Metallothionein induction in response to restraint stress. Transcriptional control, adaptation to stress, and role of glucocorticoid

Hepatic Homeostasis of Metal Ions Following Acute Repeated Stress Exposure in Rats

Essential metals such as copper, iron, and zinc are cofactors in various biological processes including oxygen utilisation, cell growth, and biomolecular synthesis. The homeostasis of these essential metals is carefully controlled through a system of protein transporters involved in the uptake, storage, and secretion. Some metal ions can be transformed by processes including reduction/oxidation (redox) reactions, and correspondingly, the breakdown of metal ion homeostasis can lead to formation of reactive oxygen and nitrogen species. We have previously demonstrated rapid biochemical responses to stress involving alterations in the redox state to generate free radicals and the resultant oxidative stress. However, the effects of stress on redox-active metals including iron and copper and redox-inert zinc have not been well characterised. Therefore, this study aims to examine the changes in these essential metals following exposure to short-term repeated stress, and to further elucidate the alterations in metal homeostasis through expression analysis of different metal transporters. Outbred male Wistar rats were exposed to unrestrained (control), 1 day, or 3 days of 6 h restraint stress (n = 8 per group). After the respective stress treatment, blood and liver samples were collected for the analysis of biometal concentrations and relative gene expression of metal transporter and binding proteins. Exposure to repeated restraint stress was highly effective in causing hepatic redox imbalance. Stress was also shown to induce hepatic metal redistribution, while modulating the mRNA levels of key metal transporters. Overall, this study is the first to characterise the gene expression profile of metal homeostasis following stress and provide insight into the changes occurring prior to the onset of chronic stress conditions.

Induction of metallothionein by stress and its molecular mechanisms

This article describes the effect of restraint stress or social reorganization stress on the induction of metallothionein (MT) in the liver, heart, lung, and spleen. Both MT-I and MT-II mRNA were elevated as much as 30-fold following just 12 h (one cycle) of restraint stress. The amount of MT protein also increased following stress. The MT induction was the highest in the liver, followed by the lung, heart, and spleen. MT-I induction was also observed in the fore, mid, and hind regions of the brain whereas the brain-specific MT-III gene was not activated by stress. The increase in MT mRNA correlated well with the rise in stress-induced serum corticosterone. The induction occurred at the transcriptional level and was mediated essentially by the activation of glucocorticoid receptor. The MT mRNA returned to the control level after nine cycles of stress. Exposure of these habituated mice to a different type of stress (treatment with heavy metals such as cadmium or zinc sulfate) led to further MT induction. Because heavy metals induced MT via activation of the factor MTF-1, distinct molecular mechanisms should be responsible for the activation of MT promoter by different inducers.

Brain and Hepatic Mt mRNA Is Reduced in Response to Mild Energy Restriction and n-3 Polyunsaturated Fatty Acid Deficiency in Juvenile Rats

Metallothioneins (MTs) perform important regulatory and cytoprotective functions in tissues including the brain. While it is known that energy restriction (ER) and dietary n-3 polyunsaturated fatty acid (PUFA) deficiency impact postnatal brain growth and development, little data exist regarding the impact of undernutrition upon MT expression in growing animals. We tested the hypothesis that ER with and without dietary n-3 PUFA deficiency reduces MT expression in juvenile rats. ER rats were individually pair-fed at 75% of the ad libitum (AL) intake of control rats provided diets consisting of either soybean oil (SO) that is α-linolenic acid (ALA; 18:3n-3) sufficient or corn oil (CO; ALA-deficient). Fatty acids (FA) and metal concentrations of liver and brain regions were analyzed. Tissue expression of MTs (Mt1-3) and modulators of MT expression including glucocorticoid receptors (Nr3c1 and Nr3c2) and several mediators of thyroid hormone regulation (Dio1-3, Mct8, Oatp1c1, Thra, and Thrb) were measured. Plasma corticosterone and triiodothyronine levels were also evaluated. ER, but not metal deficiency, reduced Mt2 expression in the cerebellum (50%) and cerebral cortex (23%). In liver, a reduction in dietary n-3 PUFA reduced Mt1, Mt2, Nr3c1, Mct8, and Thrb. ER elevated Nr3c1, Dio1, and Thrb and reduced Thra in the liver. Given MT’s role in cellular protection, further studies are needed to evaluate whether ER or n-3 PUFA deficiency may leave the juvenile brain and/or liver more susceptible to endogenous or environmental stressors.

