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Regner AM, DeLeon M, Gibbons KD, Howard S, Nesbitt DQ, Lujan TJ, Fitzpatrick CK, Farach-Carson MC, Wu D, Uzer G. Increased deformations are dispensable for cell mechanoresponse in engineered bone analogs mimicking aging bone marrow. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.24.559187. [PMID: 37905032 PMCID: PMC10614733 DOI: 10.1101/2023.09.24.559187] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Aged individuals and astronauts experience bone loss despite rigorous physical activity. Bone mechanoresponse is in-part regulated by mesenchymal stem cells (MSCs) that respond to mechanical stimuli. Direct delivery of low intensity vibration (LIV) recovers MSC proliferation in senescence and simulated microgravity models, indicating that age-related reductions in mechanical signal delivery within bone marrow may contribute to declining bone mechanoresponse. To answer this question, we developed a 3D bone marrow analog that controls trabecular geometry, marrow mechanics and external stimuli. Validated finite element (FE) models were developed to quantify strain environment within hydrogels during LIV. Bone marrow analogs with gyroid-based trabeculae of bone volume fractions (BV/TV) corresponding to adult (25%) and aged (13%) mice were printed using polylactic acid (PLA). MSCs encapsulated in migration-permissive hydrogels within printed trabeculae showed robust cell populations on both PLA surface and hydrogel within a week. Following 14 days of LIV treatment (1g, 100 Hz, 1 hour/day), type-I collagen and F-actin were quantified for the cells in the hydrogel fraction. While LIV increased all measured outcomes, FE models predicted higher von Mises strains for the 13% BV/TV groups (0.2%) when compared to the 25% BV/TV group (0.1%). Despite increased strains, collagen-I and F-actin measures remained lower in the 13% BV/TV groups when compared to 25% BV/TV counterparts, indicating that cell response to LIV does not depend on hydrogel strains and that bone volume fraction (i.e. available bone surface) directly affects cell behavior in the hydrogel phase independent of the external stimuli. Overall, bone marrow analogs offer a robust and repeatable platform to study bone mechanobiology.
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Affiliation(s)
- Alexander M Regner
- Mechanical and Biomedical Engineering Department, Boise State University
| | - Maximilien DeLeon
- Department of Diagnostic and Biomedical Sciences, UTHealth Houston School of Dentistry
- Department of Bioengineering, Rice University
- Department of Biosciences, Rice University
| | - Kalin D. Gibbons
- Mechanical and Biomedical Engineering Department, Boise State University
| | - Sean Howard
- Mechanical and Biomedical Engineering Department, Boise State University
| | | | - Trevor J. Lujan
- Mechanical and Biomedical Engineering Department, Boise State University
| | | | - Mary C Farach-Carson
- Department of Diagnostic and Biomedical Sciences, UTHealth Houston School of Dentistry
- Department of Bioengineering, Rice University
- Department of Biosciences, Rice University
| | - Danielle Wu
- Department of Diagnostic and Biomedical Sciences, UTHealth Houston School of Dentistry
- Department of Bioengineering, Rice University
- Department of Biosciences, Rice University
| | - Gunes Uzer
- Mechanical and Biomedical Engineering Department, Boise State University
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2
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Atria PJ, Castillo AB. Skeletal adaptation to mechanical cues during homeostasis and repair: the niche, cells, and molecular signaling. Front Physiol 2023; 14:1233920. [PMID: 37916223 PMCID: PMC10616261 DOI: 10.3389/fphys.2023.1233920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2023] [Accepted: 10/02/2023] [Indexed: 11/03/2023] Open
Abstract
Bones constantly change and adapt to physical stress throughout a person's life. Mechanical signals are important regulators of bone remodeling and repair by activating skeletal stem and progenitor cells (SSPCs) to proliferate and differentiate into bone-forming osteoblasts using molecular signaling mechanisms not yet fully understood. SSPCs reside in a dynamic specialized microenvironment called the niche, where external signals integrate to influence cell maintenance, behavior and fate determination. The nature of the niche in bone, including its cellular and extracellular makeup and regulatory molecular signals, is not completely understood. The mechanisms by which the niche, with all of its components and complexity, is modulated by mechanical signals during homeostasis and repair are virtually unknown. This review summarizes the current view of the cells and signals involved in mechanical adaptation of bone during homeostasis and repair, with an emphasis on identifying novel targets for the prevention and treatment of age-related bone loss and hard-to-heal fractures.
