Christopher Allan Price

Adipokines, bioactive proteins derived from adipose tissue, serve as intermediaries between energy status and reproduction, playing pivotal roles in ovarian physiology. Among them, members of the Fibronectin Type III domain‐containing the (FNDC) family, including FNDC4 and FNDC5 (the precursor of irisin), have emerged as key modulators of fertility. This study investigated the expression of FNDC4, FNDC5, and their receptors (ITGB1, ITGAV, ADGRF5) across different stages of bovine CL lifespan and evaluated irisin's effects on interferon tau (IFNT)‐mediated signaling in bovine luteal cells. The relative abundance of FNDC4 and FNDC5 mRNA was significantly greater in Early II, Middle, and Late phases when compared to the Early I. The expression of ITGB1 and ADGRF5 in bovine CL was significantly greater in the Early II, Middle, and Late phases than in the Early I phase, and the abundance of ITGAV mRNA did not differ between the evaluated phases. Also, it was observed that mRNA expression of all evaluated receptors was greater in CL of nonpregnant cows on Day 18 compared to pregnant cows. In vitro experiments demonstrated that irisin treatment enhanced interferon‐stimulated genes (ISGs) such as MX1 and MX2 in luteal cells, suggesting irisin potentiates IFNT signaling. Notably, irisin did not alter steroidogenic enzyme expression or affect cell viability, proliferation, or apoptosis markers, indicating its effects are specific to IFNT signaling pathways. The present study shows that the genes FNDC5 and FNDC4 are expressed in the bovine corpus luteum at different stages of development and that irisin increased ISGs expression in bovine luteal cells in vitro. The effects of irisin on CL function may be indirect, as plasma irisin increases during the postpartum negative energy balance in dairy cows. We propose that this is part of a compensatory mechanism to modulate IFNT signaling in CL cells and indirectly improve embryonic signaling mechanisms.

The CCN family of proteins is comprised of six matricellular proteins known to regulate multiple cellular processes such as adhesion, proliferation, differentiation, and apoptosis. CCN proteins are known to function through the binding of integrin receptors and through the regulation of growth factors and cytokines in the context of cardiovascular and skeletal development, injury repair, fibrosis, inflammation and cancer. The expression and roles of several CCNs, particularly CCN1 and CCN2, have been investigated in the ovary as they are effectors of the Hippo signaling pathway, and their role in the development of ovarian fibrosis has been described. Here we review the patterns of expression of CCN1–6 in the ovarian follicle, and the role of CCN2 in follicle development and steroidogenesis, and the expression and potential actions of CCN1–6 in ovarian cancers. We highlight the roles CCNs may play in inflammatory processes, and put forth a case for CCN involvement in the process of ovulation.

In brief: Irisin is a muscle and adipose-derived hormone that is secreted in response to negative energy balance in cattle. We show here that irisin reduced follicle growth and theca cell function. At the onset of lactation, dairy cattle are anestrous owing mainly to a state of negative energy balance. Adipose tissue is mobilized to meet the energy demands of milk production, and this alters the secretion of adipose-derived hormones, called adipokines. Irisin is a myokine/adipokine that may play a role in fertility; plasma concentrations increase in cattle postpartum, and irisin decreased progesterone and estradiol secretion from bovine granulosa cells in vitro . To our knowledge, the effects of irisin on bovine theca cell function in vitro and on follicle growth in vivo have not been reported. We hypothesized that irisin negatively affects theca cell function in vitro and causes follicle regression in vivo using well-established bovine models. Under physiological concentrations of insulin (0.2 ng/mL), irisin did not affect glucose uptake, but decreased testosterone secretion and stimulated PTK2 and MTOR phosphorylation. Inhibiting PTK2 activity abolished the ability of irisin to decrease testosterone secretion. Injection of irisin directly into a growing follicle in vivo caused follicle regression. We conclude that irisin decreases bovine theca cell steroidogenesis through PTK2 signaling, and combined effects on theca and granulosa cells cause follicle regression.

