Vesicular Trafficking, a Mechanism Controlled by Cascade Activation of Rab Proteins: Focus on Rab27.

Vesicular trafficking is essential for the cell to internalize useful proteins and soluble substances, for cell signaling or for the degradation of pathogenic elements such as bacteria or viruses. This vesicular trafficking also enables the cell to engage in secretory processes for the elimination of waste products or for the emission of intercellular communication vectors such as cytokines, chemokines and extracellular vesicles. Ras-related proteins (Rab) and their effector(s) are of crucial importance in all of these processes, and mutations/alterations to them have serious pathophysiological consequences. This review presents a non-exhaustive overview of the role of the major Rab involved in vesicular trafficking, with particular emphasis on their involvement in the biogenesis and secretion of extracellular vesicles, and on the role of Rab27 in various pathophysiological processes. Therefore, Rab and their effector(s) are central therapeutic targets, given their involvement in vesicular trafficking and their importance for cell physiology.

Highlighting In Vitro the Role of Brain-like Endothelial Cells on the Maturation and Metabolism of Brain Pericytes by SWATH Proteomics.

Within the neurovascular unit, brain pericytes (BPs) are of major importance for the induction and maintenance of the properties of the blood-brain barrier (BBB) carried by the brain microvessel endothelial cells (ECs). Throughout barriergenesis, ECs take advantage of soluble elements or contact with BPs to maintain BBB integrity and the regulation of their cellular homeostasis. However, very few studies have focused on the role of ECs in the maturation of BPs. The aim of this study is to shed light on the proteome of BPs solocultured (hBP-solo) or cocultured with ECs (hBP-coc) to model the human BBB in a non-contact manner. We first generated protein libraries for each condition and identified 2233 proteins in hBP-solo versus 2492 in hBP-coc and 2035 common proteins. We performed a quantification of the enriched proteins in each condition by sequential window acquisition of all theoretical mass spectra (SWATH) analysis. We found 51 proteins enriched in hBP-solo related to cell proliferation, contractility, adhesion and extracellular matrix element production, a protein pattern related to an immature cell. In contrast, 90 proteins are enriched in hBP-coc associated with a reduction in contractile activities as observed in vivo in 'mature' BPs, and a significant gain in different metabolic functions, particularly related to mitochondrial activities and sterol metabolism. This study highlights that BPs take advantage of ECs during barriergenesis to make a metabolic switch in favor of BBB homeostasis in vitro.

TNF-α and IL-1ß Modulate Blood-Brain Barrier Permeability and Decrease Amyloid-ß Peptide Efflux in a Human Blood-Brain Barrier Model.

The blood-brain barrier (BBB) is a selective barrier and a functional gatekeeper for the central nervous system (CNS), essential for maintaining brain homeostasis. The BBB is composed of specialized brain endothelial cells (BECs) lining the brain capillaries. The tight junctions formed by BECs regulate paracellular transport, whereas transcellular transport is regulated by specialized transporters, pumps and receptors. Cytokine-induced neuroinflammation, such as the tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß), appear to play a role in BBB dysfunction and contribute to the progression of Alzheimer's disease (AD) by contributing to amyloid-ß (Aß) peptide accumulation. Here, we investigated whether TNF-α and IL-1ß modulate the permeability of the BBB and alter Aß peptide transport across BECs. We used a human BBB in vitro model based on the use of brain-like endothelial cells (BLECs) obtained from endothelial cells derived from CD34+ stem cells cocultivated with brain pericytes. We demonstrated that TNF-α and IL-1ß differentially induced changes in BLECs' permeability by inducing alterations in the organization of junctional complexes as well as in transcelluar trafficking. Further, TNF-α and IL-1ß act directly on BLECs by decreasing LRP1 and BCRP protein expression as well as the specific efflux of Aß peptide. These results provide mechanisms by which CNS inflammation might modulate BBB permeability and promote Aß peptide accumulation. A future therapeutic intervention targeting vascular inflammation at the BBB may have the therapeutic potential to slow down the progression of AD.

