Loss of neuronal Miro1 disrupts mitophagy and induces hyperactivation of the integrated stress response.

Josef T Kittler,Corinne Morfill,Jigna V Patel,Roland Bürli,Jack H Howden,Nicholas J Brandon,Guillermo López‐Doménech,Christian Covill‐Cooke,Nicol Birsa,Damian Crowther

doi:10.15252/embj.2018100715

Abstract

Clearance of mitochondria following damage is critical for neuronal homeostasis. Here, we investigate the role of Miro proteins in mitochondrial turnover by the PINK1/Parkin mitochondrial quality control system in vitro and in vivo. We find that upon mitochondrial damage, Miro is promiscuously ubiquitinated on multiple lysine residues. Genetic deletion of Miro or block of Miro1 ubiquitination and subsequent degradation lead to delayed translocation of the E3 ubiquitin ligase Parkin onto damaged mitochondria and reduced mitochondrial clearance in both fibroblasts and cultured neurons. Disrupted mitophagy in vivo, upon post‐natal knockout of Miro1 in hippocampus and cortex, leads to a dramatic increase in mitofusin levels, the appearance of enlarged and hyperfused mitochondria and hyperactivation of the integrated stress response (ISR). Altogether, our results provide new insights into the central role of Miro1 in the regulation of mitochondrial homeostasis and further implicate Miro1 dysfunction in the pathogenesis of human neurodegenerative disease.

Highlights

Mitochondria are double-membraned organelles essential for a wide range of metabolic processes
While it is well established that Miro proteins are rapidly ubiquitinated by Parkin upon mitochondrial damage (Liu et al, 2012; Birsa et al, 2014), reciprocally, how important Miro ubiquitination may be for the mitophagic process remains less clear
We previously reported that Miro itself might act as a stabiliser of mitochondrial Parkin, acting in the first steps of Parkin-dependent mitophagy (Birsa et al, 2014)

Summary

Introduction

Mitochondria are double-membraned organelles essential for a wide range of metabolic processes. PINK1, normally imported into the mitochondrion and cleaved at the inner mitochondrial membrane (IMM), selectively accumulates in its full-length form on the outer mitochondrial membrane (OMM) of damaged mitochondria, where it phosphorylates the serine 65 (S65) residue of ubiquitin, as well as a conserved residue in the ubiquitin-like domain of Parkin This leads to the recruitment and activation of Parkin from the cytosol to the mitochondria to ubiquitinate various OMM substrates (Vives-Bauza et al, 2010; Deas et al, 2011; Cai et al, 2012; Exner et al, 2012; Sarraf et al, 2013; Lazarou et al, 2015). Loss-of-function mutations in PINK1 and Parkin are associated with rare recessive forms of Parkinson’s disease (PD) (Thomas & Beal, 2007) supporting an important role for mitophagy in neuronal survival and a link between its dysregulation and neurodegenerative diseases

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Results

Conclusion