Effect Of PJ34 On Wortmannin-induced Spatial Memory Impairment And The Underlying Mechanism

Formation of neurofibrillary tangles composed of aberrantly hyperphosphorylated tau protein is one of the hallmarks of Alzheimer's disease (AD). Many studies have demonstrated that an imbalanced regulation of specific phosphatases and kinases in neurons represented a critical step for the microtubule-associated protein tau hyperphosphorylation. Glycogen synthase kinase-3 (GSK-3), one of the most important protein kinases in brain, plays an important role in tau hyperphosphorylation. Overactivation of GSK-3 induced by wortmannin (WT) can produce AD-like pathologies and imply that upregulation of GSK-3 is promising in establishing models for the drug screening, while the upstream effectors of GSK-3 in AD brains are not clear. It is reported that poly(ADP-ribose) polymerase-1(PARP-1) gene is highly associated with AD and the increased PARP-1 maybe activate GSK-3, so we thought PARP-1 maybe promote the development of AD through regulating GSK-3.In this study, we investigated the effect of PARP-1 inhibitor PJ34 on spatial memory impairment of mice and tau hyperphosphorylation induced by WT and the underlying molecular mechanisms. The results were as follows:(1) Morris water maze results showed that WT-administration through lateral ventricle impaired the spatial memory of mice, pre or post injection of PJ34 could restore the spatial memory impairment of mice, P J34-treatment mice displayed a stochastic searching path and much shorter latency. (2) Immunohistochemistry results showed that an obviously enhanced immunoreaction at tau Ser396, Thr231 and Thr205 epitopes, and decreased staining of tau-1 and Ser214 in CAl and CA3 regions of hippocampus were observed after treatment with WT suggesting hyperphosphorylation of tau at these sites, and tau hyperphosphorylation was attenuated remarkably after co-application of PJ34 at Serl 95/198/199/202 (Tau-1) sites. (3) To further explore the mechanisms of PJ34, we treated HEK293/tau441 cells with different dose of PJ34 for 24 hours. We found the tau phosphorylation were decreased in sites Thr231, Ser396, Thr205, while the phosphorylated tau at Ser214 site, and against unphosphorylated tau at tau-l(Serl95/198/199/202) site were increased, while the total level of tau probed by tau-5 showed no obviously change. (4) The increasing of phosphorylated tau was related with activity of glycogen synthase kinase-3 (GSK-3). The different treatments showed that the activity of GSK-3 was increased after WT administration, PJ34 could inhibit the activity of GSK-3. The activity of Akt was converse with GSK-3 in different groups. (5) The Nissl staining results showed that nissl bodies decreased slightly after WT injection, while PJ34 can partially restore the staining. It suggested that PJ34 can increase the function of neurons. (6) WT treatment can down-regulate the number of dendritic spines and impair the structure of neurite, co-administrated with PJ34 partially against the inhibition of spinogenesis injury induced by WT. (7) Different dose of PJ34 could inhibit the poly(ADP-ribosy) lation of itself, indicating the inactivity alternation of PARP-1. Conclusion:WT supplement increased the level of phosphorylated tau, altered the stability of dendritic spines and neuritis and impaired the spatial memory of mice through GSK-3 activition, PJ34 treatment inhibited the activity of PARP-1, attenuated WT-induced activation of GSK-3, caused tau dephosphorylation and attenuated the impairment of mice.