Palmitate-induced impairment of autophagy turnover leads to increased apoptosis and inflammation in peripheral blood mononuclear cells

Previous works have linked high concentrations of palmitate to cellular toxicity by autophagy modulation. However, the ways in which palmitate regulates inflammation and apoptosis in peripheral blood mononuclear cells (PBMCs), has not been well characterized. In the present study, we therefore aimed to investigate the role autophagy in inflammatory responses and apoptotic death of PBMCs treated with palmitate. 0.5 mM palmitate increased the level of LC3-II at 6 h, peaked at 12 h and then decreased at 24 h. The protein level of p62 was significantly increased at 6 h and 12 h, suggesting an impairment of autophagic flux in palmitate-treated PBMCs. Inhibiting autophagy with chloroquine (CQ) and 3-Methyladenine (3-MA) significantly augmented palmitate-induced PBMCs apoptotic death as demonstrated by increased cleaved PARP level and increased the percentage of apoptotic (YO-PRO-1 positive and PI negative) cells. Furthermore, CQ pretreatment exacerbated palmitate-induced TNF-alpha and IL-6 mRNA expression in PBMCs. Moreover, induction of autophagy by pretreatment of PBMCs with rapamycin resulted in a distinct increase of palmitate-induced apoptosis. The induction of autophagy also led to a further increase in palmitate-induced expression of TNF-alpha and IL-6. These results indicate that the excess palmitate could impair autophagy, hence contributing to palmitate-induced-inflammation and apoptosis in PBMCs. Therefore, dysregulated autophagy in PBMCs may provide a novel mechanism that connects diet-induced obesity to low grade inflammation in patients with type 2 diabetes.