Gestational exposure to mercury leads to persistent changes in T-cell phenotype and function in adult DBF1mice

How fish intestinal cells responded to dietary methylmercury exposure? A single-cell transcriptomic analysis

Fish intestine is not only an important digestive and immune organ, but also serves as the first barrier to defend against methylmercury (MeHg) toxicity. Numerous studies have examined the responses of intestine to MeHg, whereas the heterogeneous responses of intestinal cells have not been addressed. In this study, the gilthead seabream were exposed to dietary MeHg, and the gene expression profiles of different intestinal cell populations were examined using scRNA-seq technique. We demonstrated that among the 14 cell types identified, enterocytes, macrophages, T cells and goblet cells were the primary target cell populations exhibiting specific responses to MeHg. Enterocytes appeared to play the most important role in the MeHg transport across the intestinal epithelium as well as intracellular storage. The immune pathways of macrophages and T cells were suppressed by MeHg, which also interfered with the mucus production and secretion in the goblet cells. Furthermore, MeHg not only affected the cell-cell adhesion of the target cells, but also resulted in disorder of lipid metabolism and immune function, thereby leading to increased susceptibility to pathogenic infections. This study provides an important understanding of the specific responses of intestinal cells to MeHg exposure at the cellular level.

Maternal gestational mercury exposure in relation to cord blood T cell alterations and placental gene expression signatures

The immunotoxic impacts of mercury during early life is poorly understood. We investigated the associations between gestational mercury exposure and frequency of cord blood T cells as well as placental gene expression. Frequency of natural Treg cells was positively associated with prenatal and postpartum mercury toenail concentrations. Frequency of NKT and activated naïve Th cells was positively associated with prenatal toenail mercury concentrations and number of maternal silver-mercury dental amalgams, respectively. Placental gene expression analyses revealed distinct gene signatures associated with mercury exposure. Decreased placental expression of a histone demethylase, KDM4DL, was associated with both higher prenatal and postpartum maternal toenail mercury levels among male infants and remained statistically significant after adjustment for fish and seafood consumption. The results suggest that gestational exposure to mercury concentrations contribute to alterations in both T cells and gene expression in placenta at birth. These alterations may inform mechanisms of mercury immunotoxicity.

Maternal blood metal concentrations and whole blood DNA methylation during pregnancy in the Early Autism Risk Longitudinal Investigation (EARLI)

The maternal epigenome may be responsive to prenatal metals exposures. We tested whether metals are associated with concurrent differential maternal whole blood DNA methylation. In the Early Autism Risk Longitudinal Investigation cohort, we measured first or second trimester maternal blood metals concentrations (cadmium, lead, mercury, manganese, and selenium) using inductively coupled plasma mass spectrometry. DNA methylation in maternal whole blood was measured on the Illumina 450 K array. A subset sample of 97 women had both measures available for analysis, all of whom did not report smoking during pregnancy. Linear regression was used to test for site-specific associations between individual metals and DNA methylation, adjusting for cell type composition and confounding variables. Discovery gene ontology analysis was conducted on the top 1,000 sites associated with each metal. We observed hypermethylation at 11 DNA methylation sites associated with lead (FDR False Discovery Rate q-value <0.1), near the genes CYP24A1, ASCL2, FAT1, SNX31, NKX6-2, LRC4C, BMP7, HOXC11, PCDH7, ZSCAN18, and VIPR2. Lead-associated sites were enriched (FDR q-value <0.1) for the pathways cell adhesion, nervous system development, and calcium ion binding. Manganese was associated with hypermethylation at four DNA methylation sites (FDR q-value <0.1), one of which was near the gene ARID2. Manganese-associated sites were enriched for cellular metabolism pathways (FDR q-value<0.1). Effect estimates for DNA methylation sites associated (p < 0.05) with cadmium, lead, and manganese were highly correlated (Pearson ρ > 0.86). DNA methylation sites associated with lead and manganese may be potential biomarkers of exposure or implicate downstream gene pathways.

