Down-regulation of peroxisome proliferator-activated receptor γ coactivator-1α expression in fatty acid-induced...

Pancreatic beta-cell apoptosis induced by lipotoxicity, to a large extent, contributes to the progression of type 2 diabetes. To investigate the mechanism of free fatty acid induced apoptosis, we aimed to study the effects of palmitic acid (PA) on the apoptosis and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) expression in βTC3 cells as well as the possible role of nuclear factor-κB (NF-κB) in this process.

Hoechst 33258 was used to detect βTC3 cell apoptosis, which was induced by PA stimulation for 12 hours. PGC-1α expression was analyzed by reverse transcription polymerase chain reaction, IκB kinase β (IKKβ), IκBα, NF-κB-inducing kinase (NIK) and Rel-B expressions were analyzed by Western blotting. MG132 was employed to block the endogenous IκBα degradation before PA administration, and then its effect on PA-inducing cell apoptosis and PGC-1α mRNA expression was analyzed.

Significant increased cell apoptosis was found at the concentration of 0.5 mmol/L and 1.0 mmol/L PA administration. PA (0.5 mmol/L) could extensively reduced the expression of PGC-1α mRNA. After exposing βTC3 cells to 0.5 mmol/L PA for different time periods (0, 4, 6, 8, 10 and 12 hours), IKKβ protein expression increased while IκBα, NIK and Rel-B protein expression declined in a time-dependent manner. Pretreatment with MG132 to inhibit the degradation of IκBα, partially prevented the down-regulation of PGC-1α mRNA expression after 12-hour PA treatment in accordance with the decrease of PA induced apoptosis.

NF-κB canonical pathway was activated in PA-mediated βTC3 cell apoptosis, whereas non-canonical pathway was inhibited. Reduced PGC-1α expression by PA in βTC3 cells could involve the activation of canonical NF-κB pathway, so as to deteriorate the PA induced apoptosis.