Altered phosphorylation of tau protein in heat-shocked rats and patients with Alzheimer disease.

Six hours after heat shocking 2- to 3-month-old male and female Sprague-Dawley rats at 42 degrees C for 15 min, we analyzed tau protein immunoreactivity in SDS extracts of cerebrums and peripheral nerves by using immunoblot analysis and immunohistochemistry with the anti-tau monoclonal antibody Tau-1, which recognizes a phosphate-dependent non-phosphorylated epitope, and with 125I-labeled protein A. In the cerebral extracts, we found altered phosphorylation of tau in heat-shocked females, characterized by a marked reduction in the amount of nonphosphorylated tau, a doubling of the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau, and the appearance of the slowest moving phosphorylated tau polypeptide (68 kDa). Similar, but milder, changes were observed in male rats. These changes progressively increased in females from 3 to 6 h after heat shocking. In contrast, both phosphorylated tau and nonphosphorylated tau were reduced in peripheral nerves after heat shocking. In immunoblots of SDS extracts from Alzheimer disease-affected brain, the two slowest moving phosphorylated tau polypeptides (62 kDa and 66 kDa, respectively) were detected by Tau-1 after dephosphorylation and by Tau-2 (an anti-tau-monoclonal antibody that recognizes a phosphate-independent epitope) without prior dephosphorylation only in regions that contained tau immunoreactivity in histologic preparations. In addition, quantitative immunoblot analysis of cortex and the underlying white matter with Tau-1 and 125I-labeled protein A showed that the amount of phosphorylated tau progressively increased in the Alzheimer disease-affected cerebral cortex, while concurrently a proportionally lesser amount of tau entered the white matter axons. The similar findings for the rat heat-shock model and Alzheimer disease suggest that life stressors may play a role in the etiopathogenesis of Alzheimer disease.