Effect of autophagy on methylmercury-induced lipid droplet formation and adipokine expression in 3T3-L1 cells

<p>Chronic exposure to methylmercury (MeHg) is positively associated with obesity and metabolic syndromes. However, the effect of MeHg on adipogenesis has not been thoroughly investigated. This study investigated the effects of continuous exposure of 0.5 µM MeHg on adipocyte differentiation in 3T3-L1 cells. As determined by Oil-red O staining and assays for triglycerides (TG), MeHg enhanced TG content. Moreover, MeHg enhanced the mRNA and protein expression of adipocyte differentiation markers including peroxisome proliferator-activated receptor gamma (PPARG), adiponectin (ADIPOQ), and fatty acid-binding protein (FABP4), and their expression levels were prominent during the late stages (days 6-8) after the induction of differentiation. Treatment of 3T3-L1 cells with chloroquine (CQ), an autophagy inhibitor, during the early stages (days 0-2) after induction of differentiation inhibited cellular lipid accumulation in the presence of 0.5 µM MeHg. However, treatment with CQ during the late stages (days 6-8) had little effect on the MeHg-induced TG content and the expression of adipocyte differentiation markers. The underlying mechanisms in the late stages remain to be completely elucidated, but the present data suggest that autophagy and other mechanisms play critical roles in adipogenesis during MeHg-induced differentiation. Importantly, our results suggest that continuous exposure to MeHg can induce TG accumulation and expression of genes related to adipogenesis, especially during the late stages of 3T3-L1 differentiation, which may contribute to an improved understanding of MeHg-induced adipogenesis.</p>