Activation of fibrillar collagen synthesis and phenotypic modulation of chondrocytes in early human osteoarthritic cartilage lesions

Objective. To study age-related (as opposed to arthritis-related) changes in collagen and proteoglycan turnover.Methods. Macroscopically nondegenerate normal ankle cartilage obtained from 30 donors (ages 16-75 years) was processed for in situ hybridization to detect messenger RNA (mRNA) of type IIB collagen (CIIB); antibodies to the C-propeptide of type II collagen (CPII), to the type II collagen (CII) collagenasegenerated cleavage neoepitope (Col2-3/4C short ), and to the CII denaturation product (Col2-3/4m) were used for immunohistochemistry analysis and immunoassay. In addition, immunoblotting was used to detect the 4 collagenases. Assays were also performed to detect glycosaminoglycan (GAG) content and the 846 epitope of aggrecan.Results. There were no significant changes in CII, GAG, and the content of the 846 epitope after the age of 30 years. Both mRNA for CIIB and the CPII were present in all zones, and CPII content did not change significantly with age. While the collagenase-cleaved CII showed a trend to increase with age, the denatured collagen did not. However, the molar ratio of cleaved versus denatured collagen was positively correlated with age. All 4 collagenases were detectable in the ankle cartilage but showed no identifiable changes in content with age.Conclusion. Synthesis and degradation of CII is associated with the pericellular matrix and is maintained at a steady state throughout life. The contents of CII and proteoglycan did not change. There was a significant reduction in the denaturation of CII with age, relative to collagenase-mediated cleavage. These observations reveal that, in aging of the intact ankle articular cartilage, there is no evidence of molecular degenerative changes of the kind observed in osteoarthritis, thereby distinguishing aging from the osteoarthritis process.The talar cartilages from the talocrural joint of the ankle offer opportunities for studying age-related changes in articular cartilage. We have shown that in a population of 470 adult organ donors (21-74 years of age), ϳ62% of the talar cartilages exhibited no macroscopic signs of degenerative changes often seen increasingly with age in other joints, such as the knee (1). Thus, samples from different donors can be studied with greater assurances that changes are associated with aging of the cartilage rather than with degenerative changes. Other advantages of using the ankle cartilages for studies of aging are that the talar cartilage is more uniform in thickness (1-2 mm [2]), representing a more consistent ratio of superficial to deep chondrocytes, and the talar cartilage is more uniform in stiffness (3,4).While degenerative changes and osteoarthritis (OA) do develop in the ankle (5), it is rare (6) compared with other joints, such as the knee. Our studies reveal that there are differences between the normal articular cartilages of the knee and ankle joints that may, in part, help to explain the differences in susceptibility to OA. Ankle cartilage is less responsive to catabolic stimulation by either fibronect...

Section: Discussionmentioning

confidence: 99%

Matrix homeostasis in aging normal human ankle cartilage

Aurich¹,

Poole²,

Reiner³

et al. 2002

“…Current hypotheses to explain the changes in OA chondrocytes include the notion that phenotypic alterations of the cells occur in response to changing signals or matrix composition (10)(11)(12)(13). It is well known that chondrocytes can adopt different phenotypes, including those associated with the growth plate (resting, proliferating, hypertrophic), those associated with the different zones of AC, and the dedifferentiated phenotype observed in monolayer culture (3,7,13,17).…”

Section: Discussionmentioning

confidence: 99%

“…These studies have shown that a major change in the chondrocyte phenotype in OA involves a switch in the types of collagen molecules that are synthesized. Clusters of chondrocytes in OA cartilage have been shown to express types I and III collagens, which are not normally found or found at very low levels in normal AC (10,12,(69)(70)(71).…”

Section: Discussionmentioning

confidence: 99%

“…These changes in the biosynthetic profile of dedifferentiated chondrocytes resemble some of the phenotypic changes displayed by OA chondrocytes, and the matrix they produce is similar to that synthesized by chondroprogenitor cells (7)(8)(9)(10)(11)(12)(13)17,(37)(38)(39)(40). However, the mechanisms responsible for the phenotypic instability of chondrocytes and the regulation of these different chondrocyte-specific phenotypes remain poorly understood.…”

mentioning

confidence: 91%

“…The chondro-cyte response may lead, in certain situations, to longterm changes in the phenotype of the cell, and therefore to an inability to properly repair or maintain the cartilage ECM (4). This is exemplified by the phenotypic changes in the patterns of production or in the temporal or spatial distribution of the synthesis of interstitial collagens, fibroblast-type proteoglycans, and production of ECM proteins associated with fetal development that occur during the development of osteoarthritis (OA), dedifferentiation in culture, or in response to certain types of cartilage injury (6)(7)(8)(9)(10)(11)(12)(13).…”

mentioning

confidence: 99%

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Assessment of the gene expression profile of differentiated and dedifferentiated human fetal chondrocytes by microarray analysis