: In brief: Dairy cattle experience a period of infertility postpartum that is caused in part by the development of IGF1/insulin resistance. This study suggests that an adipokine, FNDC3A, reduces IGF1-dependent glycolysis and may contribute to postpartum infertility. Dairy cows go through a period of subfertility after parturition, triggered in part by a disruption of energy homeostasis. The mobilization of body fat alters the secretion of adipokines, which have been shown to impact ovarian function. Fibronectin type III domain-containing 3A (FNDC3A) is a recently discovered adipokine-myokine, and FNDC3A mRNA abundance in subcutaneous adipose tissue is increased postpartum in cattle. In this study, we hypothesized that FNDC3A may compromise granulosa cell function in cattle and investigated this using a well-established in vitro cell culture model. Here, we demonstrate the presence of FNDC3A protein associated with extracellular vesicles in follicular fluid and in plasma, suggesting an endocrine role for this adipokine. FNDC3A protein and mRNA was also detected in the bovine ovary (cortex, granulosa and theca cells, cumulus, oocyte and corpus luteum). Abundance of FNDC3A mRNA in granulosa cells from small follicles was increased by in vitro treatment with the adipokines leptin and TNF but not by visfatin, resistin, adiponectin, chemerin or IGF1. Addition of recombinant FNDC3A at physiological doses (10 ng/mL) to granulosa cells decreased IGF1-dependent progesterone but not estradiol secretion and IGF1-dependent lactate secretion and abundance of GLUT3 and GLUT4 mRNA. This concentration of FNDC3A increased cell viability, abundance of mRNA encoding a putative receptor FOLR1, and increased phosphorylation of Akt. Collectively, these data suggest that FNDC3A may regulate folliculogenesis in cattle by modulating IGF1-dependent granulosa cell steroidogenesis and glucose metabolism.

Suboptimal LH surges can lead to delayed or absent ovulation during reproductive management programs in cattle. Several signaling pathways may enhance the LH signal, potentially including growth factors. In the present study, we determined whether Fibroblast growth factor 18 (FGF18), which mimics some actions of the LH surge on granulosa cells, may potentiate the action of a suboptimal dose of LH using an established bovine granulosa cell (GC) culture system. Addition of recombinant FGF18 increased the concentration of progesterone (P4) in the culture medium. A combination of LH and FGF18 in the culture medium increased the abundance of mRNA encoding EREG, EGR1 and EGR3, proteins that are early modulators of the LH-induced pre-ovulatory cascade. This study demonstrated that FGF18 may be a co-factor in the regulation of the pre-ovulatory cascade in bovine ovarian granulosa cells.

Cystic ovarian disease (COD) in dairy cattle is characterized by preovulatory follicles that become cysts, fail to ovulate and persist in the ovary; consequently, interfering with normal ovarian cyclicity. The intraovarian key players that orchestrate the alterations occurring in the preovulatory follicle and that culminate with cyst formation and persistence, however, remain uncertain. Interestingly, the Hippo pathway effector yes-associated protein (YAP) has been described in humans and mice as a key player of anovulatory cystic disorders. To start elucidating if YAP deregulation in ovarian follicle cells can be also involved in the pathogenesis of COD, we have generated a series of novel results using spontaneously occurring cystic follicles in cattle. We found that mRNA and protein levels of YAP are significantly higher in granulosa (GCs) and theca cells (TCs) isolated from cystic follicles (follicular structures of at least 20 mm in diameter) in comparison to respective cell types isolated from non-cystic large follicles (≥12 mm). In addition, immunohistochemistry and Western blot analyses used to determine YAP phosphorylation pattern suggest that YAP transcriptional activity is augmented is cystic GCs. These results were confirmed by a significant increase in the mRNA levels encoding for the classic YAP-TEAD transcriptional target genes CTGF, BIRC5 and ANKRD1 in GCs from follicle cysts in comparison to non-cystic large follicles. Taken together, these results provide considerable insight of a completely novel signaling pathway that seems to play an important role in ovarian cystic disease pathogenesis in dairy cattle.

To assess the effects of the oocyte on mRNA abundance of FSHR, AMH and major genes of the maturation cascade (AREG, EREG, ADAM17, EGFR, PTGS2, TNFAIP6, PTX

: In brief: Fertility in the dairy cow is low during the post-partum period of negative energy balance and high plasma irisin concentrations. This study shows irisin modulates granulosa cell glucose metabolism and impairs steroidogenesis. Fibronectin type III domain-containing 5 (FNDC5) is a transmembrane protein discovered in 2012 that is cleaved to release the adipokine-myokine, irisin. Originally described as an exercise hormone that browns white adipose tissue and increases glucose metabolism, irisin secretion also increases during periods of rapid adipose mobilization, such as the post-partum period in dairy cattle when ovarian activity is suppressed. The effect of irisin on follicle function is unclear and may be species-dependent. In this study, we hypothesized that irisin may compromise granulosa cell function in cattle using a well-established in vitro cell culture model. We detected FNDC5 mRNA and both FNDC5 and cleaved irisin proteins in follicle tissue and in follicular fluid. The abundance of FNDC5 mRNA was increased by the treatment of cells with the adipokine visfatin but not by other adipokines tested. The addition of recombinant irisin to granulosa cells decreased basal and insulin-like growth factor 1- and follicle-stimulating hormone-dependent estradiol and progesterone secretion and increased cell proliferation but had no effect on viability. Irisin decreased GLUT1, GLUT3, and GLUT4 mRNA levels in granulosa cells and increased lactate release in the culture medium. The mechanism of action is in part through MAPK3/1 but not Akt, MAPK14, or PRKAA. We conclude that irisin may regulate bovine folliculogenesis by modulating granulosa cell steroidogenesis and glucose metabolism.