Régulation de l'homéostasie du cholestérol par les récepteurs nucléaires PPARa et LXR dans les macrophages primaires humains

Les maladies cardiovasculaires représentent la cause majeure de mortalité dans les pays industrialisés. L'athérosclérose est à l'origine de nombreux décès par accidents ischémiques aigüs. Les macrophages jouent un rôle essentiel dans le développement de cette maladie. Les récepteurs nucléaires Peroxysome proliferators-activated receptor (PPAR) a et Liver X receptors (LXR) sont des récepteurs nucléaires exprimés dans les macrophages humains et impliqués dans la modulation du métabolisme des lipides. Des études cliniques chez l'homme et sur des modèles animaux ont montré que l'activation de PPARa et des LXR par leurs ligands synthétiques peut inhiber le développement de l'athérosclérose. Ceci, indépendamment de leur effet sur les lipides plasmatiques par leurs actions au niveau de la paroi artérielle. Dans un premier temps, nous avons montré dans les macrophages primaires humains que les agonistes des récepteurs nucléaires PPAR et LXR augmentent l'efflux de cholestérol vers l'apoAI non seulement par l'induction de l'expression du transporteur ABCA1 mais également en mobilisant le cholestérol vers la membrane plasmique par l'induction des protéines NPC-1 et NPC-2. Dans un second temps, nous avons mis en évidence que l'activation de LXR induit également la captation sélective des esters de cholestérol provenant des HDL. Cette régulation fonctionnelle est associée à une augmentation de l'efflux de cholestérol vers ces mêmes HDL et à une augmentation de l'expression de différentes protéines telles que l'apolipoprotéine E, la lipoprotéine lipase et la cavéoline impliquées dans les phénomènes de captation des esters de cholestérol. Ceci suggère que l'effet anti-athérogène de LXR soit assuré, en partie, par l'augmentation des flux du cholestérol dans le macrophage humain. Nos travaux sont donc en étroite adéquation avec l'hypothèse de propriétés anti athéroscléreuses des récepteurs nucléaires par leur action directe sur la régulation du métabolisme du cholestérol dans le macrophage.The cardiovascular diseases represent the major cause of mortality in industrial countries. Atherosclerosis is responsible of many ischemic troubles. Macrophages play a pivotal role in the development of atherosclerosis. Peroxysome proliferators-activated receptor (PPAR) alpha and Liver X receptors (LXR) are nuclear receptors expressed in human macrophages that regulate the expression of genes controlling lipid metabolism. Clinical trials and studies on animal models show that PPAR alpha and LXRs agonists can repress development of atherosclerosis by their actions on arterial wall, especially on cholesterol homeostasis regulation in macrophages. First, we have shown that PPAR and LXR agonists induce NPC-1 and NPC-2 genes and proteins expression and stimulate the postlysosomal mobilization of cholesterol to plasma membrane, associated with inhibition of cellular cholesterol esterification. Cholesterol becomes more available for its efflux to extracellular acceptors via the ABCA1 pathway. Then, we have shown that LXR agonists induce a strong increase in selective cholesteryl ester uptake. This functional regulation is associated with an induction of cholesterol efflux out of the cell and an induction in several protein expressions as apolipoprotein E, lipoprotein lipase ans caveolin. These proteins are associated to cholesteryl ester uptake phenomenae. These results suggest that the LXR athero-protective effect is mediated in part by enhanced fluxes in cholesterol intracellular trafficking in the human macrophage.LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Intestine-Liver Cross-talk in Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease

International audienceType 2 diabetes (T2D) and Non-Alcoholic Fatty Liver Disease (NAFLD) are pathologies whose prevalence continues to increase worldwide. Both diseases are precipitated by an excessive caloric intake, which promotes insulin resistance and fatty liver. The role of the intestine and its crosstalk with the liver in the development of these metabolic diseases is receiving increasing attention. Alterations in diet-intestinal microbiota interactions lead to the dysregulation of intestinal functions, resulting in altered metabolite and energy substrate production and increased intestinal permeability. Connected through the portal circulation, these changes in intestinal functions impact the liver and other metabolic organs, such as visceral adipose tissue, hence participating in the development of insulin resistance, and worsening T2D and NAFLD. Thus, targeting the intestine may be an efficient therapeutic approach to cure T2D and NAFLD. In this review, we will first introduce the signaling pathways linking T2D and NAFLD. Next, we will address the role of the gut-liver crosstalk in the development of T2D and NAFLD, with a particular focus on the gut microbiota and the molecular pathways behind the increased intestinal permeability and inflammation. Finally, we will summarize the therapeutic strategies which target the gut and its functions and are currently used or under development to treat T2D and NAFLD

Reconstitution des protéines d'enveloppe du virus de l'hépatite C en liposomes :un outil pour étudier l'attachement viral.

info:eu-repo/semantics/nonPublishe

Activation of intestinal peroxisome proliferator-activated receptor-α increases high-density lipoprotein production.

