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Tang C, Zelenak C, Völkl J, Eichenmüller M, Regel I, Fröhlich H, Kempe D, Jimenez L, Le Bellego L, Vergne S, Lang F. Hydration-sensitive gene expression in brain. Cell Physiol Biochem 2011; 27:757-68. [PMID: 21691093 DOI: 10.1159/000330084] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/17/2011] [Indexed: 12/16/2022] Open
Abstract
Dehydration has a profound influence on neuroexcitability. The mechanisms remained, however, incompletely understood. The present study addressed the effect of water deprivation on gene expression in the brain. To this end, animals were exposed to a 24 hours deprivation of drinking water and neuronal gene expression was determined by microarray technology with subsequent confirmation by RT-PCR. As a result, water deprivation was followed by significant upregulation of clathrin (light polypeptide Lcb), serum/glucocorticoid-regulated kinase (SGK) 1, and protein kinase A (PRKA) anchor protein 8-like. Water deprivation led to downregulation of janus kinase and microtubule interacting protein 1, neuronal PAS domain protein 4, thrombomodulin, purinergic receptor P2Y - G-protein coupled 13 gene, gap junction protein beta 1, neurotrophin 3, hyaluronan and proteoglycan link protein 1, G protein-coupled receptor 19, CD93 antigen, forkhead box P1, suppressor of cytokine signaling 3, apelin, immunity-related GTPase family M, serine (or cysteine) peptidase inhibitor clade B member 1a, serine (or cysteine) peptidase inhibitor clade H member 1, glutathion peroxidase 8 (putative), discs large (Drosophila) homolog-associated protein 1, zinc finger and BTB domain containing 3, and H2A histone family member V. Western blotting revealed the downregulation of forkhead box P1, serine (or cysteine) peptidase inhibitor clade H member 1, and gap junction protein beta 1 protein abundance paralleling the respective alterations of transcript levels. In conclusion, water deprivation influences the transcription of a wide variety of genes in the brain, which may participate in the orchestration of brain responses to water deprivation.
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Affiliation(s)
- Cai Tang
- Department of Physiology, University of Tübingen, Gmelinstr. 5, D-72076 Tübingen
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Korhonen RK, Julkunen P, Jurvelin JS, Saarakkala S. Structural and Compositional Changes in Peri- and Extracellular Matrix of Osteoarthritic Cartilage Modulate Chondrocyte Morphology. Cell Mol Bioeng 2011. [DOI: 10.1007/s12195-011-0178-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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103
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Huete F, Guzman-Aranguez A, Ortín J, Hoyle CHV, Pintor J. Effects of diadenosine tetraphosphate on FGF9-induced chloride flux changes in achondroplastic chondrocytes. Purinergic Signal 2011; 7:243-9. [PMID: 21559786 DOI: 10.1007/s11302-011-9234-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 04/28/2011] [Indexed: 12/22/2022] Open
Abstract
Achondroplasia, the most common type of dwarfism, is characterized by a mutation in the fibroblast growth factor receptor 3 (FGFR3). Achondroplasia is an orphan pathology with no pharmacological treatment so far. However, the possibility of using the dinucleotide diadenosine tetraphosphate (Ap(4)A) with therapeutic purposes in achondroplasia has been previously suggested. The pathogenesis involves the constitutive activation of FGFR3, resulting in altered biochemical and physiological processes in chondrocytes. Some of these altered processes can be influenced by changes in cell volume and ionic currents. In this study, the action of mutant FGFR3 on chondrocyte size and chloride flux in achondroplastic chondrocytes was investigated as well as the effect of the Ap(4)A on these processes triggered by mutant FGFR3. Stimulation with the fibroblast growth factor 9 (FGF9), the preferred ligand for FGFR3, induced an enlarged achondroplastic chondrocyte size and an increase in the intracellular chloride concentration, suggesting the blockade of chloride efflux. Treatment with the Ap(4)A reversed the morphological changes triggered by FGF9 and restored the chloride efflux. These data provide further evidence for the therapeutic potential of this dinucleotide in achondroplasia treatment.
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Affiliation(s)
- Fernando Huete
- Departamento de Bioquímica, E.U. Óptica, Universidad Complutense de Madrid, c/Arcos de Jalón 118, 28037, Madrid, Spain
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Chan SCW, Ferguson SJ, Gantenbein-Ritter B. The effects of dynamic loading on the intervertebral disc. EUROPEAN SPINE JOURNAL : OFFICIAL PUBLICATION OF THE EUROPEAN SPINE SOCIETY, THE EUROPEAN SPINAL DEFORMITY SOCIETY, AND THE EUROPEAN SECTION OF THE CERVICAL SPINE RESEARCH SOCIETY 2011; 20:1796-812. [PMID: 21541667 DOI: 10.1007/s00586-011-1827-1] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Revised: 03/21/2011] [Accepted: 04/20/2011] [Indexed: 01/08/2023]
Abstract
Loading is important to maintain the balance of matrix turnover in the intervertebral disc (IVD). Daily cyclic diurnal assists in the transport of large soluble factors across the IVD and its surrounding circulation and applies direct and indirect stimulus to disc cells. Acute mechanical injury and accumulated overloading, however, could induce disc degeneration. Recently, there is more information available on how cyclic loading, especially axial compression and hydrostatic pressure, affects IVD cell biology. This review summarises recent studies on the response of the IVD and stem cells to applied cyclic compression and hydrostatic pressure. These studies investigate the possible role of loading in the initiation and progression of disc degeneration as well as quantifying a physiological loading condition for the study of disc degeneration biological therapy. Subsequently, a possible physiological/beneficial loading range is proposed. This physiological/beneficial loading could provide insight into how to design loading regimes in specific system for the testing of various biological therapies such as cell therapy, chemical therapy or tissue engineering constructs to achieve a better final outcome. In addition, the parameter space of 'physiological' loading may also be an important factor for the differentiation of stem cells towards most ideally 'discogenic' cells for tissue engineering purpose.
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Affiliation(s)
- Samantha C W Chan
- ARTORG Center for Biomedical Engineering, Spine Research Center, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, 3014 Bern, Switzerland
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105
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Amini S, Veilleux D, Villemure I. Three-dimensional in situ zonal morphology of viable growth plate chondrocytes: a confocal microscopy study. J Orthop Res 2011; 29:710-7. [PMID: 21437950 DOI: 10.1002/jor.21294] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2010] [Accepted: 10/04/2010] [Indexed: 02/04/2023]
Abstract
Longitudinal growth, occurring in growth plates with structurally distinct zones, has clinical implications in the treatment of progressive skeletal deformities. This study documents the three-dimensional morphology of chondrocytes within histological zones of growth plate using confocal microscopy combined with fluorescent labeling techniques. Three-dimensional reconstruction of Calcein AM-labeled chondrocytes was made from stacks of confocal images recorded in situ from 4-week-old swine growth plates. Three-dimensional quantitative morphological measurements were further performed and compared at both tissue and cell levels. Chondrocyte volume and surface area increased about five- and threefold, respectively, approaching the chondro-osseous junction from the pool of reserve cells. Chondrocytes from the proliferative zone were the most discoidal cells (sphericity of 0.81 ± 0.06) among three histological zones. Minimum and maximum cell/matrix volume ratios were identified in the reserve (11.0 ± 2.2) and proliferative zones (16.8 ± 3.0), respectively. Evaluated parameters revealed the heterogeneous and zone-dependent morphological state of the growth plate. Tissue and cellular morphology may have noteworthy contribution to the growth plate behavior during growth process. The ability to obtain in situ cell morphometry and monitor the changes in the growth direction could improve our understanding of the mechanisms through which abnormal growth is triggered.
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Affiliation(s)
- Samira Amini
- Department of Mechanical Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec, Canada H3C 3A7
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106
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Osmotic stress alters chromatin condensation and nucleocytoplasmic transport. Biochem Biophys Res Commun 2011; 408:230-5. [PMID: 21463604 DOI: 10.1016/j.bbrc.2011.03.131] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Accepted: 03/30/2011] [Indexed: 11/22/2022]
Abstract
Osmotic stress is a potent regulator of biological function in many cell types, but its mechanism of action is only partially understood. In this study, we examined whether changes in extracellular osmolality can alter chromatin condensation and the rate of nucleocytoplasmic transport, as potential mechanisms by which osmotic stress can act. Transport of 10 kDa dextran was measured both within and between the nucleus and the cytoplasm using two different photobleaching methods. A mathematical model was developed to describe fluorescence recovery via nucleocytoplasmic transport. As osmolality increased, the diffusion coefficient of dextran decreased in the cytoplasm, but not the nucleus. Hyper-osmotic stress decreased nuclear size and increased nuclear lacunarity, indicating that while the nucleus was getting smaller, the pores and channels interdigitating the chromatin had expanded. The rate of nucleocytoplasmic transport was increased under hyper-osmotic stress but was insensitive to hypo-osmotic stress, consistent with the nonlinear osmotic properties of the nucleus. The mechanism of this osmotic sensitivity appears to be a change in the size and geometry of the nucleus, resulting in a shorter effective diffusion distance for the nucleus. These results may explain physical mechanisms by which osmotic stress can influence intracellular signaling pathways that rely on nucleocytoplasmic transport.
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107
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Koo J, Kim KI, Min BH, Lee GM. Controlling medium osmolality improves the expansion of human articular chondrocytes in serum-free media. Tissue Eng Part C Methods 2011; 16:957-63. [PMID: 20001269 DOI: 10.1089/ten.tec.2009.0525] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
To investigate the effects of medium osmolality on the expansion of human articular chondrocytes (HACs) with serum-free media (SFM), proprietary SFM of various osmolalities (290, 320, 350, 400, and 450 mOsm/kg), supplemented with components known to enhance chondrocyte growth, were constructed by the adjustment of NaCl concentration. It was found that HACs obtained better expansion in SFM at osmolalites lower than the average osmolality (400 mOsm/kg) of human articular cartilage in vivo. SFM at 290, 320, and 350 mOsm/kg showed similar growth, attaining up to a 1.55-fold increase in the proliferation rate compared with SFM at 400 mOsm/kg. Increasing SFM osmolality to 450 mOsm/kg resulted in a proliferation rate of 0.65-fold lower than at 400 mOsm/kg. Chondrogenic capacity was also examined via three-dimensional pellet cultures in a chondrogenic medium with HACs expanded in 320 and 400 mOsm/kg SFM. Biochemical, histological, and immunohistochemical analyses revealed similar glycosaminoglycan and collagen type II contents in both groups. Taken together, these results show that the expansion of HACs in SF cultures can be improved by adjusting the medium osmolality to be within the range of 290-350 mOsm/kg and that controlling medium osmolality during monolayer cultures does not deter the tissue-forming capability of the cells.
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Affiliation(s)
- Jane Koo
- Department of Biological Sciences, KAIST, Yuseong-gu, Daejeon, Republic of Korea
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108
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Shaked NT, Rinehart MT, Wax A. Quantitative Phase Microscopy of Biological Cell Dynamics by Wide-Field Digital Interferometry. COHERENT LIGHT MICROSCOPY 2011. [DOI: 10.1007/978-3-642-15813-1_7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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109
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Clark AL, Votta BJ, Kumar S, Liedtke W, Guilak F. Chondroprotective role of the osmotically sensitive ion channel transient receptor potential vanilloid 4: age- and sex-dependent progression of osteoarthritis in Trpv4-deficient mice. ACTA ACUST UNITED AC 2010; 62:2973-83. [PMID: 20583100 DOI: 10.1002/art.27624] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Mechanical loading significantly influences the physiology and pathology of articular cartilage, although the mechanisms of mechanical signal transduction are not fully understood. Transient receptor potential vanilloid 4 (TRPV4) is a Ca(++)-permeable ion channel that is highly expressed by articular chondrocytes and can be gated by osmotic and mechanical stimuli. The goal of this study was to determine the role of Trpv4 in the structure of the mouse knee joint and to determine whether Trpv4(-/-) mice exhibit altered Ca(++) signaling in response to osmotic challenge. METHODS Knee joints of Trpv4(-/-) mice were examined histologically and by microfocal computed tomography for osteoarthritic changes and bone structure at ages 4, 6, 9, and 12 months. Fluorescence imaging was used to quantify chondrocytic Ca(++) signaling within intact femoral cartilage in response to osmotic stimuli. RESULTS Deletion of Trpv4 resulted in severe osteoarthritic changes, including cartilage fibrillation, eburnation, and loss of proteoglycans, that were dependent on age and male sex. Subchondral bone volume and calcified meniscal volume were greatly increased, again in male mice. Chondrocytes from Trpv4(+/+) mice demonstrated significant Ca(++) responses to hypo-osmotic stress but not to hyperosmotic stress. The response to hypo-osmotic stress or to the TRPV4 agonist 4α-phorbol 12,13-didecanoate was eliminated in Trpv4(-/-) mice. CONCLUSION Deletion of Trpv4 leads to a lack of osmotically induced Ca(++) signaling in articular chondrocytes, accompanied by progressive, sex-dependent increases in bone density and osteoarthritic joint degeneration. These findings suggest a critical role for TRPV4-mediated Ca(++) signaling in the maintenance of joint health and normal skeletal structure.
