ANG2 Blockade Diminishes Proangiogenic Cerebrovascular Defects Associated With Models of Hereditary Hemorrhagic Telangiectasia

Abstract

BACKGROUND: Hereditary hemorrhagic telangiectasia (HHT) is a vascular disorder characterized by arteriovenous malformations and blood vessel enlargements. However, there are no effective drug therapies to combat arteriovenous malformation formation in patients with HHT. Here, we aimed to address whether elevated levels of ANG2 (angiopoietin-2) in the endothelium is a conserved feature in mouse models of the 3 major forms of HHT that could be neutralized to treat brain arteriovenous malformations and associated vascular defects. In addition, we sought to identify the angiogenic molecular signature linked to HHT. METHODS: Cerebrovascular defects, including arteriovenous malformations and increased vessel calibers, were characterized in mouse models of the 3 common forms of HHT using transcriptomic and dye injection labeling methods. RESULTS: Comparative RNA sequencing analyses of isolated brain endothelial cells revealed a common, but unique proangiogenic transcriptional program associated with HHT. This included a consistent upregulation in cerebrovascular expression of ANG2 and downregulation of its receptor Tyr kinase with Ig and EGF homology domains (TIE2/TEK) in HHT mice compared with controls. Furthermore, in vitro experiments revealed TEK signaling activity was hampered in an HHT setting. Pharmacological blockade of ANG2 improved brain vascular pathologies in all HHT models, albeit to varying degrees. Transcriptomic profiling further indicated that ANG2 inhibition normalized the brain vasculature by impacting a subset of genes involved in angiogenesis and cell migration processes. CONCLUSIONS: Elevation of ANG2 in the brain vasculature is a shared trait among the mouse models of the common forms of HHT. Inhibition of ANG2 activity can significantly limit or prevent brain arteriovenous malformation formation and blood vessel enlargement in HHT mice. Thus, ANG2-targeted therapies may represent a compelling approach to treat arteriovenous malformations and vascular pathologies related to all forms of HHT.

Therapeutic Targeting of the Ang2/Tie Pathway in Endothelial Cells as a Potential Treatment of Hereditary Hemorrhagic Telangiectasia

“…19 Comparative RNA sequencing analyses of isolated brain ECs from Smad4-iEC.KO , Eng-iEC.KO , and Alk1-iEC.KO mice revealed a common proangiogenic transcriptional profile associated with HHT. 1 This genetic fingerprint was in agreement with an upregulation of Ang2 in brain vessels and a downregulation of its receptor Tek/Tie2 in HHT mice compared with controls. Accordingly, a reduction of Tek signaling was also observed in vitro using human ECs mimicking the HHT2 condition.…”

“…16 Thus, increased expression of Ang2 induced by the GNAQ variant p.R183Q in human ECs was found to drive the formation of enlarged blood vessels in mice, while knockdown of Ang2 in ECs carrying the GNAQ /R183Q variant normalized the size of the vessels. 17,18 As a follow-up to the above findings, now Zhou et al 1 have further analyzed and confirmed the regulated expression and function of Ang2 not only in Smad4-iEC.KO but also in Eng-iEC.KO and Alk1-iEC.KO mouse models of HHT (Figure). In this case, the authors centered their studies on brain ECs and brain AVMs, a goal justified by the fact that ≈10% to 20% of patients with HHT present with brain AVMs.…”

“…Therapeutic Targeting of the Ang2/Tie Pathway in Endothelial Cells as a Potential Treatment of Hereditary Hemorrhagic Telangiectasia Carmelo Bernabeu A s many other rare diseases of genetic origin, hereditary hemorrhagic telangiectasia (HHT) is currently in need for a cure. In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, Zhou et al 1 present experimental evidences that pharmacological blockade of Ang2 (angiopoietin-2)-a key regulator of angiogenesis-prevents and improves the vascular lesions in the brain of 3 different genetic mouse models of HHT, suggesting that Ang2-targeted therapies could be used in patients with HHT. This exciting discovery opens up a new research avenue for therapeutic prevention and treatment of vascular malformations in HHT.…”

“…Actually, since 2000, many researchers have been using different genetic HHT animal models trying to find the way to prevent and reverse the vascular lesions (telangiectases and AVMs), which are responsible for the clinical symptoms in HHT. 14 In this context, Zhou et al 1 focus their study on Ang2-based preliminary experimental evidence supporting its involvement in HHT and AVM development. Upon RNA and chromatin immunoprecipitation sequencing experiments on BMP9-stimulated ECs and isolated ECs from a Smad4-inducible EC-specific knockout ( Smad4-iECKO ) mouse model, the same group identified the EC surface receptor Tek/Tie2 (tyrosine kinase receptor of angiopoietins) and its antagonistic ligand Ang2 as downstream targets of Smad4.…”

“…Remarkably, in vivo neutralization of Ang2 using a specific monoclonal antibody (LC10) improved, at different degrees, brain vascular lesions in the 3 HHT animal models, a finding consistent with in vitro results showing that inhibition of Ang2 normalizes the gene signature in brain ECs derived from Smad4-iEC.KO mice. 1 While providing hope for future pharmacological treatments, additional investigations are needed to better understand the underlying cellular and molecular mechanisms of Ang2 regulation and activity in the HHT setting. For example, although this study has focused on brain AVMs, patients with HHT present with additional vascular lesions like lung and hepatic AVMs or mucosal telangiectases in the nose and gastrointestinal tract.…”