A newly intervention strategy in preeclampsia: Targeting PD-1/Tim-3 signaling pathways to modulate the polarization of decidual macrophages.

Programmed cell death-1 (PD-1) and T-cell immunoglobulin mucin-3 (Tim-3) are important immune checkpoint receptors that prevent an overreacted maternal immune response to fetal antigens during pregnancy. Disruption of complex immune regulation mechanisms is associated with adverse pregnancy outcomes, including preeclampsia (PE). Our recent study showed that the Tim-3 pathway was involved in the regulation of decidual macrophage polarization. Decidual macrophages polarized to the M1 phenotype may impair uterine vessel remodeling during placentation, accounting for the occurrence of PE. Co-blockade of the PD-1/Tim-3 pathway was shown to successfully control tumor growth in preclinical cancer models. However, the effects of activating both PD-1 and Tim-3 pathways as a combined intervention strategy in PE are never reported. Herein, we observed the skew of decidual macrophage polarization toward the M1 phenotype in patients with PE and lipopolysaccharide (LPS)-induced PE-like rat model. Moreover, we found that the activation of PD-1/Tim-3 pathway by using PD-L1 and Gal-9 fusion proteins could alleviate the manifestation of the LPS-induced PE-like rats and protect their offspring. Compared with the single intervention, the combination of PD-L1and Gal-9 fusion proteins exhibited obvious advantages in the relief of PE-like symptoms, trophoblast invasion, and fetal vascular development, indicating a synergistic effect of the activated PD-1/Tim-3 pathway. The in vitro study also revealed that the combined intervention using PD-L1 and Gal-9 fusion proteins inhibited the LPS-induced M1 macrophage polarization via the synergic activation of the ERK/GSK3β/β-catenin signaling pathway. Together, our findings provide the first evidence that simultaneous activation of PD-1/Tim-3 signaling pathways may have an optimal protective effect and serve as a new potential target for PE intervention.