CALCOCO2 prevents AngII-induced atrial remodeling by regulating the interaction between mitophagy and mitochondrial stress

•We examined the role and mechanism of CALCOCO2 in atrial fibrillation.•CALCOCO2 is downregulated in various models of atrial fibrillation.•CALCOCO2 activates mitophagy in atrial tissue in atrial fibrillation.•CALCOCO2 restores mitochondrial homeostasis in atrial muscle.•DELE1 is essential for CALCOCO2-induced amelioration of mitochondrial stress in atrial fibrillation. The biological functions of mitochondrial complexes are closely related to the development of atrial fibrillation (AF). Calcium binding and coiled-coil domain 2 (CALCOCO2) is a novel and specific receptor for mitophagy; however, its function in AF remains unknown. Therefore, this study aimed to investigate the role and molecular mechanisms of CALCOCO2 in AF, especially its regulatory mechanism in mitophagy and mitochondrial stress. Mice and HL-1 cells were treated with AngII to establish in vitro and in vivo AF models. Additionally, we examined the effect of CALCOCO2 or DAP3 Binding Cell Death Enhancer 1 (DELE1) overexpression on mitophagy and mitochondrial stress in AF models. To investigate the role of mitophagy in the regulatory effects of CALCOCO2 in AF, HL-1 cells were treated with chloroquine, a mitophagy inhibitor. Moreover, mitochondrial parameters were examined using specific fluorescent probes, transmission electron microscopy, western blotting, immunohistochemistry, and confocal microscopy. AngII severely impaired the normal morphology and function of mitochondria; inhibited mitophagy; promoted atrial mitochondrial stress, fibrosis, and oxidative stress; and accelerated the progression of atrial remodeling in atrial myocytes. However, CALCOCO2 overexpression reversed/ameliorated these AF-induced changes. Additionally, CALCOCO2 overexpression restored mitochondrial homeostasis in atrial muscle by activating mitophagy and ameliorating mitochondrial stress. Mechanistically, DELE1 overexpression increased mitochondrial reactive oxygen species level and the expression of mitochondrial stress proteins (HRI, eIF2α, and ATF4) even in CALCOCO2-expressing in vitro AF models.. CALCOCO2 may serve as a potential target for AF therapy to prevent or reverse the progression of atrial remodeling by regulating mitophagy and DELE1-mediated mitochondrial stress.