New Insights into Melatonin Signaling in Hamster Leydig Cells

ROSSI SP; MATZKIN ME; TERRADAS C; PONZIO R; PUIGDOMENECH E; LEVALLE O; CALANDRA RS; FRUNGIERI MB

San Pablo

Workshop; III Workshop on Male Reproductive Biology; 2011

Universidad de Campinhas

We have previously described that melatonin, a pineal gland product, inhibits testosterone production in hamster testes via melatonin subtype 1a (mel1a) receptors and the local corticotrophin-releasing hormone (CRH) system (Endocrinology 146: 1541, 2005). This study attempted to determine the initial events of the melatonin/CRH signaling pathway. In Leydig cells from reproductively active Syrian hamsters, Western blotting, reverse transcription quantitative polymerase chain reaction (RT-qPCR) and a colorimetric assay demonstrated that both melatonin and CRH activate tyrosine phosphatases [Tyrosine phosphatase activity (nmol/min/mg protein) Basal: 5.395 + 0.434 vs melatonin: 7.766 + 0.597, n=5-6, P <0.05; Basal: 5.397 + 2.593 vs CRH: 13.267 + 6.753, n=5-6, P <0.05] and subsequently reduce the phosphorylation levels of extracellular signal-regulated kinase (erk), c-jun N-terminal kinase (jnk), and c-jun, down-regulate the expression of c-jun, c-fos and steroidogenic acute regulatory (StAR), and inhibit the production of testosterone. These effects were prevented by a highly selective CRH antagonist, thus indicating that melatonin does not exert a direct role. Furthermore, specific mitogen-activated protein kinase kinase (MEK) and jnk blockers inhibited expression of c-jun, c-fos, StAR and the production of testosterone, confirming that these are events triggered downstream of erk and jnk. By an enzyme-linked immunosorbent assay, immunohistochemical analyses, laser capture microdissection and RT-PCR, we established that melatonin, CRH, and their receptors are present not only in hamster testes but also in testicular biopsies of infertile men. As a consequence, we can conjecture about the relevance of this previously uncharacterized pathway in human fertility disorders. In summary, our study identifies crucial intracellular events triggered by melatonin/CRH in the testis that lead to a down-regulation of the steroidogenic process.