The Effects Of Chemokine CCL19 On Cognitive And Emotional Behavior

Emotion and cognition belong to the advanced neuropsychiatric activities,and are also the important part of brain science.Intriguingly,immune system mostly contributes to the activity of central nervous system including immune cells and immune molecules such as cytokines and T cells.Additionally,psychiatric disorders are closely related to the inflammation in immune system,which could be showed by the common clinical phenomenon called “comorbidity” between central nervous system and immune system,including multiple sclerosis and anxiety disorder,diabetes and Alzheimer’s disease.Cytokines and chemokines play an essential role on the of the "comorbidity" phenomenon such as Alzheimer’s disease,and mood disorders such as anxiety and depression.In 2011,the team of Tony Wyss-Coray mentioned the parabiosis model which has been recognitive by the excellent rejuvenation effect on the old mice by the young mice.This paper screened 6 system factors basing on the the series of researches of parabiosis model and thought that these six system factors might exert an important effect on the central nervous system function.Surprisingly,four of the six factors are chemokines and CCL19 is included.Chemokines CCL19 belongs to chemokine CC family and its receptor is CCR7,which plays the chemotaxis on immune cells,such as T cells,B cells and DC cells,as well as maintaining the lifespan of T cells and DC cells.However,in recent years,researches have shown that astrocytes and endothelial cells in the brain can secrete chemokine CCL19,and the astrocytes in the hippocampus and corpus callosum can express CCR7 receptor.The central nervous system inflammatory response is also accompanied by chemokines CCL19 level abnormalities,such as multiple sclerosis,cerebral ischemic injury.For the neuroinflammation disease patients,the blood and cerebrospinal fluid of chemokines CCL19 expression levels are unusually high.Additionally,a large number of literatures suggested that expression of CCL19/CCR7 is related to the disease of central nervous system,and might be closely related to cognitive function.What that proves is the ccr7 knockout mice showed impaired learning and memory,as well as depression and anxiety disorders.However,there has been no research showing the effect of chemokine CCL19 on emotion and cognition.Our paper conducted the wild C57BL/6 mice and CUMS model mice to study the effect of chemokine CCL19 on emotion and cognition.And we study the mechanism of this process by the way in terms of immune way and central nervous system.Part I.Effect of chemokine CCL19 on the emotion-and cognition-like behavior of wild micebehavior of wild mice 1.Effect of chemokine CCL19 on the emotion-and cognition-likeIn order to study the effect of CCL19 on the cognitive-like behavior and emotional-like behavior,we conducted the 2-3 month C57BL/6 mice injected CCL19(10 ug/kg)12 times by intraperitoneal injection.Choosing the radial arm water maze(RAWM)evaluated the cognition-like behavior,the elevated zero maze for the anxiety and sucrose water consumption for depression.Results showed that chemokines CCL19 didn’t affect the errors in RAWM,however significantly affect the time in open arm of elevated zero maze,and sucrose consumption.All the results suggested that chemokines CCL19 didn’t contribute to cognition-like behavior,but has significant impact on the emotion-like behavior such as depression and anxiety.But we need more studies to verify the effect of CCL19 on the anxiety and depression.2.Effect of chemokine CCL19 and CCL21 on the emotion-like behavior of wild mice and the counteracting effect of their antibodyThe results above demonstrated that the chemokine CCL19 has a significant effect on emotion-like behavior,but the effect on depression or anxiety remains unclear.And it is also unclear whether this effect is CCL19-dependent or CCR7-dependent.As well as the effect of the chemokine CCL19 on emotion-like behavior is mediated by the peripheral immune system indirectly or into the central nervous system directly.Therefore,we studied the effects of chemokine CCL19 on anxiety and depression of wild mice and the counteracting effect of their antibody.And we designed a chemokine CCL21 intraperitoneal injection group which was paralleling to chemokine CCL19 to determine whether the CCL21 has the same effect as the chemokine CCL19,thereby studied whether the effect of the chemokine CCL19 on emotion-like behavior is CCL19-dependent or CCR7-dependent.Furthermore,we investigated whether the effect of CCL19 on emotion-like behavior could be blocked by injecting chemokine CCL19 antibody into the lateral ventricle to confirm that the effect of chemokine CCL19 is achieved directly through the central nervous system or indirectly through the peripheral immune system.This section conducted the 2-3 month C57BL/6 mice injected CCL19 and CCL21(10 μg/kg)12 times by intraperitoneal and injected antibody of CCL19 and CCL21 in lateral ventricle for one time.Choosing the elevated plus maze and open field test for the anxiety and sucrose water consumption and forced swimming test for depression.Results showed that chemokine CCL19 could significantly increase the sucrose consumption and decrease the immobility time.However,the center time in open field test and time in open arm of elevated plus maze were not changed.After the antibody injected,the counteracting effect was not showed significantly.In summary,the chemokine CCL19 might exert an anti-depression effect,and the effect of CCL19 is unique but not the CCR7-dependent.And the effect of CCL19 might have weak relationship with brain directly,but might have strong relationship with immune system.PartⅡ.Effect of chemokine CCL19 on the anxiety and depression like behavior of chronic unpredictable mild stress(CUMS)miceThe results above showed that chemokine CCL19 has a significant effect on depressive behavior of wild mice,and it suggested that the possible antidepressant effect.However,due to the differences between physiological condition and pathological condition,the sensitivity of body to changes