Localization of a mutant SOD1 protein in E40K-heterozygous dogs: Implications for non-cell-autonomous pathogenesis of degenerative myelopathy

In vitro evidence consistent with an interaction between wild‐type and mutant SOD1 protein associated with canine degenerative myelopathy

“…Similar alterations in conformation and a propensity to form aggregates have also been observed in a number of fALS SOD1 mutations (Orrell, 2000;Pickles and Vande, 2012;Prudencio et al, 2009b;Rakhit and Chakrabartty, 2006). A recent study has described SOD1 aggregate accumulation in neurons and astrocytes of affected dogs suggesting a non-cellautonomous process in DM (Kobatake et al, 2017). There are common degradation mechanisms for mutant SOD1 in DM and fALS, for example perturbation of the proteasome pathway (Nakamae et al, 2015).…”

“…The formation of SOD1 aggregates in DM is a pathological feature of the homozygote spinal cord (Awano et al, 2009;Nakamae et al, 2015) compared to a much lesser extent in heterozygotes although the staining intensity reported in heterozygotes appears to be variable (Awano et al, 2009;Nakamae et al, 2015). Aggregate formation has been described in both neurons and astrocytes from homozygotes and a recent study using a DM-SOD1 specific antibody demonstrated that SOD1 aggregate formation (Awano et al, 2009;Kobatake et al, 2017;Nakamae et al, 2015;Ogawa et al, 2011) is restricted to heterozygote astrocytes (Kobatake et al, 2017). In vitro studies of aggregate formation and WT:mutant SOD1 interactions described in this study suggest that aggregates in the heterozygous scenario may be composed of both WT and mutant SOD1, possibly as protein dimers.…”

“…Our data strongly suggests some degree of WT:mutant SOD1 heterodimeric interaction in neuroblastoma co-transfectants, which subsequently form aggregates. Since aggregates are found in both neurones and astrocytes in DM homozygotes but apparently only present in heterozygous astrocytes (Kobatake et al, 2017), this suggests that the cellular environment, possibly related to protein clearance pathways may influences the fate of the various forms of the SOD1 complexes.…”

Species‐specific consequences of an E40K missense mutation in superoxide dismutase 1 (SOD1)

“…Aggregation of mutant SOD1 proteins is a hallmark of both SOD1-associated human and canine diseases: ALS and DM. 1,32 However, neither horse SOD1 variant showed an increased propensity to aggregate; conversely, as expected, the mean percentage of cells expressing the Mut-D SOD1that contained cytoplasmic aggregates was significantly higher F I G U R E 1 Conservation of the 40 th codon in SOD1 across different mammalian species. A glutamic acid residue (E) is present at the 40 th codon (blue) in most mammals with the exception of the wild-type horse, armadillo and the mutant SOD1 variant of the dog where a lysine (K) residue (red) is found than the mean percentage of cytoplasmic aggregates in cells expressing all other SOD1 variants, and control and vehicle cells ( Figure 4A and B).…”

Canine SOD1 harboring E40K or T18S mutations promotes protein aggregation without reducing the global structural stability

“…The E40 residue is exposed to the solvent and forms a salt bridge with the K91 residue of the same subunit. Since we previously reported that the T18S and E40K mutations promote formation of insoluble aggregates in neurons and glial cells (Kobatake et al, 2017), here we studied the pathological consequences of these two mutations at the level of protein folding. We also investigated the molecular mechanism underlying canine SOD1 aggregation.…”