1
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Day RN, Day KH, Pavalko FM. Direct visualization by FRET-FLIM of a putative mechanosome complex involving Src, Pyk2 and MBD2 in living MLO-Y4 cells. PLoS One 2021; 16:e0261660. [PMID: 34941939 PMCID: PMC8699642 DOI: 10.1371/journal.pone.0261660] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 12/08/2021] [Indexed: 01/12/2023] Open
Abstract
Earlier, we proposed the “mechanosome” concept as a testable model for understanding how mechanical stimuli detected by cell surface adhesion molecules are transmitted to modulate gene expression inside cells. Here, for the first time we document a putative mechanosome involving Src, Pyk2 and MBD2 in MLO-Y4 osteocytes with high spatial resolution using FRET-FLIM. Src-Pyk2 complexes were concentrated at the periphery of focal adhesions and the peri-nuclear region. Pyk2-MBD2 complexes were located primarily in the nucleus and peri-nuclear region. Lifetime measurements indicated that Src and MBD2 did not interact directly. Finally, mechanical stimulation by fluid flow induced apparent accumulation of Src-Pyk2 protein complexes in the peri-nuclear/nuclear region, consistent with the proposed behavior of a mechanosome in response to a mechanical stimulus.
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Affiliation(s)
- Richard N. Day
- Department of Anatomy, Cell Biology and Physiology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Kathleen H. Day
- Department of Anatomy, Cell Biology and Physiology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Fredrick M. Pavalko
- Department of Anatomy, Cell Biology and Physiology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
- * E-mail:
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2
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Gould NR, Leser JM, Torre OM, Khairallah RJ, Ward CW, Stains JP. In vitro Fluid Shear Stress Induced Sclerostin Degradation and CaMKII Activation in Osteocytes. Bio Protoc 2021; 11:e4251. [PMID: 35005095 PMCID: PMC8678913 DOI: 10.21769/bioprotoc.4251] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 09/18/2021] [Accepted: 09/27/2021] [Indexed: 11/19/2023] Open
Abstract
Bone is a dynamic tissue that adapts to changes in its mechanical environment. Mechanical stimuli pressurize interstitial fluid in the lacunar-canalicular system within the bone matrix, causing fluid shear stress (FSS) across bone embedded, mechano-sensitive osteocytes. Therefore, modeling this mechanical stimulus in vitro is vital for identifying mechano-transduction cascades that contribute to the regulation of mechano-responsive proteins, such as the Wnt/β-catenin antagonist, sclerostin, which is reduced in response to FSS. Recently, we reported the rapid post-translational degradation of sclerostin protein in bone cells following FSS. Given the fundamental nature of sclerostin to bone physiology and the nuances of studying its rapid post-translational control, here, we detail our FSS protocol, and adaptations that can be made, to stimulate Ocy454 osteocyte-like cells to study sclerostin protein in vitro. While this protocol is optimized for detecting sclerostin degradation by western blot, this protocol can be adapted to examine transcriptional changes with RT-qPCR, cellular dynamics with live cell imaging, or secreted factors in the FSS buffer. This protocol utilizes 3D-printed FSS tips that are compatible with commercially available 96-well plates, allowing for high experimental accessibility, versatility, and throughput. However, this protocol can be adapted for any FSS chamber. It can also be combined with pharmacological inhibitors or genetic manipulations to interrogate the role of specific cellular components. In all, this experimental set-up and protocol is highly adaptable to allow for many experimental outcomes to examine many aspects of cell mechano-transduction.
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Affiliation(s)
- Nicole R. Gould
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, USA
| | - Jenna M. Leser
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, USA
| | - Olivia M. Torre
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, USA
| | | | - Christopher W. Ward
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, USA
| | - Joseph P. Stains
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, USA
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3
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Estrogen depletion alters osteogenic differentiation and matrix production by osteoblasts in vitro. Exp Cell Res 2021; 408:112814. [PMID: 34492267 DOI: 10.1016/j.yexcr.2021.112814] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 08/20/2021] [Accepted: 09/03/2021] [Indexed: 11/21/2022]
Abstract
Recent studies have revealed that the effects of estrogen deficiency are not restricted to osteoclasts and bone resorption, but that bone matrix composition is altered and osteoblasts exhibit an impaired response to mechanical stimulation. In this study, we test the hypothesis that estrogen depletion alters osteogenic differentiation and matrix production by mechanically stimulated osteoblasts in vitro. MC3T3-E1 cells were pre-treated with estrogen for 14 days, after which estrogen was withdrawn or inhibited with Fulvestrant up to 14 days. Fluid shear stress (FSS) was applied using an orbital shaker. Under estrogen depletion in static culture, osteogenic marker (ALP) and gene expression (Runx2) were decreased at 2 and after 7 days of estrogen depletion, respectively. In addition, up to 7 day the inhibition of the estrogen receptor significantly decreased fibronectin expression (FN1) under static conditions. Under estrogen depletion and daily mechanical stimulation, changes in expression of Runx2 occurred earlier (4 days) and by 14 days, changes in matrix production (Col1a1) were reported. We propose that changes in osteoblast differentiation and impaired matrix production during estrogen depletion may contribute to the altered quality of the bone and act as a contributing factor to increased bone fragility in postmenopausal osteoporosis.
