Ubiquitin-positive NCIs, which are evident in the degenerating lower motor neurons, have long been recognized as a characteristic feature of the cellular pathology. However, TDP-43 immunostaining may reveal positive neuronal and glial cytoplasmic inclusions (NCIs and GCIs) not only in the affected lower motor neuron nuclei but also in the other apparently normal non-motor neuron nuclei, indicating that SALS is a multisystem neuronal-glial proteinopathy of TDP-43 affecting a wide range of both neurons and glial cells in the CNS.[20] TDP-43
pathology is also evident in many patients with superoxide dismutase Idelalisib 1 (SOD1)-unrelated familial ALS, in whom mutations within the TDP-43 gene (TARDBP) have been identified; interestingly, although
rare, TARDBP mutations have also been identified in patients with SALS.[21, 22] Based on these pathological and genetic findings, TDP-43 has been implicated as an important contributor to the pathogenesis of ALS. PolyQ diseases are inherited neurodegenerative disorders caused by expanded CAG repeats that encode abnormally long polyQ stretches in the disease proteins. The polyQ-positive NCIs and neuronal intranuclear inclusions (NIIs) are widespread in the CNS beyond the degenerative areas, indicating that the diseases are also multisystem neuronal proteinopathies.[23] TDP-43 pathology in the polyQ diseases was first reported in HD.[15] Unlike the neurodegenerative diseases showing TDP pathology mainly in the RAD001 in vivo limbic system, patients with HD have TDP-43-positive NCIs in the neocortex, where many polyQ-positive inclusions are also observed. More recently, intermediate-length polyQ expansions
(27–33 Qs) in ataxin 2 (ATX2), the causative gene of SCA2, were reported to be a genetic risk factor for SALS.[16] In cases of HD, Schwab et al. have reported that TDP-43 was frequently colocalized with huntingtin in dystrophic neuritis Adenosine and various intracellular inclusions, but not in intranuclear inclusions.[15] Recently, Tada et al. examined autopsied patients with genetically confirmed HD with SALS, and found that two different proteinaceous inclusions coexisted in a small number of neurons in the affected brain. However, the two disease proteins, huntingtin and TDP-43, were not co-localized within the inclusions, although the regional distributions of TDP-43-positive inclusions and expanded polyQ (1C2)-positive inclusions partly overlapped.[19] Biochemically, TDP-43 isoforms similar to those seen in SALS were observed in one of the patients examined.[19] In these cases of HD with SALS, it seems that two distinct pathological pathways may each affect the brain. It is tempting to speculate that “aging” may promote the deleterious effect of mutant huntingtin on motor neurons and on TDP-43. We have previously reported the occurrence of TDP-43 pathology in SCA3/MJD.