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The role of cardiac troponin T quantity and function in cardiac development and dilated cardiomyopathy.

ABSTRACT: Hypertrophic (HCM) and dilated (DCM) cardiomyopathies result from sarcomeric protein mutations, including cardiac troponin T (cTnT, TNNT2). We determined whether TNNT2 mutations cause cardiomyopathies by altering cTnT function or quantity; whether the severity of DCM is related to the ratio of mutant to wildtype cTnT; whether Ca(2+) desensitization occurs in DCM; and whether absence of cTnT impairs early embryonic cardiogenesis.We ablated Tnnt2 to produce heterozygous Tnnt2(+/-) mice, and crossbreeding produced homozygous null Tnnt2(-/-) embryos. We also generated transgenic mice overexpressing wildtype (TG(WT)) or DCM mutant (TG(K210Delta)) Tnnt2. Crossbreeding produced mice lacking one allele of Tnnt2, but carrying wildtype (Tnnt2(+/-)/TG(WT)) or mutant (Tnnt2(+/-)/TG(K210Delta)) transgenes. Tnnt2(+/-) mice relative to wildtype had significantly reduced transcript (0.82+/-0.06[SD] vs. 1.00+/-0.12 arbitrary units; p = 0.025), but not protein (1.01+/-0.20 vs. 1.00+/-0.13 arbitrary units; p = 0.44). Tnnt2(+/-) mice had normal hearts (histology, mass, left ventricular end diastolic diameter [LVEDD], fractional shortening [FS]). Moreover, whereas Tnnt2(+/-)/TG(K210Delta) mice had severe DCM, TG(K210Delta) mice had only mild DCM (FS 18+/-4 vs. 29+/-7%; p<0.01). The difference in severity of DCM may be attributable to a greater ratio of mutant to wildtype Tnnt2 transcript in Tnnt2(+/-)/TG(K210Delta) relative to TG(K210Delta) mice (2.42+/-0.08, p = 0.03). Tnnt2(+/-)/TG(K210Delta) muscle showed Ca(2+) desensitization (pCa(50) = 5.34+/-0.08 vs. 5.58+/-0.03 at sarcomere length 1.9 microm, p<0.01), but no difference in maximum force generation. Day 9.5 Tnnt2(-/-) embryos had normally looped hearts, but thin ventricular walls, large pericardial effusions, noncontractile hearts, and severely disorganized sarcomeres.Absence of one Tnnt2 allele leads to a mild deficit in transcript but not protein, leading to a normal cardiac phenotype. DCM results from abnormal function of a mutant protein, which is associated with myocyte Ca(2+) desensitization. The severity of DCM depends on the ratio of mutant to wildtype Tnnt2 transcript. cTnT is essential for sarcomere formation, but normal embryonic heart looping occurs without contractile activity.

SUBMITTER: Ahmad F

PROVIDER: S-EPMC2441440 | biostudies-literature | 2008 Jul

REPOSITORIES: biostudies-literature

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The role of cardiac troponin T quantity and function in cardiac development and dilated cardiomyopathy.

Ahmad Ferhaan F Banerjee Sanjay K SK Banerjee Sanjay K SK Lage Michele L ML Huang Xueyin N XN Smith Stephen H SH Saba Samir S Rager Jennifer J Conner David A DA Janczewski Andrzej M AM Tobita Kimimasa K Tinney Joseph P JP Moskowitz Ivan P IP Perez-Atayde Antonio R AR Keller Bradley B BB Mathier Michael A MA Shroff Sanjeev G SG Seidman Christine E CE Seidman J G JG

PloS one 20080709 7

<h4>Background</h4>Hypertrophic (HCM) and dilated (DCM) cardiomyopathies result from sarcomeric protein mutations, including cardiac troponin T (cTnT, TNNT2). We determined whether TNNT2 mutations cause cardiomyopathies by altering cTnT function or quantity; whether the severity of DCM is related to the ratio of mutant to wildtype cTnT; whether Ca(2+) desensitization occurs in DCM; and whether absence of cTnT impairs early embryonic cardiogenesis.<h4>Methods and findings</h4>We ablated Tnnt2 to ...[more]