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4
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Sato T, Verma S, Andrade CDC, Omeara M, Campbell N, Wang JS, Cetinbas M, Lang A, Ausk BJ, Brooks DJ, Sadreyev RI, Kronenberg HM, Lagares D, Uda Y, Pajevic PD, Bouxsein ML, Gross TS, Wein MN. A FAK/HDAC5 signaling axis controls osteocyte mechanotransduction. Nat Commun 2020; 11:3282. [PMID: 32612176 PMCID: PMC7329900 DOI: 10.1038/s41467-020-17099-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 06/11/2020] [Indexed: 11/13/2022] Open
Abstract
Osteocytes, cells ensconced within mineralized bone matrix, are the primary skeletal mechanosensors. Osteocytes sense mechanical cues by changes in fluid flow shear stress (FFSS) across their dendritic projections. Loading-induced reductions of osteocytic Sclerostin (encoded by Sost) expression stimulates new bone formation. However, the molecular steps linking mechanotransduction and Sost suppression remain unknown. Here, we report that class IIa histone deacetylases (HDAC4 and HDAC5) are required for loading-induced Sost suppression and bone formation. FFSS signaling drives class IIa HDAC nuclear translocation through a signaling pathway involving direct HDAC5 tyrosine 642 phosphorylation by focal adhesion kinase (FAK), a HDAC5 post-translational modification that controls its subcellular localization. Osteocyte cell adhesion supports FAK tyrosine phosphorylation, and FFSS triggers FAK dephosphorylation. Pharmacologic FAK catalytic inhibition reduces Sost mRNA expression in vitro and in vivo. These studies demonstrate a role for HDAC5 as a transducer of matrix-derived cues to regulate cell type-specific gene expression.
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Affiliation(s)
- Tadatoshi Sato
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Shiv Verma
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | | | - Maureen Omeara
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Nia Campbell
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Jialiang S. Wang
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Murat Cetinbas
- Department of Molecular Biology and Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Audrey Lang
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Brandon J. Ausk
- 0000000122986657grid.34477.33Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA USA
| | - Daniel J. Brooks
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA ,Center for Advanced Orthopaedic Studies, Department of Orthopedic Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA USA
| | - Ruslan I. Sadreyev
- Department of Molecular Biology and Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Henry M. Kronenberg
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - David Lagares
- Center for Immunology and Inflammatory Diseases, Fibrosis Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA
| | - Yuhei Uda
- 0000 0004 1936 7558grid.189504.1Translational Dental Medicine, Henry M. Goldman School of Dental Medicine, Boston University, Boston, MA USA
| | - Paola Divieti Pajevic
- 0000 0004 1936 7558grid.189504.1Translational Dental Medicine, Henry M. Goldman School of Dental Medicine, Boston University, Boston, MA USA
| | - Mary L. Bouxsein
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA ,Center for Advanced Orthopaedic Studies, Department of Orthopedic Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA USA
| | - Ted S. Gross
- 0000000122986657grid.34477.33Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA USA
| | - Marc N. Wein
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA USA ,grid.66859.34Broad Institute of Harvard and MIT, Cambridge, MA USA
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5
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Agarwal T, Narayana GH, Banerjee I. Keratinocytes are mechanoresponsive to the microflow-induced shear stress. Cytoskeleton (Hoboken) 2019; 76:209-218. [PMID: 30969461 DOI: 10.1002/cm.21521] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2018] [Revised: 02/27/2019] [Accepted: 04/04/2019] [Indexed: 12/11/2022]
Abstract
Here, we have reported that keratinocytes respond to the microflow-induced shear stress both at the collective and individual cell level. Using a microfluidic setup, we categorically showed that low shear stress of magnitude 0.06 dyne/cm2 could induce morphological variation and cytoskeletal reorganization in keratinocyte, whereas higher shear stress (6 dyne/cm2 ) resulted in cellular disruption. Using a series of blocker molecules specific to different mechanotransducers, we demonstrated the pivotal role of actin network in keratinocyte mechanoresponsiveness in conjugation with myosin and lipid rafts. Flow-induced shear stress also induced significant elevation in E-cadherin and Zonula occludens-1 (ZO-1) expression levels. We further showed that under the influence of shear stress, the extent of colocalization of E-cadherin and ZO-1 was more at the cell-cell junction that indicates an improvement in the epithelial phenotype. An increase in the expression of nuclear lamin was also observed in the sheared cells that suggest the transmission of mechanical signals to the nucleus. It is envisioned that this study may find its application in basic and applied organogenesis of the epidermis.
