n680s snp of the human FSH receptor impacts on basal FSH and estradiol level in women and modifies PKA nuclear translocation and creb-dependent gene transcription in vitro

International audience; Introduction: The FSH receptor (FSHR) is a G protein-Coupled Receptor (GPCR) that activates cAMP-dependent signaling pathways, leading to the phosphorylation of both cytosolic and nuclear targets by PKA [eg: ERK MAP kinases, cAMP Responsive Element Binding protein (CREB)]. In addition, upon agonist exposure, the FSHR induces β-arrestin-dependent phosphorylation of ERK MAP kinases and rpS6 (Kara et al. 2006; Wehbi et al. 2010). Moreover, it has been shown for other GPCRs that β-arrestin-dependent signaling can affect transcriptional regulation at the genomic level (Lukashova et al. 2001; Beaulieu and Caron 2005; Gesty-Palmer et al. 2005; Lee et al. 2008). A single nucleotide polymorphism (SNP) has been reported in the hFSHR at position 680 as a Serine replaces an Asparagine (N680S). This polymorphism has been reported to induce an ovarian resistance to FSH action (Greb et al. 2005), without modifying either cAMP production or global PKA activation (Simoni et al. 1999; Sudo et al. 2002). In the present study, we combined clinical and experimental approaches to further investigate the functional consequences of N680S SNP. Materials and Methods: A clinical trial (ID RCB / 2007-AO1147-46) was performed on 812 women undergoing an in vitro fertilization protocol. Various clinical parameters were evaluated (ie: ovulatory status; day 3 FSH, LH and estradiol levels; total dose of FSH; estradiol level at hCG day; oocyte number; OHSS occurrence) while 680 SNP was assessed in every patient. In vitro studies were performed with HEK293 cells stably expressing either the N680 or the S680 hFSHR. We first monitored cAMP production and PKA activation using FRET methods. Then, β-arrestin recruitment at the hFSHR upon ligand binding with co-immunoprecipitation assays and kinetics of internalization of both receptors were analyzed. We also monitored ERK and CREB phosphorylation by Western blot analysis and CREB-dependent gene transcription using a luciferase reporter gene assay. Results and Discussion: Day three FSH level were higher and day three estradiol levels were lower in S680 homozygous patient when compared to N680 homozygous or N680S heterozygous patients. Interestingly, diminished ovarian reserve was more often observed in S680 homozygous patients. Consistent with previous reports, in vitro comparison of both variants for cAMP production as well as global PKA activation did not reveal any significant difference. However, we observed an increase in β-arrestin recruitment, in the internalization of the S680 hFSHR and subtle differences in the kinetics and sensitivity of ERK phosphorylation. Interestingly, this variant exhibited decreased CREB phosphorylation, CREB-dependent gene transcription and nuclear PKA activation. Our results showed increased β-arrestin recruitment at the hFSHR which presumably results from the presence of an additional serine residue in the C-terminal tail. Thus the N680S SNP seems to impact on the compartmentalization of FSH-induced signaling pathways. Conclusion: These findings provide a mechanistic basis to the clinical impact of the N680S SNP and point to β-arrestin as a potential key player in the control of CREB-dependent transcription downstream of the FSHR.