Aconitase Causes Iron Toxicity in Drosophila pink1 Mutants

Giovanni Esposito,Sven Vilain,Stefanie Van Meensel,Jorge De Sousa Valadas,Jef Swerts,Patrik Verstreken,Melissa Vos,Onno Schaap

doi:10.1371/journal.pgen.1003478

Abstract

The PTEN-induced kinase 1 (PINK1) is a mitochondrial kinase, and pink1 mutations cause early onset Parkinson's disease (PD) in humans. Loss of pink1 in Drosophila leads to defects in mitochondrial function, and genetic data suggest that another PD-related gene product, Parkin, acts with pink1 to regulate the clearance of dysfunctional mitochondria (mitophagy). Consequently, pink1 mutants show an accumulation of morphologically abnormal mitochondria, but it is unclear if other factors are involved in pink1 function in vivo and contribute to the mitochondrial morphological defects seen in specific cell types in pink1 mutants. To explore the molecular mechanisms of pink1 function, we performed a genetic modifier screen in Drosophila and identified aconitase (acon) as a dominant suppressor of pink1. Acon localizes to mitochondria and harbors a labile iron-sulfur [4Fe-4S] cluster that can scavenge superoxide to release hydrogen peroxide and iron that combine to produce hydroxyl radicals. Using Acon enzymatic mutants, and expression of mitoferritin that scavenges free iron, we show that [4Fe-4S] cluster inactivation, as a result of increased superoxide in pink1 mutants, results in oxidative stress and mitochondrial swelling. We show that [4Fe-4S] inactivation acts downstream of pink1 in a pathway that affects mitochondrial morphology, but acts independently of parkin. Thus our data indicate that superoxide-dependent [4Fe-4S] inactivation defines a potential pathogenic cascade that acts independent of mitophagy and links iron toxicity to mitochondrial failure in a PD–relevant model.

Highlights

Parkinson’s disease (PD) is the most frequent neurodegenerative movement disorder, but the pathways that explain disease pathology remain poorly understood [1,2]
Acon harbors an iron-sulfur [4Fe-4S] cluster [23] and we show that oxidative inactivation of this cluster in pink1 mutants is a major cause of iron toxicity that contributes to mitochondrial swelling and clumping in pink1 mutants
Iron accumulation in the substantia nigra, systemic mitochondrial dysfunction and oxidative stress have all been implicated in PD pathology; a link between these factors remains elusive

Summary

Introduction

Parkinson’s disease (PD) is the most frequent neurodegenerative movement disorder, but the pathways that explain disease pathology remain poorly understood [1,2]. While the most recognized pathological feature of PD is the preferential loss of dopaminergic (DA) neurons, one of the earliest observations in post mortem PD brains was the accumulation of iron in the substantia nigra (SN) [3,4]. Iron-mediated toxicity may contribute to DA neuron dysfunction but the mechanism has not been established. Mitochondrial toxins have been linked to sporadic forms of the disease and mitochondrial defects have been described in many cell types, in SN mitochondria of PD patients [5,6]. Likewise some of the genetic factors linked to the disease point to a role for mitochondria. PD-associated mutations in pink and parkin, both affect mitochondrial function in genetic model organisms and in mammalian cells [7,8], but how mitochondrial dysfunction and iron toxicity are linked remains elusive

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