Peroxisome proliferator-activated receptor beta/delta ligands as modulators of immune response in lipopolysaccharide-stimulated porcine endometrium: insights from an in vitro study.

Inflammation in the reproductive organs is a serious threat to human and animal fertility. Recently, the possible role of peroxisome proliferator-activated receptor (PPAR) ligands as potential regulators of endometrial inflammation has been proposed. The aim of the present study was to investigate the effect of PPARβ/δ ligands on mRNA abundance and protein secretion of selected inflammatory mediators - interleukin (IL)-1β, IL-6, IL-8, IL-4, IL-10, tumor necrosis factor alpha (TNF-α), leukemia inhibitory factor (LIF), toll-like receptor 4 (TLR4) and nuclear factor kappaB (NF-κB) - in porcine endometrium during physiology and lipopolysaccharide (LPS)-stimulated inflammation in both the mid-luteal and follicular phases of the estrous cycle. In addition, two experimental setups - an ongoing and a developing inflammation - were considered. Sections of endometrial tissue were incubated in vitro with two selected PPARβ/δ ligands: agonist L-165,041 or antagonist GSK 3787 with or without LPS. The mRNA abundance was determined by real time polymerase chain reaction (RT-PCR) and protein secretion in the culture medium by enzyme-linked immunosorbent assay (ELISA). Both PPARβ/δ ligands increased the mRNA abundance of IL-1β, IL-6 and IL-8 in the inflammatory state and decreased IL-4 protein secretion in the physiological state, mainly in the mid-luteal phase of the estrous cycle. In turn, only the antagonist increased TNF-α expression. For all proinflammatory cytokines - IL-1β, IL-6, IL-8, TNF-α - we found that both hormonal and inflammatory status significantly influenced their mRNA levels, while the experimental setup notably affected the expression of IL-1β, IL-6 and TNF-α. The results show that PPARβ/δ ligands modulate the expression and secretion of cytokines involved in the inflammatory response in the porcine endometrium. The main effect of PPARβ/δ ligands was noted during the mid-luteal phase of the estrous cycle. During LPS-stimulated inflammation, PPARβ/δ ligands appear to have pro-inflammatory properties by stimulating the expression of IL-1β, IL-6, IL-8, TNF-α. The changes in the expression of immune mediators depend on the phase of the estrous cycle or the course of endometritis.