Aberrant Localization of FUS and TDP43 Is Associated with Misfolding of SOD1 in Amyotrophic Lateral Sclerosis

Abstract

BackgroundAmyotrophic lateral sclerosis (ALS) is incurable and characterized by progressive paralysis of the muscles of the limbs, speech and swallowing, and respiration due to the progressive degeneration of voluntary motor neurons. Clinically indistinguishable ALS can be caused by genetic mutations of Cu/Zn superoxide dismutase (SOD1), TAR-DNA binding protein 43 (TDP43), or fused in sarcoma/translocated in liposarcoma (FUS/TLS), or can occur in the absence of known mutation as sporadic disease. In this study, we tested the hypothesis that FUS/TLS and TDP43 gain new pathogenic functions upon aberrant accumulation in the cytosol that directly or indirectly include misfolding of SOD1.Methodology/Principal FindingsPatient spinal cord necropsy immunohistochemistry with SOD1 misfolding-specific antibodies revealed misfolded SOD1 in perikarya and motor axons of SOD1-familial ALS (SOD1-FALS), and in motor axons of R521C-FUS FALS and sporadic ALS (SALS) with cytoplasmic TDP43 inclusions. SOD1 misfolding and oxidation was also detected using immunocytochemistry and quantitative immunoprecipitation of human neuroblastoma SH-SY5Y cells as well as cultured murine spinal neural cells transgenic for human wtSOD1, which were transiently transfected with human cytosolic mutant FUS or TDP43, or wtTDP43.Conclusion/SignificanceWe conclude that cytosolic mislocalization of FUS or TDP43 in vitro and ALS in vivo may kindle wtSOD1 misfolding in non-SOD1 FALS and SALS. The lack of immunohistochemical compartmental co-localization of misfolded SOD1 with cytosolic TDP43 or FUS suggests an indirect induction of SOD1 misfolding followed by propagation through template directed misfolding beyond its site of inception. The identification of a final common pathway in the molecular pathogenesis of ALS provides a treatment target for this devastating disease.

Intercellular propagated misfolding of wild-type Cu/Zn superoxide dismutase occurs via exosome-dependent and -independent mechanisms

“…1073/pnas.1312245111/-/DCSupplemental. WTTDP-43, or expression of mutant FUS or TDP-43, is associated with HuWtSOD1 misfolding (11). Collectively, these data are consistent with SOD1 being a molecular common denominator for all types of ALS.…”

“…Using the DSE mAbs, we have previously demonstrated the presence of misfolded/oxidized SOD1 by IHC in SOD1-and FUS-FALS, and in SALS with cytoplasmic TDP43 accumulation (11). To confirm the presence of misfolded HuWtSOD1 in ALS pathology in vivo, we examined a larger series of IHC of postmortem human spinal cord sections from control, mutant-SOD1 FALS, non-SOD1 FALS (including two cases due to expansion mutations in the C9ORF72 gene) (22,23), and SALS patients (including one case of C9ORF72 expansion without family history of ALS; Table S1).…”

“…Whereas it is generally accepted SOD1 is not found in large perikaryal cytoplasmic inclusions outside of SOD1 FALS cases, misfolded SOD1 has been increasingly identified in SALS and non-SOD1 FALS (5,10,11). Indeed, we have reported that misfolded human wild-type SOD1 (HuWtSOD1) can be detected by spinal cord immunohistochemistry (IHC) in FALS secondary to FUS mutation, and in SALS patients with cytosolic WT TDP-43 accumulation (11).…”

“…Indeed, we have reported that misfolded human wild-type SOD1 (HuWtSOD1) can be detected by spinal cord immunohistochemistry (IHC) in FALS secondary to FUS mutation, and in SALS patients with cytosolic WT TDP-43 accumulation (11). Moreover, in cell models, overexpression of Significance Amyotrophic lateral sclerosis (ALS), an incurable motor neuron disease, is associated with mutation and misfolding of the Cu/Zn superoxide dismutase (SOD1) protein.…”

Disparity of outcomes: the limits of modeling amyotrophic lateral sclerosis in murine models and translating results clinically

“…protein, some groups have demonstrated positive immunolabeling in fALS cases, a finding not always recapitulated in sALS (9)(10)(11)(12). Similarly, pathological TDP-43 positive cytosolic inclusions common in sALS have not been described in mutant SOD1-linked fALS (13); a finding which is not always observed in mutant SOD1 models (14,15).…”