Mechanisms of cyanide neurotoxicity: A role for mitochondrial uncoupling protein 2
Abstract
In the central nervous system (CNS), cyanide produces apoptosis in cortical neurons and necrosis in nigral dopaminergic neurons both in vivo and in vitro. The pathways mediating the modes of cell death involve alterations in mitochondrial function and regulation of oxidative metabolism. Mitochondrial Uncoupling Protein 2 (UCP-2) is an inner mitochondrial membrane proton transporter that regulates mitochondrial function by uncoupling oxidative phosphorylation. The purpose of the present study was to explore the involvement of UCP-2 in cyanide-induced cell death in an immortalized mesencephalic cell line (N27 cell line). The selective Peroxisome Proliferator Activated Receptor α (PPARα) ligand, Wy14,643 (4-chloro-6-(2,3-xylidino)2-pyrimidinylthioacetic acid), significantly increases UCP2 expression in neuronal cells in vitro. Therefore, Wy14,643 was used as a tool to up-regulate UCP-2 for subsequent examination of mechanisms of cyanide-induced cell death. In N27 cells, Wy14,643 induces up-regulation of UCP-2 and potentiated cyanide-induced necrotic cell death by enhancing mitochondrial dysfunction, which was reflected by a marked decrease in mitochondrial membrane potential and cellular ATP. MK886 (a PPARα antagonist) or PPARα knockdown by RNA interference totally inhibited PPARα activation as shown by the peroxisome proliferator response element-luciferase reporter assay, but only partially decreased Wy14,643-induced UCP-2 up-regulation. Co-treatment with PPARα RNAi and attenuation of ROS production by glutathione ethyl ester (GSH-EE) blocked UCP-2 up-regulation by Wy14,643 and enhancement of cyanide-induced cell death, suggesting that UCP-2 up-regulation and enhanced cyanide toxicity were mediated through both a PPARα-dependent pathway and a redox sensitive pathway involving increased ROS generation. In addition, Wy14,643 enhanced cyanide-induced mitochondrial glutathione (mtGSH) depletion and oxidative stress-mediated Bcl-2 degradation. Transient transfection of cells with Bcl-2 plasmid attenuated Wy14,643-enhanced cyanide toxicity. Importantly, UCP-2 knockdown significantly blocked cyanide-induced mitochondrial dysfunction and cell death in UCP-2 up-regulated cells. It is concluded that UCP-2 is involved in cyanide neurotoxicity by acting as a regulator of mitochondrial function, and up-regulation of UCP-2 increases the sensitivity of mesencephalic neuronal cells to cyanide-induced necrosis by enhancing mitochondrial dysfunction.
Degree
Ph.D.
Advisors
Isom, Purdue University.
Subject Area
Toxicology|Surgery
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