The roles and related mechanisms of PP2A in cognitive dysfunction after the chronic cerebral ischemia

Abstract

Objective To explore the roles and related mechanisms of Protein Phosphatase 2A(PP2A)in cognitive dysfunction after the chronic cerebral ischemia. Methods 70 male Sprague Dawley rats in clean degree were divided into sham group, chronic cerebral ischemia group(Bilateral carotid arteries occlusion, 2VO), and chronic cerebral ischemia group with PP2A activation group(2VO+ aPP2A). The rats were injected intraperitoneally with 1.88 μmol/ml sodium selenate(15 μmol·kg-1·d-1) or equal volume of saline for 4 weeks. After one month, the chronic cerebral ischemia models were reproduced by the occlusion of bilateral common caroid artery. Then the abilities of learning and memory were tested by Morris water maze, electrophysiological indices were recorded to analyze the LTP changes, and destribution of synaptic vesicles was observed by electron microscope. Results Morris water maze test showed that the 2VO group had significantly longer latent time than sham group in searching platform(P<0.05), and the 2VO+ aPP2A group had dramatically shorter latent time(P<0.01) than that of 2VO group. Then removing platform to test the rats` memory, the data showed that 2VO group spent markedly longer time than sham group to reach the location of the former platform (sham group: (14.50±1.98)s ; 2VO group: (17.30±2.11)s) (P<0.01), and the 2VO+ aPP2A group((15.09±1.45)s) spent dramatically shorter latent time(P<0.05) than that of 2VO group. The electrophysiological data showed that 2VO group had the noticeably smaller field excitable postsynaptic potential slope( fEPSP) slope ratio between pre and post of the high frequency stimulations(Long-term potential, LTP) than sham group(sham group: 1.69±0.27; 2VO group: 2.02±0.137)(P<0.01), and the 2VO+ aPP2A group(1.86±0.19) had strikingly higher ratio than that of 2VO group(P<0.01). The electromicroscope observation showed that presynaptic vesicles density of 2VO was remarkably lower than that of sham group(sham group: (4.51±0.29) /μm2; 2VO group: (2.02±0.14) /μm2 ) (P<0.01), and presynaptic vesicles density of 2VO+ aPP2A group((3.58±0.50) /μm2) was noticeably higher than that of 2VO group(P<0.01). Conclusion Activating PP2A can prevent the cognitive dysfunction after chronic cerebral ischemia through regulating LTP and synaptic vesicle density. And PP2A is probably a potential target for preventing and treating the cognitive dysfunction after chronic cerebral ischemia. Key words: Chronic cerebral ischemia; PP2A; Dysfunction of learning and memory