Trichloroethylene metabolite modulates DNA methylation-dependent gene expression in Th1 polarized CD4+ T cells from autoimmune-prone mice

Trichloroethylene (TCE) is an industrial solvent and widespread environmental contaminant associated with CD4+ T cell activation and autoimmune disease. Prior studies showed that exposure to TCE in the drinking water of autoimmune-prone mice expanded effector/memory CD4+ T cells with an interferon-γ (IFN-γ)-secreting Th1-like phenotype. However, very little is known how TCE exposure skews CD4+ T cells towards this pro-inflammatory Th1 subset. As observed previously, TCE exposure was associated with hypermethylation of regions of the genome related to transcriptional repression in purified effector/memory CD4 T cells. We hypothesized that TCE modulates transcriptional and/or epigenetic programming of CD4+ T cells as they differentiate from a naïve to effector phenotype. In the current study, purified naïve CD4 T cells from both male and female autoimmune-prone MRL/MpJ mice were activated ex vivo and polarized towards a Th1 subset for 4 days in the presence or absence of the oxidative metabolite of TCE, trichloroacetaldehyde hydrate (TCAH) in vitro. An RNA-seq assessment and Reduced Representation Bisulfite sequencing for DNA methylation were conducted on Th1 cells or activated, non- polarized cells. The results demonstrated TCAH's ability to regulate key genes involved in the immune response and autoimmunity, including Ifng, by altering the level of DNA methylation at the gene promoter. Intriguing sex differences were observed and for the most part the effects were more robust in females compared to males. In conclusion, TCE via TCAH epigenetically regulates gene expression in CD4+ T cells. These results may have implications for mechanistic understanding or future therapeutics for autoimmunity.

Developmental trichloroethylene exposure enhances predictive markers of autoimmunity in a sex-specific manner in disease-resistant female mice

Trichloroethylene (TCE) is a widely used industrial chemical and common environmental pollutant. Exposure to TCE promotes CD4⁺ T cell-driven autoimmunity including autoimmune hepatitis (AIH) in both humans and female autoimmune-prone mice. Because the developing immune system is more sensitive during development, we predicted that non- autoimmune-prone, C57/Bl6 (B6) mice would exhibit some autoimmune-related changes using the Developmental Origins of Health and Disease (DOHaD) model of exposure. Both male and female mice were exposed to vehicle or an environmentally relevant dose of 5 μg/ml TCE (0.9 mg/kg/day) beginning at 2 weeks pre-conception and ending at weaning. CD4+ T cells were assessed for phenotypic markers by flow cytometry. An assessment of cytokines elicited ex vivo after 4d polarization from naïve to CD4⁺ T helper subsets (i.e., Th1, Th17, and T reg) was conducted. mRNA expression of liver genes associated with inflammation, regeneration/repair associated with AIH disease progression in autoimmune-prone mice were evaluated by qRT-PCR. The results demonstrated TCE's ability to induce autoimmune- related biomarkers in B6 mice to an even greater degree in females compared to males when exposed during development.

Sex-Dependent Effects on Liver Inflammation and Gut Microbial Dysbiosis After Continuous Developmental Exposure to Trichloroethylene in Autoimmune-Prone Mice

Trichloroethylene (TCE) is a common environmental toxicant linked with hypersensitivity and autoimmune responses in humans and animal models. While autoimmune diseases are more common in females, mechanisms behind this disparity are not clear. Recent evidence suggests that autoimmunity may be increasing in males, and occupational studies have shown that TCE-mediated hypersensitivity responses occur just as often in males. Previous experimental studies in autoimmune-prone MRL^+/+ mice have focused on responses in females. However, it is important to include both males and females in order to better understand sex-disparity in autoimmune disease. In addition, because of an alarming increase in autoimmunity in adolescents, developmental and/or early life exposures to immune-enhancing environmental pollutants should also be considered. Using MRL^+/+ mice, we hypothesized that TCE would alter markers related to autoimmunity to a greater degree in female mice relative to male mice, and that TCE would enhance these effects. Mice were continuously exposed to either TCE or vehicle beginning at gestation, continuing during lactation, and directly in the drinking water. Both male and female offspring were evaluated at 7 weeks of age. Sex-specific effects were evident. Female mice were more likely than males to show enhanced CD4⁺ T cell cytokine responses (e.g., IL-4 and IFN-γ). Although none of the animals developed pathological or serological signs of autoimmune hepatitis-like disease, TCE-exposed female mice were more likely than males in either group to express higher levels of biomarkers in the liver related to regeneration/repair and proliferation. Levels of bacterial populations in the intestinal ileum were also altered by TCE exposure and were more prominent in females as compared to males. Thus, our expectations were correct in that young adult female mice developmentally exposed to TCE were more likely to exhibit alterations in immunological and gut/liver endpoints compared to male mice.

Studying the Effect of Maternal Pregestational Diabetes on Fetal Neurodevelopment Using Magnetoencephalography

Background. Developmental origin of health and disease states that an adverse intrauterine environment can lead to different diseases in later life. In this study, we aimed to explore the effect of maternal pregestational diabetes on the fetal brain activity using magnetoencephalography (MEG). Methods. Forty participants were included in an observational study with 9 type 1 and 19 type 2 diabetic pregnant women compared with data from 12 nondiabetic participants. Spontaneous fetal MEG signals were recorded and power spectral density was computed in 4 standard frequency bands. Group differences were investigated using analysis of covariance. Results. Our results showed that type 1 group was significantly different (P < .05) from the reference group for 3 of the 4 brain activity frequency bands, while in type 2 group, 2 bands exhibited this trend. When dichotomized based on the maternal glycemic control, significant differences in all bands were observed between the poor-control and reference groups. Conclusion. The fetal background brain activity parameters appear to be altered in diabetic pregnancy in comparison with the reference low-risk group. The study showed that maternal pregestational diabetes could potentially influence in utero neurodevelopment.