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110
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Peffers M, Milner P, Tew S, Clegg P. Regulation of SOX9 in normal and osteoarthritic equine articular chondrocytes by hyperosmotic loading. Osteoarthritis Cartilage 2010; 18:1502-8. [PMID: 20800688 PMCID: PMC3078327 DOI: 10.1016/j.joca.2010.08.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2010] [Revised: 08/09/2010] [Accepted: 08/18/2010] [Indexed: 02/02/2023]
Abstract
OBJECTIVES SOX9 is a transcription factor that is essential for cartilage extracellular matrix (ECM) formation. Osteoarthritis (OA) is characterised by a loss of cartilage ECM. In chondrocytes SOX9 gene expression is regulated by osmotic loading. Here we characterise SOX9 mRNA regulation through static and cyclical application of hyperosmotic conditions in normal and OA monolayer equine chondrocytes. Furthermore, we investigate whether extracellular signal-regulated protein kinase (ERK)1/2 mitogen-activated protein kinases (MAPK) pathways have a role in this regulation of SOX9. METHODS Equine chondrocytes harvested from normal or OA joints were subjected to different osmotic loading patterns as either primary (P0) or passaged (P2) cells. The involvement of MEK-ERK signalling was demonstrated by using pharmacological inhibitors. In addition SOX9 gene stability was determined. Levels of transcripts encoding SOX9, Col2A1 and aggrecan were measured using qRT-PCR. De novo glycosaminoglycan synthesis of explants was determined with (35)S sulphate during static hyperosmolar loading. RESULTS MEK-ERK signalling increases glycosaminoglycans (GAG) synthesis in explants. Static hyperosmotic conditions significantly reduced SOX9 mRNA in normal P2 and OA P0 but not normal P0 chondrocytes. SOX9 mRNA was stabilised by hyperosmotic conditions. Cyclical loading of normal P2 and OA P0 but not normal P0 cells led to an increase in SOX9 gene expression and this was prevented by MEK1/2 inhibition. CONCLUSIONS The response to osmotic loading of SOX9 mRNA is dependent on the nature of the osmotic stimulation and the chondrocyte phenotype. This variation may be important in disease progression.
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Affiliation(s)
- M.J. Peffers
- Address correspondence and reprint requests to: Mandy Peffers, Musculoskeletal Research Group, University of Liverpool, Veterinary Teaching Hospital, Neston, CH64 7TE, UK.
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111
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Barrett-Jolley R, Lewis R, Fallman R, Mobasheri A. The emerging chondrocyte channelome. Front Physiol 2010; 1:135. [PMID: 21423376 PMCID: PMC3059965 DOI: 10.3389/fphys.2010.00135] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2010] [Accepted: 09/09/2010] [Indexed: 11/18/2022] Open
Abstract
Chondrocytes are the resident cells of articular cartilage and are responsible for synthesizing a range of collagenous and non-collagenous extracellular matrix macromolecules. Whilst chondrocytes exist at low densities in the tissue (1-10% of the total tissue volume in mature cartilage) they are extremely active cells and are capable of responding to a range of mechanical and biochemical stimuli. These responses are necessary for the maintenance of viable cartilage and may be compromised in inflammatory diseases such as arthritis. Although chondrocytes are non-excitable cells their plasma membrane contains a rich complement of ion channels. This diverse channelome appears to be as complex as one might expect to find in excitable cells although, in the case of chondrocytes, their functions are far less well understood. The ion channels so far identified in chondrocytes include potassium channels (K(ATP), BK, K(v), and SK), sodium channels (epithelial sodium channels, voltage activated sodium channels), transient receptor potential calcium or non-selective cation channels and chloride channels. In this review we describe this emerging channelome and discuss the possible functions of a range of chondrocyte ion channels.
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Affiliation(s)
- Richard Barrett-Jolley
- Musculoskeletal Research Group, Department of Comparative Molecular Medicine, School of Veterinary Science, University of LiverpoolLiverpool, UK
| | - Rebecca Lewis
- Musculoskeletal Research Group, Department of Comparative Molecular Medicine, School of Veterinary Science, University of LiverpoolLiverpool, UK
| | - Rebecca Fallman
- Musculoskeletal Research Group, Department of Comparative Molecular Medicine, School of Veterinary Science, University of LiverpoolLiverpool, UK
| | - Ali Mobasheri
- Musculoskeletal Research Group, Division of Veterinary Medicine, School of Veterinary Medicine and Science, Faculty of Medicine and Health Sciences, University of NottinghamNottingham, Leicestershire, UK
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112
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Biodegradable and injectable cure-on-demand polyurethane scaffolds for regeneration of articular cartilage. Acta Biomater 2010; 6:3471-81. [PMID: 20211278 DOI: 10.1016/j.actbio.2010.02.040] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 02/16/2010] [Accepted: 02/23/2010] [Indexed: 11/20/2022]
Abstract
This paper describes the synthesis and characterization of an injectable methacrylate functionalized urethane-based photopolymerizable prepolymer to form biodegradable hydrogels. The tetramethacrylate prepolymer was based on the reaction between two synthesized compounds, diisocyanato poly(ethylene glycol) and monohydroxy dimethacrylate poly(epsilon-caprolactone) triol. The final prepolymer was hydrated with phosphate-buffered saline (pH 7.4) to yield a biocompatible hydrogel containing up to 86% water. The methacrylate functionalized prepolymer was polymerized using blue light (450 nm) with an initiator, camphorquinone and a photosensitizer, N,N-dimethylaminoethyl methacrylate. The polymer was stable in vitro in culture media over the 28 days tested (1.9% mass loss); in the presence of lipase, around 56% mass loss occurred over the 28 days in vitro. Very little degradation occurred in vivo in rats over the same time period. The polymer was well tolerated with very little capsule formation and a moderate host tissue response. Human chondrocytes, seeded onto Cultispher-S beads, were viable in the tetramethacrylate prepolymer and remained viable during and after polymerization. Chondrocyte-bead-polymer constructs were maintained in static and spinner culture for 8 weeks. During this time, cells remained viable, proliferated and migrated from the beads through the polymer towards the edge of the polymer. New extracellular matrix (ECM) was visualized with Masson's trichrome (collagen) and Alcian blue (glycosaminoglycan) staining. Further, the composition of the ECM was typical for articular cartilage with prominent collagen type II and type VI and moderate keratin sulphate, particularly for tissue constructs cultured under dynamic conditions.
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Physiological tonicity improves human chondrogenic marker expression through nuclear factor of activated T-cells 5 in vitro. Arthritis Res Ther 2010; 12:R100. [PMID: 20492652 PMCID: PMC2911888 DOI: 10.1186/ar3031] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 04/28/2010] [Accepted: 05/21/2010] [Indexed: 01/11/2023] Open
Abstract
Introduction Chondrocytes experience a hypertonic environment compared with plasma (280 mOsm) due to the high fixed negative charge density of cartilage. Standard isolation of chondrocytes removes their hypertonic matrix, exposing them to nonphysiological conditions. During in vitro expansion, chondrocytes quickly lose their specialized phenotype, making them inappropriate for cell-based regenerative strategies. We aimed to elucidate the effects of tonicity during isolation and in vitro expansion on chondrocyte phenotype. Methods Human articular chondrocytes were isolated and subsequently expanded at control tonicity (280 mOsm) or at moderately elevated, physiological tonicity (380 mOsm). The effects of physiological tonicity on chondrocyte proliferation and chondrogenic marker expression were evaluated. The role of Tonicity-responsive Enhancer Binding Protein in response to physiological tonicity was investigated using nuclear factor of activated T-cells 5 (NFAT5) RNA interference. Results Moderately elevated, physiological tonicity (380 mOsm) did not affect chondrocyte proliferation, while higher tonicities inhibited proliferation and diminished cell viability. Physiological tonicity improved expression of chondrogenic markers and NFAT5 and its target genes, while suppressing dedifferentiation marker collagen type I and improving type II/type I expression ratios >100-fold. Effects of physiological tonicity were similar in osteoarthritic and normal (nonosteoarthritic) chondrocytes, indicating a disease-independent mechanism. NFAT5 RNA interference abolished tonicity-mediated effects and revealed that NFAT5 positively regulates collagen type II expression, while suppressing type I. Conclusions Physiological tonicity provides a simple, yet effective, means to improve phenotypical characteristics during cytokine-free isolation and in vitro expansion of human articular chondrocytes. Our findings will lead to the development of improved cell-based repair strategies for chondral lesions and provides important insights into mechanisms underlying osteoarthritic progression.
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Mobasheri A, Lewis R, Maxwell JEJ, Hill C, Womack M, Barrett-Jolley R. Characterization of a stretch-activated potassium channel in chondrocytes. J Cell Physiol 2010; 223:511-8. [PMID: 20162564 PMCID: PMC2883078 DOI: 10.1002/jcp.22075] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Chondrocytes possess the capacity to transduce load-induced mechanical stimuli into electrochemical signals. The aim of this study was to functionally characterize an ion channel activated in response to membrane stretch in isolated primary equine chondrocytes. We used patch-clamp electrophysiology to functionally characterize this channel and immunohistochemistry to examine its distribution in articular cartilage. In cell-attached patch experiments, the application of negative pressures to the patch pipette (in the range of 20-200 mmHg) activated ion channel currents in six of seven patches. The mean activated current was 45.9 +/- 1.1 pA (n = 4) at a membrane potential of 33 mV (cell surface area approximately 240 microm(2)). The mean slope conductance of the principal single channels resolved within the total stretch-activated current was 118 +/- 19 pS (n = 6), and reversed near the theoretical potassium equilibrium potential, E(K+), suggesting it was a high-conductance potassium channel. Activation of these high-conductance potassium channels was inhibited by extracellular TEA (K(d) approx. 900 microM) and iberiotoxin (K(d) approx. 40 nM). This suggests that the current was largely carried by BK-like potassium (MaxiK) channels. To further characterize these BK-like channels, we used inside-out patches of chondrocyte membrane: we found these channels to be activated by elevation in bath calcium concentration. Immunohistochemical staining of equine cartilage samples with polyclonal antibodies to the alpha1- and beta1-subunits of the BK channel revealed positive immunoreactivity for both subunits in superficial zone chondrocytes. These experiments support the hypothesis that functional BK channels are present in chondrocytes and may be involved in mechanotransduction and chemotransduction.
