Metabolic and endocrinologic interplay in the peri-ovulatory follicle to support the cumulus-oocyte-complex towards full competence

The increase in free fatty acid (FFA) levels in the circulation and follicular fluid in response to the negative energy balance of dairy cows has received significant attention during the last decades. However, until recently the potential effect of FFA on the periovulatory steroid environment has been overlooked. The well-orchestrated luteinizing hormone (LH) peak induces a steroid shift in the periovulatory follicle, from Estradiol-17β (E2) dominance around the LH peak towards progesterone (P4) dominance around ovulation, and is a prerequisite for optimal cytoplasmic and nuclear maturation in the oocyte and oocyte developmental competence. Recent insights in literature demonstrate a link between saturated and mono-unsaturated FFAs and the expression of gonadotrophin receptors, follicle stimulating hormone (FSH)R and LHR, including steroid related enzymes and E2 synthesis by in vitro granulosa cells. The current review will focus on the potential role of mono-unsaturated oleic acid, the most abundant FFA in follicular fluid, on steroidogenesis and its potential effect on the cumulus-oocyte-complex (COC) during final maturation. The data of this review suggest the potential for a regulatory interlinked system, which includes the oocyte secreted factor FGF10 and oleic acid, that modulates the steroidogenic switch from E2 to P4 in the periovulatory follicle, via actions that involve the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway in support of the delicate and well-orchestrated dialogue between the oocyte and cumulus cells during final maturation of COCs.