulus. Because of their location, podocytes are exposed to mechanical strain in the form of fluid flow shear stress (FFSS). Several human diseases are characterized by glomerular hyperfiltration, such as diabetes mellitus and hypertension. The response of podocytes to FFSS at physiological or pathological levels is not known. We exposed cultured podocytes to FFSS, and studied changes in actin cytoskeleton, prostaglandin E(2) (PGE(2)) production and expression of cyclooxygenase-1 and-2 (COX-1, COX-2). FFSS caused a reduction in transversal F-actin stress filaments and the appearance of cortical actin network in the early recovery period. Cells exhibited a pattern similar to control state by 24 h following FFSS without significant loss of podocytes or apoptosis. FFSS caused increased levels of PGE(2) as early as 30 min after onset of shear stress, levels that increased over time. PGE(2) production by podocytes at post-2 h and post-24 h was also significantly increased compared to control cells (p < 0.039 and 0.012, respectively). Intracellular PGE(2) synthesis and expression of COX-2 was increased at post-2 h following FFSS. The expression of COX-1 mRNA was unchanged. We conclude that podocytes are sensitive and responsive to FFSS, exhibiting morphological and physiological changes. We believe that PGE(2) plays an important role in mechanoperception in podocytes.
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Affiliation(s)
- Tarak Srivastava
- Section of Nephrology, Children’s Mercy Hospital and University of Missouri at Kansas City, Kansas City, MO USA
| | - Ellen T. McCarthy
- Kidney Institute, University of Kansas Medical Center, Kansas City, KS USA
| | - Ram Sharma
- Renal Research Laboratory, Research and Development, Kansas City VA Medical Center, Room F1-130, Building 15, 4801 Linwood Boulevard, Kansas City, MO 64128 USA
| | - Patricia A. Cudmore
- Section of Nephrology, Children’s Mercy Hospital and University of Missouri at Kansas City, Kansas City, MO USA
| | - Mukut Sharma
- Kidney Disease Center, Medical College of Wisconsin, Milwaukee, WI USA
| | - Mark L. Johnson
- Department of Oral Biology, University of Missouri at Kansas City—School of Dentistry, Kansas, MO USA
| | - Lynda F. Bonewald
- Department of Oral Biology, University of Missouri at Kansas City—School of Dentistry, Kansas, MO USA
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43
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Lau E, Al-Dujaili S, Guenther A, Liu D, Wang L, You L. Effect of low-magnitude, high-frequency vibration on osteocytes in the regulation of osteoclasts. Bone 2010; 46:1508-15. [PMID: 20211285 PMCID: PMC3084034 DOI: 10.1016/j.bone.2010.02.031] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 01/15/2010] [Accepted: 02/26/2010] [Indexed: 12/26/2022]
Abstract
Osteocytes are well evidenced to be the major mechanosensor in bone, responsible for sending signals to the effector cells (osteoblasts and osteoclasts) that carry out bone formation and resorption. Consistent with this hypothesis, it has been shown that osteocytes release various soluble factors (e.g. transforming growth factor-beta, nitric oxide, and prostaglandins) that influence osteoblastic and osteoclastic activities when subjected to a variety of mechanical stimuli, including fluid flow, hydrostatic pressure, and mechanical stretching. Recently, low-magnitude, high-frequency (LMHF) vibration (e.g., acceleration less than <1 x g, where g=9.81m/s(2), at 20-90 Hz) has gained much interest as studies have shown that such mechanical stimulation can positively influence skeletal homeostasis in animals and humans. Although the anabolic and anti-resorptive potential of LMHF vibration is becoming apparent, the signaling pathways that mediate bone adaptation to LMHF vibration are unknown. We hypothesize that osteocytes are the mechanosensor responsible for detecting the vibration stimulation and producing soluble factors that modulate the activity of effector cells. Hence, we applied low-magnitude (0.3 x g) vibrations to osteocyte-like MLO-Y4 cells at various frequencies (30, 60, 90 Hz) for 1h. We found that osteocytes were sensitive to this vibration stimulus at the transcriptional level: COX-2 maximally increased by 344% at 90Hz, while RANKL decreased most significantly (-55%, p<0.01) at 60Hz. Conditioned medium collected from the vibrated MLO-Y4 cells attenuated the formation of large osteoclasts (> or =10 nuclei) by 36% (p<0.05) and the amount of osteoclastic resorption by 20% (p=0.07). The amount of soluble RANKL (sRANKL) in the conditioned medium was found to be 53% lower in the vibrated group (p<0.01), while PGE(2) release was also significantly decreased (-61%, p<0.01). We conclude that osteocytes are able to sense LMHF vibration and respond by producing soluble factors that inhibit osteoclast formation.
