Heat Shock Induces Rapid Dephosphorylation of τ in Both Female and Male Rats Followed by Hyperphosphorylation Only in Female Rats: Implications for Alzheimer's Disease

Female and male 2-3-month-old Sprague-Dawley rats were heat shocked at 42 degrees C for 15 min. At 0, 3, 6, 12 and 24 h after heat shock, qualitative and quantitative immunoblot analysis of cerebral extracts and immunohistochemistry were performed using monoclonal anti-tau antibodies that recognize nonphosphorylated (Tau-1), phosphorylated (PHF-1), and phosphate-independent (Tau-5 and Tau-46) epitopes. At 0 h after heat shock, there was dephosphorylation of tau in both female and male rats as evidenced by (1) accentuation and attenuation of tau isoforms recognized by Tau-1 and PHF-1, respectively, and recognition of additional tau polypeptides by Tau-1, Tau-5, and Tau-46 but not PHF-1; (2) significant increase in the nonphosphorylated Tau-1 epitope with resultant decrease in the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau; and (3) dephosphorylation of the Tau-1 epitope in the somatodendritic compartment. By 6 h after heat shock, there was progressive hyperphosphorylation of tau in female but not male rats exemplified by (1) upward gel mobility shift recognized by PHF-1, Tau-5, and Tau-46, and by Tau-1 after dephosphorylation; (2) significant increase in the ratio of total tau to nonphosphorylated tau; and (3) rephosphorylation of the Tau-1 epitope in the somatodendritic compartment. Two-dimensional electrophoresis showed shifts to basic and acidic tau polypeptides at 0 and 6 h after heat shock, respectively. Hyperphosphorylation of tau also occurred after multiple heat-shock episodes. Microtubules were present at 6 h after heat shock. There were no differences between control and heat-shocked rats in extracts from peripheral nerves. Thus, we now have a simple rat model to study within 6 h the processes of dephosphorylation and hyperphosphorylation of tau, which are altered in Alzheimer's disease.