Effect of Preimplanataion Factor (PIF) and lipopolysaccharide on inflammatory responses of equine endometrial explants in vitro

AIMS: PIF is secreted only by viable mammalian embryos and is essential for achieving maternal immune-tolerance without immune-suppression. In human endometrium PIF coordinates and supports implantation and modulates immunity. Transposed to non-pregnant models, PIF displays immune-control and regenerative features in neuroinflammation and diabetes. The aim was to test the hypothesis that PIF exerts anti-inflammatory properties towards equine endometrium challenged with Escherichia coli-derived lipopolysaccharide (LPS) using an established endometrial explant culture model of uterine inflammation. METHODS: Luteal (n = 8), follicular (n=3), transitional (n=4) and anoestrus (n = 4) stage endometrium was collected from slaughtered mares. Explants were cultured in triplicate in serum-free medium alone (control) and with 0, 50 or 100nM sPIF (25-100nM = human physiologic dose) and ± LPS (3µg/ml). Media samples were collected at 24 and 72 h and prostaglandin F2α (PGF2α) and PGE2 secreted into cultured medium were used as markers of inflammation determined by radioimmunoassay. RESULTS: Overall mean PGF2α secretion by control explants was greater than PGE2 at both sampling points: P<0.001, 24 hours (463.9 ±58.2 vs. 15.7 ±2.7 ng/ml); P<0.001 as well?, if so state again 72 hours, 1441.5 ±106.2 vs. 53.8 ±5.8 ng/ml. When compared to the control, LPS stimulated secretion of PGE2 by 3.1 and 2.4 fold at 24 and 72 hours respectively, in explants from mares at all stages (P<0.001). PGF2α secretion was increased at 24 hours only in follicular stage explants challenged with LPS (1.8 fold change from control; P<0.05). sPIF alone did not alter prostaglandin secretion by explants compared to control. In follicular stage explants both 50 and 100 nM sPIF abrogated LPS induced PGF2α secretion at 24 hours post treatment (P<0.05). CONCLUSION AND PRACTICAL SIGNIFICANCE: The effects of LPS and sPIF on prostaglandin secretion by endometrial explants are modulated by stage of oestrous cycle. PIF treatment exerts and anti-inflammatory effect in follicular tissue blocking both LPS-induced PGF2α. Data advocates sPIF anti-inflammatory role in non-pregnant endometrium which complements PIF’s essential role in supporting embryo implantation.