Progesterone concentrations during superovulation and estrous behavior affect post-estrus endometrial gene expression in Holstein heifers.

The main objective of this study was to evaluate if different concentrations of progesterone (P4) during superovulation and different intensities of estrous expression affected endometrial gene expression 7 d after artificial insemination (AI) in Holstein heifers. Our secondary objective was to explore the potential role of estradiol (E2) concentrations before estrus in relation to these factors. Post-puberty Holstein heifers were randomly assigned into 2 treatment groups: high P4 or low P4. Animals received a presynchronization protocol followed by a protocol of superovulation that included the assigned P4 treatment. Activity was monitored by an automated wearable sensor, and estrous behavior (intensity and duration) was recorded. A total of 39 heifers (high P4: n = 19; low P4: n = 20) were submitted to uterine biopsy 7 d after AI. We conducted RNA extraction for each sample, and the count of mRNA molecules for 91 target genes were determined using the NanoString nCounter system. The intensity and duration of estrus were used to categorize heifers as high or low estrous expression using the median. Count outcome data were normalized to housekeeping genes and analyzed using a mixed linear regression model with heifer as random effect. Significance for differential expression was set at false discovery rate <0.1 and absolute fold change ≥1.5. The P4 treatment or estrous expression alone were not associated with changes in endometrial gene expression; however, their interaction significantly influenced the expression of 12 target genes. Most of these genes were related to the immune system signaling (CXCL8, IL1B, MUC1, PTX3), indicating an upregulation of this biological function in the endometrium of heifers treated with low P4 and having low estrous expression. Pathway analysis confirmed the involvement of the immune response with downstream effects linked to transmigration of leukocytes, cell movement of monocytes, accumulation of phagocytes and mobilization of neutrophils. Additional E2 analysis demonstrated that concentrations of E2 before estrus influenced the expression of genes related to extracellular matrix remodeling (MMP14, MMP19, POSTN), immune system (MUC1, IL1B, CSF1), growth factors (IGF1, IGF1R, FGF2), and eicosanoid metabolic processes (AKR1B1, AKR1C4, PTGIS, HPGD) regardless of the P4 treatment. In conclusion, heifers treated with low P4 during superovulation and exhibiting low intensity and duration of estrus had distinct endometrial gene expression profiles 7 d after AI compared with those treated with high P4. Additional E2 analysis demonstrated that concentrations of E2 2 d before estrus influenced post-estrus endometrial gene expression independently of the pre-estrus P4 profile.