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Interepithelial signaling with nephric duct is required for the formation of overlying coelomic epithelial cell sheet. Proc Natl Acad Sci U S A 2014; 111:6660-5. [PMID: 24753584 DOI: 10.1073/pnas.1316728111] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In most organs of the body, epithelial tissues are supported by their own basement membrane and underlying stroma, the latter being regarded as a complex of amorphous cells, extracellular matrices, and soluble factors. We demonstrate here that an epithelial tube can serve as a component of stroma that supports the formation of epithelial cell sheet derived from a different origin. During development of the mesonephros in chicken embryos, the intermediate mesoderm (IMM), which contains the Wolffian duct (WD) and its associated tubules, is overlain by a sheet of epithelial cells derived from lateral plate (coelomic) mesoderm. We describe that in normal embryos, epitheliogenesis of IMM tubes and the adjacent coelomic cell sheet proceed in a coordinated manner. When the WD was surgically ablated, the overlying coelomic epithelium exhibited aberrant morphology accompanied by a punctated basement membrane. Furthermore, the WD-ablated coelomic epithelium became susceptible to latent external stress; electroporation of Rac1 resulted in epithelial-to-mesenchymal transitions (EMTs) within the coelomic epithelium. The distorted coelomic epithelium was rescued by implanting fibronectin-producing cells in place of the WD, suggesting that fibronectin provided by WD has an important role acting interepithelially. This notion was corroborated further by directly visualizing a translocation of EGFP-tagged fibronectin from fibronectin-producing to -receiving epithelia in vivo. Our findings provide a novel insight into interepithelial signaling that also might occur in adult tissues to protect against EMT and suggest a possible new target for anticancer therapeutic strategy.
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52
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Govey PM, Jacobs JM, Tilton SC, Loiselle AE, Zhang Y, Freeman WM, Waters KM, Karin NJ, Donahue HJ. Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways. J Biomech 2014; 47:1838-45. [PMID: 24720889 DOI: 10.1016/j.jbiomech.2014.03.022] [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] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 03/11/2014] [Accepted: 03/11/2014] [Indexed: 01/01/2023]
Abstract
Osteocytes, positioned within bone׳s porous structure, are subject to interstitial fluid flow upon whole bone loading. Such fluid flow is widely theorized to be a mechanical signal transduced by osteocytes, initiating a poorly understood cascade of signaling events mediating bone adaptation to mechanical load. The objective of this study was to examine the time course of flow-induced changes in osteocyte gene transcript and protein levels using high-throughput approaches. Osteocyte-like MLO-Y4 cells were subjected to 2h of oscillating fluid flow (1Pa peak shear stress) and analyzed following 0, 2, 8, and 24h post-flow incubation. Transcriptomic microarray analysis, followed by gene ontology pathway analysis, demonstrated fluid flow regulation of genes consistent with both known and unknown metabolic and inflammatory responses in bone. Additionally, two of the more highly up-regulated gene products - chemokines Cxcl1 and Cxcl2, supported by qPCR - have not previously been reported as responsive to fluid flow. Proteomic analysis demonstrated greatest up-regulation of the ATP-producing enzyme NDK, calcium-binding Calcyclin, and G protein-coupled receptor kinase 6. Finally, an integrative pathway analysis merging fold changes in transcript and protein levels predicted signaling nodes not directly detected at the sampled time points, including transcription factors c-Myc, c-Jun, and RelA/NF-κB. These results extend our knowledge of the osteocytic response to fluid flow, most notably up-regulation of Cxcl1 and Cxcl2 as possible paracrine agents for osteoblastic and osteoclastic recruitment. Moreover, these results demonstrate the utility of integrative, high-throughput approaches in place of a traditional candidate approach for identifying novel mechano-sensitive signaling molecules.
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Affiliation(s)
- Peter M Govey
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Jon M Jacobs
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
| | - Susan C Tilton
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
| | - Alayna E Loiselle
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Yue Zhang
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Willard M Freeman
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Katrina M Waters
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
| | - Norman J Karin
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA
| | - Henry J Donahue
- Division of Musculoskeletal Sciences, Department of Orthopaedics and Rehabilitation, Penn State College of Medicine, Hershey, PA 17033, USA.
