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

Abstract

Evidence of misfolded wild-type superoxide dismutase 1 (SOD1) has been detected in spinal cords of sporadic ALS (sALS) patients, suggesting an etiological relationship to SOD1-associated familial ALS (fALS). Given that there are currently a number of promising therapies under development that target SOD1, it is of critical importance to better understand the role of misfolded SOD1 in sALS. We previously demonstrated the permissiveness of the G85R-SOD1:YFP mouse model for MND induction following injection with tissue homogenates from paralyzed transgenic mice expressing SOD1 mutations. This prompted us to examine whether WT SOD1 can self-propagate misfolding of the G85R-SOD1:YFP protein akin to what has been observed with mutant SOD1. Using the G85R-SOD1:YFP mice, we demonstrate that misfolded conformers of recombinant WT SOD1, produced in vitro, induce MND with a distinct inclusion pathology. Furthermore, the distinct pathology remains upon successive passages in the G85R-SOD1:YFP mice, strongly supporting the notion for conformation-dependent templated propagation and SOD1 strains. To determine the presence of a similar misfolded WT SOD1 conformer in sALS tissue, we screened homogenates from patients diagnosed with sALS, fALS, and non-ALS disease in an organotypic spinal cord slice culture assay. Slice cultures from G85R-SOD1:YFP mice exposed to spinal homogenates from patients diagnosed with ALS caused by the A4V mutation in SOD1 developed robust inclusion pathology, whereas spinal homogenates from more than 30 sALS cases and various controls failed. These findings suggest that mutant SOD1 has prion-like attributes that do not extend to SOD1 in sALS tissues.

Tryptophan residue 32 in human Cu-Zn superoxide dismutase modulates prion-like propagation and strain selection

“…Accelerated seeding of mutant SOD1 aggregation in vivo by intraspinal injection has also been observed for mice that express the ALS truncation mutant L126Z and an experimental truncation mutant terminating at residue 103 [65]. Importantly, conformational elements in the misfolded SOD1 that populates tissue homogenates can seed SOD1-G85R to deposit as distinct pathological morphologies that propagate through repeated rounds of in vivo seeding [65]. Collectively, these data are consistent with the idea that misfolded conformers of mutant SOD1 can template conformational changes to naïve SOD1 molecules by prion-like mechanisms of interaction and aggregation.…”

“…Live-imaging studies of cells that express mutant SOD1 fused to the photo-convertible fluorophore Dendra have demonstrated that intracellular aggregates of mutant SOD1 grow through recruitment of both newly-translated and pre-existing pools of soluble precursors [64]. Moreover, in vivo prion-like transmission of misfolded SOD1 seeds has been demonstrated by the intraspinal injection of spinal cord homogenates of paralyzed mice into mice that express low levels of the G85R variant of human SOD1 (expressed with or without an in-frame fusion of yellow fluorescent protein) [35,65,66]. Accelerated seeding of mutant SOD1 aggregation in vivo by intraspinal injection has also been observed for mice that express the ALS truncation mutant L126Z and an experimental truncation mutant terminating at residue 103 [65].…”

“…Moreover, in vivo prion-like transmission of misfolded SOD1 seeds has been demonstrated by the intraspinal injection of spinal cord homogenates of paralyzed mice into mice that express low levels of the G85R variant of human SOD1 (expressed with or without an in-frame fusion of yellow fluorescent protein) [35,65,66]. Accelerated seeding of mutant SOD1 aggregation in vivo by intraspinal injection has also been observed for mice that express the ALS truncation mutant L126Z and an experimental truncation mutant terminating at residue 103 [65]. Importantly, conformational elements in the misfolded SOD1 that populates tissue homogenates can seed SOD1-G85R to deposit as distinct pathological morphologies that propagate through repeated rounds of in vivo seeding [65].…”

Mutant superoxide dismutase aggregates from human spinal cord transmit amyotrophic lateral sclerosis

“…Seeding effects of whole homogenates of spinal cords from end-stage Tg mice have also been reported [4, 5]. Moreover, homogenates from two patients carrying the hSOD1 A4V mutation have been found to induce aggregation of yellow fluorescent protein-fused hSOD1 G85R in spinal cord slices from Tg mice [3]. Finally, homogenates of spinal cords from ALS patients carrying several different hSOD1 mutations have been found to trigger increased aggregation of green fluorescent protein-fused hSOD1 mutants expressed in human embryonal kidney cells [31].…”

Parsing disease‐relevant protein modifications from epiphenomena: perspective on the structural basis of SOD1‐mediated ALS

“…Recent evidence, including our collaborative work, extended this association, linking modified wild‐type SOD1 (SOD1 WT ) to sporadic ALS (sALS) (for dissenting opinions, see previous literature). This perspective outlines our hypothesis‐driven approach to characterizing the structural and toxic consequences of mutations in SOD1 that cause a subset of fALS and studies of modifications of the same protein in sporadic ALS.…”