Late endosome-loaded dynein–snapin complexes drive amphisome retrograde transport upon fusion of autophagosomes with late endosomes in distal axons.

Autophagy, a cellular self-eating mechanism, is important for maintaining cell survival and tissue homeostasis in various stressed conditions. Although the molecular mechanism of autophagy induction has been well studied, how cells terminate autophagy process remains elusive. Here, we show that ULK1, a serine/threonine kinase critical for autophagy initiation, is a substrate of the Cul3-KLHL20 ubiquitin ligase. Upon autophagy induction, ULK1 autophosphorylation facilitates its recruitment to KLHL20 for ubiquitination and proteolysis. This autophagy-stimulated, KLHL20-dependent ULK1 degradation restrains the amplitude and duration of autophagy. Additionally, KLHL20 governs the degradation of ATG13, VPS34, Beclin-1, and ATG14 in prolonged starvation through a direct or indirect mechanism. Impairment of KLHL20-mediated regulation of autophagy dynamics potentiates starvation-induced cell death and aggravates diabetes-associated muscle atrophy. Our study identifies a key role of KLHL20 in autophagy termination by controlling autophagy-dependent turnover of ULK1 and VPS34 complex subunits and reveals the pathophysiological functions of this autophagy termination mechanism.

Chronic mitochondrial stress is a central problem associated with neurodegenerative diseases. Early removal of defective mitochondria from axons constitutes a critical step of mitochondrial quality control. Here we investigate axonal mitochondrial response to mild stress in wild-type neurons and chronic mitochondrial defects in Amytrophic Lateral Sclerosis (ALS)- and Alzheimer’s disease (AD)-linked neurons. We show that stressed mitochondria are removed from axons triggered by the bulk release of mitochondrial anchoring protein syntaphilin via a new class of mitochondria-derived cargos independent of Parkin, Drp1 and autophagy. Immuno-electron microscopy and super-resolution imaging show the budding of syntaphilin cargos, which then share a ride on late endosomes for transport toward the soma. Releasing syntaphilin is also activated in the early pathological stages of ALS- and AD-linked mutant neurons. Our study provides new mechanistic insights into the maintenance of axonal mitochondrial quality through SNPH-mediated coordination of mitochondrial stress and motility before activation of Parkin-mediated mitophagy.