Direct and indirect mechanisms for wild-type SOD1 to enhance the toxicity of mutant SOD1 in bigenic transgenic mice

Abstract

Co-expression of wild-type human superoxide dismutase 1 (WT-hSOD1) with ALS mutant hSOD1 accelerates disease onset relative to mice expressing only mutant protein. Here, we analyzed the effect of co-expressed WT-hSOD1 in two established mutant mouse models (L126Z and G37R), and a new model that expresses the first 102 amino acids of SOD1 with mutations at histidines 46, 48 and 63 to eliminate Cu binding (Cu-V103Z). A subset of Cu-V103Z mice developed paralysis between 500 and 730 days. Similar to mice expressing L126Z-SOD1, the spinal cords of this new model showed SOD1 immunoreactive fibrillar inclusions. Co-expression of WT-hSOD1 with Cu-V103Z SOD1 moderately accelerated the age to paralysis, similar in magnitude to WT/L126Z mice. In either combination of these bigenic mice, the severity of fibrillar inclusion pathology was diminished and unreactive to antibodies specific for the C terminus of WT protein. Co-expression of WT-hSOD1 fused to yellow fluorescent protein (WT-hSOD1:YFP) with G37R-hSOD1 produced earlier disease, and spinal cords of paralyzed bigenic mice showed YFP fluorescent inclusion-like structures. In bigenic L126Z/WT-hSOD1:YFP mice, disease was not accelerated and WT-hSOD1:YFP remained diffusely distributed. A combination of split luciferase complementation assays and affinity capture-binding assays demonstrated that soluble G37R-hSOD1 efficiently and tightly bound soluble WT-hSOD1, whereas soluble forms of the Cu-V103Z and L126Z variants demonstrated low affinity. These data indicate that WT-hSOD1 may indirectly augment the toxicity of mutant protein by competing for protective factors, but disease onset seems to be most accelerated when WT-hSOD1 interacts with mutant SOD1 and becomes misfolded.

Distinct conformers of transmissible misfolded SOD1 distinguish human SOD1-FALS from other forms of familial and sporadic ALS

“…Only ~30% of mice from this line develop paralysis with an average age of endpoint of 19.4 months [39]. However, when we injected spinal cords of newborn V103Z mice with homogenate prepared from a paralyzed V103Z mouse, all of the injected transgenic animals (n=10) developed MND with an average age of onset of 3.7 months of age.…”

“…All animals were housed one to five to a cage and maintained on ad libitum food and water with a 14 h light and 10 h dark cycle. All the strains of transgenic mice used in this study have been previously described: G85R-SOD1:YFP mice [37], L126Z hSOD1 in the Line45 mice [38], the V103Z hSOD1 in the Line D14 mice [39], the α-synuclein M83 mice [19], and the tau JNPL3 mice [27]. The G85R-SOD1:YFP mice are maintained on the FVB/NJ background, the JNPL3 on Swiss Webster, and the L45, D14, and M83 on a hybrid background of C57Bl/6J and C3H/HeJ.…”

“…The G85R-SOD1:YFP mice are maintained on the FVB/NJ background, the JNPL3 on Swiss Webster, and the L45, D14, and M83 on a hybrid background of C57Bl/6J and C3H/HeJ. For identification of genotype, DNA was extracted from mouse tail biopsies and analyzed by PCR as previously described [39]. …”

The Disulfide Bond, but Not Zinc or Dimerization, Controls Initiation and Seeded Growth in Amyotrophic Lateral Sclerosis-linked Cu,Zn Superoxide Dismutase (SOD1) Fibrillation

“…The second feature is especially important for disease as it guarantees that fibril-seeded growth can be sustained even when the coexpressed mutant has a short half-life. Indeed, coexpression of WT exacerbates the disease profile of mice expressing mutants, and the contrast in disease profile is dramatic for short-lived mutants like A4V and L126Z (63)(64)(65). It is important to remember that the identity of the toxic species is unknown; hence, the relative contributions of spontaneous fibrillation versus seeded amyloid formation to this process are unclear.…”

New links between SOD1 and metabolic dysfunction from a yeast model of amyotrophic lateral sclerosis

“…However, it is unclear how each mutation relates to the cellular dysfunction that drives disease progression. Interestingly, the overexpression of native SOD1 also accelerates disease progression in ALS mouse models (Xu et al, 2015). In addition, the overexpression of SOD1 alone can lead to ALS symptoms in mice, providing evidence that the native Sod1 protein can participate in disease (Graffmo et al, 2013).…”