Inhibition of FKBP5 alleviates obstetric antiphospholipid syndrome by regulating macrophage polarization

Immune homeostasis disturbance within the placental microenvironment plays a key role in the pathogenesis of obstetric antiphospholipid syndrome (OAPS), although the underlying mechanisms remain poorly understood. This study aimed to investigate the immune regulatory role of FK506-binding protein 5 (FKBP5) in OAPS-associated pathological pregnancies. RNA sequencing and immunocytotyping were performed on decidual tissues from OAPS patients and healthy controls. Bone marrow-derived macrophages (BMDMs) polarization assays and macrophage‒trophoblast coculture models were employed to explore the effects and mechanisms of FKBP5 on macrophage polarization at the maternal-fetal interface. We applied an animal model of OAPS and comprehensively evaluated the therapeutic effects of the FKBP5 inhibitor SAFit2 on OAPS. The results revealed significantly greater expression of FKBP5 and inflammation-related factors in OAPS patients than in healthy controls. An imbalance in macrophage polarization was observed, with an increase in M1 (iNOS⁺/CD86⁺) macrophages and a decrease in M2 (Arg-1⁺/CD206⁺) macrophages in OAPS patients. In vitro studies demonstrated that FKBP5 may promote M1 polarization via the JAK1/STAT1 pathway and may inhibit M2 polarization through the PPARγ/STAT6 pathway. FKBP5-induced aberrant macrophage polarization impaired trophoblast migration, invasion, and proliferation. In vivo, FKBP5 knockdown in mice alleviated aPLs-induced placental injury, facilitated epithelial‒mesenchymal transition (EMT), and restored the M1/M2 macrophage balance. Furthermore, SAFit2 ameliorated pregnancy complications in the mouse OAPS model. FKBP5 regulates immune dysfunction associated with OAPS by modulating macrophage polarization, and its inhibition could mitigate aPLs-induced placental injury. These findings suggest that FKBP5 may serve as a promising therapeutic target for OAPS.