The Effect Of LPS Induced Microglia M1 Polarization On The Anxiety-like Behavior In Mice

ObjectiveTo explore the effect of M1 polarization of microglia induced by lipopolysaccharide(LPS)on anxiety-like behavior in mice.In order to further prove the effect of LPS,inhibitory peptide of Myeloid differentiation factor 88(Myd88)was applied to this study.Materials and MethodsAdult male C57 mice were randomly divided into four groups,namely control peptide-control group(CP-Con)with Control peptide of Myd88 inhibitor(CP)in the first day and normal saline(0.9% NaCl solution)injection to the brain the next day,Myd88 inhibitory peptide-control group(MIP-Con)with the Myd88 inhibitory(MIP)in the first day and NaCl injection to the brain the next day,CP-LPS group with(CP)in the first day and LPS injection in brain the next day,MIP-LPS group with the(MIP)in the first day and LPS injection to the brain the next day.Forty-eight hours after the last intracerebral injection,behavioral tests including open field and elevated plus-maze tests were conducted to observe the anxiety-like behavior of the mice.After that,immunofluorescent staining and Western blot were applied to the mice's brain to detect the expression of inducible nitric oxide synthase(iNOS)and Arg-1inase-1(Arg-1-1)in bilateral medical prefrontal cortex(mPFC)and hippocampus to identify microglia polarization in these brain regions.Western Blot was also used to detect the expression of iNOS and Arg-1-1,proinflammatory cytokine including tumor necrosis(TNF)-?and interlukin-1(IL-1)? and phosphorylated IRF3(p-IRF 3),the important molecular P-IRF3 of the Myd88 independent pathway was also explored.Results1.We clearly found that in open field test,mice in CP-LPS group spent significant less time and ran shorter distances in the center zone,compared with the other three groups.And the MIP-LPS groups appears less anxiety-behavior compared with CP-LPS group.In the elevated plus-maze test,LPS treated mice spent less time in the open arm than the control group.And also the MIP-LPS groups appears less anxiety-behavior compared with CP-LPS group.2.Immunofluorescent staining showed that microglia polarized to M1 type as iNOS expression was upregulated in microglia in CP-LPS group,while microglia polarized to M2 type as Arg-1 expression was upregulated in microglia in MIP-Con and MIP-LPS groups.3.Western Blot showed that the expression of proinflammatory cytokines IL-1?and TNF-? were significantly increased in the brain treated with CP-LPS.It also shows that iNOS expression was upregulated in microglia in CP-LPS group,and Arg-1-1expression was upregulated in microglia in MIP-Con and MIP-LPS groups.The important molecular p-IRF3 of the Myd88 independent pathway was also upregulated in the brains of MIP-Con and MIP-LPS groups.The expression level of TLR4 was the lowest in CP-Con group,compared to other group.ConclusionThese data suggest that M1 polarization be induced by LPS and may cause the anxiety-like behavior in the mice.And MIP can reverse the anxiety-like behavior through the Myd88 independent signal path via microglia polarization.