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Cardiac Muscle Ring Finger-1 (MuRF1) and Transcriptional Regulation of Ischemia-Reperfusion Injury In Vivo

ABSTRACT: We previously identified a role for the muscle-specific ubiquitin ligase MuRF1 (Muscle Ring Finger-1) in cardiac ischemia-reperfusion (I/R) injury. We found that cardiomyocyte-specific (alphaMHC-) MuRF1 transgenic mice (MuRF1 Tg+) mice were significantly protected from I/R injury. As we discovered MuRF1’s regulation of other transcriptions factors, we sought to identify other ways in which MuRF1 was cardioprotective in I/R injury. In the present study, we first identified the regulation of MuRF1 expression by qPCR in a porcine model of I/R injury. MuRF1 mRNA significantly increased within 90 minutes of I/R injury. We next assayed MuRF1 Tg+ ventricular tissue after I/R reperfusion injury by microarray (44K transcripts) to identify how MuRF1 regulates the transcriptome. We identified 71 significantly altered genes having a >1.5-fold (p<0.01) in MuRF1 Tg+ and wildtype hearts challenged with I/R injury (or sham operation). Functional annotation of the top upregulated genes found enrichment for myogenesis, cell adhesion, and nucleic acid metabolism. TRANSFAC analysis of MuRF1 Tg+ significant genes identified enrichment for genes (30-53%) with promoter regions recognized by the transcription factors MAZ, PIT1, VMW65, and BACH2. The transcription factor MAZ binds muscle creatine kinase (MCK) promoter in skeletal and cardiac myocytes, known most for its regulation of myogenin and MEF2C in cardiomyocytes. While the role of PIT1 and BACH2 in adult cardiomyocytes is not clear, VMW65 is a powerful transactivator with functions in chromatin remodeling. In neonatal cardiomycoyte I/R injury, VMW65 associates with HIF1alpha to upregulate cardioprotective VEGF, Glut-1, Glut-4, HSP70, and iNOS expression. These findings elucidate the MuRF1-specific regulation of genes in cardiac I/R injury that are associated with cardioprotection and may represent multiple additional direct or indirect mechanisms that MuRF1 regulates cardiomyocyte signaling.

ORGANISM(S): Mus musculus

PROVIDER: GSE108940 | GEO | 2019/01/05

REPOSITORIES: GEO

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Project description:Muscle ring finger-1 (MuRF1) is a muscle-specific protein implicated in the regulation of cardiac myocyte size and contractility. MuRF2, a closely related family member, redundantly interacts with protein substrates, and hetero-dimerizes with MuRF1. Mice lacking either MuRF1 or MuRF2 are phenotypically normal whereas mice lacking both proteins develop a spontaneous cardiac and skeletal muscle hypertrophy indicating cooperative control of muscle mass by MuRF1 and MuRF2. In order to identify the role that MuRF1 plays in regulating cardiac hypertrophy in vivo, we created transgenic mice expressing increased amounts of cardiac MuRF1. Adult MuRF1 transgenic (Tg+) hearts exhibited a non-progressive thinning of the left ventricular wall and a concomitant decrease in cardiac function. Experimental induction of cardiac hypertrophy by trans-aortic constriction (TAC) induced rapid failure of MuRF1 Tg+ hearts. Microarray analysis identified that the levels of genes associated with metabolism (and in particular mitochondrial processes) were significantly altered in MuRF1 Tg+ hearts, both at baseline and during the development of cardiac hypertrophy. Surprisingly, ATP levels in MuRF1 Tg+ mice did not differ from wild type mice despite the depressed contractility following TAC. To explain this discrepancy between the ongoing heart failure and maintained ATP levels in MuRF1 Tg+ hearts, we compared the level and activity of creatine kinase (CK) between wild type and MuRF1 Tg+ hearts. Although mCK and CK-M/B protein levels were unaffected in MuRF1 Tg+ hearts, total CK activity was significantly inhibited. We conclude that MuRF1’s inhibition of CK activity leads to increased susceptibility to heart failure following TAC, demonstrating for the first time that MuRF1 regulates cardiac energetics in vivo. Keywords: Genetic modification, physiological manipulation. Three-condition experiment, MuRF1 Tg+ vs. WT mice. Biological replicates: 4 WT baseline, 3 MuRF1 Tg+ baseline, cardiac overpressure hypertrophy induced by trans-aortic banding at 1 week (3 WT, 3 MurF Tg) and 4 weeks (3 WT, 3 MurF Tg), hearts harvested. One replicate per array.

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.

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Cardiac Muscle Ring Finger-1 (MuRF1) and Transcriptional Regulation of Ischemia-Reperfusion Injury In Vivo

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