Complex epigenetic patterns in cerebellum generated after developmental exposure to trichloroethylene and/or high fat diet in autoimmune-prone mice

Trichloroethylene (TCE) is an environmental contaminant associated with immune-mediated inflammatory disorders and neurotoxicity. Based on known negative effects of developmental overnutrition on neurodevelopment, we hypothesized that developmental exposure to high fat diet (HFD) consisting of 40% kcal fat would enhance neurotoxicity of low-level (6 μg per kg per day) TCE exposure in offspring over either stressor alone. Male offspring were evaluated at ∼6 weeks of age after exposure beginning 4 weeks preconception in the dams until weaning. TCE, whether used as a single exposure or together with HFD, appeared to be more robust than HFD alone in altering one-carbon metabolites involved in glutathione redox homeostasis and methylation capacity. In contrast, opposing effects of expression of key enzymes related to DNA methylation related to HFD and TCE exposure were observed. The mice generated unique patterns of anti-brain antibodies detected by western blotting attributable to both TCE and HFD. Taken together, developmental exposure to TCE and/or HFD appear to act in complex ways to alter brain biomarkers in offspring.

Examination of pain threshold and neuropeptides in patients with acute suicide risk

INTRODUCTION

One of the main challenges in suicide prevention is the limited understanding of the biological mechanisms underlying suicide. Recent findings suggest impairments in pain processing in acutely suicidal patients. However, little is known about the biological factors that may drive these discrete physiological abnormalities. In this study, we examined plasma peptides involved in analgesic and inflammatory responses and physical pain threshold in acutely suicidal patients.

METHODS

Thirty-seven depressed patients of both sexes hospitalized for severe suicidal ideation or a recent suicide attempt were characterized clinically including history of suicidal ideation and behavior. Psychological and physical pain, and pressure pain threshold was also measured. Plasma levels of β-endorphin, neurotensin, agouti-related protein (AgRP), C-reactive protein (CRP), adrenocorticotropic hormone (ACTH), and brain-derived neurotrophic factor (BDNF) were run in Milliplex multiplex assays.

RESULTS

The number of lifetime suicide attempts was positively correlated with β-endorphin (r = 0.702; p = 0.007), and neurotensin (r = 0.728, p = 0.007) plasma levels. Higher pain threshold was measured in the suicide attempt group as compared to the suicidal ideation group. Pain threshold was strongly and negatively associated with CRP plasma levels (r = -0.548; p < 0.001). In patients reporting chronic pain, lower AgRP levels and lower pain threshold were observed (t = 4.472; p = 0.001).

CONCLUSION

Our results suggest that abnormalities in the opioid and neurotensin systems may underlie the increase in pain threshold found in suicide attempters, and possibly risk for suicidal behavior. Targeting pain circuits and systems may provide therapeutic mechanisms for suicide prevention.

Continuous Developmental and Early Life Trichloroethylene Exposure Promoted DNA Methylation Alterations in Polycomb Protein Binding Sites in Effector/Memory CD4+ T Cells

Trichloroethylene (TCE) is an industrial solvent and drinking water pollutant associated with CD4⁺ T cell-mediated autoimmunity. In our mouse model, discontinuation of TCE exposure during adulthood after developmental exposure did not prevent immunotoxicity. To determine whether persistent effects were linked to epigenetic changes we conducted whole genome reduced representation bisulfite sequencing (RRBS) to evaluate methylation of CpG sites in autosomal chromosomes in activated effector/memory CD4⁺ T cells. Female MRL+/+ mice were exposed to vehicle control or TCE in the drinking water from gestation until ~37 weeks of age [postnatal day (PND) 259]. In a subset of mice, TCE exposure was discontinued at ~22 weeks of age (PND 154). At PND 259, RRBS assessment revealed more global methylation changes in the continuous exposure group vs. the discontinuous exposure group. A majority of the differentially methylated CpG regions (DMRs) across promoters, islands, and regulatory elements were hypermethylated (~90%). However, continuous developmental TCE exposure altered the methylation of 274 CpG sites in promoters and CpG islands. In contrast, only 4 CpG island regions were differentially methylated (hypermethylated) in the discontinuous group. Interestingly, 2 of these 4 sites were also hypermethylated in the continuous exposure group, and both of these island regions are associated with lysine 27 on histone H3 (H3K27) involved in polycomb complex-dependent transcriptional repression via H3K27 tri-methylation. CpG sites were overlapped with the Open Regulatory Annotation database. Unlike the discontinuous group, continuous TCE treatment resulted in 129 DMRs including 12 unique transcription factors and regulatory elements; 80% of which were enriched for one or more polycomb group (PcG) protein binding regions (i.e., SUZ12, EZH2, JARID2, and MTF2). Pathway analysis of the DMRs indicated that TCE primarily altered the methylation of genes associated with regulation of cellular metabolism and cell signaling. The results demonstrated that continuous developmental exposure to TCE differentially methylated binding sites of PcG proteins in effector/memory CD4⁺ cells. There were minimal yet potentially biologically significant effects that occurred when exposure was discontinued. These results point toward a novel mechanism by which chronic developmental TCE exposure may alter terminally differentiated CD4⁺ T cell function in adulthood.

Developmental exposure to environmental toxicant trichloroethylene alters DNA methylation in polycomb protein binding regions in effector/memory CD4 + T cells from autoimmune-prone mice

Trichloroethylene (TCE) is an industrial solvent and drinking water pollutant associated with autoimmunity in human populations. Previous studies in autoimmune-prone MRL+/+ mice revealed autoimmune pathology and CD4 + T cell autoreactivity were more robust when exposure occurred during development rather than adulthood. To determine whether these effects were linked to epigenetic changes, mice were exposed to vehicle control or TCE in the drinking water beginning at gestation until 37 weeks of age. In some mice, TCE was removed from drinking water at 22 weeks of age. Whole genome reduced representation bisulfite sequencing (RRBS) was used to compare methylation of CpG sites in autosomal chromosomes in effector/memory CD4+ T cells. Few significant changes occurred in mice when TCE was removed from drinking water. In contrast, continuous developmental TCE exposure revealed differential methylation of 252 CpG sites relative to controls. When CpG sites were overlapped with the Open Regulatory Annotation database (ORegAnno), continuous TCE treatment resulted in 130 differentially methylated regions (DMRs) that included 12 unique transcription factors. Interestingly, 80% of DMRs occurred in areas known to bind Polycomb group (PcG) proteins that form the polycomb-repressive complex 2 (PRC2) in mammalian cells, namely, SUZ12, EZH2, JARID2, and MTF2. Pathway analysis of the DMRs indicated that TCE primarily altered the methylation of genes asociated with regulation of cellular metabolism and cell signaling pathways. In summary, TCE differentially methylated binding sites of PcG proteins in effector/memory CD4+ cells, and point toward a novel mechanism by which TCE could modulate CD4 + T cell function and promote autoimmunity.

