Project description:Brain arteriovenous malformations (bAVM) are characterized by enlarged blood vessels, which direct blood through arteriovenous AV shunts, bypassing the artery-capillary-vein network and disrupting blood flow. Clinically, bAVM treatments are invasive and not routinely applicable. There is critical need to understand mechanisms of bAVM pathologies and develop pharmacological therapies. We used an in vivo mouse model of Rbpj-mediated bAVM, which develops pathologies in the early postnatal period and an siRNA in vitro system to knockdown RBPJ in human brain microvascular endothelial cells (ECs). To understand molecular events regulated by endothelial Rbpj, we conducted RNA-Seq and ChIP-Seq analyses from isolated brain ECs. Rbpj-deficient (mutant) brain ECs acquired abnormally rounded shape (with no change to cell area), altered basement membrane dynamics, and increased EC density along AV shunts, compared to controls, suggesting impaired remodeling of neonatal brain vasculature. Consistent with impaired EC dynamics, we found increased Cdc42 activity in isolated mutant ECs, suggesting that Rbpj regulates small GTPase-mediated cellular functions in brain ECs. siRNA treated, RBPJ-deficient human brain ECs displayed increased Cdc42 activity, disrupted cell polarity and focal adhesion properties, and impaired migration in vitro. RNA-Seq analysis from isolated brain ECs identified differentially expressed genes in mutants, including Apelin, which encodes a ligand for G protein-coupled receptor signaling known to influence small GTPase activity. ChIP-Seq analysis revealed chromatin loci occupied by Rbpj in brain ECs that corresponded to G-protein and Apelin signaling molecules. In vivo administration of a competitive peptide antagonist against the Apelin receptor (Aplnr/Apj) attenuated Cdc42 activity and restored EC morphology and AV connection diameter in Rbpj-mutant brain vessels. Conclusions: Our data suggest that endothelial Rbpj promotes rearrangement of brain ECs during cerebrovascular remodeling, through Apelin/Apj-mediated small GTPase activity, and prevents bAVM. By inhibiting Apelin/Apj signaling in vivo, we demonstrated pharmacological prevention of Rbpj mediated bAVM.

Project description:Background: Endothelial cells (ECs) use glycolysis to produce energy. In pre-clinical models of peripheral arterial disease (PAD), the further activation of EC glycolysis was ineffective and/or deleterious in promoting hypoxia-dependent angiogenesis while pentose phosphate pathway (PPP) activation was effective. Hexosamine biosynthesis pathway (HBP), PPP, and glycolysis are closely linked. Glucosamine directly activates HBP.Methods:Hind-limb ischemia (HLI)ineNOS-/-and Balb/c mice was used. Glucosamine (600 ug/g/day) was injected intraperitoneally. Blood flow recovery was assessed using laser Doppler perfusion imaging (LDPI), angiogenesis was studied by CD31immunostaining.In-vitro: human umbilical vein ECs (HUVECs) and mouse microvascular EC with glucosamine, L-glucose or vascular endothelial growth factor (VEGF165a), were tested underhypoxiaand serum starvation (HSS). Cell counting kit-8 (CCK-8), tube formation, intracellular reactive oxygen species (ROS), Electric Cell-substrate Impedance Sensing (ECIS) and FITC dextran permeability were assessed. Glycolysis and oxidative phosphorylation were assessed by seahorse assay. Gene expression was assessed using RNA sequencing, real-time qPCR, and western blot. Human muscle biopsies from patients with PAD were assessed for EC O-GlcNAcylation before and after supervised exercise vs. standard medical care. Results: Day-3 post-HLI,glucosamine vs. control-treated eNOS-/-had less necrosis.Beginning Day-7 post-HLI, glucosamine vs. control-treated Balb/chad higherblood flowthat persisted to Day-21whereischemic musclesshowed greaterCD31 staining/muscle fiber. In-vitro,glucosamine vs. L-glucoseshowedimproved EC survival and tube formation. RNA-sequencing of glucosamine vs. L-glucose showed increased amino acid metabolism. That resulted in increased oxidative phosphorylation and serine biosynthesis pathway (SBP) without an increase in glycolysis or PPP genes. This was associated with better barrier function and less ROS compared to activating glycolysis by VEGF165a. These effects were mediated by activating transcription factor 4 (ATF4); a driver of exercise-induced angiogenesis. Finally, in muscle biopsies from humans with PAD,EC/O-GlcNAcylation was increased by 12 weeks of supervised exercise vs. standard medical care. Conclusion: In-cells, mice, and humans activation of HBP by glucosamine in PAD inducesan “exercise-like” angiogenesis and offers a promising novel therapeutic pathway to treat this challenging disorder.

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KRAS-Dependent Metabolic Reprogramming of Endothelial Cells as a Therapeutic Vulnerability in Brain Arteriovenous Malformations

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