Mercury stimulates rat liver glucocorticoid receptor association with Hsp90 and Hsp70

Antarctic seals: Molecular biomarkers as indicators for pollutant exposure, health effects and diet

Weddell (Leptonychotes weddellii), Ross (Ommatophoca rossii) and crabeater seals (Lobodon carcinophaga) are phocid seals with a circumpolar distribution around Antarctica. As long-lived and large top predators, they bioaccumulate contaminants and are considered as sentinels of ecosystem health. Antarctic seals are increasingly exposed to climate change, pollution, shipping and fisheries. To reveal and understand possible anthropogenic impacts on their immune and health status, this study investigates sensitive biomarkers of the xenobiotic metabolism and immune system in relation to mercury (Hg) burden. Gene-transcription studies using minimally-invasive blood samples are useful to monitor physiological processes in wildlife that can be related to different stressors. Blood samples of 72 wild-caught seals (Weddell n=33; Ross n=12; crabeater n=27) in the Amundsen and Ross Seas in 2008-2011 were investigated. Copy numbers per μl mRNA transcription of xenobiotic biomarkers (aryl hydrocarbon receptor (AHR)), aryl hydrocarbon receptor nuclear translocator (ARNT) and peroxisome proliferator-activated receptor (PPARα) and immune relevant cell mediators (cytokines interleukin-2 (IL-2), interleukin-10 (IL-10) and heat-shock-protein 70 (HSP70)) were measured using reference genes Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide (YWHAZ) and ribosomal protein L4 (RPL4) by real time RT-qPCR. Hg concentration was analysed in fur. Hg concentration increased with body weight and standard length in all species. Crabeater seals showed a lower Hg concentration than Ross and Weddell seals. Species-specific differences in gene-transcription were found between all species with highest levels of AHR, ARNT and PPARα in crabeater seals. Ross seals showed highest IL-10 and HSP70 transcription, while HSP70 was exceptionally low in crabeater seals. Between Hg and HSP70 a clear negative relationship was found in all species. The species-specific, age and sex-dependent gene-transcription probably reflect dietary habits, pollutant exposure and immune status.

Mercury and psychosocial stress exposure interact to predict maternal diurnal cortisol during pregnancy

BACKGROUND

Disrupted maternal prenatal cortisol production influences offspring development. Factors influencing the hypothalamic-pituitary-adrenal axis include social (e.g., stressful life events) and physical/chemical (e.g., toxic metals) pollutants. Mercury (Hg) is a common contaminant of fish and exposure is widespread in the US. No prior study has examined the joint associations of stress and mercury with maternal cortisol profiles in pregnancy.

OBJECTIVES

To investigate potential synergistic influences of prenatal stress and Hg exposures on diurnal cortisol in pregnant women.

METHODS

Analyses included 732 women (aged 27.4 ± 5.6 years) from a Mexico City pregnancy cohort. Participants collected saliva samples on two consecutive days (mean 19.52 ± 3.00 weeks gestation) and reported life stressors over the past 6 months. Hg was assessed in toe nail clippings collected during pregnancy.

RESULTS

There were no main effects of Hg or psychosocial stress exposure on diurnal cortisol (ps > .20) but strong evidence of interaction effects on cortisol slope (interaction B = .006, SE = .003, p = .034) and cortisol at times 1 and 2 (interaction B = -.071, SE = .028, p = .013; B = -.078, SE = .032, p = .014). Women above the median for Hg and psychosocial stress exposure experienced a blunted morning cortisol response compared to women exposed to higher stress but lower Hg levels.

CONCLUSIONS

Social and physical environmental factors interact to alter aspects of maternal diurnal cortisol during pregnancy. Research focusing solely on either domain may miss synergistic influences with potentially important consequences to the offspring.

SiRNA-mediated knockdown of CiGRP78 gene expression leads cell susceptibility to heavy metal cytotoxicity

Heavy metal ion is one of the critical environmental pollutants accumulated in living organisms and causes toxic or carcinogenic effects once passed threshold levels. As an important member of Hsp70 (heat shock protein 70) family, the 78-kDa glucose-regulated protein (GRP78) can enhance cell survival rates remarkably under thermal stress. Recent studies also demonstrated that the expression of GRP78 enhances the cell survival under heavy metal stress. In this study, three most representative heavy metal ions, Pb(2+), Hg(2+) and Cd(2+), were used to stimulate Ctenopharyngodon idella kidney (CIK) cells. The results showed that cell viability under Pb(2+), Hg(2+) and Cd(2+) stress decreased significantly. The longer and the greater the concentrations of stimulation from heavy metal ions, the higher the rate of cell death was observed. Among them, Hg(2+) is the most hazardous to cells. Under the same stress condition, Hg(2+) resulted in 50% of cell death, Cd(2+) (or Pb(2+)) led to 45% (or 35%) of cell death, respectively. Western immunoblotting indicated that C. idella GRP78 (CiGRP78) protein expression level was enhanced obviously in CIK cells under Pb(2+), Hg(2+) and Cd(2+) stress, meaning CiGRP78 is involved in heavy metal cytotoxicity. To further study the role of CiGRP78 in cytoprotection, we designed the siRNA against CiGRP78 (from nucleotides +788 to +806) and transfected it into CIK cells to silence endogenous CiGRP78. The viability rate of CIK cells transfected with or without siRNA incubated with HgCl2 for 12h showed a significant decrease from 50% to 21%. Our results showed that CiGRP78 protects cells against heavy metal stimuli to some extent.

