Functional role of Nox4 in autophagy

Accumulating lines of evidence suggest that reactive oxygen species (ROS) may act as intracellular signaling molecules under cellular stress conditions, activating several molecular pathways. Autophagy, the intracellular mechanism by which cells digest and recycle unfolded proteins and dysfunctional organelles, is emerging as a major target of ROS and NADPH oxidase (Nox) enzymes, the major generators of ROS. While autophagy represents an important self-defense mechanism in promoting cell survival, it may be maladaptive in some conditions. In particular, in the cardiovascular system, moderate activation of autophagy has been shown to be protective, while excessive or insufficient activation of autophagy may be deleterious. Thus, modulating ROS-dependent autophagy may represent a novel strategy to keep autophagy within the therapeutic range. Among the Nox isoforms, Nox4 in particular plays a pivotal role in autophagy regulation. This appears to be due to its intracellular localization and its ability to produce hydrogen peroxide, a stable signaling molecule. In this chapter we review the studies relating to the functional role of Nox4 in autophagy, with particular emphasis on the heart and cardiovascular system.