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Lewis KJ. Osteocyte calcium signaling - A potential translator of mechanical load to mechanobiology. Bone 2021; 153:116136. [PMID: 34339908 DOI: 10.1016/j.bone.2021.116136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 06/25/2021] [Accepted: 07/27/2021] [Indexed: 10/20/2022]
Abstract
Osteocytes are embedded dendritic bone cells; by virtue of their position in bone tissue, ability to coordinate bone building osteoblasts and resorbing osteoclasts, and sensitivity to tissue level mechanical loading, they serve as the resident bone mechanosensor. The mechanisms osteocytes use to change mechanical loading into biological signals that drive tissue level changes has been well studied over the last 30 years, however the ways loading parameters are encoded at the cellular level are still not fully understood. Calcium signaling is a first messenger signal exhibited by osteocytes in response to mechanical forces. A body of work interrogating the mechanisms of osteocyte calcium signaling exists and is presently expanding, presenting the opportunity to better understand the relationship between calcium signaling characteristics and tuned osteocyte responses to tissue level strain features (e.g. magnitude, duration, frequency). This review covers the history of osteocyte load induced calcium signaling and highlights potential cellular mechanisms used by osteocytes to turn details about loading parameters into biological events.
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Affiliation(s)
- Karl J Lewis
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, United States of America.
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2
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Abstract
PURPOSE OF REVIEW Novel therapies for damaged and diseased bone are being developed in a preclinical testing process consisting of in vitro cell experiments followed by in vivo animal studies. The in vitro results are often not representative of the results observed in vivo. This could be caused by the complexity of the natural bone environment that is missing in vitro. Ex vivo bone explant cultures provide a model in which cells are preserved in their native three-dimensional environment. Herein, it is aimed to review the current status of bone explant culture models in relation to their potential in complementing the preclinical evaluation process with specific attention paid to the incorporation of mechanical loading within ex vivo culture systems. RECENT FINDINGS Bone explant cultures are often performed with physiologically less relevant bone, immature bone, and explants derived from rodents, which complicates translatability into clinical practice. Mature bone explants encounter difficulties with maintaining viability, especially in static culture. The integration of mechanical stimuli was able to extend the lifespan of explants and to induce new bone formation. Bone explant cultures provide unique platforms for bone research and mechanical loading was demonstrated to be an important component in achieving osteogenesis ex vivo. However, more research is needed to establish a representative, reliable, and reproducible bone explant culture system that includes both components of bone remodeling, i.e., formation and resorption, in order to bridge the gap between in vitro and in vivo research in preclinical testing.
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Affiliation(s)
- E E A Cramer
- Orthopaedic Biomechanics, Department of Biomedical Engineering and Institute of Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands
| | - K Ito
- Orthopaedic Biomechanics, Department of Biomedical Engineering and Institute of Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands
| | - S Hofmann
- Orthopaedic Biomechanics, Department of Biomedical Engineering and Institute of Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands.
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3
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Use of in vitro bone models to screen for altered bone metabolism, osteopathies, and fracture healing: challenges of complex models. Arch Toxicol 2020; 94:3937-3958. [PMID: 32910238 PMCID: PMC7655582 DOI: 10.1007/s00204-020-02906-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 09/03/2020] [Indexed: 02/06/2023]
Abstract
Approx. every third hospitalized patient in Europe suffers from musculoskeletal injuries or diseases. Up to 20% of these patients need costly surgical revisions after delayed or impaired fracture healing. Reasons for this are the severity of the trauma, individual factors, e.g, the patients’ age, individual lifestyle, chronic diseases, medication, and, over 70 diseases that negatively affect the bone quality. To investigate the various disease constellations and/or develop new treatment strategies, many in vivo, ex vivo, and in vitro models can be applied. Analyzing these various models more closely, it is obvious that many of them have limits and/or restrictions. Undoubtedly, in vivo models most completely represent the biological situation. Besides possible species-specific differences, ethical concerns may question the use of in vivo models especially for large screening approaches. Challenging whether ex vivo or in vitro bone models can be used as an adequate replacement for such screenings, we here summarize the advantages and challenges of frequently used ex vivo and in vitro bone models to study disturbed bone metabolism and fracture healing. Using own examples, we discuss the common challenge of cell-specific normalization of data obtained from more complex in vitro models as one example of the analytical limits which lower the full potential of these complex model systems.
