Endometrial responsiveness to interferon-tau and its association with subsequent reproductive performance in dairy heifers.

Our objectives were to evaluate the endometrial responsiveness of dairy heifers to an intrauterine infusion of recombinant bovine interferon-tau (rbIFN-τ) and to associate endometrial responses to rbIFN-τ with subsequent reproductive performance. In Experiments 1 and 2, cyclic heifers were enrolled in a 5-d CIDR Cosynch program for estrous synchronization, and blood sampling and ultrasonography examinations were performed on d 0, 4, 7, 11, and 14 of the estrous cycle. In Experiment 1, heifers were randomly assigned to receive an intrauterine infusion containing 2 µg of rbIFN-τ (rbIFN-τ = 19) or saline (CTRL = 19) into the uterine horn ipsilateral to the corpus luteum (CL) on d 14 of the estrous cycle. Six hours after the infusion, the infused uterine horn was flushed for sampling of the uterine luminal fluid (ULF) for analyses of composition, and the endometrium was biopsied for transcriptomics. In Experiment 2, 100 heifers received an intrauterine infusion of rbIFN-τ, and the same procedures for uterine sample collection described in Experiment 1 were performed. After the intrauterine test, heifers were enrolled in a breeding program and classified as highly fertile (HF; pregnant at first AI) or subfertile (SF; not pregnant at first AI). Statistical analyses were performed using linear regression models, which included the effects of treatment (Experiment 1: CTRL vs. rbIFN-τ) or fertility group (Experiment 2: HF vs. SF) and block of samples. Intrauterine infusion of rbIFN-τ increased the expression of classical interferon-stimulated genes in the endometrium (e.g., ISG15, MX1, OAS2, IRF9, and USP18), and an antiviral response was predicted to be the main downstream effect of the transcriptome changes. In addition, rbIFN-τ increased the abundance of cholesterol, glycerol, and the overall concentration of oxylipins in the ULF. Analysis of endometrial transcriptome between HF and SF heifers revealed important differences in the expression of proteins associated with cell signaling, metabolism, attachment, and migration, with a large representation of genes encoding extracellular matrix proteins. In general, differently expressed genes were expected to be downregulated by IFN-τ but seemed to fail to be downregulated in SF heifers, resulting in higher expression in SF compared with HF heifers. Subfertile heifers had lower concentrations of glycerol and an altered profile of oxylipins in the ULF, with lower abundance of oxylipins derived from arachidonic acid and dihomo-γ-linolenic acid, and greater abundance of oxylipins derived from linoleic acid. Measurements of ovarian function did not differ between groups and, therefore, did not influence the observed results in uterine biology. In conclusion, the endometrial responsiveness to IFN-τ is variable among individuals and associated with subsequent fertility of heifers, indicating that communication between conceptus and endometrium is critical for the uterine receptivity and survival of pregnancy.