Research On Molecular Mechanism Of Schizophrenia Caused By Two Immune Activations Through Using Mouse Model

BackgroundSchizophrenia is one of the most common mental diseases in human beings,and its clinical manifestations are complex and diverse.Recent studies suggest that both genetic and environmental factors contribute to the development of schizophrenia.Accumulating lines of evidence have shown that infection during pregnancy increasethe risk of schizophrenia in offspring and adolescent stress also increase the risk.Both the pregnant infection and adolescent stress activate immune system,however,the underlying molecular mechanism linking the immune activation to schizophrenia remains unknown.At present,the mainstream hypothesis believes that two hits work through the immune system,but what role the immune system plays in schizophrenia and how it affects disease progression still need further exploration.Therefore,we built "two-hit" mouse model for schizophrenia and illustrate the molecular mechanism linking immune activation to schizophrenia.ObjectiveWe need to make animal model for schizophrenia using two immune activations,and to illustrate the underlying molecular mechanism.MethodsThe content of this study was mainly divided into three parts:(1)Introperitoneal injection of lipopolysaccharide during pregnancy and puberty,mimicking bacterial infection,was carried out to establish "two-hit" mouse model,and behavioral tests were carried out to evaluate the "two-hit" mouse model.(2)In order to investigate the short-term and long-term immune system activation of mice subjected to immune activation at different times,immunofluorescent on brain sections was performed to detect the status of microglia activation on the postnatal day 32,37,50 and postnatal day 70.(3)The whole mouse brain was extracted for transcriptome sequencing analysis to search for molecular pathways involved in the development of schizophrenia caused by immune activations.ResultsBehavioral tests.Mice subjected to two lipopolysaccharide(LPS)injectionsin the open field test showed a significant increase in locomotor activity,but less center time compared with controls,suggesting that the "two-hit" mice have anxiety.Elevated plus maze also show the same anxiety in mice.Moreover,the "two-hit"mice showed significantly reduced the prepulse inhibition,which meets the criteria for animal model of schizophrenia.The three-chamber tests showed that the the"two-hit" mice showed significant social withdrawal and apathy compared to the controls.Other stereotyped behaviors and memory dysfunction did not show significant differences between the "two-hit" mice and controls.Immunofluorescence staining on the brain tissues.The "two-hit" mice showed higher activation than mice subjected to a single hit during pregnancy or adolescence,"one-hit" mice showed higher activationcompared the two-saline-treated mice,while two-saline-treated miceshowed higher immune activation compared to blank control group(standard-reared mice).Transcriptome sequencing on the whole brain showed that,on the postnatal day 32(i.e.,early adolescence),compared with the control group,the differentially expressed genes(DEGs)in mice subjected a single LPS injection during puberty were 2724,the DEGs in mice subjected a single LPS injection during pregnancy were751;while DEGs in mice with two LPS injections during pregnancy and puberty were 4545.On the postnatal day 50(i.e.,post-pubescent),compared to the control group,the DEGs in mice subjected a single puberty hit were 3221;the DEGs in mice subjected a single pregnant hit were 2454;DEGs in mice with two hits during pregnancy and puberty were 825.Functional enrichment analyses on the DEGs showed that the enriched Gene ontology(GO)terms and KEGG pathways in the brain of mice immune-activated at P32(short term after immune activation)mainly include pathways involved in nervous system development,axon cell generation and development,and immune activation,while the enriched Gene ontology(GO)terms and KEGG pathways in the brain of mice immune-activated at P50 include neurodegenerative disease-related pathways such as Huntington’s disease and Alzheimer’s disease.ConclusionIn short,we have constructed a "two-hit" mouse model,examined the morphology of microglia in the brain and performed transcriptome sequencing on the whole brain to search for relevant biological processes and molecular signaling pathways.We found that immune activation during pragenancy and during puberty may play a role in the development in schizophrenia through activation of mircoglia,which in turn affect synapes and nervous system development.