No description available.

Thèses (M.Sc.)--Université de Sherbrooke (Canada), 1996. / Titre de l'écran-titre (visionné le 26 juin 2008). Publié aussi en version papier.

La tendinopathie calcifiante est une cause fréquente de douleurs d’épaule. Elle est due à des dépôts d’apatite au sein des tendons de la coiffe. Sa physiopathologie est actuellement peu connue. L’objectif de cette thèse était de déterminer les mécanismes impliqués dans la constitution des dépôts et les facteurs régulant cette minéralisation pathologique. L’étude de tondons calcifiés prélevés sur cadavres a montré la présence d’une métaplasie fibro-cartilagineuse autour des dépôts contenant des cellules de type chondrocytaire produisant de la phosphatase alcaline et de l’ENPP1, deux enzymes clé de la minéralisation. In vitro, les ténocytes humains issues de la coiffe des rotateurs ont la capacité de produire des dépôts d’apatite et ceci de manière dépendante de la phosphatase alcaline. Ces cellules sur-exprimaient alors des marqueurs spécifiques des chondrocytes hypertophiques (Collagène de type X, MMP13). L’analyse de poudres calciques prélévées sur des patients souffrant de tendinopathie calcifiante a montré un enrichissement significatif en protéines associées au développement de l’os et du cartilage. Parmi celles-ci, nous avons identifié le Pigment Epithelium Derived Factor (PEDF), connue pour favoriser la minéralisation osseuse. Bien qu’il ait été identifié dans les poudres calciques et les cellules chondrocytaires présentes autour des dépôts, il n’a pas montré d’effet pro-minéralisant in vitro sur les ténocytes humains. / Calcific tendonitis is a frequent cause of shoulder pain. It is due to apatite deposits within the rotator cuff tendons. Its cause is currently poorly known. The objectives of this thesis were to better characterize the cells and mechanisms involved in depositing apatite crystals in human tendons. Histologic sections of cadaveric calcified tendons showed that calcifications were amorphous areas surrounded by a fibrocartilaginous metaplasia containing hypertrophic chondrocyte-like cells that expressed alkaline phosphatase and ENPP1, two key enzymes of the mineralization process. In vitro, tenocytes extracted from human rotator cuff were able to mineralize in an alkaline phosphatase-dependent manner. These cells expressed type X COLLAGEN and MMP13, hypertrophic chondrocytes markers. Finally, analysis of calcific powders extracted from patients suffering from calcific tendonitis showed a significant enrichment of proteins involved in bone and cartilage development. Among them, we identified Pigment Epithelium Derived Factor (PEDF). PEDF is able to promote bone mineralization. While it was identified in calcific powders and chondrocyte-like cells surrounding the deposits, it was not able to increase the mineralisation of human tenocytes in vitro.

No description available.

Little is known about the anti-inflammatory activity of creatine. The aim of this study was to evaluate the anti-inflammatory effects of creatine supplements in canine chondrocytes (CnC). CnC were stimulated with IL-1β. Release of PGE2 and TNFa was measured using ELISA. Changes in oxylipin profile was assessed using HPLC/MS. Expression of COX-2 and phosphorylated NF-kB was performed using western blot. Changes in above inflammatory responses were examined following treatment with various creatine compounds including the metabolite creatinine. COX inhibitor, Rimadyl, substantially reduced PGE2 release, despite increasing both TNFa release and COX-2 expression. All creatine compounds, including creatinine, reduced PGE2, COX-2 and TNFa in stimulated CnC. In addition, all the compounds examined reduced phosphorylated NF-kB expression. The creatine compounds were also able to interfere with the production of several oxylipins in response to IL-1β. Creatine supplements may have a beneficial role in preventing inflammation within the joint and other tissues. / May 2016

A single application of cyclic compression to bioengineered cartilage improves tissue formation through cell shape changes that are mediated by α5β1 integrin and membrane-type metalloprotease (MT1-MMP). To determine if this response is controlled by calcium, we investigated how calcium regulated cell shape changes, MT1-MMP and integrin activity in response to stimulation. Stimulation-induced changes in cell shape and MT1-MMP expression were abolished with chelation of extracellular calcium, and reinstated with its re-introduction. Spreading and retraction were inhibited by blocking the stretch-activated and L-Type voltage-gated channels, respectively; channel blocking also inhibited MT1-MMP upregulation. Channels’ role was confirmed through treatment with calcium A23187 ionophore, which alleviated the effects of channel blocking. Calcium regulated the integrin-mediated signalling pathway, which was facilitated through the kinase Src. Both calcium- and integrin-mediated pathways converged on activating ERK in response to stimulation. Understanding the molecular mechanisms regulating chondrocyte mechanotransduction may lead to the development of improved bioengineered cartilage.

