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Selected Publication:
Kraler, S.
Calcium homeostasis in autophagy-deficient mouse cardiomyocytes
Humanmedizin; [ Diplomarbeit/Master Thesis (UNI) ] Graz Medical University; 2019. pp.63. 63
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- Authors Med Uni Graz:
- Advisor:
- Holzer Senka
- Sedej Simon
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- Abstract:
- Background: Macroautophagy (hereafter referred to as autophagy) is a cytoprotective process essential for the maintenance of cardiac structure and function. Mice lacking Atg5-dependent autophagy develop profound left-ventricular dysfunction, which goes along with increased susceptibility to ß-adrenergic stimulation. In cardiac myocytes perturbations of subcellular calcium (Ca2+) handling are causally involved in hypertrophic gene program activation and, thus, may accelerate the development of heart failure. Aim: We aimed to elucidate whether loss of cardiac autophagy causes impaired subcellular Ca2+ cycling early in life, specifically during ß-adrenergic stress and increased workload. Such early alterations of intracellular Ca2+ handling may contribute to the development of contractile impairment and to accelerated remodeling of cardiomyocytes with inhibited autophagy. Methods: Left ventricular myocytes were isolated from adult (12-16 weeks old) cardiac-specific autophagy-deficient mice (Atg5-/-) with an apparently normal phenotype and from their control littermates (Atg5+/+) using a standard Liberase-based isolation procedure. Nucleoplasmic and cytoplasmic Ca2+ transients were then recorded using line-scan confocal imaging in electrically stimulated (1-4 Hz) cells loaded with Fluo-4/AM and perfused with Normal Tyrode solution containing 1 mmol/l CaCl2. To assess whether subcellular Ca2+ homeostasis is altered in response to acute β-adrenergic stress, isolated cardiomyocytes were acutely exposed to the β-adrenergic agonist isoprenaline (10 nmol/l). After each experiment, high-dose caffeine (30 mmol/l) was administered to evaluate the sarcoplasmic reticulum Ca2+ content. Results: Although autophagy-deficient myocytes displayed preserved Ca2+ cycling under basal conditions and upon acute ß-adrenergic stimulation, high-frequency pacing revealed blunted amplitudes of subcellular Ca2+ transients along with enhanced nucleoplasmic Ca2+ load, which may be an important determinant of Ca2+ dependent hypertrophic gene program activation. Conclusion: The lack of Atg5-dependent autophagy results in early alterations of subcellular Ca2+ homeostasis in left ventricular cardiomyocytes. Our results suggest that reinstating basal autophagy preserves rapid changes of the intracellular Ca2+ handling upon stress and conditions of increased workload, and may, therefore, attenuate hypertrophic remodeling and protect from heart failure.