Conventional progesterone receptors (PR) B and PRA are expressed by human chondrocytes and can be involved in the pathogenesis of osteoarthritis.

To evaluate the expression, location and role of progesterone receptors (PRs) A and B in human chondrocytic cell lines, Western blotting, real time PCR analyses, transmission electron microscopy and immunogold assays were performed. By transfection and co-transfection assays, the influence of progesterone (OHPg) on estrogen receptor alpha (ERα) promoter activity was investigated. MTT and pAKT documented OHPg effects on chondrocytes survival. The PR-B and PR-A were both observed in human chondrocytes. The PR-B was evidenced both in the nucleus and in the cytosol of the cells. OHPg, through PR-B, induced ERα expression by acting at the ER promoter level affecting chondrocytes survival. We reported for the first time the expression of PRs in human chondrocytes. Interestingly, we described a novel mechanism via progesterone induction of ERα, which may explain, at least in part, the dramatic rise in OA prevalence among postmenopausal women.