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53
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O'Brien XM, Loosley AJ, Oakley KE, Tang JX, Reichner JS. Technical advance: introducing a novel metric, directionality time, to quantify human neutrophil chemotaxis as a function of matrix composition and stiffness. J Leukoc Biol 2014; 95:993-1004. [PMID: 24511103 DOI: 10.1189/jlb.0913478] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
A direct consequence of cellular movement and navigation, migration incorporates elements of speed, direction, and persistence of motion. Current techniques to parameterize the trajectory of a chemotaxing cell most commonly pair migration speed with some measure of persistence by calculating MSD, RMS speed, TAD, and/or CI. We address inherent limitations in TAD and CI for comparative analysis by introducing two new analytical tools to quantify persistence: directionality index and directionality time. With the use of these tools, we show that the mechanical properties of the underlying substrate contribute significantly to the regulation of human neutrophil chemotaxis toward fMLP on Fgn-, Col-, and Fn-coated gels of varying elasticity. The β₁-integrin ligand Col demonstrated mechanosensitive speed. In contrast, β₂-integrin ligand Fgn supported mechanosensitive persistence. Fn, recognized by β₁ and β₂ integrins, mechanoregulated speed and persistence. Blocking β₂ integrins of cells migrating on Fn identified an underlying β₂-integrin-directed modulation of persistence. These data demonstrate that individual components of the neutrophil chemotactic response show integrin dependence and are finely tunable with different ligand, mechanotactic, and chemotactic cues, underscoring the need for sensitive analytical methods.
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Affiliation(s)
- Xian M O'Brien
- Division of Surgical Research, Department of Surgery, Rhode Island Hospital, and the Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA; and
| | | | - Katie E Oakley
- Division of Surgical Research, Department of Surgery, Rhode Island Hospital, and the Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA; and Graduate Program in Pathobiology, Brown University, Providence, Rhode Island, USA
| | | | - Jonathan S Reichner
- Division of Surgical Research, Department of Surgery, Rhode Island Hospital, and the Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA; and
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Kringelbach TM, Aslan D, Novak I, Schwarz P, Jørgensen NR. UTP-induced ATP release is a fine-tuned signalling pathway in osteocytes. Purinergic Signal 2013; 10:337-47. [PMID: 24374572 PMCID: PMC4040174 DOI: 10.1007/s11302-013-9404-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 12/10/2013] [Indexed: 11/30/2022] Open
Abstract
Osteocytes reside as a cellular network throughout the mineralised matrix of bone and are considered the primary mechanosensors of this tissue. They sense mechanical stimulation such as fluid flow and are able to regulate osteoblast and osteoclast functions on the bone surface. Previously, we found that ATP is released load-dependently from osteocytes from the onset of mechanical stimulation. Therefore, the aim of the present study was to investigate whether and how ATP release can be evoked in osteocytes via purinergic receptor activation. ATP release was quantified by real-time determination using the luciferin-luciferase assay and the release pathway was investigated using pharmacological inhibition. The P2Y receptor profile was analysed using gene expression analysis by reverse transcription polymerase chain reaction, while functional testing was performed using measurements of intracellular calcium responses to P2 receptor agonists. These investigations demonstrated that MLO-Y4 osteocytes express functional P2Y(2), P2Y(4), P2Y(12) and P2Y(13) receptors in addition to the previously reported P2X receptors. Further, we found that osteocytes respond to nucleotides such as ATP, UTP and ADP by increasing the intracellular calcium concentration and that they release ATP dose-dependently upon stimulation with 1-10 μM UTP. In addition to this, osteocytes release large amounts of ATP upon cell rupture, which might also be a source for other nucleotides, such as UTP. These findings indicate that mechanically induced ATP signals may be propagated by P2 receptor activation and further ATP release in the osteocyte network and implicate purinergic signalling as a central signalling pathway in osteocyte mechanotransduction.
