Follicle stimulating hormone activates the steroidogenic process via camp/pka and map-kinase pathways in the ovary of european sea bass (Dicentrarchus labrax)

Abstract

In fish the onset and consequent stimulation of the gametogenic process is produced by the gonadotropic hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH action is accomplished via the interaction with its specific receptor (FSHR) which is a transmembrane G-protein-coupled receptor localized in the granulosa cells. The mainstream pathway used by FSHR to transduce the signal is the cAMP/PKA route; however, alternative routes have been identified, such as the mitogen-activated protein kinase (MAPK). The extracellular signal-regulated kinases (ERKs) belong to the family of MAPKs and are activated by MEK1 and MEK2, being probably the last one the crosstalk between this signaling pathway and the cAMP/PKA route. Results concerning ERK implication in steroidogenesis and ERK activation through cAMP/PKA are still contradictory. In fish, information on the involvement of MAPK in the steroidogenic process activated by gonadotropins is scarce. The present work aimed to clarify the signaling pathways used by FSH to induce steroid synthesis in sea bass. The present study shows the involvement of the cAMP/PKA route on sea bass steroidogenesis, in agreement with findings in other species. By blocking the cAMP/PKA pathway we determined that FSH uses this pathway to up-regulate transcripts of some steroidogenic enzymes such as StAR and CYP19A, therefore increasing the synthesis of E2 and T. In line with other species [4], MAPKs also participates in the regulation of steroidogenic enzyme activity. Blocking the MAPK route shows that this pathway regulates steroidogenic enzyme transcripts in a different way than cAMP/PKA. Besides, the activity of MAPK seems to be independent of the PKA route, as has been confirmed in other species