Figure 2.

Reduction in SirT1 activity in human chondrocytes treated with TNFα. A, Outline of SirT1 and the regions detected by the N-terminal (NTerm)–specific and C-terminal (CTerm)–specific antibodies (Ab). B, Immunoblot of protein extracts from chondrocytes left untreated (Unt) or treated with TNFα with the N-terminal antibody (left) and the C-terminal antibody (right). C, SirT1 activity in chondrocytes left untreated or treated with TNFα after immunoprecipitation with a SirT1 N-terminal antibody. SirT1 was immunoprecipitated from chondrocytes, and the immunoprecipitates were processed for SirT1 activity (top) or for immunoblotting (IB; bottom). Immunoblots in B and C are representative of 6 repetitions. D, Intracellular NAD levels in chondrocyte extracts left untreated or treated with TNFα. E, Relative RNA levels in chondrocytes left untreated or treated with TNFα, determined by qPCR with the indicated human primers. Bars show the mean ± SD. * = P < 0.05 versus untreated controls. FL SirT1 = full-length SirT1 (see Figure 1 for other definitions).