Contribution à l'étude du rôle physiologique de l'apolipoprotéine O

Pour maintenir sa fonction de pompe, le cœur doit produire une quantité suffisante d'ATP. Dans un cœur adulte, 70% de l'ATP est produit par l'oxydation des acides gras et 30% provient de la glycolyse. En situation de diabète, d'obésité ou d'hypertension, le cœur consomme presque exclusivement les acides gras. Ce changement du profil métabolique entraine une accumulation de lipides dans le cœur et un dysfonctionnement mitochondrial conduisant à une lipotoxicité cardique et à l'installation d'une cardiomyopathie. L'Apolipoprotéine O ou ApoO est une nouvelle apolipoprotéine découverte en 2006 par notre équipe dans le cœur des chiens soumis à un régime gras hypercaloriques pendant 9 semaines. L'expression de cette proteine augmente également dans le cœur du patient diabétique. Durant ma thèse, j'ai participé à la recherche de la fonction de l'ApoO en étudiant les conséquences de la surexpression de l'Apo O cardiaque sur le métabolisme et la lipotoxicité. Durant cette étude nous avons réalisé des expériences " in vitro " et " in vivo " en utilisant respectivement une lignée de cardiomyoblastes (H9c2) et 3 lignées de souris transgéniques surexprimant l'Apo O au niveau cardiaque. Nous avons voulu valider les résultats obtenus dans des biopsies de cœurs humains obtenus au décours d'une circulation extracorporelle mise en place lors de chirurgies cardiaques à l'hôpital Rangueil de Toulouse. Nous avons montré que l'Apo O est localisée dans la membrane interne mitochondriale et interagit avec un des constituant/régulateur du pore de transition mitochondrial (MPTP), l'adénine nucléotide translocase (ANT). Cette interaction se traduit par une ouverture du pore, un découplage partiel et une augmentation de la consommation globale d'oxygène. L'activation de la respiration va faire appel à plus de substrats dans de la mitochondrie ce qui va se traduire par une consommation plus importante d'acides gras. Pour subvenir aux besoins de ce puits métabolique la cellule va augmenter l'expression des transporteurs des acides gras de la membrane plasmique ainsi que l'entrée de ces derniers. Lorsque les capacités oxydatives de la mitochondrie sont dépassées, des lipides toxiques tels que les diglycérides sont générés et leur accumulation potentialise l'apoptose induite par l'ouverture du pore mitochondrial. Cette cascade d'événements est inhibée lorsque l'Apo O est démunie de sa séquence d'adressage à la mitochondrie suite à la délétion de sa région N-terminale (ApoO Delta1-40) déviant ainsi sa localisation vers le cytoplasme. Les conséquences de la surexpression de l'ApoO sont également diminuées si les cardiomyoblastes sont traités avec de très faibles doses de cyclosporine, un inhibiteur du pore de transition mitochondriale (MPTP). Ces résultats proposent l'Apo O comme un nouveau régulateur du MPTP et montrent un modèle de dysfonctionnement mitochondrial conduisant à la lipotoxicité et la cardiomyopathie. L'Apo O pourrait être donc une nouvelle cible pharmacologique pour lutter contre la cardiomyopathie diabétique.The mitochondrial permeability transition pore (MPTP), first considered to play a key role in "life or death" decisions of the cell has been proposed to be a target for cardioprotection during heart disease. This pore enables free passage into the mitochondria for molecules and metabolites smaller than 1.5 kDa6, including protons thus leading to mitochondrial uncoupling. The exact protein composition of the MPTP is still under debate but minimally includes cyclophilin D and adenine nucleotide translocase (ANT) which is proposed to be a regulatory component. Thus, MPTP regulators are of central importance to the control of mitochondrial (dys)function and the fate of cardiomyocytes. In this study, we demonstrate the importance of apolipoprotein O (ApoO) as a new signal regulator of the MPTP. Through a functional genomics study aimed at identifying genes differentially regulated in the heart by obesity13, we discovered a new apolipoprotein (ApoO) as overexpressed in the heart of diabetic patients. In the present study, we sought to uncover how changes in the expression of this protein relate to modifications of cardiac function. We used cardiac myoblasts, in vivo transfected mouse liver, human heart samples and cardiac specific transgenic mouse lines constitutively expressing ApoO at physiological levels. These mice, exhibited depressed ventricular function, characteristic patterns of systolic dysfunction, and dilated cardiomyopathy. We show that ApoO localizes within mitochondria and that its expression associates with mitochondrial dysfunction in mouse and human heart. ApoO interacts with ANT and causes the MPTP to adopt an open state, inducing mild uncoupling. Consequently, mitochondrial respiration and fatty acid metabolism are enhanced. This cascade of events generates a mitochondrial metabolic sink whereby cells accumulate lipids and lipotoxic byproducts leading to apoptosis, loss of cardiac myoblasts and cardiomyopathy mimicking the metabolic phenotype of the diabetic heart. We propose a model for the original molecular mechanisms that may account for the ApoO induced mitochondrial dysfunction through the MPTP opening regulation. The molecular mechanisms that initiate, mediate and trigger mitochondrial dysfunction in response to lipid overload remain unclear. Our results distinguish the interplay between mitochondrial dysfunction and lipotoxicity and demonstrate, for the first time, the implication of the permeability transition pore in lipid metabolism in mouse and human heart. ApoO-model could be an original link between impaired mitochondrial heart function and lipid accumulation. ApoO may open up novel strategies to control lipid overload in pathophysiological situation like obesity, diabetes and cardiomyopathy