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Affiliation(s)
- Esther Lau
- Institute of Biomaterials & Biomedical Engineering, University of Toronto, Toronto, ON, Canada
| | - Saja Al-Dujaili
- Institute of Biomaterials & Biomedical Engineering, University of Toronto, Toronto, ON, Canada
| | - Axel Guenther
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada
| | - Dawei Liu
- Department of Developmental Sciences/Orthodontics, Marquette University School of Dentistry, Milwaukee, WI, USA
| | - Liyun Wang
- Center for Biomedical Engineering Research, Department of Mechanical Engineering, University of Delaware, Newark, DE, USA
| | - Lidan You
- Institute of Biomaterials & Biomedical Engineering, University of Toronto, Toronto, ON, Canada
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada
- Corresponding author: 5 King's College Road, Room 314D, Toronto, Ontario, Canada M5S 3G8, Tel: 416-978-5736 Fax: 416-978-7753,
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44
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Rath AL, Bonewald LF, Ling J, Jiang JX, Van Dyke ME, Nicolella DP. Correlation of cell strain in single osteocytes with intracellular calcium, but not intracellular nitric oxide, in response to fluid flow. J Biomech 2010; 43:1560-4. [PMID: 20189178 DOI: 10.1016/j.jbiomech.2010.01.030] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Revised: 12/21/2009] [Accepted: 01/05/2010] [Indexed: 01/01/2023]
Abstract
Osteocytes compose 90-95% of all bone cells and are the mechanosensors of bone. In this study, the strain experienced by individual osteocytes resulting from an applied fluid flow shear stress was quantified and correlated to two biological responses measured in real-time within the same individual osteocytes: (1) the upregulation of intracellular calcium and (2) changes in intracellular nitric oxide. Osteocyte-like MLO-Y4 cells were loaded with Fluo-4 AM and DAR-4M and exposed to uniform laminar fluid flow shear stresses of 2, 8, or 16 dyn/cm(2). Intracellular calcium and nitric oxide changes were determined by measuring the difference in fluorescence intensity from the cell's basal level prior to fluid flow and the level immediately following exposure. Individual cell strains were calculated using digital image correlation. MLO-Y4 cells showed a linear increase in cell strain, intracellular calcium concentration, and nitric oxide concentration with an increase in applied fluid flow rate. The increase in intracellular calcium was well correlated to the strain that each cell experienced. This study shows that osteocytes exposed to the same fluid flow experienced a range of individual strains and changes in intracellular calcium and nitric oxide concentrations, and the changes in intracellular calcium were correlated with cell strain. These results are among the first to establish a relationship between the strain experienced by osteocytes in response to fluid flow shear and a biological response at the single cell level. Mechanosensing and chemical signaling in osteocytes has been hypothesized to occur at the single cell level, making it imperative to understand the biological response of the individual cell.
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Affiliation(s)
- Amber L Rath
- Wake Forest Institute for Regenerative Medicine, Wake Forest University School of Medicine, Medical Center Boulevard, Winston Salem, NC 27157, USA.
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45
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Adachi T, Aonuma Y, Taira K, Hojo M, Kamioka H. Asymmetric intercellular communication between bone cells: Propagation of the calcium signaling. Biochem Biophys Res Commun 2009; 389:495-500. [DOI: 10.1016/j.bbrc.2009.09.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2009] [Accepted: 09/02/2009] [Indexed: 10/20/2022]
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46
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Affiliation(s)
- A Santos
- Department of Oral Cell Biology, ACTA, University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
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47
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Rangaswami H, Marathe N, Zhuang S, Chen Y, Yeh JC, Frangos JA, Boss GR, Pilz RB. Type II cGMP-dependent protein kinase mediates osteoblast mechanotransduction. J Biol Chem 2009; 284:14796-808. [PMID: 19282289 PMCID: PMC2685661 DOI: 10.1074/jbc.m806486200] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Revised: 03/02/2009] [Indexed: 01/03/2023] Open
Abstract
Continuous bone remodeling in response to mechanical loading is critical for skeletal integrity, and interstitial fluid flow is an important stimulus for osteoblast/osteocyte growth and differentiation. However, the biochemical signals mediating osteoblast anabolic responses to mechanical stimulation are incompletely understood. In primary human osteoblasts and murine MC3T3-E1 cells, we found that fluid shear stress induced rapid expression of c-fos, fra-1, fra-2, and fosB/DeltafosB mRNAs; these genes encode transcriptional regulators that maintain skeletal integrity. Fluid shear stress increased osteoblast nitric oxide (NO) synthesis, leading to activation of cGMP-dependent protein kinase (PKG). Pharmacological inhibition of the NO/cGMP/PKG signaling pathway blocked shear-induced expression of all four fos family genes. Induction of these genes required signaling through MEK/Erk, and Erk activation was NO/cGMP/PKG-dependent. Treating cells with a membrane-permeable cGMP analog partly mimicked the effects of fluid shear stress on Erk activity and fos family gene expression. In cells transfected with small interfering RNAs (siRNA) specific for membrane-bound PKG II, shear- and cGMP-induced Erk activation and fos family gene expression was nearly abolished and could be restored by transducing cells with a virus encoding an siRNA-resistant form of PKG II; in contrast, siRNA-mediated repression of the more abundant cytosolic PKG I isoform was without effect. Thus, we report a novel function for PKG II in osteoblast mechanotransduction, and we propose a model whereby NO/cGMP/PKG II-mediated Erk activation and induction of c-fos, fra-1, fra-2, and fosB/DeltafosB play a key role in the osteoblast anabolic response to mechanical stimulation.
