Markers of autophagy are downregulated in failing human heart after mechanical unloading - PubMed (original) (raw)

Markers of autophagy are downregulated in failing human heart after mechanical unloading

Christos Kassiotis et al. Circulation. 2009.

Abstract

Background: Autophagy is a molecular process that breaks down damaged cellular organelles and yields amino acids for de novo protein synthesis or energy provision. Mechanical unloading with a left ventricular assist device (LVAD) decreases the energy demand of the failing human heart. We tested the hypothesis that LVAD support reverses activation of autophagy.

Methods and results: Paired biopsy samples of left ventricular myocardium were obtained from 9 patients with idiopathic dilated cardiomyopathy (mean duration of LVAD support, 214 days) at the time of implantation and explantation of the LVAD. Transcript and protein levels of markers and mediators of autophagy and apoptosis were measured by quantitative reverse-transcription polymerase chain reaction and Western blotting. TUNEL assays, C9 immunohistochemistry, and 20S proteasome activity assays were also performed. Mechanical unloading significantly decreased mRNA transcript levels of Beclin-1, autophagy-related gene 5 (Atg5), and microtubule-associated protein-1 light chain-3 (MAP1-LC3 or LC3; P<0.02). Protein levels of Beclin-1, Atg5-Atg12 conjugate, and LC3-II were also significantly reduced after LVAD support (P<0.05). A significant increase in 20S proteasome activity was observed with unloading, in parallel to the decrease in autophagic markers. Although BNIP3 and the ratio of activated caspase 3 to procaspase 3 increased after LVAD support, Bcl-2 and TUNEL-positive nuclei were not significantly different between samples.

Conclusions: Mechanical unloading of the failing human heart decreases markers of autophagy. These findings suggest that autophagy may be an adaptive mechanism in the failing heart, and this phenomenon is attenuated by LVAD support.

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Conflict of interest statement

Conflict of Interest Disclosures

O.H.F. has received an honorarium from Thoratec. The other authors have nothing to disclose.

Figures

Figure 1

Figure 1

Transcripts of autophagy markers and mediators before (implant) and after mechanical unloading (explant). a) Atg5 transcripts, b) Beclin 1 transcripts, c) LC3 transcripts. Atg5 indicates autophagy related gene 5 and LC3 indicates microtubule associated protein 1 light chain 3. Error bars represent standard error of the mean.

Figure 2

Figure 2

Fold change of mRNA transcripts of autophagy markers and mediators following mechanical unloading plotted as a function of the duration of LVAD support. a) Atg5 transcript (fold change), b) Beclin 1 transcript (fold change), c) LC3 transcript (fold change). Abbreviations are the same as those used in Figure 1.

Figure 3

Figure 3

Protein expression of autophagy markers and mediators in the heart before and after mechanical unloading. Representative western blots from two patients are depicted on the right. a) Atg5-Atg12 conjugate, b) Beclin 1, c) LC3-II, d) Gabarapl1. Gabarapl1 indicates gamma-amino butyric acid receptor-associated protein-like 1. GAPDH was used as a loading control. Other abbreviations are as in Figure 1. Error bars represent standard error of the mean.

Figure 4

Figure 4

Protein expression of BNIP3 in the heart before and after mechanical unloading. Representative western blots from two patients are depicted. GAPDH was used as a loading control. Error bars represent standard error of the mean.

Figure 5

Figure 5

20S proteasome activity in myocardial tissue before and after mechanical unloading. Error bars represent standard error of the mean.

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