Abstract 13433: Enhancing Autophagic Flux Maintains Mitochondrial Homeostasis in Cardiac Ischemia/Reperfusion Injury

Abstract

Introduction and Hypothesis: Histone deacetylase (HDAC) inhibition enhances cardiomyocyte autophagic activity, mitochondria biogenesis, and blunts ischemia/reperfusion (I/R) injury when given at the time of reperfusion. Similarly, augmentation of autophagic flux using a specific autophagy-inducing peptide, Tat-Beclin (TB), is cardioprotective by reducing infarct ~50% and improved systolic function. TB increases autophagic flux and reduced reactive oxygen species (ROS) in the infarct border zone, which is abolished in ATG7 KO mice. We will test whether TB cleans damaged mitochondria and induces mitochondrial biogenesis during cardiac I/R injury. Methods: 8-12-week-old, wild-type, C57BL6 mice were randomized into two groups: TB and Tat-Scrambled (TS) control peptide. Each group was subjected to I/R surgery (45min ischemia, 24h reperfusion). Mitochondrial abundance, quality, and dynamics were assayed. In addition, cultured adult mouse ventricular myocytes (AMVMs) from conditional cardiomyocyte ATG7 knockout (ATG7 KO) and control mice, and neonatal rat ventricular myocytes (NRVMs) treated with ATG7 and control siRNA were used to evaluate the role of autophagy. Results: TB increased mitochondria DNA (mtDNA) content in the border zone significantly. In NRVMs subjected to I/R, TB reduced cell death by ~40%, decreased ROS, and increased mtDNA content significantly by ~50%. TB also increased the intact mtDNA significantly. Moreover, TB promoted the expression of PGC1α (a major driver of mitochondrial biogenesis) both in the infarct border zone and NRVMs subjected to I/R by ~40%, and increased levels of mitochondrial dynamics gene transcripts Drp1, Fis1, and MFN1 / 2. Conversely, ATG7 knockdown in NRVMs and cardiomyocyte-specific ATG7 KO in myocardium abolished the beneficial effects of TB on mtDNA content. To test the changes in the myocardium are cardiomyocyte-specific, we verified the effects of TB and the loss of ATG7 in isolated AMVMs. Conclusions: Autophagic flux is an essential process to mitigate myocardial reperfusion injury acting, at least in part, by inducing PGC1α-mediated mitochondrial biogenesis. Augmentation of autophagic flux may emerge as a viable clinical therapy to reduce I/R injury in myocardial infarction.