The Blood-Brain Barrier, an Evolving Concept Based on Technological Advances and Cell-Cell Communications.

The construction of the blood-brain barrier (BBB), which is a natural barrier for maintaining brain homeostasis, is the result of a meticulous organisation in space and time of cell-cell communication processes between the endothelial cells that carry the BBB phenotype, the brain pericytes, the glial cells (mainly the astrocytes), and the neurons. The importance of these communications for the establishment, maturation and maintenance of this unique phenotype had already been suggested in the pioneering work to identify and demonstrate the BBB. As for the history of the BBB, the evolution of analytical techniques has allowed knowledge to evolve on the cell-cell communication pathways involved, as well as on the role played by the cells constituting the neurovascular unit in the maintenance of the BBB phenotype, and more particularly the brain pericytes. This review summarises the key points of the history of the BBB, from its origin to the current knowledge of its physiology, as well as the cell-cell communication pathways identified so far during its development, maintenance, and pathophysiological alteration.

First step to the improvement of the blood brain barrier passage of atazanavir encapsulated in sustainable bioorganic vesicles.

The blood - brain barrier (BBB) prevents the majority of therapeutic drugs from reaching the brain following intravenous or oral administration. In this context, polymer nanoparticles are a promising alternative to bypass the BBB and carry drugs to brain cells. Amphiphilic cyclodextrins can form self-assemblies whose nanoparticles have a 100-nm-diameter range and are thus able to encapsulate drugs for controlled release. Our goal is to propose an optimized chemical synthesis of amphiphilic cyclodextrin, which remains a challenging task which commonly leads to only a low-milligram level of the high purity compound. Such cyclodextrin derivatives were used to prepare vesicles and to study their ability to vectorize a drug through the BBB. As a result, we introduced a convergent synthesis for a family of lipophosphoramidyl permethylated ß-CDs (Lip-ß-CDs) with various chain lengths. It was demonstrated that mixed vesicles comprised of phosphatidylcholine (POPC) and LipCDs were able to encapsulate atazanavir (ATV), a well-known protease inhibitor used as an antiretroviral drug against HIV. We highlighted that neo-vesicles promote the penetration of ATV in endothelial cells of the BBB, presumably due to the low fusogenicity of Lip-ß-CDs.

Ketone Bodies Promote Amyloid-ß1-40 Clearance in a Human in Vitro Blood-Brain Barrier Model.

Alzheimer's disease (AD) is characterized by the abnormal accumulation of amyloid-ß (Aß) peptides in the brain. The pathological process has not yet been clarified, although dysfunctional transport of Aß across the blood-brain barrier (BBB) appears to be integral to disease development. At present, no effective therapeutic treatment against AD exists, and the adoption of a ketogenic diet (KD) or ketone body (KB) supplements have been investigated as potential new therapeutic approaches. Despite experimental evidence supporting the hypothesis that KBs reduce the Aß load in the AD brain, little information is available about the effect of KBs on BBB and their effect on Aß transport. Therefore, we used a human in vitro BBB model, brain-like endothelial cells (BLECs), to investigate the effect of KBs on the BBB and on Aß transport. Our results show that KBs do not modify BBB integrity and do not cause toxicity to BLECs. Furthermore, the presence of KBs in the culture media was combined with higher MCT1 and GLUT1 protein levels in BLECs. In addition, KBs significantly enhanced the protein levels of LRP1, P-gp, and PICALM, described to be involved in Aß clearance. Finally, the combined use of KBs promotes Aß efflux across the BBB. Inhibition experiments demonstrated the involvement of LRP1 and P-gp in the efflux. This work provides evidence that KBs promote Aß clearance from the brain to blood in addition to exciting perspectives for studying the use of KBs in therapeutic approaches.

A High Output Method to Isolate Cerebral Pericytes from Mouse.

