Live imaging of reporter zebrafish reveals dynamics and molecular basis of physiological-stress induced mitophagy

Defects in mitophagy, the selective recycling of mitochondria through autophagy, are linked to aging, sarcopenia, and neurodegenerative diseases. To therapeutically target mitophagy, the dynamics and molecular mechanisms in vivo must be understood. Here, we describe newly generated mitophagy biosensor zebrafish, reveal widespread basal mitophagy during normal development, and illuminate the dynamics and molecular mechanisms of mitophagy induced by physiological stresses-fasting and hypoxia. In fasted muscle, volumetric quantification of mitolysosome size uncovered organelle stress-response dynamics, and live, time-lapse imaging revealed mitophagy occurred via a piecemeal rather than wholesale process. Activating Hypoxia-inducible factor through physiological hypoxia or chemical or genetic modulation also provoked mitophagy. Surprisingly, disruption of a single mitophagy receptor bnip3 mitigated the response. Disruption of bnip3la (nix) or fundc1, putative hypoxia-associated mitophagy receptors, or pink1 or prkn (Parkin) had no effect. This in vivo imaging study establishes fundamental dynamics of fasting-induced mitophagy and elucidates molecular mechanisms governing hypoxia-induced mitophagy.