A single application of cyclic compression to bioengineered cartilage improves tissue formation through cell shape changes that are mediated by α5β1 integrin and membrane-type metalloprotease (MT1-MMP). To determine if this response is controlled by calcium, we investigated how calcium regulated cell shape changes, MT1-MMP and integrin activity in response to stimulation. Stimulation-induced changes in cell shape and MT1-MMP expression were abolished with chelation of extracellular calcium, and reinstated with its re-introduction. Spreading and retraction were inhibited by blocking the stretch-activated and L-Type voltage-gated channels, respectively; channel blocking also inhibited MT1-MMP upregulation. Channels’ role was confirmed through treatment with calcium A23187 ionophore, which alleviated the effects of channel blocking. Calcium regulated the integrin-mediated signalling pathway, which was facilitated through the kinase Src. Both calcium- and integrin-mediated pathways converged on activating ERK in response to stimulation. Understanding the molecular mechanisms regulating chondrocyte mechanotransduction may lead to the development of improved bioengineered cartilage.

Chondrocytes in growth cartilage undergo proliferation, hypertrophy, and then die by a mechanism that has not been characterised. The aims of the current study were to document the morphology of dying hypertrophic chondrocytes in equine growth cartilage and to establish a culture system in which the isolated chondrocytes can be induced to undergo the same modes of hypertrophy and physiological death seen in growth cartilage in vivo. Growth cartilage from foetal and growing postnatal horses was examined by electron microscopy. Ultrastructural studies of the tissue specimens suggested that the two types of hypertrophic chondrocytes that have previously been described as dark and light cells were dying by different non-apoptotic forms of cell death. Dying hypertrophic dark chondrocytes were characterised by a dark nucleus, and their cytoplasm appeared to undergo extrusion into the extracellular matrix, whereas light chondrocytes appeared to disintegrate within the cell membrane.

No description available.

In vitro grown cartilage is functionally inferior to native tissue, and improvements in its quality should be attempted so it can be used therapeutically. In these studies we investigated the effects of cell shape on tissue quality through alteration of substrate geometry and application of mechanical stimuli. Articular chondrocytes were isolated and cultured on the surface Ti-6Al-4V substrates with various geometries. When cultured on fully porous titanium alloy substrates, chondrocyte spreading was enhanced over those grown on substrates with solid bases. Chondrocytes which remained round did not synthesize significant amounts of matrix and were thus unable to form cartilaginous tissue. In contrast, chondrocytes which were directed to spread to a limited amount, resulting in a polygonal morphology, accumulated significantly more matrix molecules and in time formed cartilage-like tissue. Computational fluid dynamics analyses demonstrated that cells on fully porous substrates experience time-dependent shear stresses that differ from those experienced by cells on substrates with solid bases where media flow-through is restricted. Integrin-blocking experiments revealed that integrins are important regulators of cell shape, and appeared to influence the accumulation of collagen and proteoglycans by chondrocytes. Furthermore, compressive mechanical stimulation induced a rapid, transient increase in chondrocyte spreading by 10 minutes, followed by a retraction to pre-stimulated size within 6 hours. This has been shown to be associated with increased accumulation of newly synthesized proteoglycans. Blocking the α5β1 integrin, or its β1 subunit, inhibited cell spreading and resulted in a partial inhibition of compression-induced increases in matrix accumulation, thereby substantiating the role of β1 integrins in this process. These results suggest that both fluid induced shear forces and compressive forces regulate chondrocyte matrix accumulation by altering cell morphology, which is mediated by integrins. Identifying the molecular mechanisms that influence chondrocyte shape and thus tissue formation may ultimately lead to the development of a tissue that more closely resembles native articular cartilage.