In recent years, cerebral pericytes have become the focus of extensive research in vascular biology and pathology. The importance of pericytes in blood brain barrier formation and physiology is now demonstrated but its molecular basis remains largely unknown. As the pathophysiological role of cerebral pericytes in neurological disorders is intriguing and of great importance, the in vitro models are not only sufficiently appropriate but also able to incorporate different techniques for these studies. Several methods have been proposed as in vitro models for the extraction of cerebral pericytes, although an antibiotic-free protocol with high output is desirable. Most importantly, a method that has increased output per extraction reduces the usage of more animals. Here, we propose a simple and efficient method for extracting cerebral pericytes with sufficiently high output. The mouse brain tissue homogenate is mixed with a BSA-dextran solution for the separation of the tissue debris and microvascular pellet. We propose a three-step separation followed by filtration to obtain a microvessel rich filtrate. With this method, the quantity of microvascular fragments obtained from 10 mice is sufficient to seed 9 wells (9.6 cm2 each) of a 6-well plate. Most interestingly with this protocol, the user can obtain 27 pericyte rich wells (9.6 cm2 each) in passage 2. The purity of the pericyte cultures are confirmed with the expression of classical pericyte markers: NG2, PDGFR-ß and CD146. This method demonstrates an efficient and feasible in vitro tool for physiological and pathophysiological studies on pericytes.

New Lipidyl-Cyclodextrins Obtained by Ring Opening of Methyl Oleate Epoxide Using Ball Milling.

Bearing grafts based on fatty esters derivatives, lipidyl-cyclodextrins (L-CDs) are compounds able to form water-soluble nano-objects. In this context, bicatenary biobased lipidic-cyclodextrins of low DS were easily synthesized from a fatty ester epoxide by means of alternative methods (ball-milling conditions, use of enzymes). The ring opening reaction of methyl oleate epoxide needs ball-milling and is highly specific of cyclodextrins in solventless conditions. L-CDs are thus composed of complex mixtures that were deciphered by an extensive structural analysis using mainly mass spectrometry and NMR spectroscopy. In addition, as part of their potential use as vectors of active drugs, these products were submitted to an integrity study on in vitro model of the blood-brain-barrier (BBB) and the intestinal epithelium. No toxicity has been observed, suggesting that applications for the vectorization of active ingredients can be expected.

ABCA7 Downregulation Modifies Cellular Cholesterol Homeostasis and Decreases Amyloid-ß Peptide Efflux in an in vitro Model of the Blood-Brain Barrier.

The role of ABCA7 in brain homeostasis and Alzheimer's disease (AD) is currently under intense scrutiny, since it has been reported that polymorphisms in the Abca7 gene and a loss of function of the protein are closely linked to excessive accumulation of amyloid peptides and disturbed cholesterol homeostasis. The blood-brain barrier (BBB), which isolates the brain from the blood compartment, is involved in both of these processes. We therefore hypothesized that ABCA7 downregulation might affect cholesterol and amyloid exchanges at the BBB. Using siRNA and primary cultures of mouse endothelial cells purified from brain microvessels and seeded on Transwell ® inserts, we investigated the role of ABCA7 in cholesterol and amyloid exchanges across the BBB. Our results showed that a decrease in ABCA7 expression at the BBB provokes in vitro a reduction in ABCA1 expression and a decrease in APOE secretion. In vitro, these decreases reduce cholesterol exchange across the BBB, particularly for high-density lipoproteins and ApoA-I particles. When ABCA7 was absent, we observed a reduction in Aß peptide basolateral-to-apical transport in the presence of ApoA-I, with non-significant changes in the expression levels of Rage, Lrp1, Abcb1, Abcc1, and Abcg2. Our study in murine BBB model highlighted a putative new role for ABCA7 in AD via the protein's involvement in cholesterol metabolism and amyloid clearance at the BBB.

Resveratrol and Grape Extract-loaded Solid Lipid Nanoparticles for the Treatment of Alzheimer's Disease.

