Knockdown of LKB1 in articular chondrocytes attenuates AMPK activity and promotes matrix catabolic responses. Human primary normal knee articular chondrocytes were transfected with liver kinase B1 (LKB1) and control siRNA. Two days after transfection, cells were either (A) used directly for western blot analysis of LKB1 expression or (B) treated with IL-1β (10 ng/ml) and TNFα (10 ng/ml) for 18 hours followed by western blot analysis for phosphorylation of AMP-activated protein kinase alpha (AMPKα) and total AMPKα. (C) Nitric oxide (NO) release, (D) matrix metalloproteinase (MMP)-3 release and (E) MMP-13 release were then analyzed from the conditioned media by Griess reaction and ELISA, respectively. Data representative of three individual experiments. *P <0.001, **P <0.01, #P <0.05 relative to the control (Ctrl).