Autophagy is a major mechanism of degradation of damaged mitochondria. Without elimination of damagedmitochondria, depolarized mitochondria and reactive oxygen species (ROS) rapidly affect healthymitochondria, leading to wide-spread mitochondrial dysfunction and cell death. Understanding how damagedmitochondria are removed will provide a key to achieving healthier mitochondria in cardiomyocytes (CMs) anddeveloping novel treatments for heart failure. Although it is believed that damaged mitochondria are degradedprimarily by Pink1-Parkin-mediated mitophagy, we have discovered that CMs degrade mitochondria through anAtg7-independent and Ulk1-dependent form of autophagy that is homologous to the “alternative” autophagypreviously reported by Nishida, and that this form of autophagy plays a significant role in the elimination ofdamaged mitochondria in response to starvation. However, neither the molecular mechanism nor the functionalsignificance of mitophagy mediated through alternative autophagy has been clearly established in CMs yet.Thus, the goal of this project is to demonstrate the functional significance of alternative autophagy ineliminating damaged mitochondria in the heart in response to relevant stresses and to elucidate the underlyingmolecular mechanisms. Hypothesis 1: In response to myocardial ischemia, the heart activates Atg7-independent/Ulk1-dependent alternative autophagy, which plays an essential role in mediating the clearance ofdamaged mitochondria and protects the heart from myocardial ischemia. Hypothesis 2: Ulk1 phosphorylatedat Ser555 acts as a scaffold to induce Rab9 interaction for autophagosome formation and phosphorylation ofDrp1 at Ser616 for mitochondrial fission, both of which are important in mediating mitochondrial autophagy inresponse to myocardial ischemia. We will: Aim 1: Demonstrate that the atg7-independent and ulk1-dependentalternative autophagy is activated by myocardial ischemia. Evaluate whether alternative autophagy protectsthe heart during myocardial ischemia. To this end, we will use cardiac-specific atg7- and ulk1-knockout mice,electron microscopy, specific reporters of alternative autophagy and mitochondrial autophagy, and functionalanalyses of mitochondria. We will show that damaged mitochondria are degraded primarily through alternativeautophagy during myocardial ischemia. Aim 2: Evaluate whether phosphorylation of Ulk1 at Ser555 plays anessential role in mediating alternative autophagy and cardioprotection during myocardial ischemia bystimulating interaction with Rab9 and Ser616-phosphorylated Drp1. To this end, we will use loss-of-functionand knock-in mouse models and unique and reliable reporters for alternative autophagy and lysosomaldegradation of mitochondria. The knowledge obtained from this aim should lead to development of specificinterventions to modulate mitophagy during myocardial ischemia. In summary, our study will demonstrate thatalternative autophagy is a novel and predominant mechanism of mitochondrial degradation, which is essentialfor the maintenance of mitochondrial quality in the heart during ischemia.
|Effective start/end date||8/15/17 → 5/31/21|
- National Institutes of Health (NIH)
Reactive Oxygen Species