The aggregation of amyloid-ß peptide (Aß) has been linked to the formation of neuritic plaques, which are pathological hallmarks of Alzheimer's disease (AD). Various natural compounds have been suggested as therapeutics for AD. Among these compounds, resveratrol has aroused great interest due to its neuroprotective characteristics. Here, we provide evidence that grape skin and grape seed extracts increase the inhibition effect on Aß aggregation. However, after intravenous injection, resveratrol is rapidly metabolized into both glucuronic acid and sulfate conjugations of the phenolic groups in the liver and intestinal epithelial cells (within less than 2 h), which are then eliminated. In the present study, we show that solid lipid nanoparticles (SLNs) functionalized with an antibody, the anti-transferrin receptor monoclonal antibody (OX26 mAb), can work as a possible carrier to transport the extract to target the brain. Experiments on human brain-like endothelial cells show that the cellular uptake of the OX26 SLNs is substantially more efficient than that of normal SLNs and SLNs functionalized with an unspecific antibody. As a consequence, the transcytosis ability of these different SLNs is higher when functionalized with OX-26.

Cyclodextrins as Emerging Therapeutic Tools in the Treatment of Cholesterol-Associated Vascular and Neurodegenerative Diseases.

Cardiovascular diseases, like atherosclerosis, and neurodegenerative diseases affecting the central nervous system (CNS) are closely linked to alterations of cholesterol metabolism. Therefore, innovative pharmacological approaches aiming at counteracting cholesterol imbalance display promising therapeutic potential. However, these approaches need to take into account the existence of biological barriers such as intestinal and blood-brain barriers which participate in the organ homeostasis and are major defense systems against xenobiotics. Interest in cyclodextrins (CDs) as medicinal agents has increased continuously based on their ability to actively extract lipids from cell membranes and to provide suitable carrier system for drug delivery. Many novel CD derivatives are constantly generated with the objective to improve CD bioavailability, biocompatibility and therapeutic outcomes. Newly designed drug formulation complexes incorporating CDs as drug carriers have demonstrated better efficiency in treating cardiovascular and neurodegenerative diseases. CD-based therapies as cholesterol-sequestrating agent have recently demonstrated promising advances with KLEPTOSE® CRYSMEB in atherosclerosis as well as with the 2-hydroxypropyl-ß-cyclodextrin (HPßCD) in clinical trials for Niemann-Pick type C disease. Based on this success, many investigations evaluating the therapeutical beneficial of CDs in Alzheimer's, Parkinson's and Huntington's diseases are currently on-going.

ß-Cyclodextrins Decrease Cholesterol Release and ABC-Associated Transporter Expression in Smooth Muscle Cells and Aortic Endothelial Cells.

Atherosclerosis is an inflammatory disease that leads to an aberrant accumulation of cholesterol in vessel walls forming atherosclerotic plaques. During this process, the mechanism regulating complex cellular cholesterol pools defined as the reverse cholesterol transport (RCT) is altered as well as expression and functionality of transporters involved in this process, namely ABCA1, ABCG1, and SR-BI. Macrophages, arterial endothelial and smooth muscle cells (SMCs) have been involved in the atherosclerotic plaque formation. As macrophages are widely described as the major cell type forming the foam cells by accumulating intracellular cholesterol, RCT alterations have been poorly studied at the arterial endothelial cell and SMC levels. Amongst the therapeutics tested to actively counteract cellular cholesterol accumulation, the methylated ß-cyclodextrin, KLEPTOSE® CRYSMEß, has recently shown promising effects on decreasing the atherosclerotic plaque size in atherosclerotic mouse models. Therefore we investigated in vitro the RCT process occurring in SMCs and in arterial endothelial cells (ABAE) as well as the ability of some modified ß-CDs with different methylation degree to modify RCT in these cells. To this aim, cells were incubated in the presence of different methylated ß-CDs, including KLEPTOSE® CRYSMEß. Both cell types were shown to express basal levels of ABCA1 and SR-BI whereas ABCG1 was solely found in ABAE. Upon CD treatments, the percentage of membrane-extracted cholesterol correlated to the methylation degree of the CDs independently of the lipid composition of the cell membranes. Decreasing the cellular cholesterol content with CDs led to reduce the expression levels of ABCA1 and ABCG1. In addition, the cholesterol efflux to ApoA-I and HDL particles was significantly decreased suggesting that cells forming the blood vessel wall are able to counteract the CD-induced loss of cholesterol. Taken together, our observations suggest that methylated ß-CDs can significantly reduce the cellular cholesterol content of cells forming atherosclerotic lesions and can subsequently modulate the expression of ABC transporters involved in RCT. The use of methylated ß-CDs would represent a valuable and efficient tool to interfere with atherosclerosis pathogenesis in patients, nonetheless their mode of action still needs further investigations to be fully understood and finely controlled at the cellular level.

