Redox regulation of hormone sensitive lipase: Potential role in the mechanism of MEHP-induced stimulation of basal steroid synthesis in MA-10 Leydig cells

Mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of di-(2-ethylhexyl) phthalate (DEHP), is a plasticizer with endocrine disruptor activity that has been shown to stimulate basal steroid biosynthesis in Leydig cells. The mechanism by which it does so is unknown. Using MA-10 mouse tumor Leydig cells, we assessed the effects of MEHP on reactive oxygen species (ROS) levels, and on the signal transduction pathways that mobilize cholesterol. Exposure to 0-300 mu M MEHP stimulated basal progesterone production in a dose-dependent manner. Progesterone stimulation was correlated with increases in the phosphorylation of hormone-sensitive lipase (HSL; aka cholesteryl ester hydrolase), which is involved in the production of free cholesterol, and of steroidogenic acute regulatory (STAR) protein expression. Co-treating MA-10 cells with MEHP and the ROS scavenger N-acetyl cysteine (NAC) blocked the activation of HSL, blunted MEHP-induced STAR, and reduced basal progesterone formation. These observations suggest that ROS generation by MEHP leads to activation of HSL and increase in STAR which, together, result in increased free-cholesterol bioavailability and progesterone formation.