Paeoniflorin alleviates fibrosis in cows with clinical endometritis by inhibiting macrophage M1 polarization

Endometritis, which can cause endometrial fibrosis, is one of the key factors leading to the decline of pregnancy and reproduction rates in cows. Macrophages can be polarized into M1 type pro-inflammatory phenotype to aggravate endometrial injury under pathological conditions. Paeoniflorin (PF) is a single glucoside extracted from Paeoniaceae, which has anti-fibrosis and anti-inflammatory effects. However, its effect on fibrosis in endometritis in cows is unknown. In this study, we examined uterine fibrosis and macrophage polarization in endometritic cows, and established a macrophage-bovine endometrial stromal cell (BESC) co-culture system to clarify PF's protective mechanism. In vivo, endometritic cattle showed prominent collagen accumulation, elevated M1 markers CD86/iNOS, reduced epithelial E-cadherin, and increased fibrotic markers N-cadherin, α-SMA and Vimentin. In vitro, LPS-induced M1 macrophages were confirmed as a vital driver of BESC fibrosis, while M0 unpolarized or IL-4-stimulated M2 macrophages exerted no fibrotic effects. Mechanistically, PF suppressed NF-κB/STAT1 phosphorylation to block M1 polarization and reverse M1-mediated BESC fibrosis. In summary, the results of the present study indicate that PF attenuates endometrial fibrosis in cows by inhibiting M1 polarization of macrophages through the NF-κB and STAT1 pathway. These results provided insights into the exploration of therapeutic targets and intervention strategies for endometritis in cows.