Abstract
BackgroundVenous malformations (VMs), most of which associated with activating mutations in the endothelial cells (ECs) tyrosine kinase receptor TIE2, are characterized by dilated and immature veins with scarce smooth muscle cells (SMCs) coverage. However, the underlying mechanism of interaction between ECs and SMCs responsible for VMs has not been fully understood.MethodsHere, we screened 5 patients with TIE2-L914F mutation who were diagnosed with VMs by SNP sequencing, and we compared the expression of platelet-derived growth factor beta (PDGFB) and α-SMA in TIE2 mutant veins and normal veins by immunohistochemistry. In vitro, we generated TIE2-L914F-expressing human umbilical vein endothelial cells (HUVECs) and performed BrdU, CCK-8, transwell and tube formation experiments on none-transfected and transfected ECs. Then we investigated the effects of rapamycin (RAPA) on cellular characteristics. Next we established a co-culture system and investigated the role of AKT/FOXO1/PDGFB in regulating cross-talking of mutant ECs and SMCs.ResultsVMs with TIE2-L914F mutation showed lower expression of PDGFB and α-SMA than normal veins. TIE2 mutant ECs revealed enhanced cell viability and motility, and decreased tube formation, whereas these phenotypes could be reversed by rapamycin. Mechanically, RAPA ameliorated the physiological function of mutant ECs by inhibiting AKT-mTOR pathway, but also facilitated the nuclear location of FOXO1 and the expression of PDGFB in mutant ECs, and then improved paracrine interactions between ECs and SMCs. Moreover, TIE2 mutant ECs strongly accelerated the transition of SMCs from contractile phenotype to synthetic phenotype, whereas RAPA could prevent the phenotype transition of SMCs.ConclusionsOur data demonstrate a previously unknown mechanistic linkage of AKT-mTOR/FOXO1 pathway between mutant ECs and SMCs in modulating venous dysmorphogenesis, and AKT/FOXO1 axis might be a potential therapeutic target for the recovery of TIE2-mutation causing VMs.52RPJ9Szvdmv-kgYy_rb11Video Graphical abstract
Highlights
Venous malformations (VMs), most of which associated with activating mutations in the endothelial cells (ECs) tyrosine kinase receptor TIE2, are characterized by dilated and immature veins with scarce smooth muscle cells (SMCs) coverage
Reduced platelet-derived growth factor beta (PDGFB) and α-smooth muscle actin (α-SMA) expression in VMs with TIE2L914F mutation We extracted DNA from paraffin section specimens from 20 patients diagnosed as VMs and found that 5 of them were identified as TIE2-L914F mutation (2740 C>T) (Fig. 1a and Additional file 1: Figure S1)
Our results showed that RAPA down-regulated the phosphorylation of Protein Kinase B (AKT), Factors transcription forkhead 1 (FOXO1), and mammalian TOR (mTOR), especially in RAPA promotes the interaction of ECs and SMCs To further investigate whether RAPA could improve effects of TIE2-L914F mutant ECs on SMCs, we cocultured two kinds of cells using a transwell chamber
Summary
Venous malformations (VMs), most of which associated with activating mutations in the endothelial cells (ECs) tyrosine kinase receptor TIE2, are characterized by dilated and immature veins with scarce smooth muscle cells (SMCs) coverage. The underlying mechanism of interaction between ECs and SMCs responsible for VMs has not been fully understood. Venous malformations (VMs) are the most common vascular anomalies with an estimated incidence of about 1/ 10000 of the population. TIE2 (TEK), a member of the receptor tyrosine kinase subfamily, is mainly expressed in endothelial cells (ECs) [7]. Human umbilical vein endothelial cells (HUVECs) engineered to express TIE2-L914F recapitulate VMs when injected in immunodeficient mice [18]. An effective inhibitor of TIE2 signaling pathway tends to be a potential target for the treatment of VMs
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