α-Synuclein Enhances Cadmium Uptake and Neurotoxicity via Oxidative Stress and Caspase Activated Cell Death Mechanisms in a Dopaminergic Cell Model of Parkinson’s Disease
This study examined the role of alpha-synuclein in regulating cadmium (Cd)-induced neurotoxicity using the N27 dopaminergic neuronal model of Parkinson’s disease (PD) that stably expresses wild-type human α-synuclein (α-Syn) or empty vector (Vec) control. We report that α-Syn significantly increased Cd-induced cytotoxicity as compared to Vec control cells upon 24 h exposure. To explore the cellular mechanisms, we examined oxidative stress, caspase activation, and Cd uptake and intracellular accumulation. Expression of α-Syn coupled with Cd-induced cytotoxicity increased oxidative stress. Inductively coupled plasma-mass spectrometry (ICP-MS) revealed an increase in Cd uptake and intracellular accumulation in α-Syn-expressing cells upon Cd exposure. Analysis of the mitochondrial mediated apoptotic pathway showed greater activation of caspase-9 and caspase-3 in α-Syn cells. To functionally evaluate the role of metal transporters in the altered Cd phenotype, we examined Cd toxicity in the presence of nontoxic levels of divalent manganese Mn(II) and iron Fe(II). Co-treatment with Fe(II) or Mn(II) did not significantly attenuate Cd-induced cytotoxicity. We report that Cd exposure decreased the divalent metal transporter 1 and Akt protein levels in the α-Syn-expressing cells without altering native PKCδ protein levels in both Vec control and α-Syn lines. In addition, we show decreased basal metallothionein-3 protein expression in α-Syn-expressing cells. Co-treatment with N-acetyl-l-cysteine was sufficient to attenuate and abolish the α-Syn × Cd-induced cytotoxicity. Collectively, these results demonstrate that α-Syn exhibits neurotoxic properties upon acute Cd exposure to cause cell death by causing oxidative stress, increasing Cd uptake, altering caspase-9 and caspase-3 activation, and diminishing the neuroprotective effect of Akt in a dopaminergic neuronal model of PD.
Keywordsα-Synuclein Cadmium Parkinson’s disease Oxidative stress Caspase Antioxidants Metal transport Neurotoxicity
This research was supported in part by Oberlin College Office of Foundation, Government and Corporate Grants (GFK), Robert Rich Research Grant at Oberlin College and Nu Rho Psi (WC), and support from the National Science Foundation and Gordon and Betty Moore Foundation (MAS). We are grateful to Edmund Mawuli Korley (Oberlin College) for his technical support.
GFK conceived the research idea, designed the experiments, coordinated the study, and wrote the paper. WC, JJ, MM, and MAS provided language help and proof read the article. GFK, WC, and JJ performed the experiments and analyzed the results shown in Figs. 1, 2, 3, 4, 5, 6, 7, 8, and 9. MM and MAS performed the ICP-MS experiments shown in Fig. 5.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflicts of interest with the contents of this article.
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