International audienceAIMS: Peroxisome proliferator-activated receptor (PPAR)-α is a transcription factor controlling lipid metabolism in liver, heart, muscle, and macrophages. Peroxisome proliferator-activated receptor-α activation increases plasma HDL cholesterol and exerts hypotriglyceridaemic actions via the liver. However, the intestine expresses PPAR-α, produces HDL and chylomicrons, and is exposed to diet-derived PPAR-α ligands. Therefore, we examined the effects of PPAR-α activation on intestinal lipid and lipoprotein metabolism. METHODS AND RESULTS: The impact of PPAR-α activation was evaluated in term of HDL-related gene expression in mice, ex vivo in human jejunal biopsies and in Caco-2/TC7 cells. Apolipoprotein-AI/HDL secretion, cholesterol esterification, and trafficking were also studied in vitro. In parallel to improving plasma lipid profiles and increasing liver and intestinal expression of fatty acid oxidation genes, treatment with the dual PPAR-α/δ ligand GFT505 resulted in a more pronounced increase in plasma HDL compared with fenofibrate in mice. GFT505, but not fenofibrate, increased the expression of HDL production genes such as apolipoprotein-AI and ATP-binding cassette A1 transporter in murine intestines. A similar increase was observed upon PPAR-α activation of human biopsies and Caco-2/TC7 cells. Additionally, HDL secretion by Caco-2/TC7 cells increased. Moreover, PPAR-α activation decreased the cholesterol esterification capacity of Caco-2/TC7 cells, modified cholesterol trafficking, and reduced apolipoprotein-B secretion. CONCLUSION: Peroxisome proliferator-activated receptor-α activation reduces cholesterol esterification, suppresses chylomicron, and increases HDL secretion by enterocytes. These results identify the intestine as a target organ of PPAR-α ligands with entero-hepatic tropism to reduce atherogenic dyslipidaemia

Retrograde cholesterol transport in the human Caco-2/TC7 cell line: A model to study trans-intestinal cholesterol excretion in atherogenic and diabetic dyslipidemia

The dyslipidemia associated with type 2 diabetes is a major risk factor for the development of atherosclerosis. Trans-intestinal cholesterol excretion (TICE) has recently been shown to contribute, together with the classical hepatobiliary route, to fecal cholesterol excretion and cholesterol homeostasis. The aim of this study was to develop an in vitro cell model to investigate enterocyte-related processes of TICE. Differentiated Caco-2/TC7 cells were grown on transwells and incubated basolaterally (blood side) with human plasma and apically (luminal side) with lipid micelles. Radioactive and fluorescent cholesterol tracers were used to investigate cholesterol uptake at the basolateral membrane, intracellular distribution and apical excretion. Our results show that cholesterol is taken up at the basolateral membrane, accumulates intracellularly as lipid droplets and undergoes a cholesterol acceptor-facilitated and progressive excretion through the apical membrane of enterocytes. The overall process is abolished at 4 A degrees C, suggesting a biologically active phenomenon. Moreover, this trans-enterocytic retrograde cholesterol transport displays some TICE features like modulation by PCSK9 and an ABCB1 inhibitor. Finally, we highlight the involvement of microtubules in the transport of plasma cholesterol from basolateral to apical pole of enterocytes. The human Caco-2/TC7 cell line appears a good in vitro model to investigate the enterocytic molecular mechanisms of TICE, which may help to identify intestinal molecular targets to enhance reverse cholesterol transport and fight against dyslipidemia

Food-Derived Hemorphins Cross Intestinal and Blood–Brain Barriers In Vitro

A qualitative study is presented, where the main question was whether food-derived hemorphins, i.e., originating from digested alimentary hemoglobin, could pass the intestinal barrier and/or the blood–brain barrier (BBB). Once absorbed, hemorphins are opioid receptor (OR) ligands that may interact with peripheral and central OR and have effects on food intake and energy balance regulation. LLVV-YPWT (LLVV-H4), LVV-H4, VV-H4, VV-YPWTQRF (VV-H7), and VV-H7 hemorphins that were previously identified in the 120 min digest resulting from the simulated gastrointestinal digestion of hemoglobin have been synthesized to be tested in in vitro models of passage of IB and BBB. LC-MS/MS analyses yielded that all hemorphins, except the LLVV-H4 sequence, were able to cross intact the human intestinal epithelium model with Caco-2 cells within 5–60 min when applied at 5 mM. Moreover, all hemorphins crossed intact the human BBB model with brain-like endothelial cells (BLEC) within 30 min when applied at 100 µM. Fragments of these hemorphins were also detected, especially the YPWT common tetrapeptide that retains OR-binding capacity. A cAMP assay performed in Caco-2 cells indicates that tested hemorphins behave as OR agonists in these cells by reducing cAMP production. We further provide preliminary results regarding the effects of hemorphins on tight junction proteins, specifically here the claudin-4 that is involved in paracellular permeability. All hemorphins at 100 µM, except the LLVV-H4 peptide, significantly decreased claudin-4 mRNA levels in the Caco-2 intestinal model. This in vitro study is a first step toward demonstrating food-derived hemorphins bioavailability which is in line with the growing body of evidence supporting physiological functions for food-derived peptides