Deletion of Gremlin-2 alters estrous cyclicity and disrupts female fertility in mice

Members of the differential screening-selected gene aberrative in neuroblastoma (DAN) protein family are developmentally conserved extracellular binding proteins that antagonize bone morphogenetic protein (BMP) signaling. This protein family includes the Gremlin proteins, GREM1 and GREM2, which are known to have key functions during embryogenesis and adult physiology. While BMPs play essential roles in adult female reproductive physiology, the role of the DAN family in ovarian function is less understood. We generated mice null for Grem2 to study its role in female fertility in addition to screening patients with primary ovarian insufficiency for variants in GREM2. Grem2-/- mice are viable and female Grem2-/- mice have diminished fecundity and irregular estrous cycles. This is accompanied by reduced serum levels of anti-Mullerian hormone, a marker of the ovarian reserve, in adult mice. Alterations in ovarian expression of inhibin and activin subunit genes, which are required for regulation of the hypothalamic-pituitary-ovarian (HPO) axis, were identified. While Grem2 mRNA transcript was not detected in the pituitary, Grem2 was expressed in the hypothalami of wild type female mice. Additionally, screening 106 women with primary ovarian insufficiency identified one individual with a heterozygous variant in GREM2 that lies within the predicted BMP-GREM2 interface. In total, these data suggest that Grem2 is necessary for female fecundity by playing a novel role in regulating the HPO axis and possibly contributing to female reproductive disease.