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Affiliation(s)
- Pablo J. Atria
- Department of Orthopedic Surgery, New York University Grossman School of Medicine, New York, NY, United States
| | - Alesha B. Castillo
- Department of Orthopedic Surgery, New York University Grossman School of Medicine, New York, NY, United States
- Department of Biomedical Engineering, New York University Tandon School of Engineering, New York, NY, United States
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3
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Yang R, Cao D, Suo J, Zhang L, Mo C, Wang M, Niu N, Yue R, Zou W. Premature aging of skeletal stem/progenitor cells rather than osteoblasts causes bone loss with decreased mechanosensation. Bone Res 2023; 11:35. [PMID: 37407584 DOI: 10.1038/s41413-023-00269-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2022] [Revised: 04/03/2023] [Accepted: 05/12/2023] [Indexed: 07/07/2023] Open
Abstract
A distinct population of skeletal stem/progenitor cells (SSPCs) has been identified that is indispensable for the maintenance and remodeling of the adult skeleton. However, the cell types that are responsible for age-related bone loss and the characteristic changes in these cells during aging remain to be determined. Here, we established models of premature aging by conditional depletion of Zmpste24 (Z24) in mice and found that Prx1-dependent Z24 deletion, but not Osx-dependent Z24 deletion, caused significant bone loss. However, Acan-associated Z24 depletion caused only trabecular bone loss. Single-cell RNA sequencing (scRNA-seq) revealed that two populations of SSPCs, one that differentiates into trabecular bone cells and another that differentiates into cortical bone cells, were significantly decreased in Prx1-Cre; Z24f/f mice. Both premature SSPC populations exhibited apoptotic signaling pathway activation and decreased mechanosensation. Physical exercise reversed the effects of Z24 depletion on cellular apoptosis, extracellular matrix expression and bone mass. This study identified two populations of SSPCs that are responsible for premature aging-related bone loss. The impairment of mechanosensation in Z24-deficient SSPCs provides new insight into how physical exercise can be used to prevent bone aging.
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Affiliation(s)
- Ruici Yang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, 200031, China
- Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Dandan Cao
- Institute for Regenerative Medicine, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, 200092, China
| | - Jinlong Suo
- Institute of Microsurgery on Extremities, and Department of Orthopedic Surgery, Shanghai Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, 200233, China
| | - Lingli Zhang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, 200031, China
| | - Chunyang Mo
- Institute for Regenerative Medicine, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, 200092, China
| | - Miaomiao Wang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, 200031, China
| | - Ningning Niu
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, 200031, China
| | - Rui Yue
- Institute for Regenerative Medicine, Shanghai East Hospital, Shanghai Key Laboratory of Signaling and Disease Research, Frontier Science Center for Stem Cell Research, School of Life Sciences and Technology, Tongji University, Shanghai, 200092, China.
| | - Weiguo Zou
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, 200031, China.
- Institute of Microsurgery on Extremities, and Department of Orthopedic Surgery, Shanghai Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, 200233, China.
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4
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Rajpar I, Kumar G, Fortina P, Tomlinson RE. Toll-like receptor 4 signaling in osteoblasts is required for load-induced bone formation in mice. iScience 2023; 26:106304. [PMID: 36950122 PMCID: PMC10025993 DOI: 10.1016/j.isci.2023.106304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 01/06/2023] [Accepted: 02/24/2023] [Indexed: 03/06/2023] Open
Abstract
In mature bone, NGF is produced by osteoblasts following mechanical loading and signals through resident sensory nerves expressing its high affinity receptor, neurotrophic tyrosine kinase receptor type 1 (TrkA), to support bone formation. Here, we investigated whether osteoblastic expression of Toll-like receptor 4 (TLR4), a key receptor in the NF-κB signaling pathway, is required to initiate NGF-TrkA signaling required for load-induced bone formation. Although Tlr4 conditional knockout mice have normal skeletal mass and strength in adulthood, the loss of TLR4 signaling significantly reduced lamellar bone formation following loading. Inhibition of TLR4 signaling reduced Ngf expression in primary osteoblasts and RNA sequencing of bones from Tlr4 conditional knockout mice and wild-type littermates revealed dysregulated inflammatory signaling three days after osteogenic mechanical loading. In total, our study reveals an important role for osteoblastic TLR4 in the skeletal adaptation of bone to mechanical forces.
