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Single histidine button in cardiac troponin I sustains heart performance in response to severe hypercapnic respiratory acidosis in vivo.

ABSTRACT: Intracellular acidosis is a profound negative regulator of myocardial performance. We hypothesized that titrating myofilament calcium sensitivity by a single histidine substituted cardiac troponin I (A164H) would protect the whole animal physiological response to acidosis in vivo. To experimentally induce severe hypercapnic acidosis, mice were exposed to a 40% CO(2) challenge. By echocardiography, it was found that systolic function and ventricular geometry were maintained in cTnI A164H transgenic (Tg) mice. By contrast, non-Tg (Ntg) littermates experienced rapid and marked cardiac decompensation during this same challenge. For detailed hemodymanic assessment, Millar pressure-conductance catheterization was performed while animals were treated with a beta-blocker, esmolol, during a severe hypercapnic acidosis challenge. Survival and load-independent measures of contractility were significantly greater in Tg vs. Ntg mice. This assay showed that Ntg mice had 100% mortality within 5 min of acidosis. By contrast, systolic and diastolic function were protected in Tg mice during acidosis, and they had 100% survival. This study shows that, independent of any beta-adrenergic compensation, myofilament-based molecular manipulation of inotropy by histidine-modified troponin I maintains cardiac inotropic and lusitropic performance and markedly improves survival during severe acidosis in vivo.

SUBMITTER: Palpant NJ

PROVIDER: S-EPMC2669425 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Single histidine button in cardiac troponin I sustains heart performance in response to severe hypercapnic respiratory acidosis in vivo.

Palpant Nathan J NJ D'Alecy Louis G LG Metzger Joseph M JM

FASEB journal : official publication of the Federation of American Societies for Experimental Biology 20090113 5

Intracellular acidosis is a profound negative regulator of myocardial performance. We hypothesized that titrating myofilament calcium sensitivity by a single histidine substituted cardiac troponin I (A164H) would protect the whole animal physiological response to acidosis in vivo. To experimentally induce severe hypercapnic acidosis, mice were exposed to a 40% CO(2) challenge. By echocardiography, it was found that systolic function and ventricular geometry were maintained in cTnI A164H transgen ...[more]

PMID: 19141534

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Project description:BackgroundCardiac troponin concentrations are used to identify patients who would benefit from urgent revascularization for acute coronary syndromes. We hypothesized that they might be used in patients with stable ischemic heart disease to identify those at high risk for cardiovascular events who might also benefit from prompt coronary revascularization.MethodsWe measured the cardiac troponin T concentration at baseline with a high-sensitivity assay in 2285 patients who had both type 2 diabetes and stable ischemic heart disease and were enrolled in the Bypass Angioplasty Revascularization Investigation in Type 2 Diabetes trial. We tested for an association between the troponin T concentration and a composite end point of death from cardiovascular causes, myocardial infarction, or stroke; we then evaluated whether random assignment to prompt revascularization reduced the rate of the composite end point in patients with an abnormal troponin T concentration (≥14 ng per liter) as compared with those with a normal troponin T concentration (<14 ng per liter).ResultsOf the 2285 patients, 2277 (99.6%) had detectable (≥3 ng per liter) troponin T concentrations and 897 (39.3%) had abnormal troponin T concentrations at baseline. The 5-year rate of the composite end point was 27.1% among the patients who had had abnormal troponin T concentrations at baseline, as compared with 12.9% among those who had had normal baseline troponin T concentrations. In models that were adjusted for cardiovascular risk factors, severity of diabetes, electrocardiographic abnormalities, and coronary anatomy, the hazard ratio for the composite end point among patients with abnormal troponin T concentrations was 1.85 (95% confidence interval [CI], 1.48 to 2.32; P<0.001). Among patients with abnormal troponin T concentrations, random assignment to prompt revascularization, as compared with medical therapy alone, did not result in a significant reduction in the rate of the composite end point (hazard ratio, 0.96; 95% CI, 0.74 to 1.25).ConclusionsThe cardiac troponin T concentration was an independent predictor of death from cardiovascular causes, myocardial infarction, or stroke in patients who had both type 2 diabetes and stable ischemic heart disease. An abnormal troponin T value of 14 ng per liter or higher did not identify a subgroup of patients who benefited from random assignment to prompt coronary revascularization. (Funded by the National Institutes of Health and Roche Diagnostics; BARI 2D ClinicalTrials.gov number, NCT00006305.).