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Affiliation(s)
- Tina M. Kringelbach
- />Research Center of Ageing and Osteoporosis, Department of Diagnostics, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />Research Center of Ageing and Osteoporosis, Department of Medicine, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />The Osteoporosis and Bone Metabolic Unit, Department of Endocrinology, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- />The Osteoporosis and Bone Metabolic Unit, Department of Clinical Biochemistry, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
| | - Derya Aslan
- />Research Center of Ageing and Osteoporosis, Department of Diagnostics, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />Research Center of Ageing and Osteoporosis, Department of Medicine, Copenhagen University Hospital Glostrup, Glostrup, Denmark
| | - Ivana Novak
- />Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
| | - Peter Schwarz
- />Research Center of Ageing and Osteoporosis, Department of Diagnostics, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />Research Center of Ageing and Osteoporosis, Department of Medicine, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark
| | - Niklas R. Jørgensen
- />Research Center of Ageing and Osteoporosis, Department of Diagnostics, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />Research Center of Ageing and Osteoporosis, Department of Medicine, Copenhagen University Hospital Glostrup, Glostrup, Denmark
- />The Osteoporosis and Bone Metabolic Unit, Department of Endocrinology, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- />The Osteoporosis and Bone Metabolic Unit, Department of Clinical Biochemistry, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- />Research Center of Ageing and Osteoporosis, Department of Diagnostics, Glostrup Hospital, Ndr. Ringvej 57, 2600 Glostrup, Denmark
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Mechanosensory responses of osteocytes to physiological forces occur along processes and not cell body and require αVβ3 integrin. Proc Natl Acad Sci U S A 2013; 110:21012-7. [PMID: 24324138 DOI: 10.1073/pnas.1321210110] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Osteocytes in the lacunar-canalicular system of the bone are thought to be the cells that sense mechanical loading and transduce mechanical strain into biomechanical responses. The goal of this study was to evaluate the extent to which focal mechanical stimulation of osteocyte cell body and process led to activation of the cells, and determine whether integrin attachments play a role in osteocyte activation. We use a novel Stokesian fluid stimulus probe to hydrodynamically load osteocyte processes vs. cell bodies in murine long bone osteocyte Y4 (MLO-Y4) cells with physiological-level forces <10 pN without probe contact, and measured intracellular Ca(2+) responses. Our results indicate that osteocyte processes are extremely responsive to piconewton-level mechanical loading, whereas the osteocyte cell body and processes with no local attachment sites are not. Ca(2+) signals generated at stimulated sites spread within the processes with average velocity of 5.6 μm/s. Using the near-infrared fluorescence probe IntegriSense 750, we demonstrated that inhibition of αVβ3 integrin attachment sites compromises the response to probe stimulation. Moreover, using apyrase, an extracellular ATP scavenger, we showed that Ca(2+) signaling from the osteocyte process to the cell body was greatly diminished, and thus dependent on ATP-mediated autocrine signaling. These findings are consistent with the hypothesis that osteocytes in situ are highly polarized cells, where mechanotransduction occurs at substrate attachment sites along the processes at force levels predicted to occur at integrin attachment sites in vivo. We also demonstrate the essential role of αVβ3 integrin in osteocyte-polarized mechanosensing and mechanotransduction.
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56
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Vaughan TJ, Verbruggen SW, McNamara LM. Are all osteocytes equal? Multiscale modelling of cortical bone to characterise the mechanical stimulation of osteocytes. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2013; 29:1361-1372. [PMID: 23897701 DOI: 10.1002/cnm.2578] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 06/18/2013] [Accepted: 06/20/2013] [Indexed: 06/02/2023]
Abstract
Bone continuously adapts its internal structure to accommodate the functional demands of its mechanical environment. This process is orchestrated by a network of mechanosensitive osteocytes that respond to external mechanical signals and recruit osteoblasts and osteoclasts to alter bone mass to meet loading demands. Because of the irregular hierarchical microarchitecture of bone tissue, the precise mechanical stimuli experienced by osteocytes located in different regions of the tissue is not well-understood. The objective of this study is to characterise the local stimulus experienced by osteocytes distributed throughout the tissue structure. Our models predict that an inhomogeneous microstructural strain field contributes to osteocytes receiving vastly different stimuli at the cellular level, depending on their location within the microstructure. In particular, osteocytes located directly adjacent to micropores experienced strain amplifications in their processes of up to nine times the applied global strain. Furthermore, it was found that the principal orientation of lamellar regions was found to contribute significantly to the magnitude of the stimulus being received at the cellular level. These findings indicate that osteocytes are not equal in terms of the mechanical stimulus being received, and we propose that only a subset of osteocytes may be sufficiently stimulated to function as mechanoreceptors.