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Affiliation(s)
- Ali Mobasheri
- Musculoskeletal Research Group, Division of Veterinary Medicine, Faculty of Medicine and Health Sciences, University of Nottingham, Leicestershire, United Kingdom
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115
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White R, Gibson JS. The effect of oxygen tension on calcium homeostasis in bovine articular chondrocytes. J Orthop Surg Res 2010; 5:27. [PMID: 20420658 PMCID: PMC2873548 DOI: 10.1186/1749-799x-5-27] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Accepted: 04/26/2010] [Indexed: 01/11/2023] Open
Abstract
Background Articular chondrocytes normally experience a lower O2 tension compared to that seen by many other tissues. This level may fall further in joint disease. Ionic homeostasis is essential for chondrocyte function but, at least in the case of H+ ions, it is sensitive to changes in O2 levels. Ca2+ homeostasis is also critical but the effect of changes in O2 tension has not been investigated on this parameter. Here we define the effect of hypoxia on Ca2+ homeostasis in bovine articular chondrocytes. Methods Chondrocytes from articular cartilage slices were isolated enzymatically using collagenase. Cytoplasmic Ca2+ levels ([Ca2+]i) were followed fluorimetrically using Fura-2 to determine the effect of changes in O2 tension. The effects of ion substitution (replacing extracellular Na+ with NMDG+ and chelating Ca2+ with EGTA) were tested. Levels of reactive oxygen species (ROS) and the mitochondrial membrane potential were measured and correlated with [Ca2+]i. Results A reduction in O2 tension from 20% to 1% for 16-18 h caused [Ca2+]i to approximately double, reaching 105 ± 23 nM (p < 0.001). Ion substitutions indicated that Na+/Ca2+ exchange activity was not inhibited at low O2 levels. At 1% O2, ROS levels fell and mitochondria depolarised. Restoring ROS levels (with an oxidant H2O2, a non-specific ROS generator Co2+ or the mitochondrial complex II inhibitor antimycin A) concomitantly reduced [Ca2+]i. Conclusions O2 tension exerts a significant effect on [Ca2+]i. The proposed mechanism involves ROS from mitochondria. Findings emphasise the importance of using realistic O2 tensions when studying the physiology and pathology of articular cartilage and the potential interactions between O2, ROS and Ca2+.
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Affiliation(s)
- Rachel White
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, CB3 OES, UK.
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Xu X, Urban JPG, Tirlapur UK, Cui Z. Osmolarity effects on bovine articular chondrocytes during three-dimensional culture in alginate beads. Osteoarthritis Cartilage 2010; 18:433-9. [PMID: 19840877 DOI: 10.1016/j.joca.2009.10.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2009] [Revised: 09/30/2009] [Accepted: 09/05/2009] [Indexed: 02/02/2023]
Abstract
OBJECTIVE With the development of engineered cartilage, the determination of the appropriate culture conditions is vital in order to maximize extracellular matrix synthesis. As osmolarity could affect the fate of chondrocytes, the purpose of this study was to determine the effects of osmolarity on chondrocytes during relatively long-term culture. DESIGN Bovine articular chondrocytes were cultured in alginate beads in a biocarbonate free system at 280, 380 and 550 mOsm at pH 7.4 for up to 12 days, respectively. Cell volume, intracellular pH (pH(i)), cell number, glucosaminoglycan (GAG) and collagen retention were measured at day 5 and 12. Cell viability and volume were monitored over the 12 days of culture. RESULTS By day 5 and 12, compared to the cell volume at 380 mOsm, around 20% (P<0.01) swelling and 15% (P<0.05) shrinkage were observed when the cells were cultured at 280 and 550 mOsm. The pH(i) over the 12 days of culture varied with osmolarity of the culture medium. In comparison with fresh cells, pH(i) became slightly more acidic by 0.15 pH units at 280 mOsm at day 5. However, by day 12, an alkalization of pH(i), by 0.2 pH units, was noted. A higher proliferation rate was seen at 280 mOsm than at other osmolarities while less GAG was produced. CONCLUSIONS Chronic exposure to anisotonic conditions results in cell swelling at 280 mOsm and shrinkage at 550 mOsm. The osmolarity of 280 mOsm appears to encourage proliferation of chondrocytes, but inhibits matrix production.
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Affiliation(s)
- X Xu
- Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK
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Increasing the osmolarity of joint irrigation solutions may avoid injury to cartilage: a pilot study. Clin Orthop Relat Res 2010; 468:875-84. [PMID: 19641975 PMCID: PMC2816775 DOI: 10.1007/s11999-009-0983-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Accepted: 06/30/2009] [Indexed: 01/31/2023]
Abstract
Saline (0.9%, 285 mOsm) and Hartmann's solution (255 mOsm) are two commonly used joint irrigation solutions that alter the extracellular osmolarity of in situ chondrocytes during articular surgery. We asked whether varying the osmolarity of these solutions influences in situ chondrocyte death in mechanically injured articular cartilage. We initially exposed osteochondral tissue harvested from the metacarpophalangeal joints of 3-year-old cows to solutions of 0.9% saline and Hartmann's solution of different osmolarity (100-600 mOsm) for 2 minutes to allow in situ chondrocytes to respond to the altered osmotic environment. The full thickness of articular cartilage then was "injured" with a fresh scalpel. Using confocal laser scanning microscopy, in situ chondrocyte death at the injured cartilage edge was quantified spatially as a function of osmolarity at 2.5 hours. Increasing the osmolarity of 0.9% saline and Hartmann's solution to 600 mOsm decreased in situ chondrocyte death in the superficial zone of injured cartilage. Compared with 0.9% saline, Hartmann's solution was associated with greater chondrocyte death in the superficial zone of injured cartilage, but not when the osmolarity of both solutions was increased to 600 mOsm. These experiments may have implications for the design of irrigation solutions used during arthroscopic and open articular surgery.
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118
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Finan JD, Guilak F. The effects of osmotic stress on the structure and function of the cell nucleus. J Cell Biochem 2010; 109:460-7. [PMID: 20024954 PMCID: PMC3616882 DOI: 10.1002/jcb.22437] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Osmotic stress is a potent regulator of the normal function of cells that are exposed to osmotically active environments under physiologic or pathologic conditions. The ability of cells to alter gene expression and metabolic activity in response to changes in the osmotic environment provides an additional regulatory mechanism for a diverse array of tissues and organs in the human body. In addition to the activation of various osmotically- or volume-activated ion channels, osmotic stress may also act on the genome via a direct biophysical pathway. Changes in extracellular osmolality alter cell volume, and therefore, the concentration of intracellular macromolecules. In turn, intracellular macromolecule concentration is a key physical parameter affecting the spatial organization and pressurization of the nucleus. Hyper-osmotic stress shrinks the nucleus and causes it to assume a convoluted shape, whereas hypo-osmotic stress swells the nucleus to a size that is limited by stretch of the nuclear lamina and induces a smooth, round shape of the nucleus. These behaviors are consistent with a model of the nucleus as a charged core/shell structure pressurized by uneven partition of macromolecules between the nucleoplasm and the cytoplasm. These osmotically-induced alterations in the internal structure and arrangement of chromatin, as well as potential changes in the nuclear membrane and pores are hypothesized to influence gene transcription and/or nucleocytoplasmic transport. A further understanding of the biophysical and biochemical mechanisms involved in these processes would have important ramifications for a range of fields including differentiation, migration, mechanotransduction, DNA repair, and tumorigenesis.
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Affiliation(s)
- John D Finan
- Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710, USA
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119
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Bansal PN, Joshi NS, Entezari V, Grinstaff MW, Snyder BD. Contrast enhanced computed tomography can predict the glycosaminoglycan content and biomechanical properties of articular cartilage. Osteoarthritis Cartilage 2010; 18:184-91. [PMID: 19815108 DOI: 10.1016/j.joca.2009.09.003] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 08/25/2009] [Accepted: 09/09/2009] [Indexed: 02/02/2023]
Abstract
OBJECTIVE An early hallmark of osteoarthritis (OA) is the progressive loss of glycosaminoglycans (GAGs), the extracellular matrix (ECM) component of articular cartilage that confers it with compressive stiffness. Our aim in this work is to establish the feasibility of using Contrast Enhanced Computed Tomography (CECT) with an anionic iodinated contrast agent - Cysto Conray II - as a minimally invasive tool to measure the changes in the GAG content as well as the compressive stiffness of articular cartilage. METHODS The GAG content of mated osteochondral plugs excised from bovine patello-femoral joints was progressively degraded using chondroitinase ABC. The mated plugs were then immersed in an anionic, tri-iodinated contrast agent, imaged using peripheral quantitative computed tomography (pQCT), subjected to an unconfined compressive stress relaxation test and the GAG content measured using 1,9-dimethylmethylene blue (DMMB) assay. Partial correlation analysis was performed to compare the variation in X-ray attenuation measured by pQCT to the variation in GAG content and in equilibrium compressive modulus. RESULTS The X-ray attenuation of cartilage exposed to an anionic, tri-iodinated, contrast agent measured by quantitative computed tomography (QCT) accounted for 83% of the variation in GAG content (r(2)=0.83, P<0.0001) and 93% of the variation in the equilibrium compressive modulus (r(2)=0.93, P<0.0001). CONCLUSION Using a mated osteochondral plug model to evaluate the biochemical composition and biomechanical properties of cartilage, this study demonstrates the interrelationships between X-ray attenuation, GAG content, and equilibrium compressive modulus, and that CECT can be used to monitor and quantify changes in the GAG content and biomechanical properties of articular cartilage.
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Affiliation(s)
- P N Bansal
- Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA
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120
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Villanueva I, Bishop NL, Bryant SJ. Medium osmolarity and pericellular matrix development improves chondrocyte survival when photoencapsulated in poly(ethylene glycol) hydrogels at low densities. Tissue Eng Part A 2009; 15:3037-48. [PMID: 19331581 DOI: 10.1089/ten.tea.2009.0001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The ability to encapsulate cells over a range of cell densities is important toward mimicking cell densities of native tissues and rationally designing strategies where cell source and/or cell numbers are clinically limited. Our preliminary findings demonstrate that survival of freshly isolated adult bovine chondrocytes dramatically decreases when photoencapsulated in poly(ethylene glycol) hydrogels at low densities (4 million cells/mL). During enzymatic digestion of cartilage, chondrocytes undergo a harsh change in their microenvironment. We hypothesize that the absence of exogenous antioxidants, the hyposmotic environment, and the loss of a protective pericellular matrix (PCM) increase chondrocytes' susceptibility to free radical damage during photoencapsulation. Incorporation of antioxidants and serum into the encapsulation medium improved cell survival twofold compared to phosphate-buffered saline. Increasing medium osmolarity from 330 to 400 mOsm (physiological) improved cell survival by 40% and resulted in approximately 2-fold increase in adenosine triphosphate (ATP) production 24 h postencapsulation. However, cell survival was only temporary. Allowing cells to reproduce some PCM before photoencapsulation in 400 mOsm medium resulted in superior cell survival during and postencapsulation for up to 15 days. In summary, the combination of antioxidants, physiological osmolarity, and the development of some PCM result in an improved robustness against free radical damage during photoencapsulation.
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Affiliation(s)
- Idalis Villanueva
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA
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121
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Contribution of the cytoskeleton to the compressive properties and recovery behavior of single cells. Biophys J 2009; 97:1873-82. [PMID: 19804717 DOI: 10.1016/j.bpj.2009.07.050] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Revised: 07/08/2009] [Accepted: 07/15/2009] [Indexed: 11/20/2022] Open
Abstract
The cytoskeleton is known to play an important role in the biomechanical nature and structure of cells, but its particular function in compressive characteristics has not yet been fully examined. This study focused on the contribution of the main three cytoskeletal elements to the bulk compressive stiffness (as measured by the compressive modulus), volumetric or apparent compressibility changes (as further indicated by apparent Poisson's ratio), and recovery behavior of individual chondrocytes. Before mechanical testing, cytochalasin D, acrylamide, or colchicine was used to disrupt actin microfilaments, intermediate filaments, or microtubules, respectively. Cells were subjected to a range of compressive strains and allowed to recover to equilibrium. Analysis of the video recording for each mechanical event yielded relevant compressive properties and recovery characteristics related to the specific cytoskeletal disrupting agent and as a function of applied axial strain. Inhibition of actin microfilaments had the greatest effect on bulk compressive stiffness ( approximately 50% decrease compared to control). Meanwhile, intermediate filaments and microtubules were each found to play an integral role in either the diminution (compressibility) or retention (incompressibility) of original cell volume during compression. In addition, microtubule disruption had the largest effect on the "critical strain threshold" in cellular mechanical behavior (33% decrease compared to control), as well as the characteristic time for recovery ( approximately 100% increase compared to control). Elucidating the role of the cytoskeleton in the compressive biomechanical behavior of single cells is an important step toward understanding the basis of mechanotransduction and the etiology of cellular disease processes.
