Homeostatic mitophagy scales mitochondrial networks

Cells scale organelle sizes to ensure physiological function. Here, we uncover a dual role for autophagy in controlling mitochondrial network size with a key function for homeostatic mitophagy. During starvation, non-selective autophagy sustains mitochondrial biogenesis in non-dividing yeast cells resulting in mitochondrial network expansion. Strikingly, Atg32/Bcl2L13-mediated mitophagy scales mitochondria back to pre-starvation size. Without mitophagy, mitochondria size increases two-fold while retaining wildtype-like structural, compositional, and metabolic features. In turn, synthetically elevated mitophagy only mildly reduces mitochondria size, suggesting cells maintain a minimal network size by compensatory biogenesis. Single-cell analysis predicts two metabolically tunable setpoints, mitochondria-to-cell and mitochondria-to-cytosol volume ratios, for mitochondria scaling by autophagy-driven biogenesis and degradation, respectively. Our work reveals how cells use autophagy to scale mitochondria to metabolic and cellular size parameters. One Sentence SummaryA homeostatic form of mitophagy controls the network size of mitochondria during starvation.