Challenging the Metallothionein (MT) Gene of Biomphalaria glabrata: Unexpected Response Patterns Due to Cadmium Exposure and Temperature Stress

Metallothioneins (MTs) are low-molecular-mass, cysteine-rich, metal binding proteins. In most animal species, they are involved in metal homeostasis and detoxification, and provide protection from oxidative stress. Gastropod MTs are highly diversified, exhibiting unique features and adaptations like metal specificity and multiplications of their metal binding domains. Here, we show that the MT gene of Biomphalaria glabrata, one of the largest MT genes identified so far, is composed in a unique way. The encoding for an MT protein has a three-domain structure and a C-terminal, Cys-rich extension. Using a bioinformatic approach involving structural and in silico analysis of putative transcription factor binding sites (TFBs), we found that this MT gene consists of five exons and four introns. It exhibits a regulatory promoter region containing three metal-responsive elements (MREs) and several TFBs with putative involvement in environmental stress response, and regulation of gene expression. Quantitative real-time polymerase chain reaction (qRT-PCR) data indicate that the MT gene is not inducible by cadmium (Cd) nor by temperature challenges (heat and cold), despite significant Cd uptake within the midgut gland and the high Cd tolerance of metal-exposed snails.

Absence of metallothionein-3 produces changes on MT-1/2 regulation in basal conditions and alters hypothalamic-pituitary-adrenal (HPA) axis

Metallothioneins (MTs) are multipurpose proteins with clear antioxidant, anti-inflammatory and metal homeostasis properties. The roles of brain MT-1 and MT-2 are similar to those described in the periphery, and are inducible by metals, inflammatory and stress stimuli. MT-3, originally named growth inhibitory factor, exists mainly in the central nervous system, is hardly ever inducible and its functional role and regulation are poorly understood and controversial. In the present study we examined how absence of MT-3 affects phenotypic characteristics and its effects on MT1/2 expression in basal situation and after induction. Hyperactive behavior was found only in young male Mt-3 KO mice and disappeared in the older ones. Absence of MT-3 was associated with a significant increase of MT-1/2 protein levels in several brain areas but decreased MT-1 mRNA levels, which might be related to lower corticosterone levels. The response to stress or inflammation on corticosterone plasma levels was similar in wild type and Mt-3 KO mice, suggesting that the relevant MT-3 role as MT-1/2 regulator in basal conditions is lost when other important regulatory factors such as glucocorticoids or cytokines appear.

Magnetic field effects on mitochondrion-activity-related optical properties in slime mold and bone forming cells

In the present study, a cellular level response of Cyto-aa3 oxidation was investigated in real time under both time-varying and strong static magnetic fields of 5 T. Two kinds of cells, a slime mold, Physarum polycephalum, and bone forming cells, MC-3T3-E1, were used for the experiments. The oxidation level of the Cyto-aa3 was calculated by optical absorptions at 690 nm, 780 nm and 830 nm. The sample, fiber-optics and an additional optical fiber for light stimulation were set in a solenoidal coil or the bore of a 5-T superconducting magnet. The solenoidal coil for time-varying magnetic fields produced sinusoidal magnetic fields of 6 mT. The slime mold showed a periodic change in Cyto-aa3 oxidation, and the oxidation-reduction cycle of Cyto-aa3 was apparently changed when visible-light irradiated the slime mold. Similarly to the case with light, time-varying magnetic stimulations changed the oxidation-reduction cycle during and after the stimulation for 10 minutes. The same phenomena were observed in the MC-3T3-E1 cell assembly, although their cycle rhythm was comparatively random. Finally, magnetic field exposure of up to 5 T exhibited a distinct suppression of Cyto-aa3 oscillation in the bone forming cells. Exposure up to 5 T was repeated five times, and the change in Cyto-aa3 oxidation reproducibly occurred.