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122
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Simultaneous computed tomography of articular cartilage and subchondral bone. Osteoarthritis Cartilage 2009; 17:1583-8. [PMID: 19615482 DOI: 10.1016/j.joca.2009.06.010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 05/08/2009] [Accepted: 06/26/2009] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Contrast agent enhanced computed tomography (CECT) may be used to detect depletion of superficial proteoglycans in articular cartilage. In principle, computed tomography can also be used to diagnose the state of subchondral bone. Because osteoarthritis affects both cartilage and bone, we aimed to evaluate the feasibility of the CECT to simultaneously assess the state of these tissues. Further, we studied the spatial variation of contrast agent content in the CECT, properties of subchondral bone and the mechanical stiffness of articular cartilage across the bovine medial tibial plateau. METHODS Osteochondral samples (n=10) were prepared from fresh and visually intact bovine medial tibial plateaus. The dynamic mechanical modulus of the samples was measured using an arthroscopic indentation device. Subsequently, the samples were scanned with a peripheral quantitative computed tomography (pQCT) device prior to and after 35.5h of immersion in an anionic iodinated contrast agent, (ioxaglate) solution. The thickness of the cartilage was measured with ultrasound and pQCT. RESULTS In the medial tibial plateau, the site-dependent variation in the dynamic modulus, thickness of the cartilage, thickness of the subchondral plate and contrast agent content in the superficial cartilage was statistically significant (P<0.01). The linear correlation between the superficial contrast agent content and the dynamic modulus was rho=-0.80 (P<0.01). DISCUSSION The CECT enabled simultaneous analysis of the contrast agent penetration into cartilage, cartilage thickness and subchondral bone density and thickness. The contrast agent content in cartilage depends on the composition and structure of the tissue. Thereby the CECT also provided indirect information on the mechanical properties of the tissue, analogously to the dGEMRIC. Thus, the CECT may provide means to diagnose simultaneously the integrity of cartilage and subchondral bone in vivo.
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Phan MN, Leddy HA, Votta BJ, Kumar S, Levy DS, Lipshutz DB, Lee SH, Liedtke W, Guilak F. Functional characterization of TRPV4 as an osmotically sensitive ion channel in porcine articular chondrocytes. ACTA ACUST UNITED AC 2009; 60:3028-37. [PMID: 19790068 DOI: 10.1002/art.24799] [Citation(s) in RCA: 221] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Transient receptor potential vanilloid 4 (TRPV4) is a Ca(2+)-permeable channel that can be gated by tonicity (osmolarity) and mechanical stimuli. Chondrocytes, the cells in cartilage, respond to their osmotic and mechanical environments; however, the molecular basis of this signal transduction is not fully understood. This study was undertaken to demonstrate the presence and functionality of TRPV4 in chondrocytes. METHODS TRPV4 protein expression was measured by immunolabeling and Western blotting. In response to TRPV4 agonist/antagonists, osmotic stress, and interleukin-1 (IL-1), changes in Ca(2+) signaling, cell volume, and prostaglandin E(2) (PGE(2)) production were measured in porcine chondrocytes using fluorescence microscopy, light microscopy, or immunoassay, respectively. RESULTS TRPV4 was expressed abundantly at the RNA and protein levels. Exposure to 4alpha-phorbol 12,13-didecanoate (4alphaPDD), a TRPV4 activator, caused Ca(2+) signaling in chondrocytes, which was blocked by the selective TRPV4 antagonist, GSK205. Blocking TRPV4 diminished the chondrocytes' response to hypo-osmotic stress, reducing the fraction of Ca(2+) responsive cells, the regulatory volume decrease, and PGE(2) production. Ca(2+) signaling was inhibited by removal of extracellular Ca(2+) or depletion of intracellular stores. Specific activation of TRPV4 restored the defective regulatory volume decrease caused by IL-1. Chemical disruption of the primary cilium eliminated Ca(2+) signaling in response to either 4alphaPDD or hypo-osmotic stress. CONCLUSION Our findings indicate that TRPV4 is present in articular chondrocytes, and chondrocyte response to hypo-osmotic stress is mediated by this channel, which involves both an extracellular Ca(2+) and intracellular Ca(2+) release. TRPV4 may also be involved in modulating the production or influence of proinflammatory molecules in response to osmotic stress.
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Affiliation(s)
- Mimi N Phan
- Duke University Medical Center, Durham, North Carolina 27710, USA
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124
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Villanueva I, Gladem SK, Kessler J, Bryant SJ. Dynamic loading stimulates chondrocyte biosynthesis when encapsulated in charged hydrogels prepared from poly(ethylene glycol) and chondroitin sulfate. Matrix Biol 2009; 29:51-62. [PMID: 19720146 DOI: 10.1016/j.matbio.2009.08.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 08/18/2009] [Accepted: 08/20/2009] [Indexed: 10/20/2022]
Abstract
This study aimed to elucidate the role of charge in mediating chondrocyte response to loading by employing synthetic 3D hydrogels. Specifically, neutral poly(ethylene glycol) (PEG) hydrogels were employed where negatively charged chondroitin sulfate (ChS), one of the main extracellular matrix components of cartilage, was systematically incorporated into the PEG network at 0%, 20% or 40% to control the fixed charge density. PEG hydrogels were employed as a control environment for extracellular events which occur as a result of loading, but which are not associated with a charged matrix (e.g., cell deformation and fluid flow). Freshly isolated bovine articular chondrocytes were embedded in the hydrogels and subject to dynamic mechanical stimulation (0.3Hz, 15% amplitude strains, 6h) and assayed for nitric oxide production, cell proliferation, proteoglycan synthesis, and collagen deposition. In the absence of loading, incorporation of charge inhibited cell proliferation by approximately 75%, proteoglycan synthesis by approximately 22-50% depending on ChS content, but had no affect on collagen deposition. Dynamic loading had no effect on cellular responses in PEG hydrogels. However, dynamically loading 20% ChS gels inhibited nitrite production by 50%, cell proliferation by 40%, but stimulated proteoglycan and collagen deposition by 162% and 565%, respectively. Dynamic loading of 40% ChS hydrogels stimulated nitrite production by 62% and proteoglycan synthesis by 123%, but inhibited cell proliferation by 54% and collagen deposition by 52%. Upon removing the load and culturing under free-swelling conditions for 36h, the enhanced matrix synthesis observed in the 20% ChS gels was not maintained suggesting that loading is necessary to stimulate matrix production. In conclusion, extracellular events associated with a charged matrix have a dramatic affect on how chondrocytes respond to mechanical stimulation within these artificial 3D matrices suggesting that streaming potentials and/or dynamic changes in osmolarity may be important regulators of chondrocytes while cell deformation and fluid flow appear to have less of an effect.
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Affiliation(s)
- Idalis Villanueva
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA
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125
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Tew SR, Peffers MJ, McKay TR, Lowe ET, Khan WS, Hardingham TE, Clegg PD. Hyperosmolarity regulates SOX9 mRNA posttranscriptionally in human articular chondrocytes. Am J Physiol Cell Physiol 2009; 297:C898-906. [PMID: 19657054 PMCID: PMC2770738 DOI: 10.1152/ajpcell.00571.2008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The transcription factor SOX9 regulates cartilage extracellular matrix gene expression and is essential for chondrocyte differentiation. We previously showed that activation of p38 MAPK by cycloheximide in human chondrocytes leads to stabilization of SOX9 mRNA (Tew SR and Hardingham TE. J Biol Chem 281: 39471–39479, 2006). In this study we investigated whether regulation of p38 MAPK caused by changes in osmotic pressure could control SOX9 mRNA levels expression by a similar mechanism. Primary human articular chondrocytes isolated from osteoarthritic cartilage at passage 2-4 showed significantly raised SOX9 mRNA levels when exposed to hyperosmotic conditions for 5 h. The effect was strongest and most reproducible when actin stress fibers were disrupted by the Rho effector kinase inhibitor Y27632, or by culturing the cells within alginate beads. Freshly isolated chondrocytes, used within 24–48 h of isolation, did not contain actin stress fibers and upregulated SOX9 mRNA in response to hyperosmolarity in the presence and absence of Y27632. In these freshly isolated chondrocytes, hyperosmolarity led to an increase in the half-life of SOX9 mRNA, which was sensitive to the p38 MAPK inhibitor SB202190. SOX9 protein levels were increased by hyperosmotic culture over 24 h, and, in passaged chondrocytes, the activity of a COL2A1 enhancer driven luciferase assay was upregulated. However, in freshly isolated chondrocytes, COL2A1 mRNA levels were reduced by hyperosmotic conditions and the half-life was decreased. The results showed that the osmotic environment regulated both SOX9 and COL2A1 mRNA posttranscriptionally, but in fresh cells resulted in increased SOX9, but decreased COL2A1.
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Affiliation(s)
- Simon R Tew
- Veterinary Clinical Sciences, University of Liverpool Veterinary Teaching Hospital, Leahurst, Neston, Cheshire, United Kingdom.
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Gibson JS, McCartney D, Sumpter J, Fairfax TPA, Milner PI, Edwards HL, Wilkins RJ. Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes. Pflugers Arch 2009; 458:1085-92. [PMID: 19629519 DOI: 10.1007/s00424-009-0695-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Revised: 06/23/2009] [Accepted: 06/25/2009] [Indexed: 10/20/2022]
Abstract
Articular chondrocytes experience low oxygen (O(2)) levels compared with many other tissues, and values fall further in disease states. Chondrocyte intracellular pH (pH(i)) is a powerful modulator of matrix synthesis and is principally regulated by Na(+)-H(+) exchange (NHE). In equine chondrocytes, NHE is inhibited when cells are incubated for 3 h at low O(2), leading to intracellular acidosis. O(2)-dependent changes in reactive oxygen species (ROS) levels appear to underlie this effect. The present study examines whether hypoxia can influence chondrocyte NHE activity and pH(i) over shorter timescales using the pH-sensitive fluoroprobe BCECF in cells isolated not only from equine cartilage but also from bovine tissue. O(2) levels in initially oxygenated solutions gassed with N(2) fell to approximately 1% within 2 h. A progressive fall in pH(i) and acid extrusion capacity was observed, with statistically significant effects (P < 0.05) apparent within 3 h. For equine and bovine cell populations subjected to step change in O(2) by resuspension in hypoxic (1%) solutions, a decline in acid extrusion and pH(i) was observed within 10 min and continued throughout the recording period. This effect represented inhibition of the NHE-mediated fraction of acid extrusion. Cells subjected to hypoxic solutions supplemented with CoCl(2) (100 microM) or antimycin A (100 microM) to raise levels of ROS did not acidify. The conserved nature and rapidity of the response to hypoxia has considerable implications for chondrocyte homeostasis and potentially for the maintenance of cartilage integrity.
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Affiliation(s)
- John S Gibson
- Department of Veterinary Medicine, Madingley Road, Cambridge, CB3 OES, UK
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127
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Okumura N, Imai S, Toyoda F, Isoya E, Kumagai K, Matsuura H, Matsusue Y. Regulatory role of tyrosine phosphorylation in the swelling-activated chloride current in isolated rabbit articular chondrocytes. J Physiol 2009; 587:3761-76. [PMID: 19528252 DOI: 10.1113/jphysiol.2009.174177] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Articular chondrocytes are exposed in vivo to the continually changing osmotic environment and thus require volume regulatory mechanisms. The present study was designed to investigate (i) the functional role of the swelling-activated Cl(-) current (I(Cl,swell)) in the regulatory volume decrease (RVD) and (ii) the regulatory role of tyrosine phosphorylation in I(Cl,swell), in isolated rabbit articular chondrocytes. Whole-cell membrane currents were recorded from chondrocytes in isosmotic, hyposmotic and hyperosmotic external solutions under conditions where Na(+), K(+) and Ca(2+) currents were minimized. The cell surface area was also measured using microscope images from a separate set of chondrocytes and was used as an index of cell volume. The isolated chondrocytes exhibited a RVD during sustained exposure to hyposmotic solution, which was mostly inhibited by the I(Cl,swell) blocker 4-(2-butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl)oxobutyric acid (DCPIB) at 20 microM. Exposure to a hyposmotic solution activated I(Cl,swell), which was also largely inhibited by 20 microM DCPIB. I(Cl,swell) in rabbit articular chondrocytes had a relative taurine permeability (P(tau)/P(Cl)) of 0.21. Activation of I(Cl,swell) was significantly reduced by the protein tyrosine kinase (PTK) inhibitor genistein (30 microM) but was only weakly affected by its inactive analogue daidzein (30 microM). Intracellular application of protein tyrosine phosphatase (PTP) inhibitor sodium orthovanadate (250 and 500 microM) resulted in a gradual activation of a Cl(-) current even in isosmotic solutions. This Cl(-) current was almost completely inhibited by 4,4-diisothiocyanatostilbene-2,2-disulfonate (DIDS, 500 microM) and was also largely suppressed by exposure to hyperosmotic solution, thus indicating a close similarity to I(Cl,swell). Pretreatment of chondrocytes with genistein significantly prevented the activation of the Cl(-) current by sodium orthovanadate, suggesting that the basal activity of endogenous PTK is required for the activation of this Cl(-) current. Our results provide evidence to indicate that activation of I(Cl,swell) is involved in RVD in isolated rabbit articular chondrocytes and is facilitated by tyrosine phosphorylation.
