NO/cGMP signaling increases mitochondrial membrane potential and affects androgenesis in Leydig cells of adult rats

Abstract

Mitochondria are a key control point for the regulation of steroid hormone biosynthesis in all steroid-producing cells, including androgen-producing Leydig cells. The first step of steroid biosynthesis is mobilization of cholesterol to the mitochondrial inner membrane, which is facilitated by the steroidogenic acute regulatory (StAR) protein. Previous studies on Leydig cells indicated the importance of mitochondrial membrane potential (Δψ_μ) on hormone stimulated androgen production. Since nitric oxide (NO) could regulate androgen production, it was of interest to explore the effects of NO-cGMP-dependent signaling on Δψ_μ and the steroidogenic activity of rat Leydig cells. The results showed that treatment of purified Leydig cells with NO-donor causes a dose-dependent increase in both Δψ_μ and cGMP production without effecting cAMP intracellular levels. In the same cells, a biphasic effect of NO-donor on testosterone production was observed; stimulatory in the dose range (0-10^-5 M) and inhibitory at 10^-3 M. Levels of mature StAR protein also exhibit a similar biphasic effect. Furthermore, NO-donor dose dependently stimulates cGMP production and Δψ_μ even in cells stimulated with a supra-maximal dose of human chorionic gonadotropin (hCG, 50 ng/ml). The hCG-treatment alone slightly increased cGMP production, and this effect was followed by a small but significant increase in Δψ_μ. Together, results from all experimental approaches stimulating cGMP production significantly correlated with Δψ_μ values, suggesting implication of cGMP signaling in the control of mitochondrial membrane polarity. In summary, our results support a positive role for cGMP signaling in the maintenance of mitochondrial membrane polarity through increased Δψ_μ, followed by stimulated androgen production.