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Dole NS, Yee CS, Mazur CM, Acevedo C, Alliston T. TGFβ Regulation of Perilacunar/Canalicular Remodeling Is Sexually Dimorphic. J Bone Miner Res 2020; 35:1549-1561. [PMID: 32282961 PMCID: PMC9126317 DOI: 10.1002/jbmr.4023] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 03/14/2020] [Accepted: 03/21/2020] [Indexed: 12/12/2022]
Abstract
Bone fragility is the product of defects in bone mass and bone quality, both of which show sex-specific differences. Despite this, the cellular and molecular mechanisms underpinning the sexually dimorphic control of bone quality remain unclear, limiting our ability to effectively prevent fractures, especially in postmenopausal osteoporosis. Recently, using male mice, we found that systemic or osteocyte-intrinsic inhibition of TGFβ signaling, achieved using the 9.6-kb DMP1 promoter-driven Cre recombinase (TβRIIocy-/- mice), suppresses osteocyte perilacunar/canalicular remodeling (PLR) and compromises bone quality. Because systemic TGFβ inhibition more robustly increases bone mass in female than male mice, we postulated that sex-specific differences in bone quality could likewise result, in part, from dimorphic regulation of PLR by TGFβ. Moreover, because lactation induces PLR, we examined the effect of TGFβ inhibition on the female skeleton during lactation. In contrast to males, female mice that possess an osteocyte-intrinsic defect in TGFβ signaling were protected from TGFβ-dependent defects in PLR and bone quality. The expression of requisite PLR enzymes, the lacunocanalicular network (LCN), and the flexural strength of female TβRIIocy-/- bone was intact. With lactation, however, bone loss and induction in PLR and osteocytic parathyroid hormone type I receptor (PTHR1) expression, were suppressed in TβRIIocy-/- bone, relative to the control littermates. Indeed, differential control of PTHR1 expression, by TGFβ and other factors, may contribute to dimorphism in PLR regulation in male and female TβRIIocy-/- mice. These findings provide key insights into the sex-based differences in osteocyte PLR that underlie bone quality and highlight TGFβ signaling as a crucial regulator of lactation-induced PLR. © 2020 American Society for Bone and Mineral Research.
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Affiliation(s)
- Neha S Dole
- Department of Orthopaedic Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Cristal S Yee
- Department of Orthopaedic Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Courtney M Mazur
- Department of Orthopaedic Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA.,University of California (UC) Berkeley-UCSF Graduate Program in Bioengineering, San Francisco, CA, USA
| | - Claire Acevedo
- Department of Mechanical Engineering, University of Utah, Salt Lake City, UT, USA
| | - Tamara Alliston
- Department of Orthopaedic Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA
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5
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Sieberath A, Della Bella E, Ferreira AM, Gentile P, Eglin D, Dalgarno K. A Comparison of Osteoblast and Osteoclast In Vitro Co-Culture Models and Their Translation for Preclinical Drug Testing Applications. Int J Mol Sci 2020; 21:E912. [PMID: 32019244 PMCID: PMC7037207 DOI: 10.3390/ijms21030912] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/10/2020] [Accepted: 01/21/2020] [Indexed: 12/23/2022] Open
Abstract
As the population of western societies on average ages, the number of people affected by bone remodeling-associated diseases such as osteoporosis continues to increase. The development of new therapeutics is hampered by the high failure rates of drug candidates during clinical testing, which is in part due to the poor predictive character of animal models during preclinical drug testing. Co-culture models of osteoblasts and osteoclasts offer an alternative to animal testing and are considered to have the potential to improve drug development processes in the future. However, a robust, scalable, and reproducible 3D model combining osteoblasts and osteoclasts for preclinical drug testing purposes has not been developed to date. Here we review various types of osteoblast-osteoclast co-culture models and outline the remaining obstacles that must be overcome for their successful translation.