Genes involved in the astrocyte-neuron lactate shuttle (ANLS) are specifically regulated in cortical astrocytes following sleep deprivation in mice

STUDY OBJECTIVES

There is growing evidence indicating that in order to meet the neuronal energy demands, astrocytes provide lactate as an energy substrate for neurons through a mechanism called "astrocyte-neuron lactate shuttle" (ANLS). Since neuronal activity changes dramatically during vigilance states, we hypothesized that the ANLS may be regulated during the sleep-wake cycle. To test this hypothesis we investigated the expression of genes associated with the ANLS specifically in astrocytes following sleep deprivation. Astrocytes were purified by fluorescence-activated cell sorting from transgenic mice expressing the green fluorescent protein (GFP) under the control of the human astrocytic GFAP-promoter.

DESIGN

6-hour instrumental sleep deprivation (TSD).

SETTING

Animal sleep research laboratory.

PARTICIPANTS

Young (P23-P27) FVB/N-Tg (GFAP-GFP) 14Mes/J (Tg) mice of both sexes and 7-8 week male Tg and FVB/Nj mice.

INTERVENTIONS

Basal sleep recordings and sleep deprivation achieved using a modified cage where animals were gently forced to move.

MEASUREMENTS AND RESULTS

Since Tg and FVB/Nj mice displayed a similar sleep-wake pattern, we performed a TSD in young Tg mice. Total RNA was extracted from the GFP-positive and GFP-negative cells sorted from cerebral cortex. Quantitative RT-PCR analysis showed that levels of Glut1, α-2-Na/K pump, Glt1, and Ldha mRNAs were significantly increased following TSD in GFP-positive cells. In GFP-negative cells, a tendency to increase, although not significant, was observed for Ldha, Mct2, and α-3-Na/K pump mRNAs.

CONCLUSIONS

This study shows that TSD induces the expression of genes associated with ANLS specifically in astrocytes, underlying the important role of astrocytes in the maintenance of the neuro-metabolic coupling across the sleep-wake cycle.

Metallothionein-I- and -II-deficient mice display increased susceptibility to cadmium-induced fetal growth restriction

Maternal cadmium exposure induces fetal growth restriction (FGR), but the underlying mechanisms remain largely unknown. The placenta is the main organ known to protect the fetus from environmental toxins such as cadmium. In this study, we examine the role of the two key placental factors in cadmium-induced FGR. The first is placental enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), which is known to protect the fetus from exposure to high cortisol levels and subsequently FGR, and the second the cadmium binding/sequestering proteins metallotheionein (MT)-I and -II. Using the MT-I/II(-/-) mouse model, pregnant mice were administered cadmium, following which pups and placentas were collected and examined. MT-I/II(-/-) pups exposed to cadmium were significantly growth restricted, but neither placental weight nor 11β-HSD2 was altered. Although cadmium administration did not result in any visible structural changes in the placenta, increased apoptosis was detected in MT-I/II(-/-) placentas following cadmium exposure, with a significant increase in levels of both p53 and caspase 3 proteins. Additionally, glucose transporter (GLUT1) was significantly reduced in MT-I/II(-/-) placentas of pups exposed to cadmium, whereas zinc transporter (ZnT-1) remained unaltered. Taken together, these results demonstrate that MT-I/II(-/-) mice are more vulnerable to cadmium-induced FGR. The present data also suggest that increased apoptosis and reduced GLUT1 expression in the placenta contribute to the molecular mechanisms underlying cadmium-induced FGR.