Exposure to per-fluoroalkyl and polyfluoroalkyl substances leads to immunotoxicity: epidemiological and toxicological evidence

In this perspective, we evaluate key and emerging epidemiological and toxicological data concerning immunotoxicity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) and seek to reconcile conflicting conclusions from two reviews published in 2016. We summarize ways that immunosuppression and immunoenhancement are defined and explain how specific outcomes are used to evaluate immunotoxicity in humans and experimental animals. We observe that different approaches to defining immunotoxicological outcomes, particularly those that do not produce clinical disease, may lead to different conclusions from epidemiological and toxicological studies. The fundamental point that we make is that aspects of epidemiological studies considered as limitations can be minimized when data from toxicological studies support epidemiological findings. Taken together, we find that results of epidemiological studies, supported by findings from toxicological studies, provide strong evidence that humans exposed to PFOA and PFOS are at risk for immunosuppression.

Irreversible effects of trichloroethylene on the gut microbial community and gut-associated immune responses in autoimmune-prone mice

The developing immune system is particularly sensitive to immunotoxicants. This study assessed trichloroethylene (TCE)-induced effects on the gut microbiome and cytokine production during the development in mice. Mice were exposed to TCE (0.05 or 500 μg/mL) at the levels that approximate to environmental or occupational exposure, respectively. Mice were subjected to a continuous developmental exposure to these doses encompassing gestation, lactation and continuing directly in the drinking water postnatally for 154 days (PND154) or PND259. To observe persistence of the effect TCE was removed from the drinking water in a subset of mice on PND154 and were provided regular drinking water until the study terminus (PND259). Abundance of total tissue-associated bacteria reduced only in mice exposed to TCE until PND259. The ratio of Firmicutes/Bacteroidetes did not alter during this continuos exposure; however, cessation of high-dose TCE at PND154 resulted in the increased abundance Bacteroidetes at PND259. Furthermore, high-dose TCE exposure until PND259 resulted in a lower abundance of the genera Bacteroides and Lactobaccilus and increased abundance of genus Bifidobactrium and bacterial family Enterobacteriaceae. TCE exposure until PND154 showed significant changes in the production of interleukin-33; that might play a dual role in maintaining the balance and homeostasis between commensal microbiota and mucosal health. At PND259, interleukin-3, granulocyte-macrophage colony-stimulating factor and Eotaxin were altered in both, the continuous exposure and cessation groups, whereas only a cessation group had a higher level of KC that may facilitate infiltration of neutrophils. The irreversible effects of TCE after a period of exposure cessation suggested a unique programming and potential toxicity of TCE even at the environmental level exposure.

Opposing Actions of Developmental Trichloroethylene and High-Fat Diet Coexposure on Markers of Lipogenesis and Inflammation in Autoimmune-Prone Mice

Trichloroethylene (TCE) is a widespread environmental pollutant associated with immunotoxicity and autoimmune disease. Previous studies showed that mice exposed from gestation through early life demonstrated CD4+ T cell alterations and autoimmune hepatitis. Determining the role of one environmental risk factor for any disease is complicated by the presence of other stressors. Based on its known effects, we hypothesized that developmental overnutrition in the form of a moderately high-fat diet (HFD) consisting of 40% kcal fat would exacerbate the immunotoxicity and autoimmune-promoting effects of low-level (<10 μg/kg/day) TCE in autoimmune-prone MRL+/+ mice over either stressor alone. When female offspring were evaluated at 27 weeks of age we found that a continuous exposure beginning at 4 weeks preconception in the dams until 10 weeks of age in offspring that TCE and HFD promoted unique effects that were often antagonistic. For a number of adiposity endpoints, TCE significantly reversed the expected effects of HFD on expression of genes involved in fatty acid synthesis/insulin resistance, as well as mean pathology scores of steatosis. Although none of the animals developed pathological signs of autoimmune hepatitis, the mice generated unique patterns of antiliver antibodies detected by western blotting attributable to TCE exposure. A majority of cytokines in liver, gut, and splenic CD4+ T cells were significantly altered by TCE, but not HFD. Levels of bacterial populations in the intestinal ileum were also altered by TCE exposure rather than HFD. Thus, in contrast to our expectations this coexposure did not promote synergistic effects.

Epigenetic underpinnings of developmental immunotoxicity and autoimmune disease

The concordance rate for developing autoimmune disease in identical twins is around 50% demonstrating that gene and environmental interactions contribute to disease etiology. The environmental contribution to autoimmune disease is a wide-ranging concept including exposure to immunotoxic environmental chemicals. Because the immune system is immature during development suggests that adult-onset autoimmunity may originate when the immune system is particularly sensitive. Among the pollutants most closely associated with inflammation and/or autoimmunity include Bisphenol-A, mercury, TCDD, and trichloroethylene. These toxicants have been shown to impart epigenetic changes (e.g., DNA methylation) that may alter immune function and promote autoreactivity. Here we review these autoimmune-promoting toxicants and their relation to immune cell epigenetics both in terms of adult and developmental exposure.

A single dose of trichloroethylene given during development does not substantially alter markers of neuroinflammation in brains of adult mice

Trichloroethylene (TCE) is a widespread environmental contaminant associated with developmental immunotoxicity and neurotoxicity. Previous studies have shown that MRL^+/+ mice exposed to TCE from gestation through early-life demonstrate robust increases in inflammatory markers in peripheral CD4⁺ T-cells, as well as glutathione depletion and increased oxidative stress in cerebellum-associated with alterations in behavior. Since increased oxidative stress is associated with neuroinflammation, we hypothesized that neuroinflammatory markers could be altered relative to unexposed mice. MRL^+/+ mice were given 0.5 mg/ml of TCE in vehicle or vehicle (water with 1% Alkamuls EL-620) from conception through early adulthood via drinking water to dams and then directly to post-weaning offspring. Animals were euthanized at 49 days of age and levels of pro- and anti-inflammatory cytokines, density of T-cell staining, and micro-glial morphology were evaluated in brains to begin to ascertain a neuroinflammatory profile. Levels of IL-6 were decreased in female animals and while not statistically significant, and levels of IL-10 were higher in brains of exposed male and female animals. Supportive of this observation, although not statistically significant, the number of ameboid microglia was higher in exposed relative to unexposed animals. This overall profile suggests the emergence of an anti-inflammatory/neuroprotective phenotype in exposed animals, possibly as a compensatory response to neuroinflammation that is known to be induced by developmental exposure to TCE.

