Effects of SOCS1 overexpression on MMPs and ADAMTS4 expression in primary human articular chondrocytes (HACs). HACs were electrotransfected with pShuttle-SOCS1 or empty vectors to overexpress SOCS1, as described in Methods. In the SOCS1-overexpressing HACs, IL-1β (10 ng/ml) induced MMPs and ADAMTS4 mRNA expression (white bars). Their expression was significantly lower by SOCS1 over-expressing (hatched bars). Data were expressed as the mean ± SEM (n = 4). *P < 0.005; †P < 0.05 by Wilcoxon signed-rank test.