The aryl hydrocarbon receptor and glucocorticoid receptor interact to activate human metallothionein 2A

Although the aryl hydrocarbon receptor (AHR) and glucocorticoid receptor (GR) play essential roles in mammalian development, stress responses, and other physiological events, crosstalk between these receptors has been the subject of much debate. Metallothioneins are classic glucocorticoid-inducible genes that were reported to increase upon treatment with AHR agonists in rodent tissues and cultured human cells. In this study, the mechanism of human metallothionein 2A (MT2A) gene transcription activation by AHR was investigated. Cotreatment with 3-methylcholanthrene and dexamethasone, agonists of AHR and GR respectively, synergistically increased MT2A mRNA levels in HepG2 cells. MT2A induction was suppressed by RNA interference against AHR or GR. Coimmunoprecipitation experiments revealed a physical interaction between AHR and GR proteins. Moreover, chromatin immunoprecipitation assays indicated that AHR was recruited to the glucocorticoid response element in the MT2A promoter. Thus, we provide a novel mechanism whereby AHR modulates expression of human MT2A via the glucocorticoid response element and protein-protein interactions with GR.

Using biomarkers in an evolutionary context: lessons from the analysis of biological responses of oligochaete annelids to metal exposure

Anthropogenic activities may lead to the accumulation of inorganic and organic compounds in topsoils. Biota living in close contact with contaminated soils may experience stress at different levels of biological organization throughout the continuum from molecular to community level. Biological responses observed at the individual or infra-individual level of biological organization led to the development of biomarkers. The development of biomarkers consists often in evidencing biological modifications following a contaminant stress in laboratory conditions, using naïve organisms and it is sometime proposed to use the biological state of individuals from sentinel species collected in the field to evaluate the level of environmental exposure. However, considering the possibility of local adaptation following long-term exposure, organisms response sampled in the field may substantially differ from laboratory specimens. In this review, we discuss this point focusing on the definition and validity of molecular biomarkers of metal pollution using earthworms of the Lumbricidae family.

Mapping acute systemic effects of inhaled particulate matter and ozone: multiorgan gene expression and glucocorticoid activity

Recent epidemiological studies have demonstrated associations between air pollution and adverse effects that extend beyond respiratory and cardiovascular disease, including low birth weight, appendicitis, stroke, and neurological/neurobehavioural outcomes (e.g., neurodegenerative disease, cognitive decline, depression, and suicide). To gain insight into mechanisms underlying such effects, we mapped gene profiles in the lungs, heart, liver, kidney, spleen, cerebral hemisphere, and pituitary of male Fischer-344 rats immediately and 24h after a 4-h exposure by inhalation to particulate matter (0, 5, and 50mg/m³ EHC-93 urban particles) and ozone (0, 0.4, and 0.8 ppm). Pollutant exposure provoked differential expression of genes involved in a number of pathways, including antioxidant response, xenobiotic metabolism, inflammatory signalling, and endothelial dysfunction. The mRNA profiles, while exhibiting some interorgan and pollutant-specific differences, were remarkably similar across organs for a set of genes, including increased expression of redox/glucocorticoid-sensitive genes and decreased expression of inflammatory genes, suggesting a possible hormonal effect. Pollutant exposure increased plasma levels of adrenocorticotropic hormone and the glucocorticoid corticosterone, confirming activation of the hypothalamic-pituitary-adrenal axis, and there was a corresponding increase in markers of glucocorticoid activity. Although effects were transient and presumably represent an adaptive response to acute exposure in these healthy animals, chronic activation and inappropriate regulation of the hypothalamic-pituitary-adrenal axis are associated with adverse neurobehavioral, metabolic, immune, developmental, and cardiovascular effects. The experimental data are consistent with epidemiological associations of air pollutants with extrapulmonary health outcomes and suggest a mechanism through which such health effects may be induced.

Role of metallothioneins in benign and malignant thyroid lesions

Recent findings in the past two decades have brought many insights into the biology of thyroid benign and malignant lesions, in particular the papillary and follicular thyroid cancers. Although, much progress have been made, thyroid cancers still pose diagnostic problems regarding differentiation of follicular lesions in relation to their aggressiveness and the treatment of advanced and undifferentiated thyroid cancers. Metallothioneins (MTs) were shown to induce cancer cells proliferation, mediate resistance to apoptosis, certain chemotherapeutics and radiotherapy. Therefore, MTs may be of utility in diagnosis and management of patients with benign and malignant lesions of the thyroid.

