Suppressing the dark side of autophagy

Abstract

A wide variety of genetic, pharmacological and nutrient manipulations that extend lifespan in model organisms do so in a manner dependent upon increased autophagic flux. However, our recent findings suggest that when mitochondrial membrane integrity is compromised, macroautophagy/autophagy can be detrimental. In C. elegans lacking the serine/threonine kinase mechanistic target of rapamycin kinase complex 2 and its downstream effector SGK-1 (Serum- and Glucocorticoid-inducible Kinase homolog), lifespan is shortened in spite of increased levels of autophagy, whereas reducing autophagy restores normal lifespan. This is due to a concomitant defect in mitochondrial permeability in mutants defective in either SGK-1 or mechanistic target of rapamycin kinase complex 2, attributable to increased VDAC-1 (VDAC Voltage Dependent Anion Channel homolog) protein level. More generally, we find that induction of mitochondrial permeability reverses each and every tested paradigm of autophagy-dependent lifespan extension and, further, exacerbates ischemia-reperfusion injury. In this punctum, we discuss our finding that autophagy with increased mitochondrial permeability is a detrimental combination conserved from nematode to mammals.