Role Of Th17/Treg Imbalance In Neurotoxicity Of Mice Following Particulate Matter And High Fat Diet Exposure

Objectives To investigated whether Th17/Treg imbalance may be implicated in the nervous injury of high fat diet mice following routine air exposure.And provide theoretical basis for prevention and treatment for injury after exposure to PM and high fat diet.Methods A total of 60 C57BL/6 mice were randomly divided into clean air group,high fat diet（HFD）group,routine air group and routine air with HFD group.The clean air group and HFD group were kept in the air filtered IVC cage,and the routine air group and the routine air with HFD group were kept in the conventional air environment.The clean air group and the routine air group were fed the common diet;the HFD group and routine air with HFD group were fed the high fat diet.After 12 months exposure,we analyzed neurobehavioral changes by using Morris water maze,open field test and new object recognition test.HE staining was used to observe brain tissue damage in mice.And western blot was used to determine the protein expression of Iba-1,ROR-γt,IL-22,Foxp3 and TGF-βin the cortex and hippocampus of mice.The contents of elements in routine air PM_2.5sample and peripheral blood of mice were detected by ICP-MS.The contents of triglycerides and total cholesterol in serum of mice were detected by ELISA kit.Meanwhile,the contents of IL-17 protein in cortex and hippocampus of mice were detected by ELISA.Changes of CD4⁺IL-17⁺Th17/CD4⁺T and CD4⁺Foxp3⁺Treg/CD4⁺T in blood were tested by using flow cytometry.Results 1 Compared to clean air group and HFD group mice,Cr,Cu,Cd and Pb content increased significantly in blood of routine air group and routine air with HFD group mice（P<0.05）.2 After feeding high fat diet for 2 months,the average weight of the mice in the HFD group and routine air with HFD group were significantly higher than that in mice feeding normal diet（P<0.05）.And the contents of triglyceride and cholesterol in serum of the mice in the HFD group and routine air with HFD group were significantly higher than that in clean air group and routine air group（P<0.05）.3 Chronic routine air exposure combined with HFD treated mice showed a significantly increasing escape latency,decreasing central residence time,lower cross lattice times and lower frequency of contact with new object than that in routine air or HFD exposure alone（P<0.05）.HE results showed that hippocampal neurons were swollen,arranged in disorder,and the nerve fiber network was loose in routine air or/and HFD exposure groups.Meanwhile,the Iba-1protein expression in cortex and hippocampus was remarkable increased due to HFD or/and routine air exposure（P<0.05）.5 The protein expression of ROR-γt in cortex of routine air with fat diet group was more significant than that in routine air or HFD group.The protein level of IL-22 and IL-17 in cortex of HFD group or routine air group was higher than those in clean air group.And IL-17 protein content in routine air with fat diet group were 1.07 and 1.14 folds than those in HFD or routine air group（P<0.05）.In addition,the protein expression of Foxp3 and TGF-βin cortex of HFD or routine air group mice was lower than those in clean air group,and Foxp3 and TGF-βexpression in HFD mice following routine air exposure were 36.7%and 33.3%,49.4%and 25.3%of those in HFD or routine air group（P<0.05）.Meanwhile,the protein expression of ROR-γt,IL-22 and IL-17 in hippocampus of HFD group or routine air group was higher than those in clean air group.And ROR-γt and IL-17 expression in routine air with HFD group were1.55 and 1.08,1.38 and 1.13 folds than those in HFD or routine air group（P<0.05）.In addition,The protein expression of Foxp3 and TGF-βwere lower than those in clean air group,and Foxp3 and TGF-βexpression in HFD mice following routine air exposure were51.2%and 28.2%,38.4%and 40.5%of those in HFD or routine air group（P<0.05）.6 The CD4⁺IL-17⁺/CD4⁺（Th17）in blood of routine air with HFD mice was significantly increased than HFD group or routine air group,and CD4⁺Foxp3⁺/CD4⁺（Treg）was remarkably decreased（P<0.05）.And data showed that ratio of Th17/Treg in HFD group and routine air group was（2.25±0.54）or（1.75±0.34）,significantly higher than that in clean air group（0.61±0.21）.And it was（4.24±1.04）in mice following routine air exposure with HFD,remarkable higher than that in routine air or HFD exposure group.Conclusions Chronic routine air exposure with high fat diet did exacerbate nerve damage,which showed neurobehavioral changes and increasing neuroinflammation in CNS.Th17/Treg imbalance may play an important role the process of aggravation of nerve damage induced by routine air exposure combined with high fat diet.