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Abstract:

Cardiovascular disease prevalence and associated mortality are higher in individuals with metabolic syndrome (MetS). MetS affects 20-25% of the world's population. Individuals with MetS have a twofold higher risk of having coronary heart disease (CHD) and myocardial infarction due to development of metabolic cardiomyopathy. Ischemia-reperfusion injury can be reduced by preconditioning (PC), an endogenous cardioprotective mechanism. The cardioprotective effect of PC can be observed as improvement of post-ischemic contractile function, decrease in the occurrence and severity of arrhythmias, and reduction of infarct size. It was demonstrated that repeated short episodes of hypoxia in mice can reliably induce PC in healthy, but not in subjects with the MetS. The cardioprotective potential of PC is largely diminished in these subjects. Despite the extensive pathophysiological characterization of the MetS heart, the molecular mechanisms governing metabolic cardiomyopathy remain poorly understood. The apparent obstacle is the complex, interdependent multifactorial nature of the metabolic syndrome itself. The heart is composed of different cell types, where cardiac myocytes account for only about a third of the total cell number. The rest includes a broad range of other cell types, including fibroblasts and other connective tissue cells, smooth muscle and endothelial cells and immune system-related cells. These distinct cell groups are not isolated from one another within the heart, but interact via paracrine, autocrine and endocrine factors. Angiotensin-converting enzyme inhibition (ACE-I) is a therapy of choice for patients with MetS. However, our understanding of the effects of ACE-I treatment on the heart and metabolic cardiomyopathy remains very limited. The study was designed to characterize the transcriptional signature in the heart of a murine model of MetS relative to a healthy, control heart and to characterize the transcriptional changes induced by ACE-I in control and MetS hearts. Furthermore, the goal of the current study was to characterize the underlying mechanisms of PC on the transcriptional level and to identify pathways and upstream regulators responsible for this phenomenon in the MetS and WT hearts. ACE-I Induces A Cardioprotective Transcriptional Response In The MetS Heart. We characterized the cardiac transcriptome in a murine MetS model (LDLR–/–; ob/ob, DKO) relative to the healthy, control heart (C57BL6/J, WT) and the transcriptional changes induced by ACE-I in those hearts. RNA-Seq, differential gene expression and transcription factor analysis identified 288 genes differentially expressed between DKO and WT hearts implicating 72 pathways. Hallmarks of metabolic cardiomyopathy were increased activity in integrin-linked kinase signalling, Rho signalling, dendritic cell maturation, production of nitric oxide and reactive oxygen species in macrophages, atherosclerosis, LXR-RXR signalling, cardiac hypertrophy, and acute phase response pathways. ACE-I had a limited effect on gene expression in WT (55 genes, 23 pathways), and a prominent effect in DKO hearts (1143 genes, 104 pathways). In DKO hearts, ACE-I appears to counteract some of the MetS-specific pathways, while also activating cardioprotective mechanisms. Pathways Underlying Impaired Cardiac PC Potential in Subjects with the MetS, and Restoration of the Potential by ACE-I. In untreated and ACE-I treated WT murine models, PC reduced infarct size significantly, but not in untreated DKO mice. In ACE-I treated DKO hearts, PC potential was partially restored with a reduction of infarct size by 16%. PC induced very few transcriptional changes in untreated DKO hearts (29 genes) when compared to untreated and ACE-I treated WT hearts (1634 and 2215 genes respectively). In ACE-I treated DKO, the number of differentially expressed genes after PC increased significantly (59 genes). On the transcriptome level, PC-induced cardioprotection is achieved via a network of shared and model-specific pathways and transcription factors. In the three groups that could phenotypically be protected, PC triggered shared pathways such as mTOR signalling, eIF2 signalling, regulation of eIF4 and p70S6K signalling and actin cytoskeleton signalling. Some model-specific pathways and transcription factor differences were detected. In WT hearts, PC also affected mitochondrial function and oxidative phosphorylation. In the ACE-I treated WT hearts, PC additionally affected immune system signalling and cell cycle regulation. In the treated DKO hearts, in addition to the shared, pathways associated with a negative inotropic effect and inhibition of myocyte growth were enriched after PC. Taken together, this study shows that that MetS and control murine hearts have unique transcriptional profiles and exhibit a partially specific transcriptional response to ACE-I. This study identified molecular mechanisms behind PC in healthy and MetS hearts. The phenotypically cardioprotective effect of PC was absent in the MetS hearts and was partially restored after ACE-I.