Oral N-Acetyl-Cysteine Attenuates Loss of Dopaminergic Terminals in α-Synuclein Overexpressing Mice

Joanne Clark,Anthony Adame,Elizabeth L. Clore,Eliezer Masliah,David K. Simon,Kangni Zheng,Mark R. Cookson

doi:10.1371/journal.pone.0012333

Joanne Clark, Anthony Adame + Show 5 more

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https://doi.org/10.1371/journal.pone.0012333

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Abstract

Levels of glutathione are lower in the substantia nigra (SN) early in Parkinson's disease (PD) and this may contribute to mitochondrial dysfunction and oxidative stress. Oxidative stress may increase the accumulation of toxic forms of α-synuclein (SNCA). We hypothesized that supplementation with n-acetylcysteine (NAC), a source of cysteine – the limiting amino acid in glutathione synthesis, would protect against α-synuclein toxicity. Transgenic mice overexpressing wild-type human α-synuclein drank water supplemented with NAC or control water supplemented with alanine from ages 6 weeks to 1 year. NAC increased SN levels of glutathione within 5–7 weeks of treatment; however, this increase was not sustained at 1 year. Despite the transient nature of the impact of NAC on brain glutathione, the loss of dopaminergic terminals at 1 year associated with SNCA overexpression was significantly attenuated by NAC supplementation, as measured by immunoreactivity for tyrosine hydroxylase in the striatum (p = 0.007; unpaired, two-tailed t-test), with a similar but nonsignificant trend for dopamine transporter (DAT) immunoreactivity. NAC significantly decreased the levels of human SNCA in the brains of PDGFb-SNCA transgenic mice compared to alanine treated transgenics. This was associated with a decrease in nuclear NFκB localization and an increase in cytoplasmic localization of NFκB in the NAC-treated transgenics. Overall, these results indicate that oral NAC supplementation decreases SNCA levels in brain and partially protects against loss of dopaminergic terminals associated with overexpression of α-synuclein in this model.

Highlights

Parkinson’s disease (PD) is a progressive neurodegenerative disorder involving loss of specific subsets of neurons, including dopaminergic neurons of the substantia nigra (SN)
Transgenic mice overexpressing SNCA showed a mean decrease of 45.2% in the percentage of striatal area covered by tyrosine hydroxylase positive (TH+) terminals compared to wild-type littermate controls at 1 year of age (Fig. 1A, 1C,1E)
Similar to the findings for TH+ terminals, the percentage of striatal area covered dopamine transporter (DAT)+ terminals was reduced by 43.2% in SNCA overexpressing mice compared to littermate controls (Fig. 1F)

Summary

Introduction

Parkinson’s disease (PD) is a progressive neurodegenerative disorder involving loss of specific subsets of neurons, including dopaminergic neurons of the substantia nigra (SN). Complex I impairment leads to an increase in the generation of reactive oxygen species (oxidative stress) [6,7,8], consistent with reports of elevated markers of oxidative damage to lipids, proteins, and DNA in the SN in PD [9]. This problem is compounded by the fact that levels of glutathione, the predominant intracellular thiol antioxidant, are severely deficient in the SN at very early stages of PD [10,11]. Increased oxidative stress due to early glutathione deficiency in the SN may lead to enhanced toxicity of SNCA in dopaminergic SN neurons, suggesting that strategies to increase glutathione or to block oxidative stress by other means may protect against SNCA toxicity

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