PIEZO1 overexpression in hereditary hemorrhagic telangiectasia arteriovenous malformations
Background: Hereditary hemorrhagic telangiectasia (HHT) is an inherited vascular disorder characterized by arteriovenous malformations (AVMs). Loss-of-function mutations in Activin receptor-like kinase 1 (ALK1) cause type 2 HHT and Alk1 knockout (KO) mice develop AVMs along with overactivation of VEGFR2/PI3K/AKT signaling. The full spectrum of signaling alterations resulting from ALK1 mutations remains unknown, and more effective and specific inhibitors to combat AVM formation in patients are needed.  Methods: Single-cell RNA sequencing of endothelial-specific Alk1 KO mouse retinas and controls was performed. Overexpression of fluid shear stress signaling signatures including the mechanosensitive ion channel PIEZO1 was confirmed in mouse and human HHT2 lesions. Genetic and pharmacological PIEZO1 inhibition was tested in Alk1 KO mice, along with downstream PIEZO1 signaling.  Results: A cluster of Alk1 mutant endothelial cells with altered arterio-venous identity overexpressed pathways related to fluid shear stress, hypoxia, inflammation, cell cycle and VEGFR2/PI3K/AKT signaling. Piezo1 deletion and pharmacological inhibition in Alk1-deficient mice mitigated AVM formation, whereas Piezo1 overexpression enhanced AVM formation induced by ALK1 ligand blockade. Mechanistically, PIEZO1 inhibition reduced elevated VEGFR2/AKT, ERK5-p62-KLF4, eNOS, hypoxia, proliferation and inflammation in ALK1 deficient endothelium.  Conclusions: PIEZO1 expression and signaling are elevated in HHT2. PIEZO1 blockade reduces AVM formation and alleviates cellular and molecular hallmarks of ALK1-deficient cells. This finding provides new insights into the mechanistic underpinnings of ALK1-related vascular diseases and identifies potential therapeutic targets to prevent AVMs. Overall design: Single-cell RNA sequencing of endothelial-specific Alk1 KO mouse retinas and controls was performed