Amyloid-β-induced occludin down-regulation and increased permeability in human brain endothelial cells is mediated by MAPK activation

Abstract

Vascular dysfunction is emerging as a key pathological hallmark in Alzheimer’s disease (AD). A leaky blood–brain barrier (BBB) has been described in AD patient tissue and in vivo AD mouse models. Brain endothelial cells (BECs) are linked together by tight junctional (TJ) proteins, which are a key determinant in restricting the permeability of the BBB. The amyloid β (Aβ) peptides of 1–40 and 1–42 amino acids are believed to be pivotal in AD pathogenesis. We therefore decided to investigate the effect of Aβ 1–40, the Aβ variant found at the highest concentration in human plasma, on the permeability of an immortalized human BEC line, hCMEC/D3. Aβ 1–40 induced a marked increase in hCMEC/D3 cell permeability to the paracellular tracer 70 kD FITC-dextran when compared with cells incubated with the scrambled Aβ 1–40 peptide. Increased permeability was associated with a specific decrease, both at the protein and mRNA level, in the TJ protein occludin, whereas claudin-5 and ZO-1 were unaffected. JNK and p38MAPK inhibition prevented both Aβ 1–40-mediated down-regulation of occludin and the increase in paracellular permeability in hCMEC/D3 cells. Our findings suggest that the JNK and p38MAPK pathways might represent attractive therapeutic targets for preventing BBB dysfunction in AD.

Role of ABC Transporters in the Pathogenesis of Alzheimer’s Disease

“…122,123 ABCG2 shows substrate overlap with ABCB1 and its involvement in Aβ peptides transport was suggested at the microvessel cells level acting as gatekeeper at the BBB to prevent blood Aβ peptides from entering into the brain. 62,124,125 The role of ABCG2 in Aβ extrusion at the BBB was investigated in Abcg2-null and wild-type mice after intravenous injection of labeled Aβ. 124 Optical imaging analyses of live animals and their brains showed that Abcg2-null mice significantly accumulated more Aβ in their brains than wildtype mice, suggesting ABCG2 may act as a gatekeeper at the BBB to prevent blood Aβ from entering into brain.…”

“…61 This result was supported by an in vitro transport study where addition of the ABCB1 inhibitors tariquidar or vinblastine did not affect the brain-to-blood transport of 125 I-Aβ 40 ; however, both inhibitors facilitated blood-to-brain transport of 125 I-Aβ 40 , which suggests the minor or lack of ABCB1 contribution to Aβ clearance from the brain and emphasizes ABCB1 role in limiting Aβ access to the brain. 62 The authors of these studies concluded that ABCB1 at the BBB does not play a role in the clearance of Aβ, but its strategic position at the luminal side of the BBB limits Aβ entry into the brain. 60−62 Further studies on the role of ABCB1 in Aβ efflux have shown that ABCB1 inhibition by verapamil, a competitive inhibitor of ABCB1, revealed a slight effect, but not significant, on Aβ peptide transport whereas GF120918 (elacridar) increased Aβ peptides transport across brain capillary endothelial cells from bovine origin.…”

“…However, it should be noted that GF120918 is ABCB1 and ABCG2 (BCRP) inhibitor, 64 and Aβ peptides have been reported as a substrate for ABCG2 as well. 62 Thus, being a dual inhibitor, it is possible that GF120918 enhanced the transport of Aβ peptide across the endothelial cells as a result of inhibition of the efflux functions of both proteins, ABCB1 and ABCG2.…”

A 1-42-RAGE Interaction Disrupts Tight Junctions of the Blood-Brain Barrier Via Ca2+-Calcineurin Signaling

“…Alteration of these TJ proteins by A␤ 1-42 occurred without affecting cell death under this experimental condition (data not shown). To evaluate whether the rearrangement and decrease in ZO-1 levels in A␤ 1-42 -treated bEnd.3 cells reflected the disruption of TJs, bEnd.3 cells were cultured in a Transwell system, and the amount of diffused FITC-dextran 40 (FD-40) was measured; FD-40 is used to measure BBB permeability in human brain endothelial cells and mice (Tai et al, 2010). A␤ 1-42 (5 M) increased FD-40 levels in the basolateral chamber (Fig.…”

La barrière hémato-encéphalique

“…Il est cependant probable que cette dysfonction observée chez certains patients soit la conséquence de la maladie et non la cause. En effet, les souris transgéniques produisant un excès de peptides A développent des lésions de la BHE comparées aux souris sauvages [27], et diverses études réalisées in vitro démontrent l'effet potentiellement néfaste des peptides A sur l'intégrité de la BHE et notamment sur l'expression et la localisation de certaines protéines de jonctions serrées [28,29]. Reste à déterminer si ce sont les formes solubles ou insolubles de peptides A qui provoquent cette réponse au niveau des CEC ainsi que les méca-nismes cellulaires et moléculaires impliqués, mais une étude récente suggère que c'est par le récepteur RAGE exprimé par les CEC qu'est déclenchée cette réponse de stress endothélial [30].…”