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Affiliation(s)
- Ted J Vaughan
- Biomechanics Research Centre (BMEC), Biomedical Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland; National Centre for Biomedical Engineering Sciences (NCBES), National University of Ireland, Galway, Ireland
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57
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Piattelli A, Artese L, Penitente E, Iaculli F, Degidi M, Mangano C, Shibli JA, Coelho PG, Perrotti V, Iezzi G. Osteocyte density in the peri-implant bone of implants retrieved after different time periods (4 weeks to 27 years). J Biomed Mater Res B Appl Biomater 2013; 102:239-43. [PMID: 24106071 DOI: 10.1002/jbm.b.33000] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 04/29/2013] [Accepted: 06/10/2013] [Indexed: 01/22/2023]
Abstract
Bone tissue is characterized by a constant turnover in response to mechanical stimuli, and osteocytes play an essential role in bone mechanical adaptation. However, little to no information has been published regarding osteocyte density as a function of implantation time in vivo. The aim of this retrospective histological study was to evaluate the osteocyte density of the peri-implant bone in implants retrieved because of different reasons in a time period from 4 weeks to 27 years. A total of 18 samples were included in the present study. Specimens were divided into 3 groups depending on the loading history of the implants: loading between 4 weeks and 7 months (group 1); loading between 1 and 5 years (group 2); loading between 14 and 27 years (group 3). All the samples were histologically evaluated and osteocyte density was obtained using the ratio of the number of osteocytes to the bone-area (mm(2) ). The osteocyte density values significantly increased in the Group 2 (1-5 years) compared with Group 1 (4 weeks-7 months), and significantly decreased in the Group 3 (14-27 years) compared to Group 2. No significant differences were detected between Group 1 and Group 3. The decrease in osteocyte density observed in samples that were in vivo for long periods of time under loading is possibly because of the fact that once the bone structure is well aligned and biomechanically competent, a lower number of osteocytes are necessary to keep the tissue homeostasis under loading.
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Affiliation(s)
- Adriano Piattelli
- Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Italy
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58
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Matrix-dependent adhesion mediates network responses to physiological stimulation of the osteocyte cell process. Proc Natl Acad Sci U S A 2013; 110:12096-101. [PMID: 23818616 DOI: 10.1073/pnas.1310003110] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Osteocytes are bone cells that form cellular networks that sense mechanical loads distributed throughout the bone tissue. Interstitial fluid flow in the lacunar canalicular system produces focal strains at localized attachment sites around the osteocyte cell process. These regions of periodic attachment between the osteocyte cell membrane and its canalicular wall are sites where pN-level fluid-flow induced forces are generated in vivo. In this study, we show that focally applied forces of this magnitude using a newly developed Stokesian fluid stimulus probe initiate rapid and transient intercellular electrical signals in vitro. Our experiments demonstrate both direct gap junction coupling and extracellular purinergic P2 receptor signaling between MLO-Y4 cells in a connected bone cell network. Intercellular signaling was initiated by pN-level forces applied at integrin attachment sites along both appositional and distal unapposed cell processes, but not initiated at their cell bodies with equivalent forces. Electrical coupling was evident in 58% of all cell pairs tested with appositional connections; coupling strength increased with the increasing number of junctional connections. Apyrase, a nucleotide-degrading enzyme, suppressed and abolished force-induced effector responses, indicating a contribution from ATP released by the stimulated cell. This work extends the understanding of how osteocytes modulate their microenvironment in response to mechanical signals and highlights mechanisms of intercellular relay of mechanoresponsive signals in the bone network.
