Mitochondrial Manganese Superoxide Dismutase Prevents Neural Apoptosis and Reduces Ischemic Brain Injury: Suppression of Peroxynitrite Production, Lipid Peroxidation, and Mitochondrial Dysfunction

Abstract

Oxidative stress is implicated in neuronal apoptosis that occurs in physiological settings and in neurodegenerative disorders. Superoxide anion radical, produced during mitochondrial respiration, is involved in the generation of several potentially damaging reactive oxygen species including peroxynitrite. To examine directly the role of superoxide and peroxynitrite in neuronal apoptosis, we generated neural cell lines and transgenic mice that overexpress human mitochondrial manganese superoxide dismutase (MnSOD). In cultured pheochromocytoma PC6 cells, overexpression of mitochondria-localized MnSOD prevented apoptosis induced by Fe2+, amyloid beta-peptide (Abeta), and nitric oxide-generating agents. Accumulations of peroxynitrite, nitrated proteins, and the membrane lipid peroxidation product 4-hydroxynonenal (HNE) after exposure to the apoptotic insults were markedly attenuated in cells expressing MnSOD. Glutathione peroxidase activity levels were increased in cells overexpressing MnSOD, suggesting a compensatory response to increased H2O2 levels. The peroxynitrite scavenger uric acid and the antioxidants propyl gallate and glutathione prevented apoptosis induced by each apoptotic insult, suggesting central roles for peroxynitrite and membrane lipid peroxidation in oxidative stress-induced apoptosis. Apoptotic insults decreased mitochondrial transmembrane potential and energy charge in control cells but not in cells overexpressing MnSOD, and cyclosporin A and caspase inhibitors protected cells against apoptosis, demonstrating roles for mitochondrial alterations and caspase activation in the apoptotic process. Membrane lipid peroxidation, protein nitration, and neuronal death after focal cerebral ischemia were significantly reduced in transgenic mice overexpressing human MnSOD. The data suggest that mitochondrial superoxide accumulation and consequent peroxynitrite production and mitochondrial dysfunction play pivotal roles in neuronal apoptosis induced by diverse insults in cell culture and in vivo.

Metabolic Regulation of Manganese Superoxide Dismutase Expression via Essential Amino Acid Deprivation

“…These studies also provided a link between chronic oxidative stress in the heterozygous mice and a premature induction of apoptosis, thus implicating the importance of MnSOD in cell death and aging. These observations are also consistent with data demonstrating the potent anti-apoptotic activity associated with overexpression of this mitochondrial localized antioxidant enzyme in a variety of mitochondria-dependent cell death pathways (23)(24)(25)(26). Additionally, the significant induction of MnSOD gene expression by pro-inflammatory cytokines (13,27,28) is also in line with a cell survival strategy that accompanies increased levels of ROS associated with the inflammatory response.…”

Role of mitochondrial function in the protective effects of ischaemic postconditioning on ischaemia/reperfusion cerebral damage

“…40 ROS are generated via a series of redox reductions in the mitochondrial matrix. 41 Mitochondria are easily damaged by ROS, as they are made up of inner and outer membrane structures that contain liquids and proteins that are prone to ROS attack. 42 In contrast to other studies that have indicated that ischaemic postconditioning attenuates oxidative stress, 19,20 the current study specifically examined the production of ROS within mitochondria.…”

Glutamate-mediated inhibition of oxidative phosphorylation in cultured retinal cells

“…Thus, the formation of O ÁÀ 2 was implicated as an obligate step in the intracellular events that culminate in cell death after NMDA and kainate receptor activation, as determined by the selective inactivation of aconitase activity, a marker of O ÁÀ 2 generation (Patel et al, 1996). Excessive formation of mitochondrial O ÁÀ 2 is metabolized by manganese superoxide dismutase (Mn-SOD), which can regulate membrane lipid peroxidation, ONOO À formation and mitochondrial dysfunction (Keller et al, 1998). Furthermore, an increased intracellular Ca 2+ may stimulate mitochondrial nitric oxide synthase (NOS), associated with the inner mitochondrial membrane (Ghafourifar and Richter, 1997), which may have a major relevance in mitochondrial degeneration.…”