Figure 4.

Chronic exposure to palmitic acid treatment induces cell cyclin D2 expression while inhibiting AKT phosphorylation. A: Mouse embryonic fibroblasts (mEFs) were exposed to 0.4 mmol/L palmitic acid (PA) or dimethyl sulfoxide (DMSO; Veh) for indicated time points in the presence of indicated glucose concentrations. Cells were harvested and immunoblotting was performed for the indicated proteins. B: Three different beta-cell cell lines were exposed to 0.4 mmol/L PA for 48 hours in the presence of 6 mmol/L glucose. Left panel, immunoblotting for cyclins, phospho-AKT (P-AKT), and total AKT (tAKT) confirmed up-regulation of G1/S cyclins and down-regulation of phospho-AKT by PA treatment. Each lane represents an independent cell culture experiment. Right panels, densitometry quantification of the ratio of cyclins versus loading control and p-AKT versus tAKT. C: Top, isolated islets were cultured in the presence or absence of 0.4 mmol/L PA for 72 hours, and immunoblotting for P-AKT showed down-regulation of P-AKT by 0.4 mmol/L PA treatment. Each lane represents an independent islet culture experiment. Bottom, islets isolated from mice fed HFD for 4 months shows down-regulation of P-AKT. Each lane represents an independent mouse. Right, densitometry quantification of the ratio of cyclins versus loading control and p-AKT versus tAKT. n = 7 to 11 (B); n = 5 to 7 (C, top); n = 3 (C, bottom). ∗P < 0.05 compared to vehicle-treated samples.