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59
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Batra N, Jiang JX. "INTEGRINating" the connexin hemichannel function in bone osteocytes through the action of integrin α5. Commun Integr Biol 2013; 5:516-8. [PMID: 23739985 PMCID: PMC3502221 DOI: 10.4161/cib.21322] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Mechanical loading influences skeletal structural integrity and bone remodeling. Application of a mechanical stimulus such as fluid flow shear stress to the bone osteocytes activates the cascade of mechanotransduction mediated by multiple signaling molecules. Hemichannels formed by connexin molecules are emerging as a candidate mechanosensor. Connexin 43 (Cx43) hemichannels open in response to mechanical stimulation to release bone modulators which influence bone remodeling. Our study identified a direct interaction between integrin α5 and Cx43 which was essential for hemichannels to open. Uncoupling the interaction blocked the hemichannels and shear stress enhanced the interaction between the two proteins to promote channel opening. More importantly, integrin α5, independent of its association with fibronectin, was activated upon shear stress through a PI3K signaling pathway. These results suggest a critical regulatory mechanism for Cx43 hemichannel opening through the association of integrin α5, resulting in release of bone anabolic factors required for bone development.
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Affiliation(s)
- Nidhi Batra
- Department of Biochemistry; University of Texas Heath Science Center; San Antonio, TX USA
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60
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Klein-Nulend J, Bakker AD, Bacabac RG, Vatsa A, Weinbaum S. Mechanosensation and transduction in osteocytes. Bone 2013; 54:182-90. [PMID: 23085083 DOI: 10.1016/j.bone.2012.10.013] [Citation(s) in RCA: 298] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 10/09/2012] [Accepted: 10/10/2012] [Indexed: 01/08/2023]
Abstract
The human skeleton is a miracle of engineering, combining both toughness and light weight. It does so because bones possess cellular mechanisms wherein external mechanical loads are sensed. These mechanical loads are transformed into biological signals, which ultimately direct bone formation and/or bone resorption. Osteocytes, since they are ubiquitous in the mineralized matrix, are the cells that sense mechanical loads and transduce the mechanical signals into a chemical response. The osteocytes then release signaling molecules, which orchestrate the recruitment and activity of osteoblasts or osteoclasts, resulting in the adaptation of bone mass and structure. In this review, we highlight current insights in bone adaptation to external mechanical loading, with an emphasis on how a mechanical load placed on whole bones is translated and amplified into a mechanical signal that is subsequently sensed by the osteocytes.
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Affiliation(s)
- Jenneke Klein-Nulend
- Department of Oral Cell Biology, ACTA-VU University Amsterdam, Research Institute MOVE, Gustav Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands.
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61
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Hoey DA, Tormey S, Ramcharan S, O'Brien FJ, Jacobs CR. Primary cilia-mediated mechanotransduction in human mesenchymal stem cells. Stem Cells 2013; 30:2561-70. [PMID: 22969057 PMCID: PMC3533782 DOI: 10.1002/stem.1235] [Citation(s) in RCA: 130] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Physical loading is a potent stimulus required to maintain bone homeostasis, partly through the renewal and osteogenic differentiation of mesenchymal stem cells (MSCs). However, the mechanism by which MSCs sense a biophysical force and translate that into a biochemical bone forming response (mechanotransduction) remains poorly understood. The primary cilium is a single sensory cellular extension, which has recently been shown to demonstrate a role in cellular mechanotransduction and MSC lineage commitment. In this study, we present evidence that short periods of mechanical stimulation in the form of oscillatory fluid flow (OFF) is sufficient to enhance osteogenic gene expression and proliferation of human MSCs (hMSCs). Furthermore, we demonstrate that the cilium mediates fluid flow mechanotransduction in hMSCs by maintaining OFF-induced increases in osteogenic gene expression and, surprisingly, to limit OFF-induced increases in proliferation. These data therefore demonstrate a pro-osteogenic mechanosensory role for the primary cilium, establishing a novel mechanotransduction mechanism in hMSCs. Based on these findings, the application of OFF may be a beneficial component of bioreactor-based strategies to form bone-like tissues suitable for regenerative medicine and also highlights the cilium as a potential therapeutic target for efforts to mimic loading with the aim of preventing bone loss during diseases such as osteoporosis. Furthermore, this study demonstrates a role for the cilium in controlling mechanically mediated increases in the proliferation of hMSCs, which parallels proposed models of polycystic kidney disease. Unraveling the mechanisms leading to rapid proliferation of mechanically stimulated MSCs with defective cilia could provide significant insights regarding ciliopathies and cystic diseases. Stem Cells2012;30:2561–2570
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Affiliation(s)
- David A Hoey
- Department of Biomedical Engineering, Columbia University, City of New York, New York, USA.