Expression and implication of clusterin in left ventricular remodeling after myocardial infarction

International audienceBACKGROUND: Left ventricular remodeling (LVR) after myocardial infarction is associated with an increased risk of heart failure and death. In spite of a modern therapeutic approach, LVR remains relatively frequent and difficult to predict in clinical practice. Our aim was to identify new biomarkers of LVR and understand their involvement in its development.METHODS AND RESULTS:Proteomic analysis of plasma from the REVE-2 study (Remodelage Ventriculaire)-a study dedicated to the analysis of LVR which included 246 patients after a first anterior myocardial infarction-identified increased plasma levels of CLU (clusterin) in patients with high LVR. We used a rat model of myocardial infarction to analyze CLU expression in the LV and found a significant increase that was correlated with LVR parameters. We found increased CLU expression and secretion in primary cultures of rat neonate cardiomyocytes hypertrophied by isoproterenol. Silencing of CLU in hypertrophied neonate cardiomyocytes induced a significant decrease in cell size, ANP (atrial natriuretic peptide), and BNP (B-type natriuretic peptide) expression, associated with a decreased ERK (extracellular signal-regulated kinase) 1/2 activity, suggesting a prohypertrophic role of CLU. We then confirmed a significant increase of both intracellular p-CLU (precursor form of CLU) and m-CLU (mature form of CLU) in failing human hearts. Finally, the circulating levels of CLU (secreted form) were increased in patients with chronic heart failure who died from cardiovascular cause during a 3-year follow-up (n=99) compared with survivors (n=99).CONCLUSIONS: Our results show for the first time that plasma CLU levels are associated with LVR post-myocardial infarction, have in part a cardiac origin, and are a predictor of early death in heart failure patients

Increased mean aliphatic lipid chain length in left ventricular hypertrophy secondary to arterial hypertension: A cross-sectional study

