The Variation Of TET2 In The Transmission Of Inflammation From The Periphery To The Central Nervous System And Its Relevance To The Expression Of IL-6 In Mesencephalon

Objective : To explore whether the The Methylcytosine Dioxygenase Ten-Eleven Translocase-2(TET2)in the rat mesencephalon is involved in the process of central nervous system(CNS)immune activation induced by peripheral inflammation and the relationship between TET2 and the expression of inflammatory factors such as IL-6.Methods:The rats were randomly divided into normal control group without any disposal(N),peripheral inflammation group(A)and peripheral blood monosytes depleted group(B).The rats of group A injected with 5mg/kg lipopolysaccharide(LPS)intraperitoneally only once.Before treated with 5mg/kg LPS,group B were received an caudal vein injection with clodronate liposome(CL).Killing rats at 4 different time points,and taking out the midbrain tissue to extract the total protein and RNA.The frozen sections of mesencephalon part were prepared for immunofluorescence staining.Then the relative mRNA level of various inflammatory factors such as IL-6、TNF-α and IL-1β was detected by RT-qPCR.Immunofluorescence was used to detect the morphology and the number of microglia and the expression of TET2 protein in the midbrain.Western blot was used to quantitative analyze the expression level of TET2 protein in the mesencephalon.Results : 1.Compared with the normal control group(group N),the number of microglia in the midbrain of rats was significantly increased after peripheral inflammation induced by intraperitoneal injection of LPS.Microglia of quiescent pherotype transform into an amoeboid phagocytic pherotype.At the same time,the expression of IL-6,IL-1 β,TNF-α presented an time-dependent up-regulating trend progressively,reaching the peak at 1 day(P < 0.05),and then induced at 7 days.2.It is noticeable that the number of microglia was decreased and its activation state was alleviated in the depleted peripheral monocyte group(group B).The expression of pro-inflammatory factors such as IL-6,IL-1 β,TNF-α in the midbrain showed a relatively stable increase trend slightly,which was significantly lower than group A(P<0.05)at each corresponding time points,and the peak value was significantly decreased(P<0.05).3.Compared with group N,the expression of TET2 protein in themidbrain of group A decreased slightly,reaching the lowest point on first day to 0.05±0.06 times of group N(P < 0.05),and slowly returning to same level of group N on the 7 days point.In contrast,compared with group N,TET2 protein’s level was rising in group B meaningfully and reaching its peak at 2 hours point(about 1.89 ±0.32 times to group N,P < 0.05).Then it was slowly returning to the same level with N at 7days point.And it was always significantly higher than that in group A at all time points(P < 0.05).4.Through the simple correlation analysis between the expression of TET2 protein and the mRNA of IL-6、TNF-α、IL-1β,the change of TET2 protein is negatively correlated with the change of IL-6 、 TNF-α 、 IL-1β mRNA,and the correlation coefficients are-0.603、-0.485 and-0.407(P<0.05).Conclusion:Peripheral inflammation can induce immune activation in CNS,and the depletion of peripheral blood monocytes can reduce the neuroinflammation which induced by peripheral inflammation.TET2 that expresses in rat mesencephalon participates in the propagation of inflammation from the periphery to the brain,and showes two contradictory trends under different inflammatory degree: low-degree neuroinflammation induced by peripheral inflammation have a time-dependent increasing expression of TET2 protein.There was a slightly decrease in TET2 protein in the high-degree neuroinflammation which is induced by peripheral inflammation.Change tendency of TET2 proteins and the expression of pro-inflammatory cytokine such as IL-6 、 TNF-α and IL-1β is the quite opposite.TET2 may be one of the negative regulators of neuroinflammation importantly.