Maternal autoimmune disease and birth defects in the National Birth Defects Prevention Study

BACKGROUND

Little is known about the association between maternal autoimmune disease or its treatment and the risk of birth defects. We examined these associations using data from the National Birth Defects Prevention Study, a multi-site, population-based, case-control study.

METHODS

Analyses included 25,116 case and 9897 unaffected control infants with estimated delivery dates between 1997 and 2009. Information on autoimmune disease, medication use, and other pregnancy exposures was collected by means of telephone interview. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for birth defects with five or more exposed cases; crude ORs and exact 95% CIs were estimated for birth defects with three to four exposed cases.

RESULTS

Autoimmune disease was reported by 373 mothers (279 case and 94 control mothers). The majority of birth defects evaluated were not associated with autoimmune disease; however, a statistically significant association between maternal autoimmune disease and encephalocele was observed (OR, 4.64; 95% CI, 1.95-11.04). Eighty-two mothers with autoimmune disease used an immune modifying/suppressing medication during pregnancy; this was associated with encephalocele (OR, 7.26; 95% CI, 1.37-24.61) and atrial septal defects (OR, 3.01; 95% CI, 1.16-7.80).

CONCLUSION

Our findings suggest maternal autoimmune disease and treatment are not associated with the majority of birth defects, but may be associated with some defects, particularly encephalocele. Given the low prevalence of individual autoimmune diseases and the rare use of specific medications, we were unable to examine associations of specific autoimmune diseases and medications with birth defects. Other studies are needed to confirm these findings. Birth Defects Research (Part A) 106:950-962, 2016. © 2016 Wiley Periodicals, Inc.

Trichloroethylene-induced alterations in DNA methylation were enriched in polycomb protein binding sites in effector/memory CD4+ T cells

Exposure to industrial solvent and water pollutant trichloroethylene (TCE) can promote autoimmunity, and expand effector/memory (CD62L) CD4+ T cells. In order to better understand etiology reduced representation bisulfite sequencing was used to study how a 40-week exposure to TCE in drinking water altered methylation of ∼337 770 CpG sites across the entire genome of effector/memory CD4+ T cells from MRL+/+ mice. Regardless of TCE exposure, 62% of CpG sites in autosomal chromosomes were hypomethylated (0-15% methylation), and 25% were hypermethylated (85-100% methylation). In contrast, only 6% of the CpGs on the X chromosome were hypomethylated, and 51% had mid-range methylation levels. In terms of TCE impact, TCE altered (≥ 10%) the methylation of 233 CpG sites in effector/memory CD4+ T cells. Approximately 31.7% of these differentially methylated sites occurred in regions known to bind one or more Polycomb group (PcG) proteins, namely Ezh2, Suz12, Mtf2 or Jarid2. In comparison, only 23.3% of CpG sites not differentially methylated by TCE were found in PcG protein binding regions. Transcriptomics revealed that TCE altered the expression of ∼560 genes in the same effector/memory CD4+ T cells. At least 80% of the immune genes altered by TCE had binding sites for PcG proteins flanking their transcription start site, or were regulated by other transcription factors that were in turn ordered by PcG proteins at their own transcription start site. Thus, PcG proteins, and the differential methylation of their binding sites, may represent a new mechanism by which TCE could alter the function of effector/memory CD4+ T cells.

Exposure Cessation During Adulthood Did Not Prevent Immunotoxicity Caused by Developmental Exposure to Low-Level Trichloroethylene in Drinking Water

Exposure to the water pollutant trichloroethylene (TCE) can promote autoimmunity in both humans and rodents. Using a mouse model we have shown that chronic adult exposure to TCE at 500 μg/ml in drinking water generates autoimmune hepatitis in female MRL+/+ mice. There is increasing evidence that developmental exposure to certain chemicals can be more toxic than adult exposure. This study was designed to test whether exposure to a much lower level of TCE (0.05 μg/ml) during gestation, lactation, and early life generated autoimmunity similar to that found following adult exposure to higher concentrations of TCE. When female MRL+/+ mice were examined at postnatal day (PND) 259 we found that developmental/early life exposure [gestational day 0 to PND 154] to TCE at a concentration 10 000 fold lower than that shown to be effective for adult exposure triggered autoimmune hepatitis. This effect was observed despite exposure cessation at PND 154. In concordance with the liver pathology, female MRL+/+ exposed during development and early life to TCE (0.05 or 500 μg/ml) generated a range of antiliver antibodies detected by Western blotting. Expression of proinflammatory cytokines by CD4+ T cells was also similarly observed at PND 259 in the TCE-exposed mice regardless of concentration. Thus, exposure to TCE at approximately environmental levels from gestational day 0 to PND 154 generated tissue pathology and CD4+ T cell alterations that required higher concentrations if exposure was limited to adulthood. TCE exposure cessation at PND 154 did not prevent the immunotoxicity.

Chronic exposure to trichloroethylene increases DNA methylation of the Ifng promoter in CD4+ T cells

CD4+ T cells in female MRL+/+ mice exposed to solvent and water pollutant trichloroethylene (TCE) skew toward effector/memory CD4+ T cells, and demonstrate seemingly non-monotonic alterations in IFN-γ production. In the current study we examined the mechanism for this immunotoxicity using effector/memory and naïve CD4+ T cells isolated every 6 weeks during a 40 week exposure to TCE (0.5mg/ml in drinking water). A time-dependent effect of TCE exposure on both Ifng gene expression and IFN-γ protein production was observed in effector/memory CD4+ T cells, with an increase after 22 weeks of exposure and a decrease after 40 weeks of exposure. No such effect of TCE was observed in naïve CD4+ T cells. A cumulative increase in DNA methylation in the CpG sites of the promoter of the Ifng gene was observed in effector/memory, but not naïve, CD4+ T cells over time. Also unique to the Ifng promoter was an increase in methylation variance in effector/memory compared to naïve CD4+ T cells. Taken together, the CpG sites of the Ifng promoter in effector/memory CD4+ T cells were especially sensitive to the effects of TCE exposure, which may help explain the regulatory effect of the chemical on this gene.

