The role of platelet-derived growth factor BB signaling pathway in the regulation of stem and progenitor Leydig cell proliferation and steroidogenesis in male rats.

Platelet-derived growth factor BB (BB) regulates cell proliferation and function. However, the roles of BB on proliferation and function of Leydig stem (LSCs) and progenitor cells (LPCs) and the underlying signaling pathways remain unclear. This study aimed to analyze the roles of PI3K and MAPK pathways in the regulation of proliferation-related and steroidogenesis-related gene expression in rat LSCs/LPCs. In this experiment, BB receptor antagonist, tyrosine kinase inhibitor IV (PKI), the PI3K inhibitor, LY294002, and the MEK inhibitor, U0126, were used to measure the effects of these pathways on the expression of cell cycle-related genes (Ccnd1 and Cdkn1b) and steroidogenesis-related genes (Star, Cyp11a1, Hsd3b1, Cyp17a1, and Srd5a1), as well as Leydig cell maturation gene Pdgfra [1]. These results showed that BB (10 ng/mL)-stimulated EdU-incorporation into LSCs and BB-mediated inhibition on its differentiation was mediated through the activation of its receptor, PDGFRB, as well as MAPK and PI3K pathways. The results of LPC experiment also showed that LY294002 and U0126 decreased BB (10 ng/mL)-upregulated Ccnd1 expression while only U0126 reversed BB (10 ng/mL)-downregulated Cdkn1b expression. U0126 significantly reversed BB (10 ng/mL)-mediated downregulation of Cyp11a1, Hsd3b1, and Cyp17a1 expression. On the other hand, LY294002 reversed the expression of Cyp17a1 and Abca1. In conclusion, BB-mediated induction of proliferation and suppression of steroidogenesis of LSCs/LPCs are dependent on the activation of both MAPK and PI3K pathways, which show distinct regulation of gene expression.