BackgroundOne of the most important and often neglected physiological stimuli contributing to the differentiation of vascular endothelial cells (ECs) into a blood-brain barrier (BBB) phenotype is shear stress (SS). With the use of a well established humanized dynamic in vitro BBB model and cDNA microarrays, we have profiled the effect of SS in the induction/suppression of ECs genes and related functions.ResultsSpecifically, we found a significant upregulation of tight and adherens junctions proteins and genes. Trans-endothelial electrical resistance (TEER) and permeability measurements to know substances have shown that SS promoted the formation of a tight and highly selective BBB. SS also increased the RNA level of multidrug resistance transporters, ion channels, and several p450 enzymes. The RNA level of a number of specialized carrier-mediated transport systems (e.g., glucose, monocarboxylic acid, etc.) was also upregulated.RNA levels of modulatory enzymes of the glycolytic pathway (e.g., lactate dehydrogenase) were downregulated by SS while those involved in the Krebs cycle (e.g., lactate and other dehydrogenases) were upregulated. Measurements of glucose consumption versus lactate production showed that SS negatively modulated the glycolytic bioenergetic pathways of glucose metabolism in favor of the more efficient aerobic respiration. BBB ECs are responsive to inflammatory stimuli. Our data showed that SS increased the RNA levels of integrins and vascular adhesion molecules. SS also inhibited endothelial cell cycle via regulation of BTG family proteins encoding genes. This was paralleled by significant increase in the cytoskeletal protein content while that of membrane, cytosol, and nuclear sub-cellular fractions decreased. Furthermore, analysis of 2D gel electrophoresis (which allows identifying a large number of proteins per sample) of EC proteins extracted from membrane sub-cellular endothelial fractions showed that SS increased the expression levels of tight junction proteins. In addition, regulatory enzymes of the Krebb's cycle (aerobic glucose metabolism) were also upregulated. Furthermore, the expression pattern of key protein regulators of the cell cycle and parallel gene array data supported a cell proliferation inhibitory role for SS.ConclusionsGenomic and proteomic analyses are currently used to examine BBB function in healthy and diseased brain and characterize this dynamic interface. In this study we showed that SS plays a key role in promoting the differentiation of vascular endothelial cells into a truly BBB phenotype. SS affected multiple aspect of the endothelial physiology spanning from tight junctions formation to cell division as well as the expression of multidrug resistance transporters. BBB dysfunction has been observed in many neurological diseases, but the causes are generally unknown. Our study provides essential insights to understand the role played by SS in the BBB formation and maintenance.

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Recent evidence has indicated that active and passive cigarette smoking are associated, in a dose-dependent manner, with dysfunction of normal endothelial physiology. Tobacco smoke (TS) may predispose individuals to atherogenic and thrombotic problems, significantly increasing the risk for ischemic manifestations such as acute coronary syndrome and stroke. Despite the strong evidence for an association between smoking and vascular impairment, the impact of TS exposure on the blood-brain barrier (BBB) has only been marginally addressed. This is a major problem given that the BBB is crucial in the maintenance of brain homeostasis. Recent data have also shown that chronic smokers have a higher incidence of small vessel ischemic disease (SVID), a pathological condition characterized by leaky brain microvessels and loss of BBB integrity. In the brain OPEN ACCESS Int. J. Environ. Res. Public Health 2010, 7 4112TS increases the risk of silent cerebral infarction (SCI) and stroke owing to the pro-coagulant and atherogenic effects of smoking. In this article we provide a detailed review and analysis of current knowledge of the pathophysiology of tobacco smoke toxicity at the cerebrovascular levels. We also discuss the potential toxicity of recently marketed "potential-reduced exposure products".

Although there is significant evidence correlating overreacting or perhaps misguided immune cells and the blood-brain barrier (BBB) with the pathogenesis of neuroinflammatory diseases, the mechanisms by which they enter the brain are largely unknown. For this purpose, we revised our humanized dynamic in vitro BBB model (DIV-BBBr) to incorporate modified hollow fibers that now feature transmural microholes (2 to 4 μm Ø) allowing for the transendothelial trafficking of immune cells. As with the original model, this new DIV-BBBr reproduces most of the physiological characteristics of the BBB in vivo. Measurements of transendothelial electrical resistance (TEER), sucrose permeability, and BBB integrity during reversible osmotic disruption with mannitol (1.6 mol/L) showed that the microholes do not hamper the formation of a tight functional barrier. The in vivo rank permeability order of sucrose, phenytoin, and diazepam was successfully reproduced in vitro. Flow cessation followed by reperfusion (Fc/Rp) in the presence of circulating monocytes caused a biphasic BBB opening paralleled by a significant increase of proinflammatory cytokines and activated matrix metalloproteinases. We also observed abluminal extravasation of monocytes but only when the BBB was breached. In conclusion, the DIV-BBBr represents the most realistic in vitro system to study the immune cell trafficking across the BBB.