White matter lesions in the brain with frontotemporal lobar degeneration with motor neuron disease: TDP-43-immunopositive inclusions co-localize with p62, but not ubiquitin

Recently, TDP-43 was established as a major component of the ubiquitinated inclusions found in both amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with motor neuron disease (FTLD-MND). However, differences in the underlying pathogenesis between ALS and FTLD-MND remain yet to be elucidated. Originally, TDP-43-immunopositive inclusions were found in neuronal cells and reported to be ubiquitinated. This study shows that TDP-43-positive inclusions were distributed throughout the subcortical white matter except for the occipital lobe in the FTLD-MND brain, but not in the ALS brain. TDP-43-positive inclusions were also prominent features of pathologically proven FTLD-MND cases (p-FTLD-MND) without history of apparent clinical cognitive decline. A substantial fraction of these inclusions was also p62-immunoreactive, and another noteworthy feature was that those inclusions did not stain positively for ubiquitin. Significant correlations between immunoreactivity for TDP-43 and p62 were observed, particularly in p-FTLD-MND (Pearson correlation coefficient, 0.976). Furthermore, TDP-43 extracted from white matter appeared to be uncleaved. These results indicate that pathological changes might take place within the white matter also in the brain with FTLD-MND, but in a different manner than within the gray matter.