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 nonphosphorylated epitope, and with I-125-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 I-125-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.