Chondrocytes are the main cells in the extracellular matrix (ECM) of articular cartilage and possess a highly differentiated phenotype that is the hallmark of the unique physiological functions of this specialised load-bearing connective tissue. The plasma membrane of articular chondrocytes contains a rich and diverse complement of membrane proteins, known as the membranome, which defines the cell surface phenotype of the cells. The membranome is a key target of pharmacological agents and is important for chondrocyte function. It includes channels, transporters, enzymes, receptors, and anchors for intracellular, cytoskeletal and ECM proteins and other macromolecular complexes. The chondrocyte channelome is a sub-compartment of the membranome and includes a complete set of ion channels and porins expressed in these cells. Many of these are multi-functional proteins with “moonlighting” roles, serving as channels, receptors and signalling components of larger molecular assemblies. The aim of this review is to summarise our current knowledge of the fundamental aspects of the chondrocyte channelome, discuss its relevance to cartilage biology and highlight its possible role in the pathogenesis of osteoarthritis (OA). Excessive and inappropriate mechanical loads, an inflammatory micro-environment, alternative splicing of channel components or accumulation of basic calcium phosphate crystals can result in an altered chondrocyte channelome impairing its function. Alterations in Ca2+ signalling may lead to defective synthesis of ECM macromolecules and aggravated catabolic responses in chondrocytes, which is an important and relatively unexplored aspect of the complex and poorly understood mechanism of OA development. 相似文献
The aim of this study was to evaluate the potential for restoration of a large cartilage defect in the goat knee with hydroxyapatite (HA) loaded with chondrocytes. Isolated chondrocytes were suspended in fibrin glue, seeded on top of the HA, and then the composite graft was implanted in the defect. After transplantation, cell behaviour, newly synthesised matrix and the HA–glue interface were assessed histologically after 2, 4, 12, 26 and 52 weeks. Special attention was paid to the incorporation process of HA in the subchondral bone and interactions between this biomaterial and the fibrin-glue–chondrocyte suspension.
Chondrocytes in the glue proved to survive the transplantation procedure and produced new metachromatically stained matrix two weeks after implantation. The glue–cell suspension had penetrated the superficial porous structure of the HA. Four weeks after surgery, islands of hyaline-like cartilage were observed at the HA–glue interface. A layer of fibrous tissue was formed surrounding the HA graft, resulting in a relatively instable fixation of the HA in the defect. This instability of the graft in the defect, possibly together with early weight bearing, resulted in a gradual loss of the newly formed hyaline cartilage-like repair tissue. Progressive resorption of the HA occurred without any sign of active bone remodelling from the host site. One year after surgery part of the defect which extended down to the cancellous bone had been predominantly restored with newly formed lamellar bone. Only small HA remnants were still present at the bottom of the original defect. Resurfacing of the joint had occurred with fibrocartilaginous repair tissue.
The absence of adequate fixation capacity of the HA near the joint space resulted in a relative instability of the graft with progressive resorption. Therefore, HA is not a suitable biomaterial to facilitate the repair of large articular cartilage defects. 相似文献
Extracellular matrix vesicles (MVs) are associated with initial calcification in a variety of tissues, but the mechanisms
by which they promote mineralization are not certain. In this study, MVs isolated from fourth passage rat growth plate chondrocyte
cultures were included within a gelatin gel into which calcium and phosphate ions diffused from opposite ends. In this gel,
apatite formation occurs by 3.5 days in the absence of mineralization promoters, allowing measurement of the ability of different
factors to ``nucleate' apatite before this time or to assess the effects of molecules which modulate the rate and extent
of mineral deposition. Mineral ion accumulation and crystal type are assayed at 5 days. In this study, MV protein content
in the central band of a 10% gelatin gel was varied by including 100 μl of a Tris-buffered solution containing 0–300 μg/ml
MV protein. There was a concentration-dependent increase in mineral accretion. Whereas 10 μg MV protein in the gel did not
significantly promote apatite formation as compared with vesicle-free gels, 20 and 30 μg MV protein in the gel did promote
apatite deposition. Inclusion of 10 mM β-glycerophosphate in the gels, along with MVs, did not significantly increase apatite
formation despite the demonstrable alkaline phosphatase activity of the MVs. In contrast, MVs at all concentrations significantly
increased apatite accumulation when proteoglycan aggregates or ATP, inhibitors of apatite formation and proliferation, were
included in the gel. Slight increases in calcium, but not phosphate accumulation, were also noted when an ionophore was included
with the MVs to facilitate Ca ion transport into the vesicles. FT-IR analysis of the mineral formed in the vesicle-containing
gels revealed the presence of a bone-like apatite. These data suggest that MVs facilitate mineralization by providing enzymes
that modify inhibitory factors in the extracellular matrix, as well as by providing a protected environment in which mineral
ions can accumulate.
Received: 28 January 1996 / Accepted: 9 August 1996 相似文献
Summary This study examined the presence of extracellular matrix processing enzymes in matrix vesicles produced by rat costochondral resting zone and growth zone chondrocytes in culture. Optimum procedures for the extraction of each enzyme activity were determined. Enzyme activity associated with chondrocyte plasma membrane microsomes was used for comparison. There was a differential distribution of the enzyme activities related to the cartilage zone from which the cells were isolated. Acid and neutral metalloproteinase (TIMP), plasminogen activator, and betaglucuronidase were highest in the growth zone chondrocyte (GC) membrane fractions when compared with matrix vesicles and plasma membranes isolated from resting zone chondrocyte (RC) cultures. There was a threefold enrichment of total and active acid metalloproteinase in GC matrix vesicles, whereas no enrichment in enzyme activity was observed in RC matrix vesicles. Total and active neutral metalloproteinase were similarly enriched twofold in GC matrix vesicles. TIMP, plasminogen activator, and betaglucuronidase activities were highest in the plasma membranes of both cell types. No collagenase, lysozyme, or hyaluronidase activity was found in any of the membrane fractions. The data indicate that matrix vesicles are selectively enriched in enzymes which degrade proteoglycans. The highest concentrations of these enzymes are found in matrix vesicles produced by growth zone chondrocytes, suggesting that this may be a mechanism by which the more differentiated cell modulates the matrix for calcification. 相似文献
Pellets formed from isolated bovine growth plate chondrocytes were grown in various capacitively coupled electrical fields. The signals chosen were 0, 10, 100, 250, 500, 750, 1,000, and 1,500 V peak-to-peak, 60 kHz. The effect on cell proliferation and matrix production of these different voltages was determined by [3H]thymidine and [35S]sulfate uptake, respectively, Cyclic AMP assays were done to determine if increases in either thymidine or sulfate uptake were associated with changes in cAMP levels. Significantly increased cell proliferation occurred at 500, 750, and 1,000 V peak to peak. The calculated electric fields were 1.5 to 3.0 x 10(-2) V/cm. Proliferation was significantly inhibited at 1,500 V peak-to-peak with a calculated field of 4.5 x 10(-2) V/cm. Little if any change was seen in cAMP levels at 30 or 60 min following application of the appropriate electric signals. 相似文献