Proteasome Impairment Induces Recovery of Mitochondrial Membrane Potential and an Alternative Pathway of Mitochondrial Fusion

Abstract

Mitochondria are vital and highly dynamic organelles that continuously fuse and divide to maintain mitochondrial quality. Mitochondrial dysfunction impairs cellular integrity and is known to be associated with various human diseases. However, the mechanism by which the quality of mitochondria is maintained remains largely unexplored. Here we show that impaired proteasome function recovers the growth of yeast cells lacking Fzo1, a pivotal protein for mitochondrial fusion. Decreased proteasome activity increased the mitochondrial oxidoreductase protein Mia40 and the ratio of the short isoform of mitochondrial intermembrane protein Mgm1 (s-Mgm1) to the long isoform (l-Mgm1). The increase in Mia40 restored mitochondrial membrane potential, while the increase in the s-Mgm1/l-Mgm1 ratio promoted mitochondrial fusion in an Fzo1-independent manner. Our findings demonstrate a new pathway for mitochondrial quality control that is induced by proteasome impairment.

ACKNOWLEDGMENTS

We thank C. Boone (University of Toronto), K. Okamoto (Osaka University), and Y. Ohya (University of Tokyo) for providing the p4339 plasmid and Y8205 yeast strain, the mt-GFP and mt-mCherry constructs, and the pYO325 and pYO326 plasmids, respectively, and Y. Sakurai for critical reading.

This work was supported by grants from the Ministry of Education, Science and Culture of Japan to S.M.