Research On The Mechanism Of ASMT In Depression-like Behaviors And Exercise-enhanced Neuroplasticity

Background: The world health organization(WHO)reported that depression,which accounts for 4.8% of the world's disease burden,would become the leading cause of morbidity by 2030.Therefore,it is of great social,economic and medical significance to reveal the pathogenesis of depression and find out the effective treatment methods.Sleep disorders are the main clinical symptoms of depression and anxiety disorders.Sleep disorders are one of the most prominent prodromal symptoms reflecting some depression or anxiety.Sleep disorders and melatonin disorders caused by circadian rhythm changes are major features of depression.Melatonin(MT)secreted mainly by the pineal gland of mammals has obvious circadian rhythm.Studies have shown that the polymorphism of ASMT gene is highly correlated with depression.Exercise can improve the neuroplasticity of the brain through a variety of neuromodulatory mechanisms,so as to alleviate the symptoms of depression.Therefore,the role of ASMT in the pathogenesis of depression and exercise intervention is worthy of further research.Objective: To explore whether the ASMT gene knockout leads to depression-like behaviors in mice,and further reveal the effects and mechanism of exercise on brain neuroplasticity,so as to provide a new target for the study on the mechanism of exercise intervention in depression and clinical research on depression.Methods: In this research,15 female homozygous ASMT knockout mice and 14 homozygous wild-type mice(C57BL/6 mice in the background)were selected,aged 6-7 weeks and weighing 24-25 g.The mice were divided into four groups according to the genotype,with 7-8mice in each group :(1)WT group(n = 7),namely the wild control group.(2)WE group(n =7),namely the wild exercise group;these experimental mice began to receive 5-weekswimming training when they were 6-7 weeks old;(3)KO group(n = 8),namely gene knockout group,was identified as ASMT gene knockout mice,and was raised normally without any intervention.(4)KE group(n = 7),namely the knockout exercise group;the ASMT knockout mice started to receive swimming training for 5 weeks when they were 6-7weeks old.After 5 weeks of exercise intervention,the mice in each group received behavioral test,after which,the mice were anesthetized for blood collection and hippocampal tissue.The contents of 5-HT,MT and NE were detected.The expression of neuroplasticity markers such as NeuN,GFAP,SYP and gap-43 in the hippocampus CA1 and dentate gyrus was detected by immunofluorescence.Results:(1)The results of depression-like behaviors experiment showed that compared with the WT group,KO group in sucrose preference test(SPT)of sucrose preference decreased significantly(P < 0.05),that the immobility time in the forced swimming test(FST)increased significantly(P < 0.05),and that the struggling time was significantly reduced(P < 0.01).While in the open field test(OFT),the central distance significantly reduced(P < 0.05).Compared with KO group,the sucrose preference in SPT was significantly increased in KE group(P < 0.05).(2)The results of electron microscopy showed that compared with the WT group,the PSD thickness in the CA1 area of the hippocampus in the KO group decreased significantly(P <0.05),while the width of the synaptic gap increased significantly(P < 0.01),and the number of synapses decreased significantly(P < 0.05).Compared with the KO group,the PSD thickness of the hippocampal CA1 region in the KE group was significantly increased(P <0.01),and the synaptic gap width was decreased,but no significant difference was achieved.(3)Immunofluorescence experiment showed that compared with WT group,KO groupshowed a significant decrease in NeuN expression in CA1 v region of hippocampus(P < 0.05),a significant increase in GFAP expression in CA1 d region(P < 0.05),a significant decrease in GAP-43 expression in DG region(P < 0.01),a significant increase in NeuN expression(P <0.05),a significant increase in GFAP expression,and a significant decrease in GFAP expression in CA1 d region of hippocampus in WE group(P < 0.05).Compared with KO group,GAP-43 expression in hippocampus CA1 v region of KE group was significantly increased(P < 0.05),GFAP expression significantly increased(P < 0.05),NeuN expression significantly increased(P < 0.05),GFAP expression significantly decreased(P < 0.01),GAP-43 expression significantly increased(P < 0.05),NeuN expression significantly decreased(P < 0.05),and GFAP expression significantly decreased(P < 0.05)in DG region.Conclusion:(1)ASMT gene knockout can induce depression-like behaviors in mice,and swimming training can significantly improve it.This improvement may be related to the level of serum MT and 5-HT.(2)ASMT gene knockout can cause damage to the synaptic structure in the hippocampal CA1 region in mice,and reduce the number of synapses.Swimming training can reverse the changes in the synaptic structure to some extent.(3)ASMT gene knockout can generally down-regulate gap-43,NeuN and SYP,and up-regulate GFAP expression in the hippocampus CA1 v,CA1d and DG regions.Swimming training can reverse these changes to some extent,but further up-regulate GFAP expression in the CA1 v region.Significance: In this research,ASMT knockout mice were used as animal models to explore whether the melatonin secretion disorder caused by ASMT gene knockout could inducedepression-like behaviors in mice,which is a new exploration on the animal model of depression.Secondly,brain neuroplasticity was used as the entry point to study the mice with ASMT gene knockout,and to explore the influence of exercise intervention on mice's depression-like behaviors and its mechanism,so as to provide more solid evidence for the anti-depression effects of exercise.