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62
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Vaughan TJ, Haugh MG, McNamara LM. A fluid-structure interaction model to characterize bone cell stimulation in parallel-plate flow chamber systems. J R Soc Interface 2013; 10:20120900. [PMID: 23365189 DOI: 10.1098/rsif.2012.0900] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Bone continuously adapts its internal structure to accommodate the functional demands of its mechanical environment and strain-induced flow of interstitial fluid is believed to be the primary mediator of mechanical stimuli to bone cells in vivo. In vitro investigations have shown that bone cells produce important biochemical signals in response to fluid flow applied using parallel-plate flow chamber (PPFC) systems. However, the exact mechanical stimulus experienced by the cells within these systems remains unclear. To fully understand this behaviour represents a most challenging multi-physics problem involving the interaction between deformable cellular structures and adjacent fluid flows. In this study, we use a fluid-structure interaction computational approach to investigate the nature of the mechanical stimulus being applied to a single osteoblast cell under fluid flow within a PPFC system. The analysis decouples the contribution of pressure and shear stress on cellular deformation and for the first time highlights that cell strain under flow is dominated by the pressure in the PPFC system rather than the applied shear stress. Furthermore, it was found that strains imparted on the cell membrane were relatively low whereas significant strain amplification occurred at the cell-substrate interface. These results suggest that strain transfer through focal attachments at the base of the cell are the primary mediators of mechanical signals to the cell under flow in a PPFC system. Such information is vital in order to correctly interpret biological responses of bone cells under in vitro stimulation and elucidate the mechanisms associated with mechanotransduction in vivo.
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Affiliation(s)
- T J Vaughan
- National Centre for Biomedical Engineering Sciences (NCBES), National University of Ireland, Galway, Ireland
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63
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Abstract
Mechanotransduction in bone is fundamental to proper skeletal development. Deficiencies in signaling mechanisms that transduce physical forces to effector cells can have severe consequences for skeletal integrity. Therefore, a solid understanding of the cellular and molecular components of mechanotransduction is crucial for correcting skeletal modeling and remodeling errors and designing effective therapies. In recent years, progress has been made on many fronts regarding our understanding of bone cell mechanotransduction, including subcellular localization of mechanosensitive components in bone cells, the discovery of mechanosensitive G-protein-coupled receptors, identification of new ion channels and larger pores (eg, hemichannels) involved in physical signal transduction, and cell adhesion proteins, among others. These and other recent mechanisms are reviewed to provide a synthesis of recent experimental findings, in the larger context of whole bone adaptation.
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Affiliation(s)
- Alexander G Robling
- Department of Anatomy & Cell Biology, Indiana University School of Medicine, 635 Barnhill Drive, MS 5035, Indianapolis, IN, 46202, USA.
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64
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Thompson WR, Rubin CT, Rubin J. Mechanical regulation of signaling pathways in bone. Gene 2012; 503:179-93. [PMID: 22575727 DOI: 10.1016/j.gene.2012.04.076] [Citation(s) in RCA: 268] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 03/20/2012] [Accepted: 04/22/2012] [Indexed: 12/21/2022]
Abstract
A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.
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Affiliation(s)
- William R Thompson
- Department of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA.
