Abstract 17583: Autophagy Protects the Heart Against Pressure Overload Induced Heart Failure

Abstract

Autophagy is an important mechanism for the degradation of cytosolic proteins and organelles. We investigated how autophagy is regulated in the heart in response to pressure overload (PO). Mice were subjected to transverse aortic constriction (TAC) for multiple durations ranging from 1 hour to 30 days. Left ventricular (LV) weight/tibial length (TL) was significantly elevated at Day 5 (6.21 ± 0.10 vs 4.59 ± 0.10, p<0.05) and thereafter. Ejection fraction (EF) was maintained at Day 7 (82.1±3.4 vs 78.4±3.2%), but gradually decreased thereafter (at Day 30, 51.0±4.5, p<0.05). The level of LC3II increased rapidly, peaking at 3 hours (2.4 fold, p<0.05), returned to normal by 24 hours, and then was significantly decreased at Day 5 (-40.0%, p<0.05) and thereafter. Autophagic flux was evaluated with tandem fluorescent LC3. At 6 hours, both GFP/RFP double positive (yellow) dots and RFP dots were significantly increased in the TAC group compared to the sham group, with or without chloroquine (CQ) (yellow 12±2 vs 4±0 CQ(-), 23±3 vs 9±1 CQ(+); RFP 13±2 vs 5±1 CQ(-), 19±1 vs 13±1 CQ(+)). However, both yellow and RFP dots were significantly decreased at Day 7 and thereafter in the TAC group compared to the sham group, with or without CQ. These data suggest that autophagic flux is activated only transiently after TAC, but is inactivated after Day 5. To examine the functional significance of autophagy during PO, beclin1 heterozygous knockout (beclin1-hetKO) mice, atg7 cardiac-specific knockout (Atg7-CKO) mice, and cardiac-specific U6-shRNA beclin1 (U6shRNAbeclin1) mice were subjected to TAC. At Day 7 and 14 of TAC, decreases in EF (60.7 ± 4.8%, 53.8 ± 2.1% and 46.7 ± 5.9%, p<0.05) and increases in lung weight/TL (8.43 ± 0.87, 11.04 ± 4.16 and 18.76 ± 3.77, p<0.05) were exacerbated in beclin1-hetKO, atg7-CKO and U6shRNAbeclin1 mice compared to in control mice. These results suggest that, after transient activation during the initial 24 hours, PO inhibits autophagy below control levels after Day 5, which coincides with the development of cardiac dysfunction. Since heart failure is exacerbated by further suppression of autophagy, autophagy during PO protects the heart from cardiac dysfunction and PO-induced downregulation of autophagy exacerbates heart failure.