The Anti‐Lipolytic Effects of Acute AICAR‐Induced AMPK Activation in Visceral and Subcutaneous Rat Adipose Tissue is Independent of HSL Phosphorylation on Serine 563 and 660 Residues

Abstract

AICAR‐induced AMP‐activated protein kinase (AMPK) activation suppresses basal and epinephrine‐stimulated lipolysis in adipocytes. Our goal was to investigate whether the anti‐lipolytic effects of AICAR‐induced AMPK activation are mediated via inhibition of hormone sensitive lipase (HSL). Isolated rat epididymal (Epi), retroperitoneal (Ret), and subcutaneous (Sc) adipocytes were acutely (1h) incubated either in the absence or presence of AICAR (10 – 500μM), under basal and epinephrine (10μM) stimulated conditions. The lipolytic response and the phosphorylation status of HSL on Ser563 and Ser660 were determined. AICAR treatment significantly inhibited basal (77%, 31%, and 80%) and epinephrine stimulated (84%, 68%, and 86%) lipolysis in Epi, Ret, and Sc adipocytes, respectively. HSL phosphorylation on both serine residues was unaffected by AICAR under basal and epinephrine stimulated conditions. Interestingly, pharmacological inhibition of AMPK increased basal and epinephrine‐stimulated lipolysis and also reversed the anti‐lipolytic effect of low (10–100μM) AICAR concentrations. Even though lipolysis was increased by the AMPK inhibitor; HSL phosphorylation was not modified. These data indicate that the anti‐lipolytic effects of AICAR‐induced AMPK activation is independent of HSL phosphorylation, and appears to occur downstream of this enzyme. Funding was provided by NSERC, CIHR and CDA.