Mitochondrial Inhibitor Models of Huntington’s Disease and Parkinson’s Disease Induce Zinc Accumulation and Are Attenuated by Inhibition of Zinc Neurotoxicity in vitro or in vivo

Abstract

Background: Inhibition of mitochondrial function occurs in many neurodegenerative diseases, and inhibitors of mitochondrial complexes I and II are used to model them. The complex II inhibitor, 3-nitroproprionic acid (3-NPA), kills the striatal neurons susceptible in Huntington’s disease. The complex I inhibitor N-methyl-4-phenylpyridium (MPP⁺) and 6-hydroxydopamine (6-OHDA) are used to model Parkinson’s disease. Zinc (Zn²⁺⁾ accumulates after 3-NPA, 6-OHDA and MPP⁺ in situ or in vivo. Objective: We will investigate the role of Zn²⁺ neurotoxicity in 3-NPA, 6-OHDA and MPP⁺. Methods: Murine striatal/midbrain tyrosine hydroxylase positive, or near-pure cortical neuronal cultures, or animals were exposed to 3-NPA or MPP⁺ and 6-OHDA with or without neuroprotective compounds. Intracellular zinc ([Zn²⁺]_i), nicotinamide adenine dinucleotide (NAD⁺), NADH, glycolytic intermediates and neurotoxicity were measured. Results: We showed that compounds or genetics which restore NAD⁺ and attenuate Zn²⁺ neurotoxicity (pyruvate, nicotinamide, NAD⁺, increased NAD⁺ synthesis, sirtuin inhibition or Zn²⁺ chelation) attenuated the neuronal death induced by these toxins. The increase in [Zn²⁺]_i preceded a reduction in the NAD⁺/NADH ratio that caused a reversible glycolytic inhibition. Pyruvate, nicotinamide and NAD⁺ reversed the reductions in the NAD⁺/NADH ratio, glycolysis and neuronal death after challenge with 3-NPA, 6-OHDA or MPP⁺, as was previously shown for exogenous Zn²⁺. To test efficacy in vivo, we injected 3-NPA into the striatum of rats and systemically into mice, with or without pyruvate. We observed early striatal Zn²⁺ fluorescence, and pyruvate significantly attenuated the 3-NPA-induced lesion and restored behavioral scores. Conclusions: Together, these studies suggest that Zn²⁺ accumulation caused by MPP⁺ and 3-NPA is a novel preventable mechanism of the resultant neurotoxicity.

Parkinson's disease-associated human ATP13A2 (PARK9) deficiency causes zinc dyshomeostasis and mitochondrial dysfunction

“…1B). Hydrogen peroxide (H 2 O 2 ), an ROS known to increase [Zn 2+ ] i by inducing the release of Zn 2+ from zinc-binding proteins (31), significantly reduced cell viability, to a greater extent in ATP13A2 −/− cells ( P < 0.01, Fig. 1C).…”

“…Since then, mitochondrial dysfunction has been recognized as a major contributor to the aetiology of sporadic (25, 26) and familial PD (27–30). A recent discovery that zinc accumulation contributes to and conversely, zinc chelation protects against MPTP-induced PD has highlighted a link between zinc and mitochondrial function in the pathogenesis of PD (31). …”

Perturbation of Transcription Factor Nur77 Expression Mediated by Myocyte Enhancer Factor 2D (MEF2D) Regulates Dopaminergic Neuron Loss in Response to 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

“…Because of the need for a more homogenous population of neurons, we utilized the MPP ϩ treatment paradigm in cultured cortical neurons. We and others (8,9,42,43) have shown that MPP ϩ can induce death in non-dopaminergic neurons, such as ceberebellar granule and cortical neurons, by non-dopamine transporter related mechanisms. Importantly, we observed that there was detectable MEF2D binding at the Nur77 promoter basally in neurons (Fig.…”

Targeting Mitochondrial Metal Dyshomeostasis for the Treatment of Neurodegeneration

“…Application of the iron chelator DFO induces Htt expression in vitro, suggesting a role for Htt in iron homeostasis [196]. The HD-associated mitochondrial toxin 3-nitropropionic acid causes zinc accumulation in vitro [197]. Whether these disruptions in metal homeostasis extend to mitochondria is yet to be confirmed.…”

“…Deficiency of ATP13A2 protein (otherwise known as PARK9, in which mutations are associated with PD) was recently shown to induce mitochondrial zinc accumulation and dysfunction [221], and PD-associated toxins cause zinc accumulation in vitro [197].…”