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Affiliation(s)
- Tarun Agarwal
- Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, India.,Department of Biotechnology, Indian Institute of Technology Kharagpur, India
| | - Gautham H Narayana
- Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, India.,Jacques Monod Institute, Paris Diderot University & CNRS, Paris, France
| | - Indranil Banerjee
- Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, India
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Xu H, Duan J, Ren L, Yang P, Yang R, Li W, Zhao D, Shang P, Jiang JX. Impact of flow shear stress on morphology of osteoblast-like IDG-SW3 cells. J Bone Miner Metab 2018; 36:529-536. [PMID: 29027016 PMCID: PMC6282752 DOI: 10.1007/s00774-017-0870-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 09/11/2017] [Indexed: 11/26/2022]
Abstract
This study constructed an in situ cell culture, real-time observation system based originally on a microfluidic channel, and reported the morphological changes of late osteoblast-like IDG-SW3 cells in response to flow shear stress (FSS). The effects of high (1.2 Pa) and low (0.3 Pa) magnitudes of unidirectional FSS and three concentrations of extracellular Type I collagen (0.1, 0.5, and 1 mg/mL) coating on cell morphology were investigated. IDG-SW3 cells were cultured in polydimethylsiloxane microfluidic channels. Cell images were recorded real-time under microscope at intervals of 1 min. Cell morphology was characterized by five parameters: cellular area, cell elongation index, cellular alignment, cellular process length, and number of cellular process per cell. Immunofluorescence assay was used to detect stress fiber distribution and vinculin expression. The results showed that 1.2 Pa, but not 0.3 Pa of FSS induced a significant morphological change in late osteoblast-like IDG-SW3 cells, which may be caused by the alteration of cellular adhesion with matrix in response to FSS. Moreover, the amount of collagen matrix, alignment of fiber stress and expression of vinculin were closely correlated with the morphological changes of IDG-SW3 cells. This study suggests that osteoblasts are very responsive to the magnitudes of FSS, and extracellular collagen matrix and focal adhesion are directly involved in the morphological changes adaptive to FSS.
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Affiliation(s)
- Huiyun Xu
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China.
| | - Jing Duan
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Li Ren
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Pengfei Yang
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Ruixin Yang
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Wenbin Li
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Dongdong Zhao
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Peng Shang
- Key Laboratory for Space Biosciences and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi'an, 710072, Shaanxi, China
| | - Jean X Jiang
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA.
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7
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Li Y, Yuan J, Wang Q, Sun L, Sha Y, Li Y, Wang L, Wang Z, Ma Y, Cao H. The collective influence of 1, 25-dihydroxyvitamin D 3 with physiological fluid shear stress on osteoblasts. Steroids 2018; 129:9-16. [PMID: 29155218 DOI: 10.1016/j.steroids.2017.11.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 09/23/2017] [Accepted: 11/12/2017] [Indexed: 11/27/2022]
Abstract
1, 25-dihydroxyvitamin D3 (1, 25 (OH)2 D3) and mechanical stimuli in physiological environment contributes greatly to osteoporosis pathogenesis. Wide investigations have been conducted on how 1, 25-dihydroxyvitamin D3 and mechanical stimuli separately impact osteoblasts. This study reports the collective influences of 1, 25-dihydroxyvitamin D3 and flow shear stress (FSS) on biological functions of osteoblasts. 1, 25 (OH)2 D3 were prepared in various kinds of concentrations (0, 1, 10, 100 nmmol/L), while physiological fluid shear stress (12 dynes/cm2) was produced by using a parallel-plate fluid flow system. 1, 25 (OH)2 D3 affects the responses of ROBs to FSS, including the inhibition of NO release and cell proliferation as well as the promotion of PGE2 release and cell differentiation. These findings provide a possible mechanism by which 1, 25(OH)2 D3 influences osteoblasts' responses to FSS, thus most probably providing guidance for the selection of 1, 25(OH)2 D3 concentration and mechanical loading in order to produce functional bone tissues in vitro.
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Affiliation(s)
- Yan Li
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China.
