Project description: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.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. 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.  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.

Project description:Aims A kinase interacting protein 1 (AKIP1) stimulates physiological growth in cultured cardiomyocytes and attenuates ischemia / reperfusion (I/R) injury in ex vivo perfused hearts. We aimed to determine whether AKIP1 modulates the cardiac response to acute and chronic cardiac stress in vivo. Methods and results Transgenic mice with cardiac-specific overexpression of AKIP1 (AKIP1-TG) were created. AKIP1-TG mice and their wild type (WT) littermates displayed similar cardiac structure and function. Likewise, cardiac remodeling in response to transverse aortic constriction or permanent coronary artery ligation was identical in AKIP1-TG and WT littermates, as evidenced by serial cardiac magnetic resonance imaging and pressure-volume loop analysis. Histological indices of remodeling, including cardiomyocyte cross-sectional diameter, capillary density and left ventricular fibrosis were also similar in AKIP1-TG mice and WT littermates. When subjected to 45 minutes of ischemia followed by 24 hours of reperfusion, AKIP1-TG mice displayed a significant 2-fold reduction in myocardial infarct size and reductions in cardiac apoptosis. In contrast to previous reports, AKIP1 did not co-immunoprecipitate with or regulate the activity of the signaling molecules NF-κB, protein kinase A or AKT. AKIP1 was, however, enriched in cardiac mitochondria and co-immunoprecipitated with a key component of the mitochondrial permeability transition (MPT) pore, ATP-synthase. Finally, mitochondria isolated from AKIP1-TG hearts displayed markedly reduced calcium induced swelling, indicative of reduced MPT pore formation. Conclusions In contrast to in vitro studies, AKIP1 overexpression does not influence cardiac remodeling in response to chronic cardiac stress. AKIP1 does, however, reduce myocardial I/R injury through stabilization of the MPT pore. These findings suggest that AKIP1 deserves further investigation as a putative treatment target for cardioprotection from I/R injury during acute myocardial infarction.

Project description:Background: Improving heart regeneration through reactivating cardiomyocyte proliferation holds a great potential for repairing diseased hearts. We recently reported that LSD1-dependent epigenetic repression of Cend1 transcription is prerequisite for cardiomyocyte proliferation and mouse heart development. This study interrogates the potential role of this LSD1-CEND1 axis in heart regeneration and repair. Methods: The cardiomyocyte-specific Lsd1 knockout or overexpression mice, Cend1null mice and cardiomyocyte-specific Cend1 overexpression mice were used to determine the role of LSD1-CEND1 axis in heart regeneration after experimental injuries. Neonatal and adult mice were subjected to apical resection or left anterior descending coronary artery ligation, respectively, to establish cardiac injury models. Echocardiography and Masson staining were employed to assess cardiac function and histopathology, respectively. The molecular changes were determined using RNA sequencing, quantitative RT-PCR, Western blotting and immunostaining. Results: Cardiomyocyte-specific deletion impeded neonatal heart regeneration, while overexpression of Lsd1 had the opposite effect. RNA sequencing revealed that Cend1, a crucial suppressor of cardiomyocyte cycling, was the most significantly elevated gene induced by Lsd1 loss during heart regeneration. Cardiomyocyte-specific Cend1 overexpression hindered neonatal heart regeneration, while Cend1 loss in nullizygous mice had the opposite effect. Cend1 deletion resulted in gene expression alterations associated with enhanced cardiomyocyte proliferation, neovascularization, and macrophage activation. Furthermore, the cardiac regeneration defect caused by Lsd1 loss was not observed when experiments were performed with mice that were nullizyogus for Cend1. Moreover, we found that either Lsd1 overexpression or Cend1 deletion could promote heart regeneration and repair, and improve cardiac function following experimental myocardial infraction in adult mice.

Project description:VEGF family members are important regulators of vascular functions. Promoting VEGFA signalling in aged mice has been shown to delay various aging phenotypes and extend the survival of aged mice. Although there is profound knowledge on functions of VEGFA, VEGFB has not been investigated in the context of cardiac aging. Our RNA data of aged mouse hearts revealed significant downregulation of Vegfb in the heart, specifically in endothelial cells and cardiomyocytes, while VEGFB expression was reduced in endothelial cells, fibroblasts and cardiomyocytes in aged human hearts. By contrast, VEGFB expression was exclusively reduced in cardiomyocytes of patients with cardiac hypertrophy. Hence, we investigated whether Vegfb gene therapy can revert age-dependent cardiac pathologies. We overexpressed Vegfb186, the soluble VEGFB isoform, via AAV9 vector transduction into 18-month-old C57Bl/6J male mice. AAV9-Vegfb treatment prevented progression age-related diastolic dysfunction and decreased cardiac fibrosis. We further found a rescue of aging-related left ventricular denervation in the hearts of AVV9-Vegfb treated old mice which was associated with an increase in heart rate variability. However, heart to body weight ratio and cardiomyocyte hypertrophy were increased in the AAV9-Vegfb treated mouse hearts, without alteration of cardiac systolic or diastolic function. Histological and transcriptomic analyses revealed that VEGFB186 induces compensatory cardiac hypertrophy which was accompanied by a rescued length-width-ratio, reduced fibrosis and the absence of cardiac inflammation. Cardiac single-nuclei RNA sequencing further suggested that AAV9-Vegfb treatment affects cardiac hypertrophy putatively via STAT3 which was validated in vitro. In conclusion, our data reveals that Vegfb overexpression partially reverses pathological alterations in the aging heart. Despite the overall improvement of the age-related cardiac phenotype, the AAV9-Vegfb-mediated induced cardiac hypertrophy which might reflect protective hypertrophy.

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PKR2 overexpression in heart

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