Abstract 18782: Cardiac-specific Ablation of Ulk1, but not of Atg7, Attenuates Mitochondrial Autophagy in the Heart in Response to Energy Stress (Best of Basic Science Abstract)
Rationale and Objective: During myocardial ischemia, mitochondria in cardiomyocytes undergo oxidative stress, develop protein damage/dysfunction, and trigger cell death. Dysfunctional mitochondria are eliminated through mitochondrial autophagy (MA). MA is mediated by both Atg7-dependent (conventional) and independent (alternative) mechanisms. We investigated the molecular mechanism mediating MA in response to prolonged myocardial ischemia.
Methods and Results: We subjected wild-type, cardiac-specific atg7 KO, and cardiac-specific ulk1 KO mice (WT, atg7cKO, or ulk1cKO, respectively) to 48-hour fasting. The protein level of LC3-II was increased more than 5-fold in WT and ulk1cKO mouse hearts in response to starvation (p<0.05), suggesting that conventional autophagy is induced. LC3-II was not detectable, and p62 was markedly accumulated in atg7cKO mouse hearts, indicating the complete absence of conventional autophagy in atg7cKO mouse hearts. Mitochondrial mass, as evaluated by the mitochondrial DNA content, was significantly increased in ulk1cKO mouse hearts (1.27-fold, p<0.05) in response to fasting, but not in WT nor atg7cKO mouse hearts. Electron microscopic analyses indicated that autophagosomes containing mitochondria were easily detected in WT and atg7cKO, but not in ulk1cKO, mouse hearts after fasting. These results suggest that Ulk1, rather than Atg7, is essential for mediating MA in response to fasting. We also subjected them to prolonged ischemia (2 hours). The size of myocardial infarction/area at risk was significantly greater in ulk1KO mouse hearts (67%, p<0.05) than in WT (37 %) and atg7cKO (40 %) mouse hearts. Although WT and atg7cKO mouse hearts exhibited a significant decrease in the protein level of COXI (0.81- and 0.82-fold, p<0.05) in the ischemic region, ulk1cKO mouse hearts exhibited an increase (1.27-fold, p<0.05). Through electron microscopy, MA was clearly observed at the ischemic area in WT and atg7cKO mouse hearts, but not in ulk1cKO mouse hearts.
Conclusions: These results suggest that Ulk1, rather than Atg7, plays an important role in mediating protection of the heart against energy stress by mediating degradation of damaged mitochondria through MA.
Author Disclosures: T. Saito: None. J. Sadoshima: None.
- © 2015 by American Heart Association, Inc.