The Synergic Role Of Caspase-3and Caspase-6Aggravates Tau Truncation At D421Induced By H₂O₂

Background: Two main hallmarks of Alzheimer’s Disease (AD) are senileplagues (SP) caused by β-amyloid deposits and neurofibrillary tangles(NFTs) caused by abnormal post-modifications of tau protein. It has beenproposed that reactive oxygen species (ROS) participate in AD. Tautruncation is one of the abnormal post-translational modifications of tauprotein and acts as the core of paired helical filaments (PHFs), which isclosely associated with AD. In addition, caspase-3and caspase-6aresuggested to induce tau truncation at D421in vivo and in vitro. Therefore,we make the hypothesis that H2O2can induce tau truncation at D421through caspases and caspase-3and caspase-6play a synergic role in tautruncation at D421.Objective: To explore whether H2O2induces tau truncation at D421through the synergic role of caspase-3and caspase-6in HEK293cellstransfected with tau441. Then we further study the interaction of caspase-3and caspase-6in tau truncation mediated by H2O2.Methods: After cell transfections and treatment, cell viability as well asMDA and SOD activity were detected to verify the establishment ofoxidative stress model; western blotting was utilized to test the effects ofH2O2and NAC on tau truncation at D421; caspase-3and caspase-6inhibitors (z-DEVD-fmk and z-VEID-fmk) along with specific siRNAagainst caspase-3and caspase-6were employed to explore whether bothcaspase-3and caspase-6contribute to tau truncation at D421and both theactivities of caspase-3and caspase-6were detected by commercial assaykit; after inhibition of caspase-6by specific inhibitor and targeted siRNA, caspase-3activity was tested by western blotting and assay kit to study therelationship between caspase-3and caspase-6.Results:(1) H2O2can cause cell damage and induce oxidative stress.(2) Tau truncation at D421increased in a dose dependent manner withH2O2. When HEK293/Tau cells were pretreated with NAC, tau truncationdecreased significantly.(3) When specific caspase-3and caspase-6inhibitors were employed,western blotting analysis demonstrated that they played a synergic role intau truncation at D421induced by H2O2. Similar results were obtainedwhen cells were transfected with specific siRNA targeted to caspase-3andcaspase-6. The conclusion was also confirmed by the assay of caspase-3and caspase-6activity.(4) During H2O2insult, inhibition of caspase-6led to a decrease incaspase-3activation.Conclusion: Caspase-3and caspase-6play a synergic role in tautruncation at D421induced by H2O2. Caspase-6may cleave caspase-3andlead to caspase-3activation, thus giving rise to more tau truncation. Thestudy of the interaction of caspase-3and caspase-6may provide new targetfor potential AD therapy in the future.