Gene expression changes in the prefrontal cortex, anterior cingulate cortex and nucleus accumbens of mood disorders subjects that committed suicide

Suicidal behaviors are frequent in mood disorders patients but only a subset of them ever complete suicide. Understanding predisposing factors for suicidal behaviors in high risk populations is of major importance for the prevention and treatment of suicidal behaviors. The objective of this project was to investigate gene expression changes associated with suicide in brains of mood disorder patients by microarrays (Affymetrix HG-U133 Plus2.0) in the dorsolateral prefrontal cortex (DLPFC: 6 Non-suicides, 15 suicides), the anterior cingulate cortex (ACC: 6NS, 9S) and the nucleus accumbens (NAcc: 8NS, 13S). ANCOVA was used to control for age, gender, pH and RNA degradation, with P≤0.01 and fold change±1.25 as criteria for significance. Pathway analysis revealed serotonergic signaling alterations in the DLPFC and glucocorticoid signaling alterations in the ACC and NAcc. The gene with the lowest p-value in the DLPFC was the 5-HT2A gene, previously associated both with suicide and mood disorders. In the ACC 6 metallothionein genes were down-regulated in suicide (MT1E, MT1F, MT1G, MT1H, MT1X, MT2A) and three were down-regulated in the NAcc (MT1F, MT1G, MT1H). Differential expression of selected genes was confirmed by qPCR, we confirmed the 5-HT2A alterations and the global down-regulation of members of the metallothionein subfamilies MT 1 and 2 in suicide completers. MTs 1 and 2 are neuro-protective following stress and glucocorticoid stimulations, suggesting that in suicide victims neuroprotective response to stress and cortisol may be diminished. Our results thus suggest that suicide-specific expression changes in mood disorders involve both glucocorticoids regulated metallothioneins and serotonergic signaling in different regions of the brain.

Nematode and snail metallothioneins

Metallobiologists have, at large, neglected soil dwelling invertebrates; exceptions are the nematode (Caenorhabditis elegans) and snails (Helix pomatia and Cantareus aspersus). This review aims to compare and contrast the molecular, protein and cellular mechanisms of the multifunctional nematode and snail metallothioneins (MTs). The C. elegans genome contains two MT genes, mtl-1, which is constitutively expressed in the pharynx and likely to act as an essential and/or toxic metal sensor, and mtl-2, which plays a negligible role under normal physiological conditions but is strongly induced (as mtl-1) in intestinal cells upon metal exposure. It has been possible to follow the intricate phenotypic responses upon the knockdown/knockout of single and multiple MT isoforms and we have started to decipher the multifunctional role of C. elegans MTs. The snails have contributed to our understanding regarding MT evolution and diversity, structure and metal-specific functionality. The H. pomatia and C. aspersus genomes contain at least three MT isoform genes. CdMT is responsible for cadmium detoxification, CuMT is involved in copper homeostasis and Cd/CuMT is a putative ancestral MT possibly only of minor importance in metal metabolism. Further investigations of nematode, snail and other invertebrate MTs will allow the development of alternative biomarker approaches and lead to an improved understanding of metallobiology, protein evolution and toxicogenomics.

Impact of stress on cancer metastasis

The influence of psychosocial factors on the development and progression of cancer has been a longstanding hypothesis since ancient times. In fact, epidemiological and clinical studies over the past 30 years have provided strong evidence for links between chronic stress, depression and social isolation and cancer progression. By contrast, there is only limited evidence for the role of these behavioral factors in cancer initiation. Recent cellular and molecular studies have identified specific signaling pathways that impact cancer growth and metastasis. This article provides an overview of the relationship between psychosocial factors, specifically chronic stress, and cancer progression.

