Kiss1 expression in the hypothalamic arcuate nucleus is lower in dairy cows of reduced fertility†.

We tested the hypothesis that divergent genetic merit for fertility of dairy cows is due to aberrant reproductive neuroendocrine function. The kisspeptin status of non-pregnant cows of either positive (POS) or negative (NEG) breeding values (BVs) for fertility was studied in three groups (n = 8), based on their previous post-partum period: POS cows, which had spontaneous ovarian cycles (POS-CYC) and NEG cows, which either cycled (NEG-CYC) or did not cycle (NEG-NONCYC). Ovarian cycles were synchronized, blood samples were taken to define endocrine status, and the animals were slaughtered in an artificial follicular phase. The brains and the pituitary glands were collected for quantitative polymerase chain reaction (qPCR) and in situ hybridization of hypothalamic GNRH1, Kiss1, TAC3, and PDYN and pituitary expression of LHB and FSHB. Gonadotropin releasing hormone (GnRH) and kisspeptin levels were quantified in snap frozen median eminence (ME). GNRH1 expression and GnRH levels in the ME were similar across groups. Kiss1 expression in the preoptic area of the hypothalamus was also similar across groups, but Kiss1 in the arcuate nucleus was almost 2-fold higher in POS-CYC cows than in NEG groups. TAC3 expression was higher in POS-CYC cows. The number of pituitary gonadotropes and the level of expression of LHB and FSHB were similar across groups. We conclude that the lower levels of Kiss1 and TAC3 in NEG cows with low fertility status and may lead to deficient GnRH and gonadotropin secretion.

Exosomes from dairy cows of divergent fertility; Action on endometrial cells.

Abnormalities in endometrial function contribute to poor fertility and reproductive failure. Exosomes are small lipid vesicles that contain transferable bioactive substances; they participate in intercellular signaling and may have critical roles in reproductive mechanisms, including endometrial remodeling in preparation for pregnancy. In this study, we evaluated the effects of exosomes from heifers with high and low genetic merit for fertility on inflammatory mediator expression by bovine endometrial epithelial and stromal cell lines. Co-incubation of exosomes from low, compared with high, fertility heifers upregulated the gene expression of pro-inflammatory IL1A and IL8 (CXCL8) but downregulated IL4 gene expression in epithelial cells. In contrast, stromal cells co-incubated with exosomes from low, compared with high, fertility heifers downregulated the gene expression of CXCL9, CXCL10, and CX3CL1. Our findings demonstrated that circulating exosomes from high fertility heifers did not alter endometrial inflammatory mediator gene expression. In contrast, circulating exosomes from low fertility heifers enhanced endometrial expression of inflammatory mediators, which may contribute to aberrant inflammation, leading to a reduced fertility in low fertility heifers. However, an in-depth investigation is required to elucidate the role of exosomes in regulating endometrial remodeling events required for enhanced reproductive performance and fertility in dairy cows.

Proteome profiling of exosomes derived from plasma of heifers with divergent genetic merit for fertility.

The current study evaluated exosomes isolated from plasma of heifers bred to have high or low fertility through developing extreme diversity in fertility breeding values, however, key animal traits (e.g., body weight, milk production, and percentage of North American genetics) remained similar between the 2 groups. The exosomes were isolated by a combined ultracentrifugation and size exclusion chromatography approach and characterized by their size distribution (nanoparticle tracking analysis), morphology (transmission electron microscopy), and presence of exosomal markers (immunoblotting). In addition, a targeted mass spectrometry approach was used to confirm the presence of 2 exosomal markers, tumor susceptibility gene 101 and flotillin 1. The number of exosomes from plasma of high fertility heifers was greater compared with low fertility heifers. Interestingly, the exosomal proteomic profile, evaluated using mass spectrometry, identified 89 and 116 proteins in the high and low fertility heifers respectively, of which 4 and 31 were unique, respectively. These include proteins associated with specific biological processes and molecular functions of fertility. Most notably, the tetratricopeptide repeat protein 41-related, glycodelin, and kelch-like protein 8 were identified in plasma exosomes unique to the low fertility heifers. These proteins are suggested to play a role in reproduction; however, the role of these proteins in dairy cow reproduction remains to be elucidated. Their identification underscores the potential for proteins within exosomes to provide information on the fertility status and physiological condition of the cow. This may potentially lead to the development of prognostic tools and interventions to improving dairy cow fertility.