Cerebral microvascular changes in permeability and tight junctions induced by hypoxia-reoxygenation

Abstract

Mark, Karen S., and Thomas P. Davis. Cerebral microvascular changes in permeability and tight junctions induced by hypoxia-reoxygenation. Am J Physiol Heart Circ Physiol 282: H1485-H1494, 2002; 10.1152/ajpheart.00645.2001.-Cerebral microvessel endothelial cells that form the bloodbrain barrier (BBB) have tight junctions (TJ) that are critical for maintaining brain homeostasis and low permeability. Both integral (claudin-1 and occludin) and membrane-associated zonula occluden-1 and -2 (ZO-1 and ZO-2) proteins combine to form these TJ complexes that are anchored to the cytoskeletal architecture (actin). Disruptions of the BBB have been attributed to hypoxic conditions that occur with ischemic stroke, pathologies of decreased perfusion, and high-altitude exposure. The effects of hypoxia and posthypoxic reoxygenation in cerebral microvasculature and corresponding cellular mechanisms involved in disrupting the BBB remain unclear. This study examined hypoxia and posthypoxic reoxygenation effects on paracellular permeability and changes in actin and TJ proteins using primary bovine brain microvessel endothelial cells (BBMEC). Hypoxia induced a 2.6-fold increase in [ 14 C]sucrose, a marker of paracellular permeability. This effect was significantly reduced (ϳ58%) with posthypoxic reoxygenation. After hypoxia and posthypoxic reoxygenation, actin expression was increased (1.4-and 2.3-fold, respectively). Whereas little change was observed in TJ protein expression immediately after hypoxia, a twofold increase in expression was seen with posthypoxic reoxygenation. Furthermore, immunofluorescence studies showed alterations in occludin, ZO-1, and ZO-2 protein localization during hypoxia and posthypoxic reoxygenation that correlate with the observed changes in BBMEC permeability. The results of this study show hypoxia-induced changes in paracellular permeability may be due to perturbation of TJ complexes and that posthypoxic reoxygenation reverses these effects. endothelial cells; cytoarchitecture; blood-brain barrier; immunofluorescence WHEREAS RESEARCH INVOLVING hypoxic stress has traditionally focused on identifying and treating risk factors associated with ischemic stroke (17,18,43), hypoxia as a result of high-altitude exposure has also been associated with impairment in neurological function (26,37). Early intervention after ischemic stroke has been shown to reduce tissue damage associated with increased cerebrovascular permeability (7, 39). Recently, research has expanded into examining cellular effects of cerebral ischemia-reperfusion. Ischemic stroke is a reduction or cessation of blood flow to the brain, which deprives the cerebral tissue of important nutrients and oxygen as well as removal of metabolic waste products. Whereas this decrease in oxygen supply to the brain (i.e., hypoxia) has been shown to increase cerebrovascular permeability (1,19), there are also reports (42, 66) of increased permeability in peripheral and cerebral endothelial cells during posthypoxic reperfusion (i.e., reoxygenation). Little is know...

Matrix Metalloproteinase-Mediated Disruption of Tight Junction Proteins in Cerebral Vessels is Reversed by Synthetic Matrix Metalloproteinase Inhibitor in Focal Ischemia in Rat

“…Breakdown of BBB in tissue surrounding brain tumors occurs with concomitant loss of occludin expression (Papadopoulos et al, 2004). In vitro, hypoxia with reoxygenation altered occludin location and molecular weight, which correlated with the observed changes in cerebral microvascular permeability (Mark and Davis, 2002;Witt et al, 2003).…”

Interendothelial Claudin-5 Expression Depends on Cerebral Endothelial Cell–Matrix Adhesion by β1-Integrins

“…Mark and Davis (2002) showed that hypoxia increases endothelial monolayer permeability, but expression of the TJ proteins ZO-1, ZO-2, and occludin changed little. The localization of these TJ proteins correlated with the permeability change.…”

Monocyte Chemoattractant Protein-1 Regulation of Blood–Brain Barrier Permeability

“…Thus, it appears that the effects of MCP-1 on BBB permeability are caused by alterations in TJ complexes. Alterations in these complexes are implicated in BBB breakdown in many CNS pathological states including malaria, viral infection, multiple sclerosis, experimental allergic encephalitis, ischemia/reperfusion injury, and trauma (Brown et al, 1999;Mark and Davis 2002;Ng et al, 2003;Kirk et al, 2003). Furthermore, direct intracerebral injections of some proinflammatory cytokines (e.g., IL-1b, TNF-a, and IL-6), which are known to modify BBB, also cause structural changes in endothelial TJs (Bolton et al, 1998).…”