Mineralocorticoid receptor and heat shock protein expression levels in peripheral lymphocytes from war trauma-exposed men with and without PTSD

Alterations in the number and functional status of mineralocorticoid (MR) and glucocorticoid receptors (GR) may contribute to vulnerability to posttraumatic stress disorder (PTSD). Corticosteroid receptors are chaperoned by heat shock proteins Hsp90 and Hsp70. We examined relations between corticosteroid receptor and heat shock protein expression levels, and related them with war trauma exposure, PTSD and resilience to PTSD. Relative levels of MR, Hsp90 and Hsp70 were determined by immunoblotting in lymphocytes from war trauma-exposed men with current PTSD (current PTSD group, n=113), with life-time PTSD (life-time PTSD group, n=61) and without PTSD (trauma control group, n=88), and from non-traumatized healthy controls (healthy control group, n=85). Between-group differences in MR, Hsp90 and Hsp70 levels and in MR/GR ratio were not observed. The level of MR was correlated with both Hsp90 and Hsp70 levels in trauma control and healthy control groups. On the other hand, GR level was correlated only with Hsp90 level, and this correlation was evident in current PTSD and trauma control groups. In conclusion, PTSD and exposure to trauma are not related to changes in lymphocyte MR, Hsp90 or Hsp70 levels, but may be associated with disturbances in corticosteroid receptors interaction with heat shock proteins.

The glucocorticoid receptor: a revisited target for toxins

The hypothalamic-pituitary-adrenal (HPA) axis activation and glucocorticoid responses are critical for survival from a number of bacterial, viral and toxic insults, demonstrated by the fact that removal of the HPA axis or GR blockade enhances mortality rates. Replacement with synthetic glucocorticoids reverses these effects by providing protection against lethal effects. Glucocorticoid resistance/insensitivity is a common problem in the treatment of many diseases. Much research has focused on the molecular mechanism behind this resistance, but an area that has been neglected is the role of infectious agents and toxins. We have recently shown that the anthrax lethal toxin is able to repress glucocorticoid receptor function. Data suggesting that the glucocorticoid receptor may be a target for a variety of toxins is reviewed here. These studies have important implications for glucocorticoid therapy.

The impact of methylmercury on 1,25-dihydroxyvitamin D3-induced transcriptomic responses in dolphin skin cells

The Atlantic bottlenose dolphin has been the focus of much attention owing to the considerable impact of environmental stress on its health and the associated implications for human health. Here, we used skin cells from the dolphin to investigate the protective role of the vitamin D pathway against environmental stressors. We previously reported that dolphin skin cells respond to 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive metabolite of vitamin D3, by upregulation of the vitamin D receptor (VDR) and expression of several genes. Methylmercury is a highly bioaccumulative environmental stressor of relevance to the dolphin. We currently report that in dolphin cells sublethal concentrations of methylmercury compromise the ability of 1,25D3 to upregulate VDR, to transactivate a vitamin D-sensitive promoter, and to express specific target genes. These results help elucidate the effects of vitamin D and methylmercury on innate immunity in dolphin skin and potentially in human skin as well, considering similarities in the vitamin D pathway between the two species.

Mercury exposure, nutritional deficiencies and metabolic disruptions may affect learning in children

Among dietary factors, learning and behavior are influenced not only by nutrients, but also by exposure to toxic food contaminants such as mercury that can disrupt metabolic processes and alter neuronal plasticity. Neurons lacking in plasticity are a factor in neurodevelopmental disorders such as autism and mental retardation. Essential nutrients help maintain normal neuronal plasticity. Nutritional deficiencies, including deficiencies in the long chain polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid, the amino acid methionine, and the trace minerals zinc and selenium, have been shown to influence neuronal function and produce defects in neuronal plasticity, as well as impact behavior in children with attention deficit hyperactivity disorder. Nutritional deficiencies and mercury exposure have been shown to alter neuronal function and increase oxidative stress among children with autism. These dietary factors may be directly related to the development of behavior disorders and learning disabilities. Mercury, either individually or in concert with other factors, may be harmful if ingested in above average amounts or by sensitive individuals. High fructose corn syrup has been shown to contain trace amounts of mercury as a result of some manufacturing processes, and its consumption can also lead to zinc loss. Consumption of certain artificial food color additives has also been shown to lead to zinc deficiency. Dietary zinc is essential for maintaining the metabolic processes required for mercury elimination. Since high fructose corn syrup and artificial food color additives are common ingredients in many foodstuffs, their consumption should be considered in those individuals with nutritional deficits such as zinc deficiency or who are allergic or sensitive to the effects of mercury or unable to effectively metabolize and eliminate it from the body.

