The oocyte-secreted factors bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are predominantly expressed by oocytes. Relative abundance of GDF9 to BMP15 determine mammalian ovulation rate and fecundity and mutations in these genes are associated with reproductive pathologies. To date, there are no validated assays available to quantitate these proteins in biological samples.
This research program developed and validated ELISAs to measure BMP15 and GDF9 in serum (n=151), follicular fluid (FF) (n=138) and on cumulus cells (CC) (n=120) collected from three cohorts of women treated for infertility. Sera were from the follicular phase of a treatment cycle. FF samples were pooled from all follicles aspirated during oocyte retrieval and normalised to total protein. CC-bound BMP15 was assessed in salt extracts from pooled CC of individual ICSI patients normalised to DNA. Concentrations were compared to clinical data, including age, number of oocytes retrieved, and polycystic ovaries/syndrome (PCO(S)).
BMP15 was detectable in 67% of serum and 76% of FF, while GDF9 was detectable in 29% of serum and 60% of FF samples. BMP15 was detectable in all CC samples. CC-bound BMP15 was higher in PCOS than non-PCO(S) women (p<0.05). Further, an age-related decline in BMP15/CC DNA was significant for non-PCO(S) women (p<0.05) but absent in PCO(S). In the FF cohort, the inverse was seen, as women with PCO(S) had a lower proportion of detectable BMP15 (p=0.06), and higher proportion of detectable GDF9 (p<0.05), suggesting high FF GDF9:BMP15 is associated with PCO(S). Sera GDF9 of non-PCOS patient increased with increasing oocytes, which was significantly different for PCO(S) (p<0.05). The inverse was observed for BMP15 (p<0.05).
These results demonstrate that BMP15 and GDF9 are aberrant in women with PCO(S) and suggest these growth factors are compartmentalised in CC, FF and serum differently in PCO(S) and non-PCO(S) women.