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LaGuardia JS, Shariati K, Bedar M, Ren X, Moghadam S, Huang KX, Chen W, Kang Y, Yamaguchi DT, Lee JC. Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design. Adv Healthc Mater 2023; 12:e2301081. [PMID: 37380172 PMCID: PMC10615747 DOI: 10.1002/adhm.202301081] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 06/20/2023] [Indexed: 06/30/2023]
Abstract
Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.
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Affiliation(s)
- Jonnby S. LaGuardia
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Kaavian Shariati
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Meiwand Bedar
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Xiaoyan Ren
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
- Research Service, Greater Los Angeles VA Healthcare System, Los Angeles, CA, 91343, USA
| | - Shahrzad Moghadam
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Kelly X. Huang
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Wei Chen
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Youngnam Kang
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
| | - Dean T. Yamaguchi
- Research Service, Greater Los Angeles VA Healthcare System, Los Angeles, CA, 91343, USA
| | - Justine C. Lee
- Division of Plastic & Reconstructive Surgery, University of California, Los Angeles David Geffen School of Medicine, Los Angeles, CA, 90095, USA
- Research Service, Greater Los Angeles VA Healthcare System, Los Angeles, CA, 91343, USA
- Department of Orthopaedic Surgery, Los Angeles, CA, 90095, USA
- UCLA Molecular Biology Institute, Los Angeles, CA, 90095, USA
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2
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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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3
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Hagan ML, Balayan V, McGee-Lawrence ME. Plasma membrane disruption (PMD) formation and repair in mechanosensitive tissues. Bone 2021; 149:115970. [PMID: 33892174 PMCID: PMC8217198 DOI: 10.1016/j.bone.2021.115970] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 03/26/2021] [Accepted: 04/17/2021] [Indexed: 01/04/2023]
Abstract
Mammalian cells employ an array of biological mechanisms to detect and respond to mechanical loading in their environment. One such mechanism is the formation of plasma membrane disruptions (PMD), which foster a molecular flux across cell membranes that promotes tissue adaptation. Repair of PMD through an orchestrated activity of molecular machinery is critical for cell survival, and the rate of PMD repair can affect downstream cellular signaling. PMD have been observed to influence the mechanical behavior of skin, alveolar, and gut epithelial cells, aortic endothelial cells, corneal keratocytes and epithelial cells, cardiac and skeletal muscle myocytes, neurons, and most recently, bone cells including osteoblasts, periodontal ligament cells, and osteocytes. PMD are therefore positioned to affect the physiological behavior of a wide range of vertebrate organ systems including skeletal and cardiac muscle, skin, eyes, the gastrointestinal tract, the vasculature, the respiratory system, and the skeleton. The purpose of this review is to describe the processes of PMD formation and repair across these mechanosensitive tissues, with a particular emphasis on comparing and contrasting repair mechanisms and downstream signaling to better understand the role of PMD in skeletal mechanobiology. The implications of PMD-related mechanisms for disease and potential therapeutic applications are also explored.
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Affiliation(s)
- Mackenzie L Hagan
- Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, 1460 Laney Walker Blvd., CB1101, Augusta, GA, USA
| | - Vanshika Balayan
- Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, 1460 Laney Walker Blvd., CB1101, Augusta, GA, USA
| | - Meghan E McGee-Lawrence
- Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, 1460 Laney Walker Blvd., CB1101, Augusta, GA, USA; Department of Orthopaedic Surgery, Augusta University, Augusta, GA, USA.
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4
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Juhl OJ, Buettmann EG, Friedman MA, DeNapoli RC, Hoppock GA, Donahue HJ. Update on the effects of microgravity on the musculoskeletal system. NPJ Microgravity 2021; 7:28. [PMID: 34301942 PMCID: PMC8302614 DOI: 10.1038/s41526-021-00158-4] [Citation(s) in RCA: 51] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 06/28/2021] [Indexed: 02/07/2023] Open
Abstract
With the reignited push for manned spaceflight and the development of companies focused on commercializing spaceflight, increased human ventures into space are inevitable. However, this venture would not be without risk. The lower gravitational force, known as microgravity, that would be experienced during spaceflight significantly disrupts many physiological systems. One of the most notably affected systems is the musculoskeletal system, where exposure to microgravity causes both bone and skeletal muscle loss, both of which have significant clinical implications. In this review, we focus on recent advancements in our understanding of how exposure to microgravity affects the musculoskeletal system. We will focus on the catabolic effects microgravity exposure has on both bone and skeletal muscle cells, as well as their respective progenitor stem cells. Additionally, we report on the mechanisms that underlie bone and muscle tissue loss resulting from exposure to microgravity and then discuss current countermeasures being evaluated. We reveal the gaps in the current knowledge and expound upon how current research is filling these gaps while also identifying new avenues of study as we continue to pursue manned spaceflight.
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Affiliation(s)
- Otto J Juhl
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Evan G Buettmann
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Michael A Friedman
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Rachel C DeNapoli
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Gabriel A Hoppock
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Henry J Donahue
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA.
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5
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Zhao D, Liu R, Li G, Chen M, Shang P, Yang H, Jiang JX, Xu H. Connexin 43 Channels in Osteocytes Regulate Bone Responses to Mechanical Unloading. Front Physiol 2020; 11:299. [PMID: 32296345 PMCID: PMC7137730 DOI: 10.3389/fphys.2020.00299] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 03/16/2020] [Indexed: 01/01/2023] Open
Abstract
Connexin (Cx) 43 forms gap junctions and hemichannels that mediate communication between osteocytes and adjacent cells or the extracellular environment in bone, respectively. To investigate the role of each channel type in response to mechanical unloading, two transgenic mouse models overexpressing dominant-negative Cx43 predominantly in osteocytes driven by a 10 kb dentin matrix protein 1 (Dmp1) promoter were generated. The R76W mutation resulted in gap junction inhibition and enhancement of hemichannels, whereas the Δ130-136 mutation inhibited both gap junctions and hemichannels. Both mutations led to cortical bone loss with increased endocortical osteoclast activity during unloading. Increased periosteal osteoclasts with decreased apoptotic osteocytes were observed only in R76W mice. These findings indicated that inhibiting osteocytic Cx43 channels promotes bone loss induced by unloading, mainly in the cortical area; moreover, hemichannels protect osteocytes against apoptosis and promote periosteal bone remodeling, whereas gap junctions modulate endocortical osteoclast activity in response to unloading.
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Affiliation(s)
- Dezhi Zhao
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Ruofei Liu
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Guobin Li
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Meng Chen
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Peng Shang
- Key Laboratory for Space Bioscience and Biotechnology, Research and Development Institute in Shenzhen, Northwestern Polytechnical University, Shenzhen, China
| | - Hui Yang
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
- Research Center of Special Environmental Biomechanics and Medical Engineering, Northwestern Polytechnical University, Xi’an, China
| | - Jean X. Jiang
- Department of Biochemistry and Structural Biology, The University of Texas Health Science Center, San Antonio, TX, United States
| | - Huiyun Xu
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
- Key Laboratory for Space Bioscience and Biotechnology, Research and Development Institute in Shenzhen, Northwestern Polytechnical University, Shenzhen, China
- Research Center of Special Environmental Biomechanics and Medical Engineering, Northwestern Polytechnical University, Xi’an, China
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6
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Curtis KJ, Oberman AG, Niebur GL. Effects of mechanobiological signaling in bone marrow on skeletal health. Ann N Y Acad Sci 2019; 1460:11-24. [PMID: 31508828 DOI: 10.1111/nyas.14232] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 08/09/2019] [Accepted: 08/15/2019] [Indexed: 01/27/2023]
Abstract
Bone marrow is a cellular tissue that forms within the pore space and hollow diaphysis of bones. As a tissue, its primary function is to support the hematopoietic progenitor cells that maintain the populations of both erythroid and myeloid lineage cells in the bone marrow, making it an essential element of normal mammalian physiology. However, bone's primary function is load bearing, and deformations induced by external forces are transmitted to the encapsulated marrow. Understanding the effects of these mechanical inputs on marrow function and adaptation requires knowledge of the material behavior of the marrow at multiple scales, the loads that are applied, and the mechanobiology of the cells. This paper reviews the current state of knowledge of each of these factors. Characterization of the marrow mechanical environment and its role in skeletal health and other marrow functions remains incomplete, but research on the topic is increasing, driven by interest in skeletal adaptation and the mechanobiology of cancer metastasis.
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Affiliation(s)
- Kimberly J Curtis
- Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, Notre Dame, Indiana.,Advanced Diagnostics and Therapeutics Initiative, University of Notre Dame, Notre Dame, Indiana
| | - Alyssa G Oberman
- Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, Notre Dame, Indiana
| | - Glen L Niebur
- Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, Notre Dame, Indiana.,Harper Cancer Research Institute, University of Notre Dame, Notre Dame, Indiana.,Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana
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Combined Fluid Shear Stress and Melatonin Enhances the ERK/Akt/mTOR Signal in Cilia-Less MC3T3-E1 Preosteoblast Cells. Int J Mol Sci 2018; 19:ijms19102929. [PMID: 30261648 PMCID: PMC6213863 DOI: 10.3390/ijms19102929] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Revised: 09/22/2018] [Accepted: 09/23/2018] [Indexed: 01/05/2023] Open
Abstract
We investigated whether combined fluid shear stress (FSS) and melatonin stimulated signal transduction in cilia-less MC3T3-E1 preosteoblast cells. MC3T3-E1 cells were treated with chloral hydrate or nocodazole, and mechanotransduction sensor primary cilia were removed. p-extracellular signal–regulated kinase (ERK) and p-Akt with/without melatonin increased with nocodazole treatment and decreased with chloral hydrate treatment, whereas p-ERK and p-Akt in FSS with/without melatonin increased in cilia-less groups compared to cilia groups. Furthermore, p-mammalian target of rapamycin (mTOR) with FSS-plus melatonin increased in cilia-less groups compared to only melatonin treatments in cilia groups. Expressions of Bcl-2, Cu/Zn-superoxide dismutase (SOD), and catalase proteins were higher in FSS with/without melatonin with cilia-less groups than only melatonin treatments in cilia groups. Bax protein expression was high in FSS-plus melatonin with chloral hydrate treatment. In chloral hydrate treatment with/without FSS, expressions of Cu/Zn-SOD, Mn-SOD, and catalase proteins were high compared to only-melatonin treatments. In nocodazole treatment, Mn-SOD protein expression without FSS was high, and catalase protein level with FSS was low, compared to only melatonin treatments. These data show that the combination with FSS and melatonin enhances ERK/Akt/mTOR signal in cilia-less MC3T3-E1, and the enhanced signaling in cilia-less MC3T3-E1 osteoblast cells may activate the anabolic effect for the preservation of cell structure and function.
