FLT1 (fms-related receptor tyrosine kinase 1) is a vascular endothelial growth factor receptor that regulates angiogenesis and placental growth factor signaling 1. FLT1 promotes osteogenesis and inhibits adipogenesis in bone marrow mesenchymal stem cells through PI3K/AKT and MAPK signaling pathways 2. The receptor is transcriptionally regulated by IL-4-activated STAT6 signaling and EGR2 transcription factors in alternatively polarized macrophages, where it suppresses proangiogenic activity 3. FLT1 expression is controlled by cAMP-response elements and ETS-binding sites in its promoter across multiple cell types including endothelial cells and trophoblasts 4. Clinically, soluble FLT1 (sFLT1), a native VEGF decoy receptor, serves as a therapeutic target in preeclampsia, where excessive sFLT1 contributes to maternal morbidity and mortality 5. Beyond angiogenesis, sFLT1 binds macrophages via heparan sulfates and neuropilin-1, modulating anti-inflammatory macrophage function and reducing chemokine receptor expression 6. These findings establish FLT1 as a multifunctional receptor with roles in vascular biology, bone metabolism, inflammation, and pregnancy complications.