Brain arteriovenous malformations (AVM) are of unknown etiology and pathogenesis; patients are at life-threatening risk of rupture and intracranial hemorrhage (ICH). This competing continuation will focus on mechanistic animal studies, derived from characterizations of the human AVM tissue, to establish plausible causal chains to explain the human phenotype. The general hypotheses are that non-ischemic venous hypertension (VH) results increases hypoxia inducible factor-1 (HIF-1) expression. Downstream upregulation of vascular endothelial growth factor (VEGF) and inflammatory cytokines, e.g., lnterleukin-6 (IL- 6), initiate the angiogenic phenotype. Consequent increased matrix metalloproteinase (MMP) activity promotes and sustains a nidus of localized angiogenesis. This nidus of excessive angiogenic stimulation, in the presence of abnormal TGF-beta signaling, i.e., endoglin deficiency, leads to creation of malformed microvascular structures.
In Aim 1, using a rat model, we will test the hypotheses that brain HIF-1 is increased by non-ischemic venous hypertension, and decreased by its reversal. We will show that venous hypertension accentuates VEGFinduced angiogenesis, and that HIF-1 blockade abolishes this increase.
In Aim 2, we will test the hypotheses that IL-6 promotes angiogenesis through activation of MMP-9; abrogating IL-6 function will decrease MMP activity. Further, we will demonstrate that leukocyte and macrophage infiltration is associated with local production of MMP expression necessary to promote focal angiogenesis. Techniques include adenoviral gene transfer to overexpress VEGF protein in IL-6 or MMP knock out mice and rescue with GFP-labeled bone marrow-derived cell transplantation (MMP-9) or IL-6 brain infusion.
In Aim 3, we will test the hypotheses that maximizing a pro-angiogenic environment by additional provision of Angiopoietin-2, in conjunction with a novel adeno-associated gene vector transducing VEGF, will further increase the amount of vascular dysplasia. We will then demonstrate that this vascular dysplasia can be attenuated by inhibition of MMP-9 activity using either minocycline or the MMP inhibitor GM6001 These aims will establish potential mechanistic pathways of AVM pathogenesis to guide clinical research and therapy development.
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