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Affiliation(s)
- Alexander Sieberath
- School of Engineering, Newcastle University, Newcastle-Upon-Tyne NE1 7RU, UK; (A.S.); (A.M.F.); (P.G.)
| | - Elena Della Bella
- AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland; (E.D.B.); (D.E.)
| | - Ana Marina Ferreira
- School of Engineering, Newcastle University, Newcastle-Upon-Tyne NE1 7RU, UK; (A.S.); (A.M.F.); (P.G.)
| | - Piergiorgio Gentile
- School of Engineering, Newcastle University, Newcastle-Upon-Tyne NE1 7RU, UK; (A.S.); (A.M.F.); (P.G.)
| | - David Eglin
- AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland; (E.D.B.); (D.E.)
| | - Kenny Dalgarno
- School of Engineering, Newcastle University, Newcastle-Upon-Tyne NE1 7RU, UK; (A.S.); (A.M.F.); (P.G.)
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6
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Iwasaki Y, Yamato H, Fukagawa M. TGF-Beta Signaling in Bone with Chronic Kidney Disease. Int J Mol Sci 2018; 19:E2352. [PMID: 30103389 PMCID: PMC6121599 DOI: 10.3390/ijms19082352] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 07/30/2018] [Accepted: 08/08/2018] [Indexed: 01/05/2023] Open
Abstract
Transforming growth factor (TGF)-β signaling is not only important in skeletal development, but also essential in bone remodeling in adult bone. The bone remodeling process involves integrated cell activities induced by multiple stimuli to balance bone resorption and bone formation. TGF-β plays a role in bone remodeling by coordinating cell activities to maintain bone homeostasis. However, mineral metabolism disturbance in chronic kidney disease (CKD) results in abnormal bone remodeling, which leads to ectopic calcification in CKD. High circulating levels of humoral factors such as parathyroid hormone, fibroblast growth factor 23, and Wnt inhibitors modulate bone remodeling in CKD. Several reports have revealed that TGF-β is involved in the production and functions of these factors in bone. TGF-β may act as a factor that mediates abnormal bone remodeling in CKD.
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Affiliation(s)
- Yoshiko Iwasaki
- Department of Health Sciences, Oita University of Nursing and Health Sciences, Oita 870-1163, Japan.
| | - Hideyuki Yamato
- Division of Nephrology and Metabolism, Tokai University School of Medicine, Kanagawa 259-119, Japan.
| | - Masafumi Fukagawa
- Division of Nephrology and Metabolism, Tokai University School of Medicine, Kanagawa 259-119, Japan.
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7
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Jähn K, Mason DJ, Ralphs JR, Evans BAJ, Archer CW, Richards RG, Stoddart MJ. Phenotype and Viability of MLO-Y4 Cells Is Maintained by TGFβ₃ in a Serum-Dependent Manner within a 3D-Co-Culture with MG-63 Cells. Int J Mol Sci 2018; 19:ijms19071932. [PMID: 29966376 PMCID: PMC6073466 DOI: 10.3390/ijms19071932] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 06/15/2018] [Accepted: 06/28/2018] [Indexed: 02/06/2023] Open
Abstract
The osteocyte network inside the bone matrix is of functional importance and osteocyte cell death is a characteristic feature of pathological bone diseases. Osteocytes have emerged as key regulators of bone tissue maintenance, yet maintaining their phenotype during in vitro culture remains challenging. A 3D co-culture system for osteocytes with osteoblasts was recently presented, enabling the determination of more physiological effects of growth factors on cells in vitro. MLO-Y4 cells were embedded within a type I collagen gel and cultured in the presence of surface MG-63 cells. Co-culture was performed in the presence or absence of TGFβ₃. Gene expression by quantitative PCR, protein expression by fluorescent immunohistochemistry and cell viability tests were performed. The 3D co-culture induced cell differentiation of MG-63 cells seen by increased type I collagen and osteocalcin mRNA expression. TGFβ₃ maintained osteocyte differentiation of MLO-Y4 cells during co-culture as determined by stable E11 and osteocalcin mRNA expression till day 4. Interestingly, most of the effects of TGFβ₃ on co-cultured cells were serum-dependent. Also, TGFβ₃ reduced cell death of 3D co-cultured MLO-Y4 cells in a serum-dependent manner. This study shows that 3D co-culture upregulates differentiation of MG-63 cells to a more mature osteoblast-like phenotype; while the addition of TGFβ₃ maintained the characteristic MLO-Y4 osteocyte-like phenotype and viability in a serum-dependent manner.
