Vascular Malformations In Hereditary Hemorrhagic Telangiectasia Research Articles

Induced Endothelial Cell Cycle Arrest Prevents Arteriovenous Malformations in Hereditary Hemorrhagic Telangiectasia.

Distinct endothelial cell cycle states (early G1 versus late G1) provide different "windows of opportunity" to enable the differential expression of genes that regulate venous versus arterial specification, respectively. Endothelial cell cycle control and arteriovenous identities are disrupted in vascular malformations including arteriovenous shunts, the hallmark of hereditary hemorrhagic telangiectasia (HHT). To date, the mechanistic link between endothelial cell cycle regulation and the development of arteriovenous malformations (AVMs) in HHT is not known. We used BMP (bone morphogenetic protein) 9/10 blocking antibodies and endothelial-specific deletion of activin A receptor like type 1 (Alk1) to induce HHT in Fucci (fluorescent ubiquitination-based cell cycle indicator) 2 mice to assess endothelial cell cycle states in AVMs. We also assessed the therapeutic potential of inducing endothelial cell cycle G1 state in HHT to prevent AVMs by repurposing the Food and Drug Administration-approved CDK (cyclin-dependent kinase) 4/6 inhibitor (CDK4/6i) palbociclib. We found that endothelial cell cycle state and associated gene expressions are dysregulated during the pathogenesis of vascular malformations in HHT. We also showed that palbociclib treatment prevented AVM development induced by BMP9/10 inhibition and Alk1 genetic deletion. Mechanistically, endothelial cell late G1 state induced by palbociclib modulates the expression of genes regulating arteriovenous identity, endothelial cell migration, metabolism, and VEGF-A (vascular endothelial growth factor A) and BMP9 signaling that collectively contribute to the prevention of vascular malformations. This study provides new insights into molecular mechanisms leading to HHT by defining how endothelial cell cycle is dysregulated in AVMs because of BMP9/10 and Alk1 signaling deficiencies, and how restoration of endothelial cell cycle control may be used to treat AVMs in patients with HHT.

Somatic Mutations in Vascular Malformations of Hereditary Hemorrhagic Telangiectasia Result in Bi-allelic Loss of ENG or ACVRL1

Hereditary hemorrhagic telangiectasia (HHT) is a Mendelian disease characterized by vascular malformations (VMs) including visceral arteriovenous malformations and mucosal telangiectasia. HHT is caused by loss-of-function (LoF) mutations in one of three genes, ENG, ACVRL1, or SMAD4, and is inherited as an autosomal-dominant condition. Intriguingly, the constitutional mutation causing HHT is present throughout the body, yet the multiple VMs in individuals with HHT occur focally, rather than manifesting as a systemic vascular defect. This disconnect between genotype and phenotype suggests that a local event is necessary for the development of VMs. We investigated the hypothesis that local somatic mutations seed the formation HHT-related telangiectasia in a genetic two-hit mechanism. We identified low-frequency somatic mutations in 9/19 telangiectasia through the use of next-generation sequencing. We established phase for seven of nine samples, which confirms that the germline and somatic mutations in all seven samples exist in trans configuration; this is consistent with a genetic two-hit mechanism. These combined data suggest that bi-allelic loss of ENG or ACVRL1 may be a required event in the development of telangiectasia, and that rather than haploinsufficiency, VMs in HHT are caused by a Knudsonian two-hit mechanism.

Pericytes in Hereditary Hemorrhagic Telangiectasia.

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder characterized by multi-systemic vascular dysplasia affecting 1 in 5000 people worldwide. Individuals with HHT suffer from many complications including nose and gastrointestinal bleeding, anemia, iron deficiency, stroke, abscess, and high-output heart failure. Identification of the causative gene mutations and the generation of animal models have revealed that decreased transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) signaling and increased vascular endothelial growth factor (VEGF) signaling activity in endothelial cells are responsible for the development of the vascular malformations in HHT. Perturbations in these key pathways are thought to lead to endothelial cell activation resulting in mural cell disengagement from the endothelium. This initial instability state causes the blood vessels to response inadequately when they are exposed to angiogenic triggers resulting in excessive blood vessel growth and the formation of vascular abnormalities that are prone to bleeding. Drugs promoting blood vessel stability have been reported as effective in preclinical models and in clinical trials indicating possible interventional targets based on a normalization approach for treating HHT. Here, we will review how disturbed TGF-β and VEGF signaling relates to blood vessel destabilization and HHT development and will discuss therapeutic opportunities based on the concept of vessel normalization to treat HHT.