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8
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Abstract
Connexons form the basis of hemichannels and gap junctions. They are composed of six tetraspan proteins called connexins. Connexons can function as individual hemichannels, releasing cytosolic factors (such as ATP) into the pericellular environment. Alternatively, two hemichannel connexons from neighbouring cells can come together to form gap junctions, membrane-spanning channels that facilitate cell-cell communication by enabling signalling molecules of approximately 1 kDa to pass from one cell to an adjacent cell. Connexins are expressed in joint tissues including bone, cartilage, skeletal muscle and the synovium. Indicative of their importance as gap junction components, connexins are also known as gap junction proteins, but individual connexin proteins are gaining recognition for their channel-independent roles, which include scaffolding and signalling functions. Considerable evidence indicates that connexons contribute to the function of bone and muscle, but less is known about the function of connexons in other joint tissues. However, the implication that connexins and gap junctional channels might be involved in joint disease, including age-related bone loss, osteoarthritis and rheumatoid arthritis, emphasizes the need for further research into these areas and highlights the therapeutic potential of connexins.
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Affiliation(s)
- Henry J Donahue
- Department of Biomedical Engineering, Virginia Commonwealth University, 601 West Main Street, Richmond, Virginia 23284, USA
| | - Roy W Qu
- Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California at Davis, One Shields Avenue, Davis, California 95616, USA
| | - Damian C Genetos
- Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California at Davis, One Shields Avenue, Davis, California 95616, USA
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9
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Abstract
Bone adaptation to changes in mechanical stimuli occurs by adjusting bone formation and resorption by osteoblasts and osteoclasts, to maintain optimal bone mass. Osteocytes coordinate the actions of these cells on the bone surface by sensing mechanical forces and producing cytokines that increase or prevent osteoblast and osteoclast differentiation and function. Channels formed by connexins (Cxs) and, in particular, connexin 43 (Cx43) in osteoblasts and osteocytes are central part of this mechanism to control bone mass. Cx43 hemichannels are opened by fluid flow and mediate the anti-apoptotic effect of mechanical stimulation in vitro, suggesting that Cx43 participates in mechanotransduction. However, mice lacking Cx43 in osteoblasts and/or osteocytes show an increased anabolic response to loading and decreased catabolic response to unloading. This evidence suggests that Cx43 channels expressed in osteoblastic cells are not required for the response to mechanical stimulation, but mediate the consequence of lack thereof. The molecular basis of these unexpected responses to mechanical stimulation is currently under investigation.
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Affiliation(s)
- Lilian I Plotkin
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, and Roudebush Veterans Administration Medical Center, 635 Barnhill Drive, MS-5035, Indianapolis, IN, 46202, USA,
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10
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Plotkin LI. Connexin 43 hemichannels and intracellular signaling in bone cells. Front Physiol 2014; 5:131. [PMID: 24772090 PMCID: PMC3983496 DOI: 10.3389/fphys.2014.00131] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 03/15/2014] [Indexed: 12/13/2022] Open
Abstract
Cell function and survival are controlled by intracellular signals, and modulated by surrounding cells and the extracellular environment. Connexin channels participate in these processes by mediating cell-to-cell communication. In bone cells, gap junction channels were detected in the early 1970s, and are present among bone resorbing osteoclasts, bone forming osteoblasts, and osteocytes - mature osteoblasts embedded in the mineralized matrix. These channels are composed mainly by Cx43, although the expression of other connexins (45, 46, and 37) has also been reported. It is now believed that undocked Cx43 hemichannels (connexons) formed in unopposed cell membranes facing the extracellular environment participate in the interaction of bone cells with the extracellular environment, and in their communication with neighboring cells. Thus, we and others demonstrated the presence of active hemichannels in osteoblastic and osteocytic cells. These hemichannels open in response to pharmacological and mechanical stimulation. In particular, preservation of the viability of osteoblasts and osteocytes by the anti-osteoporotic drugs bisphosphonates depends on Cx43 expression in vitro and in vivo, and is mediated by undocked hemichannels. Cx43 hemichannels are also required for the release of prostaglandins and ATP by osteocytes, and for cell survival induced by mechanical stimulation in vitro. Moreover, they are required for the anti-apoptotic effect of parathyroid hormone in osteoblastic cells. This review summarizes the current knowledge on the presence and function of undocked connexons, and the role of hemichannel regulation for the maintenance of bone cell viability and, potentially, bone health.
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Affiliation(s)
- Lilian I. Plotkin
- Department Anatomy and Cell Biology, Indiana University School of MedicineIndianapolis, IN, USA
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11
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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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Lloyd SA, Loiselle AE, Zhang Y, Donahue HJ. Shifting paradigms on the role of connexin43 in the skeletal response to mechanical load. J Bone Miner Res 2014; 29:275-86. [PMID: 24588015 PMCID: PMC5949871 DOI: 10.1002/jbmr.2165] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Gap junctions (GJs) are membrane-spanning channels that allow for the movement of small molecules across cell membranes. Connexin43 (Cx43) is the predominant GJ protein in bone. In vitro studies suggest that gap junctional intercellular communication (GJIC) sensitizes bone cells to mechanical signals. Additionally, mechanical signals detected by osteocytes are communicated to osteoblasts via GJIC, and osteocytic Cx43 hemichannels release anabolic factors, such as PGE2 and ATP, in response to mechanical load. These findings and others have led to near consensus among researchers in the field that GJIC, hemichannels or connexins facilitate the anabolic response of bone to mechanical load and, in their absence, bone would be less sensitive to load. However, recent in vivo evidence suggests the opposite is true. Studies from our laboratory and others demonstrate that Cx43-deficient mice have an increased anabolic response to mechanical load and are protected against the catabolic effects of mechanical unloading. These developments suggest a paradigm shift in our understanding of connexins, GJIC, and mechanotransduction in bone. That is, inhibiting bone cell Cx43 expression or GJIC has a beneficial effect on bone's response to its mechanical environment, preserving bone during unloading and enhancing its formation during loading. Here, we review literature in support of this hypothesis and suggest a mechanism by which Cx43, through interaction with WNT/β-catenin signaling, moderates both arms of bone remodeling.
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Affiliation(s)
- Shane A Lloyd
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation; Penn State College of Medicine; Hershey PA USA
| | - Alayna E Loiselle
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation; Penn State College of Medicine; Hershey PA USA
| | - Yue Zhang
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation; Penn State College of Medicine; Hershey PA USA
| | - Henry J Donahue
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation; Penn State College of Medicine; Hershey PA USA
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13
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Synergistic effects of orbital shear stress on in vitro growth and osteogenic differentiation of human alveolar bone-derived mesenchymal stem cells. BIOMED RESEARCH INTERNATIONAL 2014; 2014:316803. [PMID: 24575406 PMCID: PMC3914586 DOI: 10.1155/2014/316803] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Revised: 07/18/2013] [Accepted: 09/30/2013] [Indexed: 11/17/2022]
Abstract
Cellular behavior is dependent on a variety of physical cues required for normal tissue function. In order to mimic native tissue environments, human alveolar bone-derived mesenchymal stem cells (hABMSCs) were exposed to orbital shear stress (OSS) in a low-speed orbital shaker. The synergistic effects of OSS on proliferation and differentiation of hABMSCs were investigated. In particular, we induced the osteoblastic differentiation of hABMSCs cultured in the absence of OM by exposing hABMSCs to OSS (0.86-1.51 dyne/cm(2)). Activation of Cx43 was associated with exposure of hABMSCs to OSS. The viability of cells stimulated for 10, 30, 60, 120, and 180 min/day increased by approximately 10% compared with that of control. The OSS groups with stimulation of 10, 30, and 60 min/day had more intense mineralized nodules compared with the control group. In quantification of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) protein, VEGF protein levels under stimulation for 10, 60, and 180 min/day and BMP-2 levels under stimulation for 60, 120, and 180 min/day were significantly different compared with those of the control. In conclusion, the results indicated that exposing hABMSCs to OSS enhanced their differentiation and maturation.
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14
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Lee KL, Hoey DA, Spasic M, Tang T, Hammond HK, Jacobs CR. Adenylyl cyclase 6 mediates loading-induced bone adaptation in vivo. FASEB J 2013; 28:1157-65. [PMID: 24277577 DOI: 10.1096/fj.13-240432] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Primary cilia are single, nonmotile, antenna-like structures extending from the apical membrane of most mammalian cells. They may mediate mechanotransduction, the conversion of external mechanical stimuli into biochemical intracellular signals. Previously we demonstrated that adenylyl cyclase 6 (AC6), a membrane-bound enzyme enriched in primary cilia of MLO-Y4 osteocyte-like cells, may play a role in a primary cilium-dependent mechanism of osteocyte mechanotransduction in vitro. In this study, we determined whether AC6 deletion impairs loading-induced bone formation in vivo. Skeletally mature mice with a global knockout of AC6 exhibited normal bone morphology and responded to osteogenic chemical stimuli similar to wild-type mice. Following ulnar loading over 3 consecutive days, bone formation parameters were assessed using dynamic histomorphometry. Mice lacking AC6 formed significantly less bone than control animals (41% lower bone formation rate). Furthermore, there was an attenuated flow-induced increase in COX-2 mRNA expression levels in primary bone cells isolated from AC6 knockout mice compared to controls (1.3±0.1- vs. 2.6±0.2-fold increase). Collectively, these data indicate that AC6 plays a role in loading-induced bone adaptation, and these findings are consistent with our previous studies implicating primary cilia and AC6 in a novel mechanism of osteocyte mechanotransduction.