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Affiliation(s)
- Ibtesam Rajpar
- Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA, USA
| | - Gaurav Kumar
- Department of Cancer Biology, Thomas Jefferson University, Philadelphia, PA, USA
| | - Paolo Fortina
- Department of Cancer Biology, Thomas Jefferson University, Philadelphia, PA, USA
| | - Ryan E. Tomlinson
- Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA, USA
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5
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Functional Heterogeneity of Bone Marrow Mesenchymal Stem Cell Subpopulations in Physiology and Pathology. Int J Mol Sci 2022; 23:ijms231911928. [PMID: 36233230 PMCID: PMC9570000 DOI: 10.3390/ijms231911928] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 11/16/2022] Open
Abstract
Bone marrow mesenchymal stem cells (BMSCs) are multi-potent cell populations and are capable of maintaining bone and body homeostasis. The stemness and potential therapeutic effect of BMSCs have been explored extensively in recent years. However, diverse cell surface antigens and complex gene expression of BMSCs have indicated that BMSCs represent heterogeneous populations, and the natural characteristics of BMSCs make it difficult to identify the specific subpopulations in pathological processes which are often obscured by bulk analysis of the total BMSCs. Meanwhile, the therapeutic effect of total BMSCs is often less effective partly due to their heterogeneity. Therefore, understanding the functional heterogeneity of the BMSC subpopulations under different physiological and pathological conditions could have major ramifications for global health. Here, we summarize the recent progress of functional heterogeneity of BMSC subpopulations in physiology and pathology. Targeting tissue-resident single BMSC subpopulation offers a potentially innovative therapeutic strategy and improves BMSC effectiveness in clinical application.
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6
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Abstract
PURPOSE OF REVIEW The periosteum, the outer layer of bone, is a major source of skeletal stem/progenitor cells (SSPCs) for bone repair. Here, we discuss recent findings on the characterization, role, and regulation of periosteal SSPCs (pSSPCs) during bone regeneration. RECENT FINDINGS Several markers have been described for pSSPCs but lack tissue specificity. In vivo lineage tracing and transcriptomic analyses have improved our understanding of pSSPC functions during bone regeneration. Bone injury activates pSSPCs that migrate, proliferate, and have the unique potential to form both bone and cartilage. The injury response of pSSPCs is controlled by many signaling pathways including BMP, FGF, Notch, and Wnt, their metabolic state, and their interactions with the blood clot, nerve fibers, blood vessels, and macrophages in the fracture environment. Periosteal SSPCs are essential for bone regeneration. Despite recent advances, further studies are required to elucidate pSSPC heterogeneity and plasticity that make them a central component of the fracture healing process and a prime target for clinical applications.
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Affiliation(s)
- Simon Perrin
- Univ Paris Est Creteil, INSERM, IMRB, F-94010, Creteil, France
| | - Céline Colnot
- Univ Paris Est Creteil, INSERM, IMRB, F-94010, Creteil, France.
