Aggrecan is degraded by Aggrecanases (ADAMTS-4 and -5) and MMPs, which cleave its core protein at different sites. Transforming growth factor (TGF)beta is known to stimulate matrix formation in cartilage, and ADAMTS-4 production in synoviocytes. The aim of this in-vitro study was to examine the effects of TGFbeta on aggrecanase production in human cartilage.
Expression of ADAMTS-4 and -5 in chondrocyte cultures from normal or osteoarthritic cartilage was studied at mRNA level by RT-PCR. Aggrecanase activity was examined by western blot of aggrecanase-generated neoepitope NITEGE, and by measure of proteoglycan degradation in cartilage explants.
TGFbeta strongly increased mRNA levels of ADAMTS-4, while ADAMTS-5 was expressed in a constitutive way in chondrocytes from normal and osteoathritic cartilage. TGFbeta also increased NITEGE levels and proteoglycan degradation. Addition of an aggrecanase inhibitor blocked the increase of NITEGE, and partially inhibited proteoglycan degradation.
TGFbeta stimulates ADAMTS-4 expression and aggrecan degradation in cartilage. This catabolic action seems to be partially mediated by aggrecanases. It is, therefore, proposed that the role of TGFbeta in cartilage matrix turnover is not limited to anabolic and anti-catabolic actions, but also extends to selective degradation of matrix components such as aggrecan.