High concentrations of progesterone inhibit the expression of genes related to steroid metabolism in MA-10 Leydig cells

Leydig cells are the main testosterone-producing cells in males. During androgen synthesis, cholesterol enters the mitochondria via the STAR protein and is converted into pregnenolone by the CYP11A1 enzyme. This steroid is then exported from the mitochondria to be metabolized to progesterone by the HSD3B1 enzyme in the endoplasmic reticulum. In this study, we used 3'Tag-RNA-Seq to identify progesterone-regulated genes in MA-10 Leydig cells. Our results indicate that high concentrations of progesterone (30 μM) are involved in a negative feedback loop that inhibits cAMP/PKA-dependent activation of Star and Cyp11a1 expression and participate in cAMP/PKA-dependent down-regulation of genes related to the metabolism of steroid hormones. Linked to activation of the MAPK signaling pathway, endoplasmic reticulum stress and apoptosis, most of the genes encoding bZIP transcription factors are upregulated by progesterone in MA-10 Leydig cells. However, only DDIT3 protein levels are increased in response to progesterone in MA-10 Leydig cells. Like normal Leydig cells, MA-10 cells very weakly express the classical nuclear receptor for progesterone, suggesting that gene regulation by progesterone is rather mediated by one of the non-classical membrane receptors for progesterone However, current findings suggest that the inhibitory effect of progesterone on STAR protein increase in response to forskolin is not dependent on PGRMC1/2 or PAQR9. Furthermore, the increase in progesterone synthesis in response to activation of the cAMP/PKA pathway is rather inhibited by siRNA-mediated knockdown of PAQR9. Overall, this study shows that progesterone produced by Leydig cells participates in the regulation of steroidogenesis through autocrine action involving negative feedback upon activation of the cAMP/PKA pathway.