p‐AKT/VPS4B regulates the small extracellular vesicle size in venous malformation endothelial cells

Abstract Objective Small extracellular vesicle (sEV)‐mediated intercellular communication is increasingly the key for the understanding of venous malformations (VMs). This study aims to clarify the detailed changes of sEVs in VMs. Subjects and Methods Fifteen VM patients without treatment history and twelve healthy donors were enrolled in the study. sEVs were isolated from both fresh lesions and cell supernatant, and were examined by western blotting, nanoparticle tracking analysis and transmission electron microscopy. Western blot analysis, immunohistochemistry and immunofluorescence were adopted to screening candidate regulator of sEV size. Specific inhibitors and siRNA were employed to validate the role of dysregulated p‐AKT/vacuolar protein sorting‐associated protein 4B (VPS4B) signaling on the size of sEVs in endothelial cells. Results The size of sEVs derived from both VM lesion tissues and cell model was significantly increased. VPS4B, whose expression level was mostly significantly downregulated in VM endothelial cells, was responsible for the size change of sEVs. Targeting abnormal AKT activation corrected the size change of sEVs by recovering the expression level of VPS4B. Conclusion Downregulated VPS4B in endothelial cells, resulted from abnormally activated AKT signaling, contributed to the increased size of sEVs in VMs.