AMP-Activated Protein Kinase Activity Is Altered by Changes in Redox State in HepG2 Cells by a SIRT1-Dependent Mechanism.

Suchankova, Gabriela; Saha, Asish K.; Ido, Yasuo; Ruderman, Neil B.

AMPK can be activated by mechanisms that do not involve changes in cellular energy state. For instance, incubation of rat EDL muscle with a high glucose concentration for 2-4 hours decreases AMPK activity in the absence of changes in ATP or AMP. The observation that lactate release was increased in these muscles suggests that an alteration in redox potential may be involved. Recently, it has been demonstrated that increasing the concentration of glucose diminishes AMPK activity and the abundance of SIRT1, an NAD-dependent histone deacetylase in Hep G2 cells. To address whether these changes are redox mediated, cultured HepG2 cells were incubated for 2, 6, and 24 hr with 1 or 10 mM pyruvate or 1, 10, or 50 mM lactate. Increasing the concentration of pyruvate resulted in enhanced phosphorylation of AMPK (p-AMPK) and ACC (p-ACC), and an increased abundance of SIRT1 at both 2 and 6 hr. Conversely, increasing the concentration of lactate suppressed p-AMPK and SIRT1 abundance at 2 hr. Finally, we examined the effects of resveratrol and quercetin, agents known to enhance SIRT1 activity, on AMPK activity. Resveratrol, a polyphenol found in red wine, enhanced p-AMPK in a dose and time-dependent manner, as did quercetin, a flavonoid that reduces the βhydroxybutyrate to acetoacetate ratio, an indicator of the mitochondrial NADH/NAD redox ratio. Finally, none of the tested compounds (pyruvate, lactate and resveratrol) altered adenine nucleotide levels. Collectively, these findings suggest that AMPK can be regulated by changes in the redox potential in cultured HepG2 cells, very likely in response to changes in SIRT1. Studies in which SIRT1 is deleted are needed to confirm this mechanism. ADA-Funded Research

PROTEIN kinases; CELLS; GLUCOSE; ADENOSINE triphosphate; ADENOSINE monophosphate; HISTONES

Diabetes, 2007, Vol 56, pA394

0012-1797

Academic Journal