Myofilament calcium sensitization delays decompensated hypertrophy differently between the sexes following myocardial infarction

Deregulated Ca2+ cycling underlies the development of arrhythmia and heart disease due to mutant obscurin

Obscurins are cytoskeletal proteins with structural and regulatory roles encoded by OBSCN. Mutations in OBSCN are associated with the development of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Specifically, the R4344Q mutation present in immunoglobulin domain 58 (Ig58) was the first to be linked with the development of HCM. To assess the effects of R4344Q in vivo, we generated the respective knock-in mouse model. Mutant obscurins are expressed and incorporated normally into sarcomeres. The expression patterns of sarcomeric and Ca2+-cycling proteins are unaltered in sedentary 1-year-old knock-in myocardia, with the exception of sarco/endoplasmic reticulum Ca2+ adenosine triphosphatase 2 (SERCA2) and pentameric phospholamban whose levels are significantly increased and decreased, respectively. Isolated cardiomyocytes from 1-year-old knock-in hearts exhibit increased Ca2+-transients and Ca2+-load in the sarcoplasmic reticulum and faster contractility kinetics. Moreover, sedentary 1-year-old knock-in animals develop tachycardia accompanied by premature ventricular contractions, whereas 2-month-old knock-in animals subjected to pressure overload develop a DCM-like phenotype. Structural analysis revealed that the R4344Q mutation alters the distribution of electrostatic charges over the Ig58 surface, thus interfering with its binding capabilities. Consistent with this, wild-type Ig58 interacts with phospholamban modestly, and this interaction is markedly enhanced in the presence of R4344Q. Together, our studies demonstrate that under sedentary conditions, the R4344Q mutation results in Ca2+ deregulation and spontaneous arrhythmia, whereas in the presence of chronic, pathological stress, it leads to cardiac remodeling and dilation. We postulate that enhanced binding between mutant obscurins and phospholamban leads to SERCA2 disinhibition, which may underlie the observed pathological alterations.

Gender-related differences in patients with acute heart failure: management and predictors of in-hospital mortality

AIM AND METHODS

Gender-related differences in clinical phenotype, in-hospital management and prognosis of acute heart failure (AHF) patients have been previously reported in European and US registries. The ALARM-HF survey is the first to include a cohort of 4953 patients hospitalized for AHF in 666 hospitals in 6 European countries, Mexico and Australia.

RESULTS

Women accounted for 37% of the study population, were older and had higher rates of de novo heart failure (45% vs 36%, p<0.001) than men. An acute coronary syndrome (ACS) was the predominant precipitating factor in both genders, but to a lesser extent in females (30% vs 42%, p<0.001). Between genders comparison showed higher incidence of atrial fibrillation, valvular heart disease, diabetes, obesity, anemia and depression in women (p<0.05). Similarly, women had higher left ventricular ejection fraction (LVEF) on admission (42 ± 15% vs 36 ± 13%, p<0.001) and systolic blood pressure (135 ± 40 mm Hg vs 131 ± 39 mm Hg, p=0.001) than men. On the other hand, men had more often coronary artery disease, renal failure and chronic obstructive pulmonary disease (p<0.05). Importantly, in-hospital mortality was similar in both genders (11.1% in females vs 10.5% in males, p=0.475), and its common predictors were: systolic blood pressure at admission, creatinine>1.5mg/dL and diabetes. Furthermore, recent ACS, valvular heart disease and dementia contributed to prognosis in women, while LVEF, hypertension and anemia were independent predictors in men.

CONCLUSION

Among patients with AHF, there are significant differences in co-morbidities, precipitating factors and predictors of in-hospital mortality between genders. Nevertheless, in-hospital mortality remains similar between genders.

Beneficial effects of SR33805 in failing myocardium

AIMS

SR33805, a potent Ca(2+) channel blocker, increases cardiac myofilament Ca(2+) sensitivity in healthy rat cardiomyocytes. Therefore, the aim of the present study was to evaluate the effects of SR33805 on contractile properties in ischaemic failing hearts after myocardial infarction (MI) in vivo and in vitro at the cellular level.

METHODS AND RESULTS

The effect of SR33805 (10 µM) was tested on the excitation-contraction coupling of cardiomyocytes isolated from rat with end-stage heart failure. Cell shortening and Ca(2+) transients were measured in intact cardiomyocytes, while contractile properties were determined in Triton X-100 permeabilized myocytes. Acute treatment with SR33805 restored the MI-altered cell shortening without affecting the Ca(2+) transient amplitude, suggesting an increase of myofilament Ca(2+) sensitivity in MI myocytes. Indeed, a SR33805-induced sensitization of myofilament activation was found to be associated with a slight increase in myosin light chain-2 phosphorylation and a more significant decrease on troponin I (TnI) phosphorylation. Decreased TnI phosphorylation was related to inhibition of protein kinase A activity by SR33805. Finally, administration of a single intra-peritoneal bolus of SR33805 (20 mg/kg) improved end-systolic strain and fractional shortening of MI hearts.

CONCLUSION

The present study indicates that treatment with SR33805 improved contractility of ischaemic failing hearts after MI in the rat by selectively modulating the phosphorylation status of sarcomeric regulatory proteins, which then sensitized the myofilaments to Ca(2+). Our results gave a proof of concept that manipulation of the Ca(2+) sensitivity of sarcomeric regulatory proteins can be used to improve contractility of a failing heart.