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Affiliation(s)
- Noriaki Okumura
- Department of Physiology, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan
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128
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Ramage L, Nuki G, Salter DM. Signalling cascades in mechanotransduction: cell-matrix interactions and mechanical loading. Scand J Med Sci Sports 2009; 19:457-69. [PMID: 19538538 DOI: 10.1111/j.1600-0838.2009.00912.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Mechanical loading of articular cartilage stimulates the metabolism of resident chondrocytes and induces the synthesis of molecules to maintain the integrity of the cartilage. Mechanical signals modulate biochemical activity and changes in cell behavior through mechanotransduction. Compression of cartilage results in complex changes within the tissue including matrix and cell deformation, hydrostatic and osmotic pressure, fluid flow, altered matrix water content, ion concentration and fixed charge density. These changes are detected by mechanoreceptors on the cell surface, which include mechanosensitive ion channels and integrins that on activation initiate intracellular signalling cascades leading to tissue remodelling. Excessive mechanical loading also influences chondrocyte metabolism but unlike physiological stimulation leads to a quantitative imbalance between anabolic and catabolic activity resulting in depletion of matrix components. In this article we focus on the role of mechanical signalling in the maintenance of articular cartilage, and discuss how alterations in normal signalling can lead to pathology.
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Affiliation(s)
- L Ramage
- Osteoarticular Research Group, Centre for Inflammation Research, The Queens Medical Research Institute, The University of Edinburgh, Edinburgh, UK.
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129
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Amin AK, Huntley JS, Simpson AHRW, Hall AC. Chondrocyte survival in articular cartilage. ACTA ACUST UNITED AC 2009; 91:691-9. [DOI: 10.1302/0301-620x.91b5.21544] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The aim of this study was to determine whether subchondral bone influences in situ chondrocyte survival. Bovine explants were cultured in serum-free media over seven days with subchondral bone excised from articular cartilage (group A), subchondral bone left attached to articular cartilage (group B), and subchondral bone excised but co-cultured with articular cartilage (group C). Using confocal laser scanning microscopy, fluorescent probes and biochemical assays, in situ chondrocyte viability and relevant biophysical parameters (cartilage thickness, cell density, culture medium composition) were quantified over time (2.5 hours vs seven days). There was a significant increase in chondrocyte death over seven days, primarily within the superficial zone, for group A, but not for groups B or C (p < 0.05). There was no significant difference in cartilage thickness or cell density between groups A, B and C (p > 0.05). Increases in the protein content of the culture media for groups B and C, but not for group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival. In conclusion, subchondral bone significantly influenced chondrocyte survival in articular cartilage during explant culture. The extrapolation of bone-cartilage interactions in vitro to the clinical situation must be made with caution, but the findings from these experiments suggest that future investigation into in vivo mechanisms of articular cartilage survival and degradation must consider the interactions of cartilage with subchondral bone.
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Affiliation(s)
- A. K. Amin
- Department of Orthopaedic and Trauma Surgery, University of Edinburgh, Old Dalkeith Road, Edinburgh EH16 4SU, UK
| | - J. S. Huntley
- Department of Orthopaedic and Trauma Surgery, University of Edinburgh, Old Dalkeith Road, Edinburgh EH16 4SU, UK
| | - A. H. R. W. Simpson
- Department of Orthopaedic and Trauma Surgery, University of Edinburgh, Old Dalkeith Road, Edinburgh EH16 4SU, UK
| | - A. C. Hall
- Centre for Integrative Physiology, School of Biomedical Sciences Hugh Robson Building, George Square, University of Edinburgh, Edinburgh EH8 9XD, UK
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Li S, Duance VC, Blain EJ. Zonal variations in cytoskeletal element organization, mRNA and protein expression in the intervertebral disc. J Anat 2009; 213:725-32. [PMID: 19094188 DOI: 10.1111/j.1469-7580.2008.00998.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The intervertebral disc is important in maintaining flexibility and dissipating loads applied to the spine. The disc comprises a heterogeneous population of cells, including those of the nucleus pulposus and annulus fibrosus, which are diverse in phenotype, partly due to the different mechanical loads they experience. Several studies have implicated the cytoskeleton in mechanotransduction, but little characterization of the three major cytoskeletal elements--actin, tubulin and vimentin--in the intervertebral disc has been undertaken. In this study we show that there are differences in both the organization and the amounts of these cytoskeletal proteins across the regions of immature bovine intervertebral disc (nucleus pulposus and outer annulus fibrosus), which differs with skeletal maturity. These differences are likely to reflect the diverse mechanical characteristics of the disc regions, and the loads that they experience, i.e. tension in the annulus fibrosus and compression in the nucleus pulposus. Alterations to the organization and amount of cytoskeletal element proteins may change the ability of the cells to respond to mechanical signals, with a loss of tissue homeostasis, suggesting that the cytoskeleton has a potential role in intervertebral disc degeneration.
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Affiliation(s)
- Siyuan Li
- Connective Tissue Biology Laboratories, Biomedical Sciences Building, School of Biosciences, Cardiff University, Cardiff, UK
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131
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Finan JD, Chalut KJ, Wax A, Guilak F. Nonlinear osmotic properties of the cell nucleus. Ann Biomed Eng 2008; 37:477-91. [PMID: 19107599 DOI: 10.1007/s10439-008-9618-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Accepted: 12/03/2008] [Indexed: 12/20/2022]
Abstract
In the absence of active volume regulation processes, cell volume is inversely proportional to osmolarity, as predicted by the Boyle Van't Hoff relation. In this study, we tested the hypothesis that nuclear volume has a similar relationship with extracellular osmolarity in articular chondrocytes, cells that are exposed to changes in the osmotic environment in vivo. Furthermore, we explored the mechanism of the relationships between osmolarity and nuclear size and shape. Nuclear size was quantified using two independent techniques, confocal laser scanning microscopy and angle-resolved low coherence interferometry. Nuclear volume was osmotically sensitive but this relationship was not linear, showing a decline in the osmotic sensitivity in the hypo-osmotic range. Nuclear shape was also influenced by extracellular osmolarity, becoming smoother as the osmolarity decreased. The osmotically induced changes in nuclear size paralleled the changes in nuclear shape, suggesting that shape and volume are interdependent. The osmotic sensitivity of shape and volume persisted after disruption of the actin cytoskeleton. Isolated nuclei contracted in response to physiologic changes in macromolecule concentration but not in response to physiologic changes in ion concentration, suggesting solute size has an important influence on the osmotic pressurization of the nucleus. This finding in turn implies that the diffusion barrier that causes osmotic effects is not a semi-permeable membrane, but rather due to size constraints that prevent large solute molecules from entering small spaces in the nucleus. As nuclear morphology has been associated previously with cell phenotype, these findings may provide new insight into the role of mechanical and osmotic signals in regulating cell physiology.
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Affiliation(s)
- John D Finan
- Department of Surgery, Duke University Medical Center, 375 MSRB, Box 3093, Durham, NC 27710, USA
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132
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Pritchard S, Votta BJ, Kumar S, Guilak F. Interleukin-1 inhibits osmotically induced calcium signaling and volume regulation in articular chondrocytes. Osteoarthritis Cartilage 2008; 16:1466-73. [PMID: 18495501 PMCID: PMC3217044 DOI: 10.1016/j.joca.2008.04.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Accepted: 04/04/2008] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Articular chondrocytes respond to osmotic stress with transient changes in cell volume and the intracellular concentration of calcium ion ([Ca(2+)](i)). The goal of this study was to examine the hypothesis that interleukin-1 (IL-1), a pro-inflammatory cytokine associated with osteoarthritis, influences osmotically induced Ca(2+) signaling. METHODS Fluorescence ratio imaging was used to measure [Ca(2+)](i) and cell volume in response to hypo- or hyper-osmotic stress in isolated porcine chondrocytes, with or without pre-exposure to 10-ng/ml IL-1alpha. Inhibitors of IL-1 (IL-1 receptor antagonist, IL-1Ra), Ca(2+) mobilization (thapsigargin, an inhibitor of Ca-ATPases), and cytoskeletal remodeling (toxin B, an inhibitor of the Rho family of small GTPases) were used to determine the mechanisms involved in increased [Ca(2+)](i), F-actin remodeling, volume adaptation and active volume recovery. RESULTS In response to osmotic stress, chondrocytes exhibited transient increases in [Ca(2+)](i), generally followed by decaying oscillations. Pre-exposure to IL-1 significantly inhibited regulatory volume decrease (RVD) following hypo-osmotic swelling and reduced the change in cell volume and the time to peak [Ca(2+)](i) in response to hyper-osmotic stress, but did not affect the peak magnitudes of [Ca(2+)](i) in those cells that did respond. Co-treatment with IL-1Ra, thapsigargin, or toxin B restored these responses to control levels. The effects were associated with alterations in F-actin organization. CONCLUSIONS IL-1 alters the normal volumetric and Ca(2+) signaling response of chondrocytes to osmotic stress through mechanisms involving F-actin remodeling via small Rho GTPases. These findings provide further insights into the mechanisms by which IL-1 may interfere with normal physiologic processes in the chondrocyte, such as the adaptation or regulatory responses to mechanical or osmotic loading.
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Affiliation(s)
- Scott Pritchard
- Department of Surgery, Duke University Medical Center Durham, North Carolina, 27710 USA,Department of Biomedical Engineering, Duke University Medical Center Durham, North Carolina, 27710 USA
| | - Bartholomew J. Votta
- Department of Musculoskeletal Disease GlaxoSmithKline, Inc. 1250 S. Collegeville Rd, P.O. Box 5089 Collegeville, PA 19426-0989 USA
| | - Sanjay Kumar
- Department of Musculoskeletal Disease GlaxoSmithKline, Inc. 1250 S. Collegeville Rd, P.O. Box 5089 Collegeville, PA 19426-0989 USA
| | - Farshid Guilak
- Department of Surgery, Duke University Medical Center Durham, North Carolina, 27710 USA,Department of Biomedical Engineering, Duke University Medical Center Durham, North Carolina, 27710 USA
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133
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Dependence of zonal chondrocyte water transport properties on osmotic environment. Cell Mol Bioeng 2008; 1:339-348. [PMID: 20011231 DOI: 10.1007/s12195-008-0026-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
OBJECTIVE: The increasing concentration of proteoglycans from the surface to the deep zone of articular cartilage produces a depth-dependent gradient in fixed charge density, and therefore extracellular osmolarity, which may vary with loading conditions, growth and development, or disease. In this study we examine the relationship between in situ variations in osmolarity on chondrocyte water transport properties. Chondrocytes from the depth-dependent zones of cartilage, effectively preconditioned in varying osmolarities, were used to probe this relationship. DESIGN: First, depth variation in osmolarity of juvenile bovine cartilage under resting and loaded conditions was characterized using a combined experimental/theoretical approach. Zonal chondrocytes were isolated into two representative "baseline" osmolarities chosen from this analysis to reflect in situ conditions. Osmotic challenge was then used as a tool for determination of water transport properties at each of these baselines. Cell calcium signaling was monitored simultaneously as a preliminary examination of osmotic baseline effects on cell signaling pathways. RESULTS: Osmotic baseline exhibits a significant effect on the cell membrane hydraulic permeability of certain zonal subpopulations but not on cell water content or incidence of calcium signaling. CONCLUSIONS: Chondrocyte properties can be sensitive to changes in baseline osmolarity, such as those occurring during OA progression (decrease) and de novo tissue synthesis (increase). Care should be taken in comparing chondrocyte properties across zones when cells are tested in vitro in non-physiologic culture media.
