Project description:<p>BACKGROUND: Imbalances in cardiac branched-chain amino acid (BCAA) metabolism and mitochondrial homeostasis are implicated in the onset and development of heart failure. However, the mechanisms triggering the downregulation of cardiac BCAA metabolism in heart failure remain unclear. Here, we identify a novel role of RNA-binding protein GRSF1 (guanine-rich RNA sequence binding factor 1) in post-transcriptionally regulating cell-intrinsic BCAA metabolic pathways, ultimately contributing to the pathogenesis of heart failure.</p><p>METHODS: We examined GRSF1 expression in the heart tissues of patients with dilated cardiomyopathy and generated mice with cardiomyocyte-specific deletion or overexpression of GRSF1 in vivo to investigate its role in heart failure. The effect of GRSF1 on BCAA homeostasis was assessed through untargeted and targeted metabolomics and mitochondrial function analysis. To elucidate the mechanisms underlying GRSF1-mediated metabolic regulation, we employed mice with cardiomyocyte-specific deletion of BCKDHB, and mice with cardiomyocyte-specific expression of GRSF1 lacking a quasi-RNA recognition motif. </p><p>RESULTS: GRSF1 expression was significantly decreased in the hearts of patients with heart failure and failing murine hearts. Cardiomyocyte-specific GRSF1 deletion resulted in cardiac dysfunction, spontaneous progression to dilated cardiomyopathy, and heart failure, accompanied by increased cardiac hypertrophy and fibrosis. Conversely, GRSF1 overexpression attenuated cardiac remodeling and heart failure induced by transverse aortic constriction. Mechanistically, GRSF1 maintained BCAA homeostasis and mitochondrial function by directly interacting with the G-tracts in coding region of BCKDHB mRNA through a quasi-RNA recognition motif to promote the stability of BCKDHB mRNA at the post-transcriptional level, thereby increasing its protein expression. Functional recovery mediated by GRSF1 overexpression in cardiomyocytes was partially blocked upon cardiac-specific deletion of BCKDHB. </p><p>CONCLUSIONS: Our study identified GRSF1 as a cell-intrinsic metabolic checkpoint that maintains cardiac BCAA homeostasis by regulating BCKDHB mRNA turnover. Targeting GRSF1 may offer therapeutic benefits for heart failure and other cardiometabolic diseases requiring BCAA manipulation.</p>
Project description:To establish changes in cardiac transcription profiles brought about by heart failure we collected myocardial samples from patients undergoing cardiac transplantation whose failure arises from different etiologies (e.g. idiopathic dilated cardiomyopathy, ischemic cardiomyopathy, alcoholic cardiomyopathy, valvular cardiomyopathy, and hypertrophic cardiomyopathy) and from "normal" organ donors whose hearts cannot be used for transplants. The transcriptional profile of the mRNA in these samples will be measured with gene array technology. Changes in transcriptional profiles can be correlated with the physiologic profile of heart-failure hearts acquired at the time of transplantation. Keywords: other
Project description:Heart failure and associated cachexia is an unresolved and important problem. We report a new model of severe heart failure that consistently results in cachexia. Mice lacking the integrated stress response (ISR) induced eIF2α phosphatase, PPP1R15A, exhibit a dilated cardiomyopathy and severe weight loss following irradiation, whilst wildtype mice are unaffected. This is associated with increased expression of Gdf15 in the heart and increased levels of GDF15 in the circulation. We provide evidence that blockade of GDF15 activity prevents cachexia and slows the progression of heart failure. Our data suggests that cardiac stress mediates a GDF15 dependent pathway that drives weight loss and worsens cardiac function. We show relevance of GDF15 to lean mass and protein intake with patients with heart failure. Blockade of GDF15 could constitute a novel therapeutic option to limit cardiac cachexia and improve clinical outcomes in patients with severe systolic heart failure.
Project description:Cardiac metabolism is deranged in heart failure, but underlying mechanisms remain unclear. Lysine demethylase 8 (Kdm8) represses gene expression in the embryo and controls metabolism in cancer. However, its function in cardiac homeostasis is unknown. We show that Kdm8 maintains a mitochondrial gene network active by repressing Tbx15 to prevent dilated cardiomyopathy leading to lethal heart failure. Deletion of Kdm8 in mouse cardiomyocytes increased H3K36me2 with activation of Tbx15 and repression of target genes in the NAD+ pathway before dilated cardiomyopathy initiates. Moreover, NAD+ supplementation prevented dilated cardiomyopathy in Kdm8 mutant mice and TBX15 overexpression blunted NAD+-activated cardiomyocyte respiration. Furthermore, KDM8 was downregulated in human hearts affected by dilated cardiomyopathy and higher TBX15 expression defines a subgroup of affected hearts with the strongest downregulation of genes encoding mitochondrial proteins. Thus, KDM8 represses TBX15 to maintain cardiac metabolism. Our results suggest that epigenetic dysregulation of metabolic gene networks initiates myocardium deterioration towards heart failure and could underlie heterogeneity of dilated cardiomyopathy.