Efficient Docosahexaenoic Acid Uptake by the Brain from a Structured Phospholipid.

Docosahexaenoic acid (DHA) is the main essential omega-3 fatty acid in brain tissues required for normal brain development and function. An alteration of brain DHA in neurodegenerative diseases such as Alzheimer's and Parkinson's is observed. Targeted intake of DHA to the brain could compensate for these deficiencies. Blood DHA is transported across the blood-brain barrier more efficiently when esterified at the sn-2 position of lyso-phosphatidylcholine. We used a structured phosphatidylcholine to mimic 2-docosahexaenoyl-lysoPC (lysoPC-DHA), named AceDoPC (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that may be considered as a stabilized form of the physiological lysoPC-DHA and that is neuroprotective in experimental ischemic stroke. The aim of the present study was to investigate whether AceDoPC is a relevant delivery form of DHA to the brain in comparison with other forms of the fatty acid. By combining in vitro and in vivo experiments, our findings report for the first time that AceDoPC is a privileged and specific carrier of DHA to the brain, when compared with DHA-containing PC and non-esterified DHA. We also show that AceDoPC was hydrolyzed, in part, into lysoPC-DHA. Ex vivo autoradiography of rat brain reveals that DHA from AceDoPC was localized in specific brain regions playing key roles in memory, thoughts, and cognitive functions. Finally, using molecular modeling approaches, we demonstrate that electrostatic and lipophilic potentials are distributed very similarly at the surfaces of AceDoPC and lysoPC-DHA. Our findings identify AceDoPC as an efficient way to specifically target DHA to the brain, which would allow potential preventive and therapeutic approaches for neurological diseases.

Bexarotene Promotes Cholesterol Efflux and Restricts Apical-to-Basolateral Transport of Amyloid-ß Peptides in an In Vitro Model of the Human Blood-Brain Barrier.

One of the prime features of Alzheimer's disease (AD) is the excessive accumulation of amyloid-ß (Aß) peptides in the brain. Several recent studies suggest that this phenomenon results from the dysregulation of cholesterol homeostasis in the brain and impaired bidirectional Aß exchange between blood and brain. These mechanisms appear to be closely related and are controlled by the blood-brain barrier (BBB) at the brain microvessel level. In animal models of AD, the anticancer drug bexarotene (a retinoid X receptor agonist) has been found to restore cognitive functions and decrease the brain amyloid burden by regulating cholesterol homeostasis. However, the drug's therapeutic effect is subject to debate and the exact mechanism of action has not been characterized. Therefore, the objective of this present study was to determine bexarotene's effects on the BBB. Using an in vitro model of the human BBB, we investigated the drug's effects on cholesterol exchange between abluminal and luminal compartments and the apical-to-basolateral transport of Aß peptides across the BBB. Our results demonstrated that bexarotene induces the expression of ABCA1 but not ApoE. This upregulation correlates with an increase in ApoE2-, ApoE4-, ApoA-I-, and HDL-mediated cholesterol efflux. Regarding the transport of Aß peptides, bexarotene increases the expression of ABCB1, which in turn decreases Aß apical-to-basolateral transport. Our results showed that bexarotene not only promotes the cholesterol exchange between the brain and the blood but also decreases the influx of Aß peptides across BBB, suggesting that bexarotene is a promising drug candidate for the treatment of AD.

