Tumor necrosis factor α (TNFα) is a well-known mediator of inflammation in the context of obesity in adipose tissue. Its action appears to be directly linked to perturbations of the insulin pathway, leading to the development of insulin resistance. Visfatin has been suspected to be linked to insulin sensitivity, but the mechanism involved is still partly unknown. The aim of this study was to evaluate the role of visfatin in the impairment of the insulin pathway by TNFα activity in 3T3-L1 adipocytes and to unveil the mechanisms involved in such impairment. We demonstrated in 3T3-L1 adipocytes that visfatin was involved in TNFα-mediated insulin resistance in adipocytes. Indeed, after TNFα treatment in 3T3-L1 cells, visfatin was downregulated, leading to decreased nicotinamide adenine dinucleotide (NAD(+)) concentrations in cells. This decrease was followed by a decrease in Sirt1 activity, which was linked to an increase in PTP1B expression. The modulation of PTP1B by visfatin was likely responsible for the observed decreases in glucose uptake and Akt phosphorylation in 3T3-L1 adipocytes. Here, we demonstrated a complete pathway involving visfatin, NAD(+), Sirt1, and PTP1B that led to the perturbation of insulin signaling by TNFα in 3T3-L1 adipocytes.
Keywords: NAD; TNF; adipocytes; insulin resistance; sirtuin; visfatin.