Liver involvement in hereditary hemorrhagic telangiectasia.

Liver vascular malformations (VMs) in hereditary hemorrhagic telangiectasia (HHT) are typically diffuse and can evolve from small telangiectasias to large arteriovenous malformations, with various stages of severity. Doppler US is the ideal first-line investigation for the assessment of liver VMs in HHT due to its safety, tolerability, low costs, and accuracy for the detection of liver VMs. The caliber, course, and flow characteristics in the hepatic artery, portal vein, and hepatic vein as determined by Doppler US, together with parenchymal abnormalities, support the diagnosis of liver VMs in HHT and their severity staging. When Doppler US expertise is lacking or an assessment of HHT patients with symptoms/signs suggestive of complicated liver VMs is required, particularly if OLT is considered, multiphase CT or MRI is suitable to investigate symptomatic liver VMs. Liver biopsy is neither necessary for the diagnosis of hepatic VMs related to HHT nor should be considered in HHT patients with liver mass/es suggestive of focal nodular hyperplasia.

PROFILING AND CHARACTERIZING MICRORNAS IN PATIENTS WITH HEREDITARY HEMORRHAGIC TELANGIECTASIA

Hereditary hemorrhagic telangiectasia (HHT) is a rare, autosomal dominant, vascular disorder that affects 1 in 5000 to 8000 individuals worldwide. HHT is characterized by vascular abnormalities, such as telangiectasias and arteriovenous malformations (AVMs). Telangiectasias are dilated skin and mucocutaneous blood vessels that are susceptible to spontaneous hemorrhage. AVMs are direct connections between arteries and veins, without intervening capillaries, and can cause significant right to left shunts. HHT arises from heterozygous mutations in at least 3 genes, ENG, ACVRL1, and SMAD4. Haploinsufficiency of their respective protein products perturb TGF signalling, affecting the angiogenic potential of endothelial cells (ECs) and the migratory capacity of monocytes, contributing to vascular malformations in HHT. MicroRNAs (miRs) are small non-coding RNAs that post-transcriptionally target mRNA transcripts. We aimed to profile and characterize miRs in HHT patient derived early endothelial progenitor cells (eEPCs) and peripheral blood mononuclear cells (PBMCs) to explore their potential role in HHT pathogenesis. EEPCs are early outgrowth ECs cultured from the mononuclear cell layer (buffy coat) of peripheral blood. They have been shown to augment angiogenesis in a paracrine manner by secreting various growth factors and are a widely accepted surrogate for studying EC function 28 HHT patients with confirmed mutations, and 25 controls were recruited. 40 ml of peripheral blood was collected for eEPC culture and PBMC isolation. Total RNA was isolated from PBMCs and eEPCs. PBMC and eEPC expression profiling was conducted with a human miR array analysis. Dysregulated miRs identified from the analyses were then validated with RT-qPCR. Significant differences were determined using a two-tailed t-test. Of the 800 miRs screened, 167 and 121 dysregulated miRs were identified in PBMCs and eEPCs, respectively. Selected PBMC miRs (MiRs-28-5p, -30b-5p, -361-3p and -374a-5p) and eEPC miRs (miRs-132-3p, -221-3p and -424-5p) were validated with RT-qPCR. PBMC miR-361-3p (p=0.025) known to target IGF1, and eEPC miR-132-3p (p=0.047) known to target SMAD2, were found to be significantly decreased compared to controls. Subsequently, IGF1 messenger RNA (mRNA) levels were significantly increased (p=0.005) in PBMCs of HHT patients compared to controls. Our results show dysregulation of select miRs in PBMCs and eEPCs from HHT patients. The finding of increased IGF1 mRNA and its possible relation to decreased miR-361-3p levels is both novel and exciting. This may represent a putative pathogenic mechanism involved in HHT, and may provide a unique miR therapeutic target for the treatment of clinical manifestations. National Institutes of Health (NIH)

The ACVRL1 c.314-35A>G polymorphism is associated with organ vascular malformations in hereditary hemorrhagic telangiectasia patients with ENG mutations, but not in patients with ACVRL1 mutations.

