Signal Transduction by alphavbeta8 Integrin

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Abstract The brain is the most vascularized organ in the mammalian body, with its complex network of blood vessels interacting with neurons and glia in multicellular complexes termed neurovascular units. Growth factors and extracellular matrix (ECM) proteins coordinately regulate adhesion and signaling between neural cells and vascular cells to promote normal brain development and physiology. These events are deregulated in many brain pathologies, including developmental disorders such as germinal matrix hemorrhage and age-related neurocognitive deficits such as Vascular Dementia. We understand surprisingly little about mechanisms that regulate normal neural-vascular cell contact and communication or how these events go awry during disease pathogenesis. Here, we will analyze roles for ECM proteins and their integrin receptors in neurovascular biology and disease. Integrins are a-b heterodimeric proteins that link ECM ligands to the cytoskeleton and control intracellular signaling cascades. While a great deal is known about adhesion and signaling functions for most integrins, the pathways controlled by integrin avb8, which was discovered more than 25 years ago, remain largely unexplored. avb8 is expressed in glial cells of the central nervous system (CNS) and plays critical roles in regulating vascular endothelial cell behaviors via activation of ECM-bound latent-transforming growth factor b (TGFb) protein ligands. In this renewal project, we will develop genetically engineered mouse models and primary cell culture systems to analyze avb8 integrin-mediated adhesion and signaling pathways in neurovascular unit pathophysiology. First, we will characterize a newly developed knock-in mouse model that enables dissection of avb8 integrin extracellular adhesion from intracellular signaling in neural-vascular cell contact and communication. In particular, we will study integrin-dependent blood vessel morphogenesis and endothelial barrier formation in the brain and retina. Second, we will determine functions for the b8 cytoplasmic domain in regulating integrin inside-out activation and ECM affinity/avidity using biochemical assays and primary cell culture models. Third, we will explore paracrine signaling between avb8 integrin in perivascular glial cells and TGFb receptors in endothelial cells. A particular focus will be placed on integrin-dependent regulation of the docosahexaenoic (DHA) transporter Mfsd2a in CNS endothelial cells. Fourth, we will explore links between defective DHA metabolism and BBB dysfunction in the progressive neurodegenerative pathologies that develop in integrin mutant mice. In summary, experiments in this project will reveal new and important mechanisms underlying integrin control of neurovascular development and physiology. The mutant mouse models may also provide valuable insights into pathways involved in the pathogenesis of vascular-related neurological diseases.