About 77.9 million (1 in 4) American adults have high blood pressure. High blood pressure is the primary cause of left ventricular hypertrophy (LVH), which represents a strong predictor of future heart failure and cardiovascular mortality. Previous studies have shown an altered metabolic profile in hypertensive patients with LVH. The goal of this study was to identify blood metabolomic LVH biomarkers by H NMR to provide novel diagnostic tools for rapid LVH detection in populations of hypertensive individuals. This cross-sectional study included 48 hypertensive patients with LVH matched with 48 hypertensive patients with normal LV size, and 24 healthy controls. Two-dimensional targeted M-mode echocardiography was performed to measure left ventricular mass index. Partial least squares discriminant analysis was used for the multivariate analysis of the H NMR spectral data. From the H NMR-based metabolomic profiling, signals coming from methylene (-CH2-) and methyl (-CH3) moieties of aliphatic chains from plasma lipids were identified as discriminant variables. The -CH2-/-CH3 ratio, an indicator of the mean length of the aliphatic lipid chains, was significantly higher (P < 0.001) in the LVH group than in the hypertensive group without LVH and controls. Receiver operating characteristic curve showed that a cutoff of 2.34 provided a 52.08% sensitivity and 85.42% specificity for discriminating LVH (AUC = 0.703, P-value < 0.001). We propose the -CH2-/-CH3 ratio from plasma aliphatic lipid chains as a biomarker for the diagnosis of left ventricular remodeling in hypertension

Blood Signature of Pre-Heart Failure: A Microarrays Study

International audienceBACKGROUND: The preclinical stage of systolic heart failure (HF), known as asymptomatic left ventricular dysfunction (ALVD), is diagnosed only by echocardiography, frequent in the general population and leads to a high risk of developing severe HF. Large scale screening for ALVD is a difficult task and represents a major unmet clinical challenge that requires the determination of ALVD biomarkers. METHODOLOGY/PRINCIPAL FINDINGS: 294 individuals were screened by echocardiography. We identified 9 ALVD cases out of 128 subjects with cardiovascular risk factors. White blood cell gene expression profiling was performed using pangenomic microarrays. Data were analyzed using principal component analysis (PCA) and Significant Analysis of Microarrays (SAM). To build an ALVD classifier model, we used the nearest centroid classification method (NCCM) with the ClaNC software package. Classification performance was determined using the leave-one-out cross-validation method. Blood transcriptome analysis provided a specific molecular signature for ALVD which defined a model based on 7 genes capable of discriminating ALVD cases. Analysis of an ALVD patients validation group demonstrated that these genes are accurate diagnostic predictors for ALVD with 87% accuracy and 100% precision. Furthermore, Receiver Operating Characteristic curves of expression levels confirmed that 6 out of 7 genes discriminate for left ventricular dysfunction classification. CONCLUSIONS/SIGNIFICANCE: These targets could serve to enhance the ability to efficiently detect ALVD by general care practitioners to facilitate preemptive initiation of medical treatment preventing the development of HF

Contribution à l'étude du rôle physiologique de l'apolipoprotéine O

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Oxidative Stress in Cardiovascular Diseases

International audienceReactive oxygen species (ROS) are subcellular messengers in signal transductions pathways with both beneficial and deleterious roles. ROS are generated as a by-product of mitochondrial respiration or metabolism or by specific enzymes such as superoxide dismutases, glutathione peroxidase, catalase, peroxiredoxins, and myeloperoxidases. Under physiological conditions, the low levels of ROS production are equivalent to their detoxification, playing a major role in cellular signaling and function. In pathological situations, particularly atherosclerosis or hypertension, the release of ROS exceeds endogenous antioxidant capacity, leading to cell death. At cardiovascular levels, oxidative stress is highly implicated in myocardial infarction, ischemia/reperfusion, or heart failure. Here, we will first detail the physiological role of low ROS production in the heart and the vessels. Indeed, ROS are able to regulate multiple cardiovascular functions, such as cell proliferation, migration, and death. Second, we will investigate the implication of oxidative stress in cardiovascular diseases. Then, we will focus on ROS produced by NAPDH oxidase or during endothelial or mitochondrial dysfunction. Given the importance of oxidative stress at the cardiovascular level, antioxidant therapies could be a real benefit. In the last part of this review, we will detail the new therapeutic strategies potentially involved in cardiovascular protection and currently under study

