Phoenixin-14 and its receptor GPR173 in the bovine endometrium: Expression and regulation during the estrous cycle and impact on secretory activity

Abstract

The endometrium remodels during the estrous cycle due to many endogenous factors. Phoenixin (PNX)-14 is a relatively recently discovered neuropeptide with a pivotal role in reproduction, specifically in follicle development and the functioning of the corpus luteum and uterus. Our study aimed to determine (1) the expression of PNX-14 and G protein-coupled receptor 173 (GPR173) in the bovine endometrium during the estrous cycle, (2) the cellular localization of PNX-14 and GPR173, (3) the effect of luteotropic and luteolytic factors on PNX-14 and GPR173 expression in the endometrium, and (4) the impact of PNX-14 on the secretory activity of the endometrium. The ex vivo experiments used bovine uterine tissues collected from the four stages of the estrous cycle (days 2–5, 6–10, 11–16, and 17–20). The in vitro experiments used uteri collected from days 10–12 of the estrous cycle. The mRNA expression of small integral membrane protein 20 (SMIM20) and protein expression of PNX-14 was upregulated on days 6–10 of the estrous cycle. GRP173 protein expression was significantly higher on days 11–16. The concentration of PNX-14 in endometrial tissue homogenate was significantly lower on days 17–20 compared to all other days of the estrous cycle. In immunofluorescence analysis, luminal and glandular epithelium and endothelial cells of blood vessels were positive for PNX-14 and GPR173. Progesterone upregulated the mRNA expression of SMIM20 in the bovine endometrium, whereas progesterone and oxytocin upregulated GPR173 mRNA and protein expression. Treating endometrial slices with PNX-14 enhanced prostaglandin E₂ secretion. In conclusion, these findings indicate that PNX-14 targets the bovine endometrium and should be considered a locally acting regulator of endometrium function in non-pregnant cows.