Dataset Information

Aggrecan heterogeneity in articular cartilage from patients with osteoarthritis.

ABSTRACT: BACKGROUND:Aggrecan degradation is the hallmark of cartilage degeneration in osteoarthritis (OA), though it is unclear whether a common proteolytic process occurs in all individuals. METHODS:Aggrecan degradation in articular cartilage from the knees of 33 individuals with OA, who were undergoing joint replacement surgery, was studied by immunoblotting of tissue extracts. RESULTS:Matrix metalloproteinases (MMPs) and aggrecanases are the major proteases involved in aggrecan degradation within the cartilage, though the proportion of aggrecan cleavage attributable to MMPs or aggrecanases was variable between individuals. However, aggrecanases were more associated with the increase in aggrecan loss associated with OA than MMPs. While the extent of aggrecan cleavage was highly variable between individuals, it was greatest in areas of cartilage adjacent to sites of cartilage erosion compared to sites more remote within the same joint. Analysis of link protein shows that in some individuals additional proteolytic mechanisms must also be involved to some extent. CONCLUSIONS:The present studies indicate that there is no one protease, or a fixed combination of proteases, responsible for cartilage degradation in OA. Thus, rather than targeting the individual proteases for OA therapy, directing research to techniques that control global protease generation may be more productive.

SUBMITTER: Mort JS

PROVIDER: S-EPMC4758135 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Aggrecan heterogeneity in articular cartilage from patients with osteoarthritis.

Mort John S JS Geng Yeqing Y Fisher William D WD Roughley Peter J PJ

BMC musculoskeletal disorders 20160218

<h4>Background</h4>Aggrecan degradation is the hallmark of cartilage degeneration in osteoarthritis (OA), though it is unclear whether a common proteolytic process occurs in all individuals.<h4>Methods</h4>Aggrecan degradation in articular cartilage from the knees of 33 individuals with OA, who were undergoing joint replacement surgery, was studied by immunoblotting of tissue extracts.<h4>Results</h4>Matrix metalloproteinases (MMPs) and aggrecanases are the major proteases involved in aggrecan d ...[more]

PMID: 26891838

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Project description:BackgroundRheumatoid arthritis (RA) is an autoimmune disease of the synovial joints. The autoimmune character of RA is underscored by prominent production of autoantibodies such as those against IgG (rheumatoid factor), and a broad array of joint tissue-specific and other endogenous citrullinated proteins. Anti-citrullinated protein antibodies (ACPA) can be detected in the sera and synovial fluids of RA patients and ACPA seropositivity is one of the diagnostic criteria of RA. Studies have demonstrated that RA T cells respond to citrullinated peptides (epitopes) of proteoglycan (PG) aggrecan, which is one of the most abundant macromolecules of articular cartilage. However, it is not known if the PG molecule is citrullinated in vivo in human cartilage, and if so, whether citrulline-containing neoepitopes of PG (CitPG) can contribute to autoimmunity in RA.MethodsCitPG was detected in human cartilage extracts using ACPA+ RA sera in dot blot and Western blot. Citrullination status of in vitro citrullinated recombinant G1 domain of human PG (rhG1) was confirmed by antibody-based and chemical methods, and potential sites of citrullination in rhG1 were explored by molecular modeling. CitPG-specific serum autoantibodies were quantified by enzyme-linked immunosorbent assays, and CitPG was localized in osteoarthritic (OA) and RA cartilage using immunohistochemistry.FindingsSera from ACPA+ RA patients reacted with PG purified from normal human cartilage specimens. PG fragments (mainly those containing the G1 domain) from OA or RA cartilage extracts were recognized by ACPA+ sera but not by serum from ACPA- individuals. ACPA+ sera also reacted with in vitro citrullinated rhG1 and G3 domain-containing fragment(s) of PG. Molecular modeling suggested multiple sites of potential citrullination within the G1 domain. The immunohistochemical localization of CitPG was different in OA and RA cartilage.ConclusionsCitPG is a new member of citrullinated proteins identified in human joints. CitPG could be found in both normal and diseased cartilage specimens. Antibodies against CitPG may trigger or augment arthritis by forming immune complexes with this autoantigen in the joints of ACPA+ RA patients.

Project description:Aggrecan degradation in human intervertebral disc and articular cartilage has been studied by using anti-neoepitope antibodies specific for the N-terminal degradation products generated by cleavage within the interglobular domain at the metalloproteinase and aggrecanase sites. Immunoblot analysis of extracts of annulus fibrosus, nucleus pulposus and articular cartilage demonstrated age-related patterns in the abundance of both degradation products. In all three tissues the metalloproteinase-generated fragment was present at very low levels in young individuals but increased in abundance with age. In the disc tissues, the abundance of this degradation product levelled off in the juvenile; for cartilage this occurred in early adulthood. Despite these temporal differences, the levels attained in adults were comparable for the three tissues. In contrast, the aggrecanase-generated degradation product exhibited tissue-specific differences in the variation of its abundance with age. Whereas this degradation product increased with age in annulus fibrosus and articular cartilage and had levelled off by adulthood, in nucleus pulposus it was present in greatest abundance in young individuals and decreased to very low levels with age. Examination of discs exhibiting various degrees of degeneration did not reveal any differences in the levels of the metalloproteinase and aggrecanase-generated cleavage products that could not be accounted for by differences in age. In adults the product of aggrecanase action was much more abundant in articular cartilage than in either of the disc tissues, despite the age-related increase also observed for annulus fibrosus. Analysis of tissue extracts with an antibody recognizing the G1 domain of aggrecan identified two major degradation products whose abundance and size were correlated with the fragments detected by the anti-neoepitope antibodies. Taken together, these results indicate that cleavage at the metalloproteinase and aggrecanase sites are quantitatively important events in aggrecan catabolism in both articular cartilage and intervertebral disc in vivo. Moreover the two enzyme systems act independently and exhibit differences in the degree to which they contribute to aggrecan degradation in these tissues.

Dataset Information

Aggrecan heterogeneity in articular cartilage from patients with osteoarthritis.

Publications

Aggrecan heterogeneity in articular cartilage from patients with osteoarthritis.

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