Functional Characterization of Two Naturally Occurring Mutations (Val514Ala and Ala575Val) in Follicle-Stimulating Hormone Receptor

Context: Inactivating mutations have been reported in subjects with primary/secondary amenorrhea, whereas activating mutations are rare and seen only in women with ovarian hyperstimulation syndrome (OHSS). In the present study, we describe the functional characterization of the two mutations Val(514)Ala (novel mutation) and Ala(575)Val in FSH receptor (FSHR) identified in women with OHSS developed during in vitro fertilization and primary amenorrhea, respectively. Objective: The objective of the investigation was to study the effect of mutations (514 and 575) on FSHR activity by in vitro functional studies. Setting: The study was conducted at an academic research institute and a private in vitro fertilization clinic. Methods: The site-directed mutagenesis was carried out to generate the mutations at position 514 and 575 in pSG5-FSHR construct. Stable cell lines expressing wild type or each of the mutant receptor were generated using Chinese hamster ovary cells. Functional characteristics of both the mutant receptors were assessed by a radioreceptor assay and a cAMP assay. Results: The mutant receptor 514 showed increased cell surface expression as compared with the wild-type (WT) receptor. Although the hormone binding characteristics were similar to the WT receptor, its signaling activity was distinctly higher at lower dose of FSH as monitored by a cAMP assay. On the other hand, the mutant receptor 575 showed lower cell surface expression and higher internalized hormone receptor complex. Additionally, a dose-dependent increase in the cAMP accumulation was not observed in the case of this mutant as compared with WT. Conclusion: OHSS and primary amenorrhea observed in the two affected women, respectively, could be attributed to the functional characteristics of respective mutant FSHR.