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134
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Amin AK, Huntley JS, Bush PG, Simpson AHRW, Hall AC. Osmolarity influences chondrocyte death in wounded articular cartilage. J Bone Joint Surg Am 2008; 90:1531-42. [PMID: 18594103 DOI: 10.2106/jbjs.g.00857] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Mechanical injury results in chondrocyte death in articular cartilage. The purpose of the present study was to determine whether medium osmolarity affects chondrocyte death in injured articular cartilage. METHODS Osteochondral explants (n = 48) that had been harvested from the metacarpophalangeal joints of three-year-old cows were exposed to media with varying osmolarity (0 to 480 mOsm) for ninety seconds to allow in situ chondrocytes to respond to the altered osmotic environment. Explants were then wounded with a scalpel through the full thickness of articular cartilage, incubated in the same media for 2.5 hours, and transferred to 340-mOsm Dulbecco's Modified Eagle Medium (control medium) with further incubation for seven days. The spatial distribution of in situ chondrocyte death, percentage cell death, and marginal cell death at the wounded cartilage edge were compared as a function of osmolarity and time (2.5 hours compared with seven days) with use of confocal laser scanning microscopy. RESULTS In situ chondrocyte death was mainly localized to the superficial tangential zone of injured articular cartilage for the range of medium osmolarities (0 to 480 mOsm) at 2.5 hours and seven days. Therefore, a sample of articular cartilage from the superficial region (which included the scalpel-wounded cartilage edge) was studied with use of confocal laser scanning microscopy to compare the effects of osmolarity on percentage and marginal cell death in the superficial tangential zone. Compared with the control explants exposed to 340-mOsm Dulbecco's Modified Eagle Medium, percentage cell death in the superficial tangential zone was greatest for explants exposed to 0-mOsm (distilled water) and least for explants exposed to 480-mOsm Dulbecco's Modified Eagle Medium at 2.5 hours (13.0% at 340 mOsm [control], 35.5% at 0 mOsm, and 4.3% at 480 mOsm; p <or= 0.02 for paired comparisons) and seven days (9.9% at 340 mOsm [control], 37.7% at 0 mOsm, and 3.5% at 480 mOsm; p <or= 0.01 for paired comparisons). Marginal cell death in the superficial tangential zone decreased with increasing medium osmolarity at 2.5 hours (p = 0.001) and seven days (p = 0.002). There was no significant change in percentage cell death from 2.5 hours to seven days for explants initially exposed to any of the medium osmolarities. CONCLUSIONS Medium osmolarity significantly affects chondrocyte death in wounded articular cartilage. The greatest chondrocyte death occurs at 0 mOsm. Conversely, increased medium osmolarity (480 mOsm) is chondroprotective. The majority of cell death occurs within 2.5 hours, with no significant increase over seven days.
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Affiliation(s)
- Anish K Amin
- Department of Orthopaedic and Trauma Surgery, University of Edinburgh, Old Dalkeith Road, Edinburgh EH16 4SU, Scotland, UK.
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135
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Yang L, Reece JM, Cho J, Bortner CD, Shears SB. The nucleolus exhibits an osmotically regulated gatekeeping activity that controls the spatial dynamics and functions of nucleolin. J Biol Chem 2008; 283:11823-31. [PMID: 18299322 PMCID: PMC2431058 DOI: 10.1074/jbc.m800308200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 02/15/2008] [Indexed: 12/17/2022] Open
Abstract
We demonstrate that physiologically relevant perturbations in the osmotic environment rheostatically regulate a gatekeeping function for the nucleolus that controls the spatial dynamics and functions of nucleolin. HeLa cells and U2-OS osteosarcoma cells were osmotically challenged with 100-200 mm sorbitol, and the intranuclear distribution of nucleolin was monitored by confocal microscopy. Nucleolin that normally resides in the innermost fibrillar core of the nucleolus, where it assists rDNA transcription and replication, was expelled within 30 min of sorbitol addition. The nucleolin was transferred into the nucleoplasm, but it distributed there non-uniformly; locally high levels accumulated in 4',6-diamidino-2-phenylindole-negative zones containing euchromatic (transcriptionally active) DNA. Inositol pyrophosphates also responded within 30 min of hyperosmotic stress: levels of bisdiphosphoinositol tetrakisphosphate increased 6-fold, and this was matched by decreased levels of its precursor, diphosphoinositol pentakisphosphate. Such fluctuations in inositol pyrophosphate levels are of considerable interest, because, according to previously published in vitro data, they regulate the degree of phosphorylation of nucleolin through a novel kinase-independent phosphotransferase reaction ( Saiardi, A., Bhandari, A., Resnick, R., Cain, A., Snowman, A. M., and Snyder, S. H. (2004) Science 306, 2101-2105 ). However, by pharmacologically intervening in inositol pyrophosphate metabolism, we found that it did not supervise the osmotically driven switch in the biological activities of nucleolin in vivo.
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Affiliation(s)
- Ling Yang
- Inositol Signaling Group and
the Molecular Endocrinology Group,
NIEHS, National Institutes of Health, Department of Health and Human Services,
Research Triangle Park, North Carolina 27709 and
Reecent Technologies, LLC, Durham,
North Carolina 27713
| | - Jeff M. Reece
- Inositol Signaling Group and
the Molecular Endocrinology Group,
NIEHS, National Institutes of Health, Department of Health and Human Services,
Research Triangle Park, North Carolina 27709 and
Reecent Technologies, LLC, Durham,
North Carolina 27713
| | - Jaiesoon Cho
- Inositol Signaling Group and
the Molecular Endocrinology Group,
NIEHS, National Institutes of Health, Department of Health and Human Services,
Research Triangle Park, North Carolina 27709 and
Reecent Technologies, LLC, Durham,
North Carolina 27713
| | - Carl D. Bortner
- Inositol Signaling Group and
the Molecular Endocrinology Group,
NIEHS, National Institutes of Health, Department of Health and Human Services,
Research Triangle Park, North Carolina 27709 and
Reecent Technologies, LLC, Durham,
North Carolina 27713
| | - Stephen B. Shears
- Inositol Signaling Group and
the Molecular Endocrinology Group,
NIEHS, National Institutes of Health, Department of Health and Human Services,
Research Triangle Park, North Carolina 27709 and
Reecent Technologies, LLC, Durham,
North Carolina 27713
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136
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Koay EJ, Ofek G, Athanasiou KA. Effects of TGF-beta1 and IGF-I on the compressibility, biomechanics, and strain-dependent recovery behavior of single chondrocytes. J Biomech 2008; 41:1044-52. [PMID: 18222457 DOI: 10.1016/j.jbiomech.2007.12.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Revised: 12/03/2007] [Accepted: 12/05/2007] [Indexed: 12/15/2022]
Abstract
The responses of articular chondrocytes to physicochemical stimuli are intimately linked to processes that can lead to both degenerative and regenerative processes. Toward understanding this link, we examined the biomechanical behavior of single chondrocytes in response to growth factors (IGF-I and TGF-beta1) and a range of compressive strains. The results indicate that the growth factors alter the biomechanics of the cells in terms of their stiffness coefficient ( approximately two-fold increase over control) and compressibility, as measured by an apparent Poisson's ratio ( approximately two-fold increase over control also). Interestingly, the compressibility decreased significantly with respect to the applied strain. Moreover, we have again detected a critical strain threshold in chondrocytes at approximately 30% strain in all treatments. Overall, these findings demonstrate that cellular biomechanics change in response to both biochemical and biomechanical perturbations. Understanding the underlying biomechanics of chondrocytes in response to such stimuli may be useful in understanding various aspects of cartilage, including the study of osteoarthritis and the development of tissue-engineering strategies.
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Affiliation(s)
- Eugene J Koay
- Department of Bioengineering, Rice University, MS-142, PO Box 1892, Houston, TX 77251-1892, USA
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137
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Bush PG, Parisinos CA, Hall AC. The osmotic sensitivity of rat growth plate chondrocytes in situ; clarifying the mechanisms of hypertrophy. J Cell Physiol 2008; 214:621-9. [PMID: 17786946 DOI: 10.1002/jcp.21249] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Bone elongation is predominantly driven by the volume expansion of growth plate chondrocytes. This mechanism was initially believed to be "hypertrophy", describing a proportional increase of cell water and organelles. However, morphometrical analysis subsequently assumed the increase to be "swelling", resulting in a disproportionate increase of cell water (osmotically active fraction). Histological approaches were performed on fixed tissue, and for the "swelling" assumption to be valid, the osmotic sensitivity of living cells before and during volume increase should differ. To test this, analysis of images acquired by 2-photon laser scanning microscopy (2PLSM) were used to determine the osmotic sensitivity, and osmotically active/inactive proportions of in situ chondrocytes from 15 living rat growth plates exposed to varying media osmolarities ( approximately 0-580 mOsm). The dimensions of cell volume swelling in hypotonic media were different to the preferential lengthening seen in vivo, confirming the complexity of directional cell volume increase. Boyle-van't Hoff analysis of cell volume over the range of media osmolarity indicated no significant difference (Student's t-test) in the osmotically inactive fraction, 39.5 +/- 2.9% and 47.0 +/- 4.3% (n = 13) for proliferative and hypertrophic zones, respectively, or the sensitivity of volume to changes in media osmolarity (proliferative 15.5 +/- 0.8 and hypertrophic zone 15.5 +/- 1.2%volume . Osm). The osmotic fractions did not change as chondrocytes progress from proliferative to hypertrophic regions of the growth plate. Our data suggest cell volume increase by hypertrophy may play a greater role in cell enlargement than swelling, and should be re-evaluated as a mechanism responsible for growth plate chondrocyte volume increase and hence bone elongation.
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Affiliation(s)
- Peter G Bush
- Centre for Integrative Physiology, School of Biomedical Sciences, Hugh Robson Building, George Square, University of Edinburgh, Edinburgh, Scotland, UK
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138
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Takeno K, Kobayashi S, Negoro K, Uchida K, Miyazaki T, Yayama T, Shimada S, Baba H. Physical limitations to tissue engineering of intervertebral disc cells: effect of extracellular osmotic change on glycosaminoglycan production and cell metabolism. J Neurosurg Spine 2007; 7:637-44. [DOI: 10.3171/spi-07/12/637] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Object
In this study, the authors examined how physiological levels of extracellular osmolality influence proteoglycan accumulation in nucleus pulposus cells in a 3D culture system.
Methods
Cells were isolated from the nucleus pulposus of caudal discs obtained from 18- to 24-month-old bovines. They were cultured for 6 days in alginate beads at 4 million cells/ml in Dulbecco modified Eagle medium containing 6% fetal bovine serum under 21% O2. Medium osmolality was altered by NaCl addition between 270 and 570 mOsm and monitored using a freezing point osmometer. The cell viability profile was determined by manual counting after trypan blue staining. Profiles across intact beads were determined by manual counting by using fluorescent probes and a transmission electron microscope. Lactate production was measured enzymatically, and glycosaminoglycan (GAG) accumulation was measured using a dimethylmethylene blue assay. Rate of sulfate GAG synthesis was measured using a standard [35S]sulfate radioactive method.
Results
The cell viability was similar for the high- and low-osmolality cultures. However, confocal microscopy showed that the cells were the largest at 270 mOsm and became smaller with increasing osmotic pressure. The GAG production was largest at 370 mOsm, the capacity for GAG production and cell metabolism (lactate production) was low under hypoosmolality and hyperosmolality, and cell death was observed on electron microscopy.