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Affiliation(s)
- Kristen L Lee
- 1Columbia University, 351 Engineering Terr., 1210 Amsterdam Ave., Mail Code 8904, New York, NY 10027, USA.
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15
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Inhibition of GSK-3β rescues the impairments in bone formation and mechanical properties associated with fracture healing in osteoblast selective connexin 43 deficient mice. PLoS One 2013; 8:e81399. [PMID: 24260576 PMCID: PMC3832658 DOI: 10.1371/journal.pone.0081399] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 10/22/2013] [Indexed: 12/12/2022] Open
Abstract
Connexin 43 (Cx43) is the most abundant gap junction protein in bone and is required for osteoblastic differentiation and bone homeostasis. During fracture healing, Cx43 is abundantly expressed in osteoblasts and osteocytes, while Cx43 deficiency impairs bone formation and healing. In the present study we selectively deleted Cx43 in the osteoblastic lineage from immature osteoblasts through osteocytes and tested the hypothesis that Cx43 deficiency results in delayed osteoblastic differentiation and impaired restoration of biomechanical properties due to attenuated β-catenin expression relative to wild type littermates. Here we show that Cx43 deficiency results in alterations in the mineralization and remodeling phases of healing. In Cx43 deficient fractures the mineralization phase is marked by delayed expression of osteogenic genes. Additionally, the decrease in the RankL/ Opg ratio, osteoclast number and osteoclast size suggest decreased osteoclast bone resorption and remodeling. These changes in healing result in functional deficits as shown by a decrease in ultimate torque at failure. Consistent with these impairments in healing, β-catenin expression is attenuated in Cx43 deficient fractures at 14 and 21 days, while Sclerostin (Sost) expression, a negative regulator of bone formation is increased in Cx43cKO fractures at 21 days, as is GSK-3β, a key component of the β-catenin proteasomal degradation complex. Furthermore, we show that alterations in healing in Cx43 deficient fractures can be rescued by inhibiting GSK-3β activity using Lithium Chloride (LiCl). Treatment of Cx43 deficient mice with LiCl restores both normal bone formation and mechanical properties relative to LiCl treated WT fractures. This study suggests that Cx43 is a potential therapeutic target to enhance fracture healing and identifies a previously unknown role for Cx43 in regulating β-catenin expression and thus bone formation during fracture repair.
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16
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Loiselle AE, Paul EM, Lewis GS, Donahue HJ. Osteoblast and osteocyte-specific loss of Connexin43 results in delayed bone formation and healing during murine fracture healing. J Orthop Res 2013; 31:147-54. [PMID: 22718243 PMCID: PMC3640531 DOI: 10.1002/jor.22178] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 06/01/2012] [Indexed: 02/04/2023]
Abstract
Connexin43 (Cx43) plays an important role in osteoblastic differentiation in vitro, and bone formation in vivo. Mice with osteoblast/osteocyte-specific loss of Cx43 display decreased gap junctional intercellular communication (GJIC), bone density, and cortical thickness. To determine the role of Cx43 in fracture healing, a closed femur fracture was induced in Osteocalcin-Cre+; Cx43(flox/flox) (Cx43cKO) and Cre-; Cx43(flox/flox) (WT) mice. We tested the hypothesis that loss of Cx43 results in decreased bone formation and impaired healing following fracture. Here, we show that osteoblast and osteocyte-specific deletion of Cx43 results in decreased bone formation, bone remodeling, and mechanical properties during fracture healing. Cx43cKO mice display decreased bone volume, total volume, and fewer TRAP+ osteoclasts. Furthermore, loss of Cx43 in mature osteoblasts and osteocytes results in a significant decrease in torsional rigidity between 21 and 35 days post-fracture, compared to WT mice. These studies identify a novel role for the gap junction protein Cx43 during fracture healing, suggesting that loss of Cx43 can result in both decreased bone formation and bone resorption. Therefore, enhancing Cx43 expression or GJIC may provide a novel means to enhance bone formation during fracture healing.
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Affiliation(s)
| | | | | | - Henry J. Donahue
- Corresponding Author: Penn State College of Medicine 500 University Dr. Mail Code H089 Hershey, PA 17033 717-531-4809
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17
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Ishihara Y, Sugawara Y, Kamioka H, Kawanabe N, Kurosaka H, Naruse K, Yamashiro T. In situ imaging of the autonomous intracellular Ca(2+) oscillations of osteoblasts and osteocytes in bone. Bone 2012; 50:842-52. [PMID: 22316656 DOI: 10.1016/j.bone.2012.01.021] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 12/15/2011] [Accepted: 01/24/2012] [Indexed: 10/14/2022]
Abstract
Bone cells form a complex three-dimensional network consisting of osteoblasts and osteocytes embedded in a mineralized extracellular matrix. Ca(2+) acts as a ubiquitous secondary messenger in various physiological cellular processes and transduces numerous signals to the cell interior and between cells. However, the intracellular Ca(2+) dynamics of bone cells have not been evaluated in living bone. In the present study, we developed a novel ex-vivo live Ca(2+) imaging system that allows the dynamic intracellular Ca(2+) concentration ([Ca(2+)](i)) responses of intact chick calvaria explants to be observed without damaging the bone network. Our live imaging analysis revealed for the first time that both osteoblasts and osteocytes display repetitive and autonomic [Ca(2+)](i) oscillations ex vivo. Thapsigargin, an inhibitor of the endoplasmic reticulum that induces the emptying of intracellular Ca(2+) stores, abolished these [Ca(2+)](i) responses in both osteoblasts and osteocytes, indicating that Ca(2+) release from intracellular stores plays a key role in the [Ca(2+)](i) oscillations of these bone cells in intact bone explants. Another possible [Ca(2+)](i) transient system to be considered is gap junctional communication through which Ca(2+) and other messenger molecules move, at least in part, across cell-cell junctions; therefore, we also investigated the role of gap junctions in the maintenance of the autonomic [Ca(2+)](i) oscillations observed in the intact bone. Treatment with three distinct gap junction inhibitors, 18α-glycyrrhetinic acid, oleamide, and octanol, significantly reduced the proportion of responsive osteocytes, indicating that gap junctions are important for the maintenance of [Ca(2+)](i) oscillations in osteocytes, but less in osteoblasts. Taken together, we found that the bone cells in intact bone explants showed autonomous [Ca(2+)](i) oscillations that required the release of intracellular Ca(2+) stores. In addition, osteocytes specifically modulated these oscillations via cell-cell communication through gap junctions, which maintains the observed [Ca(2+)](i) oscillations of bone cells.
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Affiliation(s)
- Yoshihito Ishihara
- Department of Orthodontics, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, 700-8525, Japan.
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18
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York SL, Arida AR, Shah KS, Sethu P, Saunders MM. Osteocyte Characterization on Polydimethylsiloxane Substrates for Microsystems Applications. JOURNAL OF BIOMIMETICS, BIOMATERIALS, AND TISSUE ENGINEERING 2012; 16:27-42. [PMID: 30245613 PMCID: PMC6150457 DOI: 10.4028/www.scientific.net/jbbte.16.27] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the body, osteocytes reside in lacunae, lenticular shaped cavities within mineralized bone. These cells are linked to each other and surface-residing osteoblasts via physical channels known as gap junctions. It has been suggested that osteocytes sense mechanical load applied to bone and relay that signal to osteoclasts and osteoblasts. Current in vitro and in vivo models of mechanotransduction face temporal and spatial barriers. Recent advances in polydimethylsiloxane (PDMS) based microfabrication techniques may be able to overcome some of these hurdles. However, before the bone research field can effectively utilize microsystems techniques, fundamental groundwork must be completed. This study characterized the behaviour of osteocytes on PDMS coated with collagen type I (CTI) and provides the framework for bone cell mechanotransduction studies using microsystems. The goal was to determine whether osteocytes were adversely affected by the substrate material by comparing their behaviour to a standard glass substrate. In addition, optimal culture conditions and time points for growing osteocytes on PDMS substrates were determined. Results of this study suggested that use of PDMS does not adversely affect osteocyte behaviour. Furthermore, the results demonstrated that osteocytes should be cultured for no less than 72 hours prior to experimentation to allow the establishment and maintenance of phenotypic characteristics. These results completed essential groundwork necessary for further studies regarding osteocytes in microsystems modelling utilizing PDMS.
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Affiliation(s)
- Spencer L York
- Department of Biomedical Engineering, The University of Akron, 260 S Forge St, Akron, OH 44325, USA
| | - Ahmad R Arida
- Department of Biomedical Engineering, The University of Akron, 260 S Forge St, Akron, OH 44325, USA
| | - Karan S Shah
- Department of Biomedical Engineering, The University of Akron, 260 S Forge St, Akron, OH 44325, USA
| | - Palaniappan Sethu
- Department of Bioengineering, University of Louisville, 2100 S Brook St, SRB 357, Louisville, KY, 40292, USA
| | - Marnie M Saunders
- Department of Biomedical Engineering, The University of Akron, 260 S Forge St, Akron, OH 44325, USA
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19
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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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20
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Abstract
Communication between osteoblasts, osteoclasts, and osteocytes is integral to their ability to build and maintain the skeletal system and respond to physical signals. Various physiological mechanisms, including nerve communication, hormones, and cytokines, play an important role in this process. More recently, the important role of direct, cell-cell communication via gap junctions has been established. In this review, we demonstrate the integral role of gap junctional intercellular communication (GJIC) in skeletal physiology and bone cell mechanosensing.