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65
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Indra I, Beningo KA. An in vitro correlation of metastatic capacity, substrate rigidity, and ECM composition. J Cell Biochem 2012; 112:3151-8. [PMID: 21732405 DOI: 10.1002/jcb.23241] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The process of metastasis requires a metastatic cancer cell to invade a variety of micro-environments of variable stiffnesses. Unlike metastatic cells, normal cell function and viability is dependent on the stiffness of the environment and used as a cue to maintain cell health and proper tissue organization. In this study we have asked if metastatic cells can ignore the parameter of stiffness and if this ability is gradually acquired and if so, through what mechanism. Using a panel of mouse mammary tumor cells derived from the same parental tumor, but possessing different metastatic abilities, we cultured the cells on hard and soft substrates conjugated with collagen or fibronectin. Normal and non-metastatic tumor cells responded to changes in stiffness on fibronectin, but not collagen. However, the more metastatic cells ignored the change in stiffness on fibronectin-coated substrates. This lack of response on fibronectin correlated with a change in the expression level of the α3 integrin subunit, activation of the β1 subunit, and phosphorylation of FAKpY397. We conclude that through fibronectin, changes in the activation and tethering of the beta-1 integrin provides a mechanism for metastatic cells to disregard changes in compliance to survive and navigate in environments of different stiffness.
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Affiliation(s)
- Indrajyoti Indra
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA
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Hoey DA, Chen JC, Jacobs CR. The primary cilium as a novel extracellular sensor in bone. Front Endocrinol (Lausanne) 2012; 3:75. [PMID: 22707948 PMCID: PMC3374377 DOI: 10.3389/fendo.2012.00075] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 05/21/2012] [Indexed: 11/18/2022] Open
Abstract
Mechanically induced adaptation of bone is required to maintain a healthy skeleton and defects in this process can lead to dramatic changes in bone mass, resulting in bone diseases such as osteoporosis. Therefore, understanding how this process occurs could yield novel therapeutics to treat diseases of excessive bone loss or formation. Over the past decade the primary cilium has emerged as a novel extracellular sensor in bone, being required to transduce changes in the extracellular mechanical environment into biochemical responses regulating bone adaptation. In this review, we introduce the primary cilium as a novel extracellular sensor in bone; discuss the in vitro and in vivo findings of primary cilia based sensing in bone; explore the role of the primary cilium in regulating stem cell osteogenic fate commitment and finish with future directions of research and possible development of cilia targeting therapeutics to treat bone diseases.
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Affiliation(s)
- David A. Hoey
- Department of Biomedical Engineering, Columbia University in the City of New YorkNew York, NY, USA
- Department of Anatomy, Royal College of Surgeons in IrelandDublin, Ireland
- Department of Mechanical, Aeronautical and Biomedical Engineering, Centre for Applied Biomedical Engineering Research, Materials and Surface Science Institute, University of LimerickLimerick, Ireland
- *Correspondence: David A. Hoey, Department of Mechanical, Aeronautical and Biomedical Engineering, Centre for Applied Biomedical Engineering Research, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland. e-mail:
| | - Julia C. Chen
- Department of Biomedical Engineering, Columbia University in the City of New YorkNew York, NY, USA
| | - Christopher R. Jacobs
- Department of Biomedical Engineering, Columbia University in the City of New YorkNew York, NY, USA
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Batra N, Kar R, Jiang JX. Gap junctions and hemichannels in signal transmission, function and development of bone. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1909-18. [PMID: 21963408 DOI: 10.1016/j.bbamem.2011.09.018] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 09/03/2011] [Accepted: 09/15/2011] [Indexed: 10/17/2022]
Abstract
Gap junctional intercellular communication (GJIC) mediated by connexins, in particular connexin 43 (Cx43), plays important roles in regulating signal transmission among different bone cells and thereby regulates development, differentiation, modeling and remodeling of the bone. GJIC regulates osteoblast formation, differentiation, survival and apoptosis. Osteoclast formation and resorptive ability are also reported to be modulated by GJIC. Furthermore, osteocytes utilize GJIC to coordinate bone remodeling in response to anabolic factors and mechanical loading. Apart from gap junctions, connexins also form hemichannels, which are localized on the cell surface and function independently of the gap junction channels. Both these channels mediate the transfer of molecules smaller than 1.2kDa including small ions, metabolites, ATP, prostaglandin and IP(3). The biological importance of the communication mediated by connexin-forming channels in bone development is revealed by the low bone mass and osteoblast dysfunction in the Cx43-null mice and the skeletal malformations observed in occulodentodigital dysplasia (ODDD) caused by mutations in the Cx43 gene. The current review summarizes the role of gap junctions and hemichannels in regulating signaling, function and development of bone cells. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.