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7
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Harris TL, Silva MJ. Dmp1 Lineage Cells Contribute Significantly to Periosteal Lamellar Bone Formation Induced by Mechanical Loading But Are Depleted from the Bone Surface During Rapid Bone Formation. JBMR Plus 2022; 6:e10593. [PMID: 35309865 PMCID: PMC8914163 DOI: 10.1002/jbm4.10593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 11/21/2021] [Accepted: 12/14/2021] [Indexed: 11/25/2022] Open
Abstract
Previous work has shown that osteoprogenitor cells (Prx1+) and pre‐osteoblasts (Osx+) contribute to mechanical loading‐induced bone formation. However, the role of mature Dmp1‐expressing osteoblasts has not been reported. In this study we assessed the contribution of osteoblast lineage cells to bone formation at an early time point following mechanical loading (day 8 from onset of loading). We labeled Osx‐expressing and Dmp1‐expressing cells in inducible Osx and Dmp1 reporter mice (iOsx‐Ai9, iDmp1‐Ai9), respectively, 3 weeks before loading. Mice were then loaded daily for 5 days (days 1–5) and were dosed with 5‐ethynyl‐2′‐deoxyuridine (EdU) in their drinking water until euthanasia on day 8. Mice were loaded to lamellar and woven bone inducing stimulation (−7 N/1400 με, −10 N/2000 με) to assess differences in these processes. We found varied responses in males and females to the loading stimuli, inducing modest lamellar (females, −7 N), moderate lamellar (males, −10 N), and robust woven (females, −10 N) bone. Overall, we found that preexisting (ie, lineage positive) Osx‐expressing and Dmp1‐expressing cells contribute largely to the bone formation response, especially during modest bone formation, while our results stuggest that other (non‐lineage–positive) cells support the sustained bone formation response during rapid bone formation. With moderate or robust levels of bone formation, a decrease in preexisting Osx‐expressing and Dmp1‐expressing cells at the bone surface occurred, with a near depletion of Dmp1‐expressing cells from the surface in female mice loaded to −10 N (from 52% to 11%). These cells appeared to be replaced by lineage‐negative cells from the periosteum. We also found a dose response in proliferation, with 17% to 18% of bone surface cells arising via proliferation in modest lamellar, 38% to 53% in moderate lamellar, and 59% to 81% in robust woven bone formation. In summary, our results show predominant contributions by preexisting Osx and Dmp1 lineage cells to loading‐induced lamellar bone formation, whereas recruitment of earlier osteoprogenitors and increased cell proliferation support robust woven bone formation. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
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Affiliation(s)
- Taylor L. Harris
- Department of Orthopaedic Surgery and Musculoskeletal Research Center Washington University School of Medicine St. Louis MO USA
- Department of Biomedical Engineering Washington University St. Louis MO USA
| | - Matthew J. Silva
- Department of Orthopaedic Surgery and Musculoskeletal Research Center Washington University School of Medicine St. Louis MO USA
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8
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Abstract
Fracture healing is a complex, multistep process that is highly sensitive to mechanical signaling. To optimize repair, surgeons prescribe immediate weight-bearing as-tolerated within 24 hours after surgical fixation; however, this recommendation is based on anecdotal evidence and assessment of bulk healing outcomes (e.g., callus size, bone volume, etc.). Given challenges in accurately characterizing the mechanical environment and the ever-changing properties of the regenerate, the principles governing mechanical regulation of repair, including their cell and molecular basis, are not yet well defined. However, the use of mechanobiological rodent models, and their relatively large genetic toolbox, combined with recent advances in imaging approaches and single-cell analyses is improving our understanding of the bone microenvironment in response to loading. This review describes the identification and characterization of distinct cell populations involved in bone healing and highlights the most recent findings on mechanical regulation of bone homeostasis and repair with an emphasis on osteo-angio coupling. A discussion on aging and its impact on bone mechanoresponsiveness emphasizes the need for novel mechanotherapeutics that can re-sensitize skeletal stem and progenitor cells to physical rehabilitation protocols.
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Affiliation(s)
- Tareq Anani
- Department of Orthopedic Surgery, New York University Langone Health, New York, NY 10010, USA
| | - Alesha B Castillo
- Department of Orthopedic Surgery, New York University Langone Health, New York, NY 10010, USA; Department of Biomedical Engineering, Tandon School of Engineering, New York University, New York, NY 11201, USA; Department of Veterans Affairs, New York Harbor Healthcare System, Manhattan Campus, New York, NY 10010, USA.
