Mechanisms of Yangjing capsule in Leydig cell apoptosis and testosterone synthesis via promoting StAR expression.

The present study aims to investigate the roles of steroidogenic acute regulatory protein (StAR) in Yangjing Capsule (YC) induced anti-apoptotic effects on Leydig cells and the related mechanism. Leydig tumor cells (MLTC-1) were cultured and treated with YC, and immunofluorescence assay was performed to examine the expression of StAR; furthermore, luciferase reporter assay was conducted to evaluate the impact of YC on StAR promoter; next, MLTC-1 cells were treated with StAR small interfering RNA (siRNA), and flow cytometry was carried out to examine the effect of StAR siRNA on the apoptosis of the cells; furthermore, quantitative (q)RT-PCR and Western blot methods was used to determine the expression of StAR and apoptosis related molecules Bcl-2, Bax and Caspase-3 on both mRNA and protein levels in different groups; finally the secretion of testosterone in different groups was examined by radioimmunoassay. We observed that the YC can increase the expression of StAR in a dose-dependent manner, and YC can activate the promoter of StAR; moreover, transfection of StAR siRNA can block YC induced anti-apoptotic effects and increased production of testosterone. In conclusion, our results suggested that YC might suppress the apoptosis of MLTC-1 cells and enhance the production of testosterone through regulating the expression of StAR.