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Affiliation(s)
- Katharina Jähn
- Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, 22529 Hamburg, Germany.
| | - Deborah J Mason
- School of Biosciences, Cardiff University, CF10 3AX Cardiff, UK.
| | - Jim R Ralphs
- School of Biosciences, Cardiff University, CF10 3AX Cardiff, UK.
| | | | | | - R Geoff Richards
- School of Biosciences, Cardiff University, CF10 3AX Cardiff, UK.
- AO Research Institute Davos, AO Foundation, 7270 Davos, Switzerland.
| | - Martin J Stoddart
- AO Research Institute Davos, AO Foundation, 7270 Davos, Switzerland.
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Peroglio M, Gaspar D, Zeugolis DI, Alini M. Relevance of bioreactors and whole tissue cultures for the translation of new therapies to humans. J Orthop Res 2018; 36:10-21. [PMID: 28718947 DOI: 10.1002/jor.23655] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 06/30/2017] [Indexed: 02/04/2023]
Abstract
The purpose of this review is to provide a brief overview of bioreactor-based culture systems as alternatives to conventional two- and three-dimensional counterparts. The role, challenges, and future aspirations of bioreactors in the musculoskeletal field (e.g., cartilage, intervertebral disc, tendon, and bone) are discussed. Bioreactors, by recapitulating physiological processes, can be used effectively as part of the initial in vitro screening, reducing that way the number of animal required for preclinical assessment, complying with the 3R principles and, in most cases, allowing working with human tissues. The clinical significance of bioreactors is that, by providing more physiologically relevant conditions to customarily used two- and three-dimensional cultures, they hold the potential to provide a testing platform that is more predictable of a whole tissue response, thereby facilitating the screening of treatments before the initiation of clinical trials. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:10-21, 2018.
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Affiliation(s)
- Marianna Peroglio
- AO Research Institute Davos, Clavadelerstrasse 8, 7270, Davos, Switzerland
| | - Diana Gaspar
- Regenerative, Modular & Developmental Engineering Laboratory (REMODEL), National University of Ireland Galway (NUI Galway), Galway, Ireland.,Science Foundation Ireland (SFI), Centre for Research in Medical Devices (CÚRAM), National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Dimitrios I Zeugolis
- Regenerative, Modular & Developmental Engineering Laboratory (REMODEL), National University of Ireland Galway (NUI Galway), Galway, Ireland.,Science Foundation Ireland (SFI), Centre for Research in Medical Devices (CÚRAM), National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Mauro Alini
- AO Research Institute Davos, Clavadelerstrasse 8, 7270, Davos, Switzerland
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Caddeo S, Boffito M, Sartori S. Tissue Engineering Approaches in the Design of Healthy and Pathological In Vitro Tissue Models. Front Bioeng Biotechnol 2017; 5:40. [PMID: 28798911 PMCID: PMC5526851 DOI: 10.3389/fbioe.2017.00040] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 06/26/2017] [Indexed: 12/16/2022] Open
Abstract
In the tissue engineering (TE) paradigm, engineering and life sciences tools are combined to develop bioartificial substitutes for organs and tissues, which can in turn be applied in regenerative medicine, pharmaceutical, diagnostic, and basic research to elucidate fundamental aspects of cell functions in vivo or to identify mechanisms involved in aging processes and disease onset and progression. The complex three-dimensional (3D) microenvironment in which cells are organized in vivo allows the interaction between different cell types and between cells and the extracellular matrix, the composition of which varies as a function of the tissue, the degree of maturation, and health conditions. In this context, 3D in vitro models can more realistically reproduce a tissue or organ than two-dimensional (2D) models. Moreover, they can overcome the limitations of animal models and reduce the need for in vivo tests, according to the "3Rs" guiding principles for a more ethical research. The design of 3D engineered tissue models is currently in its development stage, showing high potential in overcoming the limitations of already available models. However, many issues are still opened, concerning the identification of the optimal scaffold-forming materials, cell source and biofabrication technology, and the best cell culture conditions (biochemical and physical cues) to finely replicate the native tissue and the surrounding environment. In the near future, 3D tissue-engineered models are expected to become useful tools in the preliminary testing and screening of drugs and therapies and in the investigation of the molecular mechanisms underpinning disease onset and progression. In this review, the application of TE principles to the design of in vitro 3D models will be surveyed, with a focus on the strengths and weaknesses of this emerging approach. In addition, a brief overview on the development of in vitro models of healthy and pathological bone, heart, pancreas, and liver will be presented.