of system factor may vary greatly.Therefore,we used the CUMS model mice to investigate the antidepressant effect of chemokine CCL19.This part of experiment evaluated the antidepressant effect of chemokine CCL19 and the combination of CCL19 and fluoxetine on the depression and anxiety like behavior of CUMS model mice.Chemokine CCL19 was administrated by intraperitoneal for 14 times(10 μg/kg),the fluoxetine was administrated by intraperitoneal for 10 days(10 mg/kg).Choosing the elevated plus maze and open field test for the anxiety and sucrose water consumption and forced swimming test for depression.Results showed that CUMS model mice showed the anxiety and depression like behavior and the fluoxetine significantly ameliorate the depression like behavior.Remarkably,chemokines CCL19 also significantly improved the depression like behavior.But the combination of CCL19 and fluoxetine had no obvious effect.And all the drug had no effect to the anxiety like behavior.The results suggest that chemokine CCL19 has antidepressant effect and may be a potential antidepressant target.Part Ⅲ.The mechanism of the interaction between chemokine CCL19 and depression like behaviorThe above results suggested that chemokine CCL19 is closely related to antidepressant effect.To study the effects of chemokine CCL19 on depression.In this part,we evaluated the mechanism of the effect of chemokine CCL19 on depression from both the immune system and the central nervous system pathway.1.Effect of chemokine CCL19 on the peripheral immune systemAs we now know,chemokines CCL19 is an important factor for immunity and has chemotaxis to immune cells such as T cells,B cells,DC cell,and participate in maintaining lifespan of T cells.Therefore,we first studied the effect of chemokine CCL19 on the number of immune cells in blood by flow cytometry,and observed the proliferation of spleen lymphocytes in mice by [3H]-Td R incorporation test.Then,we investigated the level of cytokine and chemokine in blood by Luminex.The results showed that chemokines CCL19 obviously inhibited the proliferation of T cells and B cells in the spleen lymphocyte with the antigen LPS and Con A.However,CCL19 differently regulated the different population of T cells,showed that increasing in the number of regulatory T cells,and reducing the number of CD4 +,CD8 + T cells.On the contrary,chemokine CCL21 showed significant stimulating both the lymphocytes proliferation,and its regulation on the number of immune cells was different from that of CCL19.In the physiological state,chemokines CCL19 significantly reduced the expression of RANTES in the hippocampus and increased the concentration of anti-inflammatory cytokines IL-10 in plasma.Compared with the CUMS model group,chemokine CCL19 injected by intraperitoneal can significantly increase the level of CX3CL1 in the hippocampus and decrease the expression of CCL17 and IL-1β in the plasma.The experimental results indicated that chemokine CCL19 had anti-inflammatory effects and had different regulation effects on different subgroups of T cells and anti-inflammatory factors and pro-inflammatory factors.Chemokine CCL19 injected by intraperitoneal in the wild mice couldn’t affect the concentration of CCL19 neither plasma nor hippocampus.However,chemokine CCL19 injected by intraperitoneal in the wild mice obviously increased the concentration of chemokine CCL19 in hippocampus.The results suggested that chemokine CCL19 may not be able to penetrate the blood brain barrier in the physiological condition,but it can penetrate the blood brain barrier and enter the brain parenchyma in the pathological condition of CUMS.2.Effect of chemokine CCL19 on the central nervous systemIt has been reported in the literature that chemokines may act as a kind of neuromodulator in the brain and regulate neurotransmitters.However,there are no researches about the effects of chemokines on neurotransmitters in the brain when chemokines are used as a systemic factor,.Therefore,this part of study investigated the effects of chemokine CCL19 on amino acid neurotransmitters and monoamine neurotransmitters in brain by HPLC.The experimental results showed that the chemokine CCL19 had a reduced effect on the excitatory amino acid neurotransmitters such as glutamate and aspartate in the hippocampus of wild mice and has no significant effect on inhibitory amino acid neurotransmitters such as glycine and GABA.The chemokine CCL19 inhibited both dopamine and norepinephrine in the hypothalamic region of mice.In summary,this topic could conclude as following:The chemokine CCL19 has no significant effect on cognitive-like behavior of wild mice,but it has a obvious effect on emotion-like behavior of wild mice.The chemokine CCL19 has a significant effect on depression-like behavior of wild mice and has no significant effect on anxiety-like behavior of wild mice.The effect of chemokine CCL21 on depression-like behavior of wild mice was not significant,suggesting that the effect of the chemokine CCL19 on mood is specific.The chemokine CCL19 has an intriguingly improved effect on depression of CUMS model mice,suggesting that the chemokine CCL19 might have an antidepressant effect.The chemokine CCL19 has a significant anti-inflammatory effect and differentially regulates different subpopulations of T cells.The chemokine CCL19 cannot enter the brain under physiological conditions but can enter the brain under pathological conditions of CUMS.It is suggested that the antidepressant effect of chemokine CCL19 may be related to its anti-inflammatory effect and its direct effect on the central nervous system.The chemokine CCL19 significantly inhibited the excitatory neurotransmitters such as glutamate and aspartate in the hippocampus of wild mice and markedly reduced dopamine and norepinephrine in the hypothalamus.In summary,the chemokine CCL19 is closely related to depression-like behavior and has a significant antidepressant effect.This antidepressant effect may be related to the inhibition of hippocampal excitatory neurotransmitters and hypothalamic dopamine level,and is closely related to the anti-inflammatory effects of chemokine CCL19.