2,3,7,8-Tetrachlorodibenzo-p-dioxin promotes migration ability of primary cultured rat astrocytes via aryl hydrocarbon receptor

Emerging evidence showed that 2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) could induce expression of certain reactivation-associated genes in astrocytes, however, the consequent cellular effects and molecular mechanisms are still unclear. During the process of astrocyte reactivation, migration is a critical cellular event. In the present study, we employed woundhealing assay and Transwell? motility assay to explore the effects of TCDD on cell migration in primary cultured rat cortical astrocytes. We found that upon TCDD treatments at relative low concentrations(10^(-10) and/or 10^(-9) mol/L), the ability of primary astrocytes to migrate horizontally and vertically was promoted. In line with this cellular effect, the mR NA expression of two promigratory genes, including cell division cycle 42(CDC42) and matrix metalloproteinase 2(MMP2)was induced by TCDD treatment. Dioxin exerts its toxic effects mainly through aryl hydrocarbon receptor(AhR) pathway. So the role of AhR pathway in the pro-migratory effects of TCDD was examined using an AhR antagonist, CH223191. We found that application of CH223191 significantly reversed the pro-migratory effects of TCDD. Interestingly, the basal ability of horizontal migration as well as basal levels of CDC42 and MMP2 expression were dramatically reduced suggesting a possible physiological role of AhR in maintaining the endogenous migration ability of the primary astrocytes. These findings support the notion that dioxin promotes astrocyte reactivation at molecular and cellular levels.

Patterns and dietary intake of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in food products in China

The health risk of polychlorinated dibenzo-p-dioxins and dibenzofurans（PCDD/Fs） and dioxin-like PCBs（d1-PCBs） to human being should be assessed regularly.To evaluate the contamination levels in various food products in the Chinese market and to assess the dietary exposure of the Chinese population,11 varieties of food groups totaling 534 samples including beef and mutton,chicken and duck,pork,fish and seafood,milk and dairy products were evaluated.The average concentrations of PCDD/Fs in all groups ranged from0.291 to 8.458 pg/g whole weight（w.w.）.The average toxic equivalency concentrations were from 0.012 pg TEQ/g w.w.for cereal to 0.357 pg TEQ/g fat for marine oil.OCDD and2,3,7,8-TCDF were the dominant congeners in foodstuffs.The dietary estimated mean intake for the Chinese rural and urban populations were 0.555 and 0.514 pg TEQ/kg body weight/day,respectively,however,the cereal group exposure were higher to the estimate daily intake and contributed 81%for rural and 48%for urban population,followed by fish and seafood which contributed 4%and 15%to the estimate daily intake.The estimated dietary intakes were compared with the toxicological reference values and showed that both rural and urban populations were well below those values.

Chronic TCDD exposure results in the dysregulation of gene expression in splenic B-lymphocytes and in the impairments in T-cell and B-cell differentiation in mouse model

2,3,7,8-Tetrachlorodibenzo-p-dioxin（TCDD） exposure in humans is associated with marked immune suppressions and increased incidence of lymphoblastic diseases.To elucidate mechanisms of impairments in humoral immune responses,we used a murine model.Following a 20-week administration of low doses of TCDD,we observed severely reduced antibody titers,dramatically decreased number of splenic Th1 and Th2 cells and an increase in CD19^＋ B cells.Transcriptional profiling of CD19^＋ B cells showed that markers of pre-B cells were significantly elevated,indicating delayed B cell maturation.These changes in B cells were accompanied by decreases of T helper cell numbers and reduced IgM and IgG titers.A transcriptome analysis of splenic B cells followed by Ingenuity Pathway Analysis（IPA） revealed a set of differentially expressed genes known to play roles in tumorigenesis,cell-proliferation and cell-migration.The most up-regulated transcript gene was Eph receptor A2（EphA2）,a known oncogene,and the most down-regulated transcript was ZBTB16 that codes for a negative transcriptional regulator important in epigenetic chromatin remodeling.IPA identified cAMP-responsive element modulator（CREM） and cAMP-responsive element binding protein 1（CREBl） as top upstream regulators.Consistently,a MAPPER promoter database analysis showed that all top dysregulated genes had CREM and/or CREBl binding sites in their promoter regions.In summary,our data showed that chronic TCDD exposure in mice caused suppressed humoral immunity accompanied with profound dysregulation of gene expression in splenic B-lymphocytes,likely through cAMP-dependent pathways.This dysregulation resulted in impairments in T-cell and B-cell differentiation and activation of the tumorigenic transcription program.

Development and characterization of monoclonal antibodies against human aryl hydrocarbon receptor

Aryl hydrocarbon receptor（Ah R）, a ligand-dependent nuclear receptor, is involved in a diverse spectrum of biological and toxicological effects. Due to the lack of three dimensional（3D）crystal or nuclear magnetic resonance structure, the mechanisms of these complex effects of AhR remain to be unclear. Also, commercial monoclonal antibodies（mA bs） against human AhR protein（h Ah R）, as alternative immunological tools, are very limited. Thus, in order to provide more tools for further studies on h Ah R, we prepared two m Abs（1D6 and 4A6） against h Ah R. The two newly generated m Abs specifically bound to amino acids 484–508（located in transcription activation domain） and amino acids 201–215（located in Per-ARNT-Sim domain）of h Ah R, respectively. These epitopes were new as compared with those of commercial m Abs.The m Abs were also characterized by enzyme-linked immunosorbent assay, western blot,immunoprecipitation and indirect immunofluorescence assay in different cell lines. The results showed that the two m Abs could recognize the linearized AhR s in six different human cell lines and a rat hepatoma cell line, as well as the h Ah R with native conformations. We concluded that the newly generated m Abs could be employed in AhR-based bioassays for analysis of environmental contaminants, and held great potential for further revealing the spatial structure of AhR and its biological functions in future studies.