Project description:Cardiac metabolism is deranged in heart failure, but underlying mechanisms remain unclear. Lysine demethylase 8 (Kdm8) represses gene expression in the embryo and controls metabolism in cancer. However, its function in cardiac homeostasis is unknown. We show that Kdm8 maintains a mitochondrial gene network active by repressing Tbx15 to prevent dilated cardiomyopathy leading to lethal heart failure. Deletion of Kdm8 in mouse cardiomyocytes increased H3K36me2 with activation of Tbx15 and repression of target genes in the NAD+ pathway before dilated cardiomyopathy initiates. Moreover, NAD+ supplementation prevented dilated cardiomyopathy in Kdm8 mutant mice and TBX15 overexpression blunted NAD+-activated cardiomyocyte respiration. Furthermore, KDM8 was downregulated in human hearts affected by dilated cardiomyopathy and higher TBX15 expression defines a subgroup of affected hearts with the strongest downregulation of genes encoding mitochondrial proteins. Thus, KDM8 represses TBX15 to maintain cardiac metabolism. Our results suggest that epigenetic dysregulation of metabolic gene networks initiates myocardium deterioration towards heart failure and could underlie heterogeneity of dilated cardiomyopathy.
Project description:Succinate dehydrogenase, which is known as mitochondrial complex II, has proven to be a fascinating machinery, attracting renewed and increased interest in its involvement in human diseases. Herein, we find that succinate dehydrogenase assembly factor 4 (SDHAF4) is downregulated in cardiac muscle in response to pathological stresses and in diseased hearts from human patients. Cardiac loss of Sdhaf4 suppresses complex II assembly and results in subunit degradation and complex II deficiency in fetal mice. These defects are exacerbated in young adults with globally impaired metabolic capacity and activation of dynamin-related protein 1, which induces excess mitochondrial fission and mitophagy, thereby causing progressive dilated cardiomyopathy and lethal heart failure in animals. Targeting mitochondria via supplementation with fumarate or inhibiting mitochondrial fission improves mitochondrial dynamics, partially restores cardiac function and prolongs the lifespan of mutant mice. Moreover, the addition of fumarate is found to dramatically improve cardiac function in myocardial infarction mice. These findings reveal a vital role for complex II assembly in the development of dilated cardiomyopathy and provide additional insights into therapeutic interventions for heart diseases.
Project description:miRNA expression in early stage mouse model of dilated cardiomyopathy Apoptosis is a hallmark of multiple etiologies of heart failure, including dilated cardiomyopathy. Since microRNAs are master regulators of cardiac development and key effectors of intracellular signaling, they represent novel candidates for understanding the mechanisms driving the increased dysfunction and loss of cardiomyocytes during cardiovascular disease progression. To determine the role of cardiac miRNAs in the apoptotic response, we used microarray technology to monitor miRNA levels in a validated murine phospholambam mutant model of dilated cardiomyopathy. 24 miRNAs were found significantly differentially expressed, most of which have not been linked to cardiac disease before. We showed that individual silencing of 6 out of 7 significantly down-regulated miRNAs (mir-1, -29c, -30d, -149, -486, -499) led to a strong apoptotic phenotype in cell culture , suggesting they repress pro-apoptotic factors. To identify putative miRNA targets most likely relevant to cell death, we computationally integrated transcriptomic, proteomic and functional annotation data. We showed the dependency of prioritized target abundance on miRNA expression using RNA interference and quantitative mass spectrometry. We concluded that down regulation of key pro-survival miRNAs causes up-regulation of apoptotic signaling effectors that contribute to cardiac cell loss, potentially leading to system decompensation and heart failure.
Project description:To establish changes in cardiac transcription profiles brought about by heart failure we collected myocardial samples from patients undergoing cardiac transplantation whose failure arises from different etiologies (e.g. idiopathic dilated cardiomyopathy, ischemic cardiomyopathy, alcoholic cardiomyopathy, valvular cardiomyopathy, and hypertrophic cardiomyopathy) and from "normal" organ donors whose hearts cannot be used for transplants. The transcriptional profile of the mRNA in these samples will be measured with gene array technology. Changes in transcriptional profiles can be correlated with the physiologic profile of heart-failure hearts acquired at the time of transplantation. Keywords: other
Project description:Analysis of ventricular derived mRNA from cardiac specific Cdk8 overexpressing mice. Results provide insight into the molecular mechanisms underlying dilated cardiomyopathy and heart failure.
Project description:Analysis of ventricular derived mRNA from cardiac specific Cdk8 overexpressing mice. Results provide insight into the molecular mechanisms underlying dilated cardiomyopathy and heart failure.