| | - Jiafeng Yuan
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Qianwen Wang
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Lijie Sun
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Yunying Sha
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Yanxiang Li
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Lizhong Wang
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Zhonghua Wang
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Yonggang Ma
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
| | - Hui Cao
- School of Pharmacy, Taizhou Polytechnic College, Taizhou 225300, China; Bone Tissue Engineering Research Center of Taizhou, Taizhou 225300, China
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8
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PYK2 mediates BzATP-induced extracellular matrix proteins synthesis. Biochem Biophys Res Commun 2017; 494:663-667. [PMID: 29061307 DOI: 10.1016/j.bbrc.2017.10.107] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2017] [Accepted: 10/20/2017] [Indexed: 10/25/2022]
Abstract
Mechanical stimuli such as fluid shear and cyclic tension force induced extracellular adenosine triphosphate (ATP) release in osteoblasts. In particular, cyclic tension force-induced ATP enhances bone formation through P2X7 activation. Proline-rich tyrosine kinase 2 (PYK2) mediate osteoblasts differentiation is induced by mechanical stimuli. Furthermore, activation of PYK2 also was a response to integrin by mechanical stimuli. Extracellular matrix protein (ECMP)s, which are important factors for bone formation are expressed by osteoblasts. However, the effect of the interaction of 2'(3)-Ο-(4-Benzoylbenzoyl) adenosine-5'-triphosphate (BzATP), which is the agonist of the mechanosensitive receptor P2X7, with PYK2 on ECMP production is poorly understood. Thus, our purpose was to investigate the effects of PYK2 on BzATP-induced ECMP production in osteoblasts. BzATP increased phospho-PYK2 protein expression on days 3 and 7 of culture. Furthermore, the PYK2 inhibitor PF431394 inhibited the stimulatory effect of BzATP on the expression of type I collagen, bone sialoprotein and osteocalcin expression. PF431396 did not inhibit the stimulatory effect of BzATP on osteopontin (OPN) mRNA expression. These results suggest that mechanical stimuli activate P2X7 might induce ECMPs expression through PYK2 except in the case of OPN expression. Altogether, mechanical stimuli-induced ECMPs production might be implicated by extracellular ATP secretion or integrin via PYK2 activation.
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9
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Fukada T, Sakajiri H, Kuroda M, Kioka N, Sugimoto K. Fluid shear stress applied by orbital shaking induces MG-63 osteosarcoma cells to activate ERK in two phases through distinct signaling pathways. Biochem Biophys Rep 2017; 9:257-265. [PMID: 28956013 PMCID: PMC5614596 DOI: 10.1016/j.bbrep.2017.01.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 11/25/2016] [Accepted: 01/05/2017] [Indexed: 11/30/2022] Open
Abstract
Fluid shear stress (FSS) induces a series of biochemical responses in osteoblasts, and this “mechanoresponse” regulates their survival, proliferation and differentiation. However, the events in cells immediately after FSS application are unclear, and how biochemical signals from soluble factors modify the mechanoresponses is largely unknown. We used the orbital shaking method, instead of the frequently used parallel plate method, to examine activation of ERK and AKT by FSS for detailed tracking of its temporal transition. We found that ERK activation by orbital shaking was biphasic. The early phase was independent of Ca2+, PI3-kinase, and Rho kinase but required RAF activity. The late phase was dependent on Ca2+ but not RAF. These results suggest that the superior time-resolving capability of the orbital shaking method to separate the previously unrecognized Ca2+-independent early phase of ERK activation from the late phase. We also found that a certain combination of serum starvation and medium renewal affected ERK activation by FSS, suggesting that a soluble factor(s) may be secreted during serum starvation, which modified the phosphorylation level of ERK. These findings revealed novel aspects of the osteoblastic mechanoresponses and indicated that the orbital shaking method would be a useful, complementary alternative to the parallel plate method for certain types of study on cellular mechanoresponses. Fluid flow by orbital shaking induces biphasic activation of ERK in osteoblasts. Early-phase ERK activation is unique because of its independence of Ca2+ signaling. Serum starvation has complex effects on ERK activation by fluid flow. Orbital shaking is useful for certain types of study on cellular mechanoresponses.
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Affiliation(s)
- Takashi Fukada
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
| | - Hiroki Sakajiri
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
| | - Mito Kuroda
- Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyou-ku, Kyoto 606-8502, Japan
| | - Noriyuki Kioka
- Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyou-ku, Kyoto 606-8502, Japan
| | - Kenji Sugimoto
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
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10
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Wittkowske C, Reilly GC, Lacroix D, Perrault CM. In Vitro Bone Cell Models: Impact of Fluid Shear Stress on Bone Formation. Front Bioeng Biotechnol 2016; 4:87. [PMID: 27896266 PMCID: PMC5108781 DOI: 10.3389/fbioe.2016.00087] [Citation(s) in RCA: 162] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2016] [Accepted: 10/25/2016] [Indexed: 01/06/2023] Open
Abstract
This review describes the role of bone cells and their surrounding matrix in maintaining bone strength through the process of bone remodeling. Subsequently, this work focusses on how bone formation is guided by mechanical forces and fluid shear stress in particular. It has been demonstrated that mechanical stimulation is an important regulator of bone metabolism. Shear stress generated by interstitial fluid flow in the lacunar-canalicular network influences maintenance and healing of bone tissue. Fluid flow is primarily caused by compressive loading of bone as a result of physical activity. Changes in loading, e.g., due to extended periods of bed rest or microgravity in space are associated with altered bone remodeling and formation in vivo. In vitro, it has been reported that bone cells respond to fluid shear stress by releasing osteogenic signaling factors, such as nitric oxide, and prostaglandins. This work focusses on the application of in vitro models to study the effects of fluid flow on bone cell signaling, collagen deposition, and matrix mineralization. Particular attention is given to in vitro set-ups, which allow long-term cell culture and the application of low fluid shear stress. In addition, this review explores what mechanisms influence the orientation of collagen fibers, which determine the anisotropic properties of bone. A better understanding of these mechanisms could facilitate the design of improved tissue-engineered bone implants or more effective bone disease models.
