73 research outputs found
Astrocyte mediated modulation of blood-brain barrier permeability does not correlate with a loss of tight junction proteins from the cellular contacts
In the central nervous system (CNS) complex endothelial tight junctions (TJs) form a restrictive paracellular diffusion barrier, the blood-brain barrier (BBB). Pathogenic changes within the CNS are frequently accompanied by the loss of BBB properties, resulting in brain edema. In order to investigate whether BBB leakiness can be monitored by a loss of TJ proteins from cellular borders, we used an in vitro BBB model where brain endothelial cells in co-culture with astrocytes form a tight permeability barrier for 3H-inulin and 14C-sucrose. Removal of astrocytes from the co-culture resulted in an increased permeability to small tracers across the brain endothelial cell monolayer and an opening of the TJs to horseradish peroxidase as detected by electron microscopy. Strikingly, opening of the endothelial TJs was not accompanied by any visible change in the molecular composition of endothelial TJs as junctional localization of the TJ-associated proteins claudin-3, claudin-5, occludin, ZO-1 or ZO-2 or the adherens junction-associated proteins β-catenin or p120cas did not change. Thus, opening of BBB TJs is not readily accompanied by the complete loss of the junctional localization of TJ protein
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Changes in the vascular extracellular matrix during embryonic vasculogenesis and angiogenesis
We have previously characterized monoclonal antibodies against chick brain cells. One of them (14-2B2) brightly stained all capillaries in frozen sections of chick brain. Here we show that this antibody is directed against chick fibronectin. Using this antibody and polyclonal antibodies against laminin, we have studied the development of the vascular extracellular matrix. Vasculogenesis, the development of capillaries from
in situ differentiating endothelial cells, was studied in yolk sac blood islands and intraembryonic dorsal aorta. Blood islands produced high levels of fibronectin but not laminin. Early intraembryonic capillaries all expressed fibronectin but little if any laminin. The dorsal aorta of a 6-day-old chick embryo has several layers of fibronectin-producing cells, but is devoid of laminin. Laminin expression commenced at Day 8 and by Day 10 an adult-like distribution was found in the aortic vascular wall. Angiogenesis, the formation of capillaries from preexisting vessels, was studied during brain development. Capillary sprouts invading the neuroectoderm at Embryonic Day 4 migrated in a fibronectin-rich matrix devoid of laminin. Ultrastructural immunolocalization demonstrated the presence of fibronectin exclusively on the abluminal site of the endothelial cells. Beginning on Day 6, laminin codistributed with fibronectin in brain capillaries. We conclude that immature capillaries migrate and proliferate in a fibronectin-rich extracellular matrix, which is subsequently remodeled acquiring basement membrane-like characteristics. We suggest that laminin expression is an early indication of vascular maturation
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