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

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.

A histological study of vascular wall resident stem cells in venous malformations.

Vascular wall resident stem cells (VW-SCs) play a key role in vascular formation and remodeling under both physiological and pathological situations. They not only serve as a reservoir to supply all types of vascular cells needed, but also regulate vascular homeostasis by paracrine effects. Venous malformations (VMs) are common congenital vascular malformations which are just characterized by the deficient quantity and abnormal function of vascular cells. However, the existence and role of VW-SCs in VMs is still unclear at present. In this study, the level and distribution of VW-SCs in 22 specimens of VMs were measured by immunochemistry, double-labeling immunofluorescence, and qPCR, followed by the Spearman rank correlation test. We found that both the protein and mRNA expression levels of CD34, vWF, VEGFR2, CD44, CD90, and CD105 were significantly downregulated in VMs compared with that in normal venules. VW-SCs were sporadically distributed or even absent within and outside the endothelium of VMs. The expression of the VW-SC-related markers was positively correlated with the density of both endothelial cells and perivascular cells. All those results and established evidence indicated that VW-SCs were more sporadically distributed with fewer amounts in VMs, which possibly contributing to the deficiency of vascular cells in VMs.