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Affiliation(s)
- Claudia Wittkowske
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - Gwendolen C Reilly
- INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK; Department of Material Science, University of Sheffield, Sheffield, UK
| | - Damien Lacroix
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
| | - Cecile M Perrault
- Department of Mechanical Engineering, University of Sheffield, Sheffield, UK; INSIGNEO Institute for in silico Medicine, University of Sheffield, Sheffield, UK
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11
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Zeng Z, Jing D, Zhang X, Duan Y, Xue F. Cyclic mechanical stretch promotes energy metabolism in osteoblast-like cells through an mTOR signaling-associated mechanism. Int J Mol Med 2015; 36:947-56. [PMID: 26251974 PMCID: PMC4564076 DOI: 10.3892/ijmm.2015.2304] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 07/28/2015] [Indexed: 01/08/2023] Open
Abstract
Energy metabolism is essential for maintaining function and substance metabolism in osteoblasts. However, the role of cyclic stretch in regulating osteoblastic energy metabolism and the underlying mechanisms remain poorly understood. In this study, we found that cyclic stretch (10% elongation at 0.1 Hz) significantly enhanced glucose consumption, lactate levels (determined using a glucose/lactate assay kit), intracellular adenosine triphosphate (ATP) levels (quantified using rLuciferase/Luciferin reagent) and the mRNA expression of energy metabolism-related enzymes [mitochondrial ATP synthase, L-lactate dehydrogenase A (LDHA) and enolase 1; measured by RT-qPCR], and increased the phosphorylation levels of Akt, mammalian target of rapamycin (mTOR) and p70s6k (measured by western blot analysis) in human osteoblast‑like MG‑63 cells. Furthermore, the inhibition of Akt or mTOR with an antagonist (wortmannin or rapamycin) suppressed the stretch-induced increase in glucose consumption, lactate levels, intracellular ATP levels and the expression of mitochondrial ATP synthase and LDHA, indicating the significance of the Akt/mTOR/p70s6k pathway in regulating osteoblastic energy metabolism in response to mechanical stretch. Thus, we concluded that cyclic stretch regulates energy metabolism in MG‑63 cells partially through the Akt/mTOR/p70s6k signaling pathway. The present findings provide novel insight into osteoblastic mechanobiology from the perspective of energy metabolism.
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Affiliation(s)
- Zhaobin Zeng
- State Key Laboratory of Military Stomatology, Department of Orthodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Da Jing
- Department of Biomedical Engineering, The Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Xiaodong Zhang
- Department of Stomatology, General Hospital of Shenyang Military Area Command, Shenyang, Liaoning 110015, P.R. China
| | - Yinzhong Duan
- State Key Laboratory of Military Stomatology, Department of Orthodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Feng Xue
- State Key Laboratory of Military Stomatology, Department of Orthodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
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12
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Patil S, Paul S. A comprehensive review on the role of various materials in the osteogenic differentiation of mesenchymal stem cells with a special focus on the association of heat shock proteins and nanoparticles. Cells Tissues Organs 2014; 199:81-102. [PMID: 25401759 DOI: 10.1159/000362226] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/13/2014] [Indexed: 11/19/2022] Open
Abstract
Mesenchymal stem cells (MSCs) have important roles in the area of regenerative medicine and clinical applications due to their pluripotent nature. Osteogenic differentiation of MSCs has been studied extensively using various stimulants to develop models of bone repair. There are several factors that enhance the differentiation of MSCs into bone tissues. This review focuses on the effects of various inducers on the osteoblast differentiation of MSCs at different stages of cellular development. We discuss the various growth factors, hormones, vitamins, cytokines, chemical stimulants, and mechanical forces applied in bioreactors that play an essential role in the proliferation, differentiation, and matrix mineralization of stem cells during osteogenesis. Various nanoparticles have also been used recently for the same purpose and the results are promising. Moreover, we review the role of various stresses, including thermal stress, and the subsequent involvement of heat shock proteins as inducers of the proliferation and differentiation of osteoblasts. We also report how various proteasome inhibitors have been shown to induce proliferation and osteogenic differentiation of MSCs in a number of cases. In this communication, the role of peptide-based scaffolds in osteoblast proliferation and differentiation is also reviewed. Based on the reviewed information, this article proposes novel possibilities for the enhancement of proliferation, differentiation, and migration of osteoblasts from MSCs. © 2014 S. Karger AG, Basel.
