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Muscle Ring Finger 1 (MuRF1) and MuRF2 are Necessary but Functionally Redundant During Developmental Cardiac Growth and Regulate E2F1-Mediated Gene Expression In Vivo

ABSTRACT: Muscle ring finger (MuRF) proteins have been implicated in the transmission of mechanical forces to nuclear cell signaling pathways through their association with the sarcomere. We recently reported that MuRF1, but not MuRF2, regulated pathologic cardiac hypertrophy in vivo. This was surprising since MuRF1 and MuRF2 interact redundantly with sarcomeric proteins in yeast two hybrid studies, and form both homo- and hetero-dimers with each other. To determine if MuRF1 and MuRF2 were functionally redundant during development, we created mice lacking either 3 or 4 of the MuRF1 and MuRF2 alleles and compared them functionally. Surprisingly, only mice missing all four MuRF1 and MuRF2 alleles (MuRF1-/-//MuRF2-/-) developed a spontaneous hypertrophic cardiomyopathy - mice that were null for one of the genes, but heterozygous for the other (i.e. MuRF1-/-//MuRF2+/- or MuRF1+/-//MuRF2-/-) were phenotypically identical to wild type mice. Electron microscopy of the hearts of MuRF1-/-//MuRF2-/-(MuRF1/MuRF2 DN) mice identified altered Z disc and M line architecture, and a distinct swelling of mitochondria. MuRF1-/-//MuRF2-/- mouse hearts displayed increased expression of genes associated with fetal cardiac metabolism, including smooth muscle actin and b myosin heavy chain, suggesting that the cardiac hypertrophy seen in these mice was associated with a reversion to a fetal gene program. Despite our prediction that we would also see an increase in glucose compared to fatty acid oxidation (another trait of fetal cardiac metabolism) we saw that MuRF1-/-//MuRF2-/- heart homogenates oxidized significantly less glucose compared to controls, suggesting an important role for MuRF1 and MuRF2 in the regulation of glucose metabolism in vivo. This study identifies a previously unreported redundancy in the function of MuRF proteins in normal cardiac development. Keywords: Genetic modification.

ORGANISM(S): Mus musculus

PROVIDER: GSE14512 | GEO | 2013/04/01

SECONDARY ACCESSION(S): PRJNA111657

REPOSITORIES: GEO

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Project description:Muscle ring finger (MuRF) proteins have been implicated in the transmission of mechanical forces to nuclear cell signaling pathways through their association with the sarcomere. We recently reported that MuRF1, but not MuRF2, regulated pathologic cardiac hypertrophy in vivo. This was surprising since MuRF1 and MuRF2 interact redundantly with sarcomeric proteins in yeast two hybrid studies, and form both homo- and hetero-dimers with each other. To determine if MuRF1 and MuRF2 were functionally redundant during development, we created mice lacking either 3 or 4 of the MuRF1 and MuRF2 alleles and compared them functionally. Surprisingly, only mice missing all four MuRF1 and MuRF2 alleles (MuRF1-/-//MuRF2-/-) developed a spontaneous hypertrophic cardiomyopathy - mice that were null for one of the genes, but heterozygous for the other (i.e. MuRF1-/-//MuRF2+/- or MuRF1+/-//MuRF2-/-) were phenotypically identical to wild type mice. Electron microscopy of the hearts of MuRF1-/-//MuRF2-/-(MuRF1/MuRF2 DN) mice identified altered Z disc and M line architecture, and a distinct swelling of mitochondria. MuRF1-/-//MuRF2-/- mouse hearts displayed increased expression of genes associated with fetal cardiac metabolism, including smooth muscle actin and b myosin heavy chain, suggesting that the cardiac hypertrophy seen in these mice was associated with a reversion to a fetal gene program. Despite our prediction that we would also see an increase in glucose compared to fatty acid oxidation (another trait of fetal cardiac metabolism) we saw that MuRF1-/-//MuRF2-/- heart homogenates oxidized significantly less glucose compared to controls, suggesting an important role for MuRF1 and MuRF2 in the regulation of glucose metabolism in vivo. This study identifies a previously unreported redundancy in the function of MuRF proteins in normal cardiac development. Keywords: Genetic modification. Four strain-matched groups of 12 week old mice were investigated: 1) MuRF1 -/- MuRF2 -/-; 2) MuRF1 +/+ MuRF2 +/+; 3) MuRF1 -/- MuRF2 +/-; 4) MuRF1 +/- MuRF2 -/-. Biological replicates: 4 WT, 4 MuRF1 -/- // MuRF2 -/-, 4 MuRF1 +/- //MuRF2 -/-, 4 MuRF1 -/- // MuRF2 +/-. Hearts harvested. One replicate per array.

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.

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Muscle Ring Finger 1 (MuRF1) and MuRF2 are Necessary but Functionally Redundant During Developmental Cardiac Growth and Regulate E2F1-Mediated Gene Expression In Vivo

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