MMP13 and synovitis: The present study aimed to determine the relative expression (either down- or upregulation) of some proinflammatory (NFκB, MMP-13, and ADAMTS-4) and anabolic (COL1A1, COL2A2, and COMP) genes implicated in OA pathophysiology in an in vitro system of equine synovitis, in which two different PRG supernatants at concentrations of 25% and 50% were evaluated.