Orexin A-mediated stimulation of 3β-HSD expression and testosterone production through MAPK signaling pathways in primary rat Leydig cells

Background Orexin A (ORA) regulates food intake, energy metabolism, gastrointestinal and reproductive functions. Aim The purpose of this study was to demonstrate whether the expression of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and testosterone was stimulated by ORA and mediated through mitogen-activated protein kinases (MAPK) in rat Leydig cells. Methods Primary Leydig cells were isolated from male rat testes, cultured, and treated with ORA under various conditions. Results Orexin receptor 1 (OX1R) mRNA, but not orexin receptor 2 mRNA, was detected in primary Leydig cells. ORA up-regulated the expression of OX1R mRNA and protein in a dose-responsive manner and increased the phosphorylation of extracellular receptor kinase 1/2 (ERK1/2) and p38 MAPK levels, but did not affect the phosphorylation of the JNK MAPK. Phosphorylation of ERK1/2 and p38 MAPKs by ORA was blocked with U0126 and SB203580 inhibitors, respectively. An OX1R-specific inhibitor, SB334867, also blocked the phosphorylation of ERK1/2 and p38 by ORA. Inhibitor treatment also blocked 3 beta-HSD expression and testosterone production. Conclusions These results demonstrate that ORA activation of OX1R up-regulates 3 beta-HSD expression and testosterone production via the ERK1/2 and p38 MAPKs signaling pathways in primary rat Leydig cells.