Mitophagy Regulation Following Myocardial Infarction

International audienceMitophagy, which mediates the selective elimination of dysfunctional mitochondria, is essential for cardiac homeostasis. Mitophagy is regulated mainly by PTEN-induced putative kinase protein-1 (PINK1)/parkin pathway but also by FUN14 domain-containing 1 (FUNDC1) or Bcl2 interacting protein 3 (BNIP3) and BNIP3-like (BNIP3L/NIX) pathways. Several studies have shown that dysregulated mitophagy is involved in cardiac dysfunction induced by aging, aortic stenosis, myocardial infarction or diabetes. The cardioprotective role of mitophagy is well described, whereas excessive mitophagy could contribute to cell death and cardiac dysfunction. In this review, we summarize the mechanisms involved in the regulation of cardiac mitophagy and its role in physiological condition. We focused on cardiac mitophagy during and following myocardial infarction by highlighting the role and the regulation of PI NK1/parkin-; FUNDC1-; BNIP3- and BNIP3L/NIX-induced mitophagy during ischemia and reperfusion

Non-coding RNAs in cardiac autophagy following myocardial infarction

International audienceMacroautophagy is an evolutionarily conserved process of the lysosome-dependent degradation of damaged proteins and organelles and plays an important role in cellular homeostasis. Macroautophagy is upregulated after myocardial infarction (MI) and seems to be detrimental during reperfusion and protective during left ventricle remodeling. Identify new regulators of cardiac autophagy may help to maintain the activity of this process and protect the heart from MI effects. Recently, it was shown that non-coding RNAs (microRNAs and long non-coding RNAs) are involved on autophagy regulation in different cell types including cardiac cells. In this review, we summarized the role of macroautophagy in the heart following MI and we focused on the non-coding RNAs and their targeted genes reported to regulate autophagy in the heart under these pathological conditions

Proteomic Profiling of Macrophages by 2D Electrophoresis

International audienc

Serum MMP-8: a novel indicator of left ventricular remodeling and cardiac outcome in patients after acute myocardial infarction.

OBJECTIVE: Left ventricular (LV) remodeling following myocardial infarction (MI) is characterized by progressive alterations of structure and function, named LV remodeling. Although several risk factors such as infarct size have been identified, LV remodeling remains difficult to predict in clinical practice. Changes within the extracellular matrix, involving matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), are an integral part of left ventricular (LV) remodeling after myocardial infarction (MI). We investigated the temporal profile of circulating MMPs and TIMPs and their relations with LV remodeling at 1 year and clinical outcome at 3 years in post-MI patients. METHODS: This prospective multicentre study included 246 patients with a first anterior MI. Serial echocardiographic studies were performed at hospital discharge, 3 months, and 1 year after MI, and analysed at a core laboratory. LV remodeling was defined as the percent change in LV end-diastolic volume (EDV) from baseline to 1 year. Serum samples were obtained at hospital discharge, 1, 3, and 12 months. Multiplex technology was used for analysis of MMP-1, -2, -3, -8, -9, -13, and TIMP-1, -2, -3, -4 serum levels. RESULTS: Baseline levels of MMP-8 and MMP-9 were positively associated with changes in LVEDV (P = 0.01 and 0.02, respectively). When adjusted for major baseline characteristics, MMP-8 levels remained an independent predictor LV remodeling (P = 0.025). By univariate analysis, there were positive relations between cardiovascular death or hospitalization for heart failure during the 3-year follow-up and the baseline levels of MMP-2 (P = 0.03), MMP-8 (P = 0.002), and MMP-9 (P = 0.03). By multivariate analysis, MMP-8 was the only MMP remaining significantly associated with clinical outcome (P = 0.02). CONCLUSION: Baseline serum MMP-8 is a significant predictor of LV remodeling and cardiovascular outcome after MI and may help to improve risk stratification