Pathways regulated by glucocorticoids in omental and subcutaneous human adipose tissues: a microarray study

Glucocorticoids (GC) are powerful regulators of adipocyte differentiation, metabolism, and endocrine function and promote the development of upper body obesity, especially visceral fat stores. To provide a comprehensive understanding of how GC affect adipose tissue and adipocyte function, we analyzed patterns of gene expression (HG U95 Affymetrix arrays) after culture of abdominal subcutaneous (Abd sc) and omental (Om) adipose tissues from severely obese subjects (3 F, 1 M) in the presence of insulin or insulin (7 nM) plus dexamethasone (Dex, 25 nM) for 7 days. About 20% (561 genes in Om and 569 genes in sc) of 2,803 adipose expressed genes were affected by long-term GC. While most of the genes (90%) were commonly regulated by Dex in both depots, 26 in Om and 34 in Abd sc were affected by Dex in only one depot. 60% of the commonly upregulated genes were involved in metabolic pathways and were expressed mainly in adipocytes. Dex suppressed genes in immune/inflammatory (IL-6, IL-8, and MCP-1, expressed in nonadipocytes) and proapoptotic pathways, yet induced genes related to the acute-phase response (SAA, factor D, haptoglobin, and RBP4, expressed in adipocytes) and stress/defense response. Functional classification analysis showed that Dex also induced expression levels of 22 transcription factors related to insulin action and lipogenesis (LXRα, STAT5α, SREBP1, and FoxO1) and immunity/adipogenesis (TSC22D3) while suppressing 17 transcription factors in both depots. Overall, these studies reveal the powerful effects of GC on gene networks that regulate many key functions in human adipose tissue.

Metallothionein and the biology of aging

Metallothionein (MT) is a low molecular weight protein with anti-apoptotic properties that has been demonstrated to scavenge free radicals in vitro. MT has not been extensively investigated within the context of aging biology. The purpose of this review, therefore, is to discuss findings on MT that are relevant to basic aging mechanisms and to draw attention to the possible role of MT in pro-longevity interventions. MT is one of just a handful of proteins that, when overexpressed, has been demonstrated to increase mouse lifespan. MT also protects against development of obesity in mice provided a high fat diet as well as diet-induced oxidative stress damage. Abundance of MT is responsive to caloric restriction (CR) and inhibition of the insulin/insulin-like signaling (IIS) pathway, and elevated MT gene expression has been observed in tissues from fasted and CR-fed mice, long-lived dwarf mice, worms maintained under CR conditions, and long-lived daf-2 mutant worms. The dysregulation of MT in these systems is likely to have tissue-specific effects on aging outcomes. Further investigation will therefore be needed to understand how MT contributes to the response of invertebrates and mice to CR and the endocrine mutations studied by aging researchers.

Proteomic analysis of chronic restraint stress-induced Gan (肝)-stagnancy syndrome in rats

OBJECTIVE

To analyze the proteomic characteristics of Gan (肝)-stagnancy syndrome (GSS) by seeking the differential protein in blood and tissues of GSS model rats.

METHODS

GSS model rats were established by chronic restraint stress, keeping rats in restrain chamber for 6 h every day for 21 successive days. Their blood and liver samples were collected at the end of experiment for differential protein detection with methods of isoelectrofocusing and polyacrylamide SDS-PAGE, silver staining, and scanning. The gel images were analyzed with Imagemaster 2D Elite software, and the excavated differential protein spots were identified with matrix assistant laser resolving TOF mass spectrometry, Western blot, ELISA, and RT-PCR, respectively.

RESULTS

A method for isolating the protein in blood serum and tissues by two-dimensional gel electrophoresis was established and optimized. Six serum proteins and three liver proteins that differentially expressed were identified. The down-regulated differential proteins in serum of GSS model rats were serum albumin precursor, beta 1 globin, antibody against muscle acetylcholine receptor, Ig lambda-2 C region, and transthyretin (TTR), and those in liver tissue were aryl sulfotransferase, enoyl-CoA hydratase, and TTR. TTR down-regulation was found in both serum and liver. Preliminary biological information analysis showed that these differential proteins involved in immune, neuroendocrine, nutrition, and substance metabolism.

CONCLUSION

Proteomic analysis of differential proteins showed that TTR, aryl sulfotransferase, and enoyl-CoA hydratase expressions are downregulated in the GSS model rats, suggesting that the susceptibility of cancer could be enhanced by chronic stress.

