The Protective Effects And Mechanisms Of FTY720 On Chronic Unpredictable Mild Stress-induced Depressive-like Behavior In Mice

The hippocampus is a critical structure involved in cognition and emotion processes,which is susceptibility to stress.Chronic stress induced structural and functional changes in the hippocampus,resulting in mood disorder.S1 P receptor modulator FTY720 is the first orally administered drug to treat multiple sclerosis?MS?through regulating immunity.In addition,existing researches indicated the neuroprotective effects of FTY720.The present study aimed to investigate whether FTY720 could alleviate depressive-like behaviors induced by chronic unpredictable mild stress?CUMS?and possible neuroprotective mechanisms.We used the chronic unpredictable mild stress model to simulate chronic stress.Adult ICR mice?18-22g?were submitted daily to two or three different stressors for 4 weeks in a chronic and unpredictable way.Mice were injected with FTY720?0.3,1mg/kg?or vehicle?normal saline?30 min before stress for 28 days.The body weight was recorded once every two days.After stressor cessation,the depressive-like behaviors were determined by sucrose prefer test?SPT?,forced swimming test?FST?,tail suspension test?TST?and non-spatial memory;morphology of hippocampal neurons was examined by HE staining.The expression of Ki67,DCX and NeuN was detected by immunofluorescence,and the levels of NeuN,DCX,Bcl-2,Bax,p-Akt,p-GSK-3bm-TOR andb-catenin of hippocampal tissues were examined by western blot.Our results:1.FTY720 did not affect the rate of body weight gain of CUMS mice.CUMS significantly decreased the rate of body weight gain of mice,while FTY720?0.3,1 mg/kg?treatment did not inhibit the reduction of rate of body weight gain.2.FTY720 alleviated depressive-like behaviors in CUMS mice.CMUS mice showed significantly less sucrose consumption in the SPT,and spent significantly more time immobile both in the FST and TST.Compared with stressed mice,Mice treated with FTY720?0.3mg/kg and 1mg/kg?showed significant increased sucrose consumption,and decreased immobility time.3.FTY720 rescued memory impairment in CUMS mice.CUMS mice spent more time to explore the displaced old object,FTY720?0.3,1mg/kg?treatment increased the identification of new object.4.FTY720 alleviated CUMS-induced apoptosis in the CA1 and CA3 region of hippocampus.The results of HE staining showed that significant degenerated neurons were observed in the hippocampus CA1 and CA3 of CUMS mice.FTY720?1mg/kg?treatment significantly alleviated the neuronal degeneration in the hippocampus CA1 and CA3.5.FTY720 treatment reversed the CUMS-induced down-regulation of Bcl-2 and up-regulation of Bax in the hippocampus.Western blot analysis showed that the protein level of Bcl-2 was decreased and the Bax was increased in the hippocampal of CUMS mice.FTY720?1mg/kg?increased the protein expression of Bcl-2,as well as restrained the protein expression of Bax.6.FTY720 alleviated neurogenesis deficiency in hippocampal induced by chronic unpredictable mild stress in mice.The results of immunofluorescence showed that the number of proliferating cells?Ki67 positive?and new neurons?DCX positive?decreased significantly in the hippocampal DG area of CUMS mice.FTY720?1mg/kg?treatment significantly increased the number of proliferating cell?Ki67positive?and new neuron?DCX positive?in the hippocampal DG.Western blot analysis showed CUMS down-regulated the expression level of DCX.FTY720?1mg/kg?reversed the CUMS-induced down-regulation of DCX.7.FTY720 has no influence on the mRNA and protein level of S1 PRs.RT-qPCR showed that CUMS didn't influence the mRNA level of S1PR₁?S1PR₂?S1PR₃?S1PR₅.Western blot showed that the protein level of S1PR₁ and S1PR₃ are comparable between experimental groups.FTY720 had no effects on the expression level of S1PR₁ in the hippocampus of CUMS mice.8.FTY720 activated Akt/GSK-3?signaling pathways in the hippocampus of CUMS mice.Western blot analysis showed that the levels of p-Akt,p-GSK-3?,p-mTOR and?-catenin in the hippocampus of CUMS mice were significantly decreased.FTY720?1mg/kg?treatment significantly increased the level of p-Akt and p-GSK-3?.However,FTY720 treatment didn't influence the protein level of p-mTOR and?-catenin.Conclusion:FTY720 alleviated CUMS-induced apoptosis in hippocampus,promoted neurogenesis deficiency,activated Akt/GSK-3?signaling pathways and protected against CUMS-induced depressive-like behaviors.Our finding suggested that S1 P receptor modulator FTY720 might be potential drugs for protecting hippocampal function from chronic stressed injury.