Activation of Nox4 in the Endoplasmic Reticulum Promotes Cardiomyocyte Autophagy and Survival During Energy Stress Through the PERK/eIF-2α/ATF4 Pathway
Rationale: Autophagy is an essential survival mechanism during energy stress in the heart. Oxidative stress is activated by energy stress, but its role in mediating autophagy is poorly understood. Nox4 is an enzyme that generates reactive oxygen species (ROS) at intracellular membranes. Whether Nox4 acts as a sensor of energy stress to mediate activation of autophagy is unknown.
Objective: We investigated whether Nox4 is involved in the regulation of autophagy and cell survival during energy stress in cardiomyocytes (CMs).
Methods and Results: Production of ROS in CMs was increased during glucose deprivation (GD) in a Nox4-dependent manner. Protein levels and the ROS-producing activity of Nox4 were increased in the endoplasmic reticulum (ER), but not in mitochondria, in response to GD. Selective knockdown of Nox4, but not Nox2, or selective reduction of ROS in the ER with ER-targeted catalase, but not mitochondria-targeted perioxiredoxin3, abrogated GD-induced autophagy. Nox4 promoted autophagy during GD through activation of the PKR-like ER kinase (PERK) pathway by suppression of prolyl hydroxylase4 (PHD4). The decrease in cell survival during GD in the presence of Nox4 knockdown was rescued by reactivation of autophagy by Atg7 overexpression, indicating that the effect of Nox4 upon cell survival is critically mediated through regulation of autophagy. Nox4 was activated during fasting and prolonged ischemia in the mouse heart, where Nox4 is also required for autophagy activation and cardioprotection.
Conclusions: Nox4 critically mediates autophagy in response to energy stress in CMs by eliciting ROS in the ER and stimulating the PERK signaling pathway.
- Received May 13, 2013.
- Revision received September 9, 2013.
- Accepted September 30, 2013.