MMP-9/gelatinase B is a gene product of human adult articular chondrocytes and increased in osteoarthritic cartilage.

OBJECTIVE Collagen fibril degeneration involves initially the cleavage within the triple helix by the collagenases 1 (MMP-1) and 3 (MMP-13), but then mainly involves also the gelatinases A (MMP-2) and B (MMP-9). The objective of this study was to determine the quantitative expression levels as well as the distribution in normal and osteoarthritic cartilage of gelatinase B and in cultured articular chondrocytes with and without stimulation by Il-1Beta. METHODS Conventional and real-time quantitative PCR technology and immunohistochemistry were used to determine gelatinase B expression on the mRNA and protein level. RESULTS Conventional PCR analysis could demonstrate the presence of gelatinase B mRNA only in osteoarthritic chondrocytes. Real-time quantitative PCR confirmed the increased expression of gelatinase B mRNA expression in osteoarthritic chondrocytes. No significant up-regulation of gelatinase B was observed by Il-1Beta. Immunostaining for gelatinase B showed the presence of gelatinase B in a subset of normal and in a large portion of osteoarthritic chondrocytes with a more extended distribution in the latter. CONCLUSION In osteoarthritic cartilage destruction, gelatinase B is involved in collagen destruction though still at a very much lower level than gelatinase A. Only a very small subset of normal adult articular chondrocytes express gelatinase B in vivo suggesting that gelatinase B unlike gelatinase A is hardly or only very focally involved in physiological collagen turnover.