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21
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Kang KS, Trosko JE. Stem cells in toxicology: fundamental biology and practical considerations. Toxicol Sci 2010; 120 Suppl 1:S269-89. [PMID: 21163910 DOI: 10.1093/toxsci/kfq370] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
This "Commentary" has examined the use of human stem cells for detection of toxicities of physical, chemical, and biological toxins/toxicants in response to the challenge posed by the NRC Report, "Toxicity Testing in the 21st Century: A vision and Strategy." Before widespread application of the use of human embryonic, pluripotent, "iPS," or adult stem cells be considered, the basic characterization of stem cell biology should be undertaken. Because no in vitro system can mimic all factors that influence cells in vivo (individual genetic, gender, developmental, immunological and diurnal states; niche conditions; complex intercellular interactions between stem, progenitor, terminal differentiated cells, and the signaling from extracellular matrices, oxygen tensions, etc.), attempts should be made to use both embryonic and adult stem cells, grown in three dimension under "niche-like" conditions. Because many toxins and toxicants work by "epigenetic" mechanisms and that epigenetic mechanisms play important roles in regulating gene expression and in the pathogenesis of many human diseases, epigenetic toxicity must be incorporated in toxicity testing. Because modulation of gap junctional intercellular communication by epigenetic agents plays a major role in homeostatic regulation of both stem and progenitor cells in normal tissues, the modulation of this biological process by both endogenous and endogenous chemicals should be incorporated as an end point to monitor for potential toxicities or chemo-preventive attributes. In addition, modulation of quantity, as well as the quality, of stem cells should be considered as potential source of a chemical's toxic potential in affecting any stem cell-based pathology, such as cancer.
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Affiliation(s)
- Kyung-Sun Kang
- Adult Stem Cell Research Center, Laboratory for Stem Cell and Tumor Biology, Department of Veterinary Public Health, College of Veterinary Medicine, Seoul National University, Sillim-Dong, Seoul 151-742, Korea
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22
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Saunders MM, Simmerman LA, Reed GL, Sharkey NA, Taylor AF. Biomimetic bone mechanotransduction modeling in neonatal rat femur organ cultures: structural verification of proof of concept. Biomech Model Mechanobiol 2010; 9:539-50. [PMID: 20169394 PMCID: PMC2908729 DOI: 10.1007/s10237-010-0195-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Accepted: 01/22/2010] [Indexed: 10/19/2022]
Abstract
The goal of this work was to develop and validate a whole bone organ culture model to be utilized in biomimetic mechanotransduction research. Femurs harvested from 2-day-old neonatal rat pups were maintained in culture for 1 week post-harvest and assessed for growth and viability. For stimulation studies, femurs were physiologically stimulated for 350 cycles 24 h post-harvest then maintained in culture for 1 week at which time structural tests were conducted. Comparing 1 and 8 days in culture, bones grew significantly in size over the 7-day culture period. In addition, histology supported adequate diffusion and organ viability at 2 weeks in culture. For stimulation studies, 350 cycles of physiologic loading 24 h post-harvest resulted in increased bone strength over the 7-day culture period. In this work, structural proof of concept was established for the use of whole bone organ cultures as mechanotransduction models. Specifically, this work established that these cultures grow and remain viable in culture, are adequately nourished via diffusion and are capable of responding to a brief bout of mechanical stimulation with an increase in strength.
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23
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Arnsdorf EJ, Tummala P, Castillo AB, Zhang F, Jacobs CR. The epigenetic mechanism of mechanically induced osteogenic differentiation. J Biomech 2010; 43:2881-6. [PMID: 20728889 DOI: 10.1016/j.jbiomech.2010.07.033] [Citation(s) in RCA: 104] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Accepted: 07/21/2010] [Indexed: 01/13/2023]
Abstract
Epigenetic regulation of gene expression occurs due to alterations in chromatin proteins that do not change DNA sequence, but alter the chromatin architecture and the accessibility of genes, resulting in changes to gene expression that are preserved during cell division. Through this process genes are switched on or off in a more durable fashion than other transient mechanisms of gene regulation, such as transcription factors. Thus, epigenetics is central to cellular differentiation and stem cell linage commitment. One such mechanism is DNA methylation, which is associated with gene silencing and is involved in a cell's progression towards a specific fate. Mechanical signals are a crucial regulator of stem cell behavior and important in tissue differentiation; however, there has been no demonstration of a mechanism whereby mechanics can affect gene regulation at the epigenetic level. In this study, we identified candidate DNA methylation sites in the promoter regions of three osteogenic genes from bone marrow derived mesenchymal stem cells (MSCs). We demonstrate that mechanical stimulation alters their epigenetic state by reducing DNA methylation and show an associated increase in expression. We contrast these results with biochemically induced differentiation and distinguish expression changes associated with durable epigenetic regulation from those likely to be due to transient changes in regulation. This is an important advance in stem cell mechanobiology as it is the first demonstration of a mechanism by which the mechanical micro-environment is able to induce epigenetic changes that control osteogenic cell fate, and that can be passed to daughter cells. This is a first step to understanding that will be vital to successful bone tissue engineering and regenerative medicine, where continued expression of a desired long-term phenotype is crucial.
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Affiliation(s)
- Emily J Arnsdorf
- Bone and Joint Rehabilitation R&D Center, VA Palo Alto Medical Center, Palo Alto, CA, United States
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24
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Thi MM, Urban-Maldonado M, Spray DC, Suadicani SO. Characterization of hTERT-immortalized osteoblast cell lines generated from wild-type and connexin43-null mouse calvaria. Am J Physiol Cell Physiol 2010; 299:C994-C1006. [PMID: 20686067 DOI: 10.1152/ajpcell.00544.2009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The gap junction protein connexin43 (Cx43) has been proposed to play key roles in bone differentiation and mineralization, but underlying cellular mechanisms are not totally understood. To further explore roles of Cx43 in these processes, we immortalized calvarial osteoblasts from wild-type and Cx43-null mice using human telomerase reverse transcriptase (hTERT). Osteoblastic (MOB) cell lines were generated from three individual wild-type and three individual Cx43-null mouse calvaria. Average population doubling times of the cell lines were higher than of the primary osteoblasts but did not greatly differ with regard to genotype. Modest to high level of Cx45 expression was detected in MOBs of both genotypes. Most of the cell lines expressed osteoblastic markers [Type I collagen, osteopontin, osteocalcin, parathyroid hormone/parathyroid hormone-related peptide receptor (PTH/PTHrP), periostin (OSF-2), osterix (Osx), runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP)], and mineralization was comparable to that of primary osteoblasts. Two MOB cell lines from each genotype with most robust maintenance of osteoblast lineage markers were analyzed in greater detail, revealing that the Cx43-null cell lines showed a significant delay in early differentiation (up to 9 days in culture). Matrix mineralization was markedly delayed in one of the Cx43-null lines and slightly delayed in the other. These findings comparing new and very stable wild-type and Cx43-null osteoblastic cell lines define a role for Cx43 in early differentiation and mineralization stages of osteoblasts and further support the concept that Cx43 plays important role in the cellular processes associated with skeleton function.
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Affiliation(s)
- Mia M Thi
- Department of Orthopaedic Surgery, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA.
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25
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Thi MM, Suadicani SO, Spray DC. Fluid flow-induced soluble vascular endothelial growth factor isoforms regulate actin adaptation in osteoblasts. J Biol Chem 2010; 285:30931-41. [PMID: 20682775 DOI: 10.1074/jbc.m110.114975] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Although load-induced mechanical signals play a key role in bone formation and maintenance of bone mass and structure, the cellular mechanisms involved in the translation of these signals are still not well understood. Recent identification of a novel flow-induced mechanosignaling pathway involving VEGF in osteoblasts and the known VEGF regulation of actin reorganization in various cell types has led us to hypothesize that fluid shear stress-induced Vegf up-regulation underlies the actin cytoskeleton adaptation observed in osteoblasts during mechanotransduction. Our results show that MC3T3-E1 cells secrete significant VEGF in response to 5 h of pulsatile fluid shear stress (PFSS; 5 dynes/cm(2) at 1 Hz), whereas expression of VEGF receptors (VEGFR-1, VEGFR-2, or NRP1) is unaffected. These receptors, in particular VEGFR-2, participate in PFSS-induced VEGF release. Exposure to flow-conditioned medium or exogenous VEGF significantly induces stress fiber formation in osteoblasts that is comparable with PFSS-induced stress fiber formation, whereas VEGF knockdown abrogates this response to PFSS, thereby providing evidence that flow-induced VEGF release plays a role in actin polymerization. Using neutralizing antibodies against the receptors and VEGF isoforms, we found that soluble VEGFs, in particular VEGF(164), play a crucial role in transient stress fiber formation during osteoblast mechanotransduction, most likely through VEGFR-2 and NRP1. Based on these data we conclude that flow-induced VEGF release from osteoblasts regulates osteoblast actin adaptation during mechanotransduction and that VEGF paracrine signaling may provide potent cross-talk among bone cells and endothelial cells that is essential for fracture healing, bone remodeling, and osteogenesis.
