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Aims Pro-protein convertase subtilisin-kexin type 9 (PCSK9), which is expressed mainly in the liver and at low levels in the heart, regulates cholesterol levels by directing low-density lipoprotein receptors to degradation. Studies to determine the role of PCSK9 in the heart are complicated by the close link between cardiac function and systemic lipid metabolism. Here, we sought to elucidate the function of PCSK9 specifically in the heart by generating and analysing mice with cardiomyocyte-specific Pcsk9 deficiency (CMPcsk9−/− mice) and by silencing Pcsk9 acutely in a cell culture model of adult cardiomyocyte-like cells. Methods and results Mice with cardiomyocyte-specific deletion of Pcsk9 had reduced contractile capacity, impaired cardiac function, and left ventricular dilatation at 28 weeks of age and died prematurely. Transcriptomic analyses revealed alterations of signalling pathways linked to cardiomyopathy and energy metabolism in hearts from CM-Pcsk9−/− mice vs. wild-type littermates. In agreement, levels of genes and proteins involved in mitochondrial metabolism were reduced in CM-Pcsk9−/− hearts. By using a Seahorse flux analyser, we showed that mitochondrial but not glycolytic function was impaired in cardiomyocytes from CM-Pcsk9−/− mice. We further showed that assembly and activity of electron transport chain (ETC) complexes were altered in isolated mitochondria from CM-Pcsk9−/− mice. Circulating lipid levels were unchanged in CM-Pcsk9−/− mice, but the lipid composition of mitochondrial membranes was altered. In addition, cardiomyocytes from CM-Pcsk9−/− mice had an increased number of mitochondria–endoplasmic reticulum contacts and alterations in the morphology of cristae, the physical location of the ETC complexes. We also showed that acute Pcsk9 silencing in adult cardiomyocyte-like cells reduced the activity of ETC complexes and impaired mitochondrial metabolism. Conclusion PCSK9, despite its low expression in cardiomyocytes, contributes to cardiac me, QC 20230907

AIMS: Cardiac injury and remodelling are associated with the rearrangement of cardiac lipids. Glycosphingolipids are membrane lipids that are important for cellular structure and function, and cardiac dysfunction is a characteristic of rare monogenic diseases with defects in glycosphingolipid synthesis and turnover. However, it is not known how cardiac glycosphingolipids regulate cellular processes in the heart. The aim of this study is to determine the role of cardiac glycosphingolipids in heart function. METHODS AND RESULTS: Using human myocardial biopsies, we showed that the glycosphingolipids glucosylceramide and lactosylceramide are present at very low levels in non-ischaemic human heart with normal function and are elevated during remodelling. Similar results were observed in mouse models of cardiac remodelling. We also generated mice with cardiomyocyte-specific deficiency in Ugcg, the gene encoding glucosylceramide synthase (hUgcg-/- mice). In 9- to 10-week-old hUgcg-/- mice, contractile capacity in response to dobutamine stress was reduced. Older hUgcg-/- mice developed severe heart failure and left ventricular dilatation even under baseline conditions and died prematurely. Using RNA-seq and cell culture models, we showed defective endolysosomal retrograde trafficking and autophagy in Ugcg-deficient cardiomyocytes. We also showed that responsiveness to β-adrenergic stimulation was reduced in cardiomyocytes from hUgcg-/- mice and that Ugcg knockdown suppressed the internalization and trafficking of β1-adrenergic receptors. CONCLUSIONS: Our findings suggest that cardiac glycosphingolipids are required to maintain β-adrenergic signalling and contractile capacity in cardiomyocytes and to preserve normal heart function.

Le cœur est un organe énergivore dont la majorité de l'ATP consommée provient du métabolisme oxydatif de la mitochondrie. Cet organite joue également un rôle central dans la régulation de l'homéostasie calcique, la production des espèces réactives de l'oxygène (ROS) et l'apoptose. Ces fonctions sont dérégulées au cours de l'insuffisance cardiaque (IC). Il est donc important d'identifier les signalisations à l'origine de ces dysfonctions et de les valider en tant que cible thérapeutique pour le traitement de l'IC. Bien que le second messager AMP cyclique (AMPc) soit essentiel à la fonction cardiaque, il contribue à la progression de l'IC. Cependant, les bases moléculaires de ses effets délétères dans les pathologies cardiaques sont loin d'être élucidées. Le but de ce travail fût de déterminer les effets mitochondriaux d'une protéine effectrice de l'AMPc, Epac1. Nous avons étudié ses rôles mitochondriaux (mitEpac1) dans deux conditions de stress cardiaque connues pour perturber le fonctionnement de la mitochondrie : un stress aigu induit par une ischémie reperfusion (I/R) et un stress chronique provoqué par un régime riche en graisse (HFD) conduisant à une cardiomyopathie diabétique. Par ailleurs, nous avons caractérisé un nouvel inhibiteur pharmacologique de Epac1 appelé AM-001 et étudié ses propriétés cardioprotectrices chez la souris. D'une part, nous montrons que la délétion génique de Epac1 (Epac1-/-) chez la souris protège des lésions de l'I/R myocardique en réduisant la taille de l'infarctus. L'inhibition pharmacologique de Epac1 par le CE3F4 prévient de l'apoptose des cardiomyocytes (CM) induite par l'hypoxie/réoxygénation (HX+R). Sur le plan mécanistique, Epac1 est activé par l'AMPc produit par l'adénylate cyclase soluble (sAC). De plus, Epac1 est associé à un complexe macromoléculaire composé du canal calcique VDAC1, de la protéine chaperonne GRP75 et du récepteur type 1 à IP3. Epac1 favorise la formation de ce complexe dans des conditions HX+R pour induire, The heart is an organ with high energy demand and the majority of consumed ATP is produced from oxidative metabolism of the mitochondria. This organelle also plays a central role in the regulation of calcium homeostasis, the production of reactive oxygen species (ROS) and apoptosis. However, these different mitochondrial functions are dysregulated in heart failure (HF). It is therefore important to identify the signaling pathways leading to the mitochondrial alterations in order to identify novel therapeutic targets for the treatment of HF. Although the second messenger cyclic AMP (cAMP) is essential for the regulation of cardiac function, this cyclic nucleotide largely contributes to HF progression. However, the molecular basis of cAMP deleterious effects in the heart are far from being elucidated. The aim of this study was to determine the mitochondrial effects of a cAMP effector protein, Epac1. We have studied the role of the mitochondrial Epac1 protein (mitEpac1) in two cardiac stress conditions known to disrupt mitochondrial function: An acute stress induced by ischemia reperfusion (I/R) and a chronic stress induced by a high fat diet (HFD) leading to diabetic cardiomyopathy. In addition, we have characterized a new pharmacological inhibitor of Epac1, named AM-001, and studied the cardioprotective properties of this small molecule in mice. Firstly, we show that Epac1 genetic ablation (Epac1-/-) protects against myocardial I/R with reduced infarct size. Pharmacological inhibition of Epac1 by CE3F4 prevents hypoxia/reoxygenation (HX/R)-induced adult cardiomyocyte apoptosis. Mechanistically, Epac1 is activated by cAMP produced by the soluble adenylate cyclase (sAC) to induce cell death. Interestingly, Epac1 is associated with a macromolecular complex composed of the calcium channel VDAC1, the chaperone protein GRP75 and the IP3 receptor 1. Epac1 favors the formation of this complex under HX/R conditions, to induce a mitochondrial Ca2+ overload and opening of the m