Isolated Cytochrome c Oxidase Deficiency in G93A SOD1 Mice Overexpressing CCS Protein

Abstract

G93A SOD1 transgenic mice overexpressing CCS protein develop an accelerated disease course that is associated with enhanced mitochondrial pathology and increased mitochondrial localization of mutant SOD1. Because these results suggest an effect of mutant SOD1 on mitochondrial function, we assessed the enzymatic activities of mitochondrial respiratory chain complexes in the spinal cords of CCS/G93A SOD1 and control mice. CCS/G93A SOD1 mouse spinal cord demonstrates a 55% loss of complex IV (cytochrome c oxidase) activity compared with spinal cord from age-matched non-transgenic or G93A SOD1 mice. In contrast, CCS/G93A SOD1 spinal cord shows no reduction in the activities of complex I, II, or III. Blue native gel analysis further demonstrates a marked reduction in the levels of complex IV but not of complex I, II, III, or V in spinal cords of CCS/G93A SOD1 mice compared with nontransgenic, G93A SOD1, or CCS/WT SOD1 controls. With SDS-PAGE analysis, spinal cords from CCS/G93A SOD1 mice showed significant decreases in the levels of two structural subunits of cytochrome c oxidase, COX1 and COX5b, relative to controls. In contrast, CCS/G93A SOD1 mouse spinal cord showed no reduction in levels of selected subunits from complexes I, II, III, or V. Heme A analyses of spinal cord further support the existence of cytochrome c oxidase deficiency in CCS/G93A SOD1 mice. Collectively, these results establish that CCS/G93A SOD1 mice manifest an isolated complex IV deficiency which may underlie a substantial part of mutant SOD1-induced mitochondrial cytopathy.

Mitochondrial dysfunction in familial amyotrophic lateral sclerosis

“…Changes in the activity of the different complexes of the electron transport chain have been described in tissues obtained from ALS patients, and in cell and animal disease models. Although some of these studies have produced mixed and somewhat contradictory results, the most consistent abnormality in mitochondrial respiratory function has been associated with reduced complex I and IV activity (Browne et al 1998;Kirkinezos et al 2005;Mattiazzi et al 2002;Menzies et al 2002;Rizzardini et al 2006;Son et al 2008). In motor neurons of mutant SOD1 G93A mice a reduction in activity of complex I was observed before disease onset and progressing to inhibition of complex IV at later stages (Jung et al 2002).…”

Cellular copper distribution: a mechanistic systems biology approach

“…Indeed, it has been shown that the mitochondrial pool of ALS-SOD1 mutants causes damage to mitochondrial function and structure [226], and the mitochondrial uptake of ALS-SOD1 mutants is increased upon CCS overexpression [227]. This uptake of ALS-SOD1 mutants results in mitochondrial respiratory defects [228] and an acceleration in SOD1-linked motor neuron disease [227,229].…”

Oligomerization of Mutant SOD1 in Mitochondria of Motoneuronal Cells Drives Mitochondrial Damage and Cell Toxicity

“…Although evidence has been provided showing that the removal of such aggregates by the elimination of reactive cysteines from mutSOD1s is able to rescue the viability of transfected cells (5,23), transgenic mice that overexpress both the G93A mutSOD1 and its copper chaperone (CCS) die from an ALS-like disease at a time when cytosolic aggregates are not present, thus questioning about a causal role of such aggregates in the pathogenesis of the disease (28). Interestingly, these mice have a clearly enhanced mitochondrial damage (28,29), and mitochondrial abnormalities appear to be shared by models and patients suffering from ALS (reviewed in Ref. 17).…”