Ubiquitinated and accumulates in a proteolytically cleaved and detergent insoluble form

Here we report that motor axons from R521C FUS-FALS and L-Asarinin wtTDP43-SALS patient spinal cords are immunoreactive for misfolded SOD1 by immunohistochemistry with SOD1 misfolding-specific mAbs. Using these same antibodies we found that transfection-driven expression of cytosolic mutants of FUS or TDP43 in vitro is associated with SOD1 misfolding by immunocytochemistry and immunoprecipitation. Motor axonal misfolded SOD1 was also observed by immunohistochemistry in SALS, in which 2-Hydroxypropyl-beta-cyclodextrin extranuclear non-mutant TDP43 is ubiquitinated and accumulates in a proteolytically cleaved and detergent insoluble form, and in neural cells in which wtTDP43 is over-expressed. Commensurate with these findings, motor neuron disease is induced by transgenic over-expression in rodents of human mutant FUS or TDP43, and by expression of wtTDP43 but not wtFUS. Cytosolic accumulation of wtFUS aggregates is not observed in SALS, and we did not detect SOD1 misfolding in neural cells over-expressing wtFUS. Given the concordance between the neuropathological immunohistochemistry, and the immunocytochemistry and immunoprecipitation of cultured cells, we conclude that cytoplasmic accumulation of FUS and/or TDP43 is associated with misfolding of human wtSOD1, both in vivo and in vitro. Is extranuclear accumulation of FUS and TDP43 a cause or consequence of SOD1 misfolding, and if causal is the interaction direct or indirect? Consistent with our studies in cell culture and in human FUS-FALS, a causal association is tenable between SOD1 misfolding and cytosolic accumulation of mutant FUS, or mutant and wtTDP43. However, accumulation of non-mutated TDP43 in SALS spinal neuronal cytosol may also be, at least partially, a consequence of cell stress, as the pathology also appears in diverse diseases including Alzheimer��s disease and frontotemporal lobar dementia. Recent work has shown that TDP43 aggregation and neurotoxic cleavage may be triggered by free radical stress secondary to mitochondrial dysfunction, a concomitant of cellular mutant SOD1 expression. Immunohistochemical differences in the distribution and abundance of misfolded SOD1 in FUS-FALS and TDP43-SALS are potentially consistent with the notion of different mechanisms of SOD1 misfolding.