Chronic exposure to water pollutant trichloroethylene increased epigenetic drift in CD4(+) T cells

AIM

Autoimmune disease and CD4(+) T-cell alterations are induced in mice exposed to the water pollutant trichloroethylene (TCE). We examined here whether TCE altered gene-specific DNA methylation in CD4(+) T cells as a possible mechanism of immunotoxicity.

MATERIALS & METHODS

Naive and effector/memory CD4(+) T cells from mice exposed to TCE (0.5 mg/ml in drinking water) for 40 weeks were examined by bisulfite next-generation DNA sequencing.

RESULTS

A probabilistic model calculated from multiple genes showed that TCE decreased methylation control in CD4(+) T cells. Data from individual genes fitted to a quadratic regression model showed that TCE increased gene-specific methylation variance in both CD4 subsets.

CONCLUSION

TCE increased epigenetic drift of specific CpG sites in CD4(+) T cells.

Inflammatory and oxidative stress-related effects associated with neurotoxicity are maintained after exclusively prenatal trichloroethylene exposure

Trichloroethylene (TCE) is a widespread environmental toxicant with immunotoxic and neurotoxic potential. Previous studies have shown that continuous developmental exposure to TCE encompassing gestation and early life as well as postnatal only exposure in the drinking water of MRL+/+ mice promoted CD4⁺ T cell immunotoxicity, glutathione depletion and oxidative stress in the cerebellum, as well increased locomotor activity in male offspring. The purpose of this study was to characterize the effects of exclusively prenatal exposure on these parameters. Another goal was to investigate potential plasma oxidative stress/inflammatory biomarkers to possibly be used as predictors of TCE-mediated neurotoxicity. In the current study, 6 week old male offspring of dams exposed gestationally to 0, 0.01, and 0.1mg/ml TCE in the drinking water were evaluated. Our results confirmed that the oxidized phenotype in plasma and cerebellum was maintained after exclusively prenatal exposure. A Phenotypic analysis by flow cytometry revealed that TCE exposure expanded the effector/memory subset of peripheral CD4⁺ T cells in association with increased production of pro-inflammatory cytokines IFN-γ and IL-17. Serum biomarkers of oxidative stress and inflammation were also elevated in plasma suggesting that systemic effects are important and may be used to predict neurotoxicity in our model. These results suggested that the prenatal period is a critical stage of life by which the developing CNS and immune system are susceptible to long-lasting changes mediated by TCE.

Modeling toxicodynamic effects of trichloroethylene on liver in mouse model of autoimmune hepatitis

Chronic exposure to industrial solvent and water pollutant trichloroethylene (TCE) in female MRL+/+mice generates disease similar to human autoimmune hepatitis. The current study was initiated to investigate why TCE-induced autoimmunity targeted the liver. Compared to other tissues the liver has an unusually robust capacity for repair and regeneration. This investigation examined both time-dependent and dose-dependent effects of TCE on hepatoprotective and pro-inflammatory events in liver and macrophages from female MRL+/+mice. After a 12-week exposure to TCE in drinking water a dose-dependent decrease in macrophage production of IL-6 at both the transcriptional and protein level was observed. A longitudinal study similarly showed that TCE inhibited macrophage IL-6 production. In terms of the liver, TCE had little effect on expression of pro-inflammatory genes (Tnfa, Saa2 or Cscl1) until the end of the 40-week exposure. Instead, TCE suppressed hepatic expression of genes involved in IL-6 signaling (Il6r, gp130, and Egr1). Linear regression analysis confirmed liver histopathology in the TCE-treated mice correlated with decreased expression of Il6r. A toxicodynamic model was developed to estimate the effects of TCE on IL-6 signaling and liver pathology under different levels of exposure and rates of repair. This study underlined the importance of longitudinal studies in mechanistic evaluations of immuntoxicants. It showed that later-occurring liver pathology caused by TCE was associated with early suppression of hepatoprotection rather than an increase in conventional pro-inflammatory events. This information was used to create a novel toxicodynamic model of IL-6-mediated TCE-induced liver inflammation.

Differential immunotoxicity induced by two different windows of developmental trichloroethylene exposure

Developmental exposure to environmental toxicants may induce immune system alterations that contribute to adult stage autoimmune disease. We have shown that continuous exposure of MRL+/+ mice to trichloroethylene (TCE) from gestational day (GD) 0 to postnatal day (PND) 49 alters several aspects of CD4(+) T cell function. This window of exposure corresponds to conception-adolescence/young adulthood in humans. More narrowly defining the window of TCE developmental exposure causes immunotoxicity that would establish the stage at which avoidance and/or intervention would be most effective. The current study divided continuous TCE exposure into two separate windows, namely, gestation only (GD0 to birth (PND0)) and early-life only (PND0-PND49). The mice were examined for specific alterations in CD4(+) T cell function at PND49. One potentially long-lasting effect of developmental exposure, alterations in retrotransposon expression indicative of epigenetic alterations, was found in peripheral CD4(+) T cells from both sets of developmentally exposed mice. Interestingly, certain other effects, such as alterations in thymus cellularity, were only found in mice exposed to TCE during gestation. In contrast, expansion of memory/activation cell subset of peripheral CD4(+) T cells were only found in mice exposed to TCE during early life. Different windows of developmental TCE exposure can have different functional consequences.

Metabolic changes and DNA hypomethylation in cerebellum are associated with behavioral alterations in mice exposed to trichloroethylene postnatally

Previous studies demonstrated that low-level postnatal and early life exposure to the environmental contaminant, trichloroethylene (TCE), in the drinking water of MRL+/+ mice altered glutathione redox homeostasis and increased biomarkers of oxidative stress indicating a more oxidized state. Plasma metabolites along the interrelated transmethylation pathway were also altered indicating impaired methylation capacity. Here we extend these findings to further characterize the impact of TCE exposure in mice exposed to water only or two doses of TCE in the drinking water (0, 2, and 28mg/kg/day) postnatally from birth until 6weeks of age on redox homeostasis and biomarkers of oxidative stress in the cerebellum. In addition, pathway intermediates involved in methyl metabolism and global DNA methylation patterns were examined in cerebellar tissue. Because the cerebellum is functionally important for coordinating motor activity, including exploratory and social approach behaviors, these parameters were evaluated in the present study. Mice exposed to 28mg/kg/day TCE exhibited increased locomotor activity over time as compared with control mice. In the novel object exploration test, these mice were more likely to enter the zone with the novel object as compared to control mice. Similar results were obtained in a second test when an unfamiliar mouse was introduced into the testing arena. The results show for the first time that postnatal exposure to TCE causes key metabolic changes in the cerebellum that may contribute to global DNA methylation deficits and behavioral alterations in TCE-exposed mice.

