Cardiac arrhythmia and pump failure are the leading causes of mortality and morbidity in the United States. Cardiac hypertrophy associated with arrhythmia is the common initial response to hemodynamic stress such as hypertension and myocardial infarction. Sustained hemodynamic stress leads to decompensated heart failure. Increased contractility stimulated by heightened adrenergic drive during early and compensated hypertrophy is brought about by enhancing intracellular Ca2+ cycling, including increased Ca2+ influx through the L-type Ca2+ channel (Cavl.2). However, the role of Cavl.2 in the progress of heart disease is not well understood. We hypothesize that increases in Ca2+ influx contribute to the development of cardiac hypertrophy, arrhythmia and myocyte apoptosis, which ultimately lead to heart failure. This hypothesis will be tested with our newly established transgenic (TG) mouse lines overexpressing the beta2a subunit of Cavl.2 at low or high levels. Our preliminary data show that low expression TG mice develop sudden cardiac death and hypertrophy while high expression TG mice have heart failure symptoms. Hemodynamic stress causes heart failure in low expression TG mice and precipitates the onset of heart failure in high expression TG mice.
The specific aims are: 1. To determine if increases in Ca2+ influx (with a transgenic mouse line with low level expression of Cavl.2beta2a) that are sufficient to increase cardiac contractility, but do not induce SR Ca2+ overload, can induce myocyte hypertrophy without causing apoptosis. 2. To determine if increases in Ca2+ influx (transgenic mouse line with high level expression of Cavl.2beta2a) that are sufficient to cause SR Ca2+ overload induce cardiac arrhythmias and myocyte apoptosis, causing heart failure with depressed cardiac pump function, however, with increased myocyte contractility. These studies will test the idea that activation of myocyte apoptosis requires a CaMK II dependent phosphorylation of Ca2+ regulatory proteins. 3. To determine if increased Ca2+ influx (transgenic mouse lines with low and high expression of Cavl.2beta2a exacerbates/reverses the adverse effects of hemodynamic stress (aortic banding and isoproterenol infusion) on cardiac pump function, and the development of heart failure. The Cavl.2beta2a gene will be turned on either before or after the introduction of stressors. The long-term goal is to identify new targets or strategies for treating heart disease.
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