Paraquat-induced intracellular Zn2+ dysregulation causes dopaminergic degeneration in the substantia nigra, but not in the striatum

Abstract

Parkinson's disease is characterized by a selective death of nigrostriatal dopaminergic neurons, while the difference in the vulnerability to the death between the substantia nigra pars compacta (SNpc) and the striatum is poorly understood. Here we tested the difference focused on paraquat (PQ)-induced intracellular Zn²⁺ toxicity via extracellular glutamate accumulation. When PQ was locally injected into the SNpc and the striatum, dopaminergic degeneration was observed in the SNpc, but not in the striatum. Intracellular hydrogen peroxide (H₂O₂) produced by PQ was increased in both the SNpc and the striatum. In contrast, extracellular glutamate accumulation was observed only in the SNpc and rescued in the presence of N-(p-amylcinnamoyl)anthranilic acid (ACA), a blocker of the transient receptor potential melastatin 2 (TRPM2) cation channels. PQ increased intracellular Zn²⁺ level in the SNpc, but not in the striatum. The increase was rescued by 1-naphthyl acetyl spermine (NASPM), a selective blocker of Ca²⁺- and Zn²⁺-permeable GluR2-lacking AMPA receptors. PQ-induced dopaminergic degeneration in the SNpc was rescued by ACA, NASPM, and GBR, a dopamine reuptake inhibitor. The present study indicates intracellular H₂O₂ produced by PQ, which is taken up through dopamine transporters, is retrogradely transported to presynaptic glutamatergic terminals, activates TRPM2 channels, accumulates glutamate in the extracellular compartment, and induces intracellular Zn²⁺ dysregulation via Ca²⁺- and Zn²⁺-permeable GluR2-lacking AMPA receptor activation, resulting in dopaminergic degeneration in the SNpc. However, H₂O₂ signaling is not the case in the striatum. Paraquat-induced Zn²⁺ dysregulation plays a key role for neurodegeneration in the SNpc, but not in the striatum.

Keywords: Dopaminergic neuron; Hydrogen peroxide; Striatum, paraquat; Substantia nigra; TRPM2 cation channel; Zn(2+).