Epigenetic alterations may regulate temporary reversal of CD4(+) T cell activation caused by trichloroethylene exposure

Previous studies have shown that short-term (4 weeks) or chronic (32 weeks) exposure to trichloroethylene (TCE) in drinking water of female MRL+/+ mice generated CD4(+) T cells that secreted increased levels of interferon (IFN)-γ and expressed an activated (CD44(hi)CD62L(lo)) phenotype. In contrast, the current study of subchronic TCE exposure showed that midway in the disease process both of these parameters of CD4(+) T cell activation were reversed. This phase of the disease process may represent an attempt by the body to counteract the inflammatory effects of TCE. The decrease in CD4(+) T cell production of IFN-γ following subchronic TCE exposure could not be attributed to skewing toward a Th2 or Th17 phenotype or to an increase in Treg cells. Instead, the suppression corresponded to alterations in markers used to assess DNA methylation, namely increased expression of retrotransposons Iap (intracisternal A particle) and Muerv (murine endogenous retrovirus). Also observed was an increase in the expression of Dnmt1 (DNA methyltransferase-1) and decreased expression of several genes known to be downregulated by DNA methylation, namely Ifng, Il2, and Cdkn1a. CD4(+) T cells from a second study in which MRL+/+ mice were treated for 17 weeks with TCE showed a similar increase in Iap and decrease in Cdkn1a. In addition, DNA collected from the CD4(+) T cells in the second study showed TCE-decreased global DNA methylation. Thus, these results described the biphasic nature of TCE-induced alterations in CD4(+) T cell function and suggested that these changes represented potentially reversible alterations in epigenetic processes.

Postnatal exposure to trichloroethylene alters glutathione redox homeostasis, methylation potential, and neurotrophin expression in the mouse hippocampus

Previous studies have shown that continuous exposure throughout gestation until the juvenile period to environmentally relevant doses of trichloroethylene (TCE) in the drinking water of MRL+/+ mice promoted adverse behavior associated with glutathione depletion in the cerebellum indicating increased sensitivity to oxidative stress. The purpose of this study was to extend our findings and further characterize the impact of TCE exposure on redox homeostasis and biomarkers of oxidative stress in the hippocampus, a brain region prone to oxidative stress. Instead of a continuous exposure, the mice were exposed to water only or two environmentally relevant doses of TCE in the drinking water postnatally from birth until 6 weeks of age. Biomarkers of plasma metabolites in the transsulfuration pathway and the transmethylation pathway of the methionine cycle were also examined. Gene expression of neurotrophins was examined to investigate a possible relationship between oxidative stress, redox imbalance and neurotrophic factor expression with TCE exposure. Our results show that hippocampi isolated from male mice exposed to TCE showed altered glutathione redox homeostasis indicating a more oxidized state. Also observed was a significant, dose dependent increase in glutathione precursors. Plasma from the TCE treated mice showed alterations in metabolites in the transsulfuration and transmethylation pathways indicating redox imbalance and altered methylation capacity. 3-Nitrotyrosine, a biomarker of protein oxidative stress, was also significantly higher in plasma and hippocampus of TCE-exposed mice compared to controls. In contrast, expression of key neurotrophic factors in the hippocampus (BDNF, NGF, and NT-3) was significantly reduced compared to controls. Our results demonstrate that low-level postnatal and early life TCE exposure modulates neurotrophin gene expression in the mouse hippocampus and may provide a mechanism for TCE-mediated neurotoxicity.

Coexposure to mercury increases immunotoxicity of trichloroethylene

We have shown previously that chronic (32 weeks) exposure to occupationally relevant concentrations of the environmental pollutant trichloroethylene (TCE) induced autoimmune hepatitis (AIH) in autoimmune-prone MRL+/+ mice. In real-life, individuals are never exposed to only one chemical such as TCE. However, very little is known about the effects of chemical mixtures on the immune system. The current study examined whether coexposure to another known immunotoxicant, mercuric chloride (HgCl(2)), altered TCE-induced AIH. Female MRL+/+ mice were treated for only 8 weeks with TCE (9.9 or 186.9 mg/kg/day in drinking water) and/or HgCl(2) (260 μg/kg/day, sc). Unlike mice exposed to either TCE or HgCl(2) alone, mice exposed to both toxicants for 8 weeks developed significant liver pathology commensurate with early stages of AIH. Disease development in the coexposed mice was accompanied by a unique pattern of anti-liver and anti-brain antibodies that recognized, among others, a protein of approximately 90 kDa. Subsequent immunoblotting showed that sera from the coexposed mice contained antibodies specific for heat shock proteins, a chaperone protein targeted by antibodies in patients with AIH. Thus, although TCE can promote autoimmune disease following chronic exposure, a shorter exposure to a binary mixture of TCE and HgCl(2) accelerated disease development. Coexposure to TCE and HgCl(2) also generated a unique liver-specific antibody response not found in mice exposed to a single toxicant. This finding stresses the importance of including mixtures in assessments of chemical immunotoxicity.

Trichloroethylene alters central and peripheral immune function in autoimmune-prone MRL(+/+) mice following continuous developmental and early life exposure

Trichloroethylene (TCE) is a widespread environmental toxicant known to promote CD4(+) T-lymphocyte activation, IFNgamma production, and autoimmunity in adult MRL(+/+) mice. Because developing tissues may be more sensitive to toxicant exposure, it was hypothesized that continuous TCE exposure beginning at conception might induce even more pronounced CD4(+) T-lymphocyte effects and exacerbate the development of autoimmunity in MRL(+/+) mice. In the current study, MRL(+/+) mice were exposed to occupationally-relevant doses of TCE from conception until adulthood (i.e., 7-8 wk-of-age). The CD4(+) T-lymphocyte effects in the thymus and periphery were evaluated, as well as serum antibody levels. TCE exposure altered the number of thymocyte subsets, and reduced the capacity of the most immature CD4-/CD8- thymocytes to undergo apoptosis in vitro. In the periphery, T-lymphocyte IFN(gamma) production was monitored in the blood prior to sacrifice by intracellular cytokine staining and flow cytometry. TCE induced a dose-dependent increase in T-lymphocyte IFN(gamma) as early as 4-5-week-of-age. However, these effects were transient, and not observed in splenic T-lymphocytes in 7-8-week-old mice. In contrast, the serum levels of anti-histone autoantibodies and total IgG(2a) were significantly elevated in the TCE-exposed offspring. The data illustrated that occupationally-relevant doses of TCE administered throughout development until adulthood affected central and peripheral immune function in association with early signs of autoimmunity. Future studies will address the possibility that early-life exposure to TCE may alter some aspect of self tolerance in the thymus, leading to autoimmune disease later in life.

