SIRT1 regulates TNF-α-induced expression of CD40 in 3T3-L1 adipocytes via NF-κB pathway

Sirtuin1 (SIRT1), a NAD(+)-dependent deacetylase, not only regulates lipid and glucose homeostasis, but also involves the regulation of proinflammatory cytokine involved in inflammation-associated diseases. The activation of CD40 triggers inflammation that plays a crucial role in the development of many chronic inflammatory diseases including obesity. Growing evidence indicated that SIRT1 exerts anti-inflammatory properties by suppressing proinflammatory cytokines production. However, the effect of SIRT1 on the expression of CD40 in adipocytes has not yet been fully elucidated. The present study showed that SIRT1 expressed both in the nucleus and cytoplasm of 3T3-L1 adipocytes. TNF-α significantly reduced the expression of SIRT1 mRNA and protein and increased the expression of CD40 mRNA and protein in time- and concentration-dependent manners. Overexpression of SIRT1 or SIRT1 activation by resveratrol obviously attenuated the expression of CD40 induced by TNF-α in 3T3-L1 adipocytes, whereas knockdown of SIRT1 or SIRT1 inhibition by nicotinamide and sirtinol significantly enhanced TNF-α-induced expression of CD40. Furthermore, overexpression of SIRT1 or SIRT1 activation by resveratrol diminished TNF-α-induced acetylation of NF-κBp65, while knockdown of SIRT1 or SIRT1 inhibition by nicotinamide and sirtinol augmented TNF-α-induced acetylation of NF-κBp65 in 3T3-L1 adipocytes. NF-κB inhibitor PDTC reduced TNF-α-induced mRNA and protein expression of CD40 in 3T3-L1 adipocytes. The combination treatment of resveratrol and PDTC significantly reduced TNF-α-induced expression of CD40, and the inhibitory effects were higher than that of the single treatment. Taken together, SIRT1 exerts anti-inflammatory property by regulating TNF-α-induced expression of CD40 partially through the NF-κB pathway in 3T3-L1 adipocytes. More importantly, the regulation of SIRT1 on the expression of CD40 provides new insight to understand the anti-inflammatory effects of SIRT1.