Cardiac autophagy is a maladaptive response to hemodynamic stress
Hongxin Zhu, … , Beverly A. Rothermel, Joseph A. Hill
Hongxin Zhu, … , Beverly A. Rothermel, Joseph A. Hill
Published July 2, 2007
Citation Information: J Clin Invest. 2007;117(7):1782-1793. https://doi.org/10.1172/JCI27523.
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Cardiac autophagy is a maladaptive response to hemodynamic stress

Abstract

Cardiac hypertrophy is a major predictor of heart failure and a prevalent disorder with high mortality. Little is known, however, regarding mechanisms governing the transition from stable cardiac hypertrophy to decompensated heart failure. Here, we tested the role of autophagy, a conserved pathway mediating bulk degradation of long-lived proteins and cellular organelles that can lead to cell death. To quantify autophagic activity, we engineered a line of “autophagy reporter” mice and confirmed that cardiomyocyte autophagy can be induced by short-term nutrient deprivation in vivo. Pressure overload induced by aortic banding induced heart failure and greatly increased cardiac autophagy. Load-induced autophagic activity peaked at 48 hours and remained significantly elevated for at least 3 weeks. In addition, autophagic activity was not spatially homogeneous but rather was seen at particularly high levels in basal septum. Heterozygous disruption of the gene coding for Beclin 1, a protein required for early autophagosome formation, decreased cardiomyocyte autophagy and diminished pathological remodeling induced by severe pressure stress. Conversely, Beclin 1 overexpression heightened autophagic activity and accentuated pathological remodeling. Taken together, these findings implicate autophagy in the pathogenesis of load-induced heart failure and suggest it may be a target for novel therapeutic intervention.

Authors

Hongxin Zhu, Paul Tannous, Janet L. Johnstone, Yongli Kong, John M. Shelton, James A. Richardson, Vien Le, Beth Levine, Beverly A. Rothermel, Joseph A. Hill

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Figure 1

Cardiomyocyte autophagy triggered by short-term nutrient deprivation or pressure-overload hemodynamic stress.

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Cardiomyocyte autophagy triggered by short-term nutrient deprivation or ...
(A) Representative electron micrographs from the septa of 48-hour sTAB LVs (WT C57BL/6 mice) demonstrate the presence of double-membrane autophagosomes (arrows) and autolysosomes containing cellular material. These features are more prominent in sTAB ventricles compared with those of sham-operated controls. Scale bar: 120 nm. (B) Representative immunoblot for LC3 showing an increase in LC3-II abundance following sTAB as early as 24 hours after operations and persisting for at least 2 weeks. (C) Quantification of LC3-II/LC3-I levels demonstrates significant autophagic activity induced by pressure overload. *P < 0.05 versus Sham. (D) Representative immunoblots for LC3 in liver and kidney demonstrating that LC3-II abundance does not change in these tissues following sTAB. (E) Under baseline conditions, GFP-LC3 Tg fusion protein is diffusely distributed throughout the cardiomyocyte cytoplasm in α-MHC–GFP–LC3 mice. Following short-term (48 hours) starvation, GFP-LC3 aggregates as autophagosome-localized GFP dots. Representative images from basal septum are shown. Scale bar: 35 μm. (F) Following sham operation, GFP-LC3 Tg fusion protein is diffusely distributed throughout the cardiomyocyte cytoplasm in α-MHC–GFP–LC3 mice. Following imposition of pressure stress by sTAB (48 hours), GFP-LC3 aggregates as autophagosome-localized GFP dots. Representative images from basal septum are shown. Scale bar: 35 μm. (G) Quantification of GFP aggregates per microscopic field (14,479 μm2) demonstrates significant autophagic activity induced by starvation. For each group, at least 4 mice were studied. ‡P < 0.01 versus fed. (H) Quantification of GFP aggregates per microscopic field (14,479 μm2) demonstrates significant autophagic activity induced by pressure overload. For each group, at least 4 mice were studied. †P < 0.01 versus sham. FW, free wall of LVs.