Hereditary hemorrhagic telangiectasia (HHT) is characterized by vascular malformations (VMs) and caused by mutations in TGFβ/BMP9 pathway genes, most commonly ENG or ACVRL1. Patients with HHT have diverse manifestations related to skin and mucosal telangiectases and organ VMs, including arteriovenous malformations (AVM). The clinical heterogeneity of HHT suggests a role for genetic modifiers. We hypothesized that the ACVRL1 c.314-35A>G and ENG c.207G>A polymorphisms, previously associated with sporadic brain AVM, are associated with organ VM in HHT. We genotyped these variants in 716 patients with HHT and evaluated association of genotype with presence of any organ VM, and specifically with brain VM, liver VM and pulmonary AVM, by multivariate logistic regression analyses stratified by HHT mutation. Among all patients with HHT, neither polymorphism was significantly associated with presence of any organ VM; ACVRL1 c.314-35A>G showed a trend toward association with pulmonary AVM (OR = 1.48, P = 0.062). ACVRL1 c.314-35A>G was significantly associated with any VM among patients with HHT with ENG (OR = 2.66, P = 0.022), but not ACVRL1 (OR = 0.79, P = 0.52) mutations. ACVRL1 c.314-35A>G was also associated with pulmonary AVM and liver VM among ENG mutation heterozygotes. There were no significant associations between ENG c.207G>A and any VM phenotype. These results suggest that common polymorphisms in HHT genes other than the mutated gene modulate phenotype severity of HHT disease, specifically presence of organ VM.

Vascular malformations of the brain in hereditary hemorrhagic telangiectasia (rendu-osler-weber disease)

Six patients with vascular malformation of the brain in hereditary hemorrhagic telangiectasia (HHT) were reviewed to determine clinical and radiographic characteristics of these lesions. There were two patients with arteriovenous fistula (AVF), three with arteriovenous malformation (AVM), and one with multiple AVMs associated with AVF. Seizures were the most common presenting symptom (seen in three patients), and two of them had intracerebral hematomas (ICH). In the remainder, the malformations were incidentally found in the course of evaluation of other diseases. Their locations were variable, but the majority was superficially confined to the cerebral cortex. Arterial supply was from mostly one feeding artery that was a cortical branch of either anterior, middle, or posterior cerebral artery. In six of nine malformations, the venous drainage was through a superficial cerebral vein into either the superior sagittal sinus or transverse sinus. Direct surgery was done on two patients with ICH, artificial embolization on one, and stereotactic radiosurgery on one. The cerebral vascular malformations in HHT are not infrequent, and in particular the importance of computed tomography and cerebral angiography should be recognized in patients with pulmonary AVF associated with HHT.

The brain in hereditary hemorrhagic telangiectasia.

While neurological symptoms are often mentioned in reports of families with hereditary hemorrhagic telangiectasia (HHT) and are frequently assumed to be due to vascular anomalies of the central nervous system, documentation of such anomalies is surprisingly rare. Two cases of surgically treated symptomatic cerebral vascular malformations in HHT have been published previously. In addition, there are three descriptions of vascular anomalies discovered at autopsy in the brains of neurologically asymptomatic patients with HHT available in the literature. A complete postmortem examination of a patient with a symptomatic cerebral vascular anomaly associated with HHT has not been recorded previously. The patient reported in this paper presented with seizures and underwent surgical resection of infarcted brain tissue associated with a venous angioma. He died six months later and, at autopsy, was found to have multiple "cryptic" venous angiomas of the brain. Hypoxic damage to brain tissue related to small venous angiomas is one mechanism whereby these lesions may become symptomatic. Hemorrhage may also occur. Neurological symptoms in patients with HHT cannot be assumed to be due to cerebral vascular anomalies, and consideration must be especially given to the complications of pulmonary arteriovenous fistula such as polycythemia, embolism, and abscess.