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Introduction Perturbations of endoplasmic reticulum (ER) functions result in the accumulation of misfolded proteins inside the ER lumen, a condition known as ER stress. As a compensatory pro-survival response, the unfolded protein response (UPR) is activated to restore normal ER function. However, in the case of severe or chronic ER stress, apoptosis is triggered to eliminate damaged cells. Recently, ER stress was implicated in the pathogenesis of various heart diseases including heart failure (HF). Previously, we have shown that SIRT1 is cardioprotective against severe ER stress by regulating the PERK pathway of the UPR, suggesting that activation of SIRT1 could be effective to limit cardiac ER stress. Objective Different natural polyphenols have been shown to activate SIRT1 in a variety of models. In this study, we thus evaluated the protective effect of 11 polyphenols (butein, fisetin, catechin…) that have been reported to activate SIRT1, against severe ER stress-induced cardiac cell death. Method Tunicamycin (TN), an inhibitor of N-glycosylation of proteins, was used to induce a severe ER stress in H9c2 cardiomyoblasts and adult rat ventricle myocytes (ARVM). Cell death was determined by fluorescence microscopy and flow cytometry and ER stress was analysed by western blot. Results As expected, TN induced an increase of the ER stress markers GRP78, GRP94 and the pro-apoptotic transcription factor CHOP associated with cardiac cell death. Three of the tested polyphenols were shown to protect H9c2 cells and ARVM against cell death induced by TN. Protection was abrogated when SIRT1 was inhibited by EX527. In addition, the level of the pro-apoptotic factor CHOP was reduced with polyphenols. Conclusion These results indicated that among the 11 polyphenols tested, 3 were able to protect cardiac cells from ER stress-induced cell death in a SIRT1-dependent manner. Activation of SIRT1 by selected polyphenols thus appears as a promising strategy to modulate ER stress and protect cardiac cells.

Introduction Mitochondrial dysfunction plays a major role in the Heart Failure (HF) pathophysiology. The AMP activated protein kinase (AMPK) is activated by a high AMP-ADP/ATP ratio and regulates a number of metabolic pathways. Many studies have highlighted a protective role of AMPK in HF, but its relevance to cardiac tissue, its metabolic part and its sex-specificity are not well established. Objective The aim of this study is to determine the role of AMPK in the healthy and failing heart in male and female mice. Method We developed and validated a mouse strain with an adult-inducible cardiac-specific deletion of AMPKα2, the major cardiac isoform, using the Cre-Lox system (40 mg/kg tamoxifen injection on two consecutive days at adult age). At four months after the deletion, cardiac contractility, morphology and metabolism were studied in control and KO mice from both sexes. Results We observed only in male KO mice a decrease of left ventricular ejection fraction (− 10%), an increase of the total fibrosis (+ 64%) and defects in mitochondrial structures. Male KO mice also showed a reduced (− 28%) mitochondrial respiration via complex I associated with a different cardiolipin species distribution. Conclusion Our results reveal in adult healthy hearts, a sex-specificity in the effects of AMPKα2 deletion, leading to impaired contractile function related to metabolic and non-metabolic alterations only in male mice.

Aims Endoplasmic reticulum (ER) stress has recently emerged as an important mechanism involved in the pathogenesis of cardiovascular diseases including heart failure. However, the molecular mechanisms by which ER stress leads to cardiac dysfunction remain poorly understood. Methods and results In the present study, we evaluated the early cardiac effects of ER stress induced by tunicamycin (TN) in mice. Electrocardiographic analysis indicated that TN-induced ER stress led to a significant impairment of the cardiac function. Electron microscopic observations revealed that ultrastructural changes of cardiomyocytes in response to ER stress manifested extensively at the level of the sarco-endoplasmic reticulum membranes. Smooth tubules of sarcoplasmic reticulum in connection with short sections of rough endoplasmic reticulum were observed. The presence of rough instead of smooth reticulum was increased at the interfibrillar space, at the level of dyads and in the vicinity of mitochondria. At a functional level, ER stress resulted in a substantial decrease in mitochondrial biogenesis as demonstrated by the decrease of the expression of PGC-1α and of its targets NRF1, Tfam, CS and COXIV. ER stress also led to an impairment of mitochondrial oxidative phosphorylation and to a metabolic remodeling characterized by a shift from fatty acid to glycolytic substrate consumption. Conclusion Our findings show that ER stress induces cytoarchitectural and metabolic alterations in cardiomyocytes and provide evidences that ER stress could represent a primary mechanism that contributes to the impairment of energy metabolism reported in most cardiac diseases.

The rough endoplasmic reticulum (rER) is the site for synthesis, folding and quality control of secreted and membrane proteins. Impairment of ER function in response to stresses such as oxidative stress, disruption of calcium homeostasis or ischemia causes the accumulation of misfolded proteins in the rER lumen, resulting in ER stress. Over the past decade, ER stress has emerged as an important mechanism involved in the pathogenesis of cardiovascular diseases including heart failure. However, the molecular mechanisms underlying the contribution of ER stress to cardiac dysfunction remain poorly understood. In the present study, we evaluated the effect of the ER stressor tunicamycin (TN) on cardiac function in mice. TN injection (2mg/kg, 72h) induced a significant impairment of systolic function as indicated by the decrease in ejection fraction and fractional shortening. However, the heart rate, left ventricular internal diameters in diastole and systole and wall thickness were not affected. Transmission electron microscopy analysis revealed that TN induced an important ultrastructural remodeling of the cardiomyocytes with an increase in the occurrence of rER. Whereas rER was essentially located near the nucleus in cardiomyocytes of control mice, we observed an expansion of the rER network near sarcomeres and around T-tubules and mitochondrial clusters after TN treatment. In addition, mitochondrial structure and network were also disorganized. When measured in skinned fibers, the rate of mitochondrial oxidation was slower and an impairment of the function of the creatine kinase energy shuttle was observed in response to TN. In addition, ER stress triggered a metabolic remodeling characterized by a shift from fatty acid to glycogenic substrates consumption. Taken together our results show for the first time that the cytoarchitectural and metabolic alterations of cardiomyocytes contribute to the cardiac injury induced by ER stress.