In vitro discrimination of the role of LRP1 at the BBB cellular level: focus on brain capillary endothelial cells and brain pericytes.

Several studies have demonstrated that the blood-brain barrier (BBB) (dynamic cellular complex composed by brain capillary endothelial cells (BCECs) and surrounded by astrocytic end feet and pericytes) regulates the exchanges of amyloid ß (Aß) peptide between the blood and the brain. Deregulation of these exchanges seems to be a key trigger for the brain accumulation of Aß peptide observed in Alzheimer's disease (AD). Whereas the involvement of receptor for advanced glycation end-products in Aß peptide transcytosis has been demonstrated in our laboratory, low-density lipoprotein receptor's role at the cellular level needs to be clarified. For this, we used an in vitro BBB model that consists of a co-culture of bovine BCECs and rat glial cells. This model has already been used to characterize low-density lipoprotein receptor-related peptide (LRP)'s involvement in the transcytosis of molecules such as tPA and angiopep-2. Our results suggest that Aß peptide efflux across the BCEC monolayer involves a transcellular transport. However, the experiments with RAP discard an involvement of LRP family members at BCECs level. In contrast, our results show a strong transcriptional expression of LRP1 in pericytes and suggest its implication in Aß endocytosis. Moreover, the observations of pericytes contraction and local downregulation of LRP1 in response to Aß treatment opens up perspectives for studying this cell type with respect to Aß peptide metabolism and AD.

Effects of oxysterols on the blood-brain barrier: implications for Alzheimer's disease.

Altered brain cholesterol homeostasis plays a key role in neurodegenerative diseases such as Alzheimer's disease (AD). For a long time, the blood-brain barrier (BBB) was basically considered as a barrier isolating the brain from circulating cholesterol, however, several lines of evidence now suggest that the BBB strictly regulates the exchanges of sterol between the brain and the peripheral circulation. Oxysterols, synthesized by neurons or by peripheral cells, cross the BBB easily and modulate the expression of several enzymes, receptors and transporters which are involved not only in cholesterol metabolism but also in other brain functions. This review article deals with the way oxysterols impact BBB cells. These perspectives open new routes for designing certain therapeutical approaches that target the BBB so that the onset and/or progression of brain diseases such as AD may be modulated.

Stroke-induced brain parenchymal injury drives blood-brain barrier early leakage kinetics: a combined in vivo/in vitro study.

The disappointing clinical outcomes of neuroprotectants challenge the relevance of preclinical stroke models and data in defining early cerebrovascular events as potential therapeutic targets. The kinetics of blood-brain barrier (BBB) leakage after reperfusion and the link with parenchymal lesion remain debated. By using in vivo and in vitro approaches, we conducted a kinetic analysis of BBB dysfunction during early reperfusion. After 60 minutes of middle cerebral artery occlusion followed by reperfusion times up to 24 hours in mice, a non-invasive magnetic resonance imaging method, through an original sequence of diffusion-weighted imaging, determined brain water mobility in microvascular compartments (D*) apart from parenchymal compartments (apparent diffusion coefficient). An increase in D* found at 4 hours post reperfusion concurred with the onset of both Evans blue/Dextran extravasations and in vitro BBB opening under oxygen-glucose deprivation and reoxygenation (R). The BBB leakage coincided with an emerging cell death in brain tissue as well as in activated glial cells in vitro. The co-culture of BBB endothelial and glial cells evidenced a recovery of endothelium tightness when glial cells were absent or non-injured during R. Preserving the ischemic brain parenchymal cells within 4 hours of reperfusion may improve therapeutic strategies for cerebrovascular protection against stroke.