Stokes¹,

Liu²,

Coimbra³

et al. 2002

152

106

Objective. To study the changes in patterns of gene expression exhibited by human chondrocytes as they dedifferentiate into fibroblastic cells in culture in order to better understand the mechanisms that control this process and its relationship to the phenotypic changes that occur in chondrocytes during the development of osteoarthritis (OA).Methods. Human fetal epiphyseal chondrocytes (HFCs) were cultured either on poly-(2-hydroxyethyl methacrylate)-coated plates (differentiated HFC cultures) or in plastic tissue culture flasks as monolayers (dedifferentiated HFC cultures). Following 11 days of culture under either condition, poly(A؉) RNA was isolated from the two cell populations and subjected to a gene expression analysis using a microarray containing ϳ5,000 known human genes and ϳ3,000 expressed sequence tags (ESTs).Results. A >2-fold difference in the expression of 62 known genes and 6 ESTs was observed between the two cell types. The differences in expression of several of the genes detected by the microarray hybridization were confirmed by Northern analyses. Two transcription factor genes, TWIST and HIF-1␣, and a cellular adhesion protein gene, cadherin 11, were markedly regulated in response to differentiation and dedifferentiation. Expression of these genes was also detected in adult normal and OA cartilage and chondrocytes. Analysis of the gene expression profile of HFCs revealed a complex pattern of gene expression, including many genes not yet reported to be expressed by chondrocytes.Conclusion. Chondrocytes in monolayer become dedifferentiated, acquiring a fibroblast-like appearance and changing their pattern of gene expression from one of expression of chondrocyte-specific genes to one that resembles a fibroblastic or chondroprogenitor-like pattern. Changes in gene expression associated with the process of dedifferentiation of HFCs in vitro were observed in a wide variety of genes, including genes encoding extracellular matrix proteins, transcription factors, and growth factors. At least 3 of the genes that were regulated in response to dedifferentiation were also found to be expressed in adult normal and OA articular cartilage and chondrocytes.

Severe disturbance of the distribution and expression of type VI collagen chains in osteoarthritic articular cartilage

Hambach

Neureiter

Zeiler³

et al. 1998

Objective. The aim of this study was to evaluate the messenger RNA (mRNA) expression and distribution of the major pericellular type VI collagen in normal and osteoarthritic (OA) cartilage.Methods. Conventional and confocal laser scanning immunohistochemistry, as well as in situ hybridization experiments, were performed for all 3 collagen type VI chains in sections of normal and OA articular cartilage.Results. individual microfibrillar network in virtually all connective tissues (1-4). In hyaline articular cartilage, type V1 collagen has thus far been described in the immediate pericellular matrix (5-8), and is therefore an integral component of the chondron, the functional unit of the articular cartilage (9,lO). This local restriction is the main reason why type VI collagen represents only a small portion (<2%) of all cartilage collagens (11).The composition of the pericellular matrix of articular chondrocytes is different in many respects from that of the territorial and interterritorial cartilage matrix. Thus, besides type VI collagen, it contains increased amounts of specifically composed proteoglycans (1 2), other collagens such as types IX (13) and XI (14), and noncollagenous components (15). The function of type VI collagen in articular cartilage is still unclear, but it is likely to be different from that in other connective tissues, where it is not associated with cells. Type VI collagen has been shown to bind to integrins of the chondrocyte membrane, though the exact interaction remains unclear (16,17). Additionally, type VI collagen binds to other proteins of the pericellular matrix, such as other collagens, decorin, fibromodulin, hyaluronan, and fibronectin (18)(19)(20). Thus. type VI collagen might act as an interface between the rigid interterritorial cartilage matrix and the chondrocyte, and is presumably involved in cell anchoring as well as matrix-cell signaling (21).The hallmark of osteoarthritic (OA) cartilage degeneration is the destruction and, finally, the erosion of the extracellular cartilage matrix. This implies degradation, as well as increased synthesis, of cartilage matrix components. Most investigations so far have analyzed the biochemistry of the major components of the interterritorial cartilage matrix, and many data have accumulated about synthesis and degradation of, for example, type I1 collagen and aggrecan (22)(23)(24)(25). Much less attention has been given to the changes in the pericellular matrix and its turnover by the chondrocytes. Poole et a1