Impact of nose-only exposure system on pulmonary gene expression

Nose-only exposure is used to study the distribution and toxicity of airborne contaminants. Restraint of animals in nose-only tubes causes stress, but the impact on pulmonary mRNA levels is unknown. Since stress and xenobiotics activate common pathways, we assessed whether nose-only exposure would alter expression of toxicologically relevant genes in the lungs. To identify candidate genes for further analysis, we first interrogated microarray data to examine time-dependent changes in gene expression in air-control animals from a nose-only inhalation study involving male wild-type C57BL/6 mice and transgenic tumor necrosis factor (TNF)-alpha over-expressing littermates. Comparison of transcript levels immediately and 24 h after a single 4-h nose-only exposure to air revealed differential expression of 280 genes (false discovery rate-adjusted, p < .05). Functional analysis revealed enrichment of immune response, apoptosis, and signalling terms, consistent with effects of restraint stress. We then selected a subset of target genes for comparison of naive animals and air-exposed animals from the inhalation study by real-time polymerase chain reaction (PCR). Expression of genes involved in stress (BNIP, sestrin-1, CDKN1A [p21], GADD45 gamma), glucocorticoid-response (GILZ, Sgk), and signal transduction (MAP3K6, C/EBP-delta) was increased as a result of nose-only exposure (p < .05). In contrast, proinflammatory factors (lymphotoxin-beta, chemokine receptor CXCR5) were decreased (p < .05). Immune gene responses observed in wild-type animals were reduced in animals with lung inflammation, indicating that pathological states can modify the response to nose-only exposure. Observed responses may warrant consideration in the evaluation of materials delivered by nose-only inhalation, and suggest that incorporation of naive animals into nose-only studies should be considered as a best practice.

Repeated restraint stress increases IgA concentration in rat small intestine

The most abundant intestinal immunoglobulin and first line of specific immunological defense against environmental antigens is secretory immunoglobulin A. To better understand the effect of repeated stress on the secretion of intestinal IgA, the effects of restraint stress on IgA concentration and mRNA expression of the gene for the alpha-chain of IgA was assessed in both the duodenum and ileum of the rats. Restraint stress induced an increase in intestinal IgA, which was blocked by an adrenalectomy, suggesting a role of catecholamines and glucocorticoids. Whereas the blocking of glucocorticoid receptors by RU-486 did not affect the increased IgA concentration, it did reduce IgA alpha-chain mRNA expression in both segments, indicating a possible mediation on the part of glucocorticoids in IgA secretion by individual cells. Treatment with corticosterone significantly increased both the IgA concentration and IgA alpha-chain mRNA expression in ileum but not in duodenum, suggesting that glucocorticoids may act directly on IgA-antibody forming cells to increase IgA secretion in the former segment. A probable role by catecholamines was evidenced by the reduction in IgA concentration and IgA alpha-chain mRNA expression in both segments after a chemical sympathectomy with 6-hydroxydopamine (6-OHDA). Additionally, norepinephrine significantly reduced IgA alpha-chain mRNA levels but increased pIgR mRNA expression and IgA concentration in both intestinal segments. We propose that the increased intestinal IgA levels caused by repeated restraint stress is likely due to the effects of catecholamines on the transport of plgA across the epithelium.

The role of stress mediators in modulation of cytokine production by ethanol

Acute ethanol exposure in humans and in animal models activates the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS); the resultant increases in concentration of neuroendocrine mediators contribute to some of the immunosuppressive effects of ethanol. However, the role of these mediators in the ethanol-induced inhibition of inflammatory responses is not clear. This is complicated by the fact that most inflammatory stimuli also activate the HPA axis and SNS, and it has not been determined if ethanol plus an inflammatory stimulus increases these stress responses. Addressing this issue is the major focus of the study described herein. Complementary approaches were used, including quantitative assessment of the stress response in mice treated with polyinosinic-polycytidylic acid (poly I:C, as an inflammatory stimulus) and inhibition of the production or action of key HPA axis and SNS mediators. Treatment of mice with ethanol shortly before treatment with poly I:C yielded a significant increase in the corticosterone response as compared to the response to poly I:C alone, but the increase was small and not likely sufficient to account for the anti-inflammatory effects of ethanol. Inhibition of catecholamine and glucocorticoid production by adrenalectomy, and inhibition of catecholamine action with a sustained release antagonist (nadalol) supported this conclusion and revealed that "excess" stress responses associated with ethanol treatment is not the mechanism of suppression of pro-inflammatory cytokine production, but stress-induced corticosterone does regulate production of several of these cytokines, which has not previously been reported.

