The ERK1/2 pathway regulates testosterone synthesis by coordinately regulating the expression of steroidogenic genes in Leydig cells

Abstract

Adult mice with a Leydig cell specific deletion of MAPK kinase (MEK) 1 and 2 (Mek1f/f;Mek2−/−;Cre+) mice display Leydig cell hypoplasia and hypergonadotropic hypogonadism. We used radioimmunoassays and quantitative PCR to evaluate the function and expression of the Leydig cell genes involved in the conversion of cholesterol to testosterone (Star, Cyp11a1, Hsd3b6, Cyp17a1 and Hsd17b3), androgen metabolism (Srda1 and Dhrs9), and four transcription factors (Creb1, Nr5a1, Nr4a1 and Nr0b1) that regulate the expression of steroidogenic genes. We show that Star, Hsd3b6, Cyp17a1 and Hsd17b3 are downregulated in Ledyig cells of adult Mek1f/f;Mek2−/−;Cre+ mice whereas Srda1 and Dhrs9 are upregulated and Creb1, Nr5a1, Nr4a1 and Nr0b1 are unchanged or upregulated. Functionally, all the downregulated genes but none of the upregulated genes contribute to the decrease in testosterone synthesis in Leydig cells of adult Mek1f/f;Mek2−/−;Cre+ mice because they produce low testosterone and dihydrotestosterone when stimulated with hCG or when incubated with testosterone precursors such as progesterone or androstenedione.

Human LH and hCG stimulate differently the early signalling pathways but result in equal testosterone synthesis in mouse Leydig cells in vitro

“…Results from the gene expression analysis corroborate the pCreb activation pattern, since no different increase of LH- and hCG-induced Stard1 gene expression levels were observed. Indeed, in murine Leydig cells, Stard1 gene expression occurs as a pCreb-dependent event [13], although several other modulators of the steroidogenic response were described [43]. …”

“…Hormone binding to LHCGR triggers the activation of adenylyl cyclase through Gαs protein, resulting in intracellular cyclic adenosine-monophosphate (cAMP) increase, in downstream activation of the protein kinase A (PKA) [11, 12] which, in turn, induces extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation [13]. PKA also mediates the activation of the cAMP-response element-binding protein (CREB), modulating the expression of target genes, such as the steroidogenic acute regulatory protein ( STARD1 ) gene, and testosterone production.…”

“…Especially, cAMP production, ERK1/2 and CREB phosphorylation (pERK1/2 and pCREB, respectively), target gene expression and testosterone synthesis were evaluated. Mouse cells are naturally expressing the murine LH receptor, which shares high, but not complete sequence identity with LHCGR, as well as binding capability to human LH and hCG [13, 22]. However, it should be taken into account that some discrepancy may be observed between human and rodent LH receptor-mediated signals, as previously observed in the monkey Callithrix jacchus [23].…”

Localization and expression patterns of prolactin-like protein J in mouse testis

“…Testosterone production by Leydig cells is regulated by complex interplay between multiple molecules including those involved in endocrine and paracrine signaling, and proper regulation is critical for optimum reproductive capacity. As a result, a number of Leydig cell-specific genes have been identified as important regulators of reproductive processes (26)(27)(28)(29)(30). As PLP-J is specifically expressed in Leydig cells of the testis and its expression peaks in the adult, similar to the expression pattern of testosterone, we hypothesized that PLP-J is also involved in testosterone biogenesis.…”

Molecular regulation of steroidogenesis in endocrine Leydig cells

“…It was later reported that activation of LHCGR leads to a transient cAMP-dependent activation of the EGFR and downstream mitogen-activated protein kinase (MAPK) cascade [75]. The involvement of the MAP kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2) downstream of PKA have long been known to be essential for proper LH-induced steroidogenesis in Leydig cells [76][77][78][79][80][81][82] (Fig. 1).…”