Manganese is associated with increased plasma interleukin-1β during pregnancy, within a mixtures analysis framework of urinary trace metals

Exposure to trace metals may impact reproductive health outcomes through perturbations in maternal immune signaling molecules. We conducted a cross-sectional study of 390 pregnant women from the LIFECODES birth cohort and investigated the associations between 17 urinary metals and five immune biomarkers measured in the 3rd trimester (median 26 weeks gestation). We used linear regression to estimate pair-wise associations and applied elastic net and Bayesian kernel machine regression to identify important contributing exposures analytes as well as non-linear effects. Maternal urinary manganese, nickel, and barium were positively associated with maternal plasma interleukin-1β (IL-1β). Elastic net and Bayesian kernel machine regression identified manganese as the dominant trace metal in association with IL-1β. An interquartile range difference in manganese (0.6 μg/L) was associated with a 29 % increase in IL-1β (95 % CI: 12.4-48.2). In conclusion, trace metal exposures were associated with biomarkers of immune perturbations, and this warrants further investigation.

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.

Effects of Periconception Cadmium and Mercury Co-Administration to Mice on Indices of Chronic Diseases in Male Offspring at Maturity

BACKGROUND

Long-term exposure to the heavy metals cadmium (Cd) and mercury (Hg) is known to increase the risk of chronic diseases. However, to our knowledge, exposure to Cd and Hg beginning at the periconception period has not been studied to date.

OBJECTIVE

We examined the effect of Cd and Hg that were co-administered during early development on indices of chronic diseases in adult male mice.

METHODS

Adult female CD1 mice were subcutaneously administered a combination of cadmium chloride (CdCl₂) and methylmercury (II) chloride (CH₃HgCl) (0, 0.125, 0.5, or 2.0 mg/kg body weight each) 4 days before and 4 days after conception (8 days total). Indices of anxiety-like behavior, glucose homeostasis, endocrine and molecular markers of insulin resistance, and organ weights were examined in adult male offspring.

RESULTS

Increased anxiety-like behavior, impaired glucose homeostasis, and higher body weight and abdominal adipose tissue weight were observed in male offspring of treated females compared with controls. Significantly increased serum leptin and insulin concentrations and impaired insulin tolerance in the male offspring of dams treated with 2.0 mg/kg body weight of Cd and Hg suggested insulin resistance. Altered mRNA abundance for genes associated with glucose and lipid homeostasis (GLUT4, IRS1, FASN, ACACA, FATP2, CD36, and G6PC) in liver and abdominal adipose tissues as well as increased IRS1 phosphorylation in liver (Ser 307) provided further evidence of insulin resistance.

CONCLUSIONS

Results suggest that the co-administration of Cd and Hg to female mice during the early development of their offspring (the periconception period) was associated with anxiety-like behavior, altered glucose metabolism, and insulin resistance in male offspring at adulthood.

Identification of a unique gene expression signature in mercury and 2,3,7,8-tetrachlorodibenzo-p-dioxin co-exposed cells

Mercury (Hg) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are major environmental contaminants that commonly co-occur in the environment. Both Hg and TCDD are associated with a number of human diseases including cancers. While the individual toxicological effects of Hg and TCDD have been extensively investigated, studies on co-exposure are limited to a few genes and pathways. Therefore, a significant knowledge gap exists in the understanding of the deleterious effects of co-exposure to Hg and TCDD. Due to the prevalence of Hg and TCDD co-contamination in the environment and the major human health hazards they pose, it is important to obtain a fuller understanding of genome-wide effects of Hg and TCDD co-exposure. In this study, by performing a comprehensive transcriptomic analysis of human bronchial epithelial cells (BEAS-2B) exposed to Hg and TCDD individually and in combination, we have uncovered a subset of genes with altered expression only in the co-exposed cells. We also identified the additive as well as antagonistic effects of Hg and TCDD on gene expression. Moreover, we found that co-exposure impacted several biological and disease processes not affected by Hg or TCDD individually. Our studies show that the consequences of Hg and TCDD co-exposure on the transcriptional program and biological processes could be substantially different from single exposures, thus providing new insights into the co-exposure-specific pathogenic processes.

