Endometrial stromal cell-derived TMAO sustains decidualization to prevent recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA), often linked to defective endometrial stromal cell (ESC) decidualization, lacks effective metabolism-targeted therapies. Here, we identify the in situ synthesis of trimethylamine N-oxide (TMAO) in human decidua as a critical safeguard. Metabolomics revealed significantly lower TMAO levels in decidual tissues of individuals experiencing RSA. Mechanistically, cyclic AMP (cAMP)-protein kinase A (PKA)-cAMP-responsive element-binding protein 1 (CREB1) signaling upregulated flavin-containing monooxygenase 3 (FMO3) in ESCs, driving local TMAO accumulation. TMAO directly bound the C terminus of 14-3-3η, enhancing its interaction with phosphoinositide-dependent protein kinase 1 (PDK1) to relieve PDK1-mediated suppression of forkhead box protein O1 (FOXO1). This promoted FOXO1 nuclear translocation and the activation of decidualization markers. Through mouse models employing dietary choline restriction, and FMO3 inhibition via pharmacological or genetic knockout, we demonstrated that endometrial TMAO deficiency impairs decidualization and increases pregnancy loss. Strikingly, TMAO restored decidualization capacity in 15% of patient-derived ESCs with inherent dysfunction. Our findings unveil endometrial TMAO synthesis as a metabolic checkpoint for decidualization and propose it as a therapeutic candidate for RSA.