Anti-Müllerian hormone binds heat shock protein glucose-regulated protein 78 in human follicular fluid

Anti-Müllerian hormone (AMH) regulates key steps in folliculogenesis, yet unlike other TGF-β family members, no soluble AMH-binding proteins have been identified. We hypothesized that AMH may bind shuttling proteins in human follicular fluid (FF).

Discarded pooled FF was collected from women undergoing oocyte retrieval at an academic fertility center. AMH-binding soluble proteins in FF were co-immunoprecipitated with AMH, identified by mass spectrometry, and their association was validated by western blot. We characterized the spatiotemporal expression of candidate binding protein glucose-regulated protein 78 (GRP78) in the mouse ovary across the cycle by immunohistochemistry. We used enzyme-linked immunoassay (ELISA) to measure AMH and GRP78 concentrations in patient FF. We used transient transfections in Chinese hamster ovary (CHO) cells to understand the interaction between AMH and GRP78.

Co-immunoprecipitation of AMH in FF identified multiple soluble AMH-binding candidates in the heat-shock protein family, which was confirmed by reciprocal co-immunoprecipitation. We found that GRP78, the most abundant candidate, was enriched in antral follicles of mice at estrus and was present in higher concentrations in human FF than AMH. Finally, we found that AMH overexpression increased endoplasmic reticulum stress and induced GRP78 expression in CHO cells; further ectopic overexpression of GRP78 facilitated the secretion of AMH.

This work describes AMH-binding protein candidates identified in human FF and suggests that GRP78 may chaperone AMH during secretion and remain bound in FF. Further study is warranted to understand how heat shock proteins may modulate other biological aspects of AMH and their effects on fertility.