The secretion of the tissue inhibitor of metalloproteinases (TIMP) by human synovial fibroblasts is modulated by all-trans-retinoic acid.

The matrix metalloproteinases are a family of enzymes involved in the turnover of the connective tissues. The regulation of these enzymes is complex, involving the control of synthesis, the activation of proenzyme forms and the presence of specific inhibitors. Retinoids have been reported to inhibit the production of metalloproteinases by human and rabbit synovial fibroblasts and by human skin fibroblasts. The production of the highly specific tissue inhibitor of metalloproteinases (TIMP) by connective tissue cells may be crucial in the regulation of connective tissue breakdown and this present study was undertaken to determine if retinoic acid (RA) could modulate TIMP and collagenase production by synovial fibroblasts. The results show that RA at concentrations from 10(-7) to 10(-5) M significantly stimulated the secretion of TIMP by two of three human synovial cell lines. The effect of mononuclear cell factor (MCF) on TIMP and collagenase levels was also investigated. The apparent reduction of collagenase levels in the presence of RA, could result from a failure to accurately measure this enzyme in the presence of increased levels of TIMP.