Conclusions
In the authors' model, the prevailing osmolality was a powerful regulator of GAG accumulation by cultured nucleus cells. Thus, these results indicate that GAG synthesis rates are regulated by GAG concentration, with implications both for the cause of degeneration and for tissue engineering.
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139
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Sauerland K, Steinmeyer J. Intermittent mechanical loading of articular cartilage explants modulates chondroitin sulfate fine structure. Osteoarthritis Cartilage 2007; 15:1403-9. [PMID: 17574451 DOI: 10.1016/j.joca.2007.05.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 05/01/2007] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Alterations in the sulfation pattern of chondroitin sulfate (CS) chains of proteoglycans have been associated with aging and degeneration of articular cartilage. The purpose of the present study was to investigate systematically the effect of load amplitudes, frequencies and load durations of intermittently applied mechanical pressure on the sulfation of CS chains of cultured bovine articular cartilage explants. METHODS Using a sinusoidal waveform of 0.5 Hz frequency, cyclic compressive pressure of 0.1-1.0 MPa was applied for 10s followed by a period of unloading lasting 10-1000 s. These intermittent loading protocols were repeated for a total duration of 1-6 days. Newly synthesized as well as endogenous CS chains were isolated, depolymerized and subsequently quantitated after fractionation by high-performance anion-exchange chromatography. RESULTS Increasing the mechanical demands on cartilage explants by elevating either the duration or the frequency of loading can significantly alter the fine structure of newly synthesized CS in that less chains terminate on galNAc4,6S and, in that simultaneously the ratio of the internal disaccharides DeltaDi6S to DeltaDi4S is increased. Similar results were obtained with explants being slightly mechanically challenged by low magnitudes of loads. CONCLUSION Our data show for the first time that intermittent loading of articular cartilage explants can significantly alter the sulfation pattern of the terminal CS residues as well as of the internal disaccharides. Furthermore, our results indicate that explants possess a physiological window of stress in which they are able to produce also a normal extracellular matrix.
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Affiliation(s)
- K Sauerland
- Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University Clinics Giessen and Marburg GmbH, Paul-Meimberg-Strasse 3, 35385 Giessen, Germany
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140
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Wuertz K, Urban JPG, Klasen J, Ignatius A, Wilke HJ, Claes L, Neidlinger-Wilke C. Influence of extracellular osmolarity and mechanical stimulation on gene expression of intervertebral disc cells. J Orthop Res 2007; 25:1513-22. [PMID: 17568421 DOI: 10.1002/jor.20436] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Intervertebral discs (IVD) have a higher extracellular osmolarity than most other tissues; moreover their osmolarity changes by around 25% during each diurnal cycle. In this study, changes in aggrecan, collagen I and collagen II expression of IVD cells were examined after exposure to osmotic environment alterations or mechanical stimulation under different osmotic conditions. Human and bovine IVD cells seeded in three-dimensional (3D) collagen type I matrices were cultured under hypo-osmotic (300 mOsm), iso-osmotic (400 mOsm), or hyperosmotic (500 mOsm) conditions. Osmolarity-induced changes in gene expression of IVD cells were measured after 5 days. Load-induced changes in gene expression under the different osmotic conditions were measured after application of hydrostatic pressure (0.25 MPa, 0.1 Hz, 30 min) or cyclic strain (4%, 1 Hz, 24 h). The results showed that IVD cells respond strongly to changes in the osmotic environment by altering mRNA expression. Human cells cultured over 5 days increased expression of aggrecan and collagen II in both nucleus and annulus cells under increasing osmolarity. In contrast, collagen I expression was inhibited at high osmolarity in both cell types. Mechanically induced alterations in gene expression appear to have only modest effects on matrix protein expression, but the same stimulus partly resulted in an inhibition or stimulation of gene expression, depending on the osmotic conditions. This study showed that the osmotic environment does not only have an appreciable effect on gene expression but also affects responses to mechanical stimuli. This suggests that the osmotic conditions cannot be ignored when examining physiological and pathological behavior of IVD cells.
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Affiliation(s)
- K Wuertz
- Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, 89081 Ulm, Germany
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141
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Simpkin VL, Murray DH, Hall AP, Hall AC. Bicarbonate-dependent pH(i) regulation by chondrocytes within the superficial zone of bovine articular cartilage. J Cell Physiol 2007; 212:600-9. [PMID: 17458896 DOI: 10.1002/jcp.21054] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Control of chondrocyte pH (pH(i)) determines articular cartilage matrix metabolism. However, the transporters of chondrocytes in situ throughout cartilage zones are unclear, and we tested the hypothesis that chondocytes within the superficial zone (SZ) utilise a HCO(3) (-)-dependent system absent from other zones. Imaging of single BCECF-labelled cells was used to monitor the pH(i) of in situ chondrocytes within the cartilage zones, and also that of cells isolated from the SZ or full depth (FD) explants. Resting pH(i) and intrinsic buffering power (beta(i)) in HEPES-buffered saline was not different between SZ and DZ cells, however the pH(i) of SZ chondrocytes was lower in HCO(3) (-) saline. Ammonium pre-pulse was used to acid-load cells and pH(i) recovery by in situ or isolated SZ chondrocytes shown to be totally dependent on HCO(3) (-). pH(i) recovery rate was significantly (P < 0.05) greater for in situ cells, suggesting that isolation damaged the HCO(3) (-)-dependent system. Recovery of pH(i) by in situ cells was blocked by the anion transport inhibitor DIDS, and partially inhibited by EIPA probably non-specifically. Recovery of pH(i) by acidified MZ or DZ cells or those isolated from FD explants was not affected by HCO(3) (-) (P > 0.05). Na(+)-dependent HCO(3) (-)-(NBC) transporters were identified in SZ chondrocytes by fluorescence immunohistochemistry suggesting that this system might account for the HCO(3) (-)-dependent recovery of pH(i). Bovine articular cartilage chondrocytes possess a HCO(3) (-)-dependent transporter which plays a key role in pH(i) regulation in cells in the SZ, but not in chondrocytes within deeper cartilage zones.
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Affiliation(s)
- Victoria L Simpkin
- School of Biomedical Sciences, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, Scotland, UK
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142
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Gibson JS, Milner PI, White R, Fairfax TPA, Wilkins RJ. Oxygen and reactive oxygen species in articular cartilage: modulators of ionic homeostasis. Pflugers Arch 2007; 455:563-73. [PMID: 17849146 DOI: 10.1007/s00424-007-0310-7] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Accepted: 06/20/2007] [Indexed: 11/26/2022]
Abstract
Articular cartilage is an avascular tissue dependent on diffusion mainly from synovial fluid to service its metabolic requirements. Levels of oxygen (O(2)) in the tissue are low, with estimates of between 1 and 6%. Metabolism is largely, if not entirely, glycolytic, with little capacity for oxidative phosphorylation. Notwithstanding, the tissue requires O(2) and consumes it, albeit at low rates. Changes in O(2) tension also have profound effects on chondrocytes affecting phenotype, gene expression, and morphology, as well as response to, and production of, cytokines. Although chondrocytes can survive prolonged anoxia, low O(2) levels have significant metabolic effects, inhibiting glycolysis (the negative Pasteur effect), and also notably matrix production. Why this tissue should respond so markedly to reduction in O(2) tension remains a paradox. Ion homeostasis in articular chondrocytes is also markedly affected by the extracellular matrix in which the cells reside. Recent work has shown that ion homeostasis also responds to changes in O(2) tension, in such a way as to produce significant effects on cell function. For this purpose, O(2) probably acts via alteration in levels of reactive oxygen species. We discuss the possibility that O(2) consumption by this tissue is required to maintain levels of ROS, which are then used physiologically as an intracellular signalling device. This postulate may go some way towards explaining why the tissue is dependent on O(2) and why its removal has such marked effects. Understanding the role of oxygen has implications for disease states in which O(2) or ROS levels may be perturbed.
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Affiliation(s)
- J S Gibson
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, England
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143
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Zhou Y, Millward-Sadler SJ, Lin H, Robinson H, Goldring M, Salter DM, Nuki G. Evidence for JNK-dependent up-regulation of proteoglycan synthesis and for activation of JNK1 following cyclical mechanical stimulation in a human chondrocyte culture model. Osteoarthritis Cartilage 2007; 15:884-93. [PMID: 17408985 DOI: 10.1016/j.joca.2007.02.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Accepted: 02/04/2007] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To examine the expression of mitogen-activated protein kinases (MAPKs) in human chondrocytes, to investigate whether selective activation of MAPKs is involved in up-regulation of proteoglycan (PG) synthesis following cyclical mechanical stimulation (MS), and to examine whether MS is associated with integrin-dependent or independent activation of MAPKs. METHODS The C-28/I2 and C-20/A4 human chondrocyte cell lines were mechanically stimulated in monolayer cell culture. PG synthesis was assessed by [(35)S]-sulphate incorporation in the presence and absence of the p38 inhibitor SB203580, and the extracellular-regulated kinase (ERK1/2) inhibitor PD98059. Kinase expression and activation were assessed by Western blotting using phosphorylation status-dependent and independent antibodies, and by kinase assays. The Jun N-terminal kinase (JNK) inhibitor SP600125 and the anti-beta(1) integrin (CD29) function-blocking antibody were used to assess JNK activation and integrin dependence, respectively. RESULTS Increased PG synthesis following 3 h of cyclic MS was abolished by pretreatment with 10 microM SB203580, but was not affected by 50 microM PD98059. The kinases p38, ERK1/ERK2 and JNKs were expressed in both stimulated and unstimulated cells. Phosphorylated p38 was detected at various time points following 0.5, 1, 2 and 3 h MS in C-28/I2, but not detected in C-20/A4 cell lines. Phosphorylation of ERK1 and ERK2 was not significantly affected by MS. Phosphorylation of the 54 and 46 kDa JNKs increased following 0.5, 1, 2 and 3 h of MS, and following CO(2) deprivation. MS-induced JNK phosphorylation was inhibited by SB203580 at concentrations > or =5 microM and activation of JNK1 following MS was blocked by SP600125 and partially inhibited by anti-CD29. CONCLUSIONS The data suggest JNK, rather than p38 or ERK dependent increases in PG synthesis, and selective, partially integrin-dependent, activation of JNK kinases in human chondrocyte cell lines following cyclical MS. JNK activation is also very sensitive to changes in CO(2)/pH in this chondrocyte culture model.
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Affiliation(s)
- Y Zhou
- University of Edinburgh, Osteoarticular Research Group, Queen's Medical Research Institute, Edinburgh, Scotland, UK
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144
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Racz B, Reglodi D, Fodor B, Gasz B, Lubics A, Gallyas F, Roth E, Borsiczky B. Hyperosmotic stress-induced apoptotic signaling pathways in chondrocytes. Bone 2007; 40:1536-43. [PMID: 17392049 DOI: 10.1016/j.bone.2007.02.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Revised: 12/29/2006] [Accepted: 02/09/2007] [Indexed: 11/15/2022]
Abstract
Articular chondrocytes have a well-developed osmoregulatory system that enables cells to survive in a constantly changing osmotic environment. However, osmotic loading exceeding that occurring under physiological conditions severely compromises chondrocyte function and leads to degenerative changes. The aim of the present study was to investigate the form of cell death and changes in apoptotic signaling pathways under hyperosmotic stress using a primary chondrocyte culture. Cell viability and apoptosis assays performed with annexin V and propidium iodide staining showed that a highly hyperosmotic medium (600 mOsm) severely reduced chondrocyte viability and led mainly to apoptotic cell death, while elevating osmotic pressure within the physiological range caused no changes compared to isosmotic conditions. Western blot analysis revealed that a 600 mOsm hyperosmotic environment induced the activation of proapoptotic members of the mitogen-activated protein kinase family such as c-Jun N-terminal kinase (JNK) and p38, and led to an increased level of extracellular signal regulated kinase (ERK1/2). Hyperosmotic stress also induced the activation of caspase-3. In summary, our results show that hyperosmotic stress leads to mainly apoptotic cell death via the involvement of proapoptotic signaling pathways in a primary chondrocyte culture.
