Protection Of Berberine On Tau Hyperphosphorylation Induced By Calyculin A And Its Mechanism

Berberine is an isoquinoline alkaloid extracted from Chinese herbs such as Coptidis rhizome. In the past several years, there are lots of pharmacodynamic studies of berberine which indicates its potential role in the treatment of Alzheimer's Disease (AD). These results involve that berberine chloride can ameliorate the spatial memory impairment and increase the expression of interleukin-1beta and inducible nitric oxide synthase in the rat model of Alzheimer's disease; berberine alters the processing of Alzheimer's amyloid precursor protein to decrease Abeta secretion; tetrohydroberbine could protect against the apoptosis induced by beta-AP by reducing hippocampal neuronal intracellar free Ca2+; berberine has anticholinesterase activities. Above all, berberine becomes a potent drug for Alzheimer's Disease. There is positive correlation between the content of NFTs constituted by hyperphosphorylation of microtubule-associated protein tau and clinical dementia degree, which suggests tau hyperphosphorylation-induced NFTs conformation plays a key role in Alzheimer's disease onset. The imbalance between protein kinease and protein phosphatase of involved neurons is the main biochemical mechanism inducing tau hyperphosphorylation. In addition, there is one report that berberine can affect GSK-3βactivity in HCT116 cells, and GSK-3βis one of the protein kinases which play important role in Alzheimer's disease onset. Until now, there is no direct evidence that shows berberine can affect tau phosphorylation by affecting protein kinase/phosphatase in brains of AD-like animals or patients with Alzheimer's disease. This study is to confirm whether berberine has any effect on tau hyperphosphorylation and the underlying mechanism. The longest human tau (tau441) cDNA was stably transfected into HEK293 cells (HEK293/tau) and hyperphosphorylation of tau was induced by 2.5 nM calyculin-A for 12h. After different drug dose exposure, cell viability was detected by cck-8 technique to make sure a proper drug dose, along with microscope imaging and hoechst staining which were done to observe cellular morphous and apoptosis condition. Tau hyperphosphorylation and the related enzymes were assayed by Western blot and cell immunochemistry. The results show that hyperphosphor- ylation of tau at ser198/199/202, ser396/404 epitopes was reduced by 20μg/ml berberine treatment for 24h together with decreased phosphorylation of glycogen synthase kinase-3β(GSK-3β) at Tyr216 and decreased phosphorylation of catalytic subunit of protein phosphotase 2A (PP-2Ac) at Y307. 20μg/ml berberine can reduce tau hyperphosphorylation induced by 2.5nM calyculin-A specifically at the ser198/199/202, ser396/404 sites. However, almost no alteration at Thr231 was observed. Level of phosphorylated GSK-3βat Tyr216 and phosphorylation of catalytic subunit of protein phosphotase 2A (PP-2Ac) at Tyr307 were obviously decreased after 20μg/ml berberine treatment. Berberine may be used to reduce tau hyperphosphorylation in AD-like tauopathy by reducing GSK-3βactivity and activating PP2A, which make it become a potential drug for Alzheimer's Disease.