High prevalence of thorn-shaped astrocytes in the aged human medial temporal lobe.

Thorn-shaped astrocytes (TSA) are glial fibrillary tangles that contain abnormally phosphorylated and aggregated microtubule-associated tau protein. The present study examines the prevalence of TSA in the human medial temporal lobe of 100 autopsy brains aged 42-97 years (mean age: 65 years). Serial brain sections were cut at 100 microm and stained using phosphorylation-dependent anti-tau antibodies (AT8, PHF-1, TG3, Alz-50) and silver staining methods for neurofibrillary changes and beta-amyloid deposits. TSA preferentially were distributed in periventricular, subependymal, and subpial areas of the mediobasal temporal lobe (MTL). Double-labeling with AT8 and anti-GFAP antibodies demonstrated that the abnormal tau protein was deposited in astroglial cell bodies and in proximal and distal astroglial processes. A pronounced inter-individual variation was noted in the density of AT8-positive TSA, thereby allowing distinction of mild, moderate, and severe involvement. TSA were absent in individuals younger than 60 years. A significant increase in the prevalence of TSA was noted with advancing age. In the age-range of 75-98 years TSA were found in approximately 50% of all individuals. The development of TSA was not correlated with the severity of Alzheimer-related cortical pathology. In summary, this study suggests that TSA is a distinct form of glial tau pathology that occurs with a high frequency in elderly individuals.