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Affiliation(s)
- Mia M Thi
- Department of Orthopaedic Surgery, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA
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26
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Jacobs CR, Temiyasathit S, Castillo AB. Osteocyte Mechanobiology and Pericellular Mechanics. Annu Rev Biomed Eng 2010; 12:369-400. [PMID: 20617941 DOI: 10.1146/annurev-bioeng-070909-105302] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Christopher R. Jacobs
- Department of Biomedical Engineering, Columbia University, New York, New York 10027;
| | - Sara Temiyasathit
- Bioengineering and Mechanical Engineering, Stanford University, Stanford, California 94305
| | - Alesha B. Castillo
- Bone and Joint Center, Department of Rehabilitation Research and Development, Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304
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27
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Shivaram GM, Kim CH, Batra NN, Yang W, Harris SE, Jacobs CR. Novel early response genes in osteoblasts exposed to dynamic fluid flow. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2010; 368:605-16. [PMID: 20047941 PMCID: PMC2944389 DOI: 10.1098/rsta.2009.0231] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Cyclic mechanical loads applied to the skeleton from habitual physical activity result in increased bone formation. These loads lead to dynamic pressure gradients and oscillatory flow of bone interstitial fluid, which, in turn, exposes cells resident in the bony matrix to oscillatory fluid shear stress. Dynamic fluid flow has previously been shown to be a potent anabolic stimulus for cultured osteoblasts. In this study, we used cDNA microarrays to examine early phase, broad-spectrum gene expression in MC3T3-E1 osteoblasts in response to physical stimulation. RNA was harvested at 30 min and 1 h post-stimulation. RNA was used for microarray hybridization as well as subsequent reverse transcription polymerase chain reaction (RT-PCR) validation of expression levels for selected genes. Microarray results were analysed by both functional and expression profile clustering. We identified a small number of genes at both the 30 min and 1 h timepoints that were either upregulated or downregulated with flow compared to no-flow control by twofold or more. From the group of genes upregulated at 30 min, we selected nine for RT-PCR confirmation. All were found to be upregulated by at least twofold. We identify a novel set of early response genes potentially involved in mediating the anabolic response of MC3T3 osteoblasts to flow, and provide functional groupings of these genes that may shed light on the relevant mechanosensory pathways involved.
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Affiliation(s)
- Giridhar M. Shivaram
- Bone and Joint Rehabilitation Research and Development Center, Veterans Affairs Medical Center, Palo Alto, CA 94304, USA
- Stanford University School of Medicine, Stanford, CA 94305, USA
- Department of Mechanical Engineering, Stanford University, Stanford CA 94305, USA
| | - Chi Hyun Kim
- Department of Biomedical Engineering, Yonsei University, Wonju, South Korea
| | - Nikhil N. Batra
- Bone and Joint Rehabilitation Research and Development Center, Veterans Affairs Medical Center, Palo Alto, CA 94304, USA
- Department of Mechanical Engineering, Stanford University, Stanford CA 94305, USA
| | - Wuchen Yang
- Department of Periodontics and Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
| | - Stephen E. Harris
- Department of Periodontics and Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
| | - Christopher R. Jacobs
- Bone and Joint Rehabilitation Research and Development Center, Veterans Affairs Medical Center, Palo Alto, CA 94304, USA
- Stanford University School of Medicine, Stanford, CA 94305, USA
- Department of Mechanical Engineering, Stanford University, Stanford CA 94305, USA
- Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA
- Author for correspondence ()
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28
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Huo B, Lu XL, Guo XE. Intercellular calcium wave propagation in linear and circuit-like bone cell networks. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2010; 368:617-33. [PMID: 20047942 PMCID: PMC3263793 DOI: 10.1098/rsta.2009.0221] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
In the present study, the mechanism of intercellular calcium wave propagation in bone cell networks was identified. By using micro-contact printing and self-assembled monolayer technologies, two types of in vitro bone cell networks were constructed: open-ended linear chains and looped hexagonal networks with precisely controlled intercellular distances. Intracellular calcium responses of the cells were recorded and analysed when a single cell in the network was mechanically stimulated by nano-indentation. The looped cell network was shown to be more efficient than the linear pattern in transferring calcium signals from cell to cell. This phenomenon was further examined by pathway-inhibition studies. Intercellular calcium wave propagation was significantly impeded when extracellular adenosine triphosphate (ATP) in the medium was hydrolysed. Chemical uncoupling of gap junctions, however, did not significantly decrease the transferred distance of the calcium wave in the cell networks. Thus, it is extracellular ATP diffusion, rather than molecular transport through gap junctions, that dominantly mediates the transmission of mechanically elicited intercellular calcium waves in bone cells. The inhibition studies also demonstrated that the mechanical stimulation-induced calcium responses required extracellular calcium influx, whereas the ATP-elicited calcium wave relied on calcium release from the calcium store of the endoplasmic reticulum.
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Affiliation(s)
- Bo Huo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, University of Columbia, 351 Engineering Terrace, PO Box 8904, 1210 Amsterdan Avenue, New York, NY 10027, USA
- Centre for Biomechanics and Bioengineering, Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Xin L. Lu
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, University of Columbia, 351 Engineering Terrace, PO Box 8904, 1210 Amsterdan Avenue, New York, NY 10027, USA
| | - X. Edward Guo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, University of Columbia, 351 Engineering Terrace, PO Box 8904, 1210 Amsterdan Avenue, New York, NY 10027, USA
- Author for correspondence ()
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29
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Frias C, Reis J, Capela e Silva F, Potes J, Simões J, Marques AT. Polymeric piezoelectric actuator substrate for osteoblast mechanical stimulation. J Biomech 2010; 43:1061-6. [PMID: 20116061 DOI: 10.1016/j.jbiomech.2009.12.010] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2009] [Revised: 12/15/2009] [Accepted: 12/17/2009] [Indexed: 12/11/2022]
Abstract
Bone mass distribution and structure are dependent on mechanical stress and adaptive response at cellular and tissue levels. Mechanical stimulation of bone induces new bone formation in vivo and increases the metabolic activity and gene expression of osteoblasts in culture. A wide variety of devices have been tested for mechanical stimulation of cells and tissues in vitro. The aim of this work was to experimentally validate the possibility to use piezoelectric materials as a mean of mechanical stimulation of bone cells, by converse piezoelectric effect. To estimate the magnitude and the distribution of strain, finite numerical models were applied and the results were complemented with the optical tests (Electronic Speckle Pattern Interferometric Process). In this work, osteoblasts were grown on the surface of a piezoelectric material, both in static and dynamic conditions at low frequencies, and total protein, cell viability and nitric oxide measurement comparisons are presented.
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Affiliation(s)
- C Frias
- Mechanical Engineering Department, Faculty of Engineering of Porto University, Campus FEUP, Rua Roberto Frias s/n, 4200-465 Porto, Portugal.
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Lima F, Niger C, Hebert C, Stains JP. Connexin43 potentiates osteoblast responsiveness to fibroblast growth factor 2 via a protein kinase C-delta/Runx2-dependent mechanism. Mol Biol Cell 2009; 20:2697-708. [PMID: 19339281 PMCID: PMC2688549 DOI: 10.1091/mbc.e08-10-1079] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2008] [Revised: 03/20/2009] [Accepted: 03/24/2009] [Indexed: 12/13/2022] Open
Abstract
In this study, we examine the role of the gap junction protein, connexin43 (Cx43), in the transcriptional response of osteocalcin to fibroblast growth factor 2 (FGF2) in MC3T3 osteoblasts. By luciferase reporter assays, we identify that the osteocalcin transcriptional response to FGF2 is markedly increased by overexpression of Cx43, an effect that is mediated by Runx2 via its OSE2 cognate element, but not by a previously identified connexin-responsive Sp1/Sp3-binding element. Furthermore, disruption of Cx43 function with Cx43 siRNAs or overexpression of connexin45 markedly attenuates the response to FGF2. Inhibition of protein kinase C delta (PKCdelta) with rottlerin or siRNA-mediated knockdown abrogates the osteocalcin response to FGF2. Additionally, we show that upon treatment with FGF2, PKCdelta translocates to the nucleus, PKCdelta and Runx2 are phosphorylated and these events are enhanced by Cx43 overexpression, suggesting that the degree of activation is enhanced by increased Cx43 levels. Indeed, chromatin immunoprecipitations of the osteocalcin proximal promoter with antibodies against Runx2 demonstrate that the recruitment of Runx2 to the osteocalcin promoter in response to FGF2 treatment is dramatically enhanced by Cx43 overexpression. Thus, Cx43 plays a critical role in regulating the ability of osteoblasts to respond to FGF2 by impacting PKCdelta and Runx2 function.
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Affiliation(s)
- Florence Lima
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Corinne Niger
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Carla Hebert
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Joseph P. Stains
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201
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Jekir MG, Donahue HJ. Gap junctions and osteoblast-like cell gene expression in response to fluid flow. J Biomech Eng 2009; 131:011005. [PMID: 19045921 DOI: 10.1115/1.3005201] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Bone formation occurs in vivo in response to mechanical stimuli, but the signaling pathways involved remain unclear. The ability of bone cells to communicate with each other in the presence of an applied load may influence the overall osteogenic response. The goal of this research was to determine whether inhibiting cell-to-cell gap junctional communication between bone-forming cells would affect the ensemble cell response to an applied mechanical stimulus in vitro. In this study, we investigated the effects of controlled oscillatory fluid flow (OFF) on osteoblastic cells in the presence and the absence of a gap-junction blocker. MC3T3-E1 Clone 14 cells in a monolayer were exposed to 2 h of OFF at a rate sufficient to create a shear stress of 20 dyne/cm(2) at the cell surface, and changes in steady-state mRNA levels for a number of key proteins known to be involved in osteogenesis were measured. Of the five proteins investigated, mRNA levels for osteopontin (OPN) and osteocalcin were found to be significantly increased 24 h postflow. These experiments were repeated in the presence of 18 beta-glycyrrhetinic acid (BGA), a known gap-junction blocker, to determine whether gap-junction intercellular communication is necessary for this response. We found that the increase in OPN mRNA levels is not observed in the presence of BGA, suggesting that gap junctions are involved in the signaling process. Interestingly, enzyme linked immunosorbent assay data showed that levels of secreted OPN protein increased 48 h postflow and that this increase was unaffected by the presence of intact gap junctions.
