Annual Meeting of Japanese Society of Pediatric Cardiology and Cardiac Surgery

Background:Recent studies have suggested that endoplasmic reticulum-selective autophagy (ER-phagy) plays a cell-protective role by mediating degradation of damaged ER. We aimed to investigate whether ER-phagy protects cardiomyocytes from ER stress-mediated injury.Methods:ER-phagy activity was assessed using ss-RFP-GFP-KDEL protein, an ER-phagy reporter. The H9c2 cells and cardiomyocyte-specific transgenic mice, both expressing ss-RFP-GFP-KDEL proteins (tfH9c2 cells and Tg-mice), were utilized as reporter models. RNA interference or Gene-trap mutagenesis was performed to generate loss-of-function models. Assessment of phenotypes and molecular signaling pathways were carried out with immunoblotting, qPCR, cell viability assays, histopathological analyses and cardiac ultrasonography.Results:Treatment with Doxorubicin (Dox) showed marked elevations of the amount of RFP fragments in tfH9c2 and Tg-mice hearts, suggesting the increase in ER-phagy activity. qPCR analyses revealed treatment with Dox enhanced the expression of CCPG1, one of the ER-phagy receptors, in tfH9c2 cells. shRNA-mediated silencing of CCPG1 resulted in the reduction of ER-phagy activity, accumulation of pro-apoptotic proteins and deterioration of cell survival in response to Dox treatment. Consistently, CCPG1-hypomorphic mice developed more severe deterioration in systolic function against Dox treatment, than wild-type mice (Ejection fraction: 47.2±4.1% vs. 54.4±5.0%; p＜0.05).Conclusions:ER-phagy plays a protective role in cardiomyocytes against Dox toxicity, possibly through CCPG1-mediated signaling.