Follicle-Stimulating Hormone Receptor: Advances and Remaining Challenges.

Follicle-stimulating hormone (FSH) is produced in the pituitary and is essential for reproduction. It specifically binds to a membrane receptor (FSHR) expressed in somatic cells of the gonads. The FSH/FSHR system presents many peculiarities compared to classical G protein-coupled receptors (GPCRs). FSH is a large naturally heterogeneous heterodimeric glycoprotein. The FSHR is characterized by a very large NH2-terminal extracellular domain, which binds FSH and participates to the activation/inactivation switch of the receptor. Once activated, the FSHR couples to Gαs and, in some instances, to other Gα-subunits. GPCR kinases and β-arrestins are also recruited to the FSHR and account for its desensitization, the control of its trafficking and its intracellular signaling. Of note, the FSHR internalization and recycling are very fast and involve very early endosomes (EE) instead of EE. All the transduction mechanisms triggered upon FSH stimulation lead to the activation of a complex signaling network that controls gene expression by acting at multiple levels. The integration of these mechanisms not only leads to context-adapted responses from the target gonadal cells but also indirectly affects the fate of germ cells. Depending on the physiological/developmental stage, FSH elicits proliferation, differentiation, or apoptosis in order to maintain the homeostasis of the reproductive system. Pharmacological tools targeting FSHR recently came to the fore and open promising prospects both for basic research and therapeutic applications. This chapter provides an updated review of the most salient aspects and peculiarities of FSHR biology and pharmacology.