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Affiliation(s)
- Michael G Jekir
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
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Rossello RA, Kohn DH. Gap junction intercellular communication: a review of a potential platform to modulate craniofacial tissue engineering. J Biomed Mater Res B Appl Biomater 2009; 88:509-18. [PMID: 18481782 DOI: 10.1002/jbm.b.31127] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Defects in craniofacial tissues, resulting from trauma, congenital abnormalities, oncologic resection or progressive deforming diseases, may result in aesthetic deformity, pain and reduced function. Restoring the structure, function and aesthetics of craniofacial tissues represents a substantial clinical problem in need of new solutions. More biologically-interactive biomaterials could potentially improve the treatment of craniofacial defects, and an understanding of developmental processes may help identify strategies and materials that can be used in tissue engineering. One such strategy that can potentially advance tissue engineering is cell-cell communication. Gap junction intercellular communication is the most direct way of achieving such signaling. Gap junction communication through connexin-mediated junctions, in particular connexin 43 (Cx43), plays a major role bone development. Given the important role of Cx43 in controlling development and differentiation, especially in bone cells, controlling the expression of Cx43 may provide control over cell-to-cell communication and may help overcome some of the challenges in craniofacial tissue engineering. Following a review of gap junctions in bone cells, the ability to enhance cell-cell communication and osteogenic differentiation via control of gap junctions is discussed, as is the potential utility of this approach in craniofacial tissue engineering.
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Affiliation(s)
- Ricardo A Rossello
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2099, USA
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Friedl KE, Evans RK, Moran DS. Stress fracture and military medical readiness: bridging basic and applied research. Med Sci Sports Exerc 2009; 40:S609-22. [PMID: 18849874 DOI: 10.1249/mss.0b013e3181892d53] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
PURPOSE Military recruits and distance runners share a special risk of stress fracture injury. Recent efforts by US and Israeli military-sponsored researchers have uncovered important mechanisms and practical low-cost interventions. This article summarizes key findings relevant to prevention of stress fracture, including simple strategies to identify and to mitigate risk. METHODS Published research supported through the Bone Health and Military Medical Readiness research program and related military bone research was analyzed for contributions to preventing stress fracture in military recruits and optimizing bone health. RESULTS Thousands of military recruits helped test hypotheses about predictors of risk, safer exercise regimens, and rest, nutrition, gait training, and technology interventions to reduce stress fracture risk. Concurrent cellular, animal, and human laboratory studies were used to systematically investigate mechanisms of mechanical forces acting on bone and interactions through muscle, hormonal and genetic influences, and metabolism. The iterative and sometimes simultaneous process of basic discovery and field testing produced new knowledge that will provide safer science-based physical training. DISCUSSION Human training studies evaluating effects on bone require special commitment from investigators and funders due to volunteer compliance and attrition challenges. The findings from multiple studies indicate that measures of bone elasticity, fragility, and geometry are as important as bone mineral density in predicting fracture risk, with applications for new measurement technologies. Risk may be reduced by high intakes of calcium, vitamin D, and possibly protein (e.g., milk products). Prostaglandin E2, insulin-like growth factor 1, and estrogens are important mediators of osteogenesis, indicating reasons to limit the use of certain drugs (e.g., ibuprofen), to avoid excessive food restriction, and to treat hypogonadism. Abnormal gait may be a correctable risk factor. Brief daily vibration may stimulate bone mineral accretion similar to weight-bearing exercise. Genetic factors contribute importantly to bone quality, affecting fracture susceptibility and providing new insights into fracture healing and tissue reengineering.
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Affiliation(s)
- Karl E Friedl
- Telemedicine and Advanced Technology Research Center, Fort Detrick, MD 21702-5012, USA.
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Riddle RC, Donahue HJ. From streaming-potentials to shear stress: 25 years of bone cell mechanotransduction. J Orthop Res 2009; 27:143-9. [PMID: 18683882 DOI: 10.1002/jor.20723] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mechanical loads are vital regulators of skeletal mass and architecture as evidenced by the increase in bone formation following the addition of exogenous loads and loss of bone mass following their removal. While our understanding of the molecular mechanisms by which bone cells perceive changes in their mechanical environment has increased rapidly in recent years, much remains to be learned. Here, we outline the effects of interstitial fluid flow, a potent biophysical signal induced by the deformation of skeletal tissue in response to applied loads, on bone cell behavior. We focus on the molecular mechanisms by which bone cells are hypothesized to perceive interstitial fluid flow, the cell signaling cascades activated by fluid flow, and the use of this signal in tissue engineering protocols.
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Affiliation(s)
- Ryan C Riddle
- Division of Cellular and Molecular Pathology, Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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Riddle RC, Hippe KR, Donahue HJ. Chemotransport contributes to the effect of oscillatory fluid flow on human bone marrow stromal cell proliferation. J Orthop Res 2008; 26:918-24. [PMID: 18327808 DOI: 10.1002/jor.20637] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mechanical loads produce a diverse set of biophysical signals that may regulate bone cell activity, but accumulating evidence suggests that interstitial fluid flow is the primary signal that bone cells perceive. Because we previously demonstrated that oscillatory fluid flow increases human bone marrow stromal cell proliferation, we investigated the contribution of fluid shear stress and chemotransport, two stimuli induced by interstitial fluid flow. Alterations in flow rate at a constant peak shear stress were associated with decreases in oscillatory fluid flow-induced marrow stromal cell proliferation, while variations in peak fluid shear stress had no significant effect. Modulation of marrow stromal cell proliferation by flow rate may be attributed to changes in the release of ATP and intracellular calcium signaling. We found that if the flow rate is decreased while maintaining a constant peak fluid shear stress, marrow stromal cells release less ATP into the extracellular environment. Moreover, as the flow rate decreased fewer cells respond to fluid flow with an increase in intracellular calcium concentration. These data suggest that chemotransport is a prerequisite for marrow stromal cells to respond to interstitial fluid flow.
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Affiliation(s)
- Ryan C Riddle
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033, USA
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Attenuated response to in vivo mechanical loading in mice with conditional osteoblast ablation of the connexin43 gene (Gja1). J Bone Miner Res 2008; 23:879-86. [PMID: 18282131 PMCID: PMC2677086 DOI: 10.1359/jbmr.080222] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
INTRODUCTION In vitro data suggest that gap junctional intercellular communication mediated by connexin43 (Cx43) plays an important role in bone cell response to mechanical stimulation. We tested this hypothesis in vivo in a model of genetic deficiency of the Cx43 gene (Gja1). MATERIALS AND METHODS Four-month-old female mice with a conditional Gja1 ablation in osteoblasts (ColCre;Gja1(-/flox)), as well as wildtype (Gja1(+/flox)) and heterozygous equivalent (Gja1(-/flox)) littermates (eight per genotype), were subjected to a three-point bending protocol for 5 d/wk for 2 wk. Microstructural parameters and dynamic indices of bone formation were estimated on sections of loaded and control contralateral tibias. RESULTS ColCre;Gja1(-/flox) mice had significantly thinner cortices, but larger marrow area and total cross-sectional area in the tibial diaphysis, compared with the other groups. The ColCre;Gja1(-/flox) mice needed approximately 40% more force to generate the required endocortical strain. In Gja1(+/flox) mice, the loading regimen produced abundant double calcein labels at the endocortical surface, whereas predominantly single labels were seen in ColCre;Gja1(-/flox) mice. Accordingly, mineral apposition rate and bone formation rate were significantly lower (54.8% and 50.2%, respectively) in ColCre;Gja1(-/flox) relative to Gja1(+/flox) mice. Intermediate values were found in Gja1(-/flox) mice. CONCLUSIONS Gja deficiency results in thinner but larger tibial diaphyses, resembling changes occurring with aging, and it attenuates the anabolic response to in vivo mechanical loading. Thus, Cx43 plays an instrumental role in this adaptive response to physical stimuli.
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Huo B, Lu XL, Hung CT, Costa KD, Xu Q, Whitesides GM, Guo XE. Fluid Flow Induced Calcium Response in Bone Cell Network. Cell Mol Bioeng 2008; 1:58-66. [PMID: 20852730 DOI: 10.1007/s12195-008-0011-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In our previous work, bone cell networks with controlled spacing and functional intercellular gap junctions had been successfully established by using microcontact printing and self assembled monolayers technologies [Guo, X. E., E. Takai, X. Jiang, Q. Xu, G. M. Whitesides, J. T. Yardley, C. T. Hung, E. M. Chow, T. Hantschel, and K. D. Costa. Mol. Cell. Biomech. 3:95-107, 2006]. The present study investigated the calcium response and the underlying signaling pathways in patterned bone cell networks exposed to a steady fluid flow. The glass slides with cell networks were separated into eight groups for treatment with specific pharmacological agents that inhibit pathways significant in bone cell calcium signaling. The calcium transients of the network were recorded and quantitatively evaluated with a set of network parameters. The results showed that 18α-GA (gap junction blocker), suramin (ATP inhibitor), and thapsigargin (depleting intracellular calcium stores) significantly reduced the occurrence of multiple calcium peaks, which were visually obvious in the untreated group. The number of responsive peaks also decreased slightly yet significantly when either the COX-2/PGE(2) or the NOS/nitric oxide pathway was disrupted. Different from all other groups, cells treated with 18α-GA maintained a high concentration of intracellular calcium following the first peak. In the absence of calcium in the culture medium, the intracellular calcium concentration decreased slowly with fluid flow without any calcium transients observed. These findings have identified important factors in the flow mediated calcium signaling of bone cells within a patterned network.