Ability of trichloroethylene metabolite to promote immune pathology is strain-specific

Chronic low-level exposure to the environmental pollutant trichloroethylene has been shown to promote autoimmune disease in association with CD4(+) T-lymphocyte activation in lupus-prone MRL(+/+) mice. One of the primary metabolites of trichloroethylene, trichloroacetaldehyde hydrate (TCAH), was similarly shown to increase the percentage of IFNgamma-producing CD4(+) T-lymphocytes when added to the drinking water of MRL(+/+) mice. In addition, TCAH-treated MRL(+/+) mice developed skin inflammation and alopecia. In the present study TCAH was tested for its ability to accelerate the development of alopecia in C3H/HeJ mice which tend to develop the disorder spontaneously late in life. In contrast to MRL(+/+) mice, C3H/HeJ mice treated with TCAH did not develop alopecia at an increased rate. In addition, TCAH did not promote the expansion of activated IFNgamma-producing CD4(+) T-lymphocytes in C3H/HeJ mice. CD4(+) T-lymphocytes from TCAH-treated C3H/HeJ mice, unlike their MRL(+/+) counterparts, did not become resistant to activation-induced apoptosis following in vivo exposure to TCAH. Taken together, it appears that the ability of TCAH to promote immune-mediated pathology is strain-specific and may require an autoimmune-prone genetic background.

Environmental contaminant trichloroethylene promotes autoimmune disease and inhibits T-cell apoptosis in MRL(+/+) mice

The ability of environmental contaminant trichloroethylene to alter immune function and promote autoimmunity was tested in female MRL(+/+) mice. MRL(+/+) mice exposed to occupationally relevant doses of trichloroethylene in their drinking water for 32 weeks developed autoantibodies and pathological evidence of autoimmune hepatitis. The ability of trichloroethylene (TCE) to promote autoimmunity was associated with the expansion of activated (CD44(hi) CD62L(lo)) CD4(+) T-lymphocytes that produced increased levels of the pro-inflammatory cytokine interferon (IFN)-gamma. Activated T-lymphocytes can accumulate if activation-induced apoptosis is suppressed. Consequently, the effect of TCE on apoptosis in CD4(+) T-lymphocytes was investigated. These experiments were conducted with TCE and one of the major oxidative metabolites of trichloroethylene, namely trichloroacetaldehyde hydrate (TCAH). CD4(+) T-lymphocytes isolated from MRL(+/+) mice exposed to TCE or TCAH in their drinking water for 4 weeks were resistant to activation-induced apoptosis in vitro. The TCE-or TCAH-induced decrease in activation-induced apoptosis was associated with decreased expression of FasL, one of the cell surface molecules that mediate apoptosis. These results suggest that exposure to the common water contaminant TCE or its metabolite TCAH inhibits activation-induced apoptosis in CD4+ T-lymphocytes, thereby promoting autoimmune disease by suppressing the process that would otherwise delete activated self-reactive T-lymphocytes.

Delineating liver events in trichloroethylene-induced autoimmune hepatitis

Exposure to the environmental pollutant trichloroethylene (TCE) has been linked to autoimmune disease development in humans. Chronic (32-week) low-level exposure to TCE has been shown to promote autoimmune hepatitis in association with CD4(+) T cell activation in autoimmune-prone MRL+/+ mice. MRL+/+ mice are usually thought of as a model of systemic lupus rather than an organ-specific disease such as autoimmune hepatitis. Consequently, the present study examined gene expression and metabolites to delineate the liver events that skewed the autoimmune response toward that organ in TCE-treated mice. Female MRL+/+ mice were treated with 0.5 mg/mL TCE in their drinking water. The results showed that TCE-induced autoimmune hepatitis could be detected in as little as 26 weeks. TCE exposure also generated a time-dependent increase in the number of antibodies specific for liver proteins. The gene expression correlated with the metabolite analysis to show that TCE upregulated the methionine/homocysteine pathway in the liver after 26 weeks of exposure. The results also showed that TCE exposure altered the expression of selective hepatic genes associated with immunity and inflammation. On the basis of these results, future mechanistic studies will focus on how alterations in genes associated with immunity and inflammation, in conjunction with protein alterations in the liver, promote liver immunogenicity in TCE-treated MRL+/+ mice.

Chronic exposure to a trichloroethylene metabolite in autoimmune-prone MRL+/+ mice promotes immune modulation and alopecia

The industrial solvent trichloroethylene (TCE) is a widespread environmental contaminant known to impact the immune system. In the present study, female MRL+/+ mice were treated for 40 weeks with trichloroacetaldehyde hydrate (TCAH), a metabolite of TCE, in the drinking water. The results were compared with the data from an earlier study in which MRL+/+ mice were exposed to TCAH for 4 weeks. Following a 40-week exposure, the mice developed skin inflammation and dose-dependent alopecia. In addition, TCAH appeared to modulate the CD4(+) T-cell subset by promoting the expression of an activated/effector (i.e., CD62L(lo)) phenotype with an increased capacity to secrete the proinflammatory cytokine interferon-gamma. However, unlike what was observed after only 4 weeks of exposure, TCAH did not significantly attenuate activation-induced cell death (AICD) or the expression of the death receptor FasL in CD4(+) T cells. Some metalloproteinases (MMPs) are thought to play a role in susceptibility to AICD by inducing FasL shedding. Thus, both the 4- and 40-week sera were tested for MMP-7 levels in an attempt to explain the disparate results of TCAH on AICD and FasL expression. Serum MMP-7 levels were significantly higher in mice exposed to TCAH for 4 weeks. In contrast, the serum MMP-7 levels were increased in all the mice by 40 weeks when compared with a nonautoimmune strain. Taken together, a chronic exposure to TCAH promotes alopecia and skin inflammation. The early effects of TCAH on MMP-7 levels may provide a mechanism by which TCAH promotes skin pathology.

