Annexin A5 regulates Leydig cell testosterone production via ERK1/2 pathway

This study was to investigate the effect of annexin A5 on testosterone secretion from primary rat Leydig cells and the underlying mechanisms. Isolated rat Leydig cells were treated with annexin A5. Testosterone production was detected by chemiluminescence assay. The protein and mRNA of Steroidogenic acute regulatory (StAR), P450scc, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), and 17 alpha-hydroxylase were examined by Western blotting and semi-quantitative RT-PCR, respectively. Annexin A5 significantly stimulated testosterone secretion from rat Leydig cells in dose- and time-dependent manners and increased mRNA and protein expression of StAR, P450scc, 3 beta-HSD, and 17 beta-HSD but not 17a-hydroxylase. Annexin A5 knockdown by siRNA significantly decreased the level of testosterone and protein expression of P450scc, 3 beta-HSD, and 17 beta-HSD. The significant activation of ERK1/2 signaling was observed at 5, 10, and 30 min after annexin A5 treatment. After the pretreatment of Leydig cells with ERK inhibitor PD98059 (50 mu mol l(-1)) for 20 min, the effects of annexin A5 on promoting testosterone secretion and increasing the expression of P450scc, 3 beta-HSD, and 17 beta-HSD were completely abrogated (P < 0.05). Thus, ERK1/2 signaling is involved in the roles of annexin A5 in mediating testosterone production and the expression of P450scc, 3 beta-HSD, and 17 beta-HSD in Leydig cells.