It has been demonstrated that cytoplasmic round inclusions and aggregates observed in human ALS motoneurons are composed of non-membrane bound electron-dense granular FK228 materials and filamentous structures.[46] We consider that the ultrastructural characteristics of cytoplasmic

aggregates in infected motoneurons shown in the present study are, although not identical, very similar to those of aggregates observed in human ALS motoneurons. On the other hand, a number of transgenic mice and rats expressing human wild-type and mutant TDP-43 and FUS showed cytoplasmic aggregate formation in spinal motoneurons.[47-55] However, ultrastructurally many of these aggregates were predominantly composed of mitochondrial clusters,[7, 47-49, 52, 55] instead of amorphous/filamentous structures observed in human ALS motoneurons[46] and in infected rat motoneurons demonstrated

in the present study. It remains unknown what these structural differences imply; we also occasionally observed mitochondrial clusters as well as cytoplasmic aggregates in infected motoneurons as shown in Figure 9, which should be investigated further using immunoelectron microscopic selleck compound techniques to identify TDP-43 or FUS immunoreactivity in these structures. In addition, we failed in our preliminary study to demonstrate immunoreactivity for ubiquitin and p62 in the cytoplasmic aggregates induced by adenovirus infection of facial motoneurons; whether these structures are truly immunonegative for ubiquitin or p62

should be further examined. We also did (-)-p-Bromotetramisole Oxalate not examine the relationship between aggregate formation, motoneuron death and glial reaction in the present study, which should be investigated in future studies to clarify whether aggregate formation is the cause of motoneuron death or the protective response of diseased motoneurons. It is interesting to note that both TDP-43 and FUS proteins were accumulated in the cytoplasm of motoneurons in normal aged animals.[56] TDP-43 deposition occurs in a substantial subset of cognitively normal elderly human subjects.[57, 58] Since the efficiency of protein degradation machineries that include proteasome and autophagic systems declines with age in rodents as well as in humans,[13, 59, 60] aggregate formation observed in ALS motoneurons may be partially attributed to the impairment of protein degradation machineries by aging. Indeed, impaired proteasome function in sporadic ALS has been reported.[61] It has also been described that a transgenic mouse with motoneuron-specific knockout of proteasome showed motoneuron degeneration with cytoplasmic aggregate formation that replicates ALS in humans.[62] An autophagy activator rapamycin decreased aggregate formation of TDP-43 in a mouse model of frontotemporal lobar dementia with ubiquitinated inclusions (FTLD-U).