20.500.12556/DKUM-90833 Loss of autophagy protein ATG5 impairs cardiac capacity in mice and humans through diminishing mitochondrial abundance and disrupting Ca2+ cycling Aims: Autophagy protects against the development of cardiac hypertrophy and failure. While aberrant Ca2+ handling promotes myocardial remodelling and contributes to contractile dysfunction, the role of autophagy in maintaining Ca2+ homeostasis remains elusive. Here, we examined whether Atg5 deficiency-mediated autophagy promotes early changes in subcellular Ca2+ handling in ventricular cardiomyocytes, and whether those alterations associate with compromised cardiac reserve capacity, which commonly precedes the onset of heart failure. Methods and results: RT-qPCR and immunoblotting demonstrated reduced Atg5 gene and protein expression and decreased abundancy of autophagy markers in hypertrophied and failing human hearts. The function of ATG5 was examined using cardiomyocyte-specific Atg5-knockout mice (Atg5-/-). Before manifesting cardiac dysfunction, Atg5-/- mice showed compromised cardiac reserve in response to β-adrenergic stimulation. Consequently, effort intolerance and maximal oxygen consumption were reduced during treadmill-based exercise tolerance testing. Mechanistically, cellular imaging revealed that Atg5 deprivation did not alter spatial and functional organization of intracellular Ca2+ stores or affect Ca2+ cycling in response to slow pacing or upon acute isoprenaline administration. However, high-frequency stimulation exposed stunted amplitude of Ca2+ transients, augmented nucleoplasmic Ca2+ load, and increased CaMKII activity, especially in the nuclear region of hypertrophied Atg5-/- cardiomyocytes. These changes in Ca2+ cycling were recapitulated in hypertrophied human cardiomyocytes. Finally, ultrastructural analysis revealed accumulation of mitochondria with reduced volume and size distribution, meanwhile functional measurements showed impaired redox balance in Atg5-/- cardiomyocytes, implying energetic unsustainability due to overcompensation of single mitochondria, particularly under increased workload. Conclusion: Loss of cardiac Atg5-dependent autophagy reduces mitochondrial abundance and causes subtle alterations in subcellular Ca2+ cycling upon increased workload in mice. Autophagy-related impairment of Ca2+ handling is progressively worsened by β-adrenergic signalling in ventricular cardiomyocytes, thereby leading to energetic exhaustion and compromised cardiac reserve. autophagy beta-adrenergic signalling calcium cardiomyocytes mitochondria avtofagija beta-adrenergični signali kalcij kardiomiociti mitohondriji true false true British Medical Association, Oxford University Press Angleški jezik Slovenski jezik Znanstveno delo 2024-09-26 14:42:36 2024-09-26 14:59:32 2024-09-28 03:21:55 0000-00-00 00:00:00 2022 0 0 Str. 1492-1505 Št. 6 Letn. 118 2022 0000-00-00 Zaloznikova Objavljeno NiDoloceno 2021-01-23 2021-03-19 2021-03-22 616.12 159499267 10.1093/cvr/cvab112 1755-3245 Ljubojevic-Holz-2022-Loss_of_autophagy_protein.pdf Ljubojevic-Holz-2022-Loss_of_autophagy_protein.pdf 1 3080780ED9DC2DF458D27CD92C6E64BE 9490a62edfec17a5684507957d3d73cbeb470a5ccaaa5c11e315329f5d7d3eae d85f9fe4-7c06-11ef-8e3e-00155d000105 https://dk.um.si/Dokument.php?lang=slv&id=185943 https://doi.org/10.1093/cvr/cvab112 0 d2bcdea5-7c04-11ef-8e3e-00155d000105 https://dk.um.si/Dokument.php?lang=slv&id=185940 Medicinska fakulteta 0 0 0