KISS1R signaling modulates gonadotropin sensitivity in mouse Leydig cell

Kisspeptin and its receptor KISS1R have been proven as pivotal regulators on controlling the hypothalamus-pituitary-gonad axis. Inactivating mutations in one of them cause idiopathic hypogonadotropic hypogonadism in human as well as rodent models. Notably, gonadotropin insensitivity, failure in hCG response, was presented in the male patients with loss-function-mutations in KISS1R gene; this reveals the essential role of KISS1R signaling in regulating testosterone production beyond the hypothalamic functions of kisspeptin. In this study, we hypothesized that the autocrine action of kisspeptin on Leydig cells may modulate steroidogenesis. Based on the mouse cell model, we first demonstrated that the cAMP/protein kinase A (PKA)/cAMP response element-binding protein (CREB) signaling pathway mediated gonadotropin-induced kisspeptin expression. By using siRNA interfering technique, knockdown of Kiss1r in MA-10 cells, a mouse Leydig tumor cell line, significantly reduced progesterone productions in both basal and hCG-treated conditions. Integrating the results from both quantitative real-time PCR and steroidogenic enzyme-activity assay, we found that this steroidogenic defect was associated with decreased luteinizing hormone/choriogonadotropin receptor (Lhcgr) and StAR protein (Star) expressions. Furthermore, exogenous expression of human LHCGR completely rescued hCG-stimulated progesterone production in the KISS1R-deficient cells. In conclusion, we proposed that the reproductive functions of KISS1R signaling in Leydig cell include modulating Lhcgr and steroidogenic gene expressions, which may shed the light on the pathophysiology of gonadotropin insensitivity.