Expression profiling of selected miRNAs in equine endometrium in response to LPS challenge in vitro: A new understanding of the inflammatory immune response

Bacterial infections of the genital tract are the major cause of reproductive failure in the mares. MiRNAs are important regulators of gene expression, mostly through transcriptional and translational regression. We hypothesized that LPS induced aberrant expression of miRNAs and their targets, which are involved in regulation of uterine homeostasis. Three groups of primary endometrial epithelial and stromal cells, and endometrial tissue explants were cultured. The 1st group was kept as control, while the 2nd and 3rd groups were challenged with low (0.5 mu g/mL) or high (3.0 mu g/mL) doses of Lipopolysaccharides (LPS). Cell pellets and tissue explants were collected after 24 and 48 h, for total RNA isolation and qRT-PCR of the selected miRNAs and their targets. Culture media and cell lysates were collected after 24 and 48 h, for cytokines (IL6 and TNF alpha) and prostaglandins (PGE(2) & PGF(alpha 2)) measurement. Both endometrial cells expressed TLR4 and its accessory molecules (MyD88 & CD14) that are required for triggering inflammatory immune response after LPS, via up-regulation of TRAF6, TNF alpha, IL6 and IL8, compared to the respective control. After both doses of LPS challenge, miR-155, miR-223 and miR-17 were significantly increased; miR-181b, miR-21 and let-7a were significantly decreased compared to respective controls. Interestingly, miR-24 and miR-532-5p were clearly up-regulated after only the low LPS dose. TNF alpha, IL6 and PGs in culture media and from cell lysates revealed dose- and time-dependent patterns, after LPS. Results indicated that both epithelial and stromal cells have a primary role in innate immune response after LPS challenge, while this recognition occurred via TLR4 and its accessory molecules. Dysregulation of miRNAs and their targets expression after LPS might affect normal uterine function through perturbation of PG and cytokine secretion.