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9
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Birks S, Uzer G. At the nuclear envelope of bone mechanobiology. Bone 2021; 151:116023. [PMID: 34051417 PMCID: PMC8600447 DOI: 10.1016/j.bone.2021.116023] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 05/11/2021] [Accepted: 05/21/2021] [Indexed: 02/06/2023]
Abstract
The nuclear envelope and nucleoskeleton are emerging as signaling centers that regulate how physical information from the extracellular matrix is biochemically transduced into the nucleus, affecting chromatin and controlling cell function. Bone is a mechanically driven tissue that relies on physical information to maintain its physiological function and structure. Disorder that present with musculoskeletal and cardiac symptoms, such as Emery-Dreifuss muscular dystrophies and progeria, correlate with mutations in nuclear envelope proteins including Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, Lamin A/C, and emerin. However, the role of nuclear envelope mechanobiology on bone function remains underexplored. The mesenchymal stem cell (MSC) model is perhaps the most studied relationship between bone regulation and nuclear envelope function. MSCs maintain the musculoskeletal system by differentiating into multiple cell types including osteocytes and adipocytes, thus supporting the bone's ability to respond to mechanical challenge. In this review, we will focus on how MSC function is regulated by mechanical challenges both in vitro and in vivo within the context of bone function specifically focusing on integrin, β-catenin and YAP/TAZ signaling. The importance of the nuclear envelope will be explored within the context of musculoskeletal diseases related to nuclear envelope protein mutations and nuclear envelope regulation of signaling pathways relevant to bone mechanobiology in vitro and in vivo.
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Affiliation(s)
- Scott Birks
- Boise State University, Micron School of Materials Science and Engineering, United States of America
| | - Gunes Uzer
- Boise State University, Mechanical and Biomedical Engineering, United States of America.
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Harris TL, Silva MJ. Gene expression of intracortical bone demonstrates loading-induced increases in Wnt1 and Ngf and inhibition of bone remodeling processes. Bone 2021; 150:116019. [PMID: 34023542 PMCID: PMC8408835 DOI: 10.1016/j.bone.2021.116019] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2021] [Revised: 04/27/2021] [Accepted: 05/18/2021] [Indexed: 12/18/2022]
Abstract
Osteocytes are the primary mechanosensitive cells in bone. However, their location in mineralized matrix has limited the in vivo study of osteocytic genes induced by mechanical loading. Laser Capture Microdissection (LCM) allows isolation of intracortical bone (Intra-CB), enriched for osteocytes, from bone tissue for gene expression analysis. We used microarray to analyze gene expression from mouse tibial Intra-CB dissected using LCM 4 h after a single loading bout or after 5 days of loading. Osteocyte enrichment was supported by greater expression of Sost, Dmp1, Dkk1, and Mepe in Intra-CB regions vs. Mixed regions containing periosteum and muscle (fold-change (FC) = 3.4, 2.2, 5.1, 3.0, respectively). Over 150 differentially expressed genes (DEGs) due to loading (loaded vs. contralateral control) in Intra-CB were found on Day 1 and Day 5, but only 10 genes were differentially expressed on both days, including Ngf (Day 1 FC = 13.5, Day 5 FC = 11.1) and Wnt1 (Day 1 FC = 1.5, Day 5 FC = 5.1). The expression of Ngf and Wnt1 within Intra-CB was confirmed by in situ hybridization, and a significant increase in number of Wnt1 mRNA molecules occurred on day 1. We also found changes in extracellular matrix remodeling with Timp1 (FC = 3.1) increased on day 1 and MMP13 (FC = 0.3) decreased on day 5. Supporting this result, IHC for osteocytic MMP13 demonstrated a marginal decrease due to loading on day 5. Gene Ontology (GO) biological processes for loading DEGs indicated regulation of vasculature, neuronal and immune processes while cell-type specific gene lists suggested regulation of osteoclast, osteoblast, and endothelial related genes. In summary, microarray analysis of microdissected Intra-CB revealed differential regulation of Ngf, Wnt1, and MMP13 due to loading in osteocytes.
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Affiliation(s)
- Taylor L Harris
- Department of Orthopaedic Surgery and Musculoskeletal Research Center, Washington University School of Medicine, Saint Louis, MO, United States; Department of Biomedical Engineering, Washington University, Saint Louis, MO, United States.