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Affiliation(s)
- Supriya Patil
- Structural Biology and Nanomedicine Laboratory, Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, Rourkela, India
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Liu YS, Lee OK. In search of the pivot point of mechanotransduction: mechanosensing of stem cells. Cell Transplant 2014; 23:1-11. [PMID: 24439034 DOI: 10.3727/096368912x659925] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Stem cells are undifferentiated cells with the ability to self-renew and to differentiate into diverse specialized cell types; hence, they have great potential in tissue engineering and cell therapies. In addition to biochemical regulation, the physical properties of the microenvironments, such as scaffold topography, substrate stiffness, and mechanical forces, including fluid shear stress, compression, and tensile strain, can also regulate the proliferation and differentiation of stem cells. Upon physical stimuli, cytoskeleton rearrangements are expected to counterbalance the extracellular mechanical forces, trigger signaling cascades, and eventually cause epigenetic modifications. This article mainly focuses on the mechanosensing, which is the upstream event of stem cell mechanotransduction and the downstream one of physical stimuli. Putative mechanosensors such as ion channels, integrins, and cell membrane as well as primary cilia are discussed. Because mechanical environment is an important stem cell niche, identification of mechanosensors not only can elucidate the mechanisms of mechanotransduction and fate commitments but also bring new prospects of the mechanical control as well as drug development for clinical application.
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Affiliation(s)
- Yi-Shiuan Liu
- Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
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14
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Mechanical loading in osteocytes induces formation of a Src/Pyk2/MBD2 complex that suppresses anabolic gene expression. PLoS One 2014; 9:e97942. [PMID: 24841674 PMCID: PMC4026426 DOI: 10.1371/journal.pone.0097942] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Accepted: 04/25/2014] [Indexed: 11/19/2022] Open
Abstract
Mechanical stimulation of the skeleton promotes bone gain and suppresses bone loss, ultimately resulting in improved bone strength and fracture resistance. The molecular mechanisms directing anabolic and/or anti-catabolic actions on the skeleton during loading are not fully understood. Identifying molecular mechanisms of mechanotransduction (MTD) signaling cascades could identify new therapeutic targets. Most research into MTD mechanisms is typically focused on understanding the signaling pathways that stimulate new bone formation in response to load. However, we investigated the structural, signaling and transcriptional molecules that suppress the stimulatory effects of loading. The high bone mass phenotype of mice with global deletion of either Pyk2 or Src suggests a role for these tyrosine kinases in repression of bone formation. We used fluid shear stress as a MTD stimulus to identify a novel Pyk2/Src-mediated MTD pathway that represses mechanically-induced bone formation. Our results suggest Pyk2 and Src function as molecular switches that inhibit MTD in our mechanically stimulated osteocyte culture experiments. Once activated by oscillatory fluid shear stress (OFSS), Pyk2 and Src translocate to and accumulate in the nucleus, where they associate with a protein involved in DNA methylation and the interpretation of DNA methylation patterns –methyl-CpG-binding domain protein 2 (MBD2). OFSS-induced Cox-2 and osteopontin expression was enhanced in Pyk2 KO osteoblasts, while inhibition of Src enhanced osteocalcin expression in response to OFSS. We found that Src kinase activity increased in the nucleus of osteocytes in response to OFSS and an interaction activated between Src (Y418) and Pyk2 (Y402) increased in response to OFSS. Thus, as a mechanism to prevent an over-reaction to physical stimulation, mechanical loading may induce the formation of a Src/Pyk2/MBD2 complex in the nucleus that functions to suppress anabolic gene expression.
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Castillo AB, Triplett JW, Pavalko FM, Turner CH. Estrogen receptor-β regulates mechanical signaling in primary osteoblasts. Am J Physiol Endocrinol Metab 2014; 306:E937-44. [PMID: 24619882 PMCID: PMC3989741 DOI: 10.1152/ajpendo.00458.2013] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mechanical loading is an important regulator in skeletal growth, maintenance, and aging. Estrogen receptors have a regulatory role in mechanically induced bone adaptation. Estrogen receptor-α (ERα) is known to enhance load-induced bone formation, whereas ERβ negatively regulates this process. We hypothesized that ERβ regulates mechanical signaling in osteoblasts. We tested this hypothesis by subjecting primary calvarial cells isolated from wild-type and ERβ-knockout mice (BERKO) to oscillatory fluid flow in the absence or presence of estradiol (E2). We found that the known responses to fluid shear stress, i.e., phosphorylation of the mitogen-activated protein kinase ERK and upregulation of COX-2 expression, were inhibited in BERKO cells in the absence of E2. Flow-induced increase in prostaglandin E2 (PGE2) release was not altered in BERKO cells in the absence of E2, but was increased when E2 was present. Additionally, immunofluorescence analysis and estrogen response element luciferase assays revealed increased ERα expression and flow- and ligand-induced nuclear translocation as well as transcriptional activity in BERKO cells in both the presence and absence of E2. Taken together, these data suggest that ERβ plays both ligand-dependent and ligand-independent roles in mechanical signaling in osteoblasts. Furthermore, our data suggest that one mechanism by which ERβ regulates mechanotransduction in osteoblasts may result from its inhibitory effect on ERα expression and function. Targeting estrogen receptors (e.g., inhibiting ERβ) may represent an effective approach for prevention and treatment of age-related bone loss.