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Affiliation(s)
- Bo Huo
- Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, 351 Engineering Terrace, 1210 Amsterdam Avenue, Mail Code 8904, New York, NY 10027, USA
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Genetos DC, Kephart CJ, Zhang Y, Yellowley CE, Donahue HJ. Oscillating fluid flow activation of gap junction hemichannels induces ATP release from MLO-Y4 osteocytes. J Cell Physiol 2007; 212:207-14. [PMID: 17301958 PMCID: PMC2929812 DOI: 10.1002/jcp.21021] [Citation(s) in RCA: 230] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mechanical loads are required for optimal bone mass. One mechanism whereby mechanical loads are transduced into localized cellular signals is strain-induced fluid flow through lacunae and canaliculi of bone. Gap junctions (GJs) between osteocytes and osteoblasts provides a mechanism whereby flow-induced signals are detected by osteocytes and transduced to osteoblasts. We have demonstrated the importance of GJ and gap junctional intercellular communication (GJIC) in intracellular calcium and prostaglandin E(2) (PGE(2)) increases in response to flow. Unapposed connexons, or hemichannels, are themselves functional and may constitute a novel mechanotransduction mechanism. Using MC3T3-E1 osteoblasts and MLO-Y4 osteocytes, we examined the time course and mechanism of hemichannel activation in response to fluid flow, the composition of the hemichannels, and the role of hemichannels in flow-induced ATP release. We demonstrate that fluid flow activates hemichannels in MLO-Y4, but not MC3T3-E1, through a mechanism involving protein kinase C, which induces ATP and PGE(2) release.
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Affiliation(s)
- Damian C. Genetos
- Department of Orthopaedic Surgery, University of California at Davis, Sacramento, CA, 95817
| | - Curtis J. Kephart
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, 17033
| | - Yue Zhang
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, 17033
| | - Clare E. Yellowley
- Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California at Davis, Davis, CA, 95616
| | - Henry J. Donahue
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, 17033
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Devlin MJ, Lieberman DE. Variation in estradiol level affects cortical bone growth in response to mechanical loading in sheep. ACTA ACUST UNITED AC 2007; 210:602-13. [PMID: 17267646 DOI: 10.1242/jeb.02675] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Although mechanical loading can stimulate cortical bone growth, little is known about how individual physiology affects this response. This study demonstrates that in vivo variation in estradiol (E2) level alters osteoblast sensitivity to exercise-induced strains, affecting cortical bone responses to mechanical loading. Subadult sheep were divided into treatment groups that varied in terms of circulating E2 levels and loading (exercised and sedentary). After 45 days, periosteal cortical bone growth rates and cross-sectional properties were measured at the midshafts of hindlimb bones and compared with strain data. The results indicate significant interactions between E2 and strain. Cortical bone growth in exercised animals with elevated E2 levels was 27% greater in the femur, 6% greater in the tibia, and 14% greater in the metatarsal than in exercised animals with lower E2 levels, or sedentary animals regardless of E2 dose (P<0.05). There was also a trend toward greater resistance to deformation in the tibia, but not the metatarsal, in the exercised, high-E2 group compared to the other treatment groups. These results demonstrate that E2 plays a role in mediating skeletal responses to strain, such that physiological variation in E2 levels among individuals may lead to differential growth responses to similar mechanical loading regimes. Efforts to model the relationship between environmental strain and bone morphology should include the effects of physiological variation in hormone levels.
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Affiliation(s)
- Maureen J Devlin
- Department of Anthropology, Peabody Museum, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA.
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Riddle RC, Taylor AF, Rogers JR, Donahue HJ. ATP release mediates fluid flow-induced proliferation of human bone marrow stromal cells. J Bone Miner Res 2007; 22:589-600. [PMID: 17243863 DOI: 10.1359/jbmr.070113] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
UNLABELLED Oscillatory fluid flow induced the vesicular release of ATP from human BMSCs that directly contributes to the induction of BMSC proliferation. Degrading extracellular nucleotides prevents fluid flow-induced increases in intracellular calcium concentration, the activation of calcineurin, and the nuclear translocation of NFAT. INTRODUCTION Regulation of bone cell activity by autocrine/paracrine factors is a well-established mechanism by which skeletal homeostasis is regulated by mechanical signals. The release of extracellular nucleotides in particular has been shown to induce many of the responses thought to be necessary for load-induced bone formation. In these studies, we examined the effect of oscillatory fluid flow on the release of ATP from bone marrow stromal cells (BMSCs) and the effect of ATP release on BMSC proliferation and intracellular calcium signaling pathways. MATERIALS AND METHODS BMSCs were exposed to oscillatory fluid flow, and the concentration of ATP in conditioned media samples was determined using a luciferin:luciferase-based reaction. Western blot analysis was used to examine the expression of purinergic receptors. Using pharmacological antagonists of gap junction hemichannels and vesicular trafficking, we studied the mechanism of ATP release from BMSCs. Apyrase was used to study the effect of extracellular nucleotides on intracellular calcium concentration, calcineurin activity, and nuclear factor of activated T cells (NFAT) nuclear translocation. RESULTS AND CONCLUSIONS Fluid flow exposure induced the flow rate-dependent release of ATP from BMSCs that was attenuated by treatment with monensin and N-ethylmaleimide, suggesting a vesicular mechanism. Treating BMSCs with ATP, but not other nucleotides, increased cellular proliferation. Moreover, extracellular ATP was a prerequisite for fluid flow-induced increases in intracellular calcium concentration, activation of calcineurin, the nuclear translocation of NFATc1, and proliferation. These data indicate that ATP regulates not only osteoblastic and osteocytic cell behavior but also that of mesenchymal precursors and support our hypothesis that similar mechanotransduction mechanisms are activated by fluid flow in these cell types.
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Affiliation(s)
- Ryan C Riddle
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Pennsylvania State University College of Medicine, Milton S Hershey Medical Center, Hershey, PA 17033, USA
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Malone AMD, Batra NN, Shivaram G, Kwon RY, You L, Kim CH, Rodriguez J, Jair K, Jacobs CR. The role of actin cytoskeleton in oscillatory fluid flow-induced signaling in MC3T3-E1 osteoblasts. Am J Physiol Cell Physiol 2007; 292:C1830-6. [PMID: 17251324 PMCID: PMC3057612 DOI: 10.1152/ajpcell.00352.2005] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fluid flow due to loading in bone is a potent mechanical signal that may play an important role in bone adaptation to its mechanical environment. Previous in vitro studies of osteoblastic cells revealed that the upregulation of cyclooxygenase-2 (COX-2) and c-fos induced by steady fluid flow depends on a change in actin polymerization dynamics and the formation of actin stress fibers. Exposing cells to dynamic oscillatory fluid flow, the temporal flow pattern that results from normal physical activity, is also known to result in increased COX-2 expression and PGE(2) release. The purpose of this study was to determine whether dynamic fluid flow results in changes in actin dynamics similar to steady flow and to determine whether alterations in actin dynamics are required for PGE(2) release. We found that exposure to oscillatory fluid flow did not result in the development of F-actin stress fibers in MC3T3-E1 osteoblastic cells and that inhibition of actin polymerization with cytochalasin D did not inhibit intracellular calcium mobilization or PGE(2) release. In fact, PGE(2) release was increased threefold in the polymerization inhibited cells and this PGE(2) release was dependent on calcium release from the endoplasmic reticulum. This was in contrast to the PGE(2) release that occurs in normal cells, which is independent of calcium flux from endoplasmic reticulum stores. We suggest that this increased PGE(2) release involves a different molecular mechanism perhaps involving increased deformation due to the compromised cytoskeleton.
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Affiliation(s)
- Amanda M D Malone
- Bone and Joint Rehabilitation R and D Center, Veterans Affairs Medical Center, Palo Alto, CA, USA
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Chung DJ, Castro CHM, Watkins M, Stains JP, Chung MY, Szejnfeld VL, Willecke K, Theis M, Civitelli R. Low peak bone mass and attenuated anabolic response to parathyroid hormone in mice with an osteoblast-specific deletion of connexin43. J Cell Sci 2006; 119:4187-98. [PMID: 16984976 DOI: 10.1242/jcs.03162] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Connexin43 (Cx43) is involved in bone development, but its role in adult bone homeostasis remains unknown. To overcome the postnatal lethality of Cx43 null mutation, we generated mice with selective osteoblast ablation of Cx43, obtained using a Cx43fl allele and a 2.3-kb fragment of the alpha1(I) collagen promoter to drive Cre in osteoblasts (ColCre). Conditionally osteoblast-deleted ColCre;Cx43-/fl mice show no malformations at birth, but develop low peak bone mass and remain osteopenic with age, exhibiting reduced bone formation and defective osteoblast function. By both radiodensitometry and histology, bone mineral content increased rapidly and progressively in adult Cx43+/fl mice after subcutaneous injection of parathyroid hormone (PTH), an effect significantly attenuated in ColCre;Cx43-/fl mice, with Cx43-/fl exhibiting an intermediate response. Attenuation of PTH anabolic action was associated with failure to increase mineral apposition rate in response to PTH in ColCre;Cx43-/fl, despite an increased osteoblast number, suggesting a functional defect in Cx43-deficient bone-forming cells. In conclusion, lack of Cx43 in osteoblasts leads to suboptimal acquisition of peak bone mass, and hinders the bone anabolic effect of PTH. Cx43 represents a potential target for modulation of bone anabolism.