| | - Matthew J Silva
- Department of Orthopaedic Surgery and Musculoskeletal Research Center, Washington University School of Medicine, Saint Louis, MO, United States
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11
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Activation of creER recombinase in the mouse calvaria induces local recombination without effects on distant skeletal segments. Sci Rep 2021; 11:8214. [PMID: 33859263 PMCID: PMC8050205 DOI: 10.1038/s41598-021-87611-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 03/31/2021] [Indexed: 02/02/2023] Open
Abstract
Conditional creER-mediated gene inactivation or gene induction has emerged as a robust tool for studying gene functions in mouse models of tissue development, homeostasis, and regeneration. Here, we present a method to conditionally induce cre recombination in the mouse calvarial bone while avoiding systemic recombination in distal bones. To test our method, we utilized Prx1creER-egfp;td-Tomato mice and delivered 4-hydroxytamoxifen (4-OHT) to the mouse calvaria, subperiosteally. First, we showed that two calvaria subperiosteal injections of 10 µg of 4-OHT (3.3 mg of 4-OHT/kg of body weight) can induce local recombination as efficiently as two intraperitoneal systemic injections of 200 μg of tamoxifen (70 mg of tamoxifen/kg of body weight). Then, we studied the recombination efficiency of various subperiosteal calvaria dosages and found that two subperiosteal injections of 5 µg 4-OHT (1.65 mg of 4-OHT/kg of body weight) uphold the same recombination efficiency observed with higher dosages. Importantly, the result indicated that the low dosage does not induce significant systemic recombination in remote skeletal tissues. With the proposed local low dosage protocol, the recombination efficiency at the injection site (calvarial bone) reached 94%, while the recombination efficiency at the mandible and the digits was as low as the efficiency measured in control animals.
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12
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Chermside-Scabbo CJ, Harris TL, Brodt MD, Braenne I, Zhang B, Farber CR, Silva MJ. Old Mice Have Less Transcriptional Activation But Similar Periosteal Cell Proliferation Compared to Young-Adult Mice in Response to in vivo Mechanical Loading. J Bone Miner Res 2020; 35:1751-1764. [PMID: 32311160 PMCID: PMC7486279 DOI: 10.1002/jbmr.4031] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 03/27/2020] [Accepted: 04/08/2020] [Indexed: 12/12/2022]
Abstract
Mechanical loading is a potent strategy to induce bone formation, but with aging, the bone formation response to the same mechanical stimulus diminishes. Our main objectives were to (i) discover the potential transcriptional differences and (ii) compare the periosteal cell proliferation between tibias of young-adult and old mice in response to strain-matched mechanical loading. First, to discover potential age-related transcriptional differences, we performed RNA sequencing (RNA-seq) to compare the loading responses between tibias of young-adult (5-month) and old (22-month) C57BL/6N female mice following 1, 3, or 5 days of axial loading (loaded versus non-loaded). Compared to young-adult mice, old mice had less transcriptional activation following loading at each time point, as measured by the number of differentially expressed genes (DEGs) and the fold-changes of the DEGs. Old mice engaged fewer pathways and gene ontology (GO) processes, showing less activation of processes related to proliferation and differentiation. In tibias of young-adult mice, we observed prominent Wnt signaling, extracellular matrix (ECM), and neuronal responses, which were diminished with aging. Additionally, we identified several targets that may be effective in restoring the mechanoresponsiveness of aged bone, including nerve growth factor (NGF), Notum, prostaglandin signaling, Nell-1, and the AP-1 family. Second, to directly test the extent to which periosteal cell proliferation was diminished in old mice, we used bromodeoxyuridine (BrdU) in a separate cohort of mice to label cells that divided during the 5-day loading interval. Young-adult and old mice had an average of 15.5 and 16.7 BrdU+ surface cells/mm, respectively, suggesting that impaired proliferation in the first 5 days of loading does not explain the diminished bone formation response with aging. We conclude that old mice have diminished transcriptional activation following mechanical loading, but periosteal proliferation in the first 5 days of loading does not differ between tibias of young-adult and old mice. © 2020 American Society for Bone and Mineral Research.
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Affiliation(s)
- Christopher J Chermside-Scabbo
- Musculoskeletal Research Center Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA
- Medical Scientist Training Program, Washington University School of Medicine, Washington University, St. Louis, MO, USA
| | - Taylor L Harris
- Musculoskeletal Research Center Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA
- Department of Biomedical Engineering, Washington University, St. Louis, MO, USA
| | - Michael D Brodt
- Musculoskeletal Research Center Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA
| | - Ingrid Braenne
- Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA
| | - Bo Zhang
- Center of Regenerative Medicine, Department of Developmental Biology, Washington University, St. Louis, MO, USA
| | - Charles R Farber
- Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA, USA
- Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA
| | - Matthew J Silva
- Musculoskeletal Research Center Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA
- Department of Biomedical Engineering, Washington University, St. Louis, MO, USA
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