Too much or not enough of a good thing - The Janus faces of autophagy in cardiac fuel and protein homeostasis

Cells respond to changes in their environment and in their intracellular milieu by altering specific pathways of protein synthesis and degradation. Autophagy is a highly conserved catabolic process involved in the degradation of long-lived proteins, damaged organelles, and subcellular structures. The process is orchestrated by the autophagy related protein (Atg) to form the double-membrane structure autophagosomes, which then fuse with lysosomes to generate autophagolysosomes where subcellular contents are degraded for a variety of cellular processes. Alterations in autophagy play an important role in diseases including cancer, neurodegenerative diseases, aging, metabolic diseases, inflammation and cardiovascular diseases. In the latter, dysregulated autophagy is speculated to contribute to the onset and development of atherosclerosis, ischemia/reperfusion injury, cardiomyopathy, diabetes mellitus, and hypertension. Autophagy may be both adaptive and beneficial for cell survival, or maladaptive and detrimental for the cell. Basal autophagy plays an essential role in the maintenance of cellular homeostasis whereas excessive autophagy may lead to autophagic cell death. The point and counterpoint discussion highlights adaptive vs. maladaptive autophagy. In this review, we discuss the molecular control of autophagy, focusing particularly on the regulation of physiologic vs. defective autophagy.