Defending the mitochondria: The pathways of mitophagy and mitochondrial-derived vesicles.

Mitochondria are the powerhouses for the cell, consuming oxygen to generate sufficient energy for the maintenance of normal cellular processes. However, a deleterious consequence of this process are reactive oxygen species generated as side-products of these reactions. As a means to protect mitochondria from damage, cells and mitochondria have developed a wide-range of mitochondrial quality control mechanisms that remove damaged mitochondrial cargo, enabling the mitochondria to repair the damage and ultimately restore their normal function. If the damage is extensive and mitochondria can no longer be repaired, a process termed mitophagy is initiated in which the mitochondria are directed for autophagic clearance. Canonical mitophagy is regulated by two proteins, PINK1 and Parkin, which are mutated in familial forms of Parkinson's disease. In this review, we discuss recent work elucidating the mechanism of PINK1/Parkin-mediated mitophagy, along with recently uncovered PINK1/Parkin-independent mitophagy pathways. Moreover, we describe a novel mitochondrial quality control pathway, involving mitochondrial-derived vesicles that direct distinct and damaged mitochondrial cargo for degradation in the lysosome. Finally, we discuss the association between mitochondrial quality control, cardiac, hepatic and neurodegenerative disease and discuss the possibility of targeting these pathways for therapeutic purposes.