Exposure to a metabolite of the environmental toxicant, trichloroethylene, attenuates CD4+ T cell activation-induced cell death by metalloproteinase-dependent FasL shedding

Long-term exposure to the environmental contaminant trichloroethylene (TCE) in drinking water has been shown to promote autoimmune disease in association with the expansion of activated CD4+ T cells. The effects of TCE on CD4+ T cells were linked in the present study to the ability of TCE metabolite, trichloroacetaldehyde hydrate (TCAH), to inhibit activation-induced cell death (AICD) in CD4+ T cells. TCAH attenuated AICD in CD4+ T cells by decreasing FasL (CD178) expression but not by altering Fas (CD95) expression or by interfering with Fas-signaling events following direct engagement of the Fas receptor. The TCAH-induced decrease in FasL expression did not appear to be mediated at the transcriptional level but was instead due to increased shedding of FasL from the surface of the CD4+ T cells. The ability of TCAH to cleave FasL and thereby decrease AICD appeared to be mediated by metalloproteinases and correlated with a TCAH-induced increase in matrix metalloproteinase-7. Thus, this study presents the novel finding that the environmental contaminant TCE works via its metabolite TCAH to attenuate AICD by increasing metalloproteinase activity that cleaves FasL from CD4+ T cells. This represents a mechanism by which an environmental trigger inhibits AICD in CD4+ T cells and may thereby promote CD4+ T cell-mediated autoimmune disease.

Activation and attenuation of apoptosis of CD4+ T cells following in vivo exposure to two common environmental toxicants, trichloroacetaldehyde hydrate and trichloroacetic acid

Exposure to occupationally relevant concentrations of the environmental pollutant, trichloroethylene (TCE), in the drinking water of autoimmune-prone MRL+/+ mice has been shown to promote the generation of lupus and autoimmune hepatitis in association with the activation of Interferon-gamma (IFN-gamma)-producing CD4+ T cells. Since blocking TCE metabolism suppressed the TCE-induced alteration in immune function, the present study was initiated to determine whether the major metabolites of TCE, trichloroacetaldehyde hydrate (TCAH) and trichloroacetic acid (TCA) could also mediate these immunoregulatory affects in vivo. TCAH and TCA were administered to the drinking water of MRL+/+ mice for 4 weeks. CD4+ T cells from TCAH and TCA-treated MRL+/+ mice, unlike CD4+ T cells from control mice, demonstrated functional and phenotypic signs of activation, as evidenced by increased IFN-gamma production in association with the increased percentage of CD62L(lo) CD4+ T cells. Interestingly, it was also found that the CD4+ T cells from the TCAH and TCA-treated mice showed a decreased susceptibility to the activation-induced cell death (AICD) form of apoptosis following re-stimulation in vitro. By demonstrating that TCAH and TCA can activate CD4+ T cells and inhibit their apoptosis following in vivo exposure represents a mechanism by which environmental toxicants may induce or accelerate the development of autoimmune disease.

B cells from autoimmune BXSB mice are hyporesponsive to signals provided by CD4+ T cells

Male BXSB mice, unlike female BXSB mice, develop an early-onset, lupus-like disease characterized by high levels of anti-nuclear antibodies (Abs) and total Ig. It has recently been shown that the male BXSB mice contain an expanded population of large B cells which are hyperresponsive to stimulation by anti-CD40 mAb. The present study was undertaken to determine whether their potential for extra CD40 signaling enabled the B cells from male BXSB mice to hyper-respond to CD40L-expressing CD4+ T cells. In contrast to expectations, large B cells from male BXSB mice did not interact with CD4+ T cells in a positive manner; cultures of B cells from antigen (Ag)-primed male BXSB mice, unlike cultures of B cells from Ag-primed female mice, generated few antibody forming cells (AFC) following interaction with activated CD4+T cells. In addition, B cells from male BXSB mice, unlike B cells from female BXSB mice, failed to upregulate MHC class II molecules following interaction with activated CD4+ T cells. Subsequent experiments revealed that the inability of the B cells from the male mice to upregulate MHC class II molecules in response to T cell-mediated activation resided primarily in the population of large B cells. Large B cells from male BXSB mice were also defective in their ability to proliferate following stimulation with activated CD4+ T cells. Taken together, these findings demonstrated that similar to B cells in lupus patients, large B cells from male BXSB mice could function in a hyporesponsive manner, and that this hyporesponsiveness related to the inability of the B cells to interact in a positive manner with CD4+T cells.

Trichloroethylene accelerates an autoimmune response by Th1 T cell activation in MRL +/+ mice

Trichloroethylene (1,1,2-trichloroethene) is a major environmental contaminant. There is increasing evidence relating exposure to trichloroethylene with autoimmunity. To investigate potential mechanisms, we treated the autoimmune-prone MRL +/+ mice with trichloroethylene in the drinking water at 0, 2.5 or 5.0 mg/ml and sacrificed them at 4, 8 and 22 weeks. As early as 4 weeks of treatment, Western blot analysis showed a dose-dependent increase in the level of trichloroethylene-modified proteins, indicating that a reactive metabolite of trichloroethylene was formed. Significant increases in antinuclear antibodies (ANA) and total serum immunoglobulins were found following 4-8 weeks of trichloroethylene treatment, indicating that trichloroethylene was accelerating an autoimmune response. Investigation into possible mechanisms of this autoimmune response revealed that trichloroethylene treatment dramatically increased the expression of the activation marker CD44 on splenic CD4+ T cells at 4 weeks. In addition, splenic T cells from mice treated for 4 weeks with trichloroethylene secreted more IFN-gamma and less IL-4 than control T cells, consistent of a T-helper type 1 (Th1) type immune or inflammatory response. A specific immune response directed against dichloroacetylated proteins was found at 22 weeks of trichloroethylene treatment. Taken collectively, the results suggest that trichloroethylene treatment accelerated an autoimmune response characteristic of MRL +/+ mice in association with nonspecific activation of Th1 cells. In addition, long-term treatment with trichloroethylene led to the initiation of a trichloroethylene-specific immune response.