The effect of Toxoplasma gondii infection on Galectin-9 expression in decidual macrophages contributing to dysfunction of decidual NK cells during pregnancy

Abstract Background: Toxoplasma gondii infection causes adverse pregnancy outcomes by affecting the expression of immunotolerant molecules in decidual immune cells. Galectin-9 (Gal-9) is widely expressed in decidual macrophages (dMφ) and is crucial for maintaining normal pregnancy by interacting with the immunomodulatory protein Tim-3. However, the effects of T. gondii infection on Gal-9 expression levels in dMφ during pregnancy, as well as the impact of altered Gal-9 expression levels on the maternal-fetal tolerance function of dNK cells, are still unknown. Methods: Pregnancy outcomes of T. gondii infected C57BL/6 and Lgals9-/- pregnant mice models were recorded. The pathological change was evaluated by HE staining. The expression of Gal-9 in T. gondii infected dMφ were examined using flow cytometry and immunofluorescence. Expressions of Gal-9, JNK, p-JNK, FOXO1 were detected by Western Blot. The binding of FOXO1 to the promoter of Lgals9 was determined by ChIP-PCR. Supernatants from control or infected dMφ was co-cultured with purified human dNK cells with or without recombinant human Gal-9 protein (rhGal-9) or neutralized antibody of Tim-3, the expression of ERK, p-ERK, CREB, p-CREB, T-bet, IL-10 and IFN-γ were assayed by Western Blot. Results: T. gondii infection promoted JNK phosphorylation and increased FOXO1 expression in dMφ, resulting in reduction of Gal-9 due to the elevated binding of FOXO1 with Lgals9 promoter. Downregulation of Gal-9 enhanced the phosphorylation of ERK and inhibited phosphorylation of CREB and expression of IL-10, and promoted the expression of T-bet and IFN-γ. In mice model, knockout of Gal-9 aggravated adverse pregnancy outcomes caused by T. gondii infection during pregnancy. Conclusions: T. gondii infection suppressed Gal-9 expression in dMφ by activating the JNK/FOXO1 signaling pathway, and reduction of Gal-9 resulted in dysfunction of dNK via Gal-9/Tim-3 interaction. This study provided new insights for the molecular mechanisms of the adverse pregnancy outcomes caused by T. gondii.