Project description:In striated muscle, the protein troponin complex turns contraction on and off in a calcium-dependent manner. The calcium-sensing component of the complex is troponin C, which is expressed from the TNNC1 gene in both cardiac muscle and slow-twitch skeletal muscle (identical transcript in both tissues) and the TNNC2 gene in fast-twitch skeletal muscle. Cardiac troponin C (cTnC) is made up of two globular EF-hand domains connected by a flexible linker. The structural C-domain (cCTnC) contains two high affinity calcium-binding sites that are always occupied by Ca(2+) or Mg(2+) under physiologic conditions, stabilizing an open conformation that remains anchored to the rest of the troponin complex. In contrast, the regulatory N-domain (cNTnC) contains a single low affinity site that is largely unoccupied at resting calcium concentrations. During muscle activation, calcium binding to cNTnC favors an open conformation that binds to the switch region of troponin I, removing adjacent inhibitory regions of troponin I from actin and allowing muscle contraction to proceed. Regulation of the calcium binding affinity of cNTnC is physiologically important, because it directly impacts the calcium sensitivity of muscle contraction. Calcium sensitivity can be modified by drugs that stabilize the open form of cNTnC, post-translational modifications like phosphorylation of troponin I, or downstream thin filament protein interactions that impact the availability of the troponin I switch region. Recently, mutations in cTnC have been associated with hypertrophic or dilated cardiomyopathy. A detailed understanding of how calcium sensitivity is regulated through the troponin complex is necessary for explaining how mutations perturb its function to promote cardiomyopathy and how post-translational modifications in the thin filament affect heart function and heart failure. Troponin modulating drugs are being developed for the treatment of cardiomyopathies and heart failure.

Project description:BackgroundCardiac troponin is an independent predictor of cardiovascular mortality in individuals without symptoms or signs of cardiovascular disease. The mechanisms for this association are uncertain, and a role for troponin testing in the prevention of coronary heart disease has yet to be established.ObjectivesThis study sought to determine whether troponin concentration could predict coronary events, be modified by statins, and reflect response to therapy in a primary prevention population.MethodsWOSCOPS (West of Scotland Coronary Prevention Study) randomized men with raised low-density lipoprotein cholesterol and no history of myocardial infarction to pravastatin 40 mg once daily or placebo for 5 years. Plasma cardiac troponin I concentration was measured with a high-sensitivity assay at baseline and at 1 year in 3,318 participants.ResultsBaseline troponin was an independent predictor of myocardial infarction or death from coronary heart disease (hazard ratio [HR]: 2.3; 95% confidence interval [CI]: 1.4 to 3.7) for the highest (?5.2 ng/l) versus lowest (?3.1 ng/l) quarter of troponin (p < 0.001). There was a 5-fold greater reduction in coronary events when troponin concentrations decreased by more than a quarter, rather than increased by more than a quarter, for both placebo (HR: 0.29; 95% CI: 0.12 to 0.72 vs. HR: 1.95; 95% CI: 1.09 to 3.49; p < 0.001 for trend) and pravastatin (HR: 0.23; 95% CI: 0.10 to 0.53 vs. HR: 1.08; 95% CI: 0.53 to 2.21; p < 0.001 for trend). Pravastatin reduced troponin concentration by 13% (10% to 15%; placebo adjusted, p < 0.001) and doubled the number of men whose troponin fell more than a quarter (p < 0.001), which identified them as having the lowest risk for future coronary events (1.4% over 5 years).ConclusionsTroponin concentration predicts coronary events, is reduced by statin therapy, and change at 1 year is associated with future coronary risk independent of cholesterol lowering. Serial troponin measurements have major potential to assess cardiovascular risk and monitor the impact of therapeutic interventions.

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Single histidine button in cardiac troponin I sustains heart performance in response to severe hypercapnic respiratory acidosis in vivo.

Publications

Single histidine button in cardiac troponin I sustains heart performance in response to severe hypercapnic respiratory acidosis in vivo.

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