Primary Leydig cells naturally expressing mouse LHR do not discriminate between LH- and hCGmediated signaling in vitro

Human luteinizing hormone (LH) and chorionic gonadotropin (hCG) are glycoprotein hormones fundamental for development and reproduction. These hormones were considered biologically equivalent for decades due to structural similarities and binding to the same receptor (LHCGR), although they mediate different physiological roles. Previous reports demonstrated LH- and hCGspecific intracellular signaling mediated by LHCGR in human primary granulosa cells, but few studies using rodent receptor (Lhr) are available. We investigated the Lhr-mediated activation of the cAMP/PKA-pathway, ERK1/2 and CREB phosphorylation, gene expression and steroidogenesis, in murine Leydig cells treated with LH and hCG. We found that hCG is more potent than LH in inducing cAMP production, as well as downstream the pERK1/2 activation. However, similar levels of CREB phosphorylation, Stard1 gene expression and testosterone production occurred upon LH and hCG treatment in vitro. These findings revealed that rodent Lhr mediates quantitatively, but not qualitatively, different LH- and hCG-dependent signaling, which results in similar testosterone synthesis. These data suggest that in vivo bioassay using a model expressing rodent receptor, which rely on the evaluation of testosterone-dependent endpoints, may be not suitable to quantify gonadotropins activity for clinical purpose.