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Published on: July 13, 2018
Activation of Autophagic Flux Maintains Mitochondrial Homeostasis during Cardiac Ischemia/Reperfusion Injury
Lihao He1,2, Yuxin Chu1,3, Jing Yang1
1Department of Medicine, Division of Cardiovascular Disease, University of Alabama at Birmingham, Birmingham, AL 35233, USA.
Insights
Tat-Beclin 1 peptide enhances autophagic flux, protecting the heart from reperfusion injury by preserving mitochondrial homeostasis and promoting mitochondrial biogenesis.
Area of Science:
- Cardiovascular Biology
- Mitochondrial Medicine
- Autophagy Research
Background:
- Reperfusion injury significantly contributes to myocardial infarct size, lacking standard therapeutic interventions.
- Histone deacetylase (HDAC) inhibition shows promise by reducing infarct size and enhancing cardiomyocyte autophagy and PGC1α-mediated mitochondrial biogenesis.
- Tat-Beclin 1 (TB), an autophagy-inducing peptide, has demonstrated infarct-reducing effects, but its specific role in maintaining mitochondrial homeostasis during ischemia/reperfusion (I/R) injury requires clarification.
Purpose of the Study:
- To investigate whether augmenting autophagic flux with TB provides cardioprotection by preserving mitochondrial homeostasis in vitro and in vivo.
- To elucidate the role of autophagic flux in mitigating myocardial reperfusion injury.
- To determine if PGC1α-mediated mitochondrial biogenesis is involved in TB-induced cardioprotection.
Main Methods:
- Utilized wild-type mice subjected to myocardial I/R surgery, randomized to receive Tat-Scrambled (TS) peptide or TB.
- Assayed autophagic flux, mitochondrial DNA (mtDNA) content, mitochondrial morphology, and mitochondrial dynamic gene expression in cardiac tissue.
- Employed cultured neonatal rat ventricular myocytes (NRVMs) and isolated adult mouse ventricular myocytes (AMVMs), including ATG7 conditional cardiomyocyte-specific knockout (ATG7 cKO) mice, to assess cardiomyocyte-specific effects and autophagy dependency.
Main Results:
- In NRVMs, TB treatment increased autophagic flux, mtDNA content, and mitochondrial function, while reducing reactive oxygen species (ROS) and mtDNA damage following simulated I/R.
- In the infarct border zone of mouse hearts, TB induced autophagy, enlarged mitochondria, increased mtDNA content, and upregulated PGC1α and mitochondrial dynamic genes.
- Ablation of ATG7 in adult cardiomyocytes abolished the protective effects of TB on mitochondrial homeostasis, underscoring the essential role of autophagy.
Conclusions:
- Augmented autophagic flux via TB confers cardioprotection against myocardial reperfusion injury.
- Maintaining mitochondrial homeostasis is a key mechanism by which TB exerts its protective effects.
- TB partially induces PGC1α-mediated mitochondrial biogenesis, contributing to its cardioprotective role.
Abstract:
Reperfusion injury after extended ischemia accounts for approximately 50% of myocardial infarct size, and there is no standard therapy. HDAC inhibition reduces infarct size and enhances cardiomyocyte autophagy and PGC1α-mediated mitochondrial biogenesis when administered at the time of reperfusion. Furthermore, a specific autophagy-inducing peptide, Tat-Beclin 1 (TB), reduces infarct size when administered at the time of reperfusion. However, since SAHA affects multiple pathways in addition to inducing autophagy, whether autophagic flux induced by TB maintains mitochondrial homeostasis during ischemia/reperfusion (I/R) injury is unknown. We tested whether the augmentation of autophagic flux by TB has cardioprotection by preserving mitochondrial homeostasis both in vitro and in vivo. Wild-type mice were randomized into two groups: Tat-Scrambled (TS) peptide as the control and TB as the experimental group. Mice were subjected to I/R surgery (45 min coronary ligation, 24 h reperfusion). Autophagic flux, mitochondrial DNA (mtDNA), mitochondrial morphology, and mitochondrial dynamic genes were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were treated with a simulated I/R injury to verify cardiomyocyte specificity. The essential autophagy gene, ATG7, conditional cardiomyocyte-specific knockout (ATG7 cKO) mice, and isolated adult mouse ventricular myocytes (AMVMs) were used to evaluate the dependency of autophagy in adult cardiomyocytes. In NRVMs subjected to I/R, TB increased autophagic flux, mtDNA content, mitochondrial function, reduced reactive oxygen species (ROS), and mtDNA damage. Similarly, in the infarct border zone of the mouse heart, TB induced autophagy, increased mitochondrial size and mtDNA content, and promoted the expression of PGC1α and mitochondrial dynamic genes. Conversely, loss of ATG7 in AMVMs and in the myocardium of ATG7 cKO mice abolished the beneficial effects of TB on mitochondrial homeostasis. Thus, autophagic flux is a sufficient and essential process to mitigate myocardial reperfusion injury by maintaining mitochondrial homeostasis and partly by inducing PGC1α-mediated mitochondrial biogenesis.
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