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Affiliation(s)
- Alesha B Castillo
- Rehabilitation Research and Development, Veterans Affairs Palo Alto Health Care System, Palo Alto, California
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16
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Enhancement of Flow-Induced AP-1 Gene Expression by Cyclosporin A Requires NFAT-Independent Signaling in Bone Cells. Cell Mol Bioeng 2014; 7:254-265. [PMID: 25484988 DOI: 10.1007/s12195-014-0321-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Growing evidence suggests that aging compromises the ability of the skeleton to respond to anabolic mechanical stimuli. Recently, we reported that treating senescent mice with Cyclosporin A (CsA) rescued aging-related deficits in loading-induced bone formation. Given that the actions of CsA are often attributed to inhibition of the calcineurin/NFAT axis, we hypothesized that CsA enhances gene expression in bone cells exposed to fluid flow, by inhibiting nuclear NFATc1 accumulation. When exposed to flow, MC3T3-E1 osteoblastic cells exhibited rapid nuclear accumulation of NFATc1 that was abolished by CsA treatment. Under differentiation conditions, intermittent CsA treatment enhanced gene expression of late osteoblastic differentiation markers and activator protein 1 (AP-1) family members. Superimposing flow upon CsA further enhanced expression of the AP-1 members Fra-1 and c-Jun. To delineate the contribution of NFAT in this response, cells were treated with VIVIT, a specific inhibitor of the calcineurin/NFAT interaction. Treatment with VIVIT blocked flow-induced nuclear NFATc1 accumulation but did not recapitulate the CsA-mediated enhancement of flow-induced AP-1 component gene expression. Taken together, our study is the first to demonstrate that CsA enhances mechanically-induced gene expression of AP-1 components in bone cells, and suggests that this response requires calcineurin-dependent mechanisms that are independent of inhibiting NFATc1 nuclear accumulation.
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Worton LE, Ausk BJ, Downey LM, Bain SD, Gardiner EM, Srinivasan S, Gross TS, Kwon RY. Systems-based identification of temporal processing pathways during bone cell mechanotransduction. PLoS One 2013; 8:e74205. [PMID: 24040202 PMCID: PMC3770665 DOI: 10.1371/journal.pone.0074205] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 07/26/2013] [Indexed: 11/25/2022] Open
Abstract
Bone has long been established to be a highly mechanosensitive tissue. When subjected to mechanical loading, bone exhibits profoundly different anabolic responses depending on the temporal pattern in which the stimulus is applied. This phenomenon has been termed temporal processing, and involves complex signal amplification mechanisms that are largely unidentified. In this study, our goal was to characterize transcriptomic perturbations arising from the insertion of intermittent rest periods (a temporal variation with profound effects on bone anabolism) in osteoblastic cells subjected to fluid flow, and assess the utility of these perturbations to identify signaling pathways that are differentially activated by this temporal variation. At the level of the genome, we found that the common and differential alterations in gene expression arising from the two flow conditions were distributionally distinct, with the differential alterations characterized by many small changes in a large number of genes. Using bioinformatics analysis, we identified distinct up- and down-regulation transcriptomic signatures associated with the insertion of rest intervals, and found that the up-regulation signature was significantly associated with MAPK signaling. Confirming the involvement of the MAPK pathway, we found that the insertion of rest intervals significantly elevated flow-induced p-ERK1/2 levels by enabling a second spike in activity that was not observed in response to continuous flow. Collectively, these studies are the first to characterize distinct transcriptomic perturbations in bone cells subjected to continuous and intermittent stimulation, and directly demonstrate the utility of systems-based transcriptomic analysis to identify novel acute signaling pathways underlying temporal processing in bone cells.
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Affiliation(s)
- Leah E. Worton
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Brandon J. Ausk
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Leah M. Downey
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Steven D. Bain
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Edith M. Gardiner
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Sundar Srinivasan
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Ted S. Gross
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
| | - Ronald Y. Kwon
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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18
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New insights into adhesion signaling in bone formation. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 305:1-68. [PMID: 23890379 DOI: 10.1016/b978-0-12-407695-2.00001-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mineralized tissues that are protective scaffolds in the most primitive species have evolved and acquired more specific functions in modern animals. These are as diverse as support in locomotion, ion homeostasis, and precise hormonal regulation. Bone formation is tightly controlled by a balance between anabolism, in which osteoblasts are the main players, and catabolism mediated by the osteoclasts. The bone matrix is deposited in a cyclic fashion during homeostasis and integrates several environmental cues. These include diffusible elements that would include estrogen or growth factors and physicochemical parameters such as bone matrix composition, stiffness, and mechanical stress. Therefore, the microenvironment is of paramount importance for controlling this delicate equilibrium. Here, we provide an overview of the most recent data highlighting the role of cell-adhesion molecules during bone formation. Due to the very large scope of the topic, we focus mainly on the role of the integrin receptor family during osteogenesis. Bone phenotypes of some deficient mice as well as diseases of human bones involving cell adhesion during this process are discussed in the context of bone physiology.
