Prolonged AICAR-induced AMP-kinase activation promotes energy dissipation in white adipocytes: novel mechanisms integrating HSL and ATGL.

This study was designed to investigate the effects of prolonged activation of AMP-activated protein kinase (AMPK) on lipid partitioning and the potential molecular mechanisms involved in these processes in white adipose tissue (WAT). Rat epididymal adipocytes were incubated with 5'-aminoimidasole-4-carboxamide-1-beta-d-ribofuranoside (AICAR;0.5 mM) for 15 h. Also, epididymal adipocytes were isolated 15 h after AICAR was injected (i.p. 0.7 g/kg body weight) in rats. Adipocytes were utilized for various metabolic assays and for determination of gene expression and protein content. Time-dependent in vivo plasma NEFA concentrations were determined. AICAR treatment significantly increased AMPK activation, inhibited lipogenesis, and increased FA oxidation. This was accompanied by upregulation of peroxisome proliferator-activated receptor (PPAR)alpha, PPARdelta, and PPARgamma-coactivator-1alpha (PGC-1alpha) mRNA levels. Lipolysis was first suppressed, but then increased, both in vitro and in vivo, with prolonged AICAR treatment. Exposure to AICAR increased adipose triglyceride lipase (ATGL) content and FA release, despite inhibition of basal and epinephrine-stimulated hormone-sensitive lipase (HSL) activity. Here, we provide evidence that prolonged AICAR-induced AMPK activation can remodel adipocyte metabolism by upregulating pathways that favor energy dissipation versus lipid storage in WAT. Additionally, we show novel time-dependent effects of AICAR-induced AMPK activation on lipolysis, which involves antagonistic modulation of HSL and ATGL.