Cumulin and FSH cooperate to regulate inhibin B and activin B production by human granulosa-lutein cells in vitro

Abstract

The oocyte-secreted factors bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) interact functionally and it is hypothesised that this interaction may be mediated by formation of a GDF9:BMP15 heterodimer, termed cumulin. GDF9 and BMP15 regulate folliculogenesis and ovulation rate, and have been shown to regulate inhibin and activin, local regulators of folliculogenesis. The objective of this study was to determine if cumulin regulates granulosa cell inhibin and activin production, and if this requires cooperation with FSH. Human granulosa-lutein (hGL) cells collected from IVF patients were cultured ± FSH with various forms of recombinant cumulin (native and cysteine mutants, and with/without the pro-domains), and cysteine mutant GDF9 or BMP15. Messenger RNA expression of the subunits of inhibins/activins (INHA, INHBA, INHBB) and secretion of inhibin A, inhibin B, and activin B were measured. Mature- and pro-forms of cumulin stimulated comparable INHBB mRNA expression and secretion of inhibin B and activin B, whereas GDF9 or BMP15 exhibited no effect. Cumulin, but not GDF9 or BMP15, interacted synergistically with FSH to increase INHBB mRNA and inhibin B expression. FSH markedly stimulated INHA, which encodes the a subunit of inhibin A/B, and suppressed activin B. Cumulin ± FSH did not significantly alter inhibin A. Together these data demonstrate that cumulin, but not GDF9 or BMP15, exerts paracrine control of FSH-induced regulation of inhibin B and activin B. The pro-domains of cumulin may have a minimal role in its actions on granulosa cells.