Amyloid-ß peptides, Alzheimer's disease and the blood-brain barrier.

Ever since amyloid-ß (Aß) peptides were first identified in cerebral plaques in patients with Alzheimer's disease (AD), much research work has focused on the complex mechanisms through which these peptides are synthesized, transported and degraded. Although new information emerges on a regular basis, we consider that the importance of the blood-brain barrier (BBB) in the pathogenesis of AD has been underestimated. In fact, there are a number of obstacles that make it difficult to convince specialists in AD that the BBB indeed plays a key role in this disease: these include the complex physiology of the BBB and the technical difficulty of studying the barrier in vivo and reproducing its main properties in vitro. With these considerations in mind, the present review sets out summarize our current knowledge about the physiology of the BBB and describe recent research findings on the barrier's role in Aß peptide proteostasis and thus in the mechanism of AD.

Oxysterols decrease apical-to-basolateral transport of Aß peptides via an ABCB1-mediated process in an in vitro Blood-brain barrier model constituted of bovine brain capillary endothelial cells.

It is known that activation of the liver X receptors (LXRs) by natural or synthetic agonists decreases the amyloid burden and enhances cognitive function in transgenic murine models of Alzheimer's disease (AD). Recent evidence suggests that LXR activation may affect the transport of amyloid ß (Aß) peptides across the blood-brain barrier (the BBB, which isolates the brain from the peripheral circulation). By using a well-characterized in vitro BBB model, we demonstrated that LXR agonists (24S-hydroxycholesterol, 27-hydroxycholesterol and T0901317) modulated the expression of target genes involved in cholesterol homeostasis (such as ATP-binding cassette sub-family A member 1 (ABCA1)) and promoted cellular cholesterol efflux to apolipoprotein A-I and high density lipoproteins. Interestingly, we also observed a decrease in Aß peptide influx across brain capillary endothelial cells, although ABCA1 did not appear to be directly involved in this process. By focusing on others receptors and transporters that are thought to have major roles in Aß peptide entry into the brain, we then demonstrated that LXR stimulation provoked an increase in expression of the ABCB1 transporter (also named P-glycoprotein (P-gp)). Further investigations confirmed ABCB1's involvement in the restriction of Aß peptide influx. Taken as a whole, our results not only reinforce the BBB's key role in cerebral cholesterol homeostasis but also demonstrate the importance of the LXR/ABCB1 axis in Aß peptide influx-highlighting an attractive new therapeutic approach whereby the brain could be protected from peripheral Aß peptide entry.

Brain pericytes ABCA1 expression mediates cholesterol efflux but not cellular amyloid-ß peptide accumulation.

In brain, excess cholesterol is metabolized into 24S-hydroxycholesterol (24S-OH-chol) and eliminated into the circulation across the blood-brain barrier. 24S-OH-chol is a natural agonist of the nuclear liver X receptors (LXRs) involved in peripheral cholesterol homeostasis. The effects of this oxysterol on the pericytes embedded in the basal lamina of this barrier (close to the brain compartment) have not been previously studied. We used primary cultures of brain pericytes to demonstrate that the latter express LXR nuclear receptors and their target gene ATP-binding cassette, sub-family A, member 1 (ABCA1), known to be one of the major transporters involved in peripheral lipid homeostasis. Treatment with 24S-OH-chol caused an increase in ABCA1 expression that correlated with a reverse cholesterol transfer to apolipoprotein E, apolipoprotein A-I, and high density lipoprotein particles. Inhibition of ABCA1 decreased this efflux. As pericytes are able to internalize the amyloid-ß peptides which accumulate in brain of Alzheimer's disease patients, we then investigated the effects of 24S-OH-chol on this process. We found that the cellular accumulation process was not modified by 24S-OH-chol treatment. Overall, our results highlight the importance of the LXR/ABCA1 system in brain pericytes and suggest a new role for these cells in brain cholesterol homeostasis.