Heat Stress Impairs Maternal Endometrial Integrity and Results in Embryo Implantation Failure by Regulating Transport-Related Gene Expression in Tongcheng Pigs

Heat stress (HS) poses a significant threat to production and survival in the global swine industry. However, the molecular regulatory effects of heat stress on maternal endometrial cells are poorly understood in pigs during early embryo implantation. In this study, we systematically examined morphological changes in the endometrium and the corresponding regulation mechanism in response to HS by combining scanning electron microscopy (SEM), hematoxylin/eosin (H&E) staining, western blot, and RNA-seq analyses. Our results showed that HS led to porcine endometrium damage and endometrial thinness during embryo implantation. The expression levels of cell adhesion-related proteins, including N-cadherin and E-cadherin, in the uterus were significantly lower in the heat stress group (39 ± 1 °C, n = 3) than in the control group (28 ± 1 °C, n = 3). A total of 338 up-regulated genes and 378 down-regulated genes were identified in porcine endometrium under HS. The down-regulated genes were found to be mainly enriched in the pathways related to the microtubule complex, immune system process, and metalloendopeptidase activity, whereas the up-regulated genes were mainly involved in calcium ion binding, the extracellular region, and molecular function regulation. S100A9 was found to be one of the most significant differentially expressed genes (DEGs) in the endometrium under HS, and this gene could promote proliferation of endometrial cells and inhibit their apoptosis. Meanwhile, HS caused endometrial epithelial cell (EEC) damage and inhibited its proliferation. Overall, our results demonstrated that HS induced uterine morphological change and tissue damage by regulating the expression of genes associated with calcium ions and amino acid transport. These findings may provide novel molecular insights into endometrial damage under HS during embryo implantation.