PMID: 18612386

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Project description:BACKGROUND:Myocardial metabolic impairment is a major feature in chronic heart failure. As the major coenzyme in fuel oxidation and oxidative phosphorylation and a substrate for enzymes signaling energy stress and oxidative stress response, nicotinamide adenine dinucleotide (NAD+) is emerging as a metabolic target in a number of diseases including heart failure. Little is known on the mechanisms regulating homeostasis of NAD+ in the failing heart. METHODS:To explore possible alterations of NAD+ homeostasis in the failing heart, we quantified the expression of NAD+ biosynthetic enzymes in the human failing heart and in the heart of a mouse model of dilated cardiomyopathy (DCM) triggered by Serum Response Factor transcription factor depletion in the heart (SRFHKO) or of cardiac hypertrophy triggered by transverse aorta constriction. We studied the impact of NAD+ precursor supplementation on cardiac function in both mouse models. RESULTS:We observed a 30% loss in levels of NAD+ in the murine failing heart of both DCM and transverse aorta constriction mice that was accompanied by a decrease in expression of the nicotinamide phosphoribosyltransferase enzyme that recycles the nicotinamide precursor, whereas the nicotinamide riboside kinase 2 (NMRK2) that phosphorylates the nicotinamide riboside precursor is increased, to a higher level in the DCM (40-fold) than in transverse aorta constriction (4-fold). This shift was also observed in human failing heart biopsies in comparison with nonfailing controls. We show that the Nmrk2 gene is an AMP-activated protein kinase and peroxisome proliferator-activated receptor ? responsive gene that is activated by energy stress and NAD+ depletion in isolated rat cardiomyocytes. Nicotinamide riboside efficiently rescues NAD+ synthesis in response to FK866-mediated inhibition of nicotinamide phosphoribosyltransferase and stimulates glycolysis in cardiomyocytes. Accordingly, we show that nicotinamide riboside supplementation in food attenuates the development of heart failure in mice, more robustly in DCM, and partially after transverse aorta constriction, by stabilizing myocardial NAD+ levels in the failing heart. Nicotinamide riboside treatment also robustly increases the myocardial levels of 3 metabolites, nicotinic acid adenine dinucleotide, methylnicotinamide, and N1-methyl-4-pyridone-5-carboxamide, that can be used as validation biomarkers for the treatment. CONCLUSIONS:The data show that nicotinamide riboside, the most energy-efficient among NAD precursors, could be useful for treatment of heart failure, notably in the context of DCM, a disease with few therapeutic options.

Project description:BackgroundBiased agonism of the angiotensin II receptor is known to promote cardiac contractility. Our laboratory indicated that these effects may be attributable to changes at the level of the myofilaments. However, these signaling mechanisms remain unknown. Because a common finding in dilated cardiomyopathy is a reduction in the myofilament-Ca2+ response, we hypothesized that β-arrestin signaling would increase myofilament-Ca2+ responsiveness in a model of familial dilated cardiomyopathy and improve cardiac function and morphology.MethodsWe treated a dilated cardiomyopathy-linked mouse model expressing a mutant tropomyosin (Tm-E54K) for 3 months with either TRV120067, a β-arrestin 2-biased ligand of the angiotensin II receptor, or losartan, an angiotensin II receptor blocker. At the end of the treatment protocol, we assessed cardiac function using echocardiography, the myofilament-Ca2+ response of detergent-extracted fiber bundles, and used proteomic approaches to understand changes in posttranslational modifications of proteins that may explain functional changes. We also assessed signaling pathways altered in vivo and by using isolated myocytes.ResultsTRV120067- treated Tm-E54K mice showed improved cardiac structure and function, whereas losartan-treated mice had no improvement. Myofilaments of TRV120067-treated Tm-E54K mice had significantly improved myofilament-Ca2+ responsiveness, which was depressed in untreated Tm-E54K mice. We attributed these changes to increased MLC2v and MYPT1/2 phosphorylation seen only in TRV120067-treated mice. We found that the functional changes were attributable to an activation of ERK1/2-RSK3 signaling, mediated through β-arrestin, which may have a novel role in increasing MLC2v phosphorylation through a previously unrecognized interaction of β-arrestin localized to the sarcomere.ConclusionsLong-term β-arrestin 2-biased agonism of the angiotensin II receptor may be a viable approach to the treatment of dilated cardiomyopathy by not only preventing maladaptive signaling, but also improving cardiac function by altering the myofilament-Ca2+ response via β-arrestin signaling pathways.

Dataset Information

The role of cardiac troponin T quantity and function in cardiac development and dilated cardiomyopathy.

Publications

The role of cardiac troponin T quantity and function in cardiac development and dilated cardiomyopathy.

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