Role of Cytochrome c as a Stimulator of α-Synuclein Aggregation in Lewy Body Disease

Makoto Hashimoto,Ayako Takeda,Leigh J Hsu,Takato Takenouchi,Eliezer Masliah

doi:10.1074/jbc.274.41.28849

Abstract

alpha-Synuclein is a major component of aggregates forming amyloid-like fibrils in diseases with Lewy bodies and other neurodegenerative disorders, yet the mechanism by which alpha-synuclein is intracellularly aggregated during neurodegeneration is poorly understood. Recent studies suggest that oxidative stress reactions might contribute to abnormal aggregation of this molecule. In this context, the main objective of the present study was to determine the potential role of the heme protein cytochrome c in alpha-synuclein aggregation. When recombinant alpha-synuclein was coincubated with cytochrome c/hydrogen peroxide, alpha-synuclein was concomitantly induced to be aggregated. This process was blocked by antioxidant agents such as N-acetyl-L-cysteine. Hemin/hydrogen peroxide similarly induced aggregation of alpha-synuclein, and both cytochrome c/hydrogen peroxide- and hemin/hydrogen peroxide-induced aggregation of alpha-synuclein was partially inhibited by treatment with iron chelator deferoxisamine. This indicates that iron-catalyzed oxidative reaction mediated by cytochrome c/hydrogen peroxide might be critically involved in promoting alpha-synuclein aggregation. Furthermore, double labeling studies for cytochrome c/alpha-synuclein showed that they were colocalized in Lewy bodies of patients with Parkinson's disease. Taken together, these results suggest that cytochrome c, a well known electron transfer, and mediator of apoptotic cell death may be involved in the oxidative stress-induced aggregation of alpha-synuclein in Parkinson's disease and related disorders.

Highlights

Taken together, these results suggest that cytochrome c, a well known electron transfer, and mediator of apoptotic cell death may be involved in the oxidative stressinduced aggregation of ␣-synuclein in Parkinson’s disease and related disorders
The abbreviations used are: PD, Parkinsons’s disease; LB, Lewy bodies; LBD, Lewy body disease; A␤, amyloid ␤-protein; DLBD, diffuse nerve cell loss and presence of neuronal inclusion bodies and dystrophic neurites in the substantia nigra and various other regions in the brain [2], the synaptic protein ␣-synuclein was found to abnormally accumulate in LBs [3,4,5,6]. ␣-Synuclein is a major constitute of LBs in PD and related disorders, whereby as a whole molecule was shown to be aggregated to form amyloid-like fibrils [7,8,9]
Cytochrome c Is Aggregated in the Presence of H2O2—Since the main objective of the present study was to determine whether the heme-containing protein cytochrome c promoted aggregation of ␣-synuclein under oxidative stress conditions, we first determined whether the structure of cytochrome c was affected by oxidation

Summary

Introduction

These results suggest that cytochrome c, a well known electron transfer, and mediator of apoptotic cell death may be involved in the oxidative stressinduced aggregation of ␣-synuclein in Parkinson’s disease and related disorders. Recombinant ␣-synuclein is induced to form amyloid-like fibrils under certain conditions, such as long time lag and high temperature, providing a model system that ␣-synuclein by its full-length molecule acts as an amyloidogenic protein [11] In this respect, it was recently reported that the mutant ␣-synucleins (A53T and A30P) associated with rare form of familial PD tend to be more aggregated than wild type ␣-synuclein [12, 13]. We have shown that ␣-synuclein was significantly aggregated by the iron-catalyzed oxidative reaction in vitro [20] These aggregates displayed Thioflavine-S/Congo redpositive filamentous structures, reminiscent of amyloid-like fibrils found in LBs of PD brain [20]. Iron is known to exist abundantly in the substantia nigra and its increase in the PD brain has been consistently reported [22]

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Conclusion