Lysyl-tRNA Synthetase Is a Target for Mutant SOD1 Toxicity in Mitochondria

Hibiki Kawamata,Jordi Magrané,Catherine Kunst,Michael P King,Giovanni Manfredi

doi:10.1074/jbc.m805599200

Hibiki Kawamata, Jordi Magrané + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m805599200

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Abstract

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease affecting the motor neurons. The majority of familial forms of ALS are caused by mutations in the Cu,Zn-superoxide dismutase (SOD1). In mutant SOD1 spinal cord motor neurons, mitochondria develop abnormal morphology, bioenergetic defects, and degeneration. However, the mechanisms of mitochondrial toxicity are still unclear. One possibility is that mutant SOD1 establishes aberrant interactions with nuclear-encoded mitochondrial proteins, which can interfere with their normal trafficking from the cytosol to mitochondria. Lysyl-tRNA synthetase (KARS), an enzyme required for protein translation that was shown to interact with mutant SOD1 in yeast, is a good candidate as a target for interaction with mutant SOD1 at the mitochondrion in mammals because of its dual cytosolic and mitochondrial localization. Here, we show that in mammalian cells mutant SOD1 interacts preferentially with the mitochondrial form of KARS (mitoKARS). KARS-SOD1 interactions occur also in the mitochondria of the nervous system in transgenic mice. In the presence of mutant SOD1, mitoKARS displays a high propensity to misfold and aggregate prior to its import into mitochondria, becoming a target for proteasome degradation. Impaired mitoKARS import correlates with decreased mitochondrial protein synthesis. Ultimately, the abnormal interactions between mutant SOD1 and mitoKARS result in mitochondrial morphological abnormalities and cell toxicity. mitoKARS is the first described member of a group of mitochondrial proteins whose interaction with mutant SOD1 contributes to mitochondrial dysfunction in ALS.

Highlights

Amyotrophic lateral sclerosis (ALS)2 is a progressive neurodegenerative disorder of motor neurons that results in paralysis
Upon transient transfection in COS cells, mitoKARS is distributed to the mitochondria, as shown by co-localization of Myc immunostaining with the mitochondrial matrix protein MnSOD (Fig. 1B)
Cellular and transgenic mouse models of familial ALS expressing mutant SOD1 show mitochondrial degeneration resulting in loss of membrane potential, ATP production, and calcium handling [14]

Summary

Introduction

Amyotrophic lateral sclerosis (ALS)2 is a progressive neurodegenerative disorder of motor neurons that results in paralysis. KARS is a potential candidate for abnormal interactions with SOD1 affecting mitochondria, because it exists both as a cytosolic (cytoKARS) and as a mitochondrially imported (mitoKARS) enzyme. Mutant hSOD1-mitoKARS interactions result in the formation of high molecular weight protein aggregates that correlate with impaired mtDNA-encoded protein synthesis, mitochondrial morphological abnormalities, and decreased cell survival.

Results

Conclusion