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Affiliation(s)
- Nidhi Batra
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX, USA
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Crockett JC, Rogers MJ, Coxon FP, Hocking LJ, Helfrich MH. Bone remodelling at a glance. J Cell Sci 2011; 124:991-8. [PMID: 21402872 DOI: 10.1242/jcs.063032] [Citation(s) in RCA: 312] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Julie C Crockett
- Musculoskeletal Research Programme, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
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Weinbaum S, Duan Y, Thi MM, You L. An Integrative Review of Mechanotransduction in Endothelial, Epithelial (Renal) and Dendritic Cells (Osteocytes). Cell Mol Bioeng 2011; 4:510-537. [PMID: 23976901 DOI: 10.1007/s12195-011-0179-6] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In this review we will examine from a biomechanical and ultrastructural viewpoint how the cytoskeletal specialization of three basic cell types, endothelial cells (ECs), epithelial cells (renal tubule) and dendritic cells (osteocytes), enables the mechano-sensing of fluid flow in both their native in vivo environment and in culture, and the downstream signaling that is initiated at the molecular level in response to fluid flow. These cellular responses will be discussed in terms of basic mysteries and paradoxes encountered by each cell type. In ECs fluid shear stress (FSS) is nearly entirely attenuated by the endothelial glycocalyx that covers their apical membrane and yet FSS is communicated to both intracellular and junctional molecular components in activating a wide variety of signaling pathways. The same is true in proximal tubule (PT) cells where a dense brush border of microvilli covers the apical surface and the flow at the apical membrane is negligible. A four decade old unexplained mystery is the ability of PT epithelia to reliably reabsorb 60% of the flow entering the tubule regardless of the glomerular filtration rate. In the cortical collecting duct (CCD) the flow rates are so low that a special sensing apparatus, a primary cilia is needed to detect very small variations in tubular flow. In bone it has been a century old mystery as to how osteocytes embedded in a stiff mineralized tissue are able to sense miniscule whole tissue strains that are far smaller than the cellular level strains required to activate osteocytes in vitro.
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Affiliation(s)
- Sheldon Weinbaum
- Department of Biomedical Engineering, The City College of the City University of New York, New York, NY 10031, USA
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Wu D, Ganatos P, Spray DC, Weinbaum S. On the electrophysiological response of bone cells using a Stokesian fluid stimulus probe for delivery of quantifiable localized picoNewton level forces. J Biomech 2011; 44:1702-8. [PMID: 21511259 DOI: 10.1016/j.jbiomech.2011.03.034] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Revised: 03/25/2011] [Accepted: 03/28/2011] [Indexed: 10/18/2022]
Abstract
A Stokesian fluid stimulus probe (SFSP), capable of delivering quantifiable pN level hydrodynamic forces, is developed to distinguish the electrophysiological response of the cell process and cell body of osteocyte-like MLO-Y4 cells without touching the cell or its substrate. The hydrodynamic disturbance is a short lived (100 ms), constant strength pressure pulse that propagates nearly instantaneously through the medium creating a nearly spherical expanding fluid bolus surrounding a 0.8 μm micropipette tip. Laboratory model experiments show that the growth of the bolus and the pressure field can be closely modeled by quasi-steady Stokes flow through a circular orifice provided the tip Reynolds number, Re(t)<0.03. By measuring the deflection of the dendritic processes between discrete attachment sites, and applying a detailed ultrastructural model for the central actin filament bundle within the process, one is able to calculate the forces produced by the probe using elastic beam theory. One finds that forces between 1 and 2.3 pN are sufficient to initiate electrical signaling when applied to the cell process, but not the much softer cell body. Even more significantly, cellular excitation by the process only occurs when the probe is directed at discrete focal attachment sites along the cell process. This suggests that electrical signaling is initiated at discrete focal attachments along the cell process and that these sites are likely integrin-mediated complexes associated with stretch-activated ion channels though their molecular structure is unknown.
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Affiliation(s)
- Danielle Wu
- Department of Biomedical Engineering, The City College of New York, Steinman Hall, Room T-404B, Convent Avenue and 140th Street, New York, NY 10031, USA
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