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Affiliation(s)
- Hema Rangaswami
- Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, California 92093, USA
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48
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Wise GE, King GJ. Mechanisms of tooth eruption and orthodontic tooth movement. J Dent Res 2008; 87:414-34. [PMID: 18434571 DOI: 10.1177/154405910808700509] [Citation(s) in RCA: 354] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Teeth move through alveolar bone, whether through the normal process of tooth eruption or by strains generated by orthodontic appliances. Both eruption and orthodontics accomplish this feat through similar fundamental biological processes, osteoclastogenesis and osteogenesis, but there are differences that make their mechanisms unique. A better appreciation of the molecular and cellular events that regulate osteoclastogenesis and osteogenesis in eruption and orthodontics is not only central to our understanding of how these processes occur, but also is needed for ultimate development of the means to control them. Possible future studies in these areas are also discussed, with particular emphasis on translation of fundamental knowledge to improve dental treatments.
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Affiliation(s)
- G E Wise
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
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Liu D, Genetos DC, Shao Y, Geist DJ, Li J, Ke HZ, Turner CH, Duncan RL. Activation of extracellular-signal regulated kinase (ERK1/2) by fluid shear is Ca(2+)- and ATP-dependent in MC3T3-E1 osteoblasts. Bone 2008; 42:644-52. [PMID: 18291742 PMCID: PMC2937351 DOI: 10.1016/j.bone.2007.09.058] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2007] [Revised: 08/17/2007] [Accepted: 09/28/2007] [Indexed: 01/09/2023]
Abstract
To determine the role of Ca2+ signaling in activation of the Mitogen-Activated Protein Kinase (MAPK) pathway, we subjected MC3T3-E1 pre-osteoblastic cells to inhibitors of Ca2+ signaling during application of fluid shear stress (FSS). FSS only activated ERK1/2, rapidly inducing phosphorylation within 5 min of the onset of shear. Phosphorylation of ERK1/2 (pERK1/2) was significantly reduced when Ca2+i was chelated with BAPTA or when Ca2+ was removed from the flow media. Inhibition of both the L-type voltage-sensitive Ca2+ channel and the mechanosensitive cation-selective channel blocked FSS-induced pERK1/2. Inhibition of phospholipase C with U73122 significantly reduced pERK1/2. This inhibition did not result from blockage of intracellular Ca2+ release, but a loss of PKC activation. Recent data suggests a role of ATP release and purinergic receptor activation in mechanotransduction. Apyrase-mediated hydrolysis of extracellular ATP completely blocked FSS-induced phosphorylation of ERK1/2, while the addition of exogenous ATP to static cells mimicked the effects of FSS on pERK1/2. Two P2 receptors, P2Y2 and P2X7, have been associated with the anabolic responses of bone to mechanical loading. Using both iRNA techniques and primary osteoblasts isolated from P2X7 knockout mice, we found that the P2X7, but not the P2Y2, purinergic receptor was involved in ERK1/2 activation under FSS. These data suggest that FSS-induced ERK1/2 phosphorylation requires Ca2+-dependent ATP release, however both increased Ca2+i and PKC activation are needed for complete activation. Further, this ATP-dependent ERK1/2 phosphorylation is mediated through P2X7, but not P2Y2, purinergic receptors.
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Affiliation(s)
- Dawei Liu
- Department of Developmental Sciences and Orthodontics, Marquette University School of Dentistry, Milwaukee, WI, USA; Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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Poulsen RC, Moughan PJ, Kruger MC. Long-chain polyunsaturated fatty acids and the regulation of bone metabolism. Exp Biol Med (Maywood) 2008; 232:1275-88. [PMID: 17959840 DOI: 10.3181/0704-mr-100] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The role of prostaglandin E2 (PGE2) in the regulation of bone remodeling is well established. There is increasing evidence that various long-chain polyunsaturated fatty acids (LCPUFAs), as well as nonprostanoid LCPUFA metabolites, also have critical roles in regulating bone metabolism and may have therapeutic potential in the management of postmenopausal osteoporosis. Although only the 18-carbon precursors for the n-3 and n-6 LCPUFAs are deemed "dietary essential," the ability of the body to convert these precursor fatty acids into the more highly unsaturated 20- and 22-carbon LCPUFAs decreases with aging, menopause, and various lifestyle factors (e.g., smoking). Increasing dietary LCPUFA intake increases tissue and blood LCPUFA concentrations, as well as the concentrations of their metabolites. Modification of dietary LCPUFA content, particularly increasing the intake of n-3 LCPUFAs, has been shown to minimize the decline in bone mass caused by menopause in women and ovariectomy in animal models. This review summarizes findings from both in vivo and in vitro studies and outlines the effects of LCPUFAs and their metabolites on calcium balance, osteoblastogenesis, osteoclastogenesis, and osteoblast and osteoclast function.
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Affiliation(s)
- Raewyn C Poulsen
- Institute of Food, Nutrition and Human Health, Private Bag 11-222, Palmerston North, New Zealand.
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