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Affiliation(s)
- Silvia Caddeo
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
- Department of Oral Cell Biology, Academic Center for Dentistry Amsterdam, Amsterdam, Netherlands
| | - Monica Boffito
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
| | - Susanna Sartori
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
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Torcasio A, Jähn K, Van Guyse M, Spaepen P, Tami AE, Vander Sloten J, Stoddart MJ, van Lenthe GH. Trabecular bone adaptation to low-magnitude high-frequency loading in microgravity. PLoS One 2014; 9:e93527. [PMID: 24787094 PMCID: PMC4008366 DOI: 10.1371/journal.pone.0093527] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 03/07/2014] [Indexed: 11/18/2022] Open
Abstract
Exposure to microgravity causes loss of lower body bone mass in some astronauts. Low-magnitude high-frequency loading can stimulate bone formation on earth. Here we hypothesized that low-magnitude high-frequency loading will also stimulate bone formation under microgravity conditions. Two groups of six bovine cancellous bone explants were cultured at microgravity on a Russian Foton-M3 spacecraft and were either loaded dynamically using a sinusoidal curve or experienced only a static load. Comparable reference groups were investigated at normal gravity. Bone structure was assessed by histology, and mechanical competence was quantified using μCT and FE modelling; bone remodelling was assessed by fluorescent labelling and secreted bone turnover markers. Statistical analyses on morphometric parameters and apparent stiffness did not reveal significant differences between the treatment groups. The release of bone formation marker from the groups cultured at normal gravity increased significantly from the first to the second week of the experiment by 90.4% and 82.5% in response to static and dynamic loading, respectively. Bone resorption markers decreased significantly for the groups cultured at microgravity by 7.5% and 8.0% in response to static and dynamic loading, respectively. We found low strain magnitudes to drive bone turnover when applied at high frequency, and this to be valid at normal as well as at microgravity. In conclusion, we found the effect of mechanical loading on trabecular bone to be regulated mainly by an increase of bone formation at normal gravity and by a decrease in bone resorption at microgravity. Additional studies with extended experimental time and increased samples number appear necessary for a further understanding of the anabolic potential of dynamic loading on bone quality and mechanical competence.
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Affiliation(s)
| | | | | | | | | | | | | | - G. Harry van Lenthe
- Biomechanics Section, KU Leuven, Leuven, Belgium
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
- * E-mail:
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11
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Finley MJ, Clark KA, Alferiev IS, Levy RJ, Stachelek SJ. Intracellular signaling mechanisms associated with CD47 modified surfaces. Biomaterials 2013; 34:8640-9. [PMID: 23948164 DOI: 10.1016/j.biomaterials.2013.07.088] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 07/25/2013] [Indexed: 01/07/2023]
Abstract
We have previously established that recombinant CD47 can ameliorate the inflammatory response to synthetic polymeric surfaces. Here, we begin to profile, at the transcriptional, translational and cell signaling level, the inflammatory cell response when blood interacts with CD47 modified polyvinyl chloride (PVC) (CD47-PVC). We used qPCR arrays to compare transcriptional changes between human whole blood exposed to CD47-PVC or PVC. Transcription of IL1F5, IL1F10, IL17F, CCL3, CCL8, CCL28, CXCL12, and CXCL13 was upregulated in blood exposed to PVC, compared to CD47-PVC. The increase in CCL3 and CCL8 transcription correlated with an increase in the chemokines' presence in the plasma. Exposure of blood to CD47-PVC resulted in an increase, compared to PVC, in transcription of CCL2, CCL4, CCL20, CXCL1, TGFβ3, GDF3, GDF10, CD40LG, and TNFSF10. CD47-PVC exposure resulted in an increase of the following matrix metalloproteinase related genes: MMP1, MMP7, MMP13, and MMP16. Phosflow cytometry, and assays examining transcription factor binding, cell attachment, and genome-wide chromatin association indicated that members of the JAK-STAT signaling pathway, particularly JAK2 and STAT5, mediate inflammatory cell interactions with CD47-PVC. Our data demonstrate that differential molecular responses to CD47 involve downregulation of cytokines, upregulation of MMPs, and JAK/STAT signaling mechanisms.