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Affiliation(s)
- Boglarka Racz
- Department of Surgical Research and Techniques, Pecs University Medical School, Kodaly Z. u. 20, 7624 Pecs, Hungary.
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145
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Kallioniemi AS, Jurvelin JS, Nieminen MT, Lammi MJ, Töyräs J. Contrast agent enhanced pQCT of articular cartilage. Phys Med Biol 2007; 52:1209-19. [PMID: 17264381 DOI: 10.1088/0031-9155/52/4/024] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The delayed gadolinium enhanced MRI of cartilage (dGEMRIC) technique is the only non-invasive means to estimate proteoglycan (PG) content in articular cartilage. In dGEMRIC, the anionic paramagnetic contrast agent gadopentetate distributes in inverse relation to negatively charged PGs, leading to a linear relation between T1,Gd and spatial PG content in tissue. In the present study, for the first time, contrast agent enhanced peripheral quantitative computed tomography (pQCT) was applied, analogously to dGEMRIC, for the quantitative detection of spatial PG content in cartilage. The suitability of two anionic radiographic contrast agents, gadopentetate and ioxaglate, to detect enzymatically induced PG depletion in articular cartilage was investigated. First, the interrelationships of x-ray absorption, as measured with pQCT, and the contrast agent solution concentration were investigated. Optimal contrast agent concentrations for the following experiments were selected. Second, diffusion rates for both contrast agents were investigated in intact (n=3) and trypsin-degraded (n=3) bovine patellar cartilage. The contrast agent concentration of the cartilaginous layer was measured prior to and 2-27 h after immersion. Optimal immersion time for the further experiments was selected. Third, the suitability of gadopentetate and ioxaglate enhanced pQCT to detect the enzymatically induced specific PG depletion was investigated by determining the contrast agent concentrations and uronic acid and water contents in digested and intact osteochondral samples (n=16). After trypsin-induced PG loss (-70%, p<0.05) the penetration of gadopentetate and ioxaglate increased (p<0.05) by 34% and 48%, respectively. Gadopentetate and ioxaglate concentrations both showed strong correlation (r=-0.95, r=-0.94, p<0.01, respectively) with the uronic acid content. To conclude, contrast agent enhanced pQCT provides a technique to quantify PG content in normal and experimentally degraded articular cartilage in vitro. As high resolution imaging of e.g. the knee joint is possible with pQCT, the present technique may be further developed for in vivo quantification of PG depletion in osteoarthritic cartilage. However, careful in vitro and in vivo characterization of diffusion mechanics and optimal contrast agent concentrations are needed before diagnostic applications are feasible.
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Affiliation(s)
- A S Kallioniemi
- Department of Physics, University of Kuopio, and Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, Finland.
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146
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Alfieri RR, Petronini PG. Hyperosmotic stress response: comparison with other cellular stresses. Pflugers Arch 2007; 454:173-85. [PMID: 17206446 DOI: 10.1007/s00424-006-0195-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Accepted: 11/24/2006] [Indexed: 10/23/2022]
Abstract
Cellular responses induced by stress are essential for the survival of cells under adverse conditions. These responses, resulting in cell adaptation to the stress, are accomplished by a variety of processes at the molecular level. After an alteration in homeostatic conditions, intracellular signalling processes link the sensing mechanism to adaptive or compensatory changes in gene expression. The ability of cells to adapt to hyperosmotic stress involves early responses in which ions move across cell membranes and late responses characterized by increased synthesis of either membrane transporters essential for uptake of organic osmolytes or of enzymes involved in their synthesis. The goal of these responses is to return the cell to its normal size and maintain cellular homeostasis. The enhanced synthesis of molecular chaperones, such as heat shock proteins, is another important component of the adaptive process that contributes to cell survival. Some responses are common to different stresses, whereas others are specific. In the first part of the review, we illustrate the characteristic and specific features of adaptive response to hypertonicity; we then describe similarities to and differences from other cellular stresses, such as genotoxic agents, nutrient starvation and heat shock.
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Affiliation(s)
- Roberta R Alfieri
- Dipartimento di Medicina Sperimentale, Sezione di Patologia Molecolare e Immunologia, Università degli Studi di Parma, 43100 Parma, Italy.
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147
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Haschtmann D, Stoyanov JV, Ferguson SJ. Influence of diurnal hyperosmotic loading on the metabolism and matrix gene expression of a whole-organ intervertebral disc model. J Orthop Res 2006; 24:1957-66. [PMID: 16917902 DOI: 10.1002/jor.20243] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
It is generally agreed that the mechanical environment of intervertebral disc cells plays an important role in maintaining a balanced matrix metabolism. The precise mechanism by which the signals are transduced into the cells is poorly understood. Osmotic changes in the extracellular matrix (ECM) are thought to be involved. Current in-vitro studies on this topic are mostly short-term and show conflicting data on the reaction of disc cells subjected to osmotic changes which is partially due to the heterogenous and often substantially-reduced culture systems. The aim of the study was therefore to investigate the effects of cyclic osmotic loading for 4 weeks on metabolism and matrix gene expression in a full-organ intervertebral disc culture system. Intervertebral disc/endplate units were isolated from New Zealand White Rabbits and cultured either in iso-osmotic media (335 mosmol/kg) or were diurnally exposed for 8 hours to hyper-osmotic conditions (485 mosmol/kg). Cell viability, metabolic activity, matrix composition and matrix gene expression profile (collagen types I/II and aggrecan) were monitored using Live/Dead cell viability assay, tetrazolium reduction test (WST 8), proteoglycan and DNA quantification assays and quantitative PCR. The results show that diurnal osmotic stimulation did not have significant effects on proteoglycan content, cellularity and disc cell viability after 28 days in culture. However, hyperosmolarity caused increased cell death in the early culture phase and counteracted up-regulation of type I collagen gene expression in nucleus and annulus cells. Moreover, the initially decreased cellular dehydrogenase activity recovered with osmotic stimulation after 4 weeks and aggrecan gene down-regulation was delayed, although the latter was not significant according to our statistical criteria. In contrast, collagen type II did not respond to the osmotic changes and was down-regulated in both groups. In conclusion, diurnal hyper-osmotic stimulation of a whole-organ disc/endplate culture partially inhibits a matrix gene expression profile as encountered in degenerative disc disease and counteracts cellular metabolic hypo-activity.
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Affiliation(s)
- Daniel Haschtmann
- MEM Research Center for Orthopaedic Surgery, Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, CH-3014 Bern, Switzerland.
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148
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Chao PHG, West AC, Hung CT. Chondrocyte intracellular calcium, cytoskeletal organization, and gene expression responses to dynamic osmotic loading. Am J Physiol Cell Physiol 2006; 291:C718-25. [PMID: 16928775 DOI: 10.1152/ajpcell.00127.2005] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
While chondrocytes in articular cartilage experience dynamic stimuli from joint loading activities, few studies have examined the effects of dynamic osmotic loading on their signaling and biosynthetic activities. We hypothesize that dynamic osmotic loading modulates chondrocyte signaling and gene expression differently than static osmotic loading. With the use of a novel microfluidic device developed in our laboratory, dynamic hypotonic loading (−200 mosM) was applied up to 0.1 Hz and chondrocyte calcium signaling, cytoskeleton organization, and gene expression responses were examined. Chondrocytes exhibited decreasing volume and calcium responses with increasing loading frequency. Phalloidin staining showed osmotic loading-induced changes to the actin cytoskeleton in chondrocytes. Real-time PCR analysis revealed a stimulatory effect of dynamic osmotic loading compared with static osmotic loading. These studies illustrate the utility of the microfluidic device in cell signaling investigations, and their potential role in helping to elucidate mechanisms that mediate chondrocyte mechanotransduction to dynamic stimuli.
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Affiliation(s)
- Pen-Hsiu Grace Chao
- Department of Biomedical Engineering, Columbia University, New York, New York, USA
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149
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Kobayashi S, Baba H, Uchida K, Negoro K, Sato M, Miyazaki T, Nomura E, Murakami K, Shimizubata M, Meir A. Microvascular system of anterior cruciate ligament in dogs. J Orthop Res 2006; 24:1509-20. [PMID: 16732615 DOI: 10.1002/jor.20183] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This study was done to investigate the microvascular system of anterior cruciate ligament (ACL) using dogs. The objective was to study the microvascular architecture and the status of the barrier function of the capillary wall in the ACL by using microangiogram, scanning (SEM), and transmission electron microscopy (TEM). The vascular system in the ACL has been intensively studied by a number of researchers, using several microangiographic techniques in dogs, rabbits, and humans. However, most of these microangiographic studies had significant shortcomings, including the lack of three-dimensional observations and function of the blood-joint barrier in the ACL. In this study, the microstructure of the ACL was examined using microangiogram, SEM, and TEM. We investigated the vasculature of the ACL with SEM of vascular corrosion casts. In addition, we examined the status of the barrier function of the capillary wall in the ACL using the protein tracer horseradish peroxidase (HRP). Feeding vessels of the ligament were predominantly coming from the synovial-derived vessels originating from the synovium attached to the ligament near the tibial and femoral bone insertions of the ACL. The anterior cruciate ligament was surrounded by synovium, which had abundant vessels. The branches of these synovial vessels were penetrating into the ligament and making the intrinsic vascular network. It was also ascertained under SEM that the perivascular space around the intrinsic vessels were communicating through the intrinsic ligament fiber bundles and the mesh-like synovial membrane. The capillaries in the ACL were all of the continuous type under TEM. The protein tracer that was injected into the joint space passed through the synovial membrane and entered into the capillary lumen in the ACL, but the tracer that was injected intravenously did not appear in the perivascular space. The existence of a blood-ACL barrier does not necessarily imply the existence of an ACL-blood barrier. We think that the blood flow in the ACL is definitely affected by the status of joint fluid and these barriers of endothelium. The clinical relevance of the fine vascular anatomy of the ACL in trauma surgery is considered. This deserves further consideration.
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Affiliation(s)
- Shigeru Kobayashi
- Department of Orthopaedics and Rehabilitation Medicine, Fukui University School of Medicine, Shimoaizuki 23, Matsuoka, Fukui, 910-1193, and Department of Orthopedics, Kawasaki Municipal Hospital, Japan.
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150
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Zhang Z, Fan J, Becker KG, Graff RD, Lee GM, Francomano CA. Comparison of gene expression profile between human chondrons and chondrocytes: a cDNA microarray study. Osteoarthritis Cartilage 2006; 14:449-59. [PMID: 16414292 DOI: 10.1016/j.joca.2005.11.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Accepted: 11/19/2005] [Indexed: 02/02/2023]
Abstract
OBJECTIVE The chondron is a basic unit of articular cartilage that includes the chondrocyte and its pericellular matrix (PCM). This current study was designed to investigate the effects of the chondron PCM on the gene expression profile of chondrocytes. DESIGN Chondrons and chondrocytes were enzymatically isolated from human articular cartilage, and maintained in pellet culture. Pellets of chondrons or chondrocytes were collected at days 1, 3 and 5 for cDNA microarray analysis. RESULTS In comparison with chondrocytes alone, chondrons had 258 genes, in a broad range of functional categories, either up- or downregulated at the three time points tested. At day 1, 26 genes were significantly upregulated in chondrons and four downregulated in comparison to chondrocytes. At day 3, the number of upregulated chondron genes was 97 and the number downregulated was 43. By day 5, there were more downregulated genes (56) than upregulated genes (32) in chondrons. Upregulation of a group of heat shock proteins (HSPA1A, HSPA2 and HSPA8) in chondrons was validated by real time reverse transcription polymerase chain reaction (RT-PCR). Genes related to chondrocyte hypertrophy and dedifferentiation such as SSP1 and DCN were downregulated in chondrons as compared to the expression in chondrocytes. CONCLUSION The presence of the PCM in chondrons has a profound influence on chondrocyte gene expression. Upregulation of the heat shock protein 70 may contribute to the robustness and active matrix production of chondrons. The intact PCM may further stabilize the phenotype of chondrocytes within chondrons.
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Affiliation(s)
- Z Zhang
- Department of Biomedical Engineering, Johns Hopkins University, 3400 N. Charles Street, Clark Hall 102, Baltimore, MD 21218, USA.
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