Activation of the 5′-AMP-Activated Protein Kinase in the Cerebral Cortex of Young Senescence-Accelerated P8 Mice and Association with GSK3β- and PP2A-Dependent Inhibition of p-tau396 Expression

The 5'-AMP-activated protein kinase (AMPK), which is a sensor of cellular energy, regulates neuronal survival and energy homeostasis. However, the roles of AMPK in the pathogenesis of Alzheimer's disease (AD) are unclear. The senescence-accelerated mouse prone 8 (SAMP8) strain is characterized by deficits in learning and memory, exhibits pathological characteristics of AD as early as 5 months of age, and is being increasingly recognized as a model of AD. Here, we investigated the relationship between AMPK activation and phosphorylation of the tau protein in the brain of young (2-month-old) SAMP8 animals and in differentiated SH-SY5Y cells. Upregulation of p-AMPK, p-ACC, and p-GSK3βS9 and downregulation of p-tau396 and sirtuin 1 (Sirt1) were observed in the cerebral cortex of young SAMP8 mice compared with that of age-matched SAMR1 animals. The hippocampal levels of p-AMPK and p-tau396 in SAMP8 animals were not significantly different from those of SAMR1, whereas upregulation of p-GSK3βS9 and downregulation of sirt1 was observed in the hippocampus of SAMP8 mice. Consistent with in vivo findings in the cortex, AMPK activation in SH-SY5Y cells upregulated p-GSK3βS9 but downregulated p-tau396, whereas it had no significant effect on p-tau262 expression. In addition, the AMPK-mediated inhibition of p-tau396 expression was attenuated by okadaic acid, a protein phosphatase 2A (PP2A) inhibitor. Taken together, our data showed that AMPK activation inhibits p-tau396 expression in a GSK3β- and PP2A-dependent manner, and suggest that differential regulation of tau phosphorylation in young SAMP8 mice by AMPK plays a compensatory role against accelerated senescence in this AD animal model.