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19
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Macro and microfluidic flows for skeletal regenerative medicine. Cells 2012; 1:1225-45. [PMID: 24710552 PMCID: PMC3901127 DOI: 10.3390/cells1041225] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Revised: 11/07/2012] [Accepted: 12/04/2012] [Indexed: 11/16/2022] Open
Abstract
Fluid flow has a great potential as a cell stimulatory tool for skeletal regenerative medicine, because fluid flow-induced bone cell mechanotransduction in vivo plays a critical role in maintaining healthy bone homeostasis. Applications of fluid flow for skeletal regenerative medicine are reviewed at macro and microscale. Macroflow in two dimensions (2D), in which flow velocity varies along the normal direction to the flow, has explored molecular mechanisms of bone forming cell mechanotransduction responsible for flow-regulated differentiation, mineralized matrix deposition, and stem cell osteogenesis. Though 2D flow set-ups are useful for mechanistic studies due to easiness in in situ and post-flow assays, engineering skeletal tissue constructs should involve three dimensional (3D) flows, e.g., flow through porous scaffolds. Skeletal tissue engineering using 3D flows has produced promising outcomes, but 3D flow conditions (e.g., shear stress vs. chemotransport) and scaffold characteristics should further be tailored. Ideally, data gained from 2D flows may be utilized to engineer improved 3D bone tissue constructs. Recent microfluidics approaches suggest a strong potential to mimic in vivo microscale interstitial flows in bone. Though there have been few microfluidics studies on bone cells, it was demonstrated that microfluidic platform can be used to conduct high throughput screening of bone cell mechanotransduction behavior under biomimicking flow conditions.
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Li P, Ma YC, Sheng XY, Dong HT, Han H, Wang J, Xia YY. Cyclic fluid shear stress promotes osteoblastic cells proliferation through ERK5 signaling pathway. Mol Cell Biochem 2012; 364:321-7. [PMID: 22286747 DOI: 10.1007/s11010-012-1233-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Accepted: 01/13/2012] [Indexed: 10/14/2022]
Abstract
Fluid shear stress plays an important role in bone remodeling, however, the mechanism of mechanotransduction in bone tissue remains unclear. Recently, ERK5 has been found to be involved in multiple cellular processes. This study was designed to investigate the potential involvement of ERK5 in the proliferative response of osteoblastic cells to cyclic fluid shear stress. We reported here that cyclic fluid shear stress promoted ERK5 phosphorylation in MC3T3-E1 cells. Inhibition of ERK5 phosphorylation attenuated the increased expression of AP-1 and cyclin D1 and cell proliferation induced by cyclic fluid flow, but promoted p-16 expression. Further more, we found that cyclic fluid shear stress was a better stimuli for ERK5 activation and cyclin D1 expression compared with continuous fluid shear stress. Moreover, the pharmacological ERK5 inhibitor, BIX02189, which inhibited ERK5 phosphorylation in a time-dependent manner and the suppression lasted for at least 4 h. Taken together, we demonstrate that ERK5/AP-1/cyclin D1 pathway is involved in the mechanism of osteoblasts proliferation induced by cyclic fluid shear stress, which is superior in promoting cellular proliferation compared with continuous fluid shear stress.
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Affiliation(s)
- Peng Li
- Institute of Orthopaedics, The Lanzhou University Second Hospital, Lanzhou 730030 Gansu, People's Republic of China
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Rangaswami H, Schwappacher R, Tran T, Chan GC, Zhuang S, Boss GR, Pilz RB. Protein kinase G and focal adhesion kinase converge on Src/Akt/β-catenin signaling module in osteoblast mechanotransduction. J Biol Chem 2012; 287:21509-19. [PMID: 22563076 DOI: 10.1074/jbc.m112.347245] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mechanical loading of bone induces interstitial fluid flow, leading to fluid shear stress (FSS) of osteoblasts. FSS rapidly increases the intracellular calcium concentration ([Ca(2+)]) and nitric oxide (NO) synthesis in osteoblasts and activates the protein kinase Akt. Activated Akt stimulates osteoblast proliferation and survival, but the mechanism(s) leading to Akt activation is not well defined. Using pharmacological and genetic approaches in primary human and mouse osteoblasts and mouse MC3T3 osteoblast-like cells, we found that Akt activation by FSS occurred through two parallel pathways; one required calcium stimulation of NO synthase and NO/cGMP/protein kinase G II-dependent activation of Src, and the other required calcium activation of FAK and Src, independent of NO. Both pathways cooperated to increase PI3K-dependent Akt phosphorylation and were necessary for FSS to induce nuclear translocation of β-catenin, c-fos, and cox-2 gene expression and osteoblast proliferation. These data explain how mechanical stimulation of osteoblasts leads to increased signaling through a growth regulatory pathway essential for maintaining skeletal integrity.
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Affiliation(s)
- Hema Rangaswami
- Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, California 92093, USA
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