Human Serum Albumin−Mercurial Species Interactions

Binding of metal ions to the heteroatomic sites of proteins is undoubtedly fundamental to their observed physiological effects. In this paper, the interactions of inorganic mercury (Hg2+), methylmercury (MeHg+), ethylmercury (EtHg+), and phenylmercury (PhHg+) with human serum albumin (HSA) were studied from the electrophoretic behaviors, stoichiometry, thermodynamics, and kinetics by using a new hybrid technique, capillary electrophoresis on-line coupled with electrothermal atomic absorption spectrometry (CE-ETAAS), together with the consequent structural information from circular dichroism and Raman spectroscopy. The stoichiometry (mercurial species to HSA) for the interactions of Hg2+, MeHg+, EtHg+, and PhHg+ with HSA was found to be 6:1, 4:1, 4:1, and 3:1, respectively. Two types of binding sites in HSA were observed for the binding of mercurial species with the orders of magnitude of binding constants of 10(7) and 10(6) L mol-1, respectively, showing strong affinity of mercurial species for HSA. The interactions of mercurial species with both types of binding sites in HSA are exothermic and thermodynamically favorable and are both enthalpically and entropically driven. The binding of mercurial species to HSA follows the first-order kinetics for mercurial species and zero-order kinetics for HSA with the apparent activation energy of 57-59 kJ mol-1. Among the four mercurial species examined, only Hg2+ induces the secondary structure transition of HSA. Mercury-HSA adducts are formed mainly through metal-sulfur binding with participation of C=O and/or C-N groups of amino acid residues in HSA molecules. The present work represents the most comprehensive study on the interactions between various mercurial species with HSA and provides new evidence for and insights into the interactions of mercurial species with HSA for further understanding of the toxicological effects of mercurial species.

Mercury influences rat liver tyrosine aminotransferase activity and induction by dexamethasone

The effects of mercury (Hg) on basal and dexamethasone-induced tyrosine aminotransferase (TAT) activity in rat liver were studied. Comparison of TAT activity after in vitro and in vivo mercury application revealed the influence of the metal only when applied in vivo, suggesting that the effects are expressed at the level of TAT gene transcription. Intraperitoneal administration of mercury at 1, 2 or 3 mg Hg kg(-1) b.w. 4 h before decapitation was shown to stimulate the basal activity of TAT. The most prominent increase was observed 4 h after the metal administration. When applied at 1 and 2 mg Hg kg(-1) b.w. mercury was also shown to reduce partially the extent of the enzyme induction by dexamethasone, which was injected intraperitoneally at 5 mg kg(-1) b.w. 5 h before death. The highest dose of mercury (3 mg Hg kg(-1) b.w.) almost completely abolished the dexamethasone effect. The finding that mercury increases basal activity of the enzyme while decreasing its induction by dexamethasone suggests that stimulatory effects of this metal on TAT activity are probably mediated by factors other than glucocorticoids.

Interaction of rat renal glucocorticoid receptor with Hsp90 and Hsp70 upon stress provoked by mercury

The influence of mercury on the association of rat kidney glucocorticoid receptor (GR) with heat shock proteins Hsp90 and Hsp70 was investigated. The GR heterocomplexes with Hsp90 and Hsp70 were immunopurified from the renal cytosol of rats administered different doses of mercury (1, 2 and 3 mg Hg kg(-1) b.w.). A quantitative immunoblotting procedure was applied to determine the levels of GR, Hsp90 and two nucleocytoplasmic Hsp70 isoforms (constitutive Hsp73 and inducible Hsp72) in the renal cytosol, as well as the amounts of these proteins within GR heterocomplexes immunoprecipitated by anti-GR antibody. Mercury was found to stimulate GR association with all the examined Hsps. The most prominent effect of the metal was stimulation of Hsp72 interaction with GR. On the other hand, the metal administration led to an increase of Hsp90 level in the cytosol, while the cytosolic levels of Hsp70 isoforms remained unaltered. These findings suggest that association of Hsps, at least Hsp70, with the GR might be ascribed to changes in the affinity of their interaction rather than to changes in the Hsp availability in the cytosol. Therefore, GR heterocomplex assembly seems to be a controlled process enabling chaperoning and functioning of the GR to be in concert with physiological demands.

Alteration of glucocorticoid receptor subcellular distribution by hyperthermic stress

The aim of the present study was to examine intracellular redistribution of the glucocorticoid receptor (GR) in rat liver cells during a 24-h time period after exposure of the animals to 41?C whole body hyperthermic stress. The level of the receptor protein in the cytoplasmic and nuclear compartments was measured by immunoblotting procedures applied to both crude cytosol and immunopurified GR, as well as by immunocytochemical analyses applied to both paraffin-embedded liver sections and unfixed nuclear smears. All the experimental approaches employed in the study provided similar results, demonstrating that the transient stress-related decline of the cytoplasmic GR observed during the first five hours after exposure of the animals to whole-body hyperthermic stress is accompanied by enhanced nuclear accumulation of the receptor. The study can contribute to a better understanding of the influence of stress on the glucocorticoid signal transduction pathway. .