ABSTRACT
Aim Fuzhisan ( FZS ) , a Chinese herbal complex prescription that has been used for the treat-ment of AD for over 15 years, is known to enhance the cognitive ability in AD patients. In this study, to in-vestigate whether FZS reduces Aβ25-35-induced Tau protein hyperphosphorylation in neonatal rat cortical neurons by suppressing the cyclin-dependent kinase 5 ( CDK5 ) pathway. Methods Neonatal Wistar rats born within 24 h were selected to separate and purify their cortical neurons for culture in vitro. After 7-day culture of cortical neurons in vitro, 20 μmol · L-1 Aβ25-35 was used to act on them for 24 h. Medication groups were pretreated with FZS ( 20 mg · L-1 ) , CDK5 inhibitor roscovitine ( 15 μmol · L-1 ) and cal-pain preparation calpeptin (20 μmol·L-1 ) for 24 h, followed by reaction with 20 μmol·L-1 Aβ25-35 for 24 h. Tau protein phosphorylation levels at Ser396, Ser202 and Thr231 and the protein level of CDK5 acti-vator proteins p25/p35 were assayed by Western blot. Fluorescence intensity was measured with a fluores-cence microplate reader to reflect calpain activity. CDK5 kinase activity was assayed by immunoprecipita-tion. Results After 20 μmol·L-1 Aβ25-35 acting on cortical neurons for 24h, there were increments in the following: Tau protein phosphorylation levels at Ser396, Ser202 and Thr231, CDK5 kinase activity, CDK5 activator protein p25 level, and calpain activity. In the 20 mg·L-1 FZS treatment group, Aβ25-35 was suppressed markedly, resulting in increments in Tau protein phosphorylation levels at Ser396 , Ser202 and Thr231 , suppression of CDK5 kinase activity and p25 protein level, and elevation in calpain activity. Both CDK5 inhibitor roscovitine and calpain preparation cal-peptin, as positive control drugs, also played a role in suppressing Tau protein hyperphosphorylation. Con-clusion FZS can suppress Aβ25-35-induced Tau pro-tein hyperphosphorylation in cortical neurons through the calpain/CDK5 pathway.