Activation of PPARα Is Positively Associated with the Upregulation of AMPKα Expression Impaired by Palmitate in INS-1 Beta Cells.

Ying Sun; Ling Gao; Meng Ren; Wei Xin; Jia J. Zhao

Peroxisome proliferator activated receptor alpha (PPARα), as a transcription factor controlling lipid and glucose homeostasis, could be important for the regulation of insulin synthesis and secretion in beta cells. AMP-activated protein kinase (AMPK) is also regarded as a vital regulator for maintaining glucose homeostasis. In the present study, we aimed to elucidate the effects of PPARα activation on AMPKα expression in INS-1 β-cell. INS-1 cells were incubated in the presence and absence of palmitate, treated with and without fenofibrate (PPARα agonist) or MK886 (PPARα antagonist) for 48 hours. Then mRNA content was detected by Real-time PCR and protein expression was monitored by western blotting or immunoprecipitation, respectively. EMSA was performed to measure the binding activity between PPARα and DNA. Results showed that in comparison with untreated control, INS-1 cells exposed to palmitate alone decreased the mRNA level of PPARα by 38%, in turn, lowered PPARα protein expression and its DNA binding activity. A similar slight reduction by 10% in the AMPKα1 gene transcript was observed, but the protein expression of total-AMPKα (T-AMPKα) and phosphorylated-AMPKα (P-AMPKα) showed a marked decrease. By contrast, when cells were treated with palmitate and fenofibrate together, fenofibrate-induced PPARα activation ameliorated these changes impaired by palmitate, and exhibited a significant elevating in PPARα mRNA content by > 61% over the level in the cells with palmitate alone, as well as upregulation in the protein expression and DNA binding activity of PPARα. It is notable that both AMPKα1 and AMPKα2 mRNA levels increased, resulting in the enhanced protein expression of T-AMPKα and P-AMPKα. Furthermore, inhibition of PPARα by MK886 in palmitate-treated cells showed a much more reduction in protein expression of T-AMPKα and P-AMPKα relative to control. In conclusion, our findings suggest that PPARα activation is associated with the upregulation of AMPKα expression impaired by palmitate. It contributes to the autoregulation of maintaining insulin synthesis hemeostasis and glucose metabolism in beta cells.

NUCLEAR receptors (Biochemistry); PROTEIN kinases; PALMITIC acid; PANCREATIC beta cells; INSULIN; GLUCOSE

Diabetes, 2007, Vol 56, pA685

0012-1797

Academic Journal