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Aim:This study was to investigate the effect of dehydroevodiamine (DHED) on Alzheimer’s disease (AD)-like tan hyperphosphorylation induced by calyculin A (CA),an inhibitor of protein phosphatase (PP)-2A and PP-1,and the involvement of PP-2A in metabolically competent rat brain slices. Methods:Rat brain slices were pre-incubated at 33 ℃ in the presence (10,100,and 200 μmol/L,respectively)or absence of DHED for 1 h. Then,CA 0.1 μmol/L was added and the slices were treated for another 2 h. West blotting and/or immunohistochemistry were used to measure the phosphorylation level of tau and PP-2A. Results:CA treatment could remarkably increase the immunoreactivity of pS262 and decrease the staining of Tan-1,representing tau hyperphosphorylation at Ser262 (pS262) and Ser198/199/202 (Tau-1,as the antibody reacts with unphosphorylated tau,therefore,decreased staining represents increased phosphorylation). Pre-incubation of the brain slices with DHED could efficiently attenuate the CA-induced tan hyperphosphorylation at the above AD-related sites. Additionally,DHED also decreased the basal phosphorylation level of tan at Ser396,although CA failed to induce tan hyperphosphorylation at this site. Furthermore,CA treatment induced an increased level of Tyr307-phosphorylated PP-2A,which represents inactivation of the phosphatase,whereas DHED arrested the elevation of the inhibitory modification of PP-2A. Conclusion:DHED can attenuate CA-induced tau hyperphosphorylation at multiple AD-related sites in metabolically active rat brain slices. The underlying mechanism may involve a decreased inhibitory phosphorylation of PP-2A at Tyr307.AcknowledgementsWe thank Dr Khalid IQBAL,Dr Inge GRUNDKE-IQBAL,Dr Cheng-xin GONG,and Dr Fei LIU at New York State Institute for Basic Research for technical support.