Abstract 14078: Mammalian UNC-51-Like Kinase (ULK)-1 Plays a Crucial Role in Mediating Autophagy Under Stress Conditions in the Heart
Autophagy plays an important role in mediating protein quality control (QC) in cells. Inhibition of autophagy below physiological levels induces protein aggregation and cellular dysfunction. On the other hand, unrestrained activation of autophagy could lead to cell death. Mammalian UNC-51-like kinase-1 (ULK1), a serine/threonine kinase and the mammalian ortholog of yeast Atg1, is regulated by mTOR and involved in autophagy in mammalian cells. To elucidate the function of endogenous ULK1 in the heart, we used ULK1 knock out mice (ulk1-/-). The autophagic activity of cardiomyocytes (CMs) at baseline, as evaluated by LC3-II/LC3-I ratio and the protein level of p62, was similar in ulk1-/- and wild type mice (WT), and there was no significant difference in cardiac phenotype at 3 months of age, suggesting that ULK1 may be dispensable at baseline. In response to pressure overload (PO) caused by transverse aortic constriction (TAC) for 4 weeks, however, left ventricular weight (LVW) / tibial length (TL) was significantly greater in ulk1-/- than in WT (9.5±0.4 vs 7.4±0.5, p<0.05). LV ejection fraction (LVEF) was significantly lower in ulk1-/- than in WT (47±8% vs 69±3%, p<0.05), whereas lung weight/TL was greater in ulk1-/- than in WT (17.4±2.9 vs 9.9±0.5, p<0.05). Histological analyses indicated that LV fibrosis was greater in ulk1-/- than in WT. Furthermore, staining with ProteoStat® aggresome detection reagent was significantly increased in the peri-nuclear region of CMs in ulk1-/- mice compared to WT, suggesting that protein aggresomes are accumulated in ulk1-/- mice after TAC. The protein aggresomes co-stained with p62 in ulk1-/- mice, suggesting that autophagic flux is inhibited in ulk1-/- after TAC. In addition, at 12-15 months of age, ulk1-/- exhibited a greater LVW/TL (6.7±0.3 vs 5.9±0.3, p<0.05) and lower LVEF (55±3% vs 72±2%, p<0.05) than WT, even at baseline, accompanied by accumulation of p62, indicating a decrease in autophagic flux. In cultured CMs, transduction with adenovirus harboring kinase-dead ULK1 (K46N) suppressed starvation-induced autophagy. These results suggest that ULK1 plays a crucial role in mediating autophagy in the heart therein under stress conditions, thereby mediating protein QC and maintaining cardiac function in the heart.
- © 2011 by American Heart Association, Inc.