An Imbalance of IL-33/ST2-AXL-Efferocytosis Axis Induces Pregnancy Loss Through Metabolic Reprogramming of Decidual Macrophage

Abstract During the implantation of embryo, apoptosis is inevitable. These apoptotic cells (AC) are removed by efferocytosis, which fills the macrophage with a metabolite load nearly equal to the phagocyte itself. A timely question pertains to the interrelationship between efferocytosis metabolism and the immune behavior of decidual macrophages (dMΦs) and its effect on pregnancy outcome. Here we report a positive feedback of IL-33/ST2-AXL-efferocytosis leading to pregnancy failure through metabolic reprogramming of dMΦs. We compared the serum level of IL-33, sST2, along with IL-33, ST2, efferocytosis and metabolism of dMΦs from both normal gravidas and unexplained recurrent pregnancy loss (RPL) patients. And we revealed the disturbance of IL-33/ST2 axis, increased apoptotic cells and elevated efferocytosis of dMΦs from the patients with RPL. Afterwards the dMΦs swallowing so many apoptotic cells secreted more sST2 and less TGF-β, which polarized dMΦs towards M1 phenotype. Moreover, the elevated sST2 biased the efferocytosis metabolism of RPL dMΦs towards oxidative phosphorylation and exacerbated the disruption of IL-33/ST2 signaling pathway. The metabolic disorders also led to the dysfunction of efferocytosis, resulting in more uncleared apoptotic cells and the secondary necrosis occurred. We also screened efferocytotic molecule AXL regulated by IL-33/ST2. This positive feedback of IL-33/ST2-AXL-efferocytosis led to pregnancy failure. And the IL-33 knockout mice demonstrated poor pregnancy outcomes, and exogenous supplementation of mouse IL-33 could partially alleviate the fate of embryo losses. These findings highlight a new etiological mechanism whereby dMΦs leverage immunometabolism for the homeostasis of microenvironment at the maternal-fetal interface.