Chronic MeHg exposure modifies the histone H3K4me3 epigenetic landscape in Caenorhabditis elegans

Methylmercury (MeHg) is a persistent environmental pollutant that occurs in the food chain, at occupational sites, and via medical procedures. Exposure in humans and animal models results in renal, neuro, and reproductive toxicities. In this study, we demonstrate that chronic exposure to MeHg (10μM) causes epigenetic landscape modifications of histone H3K4 trimethylation (H3K4me3) marks in Caenorhabditis elegans using chromatin immuno-precipitation sequencing (ChIP-seq). The modifications correspond to the locations of 1467 genes with enhanced and 508 genes with reduced signals. Among enhanced genes are those encoding glutathione-S-transferases, lipocalin-related protein and a cuticular collagen. ChIP-seq enhancement of these genes was confirmed with increased mRNA expression levels revealed by qRT-PCR. Furthermore, we observed enhancement of H3K4me3 marks in these genes in animals exposed to MeHg in utero and assayed at L4 stage. In utero exposure enhanced marks without alterations in mRNA expression except for the lpr-5 gene. Finally, knockdown of lipocalin-related protein gene lpr-5, which is involved in intercellular signaling, and cuticular collagen gene dpy-7, structural component of the cuticle, by RNA interference (RNAi) resulted in increased lethality of animals after MeHg exposure. Our results provide new data on the epigenetic landscape changes elicited by MeHg exposure, as well as describe a unique model for studying in utero effects of heavy metals. Together, these findings may help to understand the toxicological effects of MeHg at the molecular level.

Renal oxidative stress and renal CD8(+) T-cell infiltration in mercuric chloride-induced nephropathy in rats: role of angiotensin II

Mercuric chloride (HgCl2) induces kidney damage, in part, through oxidative stress. A role for angiotensin II (Ang II) in pro-inflammatory events in a model of acute HgCl2-induced nephropathy was reported. Ang II is a potent oxidative stress inducer; however, its role in oxidative/anti-oxidative events in HgCl2-induced nephropathy remains unknown. The aim of this study was to determine the role of Ang II in the oxidative stress and renal infiltration of CD8(+) T-cells after an acute HgCl2 intoxication. Three groups of Sprague Dawley rats were treated with a single subcutaneous dose of 2.5 mg/kg HgCl2: for 3 days prior to and for 4 days after that injection, rats in one group received Losartan (30 mg/kg), in another group Enalapril (30 mg/kg) or normal saline in the last group. Two other groups of drug-treated rats received saline in place of HgCl2. A final group of rats received saline in place of HgCl2 and the test drugs. All treatments were via gastric gavage. At 96 h after the vehicle/HgCl2 injection, blood and kidney samples were harvested. Renal sections were homogenized for measures of malondialdehyde (MDA), reduced glutathione (GSH) and catalase activity. Frozen sections were studied for the presence of superoxide anion ([Formula: see text]) and CD8(+) T-cells. HgCl2-treated rats had increased interstitial and tubular expression of [Formula: see text], high levels of MDA, normal catalase activity and GSH content, increased levels of interstitial CD8(+) T-cells and an increased percentage of necrotic tubules. Anti-Ang II treatments diminished the HgCl2-induced increases in interstitial [Formula: see text], CD8(+) T-cells and tubular damage and increased catalase and GSH expression above that due to HgCl2 alone; the HgCl2-induced high MDA levels were unaffected by the drugs. These data provide new information regarding the potential role of Ang II in the oxidative stress and renal CD8(+) T-cell infiltration that occur during HgCl2 nephropathy.