Nicotine-induced activation of AMP-activated protein kinase inhibits fatty acid synthase in 3T3L1 Adipocytes - A role for oxidant stress (Publication with Expression of Concern. See vol. 294, pg. 10025, 2019) (Withdrawn Publication. See vol. 295, pg. 667, 2020)

Recent studies suggest that the AMP-activated protein kinase ( AMPK) acts as a major energy sensor and regulator in adipose tissues. The objective of this study was to investigate the role of AMPK in nicotine-induced lipogenesis and lipolysis in 3T3L1 adipocytes. Exposure of 3T3L1 adipocytes to smoking-related concentrations of nicotine increased lipolysis and inhibited fatty acid synthase ( FAS) activity in a time-and dose-dependent manner. The effects of nicotine on FAS activity were accompanied by phosphorylation of both AMPK ( Thr(172)) and acetyl-CoA carboxylase ( ACC; Ser(79)). Nicotine-induced AMPK phosphorylation appeared to be mediated by reactive oxygen species based on the finding that nicotine significantly increased superoxide anions and 3-nitrotyrosine positive proteins, exogenous peroxynitrite( ONOO (-)) mimicked the effects of nicotineon AMPK, and N-acetylcysteine( NAC) abolished nicotine-enhanced AMPK phosphorylation. Inhibition of AMPK using either pharmacologic ( insulin, compound C) or genetic means ( overexpression of dominant negative AMPK; AMPK-DN) abolished FAS inhibition induced by nicotine or ONOO (-). Conversely, activation of AMPK by pharmacologic ( nicotine, ONOO (-), metformin, and AICAR) or genetic ( overexpression of constitutively active AMPK) means inhibited FAS activity. Notably, AMPK activation increased threonine phosphorylation of FAS, and this effect was blocked by adenovirus encoding dominant negative AMPK. Finally, AMPK-dependent FAS phosphorylation was confirmed by P-32 incorporation into FAS in adipocytes. Taken together, our results strongly suggest that nicotine, via ONOO (-), activates AMPK, resulting in enhanced threonine phosphorylation and consequent inhibition of FAS.