Metabolomic and transcriptomic landscape of the bovine uterine lumen during the second week of the estrous cycle.

BACKGROUND

In cattle, the second week after estrus encompasses critical changes in uterine function. The endometrium will either prepare for the release of luteolytic pulses of prostaglandin-F2 alpha or for the support of an eventual pregnancy. We hypothesized that concentrations of amino acids and lipids in the uterine luminal fluid (ULF), and the gene expression in luminal epithelial cells (LE), change across the second week of the estrous cycle. The objective was to compare amino acid and lipid concentrations in ULF and target gene expression in LE 7 (D7), 10 and 14 d after estrus. The ULF and LE samples were collected from the uterine body of five primiparous, non-lactating, cyclic Bos indicus-influenced crossbred cows using a cytological brush on each day after synchronized estrus. Targeted metabolomics of ULF was performed using mass spectrometry, and gene expression in LE was assessed using RNA sequencing. Data were analyzed by uni- and multivariate statistics.

RESULTS

Multivariate analyses separated D7, D10, and D14, with amino acid metabolism and lipid biosynthesis as enriched pathways. Luminal concentrations of amino acids (e.g., arginine, histidine) and lipids (e.g., CE(17:1), PC aa C34:1) increased from D7 to D10, but from D10 to D14 concentrations of amino acids (e.g., glutamine, glutamic acid) decreased while that of lipids (e.g., CE(18:2), SM C16:0) continued to increase. Transcriptomic profiling revealed temporal regulation of 186 amino acid-related and 133 lipid-related genes. Between D7 and D10, there was increased expression of genes for oxidative phosphorylation and extracellular secretion pathways supporting secretory capacity, while decreased expression of genes in arginine-proline metabolism and solute carrier-mediated transport pathways promoted luminal metabolite accumulation. From D10 to D14, there was increased expression of genes in fatty acid elongation and sphingolipid metabolism pathways likely driving lipid synthesis and amino acid catabolism, while decreased expression of genes in protein digestion/absorption and PI3K/AKT signaling pathways reduced nutrient export to the lumen.

CONCLUSIONS

ULF composition and LE gene expression changed markedly during the second week of the estrous cycle. It is plausible that the dynamic shifts in amino acid and lipid metabolites in the uterine lumen reflect changing responses to sex steroids. The influence of such changes on embryo development and pregnancy success in cattle warrants investigation.