Mechanisms Of Neuroinflammation And Neuroplasticity In Swimming Exercise Therapy For Depression Induced By Chronic Unpredictable Mild Stress

Background:Depression is the most common mental and psychological disease,with low mood,retardation of thinking and hypovolitional activity as the main clinical manifestations.Approximately 5.0%of adults worldwide suffer from depression,and depression is now the most serious non-fatal neuropsychiatric disorder and is projected to become the most serious global burden of disease by 2030.Consequently,early prevention and early diagnosis and treatment are of great significance.It is urgent to study the pathogenesis of depression and develop new therapies in clinical treatment.At present,the treatment methods of depression mainly include pharmacotherapy,psychological therapy,biological interventions and naturopathic interventions.Antidepressants play a significant role in the treatment of depression and are widely used.However,they have long side effects with poor compliance.Patients usually prefer to choose non-drug therapy.In recent years,exercise therapy as a non-pharmacological treatment is gaining momentum and is a new viable option for the treatment of depression.Its advantages include straightforward operation,low cost,fewer side effects and positive effects on the overall body function,etc.More and more basic and clinical studies show that exercise relieve the symptoms of depression.And in clinical application,it can be used as an adjuvant therapy or a single therapy to treat depression.However,the molecular mechanism of exercise therapy in the treatment of depression is not fully clarified.Objectives:This study was aimed to explore the effect of swimming exercise for the depressive behaviors induced by chronic unpredictable mild stress(CUMS),and the alteration of the gut microbiota influenced by the two factors,to further explore the antidepressant mechanisms of swimming exercise related to neuroinflammation and neuroplasticity,to provide new basis for the treatment of depression.Methods:1.Effects of swimming exercise on depression-like behavior induced by chronic unpredictable mild stressA 6-week CUMS exposure was used to build the mice model of depression,thena 5-week swimming protocol was used to construct the mice model of exercise therapy.Open field test(OFT),elevated plus-maze(EPM)test,tail suspension test(TST)and sucrose preference test(SPT)were conducted after the two procedures,to detect the depression-like behavior of mice.2.Effects of swimming exercise and chronic unpredictable mild stress on composition and metabolic pathways of gut microbiotaAfter constructing CUMS and swimming mice model,16SrRNA gene sequencing technology was used to explore the effects of CUMS and swimming exercise models on the composition and metabolism of gut microbiota in mice,and to explore whether the abundance and metabolic pathways of gut microbiota were regulated.3.Effects of swimming exercise on neuroinflammation and neuroplasticity in depressive-like mice induced by chronic unpredictable mild stressAfter constructing CUMS and swimming mice model,Western blot and Immunofluorescence staining were utilized to determine the expressions of NLRP3,Ibal,procaspase-1 and cleaved caspase-1 in the hippocampi of the mice,and the expressions of AKT,GSK3β,and CRMP2 and the expressions of their phosphorylations.In addition,the expressions of Tyr-tubulin and Acet-tubulin related to microtubule dynamics were detected.4.Effects of regulation of neuroinflammatory pathways on chronic unpredictable mild stress and swimming exercise,and related molecular alterationsAfter constructing CUMS and swimming mice model,brain stereotaxic surgery was conducted to inject AAV-NLRP3 to bilateral hippocampus of mice to overexpress NLRP3.Four behavioral tests were conducted to detect the depressionlike behavior of mice.Subsequently,western blot and immunofluorescence staining were used to detect the molecular expressions related to neuroinflammation and neuroplasticity,verifying the effects of swimming exercise on neuroplasticity and neuroinflammation.Results:1.Effects of swimming exercise on depression-like behavior induced by chronic unpredictable mild stressA 6-week CUMS exposure induced depressive-like behavior,while a 5-week swimming exercise protocol improved CUMS-induced depression-like behaviors.2.Effects of swimming exercise and chronic unpredictable mild stress on composition and metabolic pathways of gut microbiotaAt phyla level,CUMS significantly affected the relative abundance of Firmicutes and Bacteroidetes.CUMS increased the relative abundance of Firmicutes and decreased the relative abundance of Bacteroidetes.At genus level,CUMS significantly affected the relative abundance of Streptococcus and p-75-a5.CUMS increased the relative abundance of Streptococcus and p-75-a5.Among the metabolic pathways,aromatic biogenic amine degradation(PWY-7431),mono-trans and polycis decaprenyl phosphate biosynthesis(PWY-6383),chlorosalicylate degradation(PWY6107),mycothiol biosynthesis(PWY1G-0),mycolyl-arabinogalactan-peptidoglycan complex biosynthesis(PWY-6397),toluene degradation Ⅰ(aerobic)(PWY-5180),toluene degradation Ⅱ(aerobic)(PWY-5182),starch degradation Ⅲ(PWY-6731)and L-histidine degradation Ⅱ(PWY-5028),may be related to the mechanism of anti-depression effect.3.Effects of swimming exercise on neuroinflammation and neuroplasticity in depressive-like mice induced by chronic unpredictable mild stressSwimming exercise reduced the expression of NLRP3,Ibal,procaspase-1 and cleaved caspase-1 in the hippocampus of CUMS mice.Swimming exercise increased the expression level of p-Akt,p-GSK3β and CRMP2 in hippocampus of CUMS mice,but decreased the expression level of p-CRMP2.Swimming exercise increased the expression of Tyr-tubulin and decreased the expression of Acet-tubulin in hippocampus of CUMS mice,increasing the microtubule dynamics.Swimming exercise increased the interaction between CRMP2 and a-tubulin in the mouse hippocampus.4.Effects of regulation of inflammatory pathways on chronic unpredictable mild stress and swimming exercise and related molecular alterationsSwimming exercise improved CUMS-induced depression-like behavior in mice,while NLRP3 overexpression inhibited the improvement.Laboratory tests suggested that NLRP3 overexpression increased the expression of NLRP3,Ibal,procaspase-1 and cleaved caspase-1 in the hippocampus of CUMS and exercised mice.The overexpression of NLRP3 decreased the expression of p-Akt,p-GSK3β and CRMP2,and increased the expression of p-CRMP2 in hippocampus of CUMS and exercised mice.Overexpression of NLRP3 decreased the expression of Tyr-tubulin and increased the expression of Acet-tubulin in hippocampus of CUMS and exercised mice,decreasing microtubule dynamics.Overexpression of NLRP3 reduced the interaction between CRMP2 and α-tubulin in the hippocampus of CUMS and exercised mice.Conclusions:In conclusion,this study suggested that a 5-week swimming exercise alleviated the depression-like behaviors in mice induced by CUMS.In addition,CUMS and swimming exercise regulated the composition and metabolic pathways in gut microbiota.Further molecular detection hinted the antidepressant mechanism of swimming was involved in the alleviation of neuroinflammation and enhancement of neuroplasticity.This study is expected to provide new clues for non-drug treatment of depression and lay a foundation for the application of exercise therapy to clinical treatment in the future.