Figure 2.

Mitochondrial quality control pathways. Mechanisms governing mitochondrial turnover can be subdivided into six major pathways (see Box 1 for further detail). Representative cellular cues that stimulate each pathway are at the top and examples of the process and the proteins required for each pathway are listed at the bottom. Pathways 1–5 ultimately result in the mitochondrion engulfed in an autophagosome membrane (green) that will fuse with the lysosome, destroying the organelle. The source of this membrane differs depending on the pathway (pathways 3 and 4) and in some instances has not yet been identified (pathways 1 and 2). Mitochondria are also turned over by non-selective autophagy (pathway 5). Mitochondrial derived vesicles turn over small portions of the mitochondrion (Sugiura et al. 2014) by transporting them to the lysosome, arguably distinct from mitophagy because autophagosomes are not involved (pathway 6). RAB9-dependent alternative/non-canonical mitophagy involves autophagosomes but not ATG5 or 7 (Arakawa et al. 2017). Figure created with BioRender.