Granulosa Cell Dysfunction Is Associated With Diminished Ovarian Response in FMR1 Premutation Carriers

Abstract

FMR1 premutation (PM) carriers are at increased risk of ovarian impairment resulting in diminished ovarian response (DOR) to exogenous follicle-stimulating hormone (FSH) stimulation. Expanded CGG repeat transcript and RAN-associated protein (FMRpolyG) have been shown to accumulate in cellular aggregates and sequester proteins, thus impairing their function. Sam68 is a multifunctional RNA-binding protein highly expressed in the gonads involved in FSH receptor (FSHR) transcript maturation during FSH-dependent follicular development. The present study examined a possible pathophysiological explanation for DOR to exogenous FSH stimulation in FMR1 PM carriers. We used both a human granulosa cell (GC) line model and human GCs from FMR1 PM carriers to evaluate whether Sam68 is sequestered with expanded CGG repeat transcript. We show that Sam68 is sequestered in GCs, most likely by interaction with the expanded CGG repeat transcript. The sequestration may lead to reduced levels of free Sam68 available for FHSR precursor transcript processing, causing dysregulation of FSHR transcript maturation, and a consequent decrease in FSHR protein levels. Sam68 sequestration may underlie the diminished ovarian response to FSH stimulation in FMR1 PM carriers.