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Localization of a toxic form of superoxide dismutase 1 protein to pathologically affected tissues in familial ALS.

ABSTRACT: Mutations in the gene encoding superoxide dismutase 1 (SOD1) account for about 20% of the cases of familial amyotrophic lateral sclerosis (fALS). It is not known how the mutant protein causes disease, or why only a subset of cell types (motor neurons) are targeted. The aggregation and misfolding of mutant SOD1 are implicated in disease pathogenesis in both animal models and humans. We used a monoclonal antibody, C4F6, which specifically reacts with mutant and/or "misfolded" SOD1, to investigate the regional distribution of mutant SOD1 protein in rodent and human tissues. C4F6 reacted only with mutant SOD1 and showed remarkable selectivity for disease-affected tissues and cells. Tissue not affected by disease but containing high levels of mutant protein (sensory neurons) did not stain with C4F6. Additionally, C4F6 intensely stained some motor neurons while leaving adjacent motor neurons unstained. Although C4F6 was generated against the G93A SOD1 mutant, it also recognized other SOD1 mutants. In human autopsy tissues from patients carrying SOD1 mutations, C4F6 identified skein-like intracellular inclusions in motor neurons, similar to those seen in rodents, and again stained only a subset of motor neurons. In spinal cords from patients with sporadic ALS, other neurodegenerative diseases, and normal controls, C4F6-immunoreactive inclusions were not detected, but the antibody did reveal diffuse immunostaining of some spinal motor neurons. The ability of C4F6 to differentiate pathologically affected tissue in mutant SOD1 ALS rodent models and humans, specifically motor neuron populations, suggests that this antibody may recognize a "toxic" form of the mutant SOD1 protein.

SUBMITTER: Brotherton TE

PROVIDER: S-EPMC3325721 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Localization of a toxic form of superoxide dismutase 1 protein to pathologically affected tissues in familial ALS.

Brotherton Terrell E TE Li Yingjie Y Cooper Deborah D Gearing Marla M Julien Jean-Pierre JP Rothstein Jeffrey D JD Boylan Kevin K Glass Jonathan D JD

Proceedings of the National Academy of Sciences of the United States of America 20120319 14

Mutations in the gene encoding superoxide dismutase 1 (SOD1) account for about 20% of the cases of familial amyotrophic lateral sclerosis (fALS). It is not known how the mutant protein causes disease, or why only a subset of cell types (motor neurons) are targeted. The aggregation and misfolding of mutant SOD1 are implicated in disease pathogenesis in both animal models and humans. We used a monoclonal antibody, C4F6, which specifically reacts with mutant and/or "misfolded" SOD1, to investigate ...[more]

PMID: 22431618

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Project description:Over 130 mutations to copper, zinc superoxide dismutase (SOD) are implicated in the selective death of motor neurons found in 25% of patients with familial amyotrophic lateral sclerosis (ALS). Despite their widespread distribution, ALS mutations appear positioned to cause structural and misfolding defects. Such defects decrease SOD's affinity for zinc, and loss of zinc from SOD is sufficient to induce apoptosis in motor neurons in vitro. To examine the importance of the zinc site in the structure and pathogenesis of human SOD, we determined the 2.0-A-resolution crystal structure of a designed zinc-deficient human SOD, in which two zinc-binding ligands have been mutated to hydrogen-bonding serine residues. This structure revealed a 9 degrees twist of the subunits, which opens the SOD dimer interface and represents the largest intersubunit rotational shift observed for a human SOD variant. Furthermore, the electrostatic loop and zinc-binding subloop were partly disordered, the catalytically important Arg143 was rotated away from the active site, and the normally rigid intramolecular Cys57-Cys146 disulfide bridge assumed two conformations. Together, these changes allow small molecules greater access to the catalytic copper, consistent with the observed increased redox activity of zinc-deficient SOD. Moreover, the dimer interface is weakened and the Cys57-Cys146 disulfide is more labile, as demonstrated by the increased aggregation of zinc-deficient SOD in the presence of a thiol reductant. However, equimolar Cu,Zn SOD rapidly forms heterodimers with zinc-deficient SOD (t1/2 approximately 15 min) and prevents aggregation. The stabilization of zinc-deficient SOD as a heterodimer with Cu,Zn SOD may contribute to the dominant inheritance of ALS mutations. These results have general implications for the importance of framework stability on normal metalloenzyme function and specific implications for the role of zinc ion in the fatal neuropathology associated with SOD mutations.

Dataset Information

Localization of a toxic form of superoxide dismutase 1 protein to pathologically affected tissues in familial ALS.

Publications

Localization of a toxic form of superoxide dismutase 1 protein to pathologically affected tissues in familial ALS.

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