Application of specific ELISAs for BMP15 and GDF9 to cumulus cell extracts from infertile women

Impact of female age on concentrations of reproductive hormones and oocyte-specific growth factors in follicular fluid from human small antral follicles

STUDY QUESTION

Does maternal age impact hormonal secretions from granulosa cells, theca cells, and the oocyte in human small antral follicles?

SUMMARY ANSWER

Major hormones secreted by granulosa and theca cells, as well as the oocyte-specific TGF-β members-GDF9, BMP15, and the GDF9/BMP15 heterodimer cumulin-maintain a consistent concentration within the follicular fluid of human small antral follicles, regardless of maternal age.

WHAT IS KNOWN ALREADY

It is well established that female fertility declines with increasing age. However, it is not known whether this decline is exclusively due to a reduction in oocyte quality and quantity or also involves a decline in the hormone-secreting capabilities of granulosa cells, theca cells, and the oocyte itself.

STUDY DESIGN, SIZE, DURATION

This is a retrospective study of follicular fluid obtained from human small antral follicles collected in connection with cryopreservation of ovarian tissue at the Laboratory of Reproductive Biology, University Hospital Copenhagen, Rigshospitalet, Denmark, between 2010 and 2020 as part of the hospital's fertility preservation program.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicular fluid samples from human small antral follicles measuring 3-13 mm in diameter from macroscopically normal ovaries of 381 patients aged 5-43 years were included in the study, provided that at least one of the following parameters was measured: AMH, Inhibin A, Inhibin B, oestradiol (E2), progesterone (P4), androstenedione, testosterone, and/or the oocyte-specific TGF-β members GDF9, BMP15, or cumulin.

MAIN RESULTS AND THE ROLE OF CHANCE

In a linear regression analysis adjusted for follicular volume, female age did not predict the follicular fluid concentrations of AMH, Inhibin B, Inhibin A, E2, androstenedione, testosterone, GDF9, BMP15, or cumulin. Although a significant association was observed between female age and follicular fluid P4 levels, the predictive value of age was poor, accounting for at most 5% of the variation in P4.

LIMITATIONS, REASONS FOR CAUTION

Hormonal levels may vary with the degree of atresia in each follicle; however, the health status of the small antral follicles in this study was not characterized. Additionally, we cannot exclude possible age-related differences in human follicles larger than 10 mm, as very few of these were included. Furthermore, we did not include women above the age of 43, despite the potential for more pronounced age-related effects in these patients.

WIDER IMPLICATIONS OF THE FINDINGS

Our results support the idea that the age-related decline in female fertility is primarily due to a reduction in oocyte quality and quantity, but further research is needed to confirm this.

STUDY FUNDING/COMPETING INTEREST(S)

No specific funding was obtained, and the authors have no conflicts of interest to declare in relation to this work.

TRIAL REGISTRATION NUMBER

N/A.

Oocyte and cumulus cell cooperativity and metabolic plasticity under the direction of oocyte paracrine factors

Mammalian oocytes develop and mature in a mutually dependent relationship with surrounding cumulus cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble paracrine oocyte-secreted factors (OSFs). We characterized the molecular mechanisms by which two model OSFs, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Exposure to these OSFs during mouse oocyte maturation in vitro altered the proteomic and multispectral autofluorescence profiles of both the oocyte and cumulus cells. In oocytes, cumulin significantly upregulated proteins involved in nuclear function. In cumulus cells, both OSFs elicited marked upregulation of a variety of metabolic processes (mostly anabolic), including lipid, nucleotide, and carbohydrate metabolism, whereas mitochondrial metabolic processes were downregulated. The mitochondrial changes were validated by functional assays confirming altered mitochondrial morphology, respiration, and content while maintaining ATP homeostasis. Collectively, these data demonstrate that cumulin and BMP15 remodel cumulus cell metabolism, instructing them to upregulate their anabolic metabolic processes, while routine cellular functions are minimized in the oocyte during maturation, in preparation for ensuing embryonic development.NEW & NOTEWORTHY Oocyte-secreted factors (OSFs) promote oocyte and cumulus cell cooperativity by altering the molecular composition of both cell types. OSFs downregulate protein catabolic processes and upregulate processes associated with DNA binding, translation, and ribosome assembly in oocytes. In cumulus cells, OSFs alter mitochondrial number, morphology, and function, and enhance metabolic plasticity by upregulating anabolic pathways. Hence, the oocyte via OSFs, instructs cumulus cells to increase metabolic processes on its behalf, thereby subduing oocyte metabolism.