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Affiliation(s)
- Matthew J Finley
- Division of Cardiology, Department of Pediatrics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA
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12
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Tang SY, Alliston T. Regulation of postnatal bone homeostasis by TGFβ. BONEKEY REPORTS 2013; 2:255. [PMID: 24404376 DOI: 10.1038/bonekey.2012.255] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Accepted: 11/22/2012] [Indexed: 12/30/2022]
Abstract
Perhaps more so than any other tissue, bone has pivotal mechanical and biological functions. Underlying the ability of bone to execute these functions, whether providing structural support or preserving mineral homeostasis, is the dynamic remodeling of bone matrix. Cells within bone integrate multiple stimuli to balance the deposition and resorption of bone matrix. Transforming growth factor-β (TGFβ) uniquely coordinates bone cell activity to maintain bone homeostasis. TGFβ regulates the differentiation and function of both osteoblasts and osteoclasts, from lineage recruitment to terminal differentiation, to balance bone formation and resorption. TGFβ calibrates the synthesis and material quality of bone matrix and bone's responsiveness to applied mechanical loads. Therefore, by coupling the activity of bone forming and resorbing cells, and by sensing, responding to and defining physical cues, TGFβ integrates physical and biochemical stimuli to maintain bone homeostasis. Disruption of TGFβ signaling has significant consequences on bone mass and quality. Alternatively, TGFβ is a powerful lever that has the potential to yield therapeutic benefit in cases where bone homeostasis needs to be recalibrated.
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Affiliation(s)
- Simon Y Tang
- Department of Orthopaedic Surgery, School of Medicine, Washington University in St Louis , St Louis, MO, USA
| | - Tamara Alliston
- Department of Orthopaedic Surgery, School of Medicine, University of California, San Francisco , San Francisco, CA, USA
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13
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Abstract
Proper development of the skeleton in utero and during growth requires mechanical stimulation. Loading results in adaptive changes in bone that strengthen bone structure. Bone's adaptive response is regulated by the ability of resident bone cells to perceive and translate mechanical energy into a cascade of structural and biochemical changes within the cells a process known as mechanotransduction. Mechanotransduction pathways are among the most anabolic in bone, and consequently, there is great interest in elucidating how mechanical loading produces its observed effects, including increased bone formation, reduced bone loss, changes in bone cell differentiation and lifespan, among others. A molecular understanding of these processes is developing, and with it comes a profound new insight into the biology of bone. In this article, we review the nature of the physical stimulus to which bone cells mount an adaptive response, including the identity of the sensor cells, their attributes and physical environment, and putative mechanoreceptors they express. Particular attention is allotted to the focal adhesion and Wnt signaling, in light of their emerging role in bone mechanotransduction. Te cellular mechanisms for increased bone loss during disuse, and reduced bone loss during loading are considered. Finally, we summarize the published data on bone cell accommodation, whereby bone cells stop responding to mechanical signaling events. Collectively, these data highlight the complex yet finely orchestrated process of mechanically regulated bone homeostasis.
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Affiliation(s)
- Alexander G. Robling
- Department of Anatomy & Cell Biology, Indiana University School of Medicine
- Department of Biomedical Engineering, Indiana University/Purdue University at Indianapolis (IUPUI)
| | - Charles H. Turner
- Department of Biomedical Engineering, Indiana University/Purdue University at Indianapolis (IUPUI)
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN 46202 USA
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