Astrocytic inclusions in progressive supranuclear palsy and corticobasal degeneration

Tufted astrocytes (TAs) in progressive supranuclear palsy (PSP) and astrocytic plaques (APs) in corticobasal degeneration (CBD) have been regarded as the pathological hallmarks of major sporadic 4-repeat tauopathies. To better define the astrocytic inclusions in PSP and CBD and to outline the pathological features of each disease, we reviewed 95 PSP cases and 30 CBD cases that were confirmed at autopsy. TAs exhibit a radial arrangement of thin, long, branching accumulated tau protein from the cytoplasm to the proximal processes of astrocytes. APs show a corona-like arrangement of tau aggregates in the distal portions of astrocytic processes and are composed of fuzzy, short processes. Immunoelectron microscopic examination using quantum dot nanocrystals revealed filamentous tau accumulation of APs located in the immediate vicinity of the synaptic structures, which suggested synaptic dysfunction by APs. The pathological subtypes of PSP and CBD have been proposed to ensure that the clinical phenotypes are in accordance with the pathological distribution and degenerative changes. The pathological features of PSP are divided into 3 representative subtypes: typical PSP type, pallido-nigro-luysian type (PNL type), and CBD-like type. CBD is divided into three pathological subtypes: typical CBD type, basal ganglia- predominant type, and PSP-like type. TAs are found exclusively in PSP, while APs are exclusive to CBD, regardless of the pathological subtypes, although some morphological variations exist, especially with regard to TAs. The overlap of the pathological distribution of PSP and CBD makes their clinical diagnosis complicated, although the presence of TAs and APs differentiate these two diseases. The characteristics of tau accumulation in both neurons and glia suggest a different underlying mechanism with regard to the sites of tau aggregation and fibril formation between PSP and CBD: proximal-dominant aggregation of TAs and formation of filamentous NFTs in PSP in contrast to the distal-dominant aggregation of APs and formation of less filamentous pretangles in CBD.