The role of shear stress in Blood-Brain Barrier endothelial physiology

Abstract

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.

Shear stress activation of nuclear receptor PXR in endothelial detoxification

“…P-glycoprotein, a member of the ABC superfamily, is encoded by the MDR l gene and has been demonstrated to act as a very efficient toxin efflux molecule and to confer resistance to a wide range of insults (21). Previous studies have shown that LSS could induce the endothelial expression of drug transporters and metabolic properties that allow the blood-brain barrier to shield the central nerve system from potentially harmful substances (22). The LSSinduced MDR1 and other exporters (such as ABCB4, ABCD2, and ABCG2) (23,24), together with other metabolizing enzymes (such as CYP1B1, CYP24A1, CYP27A1, and SULT1A1), may orchestrate a multistep detoxification program composed of metabolization and efflux.…”

Role and Function of Dehydrogenases in CNS and Blood-Brain Barrier Pathophysiology

“…The BBB ECs are also characterized by very high density of mitochondria denoting high metabolic activity (23) to support all the specialized cellular activities bestowed upon these highly specialized cells. In addition, previous work from our group has shown that blood flow can modulate the bioenergetic behavior of the BBB endothelial cells favoring the expression of the key metabolic enzyme pyruvate dehydrogenase (switch controller from anaerobic to aerobic pathway) (19). Contrarily, the RNA level of lactate dehydrogenase (switch controller from aerobic to anaerobic pathway) showed decreased expression.…”

“…Topographic membrane localization of these transporters is indicative of the polarity of the endothelial functions and differentiation that sets apart the BBB endothelium from other vascular beds. The BBB endothelial cytoplasm is richly endowed with enzymes(18) including adenosine triphosphatase, acid and alkaline phosphatases, Na + /K + /ATPase, monoamine oxidase, cytochrome p450s and various dehydrogenases (19)(20)(21)(22). The BBB ECs are also characterized by very high density of mitochondria denoting high metabolic activity (23) to support all the specialized cellular activities bestowed upon these highly specialized cells.…”

Hollow Fiber Bioreactor Technology for Tissue Engineering Applications

“…A pulsatile flow was imposed to better mimic the fluid dynamic conditions in vivo. It was shown that ECs exposed to shear stress and fluid pressure had a comparable morphology and functionality with respect to their in vivo counterparts (56,57). Thus, DIV-BBB models may be used to further investigate in vitro the immune cell trafficking across the BBB (Tab.…”

“…For example, to study the physiological and functional behavior of distinct segments of the human cerebrovascular network, a novel capillary-venule modular system composed of a combination of 2 DIV-BBBs was presented (56,57). Both the venule and the capillary module were configured as cHFBs.…”