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Affiliation(s)
- Dong Jin Chung
- Division of Bone and Mineral Diseases, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USA
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Mullender MG, Dijcks SJ, Bacabac RG, Semeins CM, Van Loon JJWA, Klein-Nulend J. Release of nitric oxide, but not prostaglandin E2, by bone cells depends on fluid flow frequency. J Orthop Res 2006; 24:1170-7. [PMID: 16705700 DOI: 10.1002/jor.20179] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Loading frequency is an important parameter for the stimulation of bone formation in vivo. It is still unclear how the information of external loading characteristics is conveyed to osteoblasts and osteoclasts. Osteocytes are thought to detect mechanical loads by sensing fluid flow through the lacuno-canalicular network within bone and to translate this information into chemical signals. The signaling molecules nitric oxide (NO) and prostaglandin E2 (PGE2) are known to play important roles in the adaptive response of bone to mechanical loads. We have investigated the effects of fluid flow frequency on the production of PGE2 and NO in bone cells in vitro. Pulsatile fluid flow with different frequencies stimulated the release of NO by MC3T3-E1 osteoblasts in a dose-dependent manner. In contrast, PGE2 production was enhanced consistently by all fluid flow regimes, independent of flow frequency. This implies that the NO response may play a role in mediating the differential effects of the various loading patterns on bone.
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Affiliation(s)
- Margriet G Mullender
- ACTA-Vrije Universiteit, Department of Oral Cell Biology, Van der Boechorststraat 7, NL-1081 BT Amsterdam, The Netherlands.
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Abstract
Analysis of cellular mechanotransduction, the mechanism by which cells convert mechanical signals into biochemical responses, has focused on identification of critical mechanosensitive molecules and cellular components. Stretch-activated ion channels, caveolae, integrins, cadherins, growth factor receptors, myosin motors, cytoskeletal filaments, nuclei, extracellular matrix, and numerous other structures and signaling molecules have all been shown to contribute to the mechanotransduction response. However, little is known about how these different molecules function within the structural context of living cells, tissues, and organs to produce the orchestrated cellular behaviors required for mechanosensation, embryogenesis, and physiological control. Recent work from a wide range of fields reveals that organ, tissue, and cell anatomy are as important for mechanotransduction as individual mechanosensitive proteins and that our bodies use structural hierarchies (systems within systems) composed of interconnected networks that span from the macroscale to the nanoscale in order to focus stresses on specific mechanotransducer molecules. The presence of isometric tension (prestress) at all levels of these multiscale networks ensures that various molecular scale mechanochemical transduction mechanisms proceed simultaneously and produce a concerted response. Future research in this area will therefore require analysis, understanding, and modeling of tensionally integrated (tensegrity) systems of mechanochemical control.
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Affiliation(s)
- Donald E Ingber
- Vascular Biology Program, Karp Family Research Laboratories 11.127, Department of Pathology, Harvard Medical School and Children's Hospital, 300 Longwood Ave., Boston, Massachusetts 02115, USA.
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Rubin J, Rubin C, Jacobs CR. Molecular pathways mediating mechanical signaling in bone. Gene 2006; 367:1-16. [PMID: 16361069 PMCID: PMC3687520 DOI: 10.1016/j.gene.2005.10.028] [Citation(s) in RCA: 297] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2005] [Accepted: 10/03/2005] [Indexed: 12/26/2022]
Abstract
Bone tissue has the capacity to adapt to its functional environment such that its morphology is "optimized" for the mechanical demand. The adaptive nature of the skeleton poses an interesting set of biological questions (e.g., how does bone sense mechanical signals, what cells are the sensing system, what are the mechanical signals that drive the system, what receptors are responsible for transducing the mechanical signal, what are the molecular responses to the mechanical stimuli). Studies of the characteristics of the mechanical environment at the cellular level, the forces that bone cells recognize, and the integrated cellular responses are providing new information at an accelerating speed. This review first considers the mechanical factors that are generated by loading in the skeleton, including strain, stress and pressure. Mechanosensitive cells placed to recognize these forces in the skeleton, osteoblasts, osteoclasts, osteocytes and cells of the vasculature are reviewed. The identity of the mechanoreceptor(s) is approached, with consideration of ion channels, integrins, connexins, the lipid membrane including caveolar and non-caveolar lipid rafts and the possibility that altering cell shape at the membrane or cytoskeleton alters integral signaling protein associations. The distal intracellular signaling systems on-line after the mechanoreceptor is activated are reviewed, including those emanating from G-proteins (e.g., intracellular calcium shifts), MAPKs, and nitric oxide. The ability to harness mechanical signals to improve bone health through devices and exercise is broached. Increased appreciation of the importance of the mechanical environment in regulating and determining the structural efficacy of the skeleton makes this an exciting time for further exploration of this area.
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Affiliation(s)
- Janet Rubin
- Department of Medicine, VAMC and Emory University School of Medicine, Atlanta GA, VAMC-151, 1670 Clairmont Rd, Decatur, GA 30033, USA.
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Gluhak-Heinrich J, Gu S, Pavlin D, Jiang JX. Mechanical loading stimulates expression of connexin 43 in alveolar bone cells in the tooth movement model. CELL COMMUNICATION & ADHESION 2006; 13:115-25. [PMID: 16613785 PMCID: PMC1797153 DOI: 10.1080/15419060600634619] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Bone osteoblasts and osteocytes express large amounts of connexin (Cx) 43, the component of gap junctions and hemichannels. Previous studies have shown that these channels play important roles in regulating biological functions in response to mechanical loading. Here, we characterized the distribution of mRNA and protein of Cx43 in mechanical loading model of tooth movement. The locations of bone formation and resorption have been well defined in this model, which provides unique experimental systems for better understanding of potential roles of Cx43 in bone formation and remodeling under mechanical stimulation. We found that mechanical loading increased Cx43 mRNA expression in osteoblasts and bone lining cells, but not in osteocytes, at both formation and resorption sites. Cx43 protein, however, increased in both osteoblasts and osteocytes in response to loading. Interestingly, the upregulation of Cx43 protein by loading was even more pronounced in osteocytes compared to other bone cells, with an appearance of punctate staining on the cell body and dendritic process. Cx45 was reported to be expressed in several bone cell lines, but here we did not detect the Cx45 protein in the alveolar bone cells. These results further suggest the potential involvement of Cx43-forming gap junctions and hemichannels in the process of mechanically induced bone formation and resorption.
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Affiliation(s)
- Jelica Gluhak-Heinrich
- Department of Orthodontics, University of Texas Health Science Center, San Antonio, 78229-3900, USA
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Stains JP, Civitelli R. Gap junctions in skeletal development and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1719:69-81. [PMID: 16359941 DOI: 10.1016/j.bbamem.2005.10.012] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Revised: 10/26/2005] [Accepted: 10/28/2005] [Indexed: 11/29/2022]
Abstract
Gap junctions play a critical role in the coordinated function and activity of nearly all of the skeletal cells. This is not surprising, given the elaborate orchestration of skeletal patterning, bone modeling and subsequent remodeling, as well as the mechanical stresses, strains and adaptive responses that the skeleton must accommodate. Much remains to be learned regarding the role of gap junctions and hemichannels in these processes. A common theme is that without connexins none of the cells of bone function properly. Thus, connexins play an important role in skeletal form and function.
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Affiliation(s)
- Joseph P Stains
- University of Maryland School of Medicine, Department of Orthopaedics, Baltimore, MD 21201, USA
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Mi LY, Basu M, Fritton SP, Cowin SC. Analysis of avian bone response to mechanical loading. Part two: Development of a computational connected cellular network to study bone intercellular communication. Biomech Model Mechanobiol 2005; 4:132-46. [PMID: 16365733 DOI: 10.1007/s10237-004-0066-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Accepted: 12/06/2004] [Indexed: 10/25/2022]
Abstract
Mechanical loading-induced signals are hypothesized to be transmitted and integrated by connected bone cells before reaching the bone surfaces where adaptation occurs. A computational connected cellular network (CCCN) model is developed to explore how bone cells perceive and transmit the signals through intercellular communication. This is part two of a two-part study in which a CCCN is developed to study the intercellular communication within a grid of bone cells. The excitation signal was computed as the loading-induced bone fluid shear stress in part one. Experimentally determined bone adaptation responses (Gross et al. in J Bone Miner Res 12:982-988, 1997 and Judex et al. in J Bone Miner Res 12:1737-1745, 1997) are correlated with the fluid shear stress by the CCCN, which adjusts cell sensitivities (loading and signal thresholds) and connection weights. Intercellular communication patterns extracted by the CCCN indicate the cell population responsible for perceiving the loading-induced signal, and loading threshold is shown to play an important role in regulating the bone response.
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Affiliation(s)
- Li Y Mi
- Department of Electrical Engineering, New York Center for Biomedical Engineering, The City College of New York/CUNY, 10031, New York, USA
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Matsumoto S, Shibuya I, Kusakari S, Segawa K, Uyama T, Shimada A, Umezawa A. Membranous osteogenesis system modeled with KUSA-A1 mature osteoblasts. Biochim Biophys Acta Gen Subj 2005; 1725:57-63. [PMID: 15996824 DOI: 10.1016/j.bbagen.2005.05.027] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2004] [Revised: 05/16/2005] [Accepted: 05/17/2005] [Indexed: 12/01/2022]
Abstract
Several stromal cells were established from murine bone marrow cultures. One of the KUSA subclones, KUSA-A1 cells, displays osteogenic characteristics in vitro and in vivo. The calcium deposition, osteocalcin release, and parathyroid hormone (PTH) responsiveness of KUSA-A1 cells indicate that they are mature osteoblasts or osteocytes. Bone had formed in subcutaneous tissue 1 week after subcutaneous injection of cells into immunodeficient mice. The osteogenesis by KUSA-A1 was not mediated by chondrogenesis and thus was considered to be membranous ossification. These unique characteristics of KUSA-A1 cells provide an opportunity to analyze the process of membranous ossification in detail.
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Affiliation(s)
- Satoshi Matsumoto
- Department of Reproductive Biology and Pathology, National Institute for Child Health and Development, Setagaya-ku, Tokyo 157-8535, Japan
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