title: Integrin alpha(v)beta8-mediated activation of transforming growth factor-beta by perivascular astrocytes: an angiogenic control switch.
abstract: Brain hemorrhage is a severe complication of both neoplastic and nonneoplastic brain disease. Mice deficient in the alpha(v)beta8 integrin display defective brain vessel formation resulting in hemorrhage and perinatal death, but the mechanism of brain hemorrhage is unknown. Because the alpha(v)beta8 integrin is expressed by astrocytes and not expressed by endothelium, paracrine interactions between astrocytes and endothelial cells could contribute to the maintenance of brain vessel integrity. We have investigated the mechanisms underlying astrocytic-endothelial paracrine signaling and have found that integrin-mediated activation of transforming growth factor (TGF)-beta by astrocytes influences endothelial cell function. Thus, we identified the integrin alpha(v)beta8 in human perivascular glial cell processes surrounding developing blood vessels. Human astrocytic alpha(v)beta8 was a major cell surface receptor for latent TGF-beta, and alpha(v)beta8-dependent activation of TGF-beta was the major mechanism of TGF-beta activation in primary cultures of astrocytes or freshly dissociated fetal brain cells. This activation of TGF-beta was sufficient to inhibit endothelial migration in fibrin gels and to alter expression of genes affecting proteolytic and angiogenic pathways. Taken together, our data suggest that astrocytic alpha(v)beta8 acts as a central regulator of brain vessel homeostasis through regulation of TGF-beta activation and expression of TGF-beta-responsive genes that promote vessel differentiation and stabilization, most notably plasminogen activator inhibitor-1 and thrombospondin-1.
authors.affiliation: Department of Pathology, University of California San Francisco, San Francisco, CA 94110, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Cambier
authors.forename: Stephanie
authors.initials: S
authors.lastname: Gline
authors.forename: Dezhi
authors.initials: D
authors.lastname: Mu
authors.forename: Rodney
authors.initials: R
authors.lastname: Collins
authors.forename: Jun
authors.initials: J
authors.lastname: Araya
authors.forename: Gregory
authors.initials: G
authors.lastname: Dolganov
authors.forename: Steven
authors.initials: S
authors.lastname: Einheber
authors.forename: Nancy
authors.initials: N
authors.lastname: Boudreau
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Nishimura
mesh_terms: D001253:Astrocytes / Q000378:metabolism*; D015153:Blotting, Western; D001921:Brain / Q000098:blood supply* / Q000196:embryology; D002448:Cell Adhesion / Q000502:physiology; D002450:Cell Communication; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism; D004789:Enzyme Activation; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D039641:Integrin beta Chains / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism*; D008954:Models, Biological; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019700:Thrombospondin 1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D039641:Integrin beta Chains; D016023:Integrins; D017395:Plasminogen Activator Inhibitor 1; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; C403414:integrin alphavbeta8; C094865:integrin beta8