Toxicogenomic analysis of susceptibility to inhaled urban particulate matter in mice with chronic lung inflammation

Background

Individuals with chronic lung disease are at increased risk of adverse health effects from airborne particulate matter. Characterization of underlying pollutant-phenotype interactions may require comprehensive strategies. Here, a toxicogenomic approach was used to investigate how inflammation modifies the pulmonary response to urban particulate matter.

Results

Transgenic mice with constitutive pulmonary overexpression of tumour necrosis factor (TNF)-α under the control of the surfactant protein C promoter and wildtype littermates (C57BL/6 background) were exposed by inhalation for 4 h to particulate matter (0 or 42 mg/m³ EHC-6802) and euthanized 0 or 24 h post-exposure. The low alveolar dose of particles (16 μg) did not provoke an inflammatory response in the lungs of wildtype mice, nor exacerbate the chronic inflammation in TNF animals. Real-time PCR confirmed particle-dependent increases of CYP1A1 (30–100%), endothelin-1 (20–40%), and metallothionein-II (20–40%) mRNA in wildtype and TNF mice (p < 0.05), validating delivery of a biologically-effective dose. Despite detection of striking genotype-related differences, including activation of immune and inflammatory pathways consistent with the TNF-induced pathology, and time-related effects attributable to stress from nose-only exposure, microarray analysis failed to identify effects of the inhaled particles. Remarkably, the presence of chronic inflammation did not measurably amplify the transcriptional response to particulate matter.

Conclusion

Our data support the hypothesis that health effects of acute exposure to urban particles are dominated by activation of specific physiological response cascades rather than widespread changes in gene expression.

Tissue-dependent preventive effect of metallothionein against DNA damage in dyslipidemic mice under repeated stresses of fasting or restraint

AIMS

To investigate the effect of repeated stress on DNA damage in seven organs of dyslipidemic mice, and the preventive role of metallothionein (MT).

MAIN METHODS

Female adult 129/Sv wild-type and MT-null mice fed high-fat diet (HFD) were repeatedly subjected to mild stress of fasting or restraint in weeks 2 to 4 of 4-week study period. Serum cholesterol level, DNA damage in the liver, pancreas, spleen, bone marrow, kidney, lung and gastric mucosa, and other parameters were determined.

KEY FINDINGS

Body weights were increased in both types of mice fed HFD compared to those fed standard diet (STD), and further increased by 12 h-fasting, while they were markedly decreased by 1-3 h-restraint. Fasting accelerated accumulation of fat in the liver, and increase in serum cholesterol of both types of mice fed HFD. Feeding of HFD increased DNA damage in the pancreas, spleen and bone marrow of both types of mice, compared with those fed STD. In the wild-type mice fed HFD, 24 h-fasting increased DNA damage in the liver and spleen, while restraint increased the damage in the liver, pancreas, spleen and bone marrow. DNA damage in the cells of organs was markedly increased in the MT-null mice. Specifically, damage in the liver, pancreas, spleen and bone marrow was greatly increased with the intensity of stress increased, and the damage was much greater in the restraint mice than in the fasting mice.

SIGNIFICANCE

MT plays a tissue-dependent preventive role against DNA damage in various murine organs induced by repeated stress.

Analysis of the bovine neutrophil transcriptome during glucocorticoid treatment

The objective of this study was to characterize a large portion of the bovine neutrophil transcriptome following treatment with the anti-inflammatory glucocorticoid dexamethasone (Dex). Total RNA was isolated from blood neutrophils of healthy cattle (5 castrated male Holsteins) immediately following cell purification (0 h) or after ex vivo aging for 4 h with or without added Dex. Additional neutrophils were cotreated with a glucocorticoid receptor (GR) antagonist (RU486) and Dex for 4 h. RNA was amplified, dye labeled (Cy3 or Cy5), and hybridized to a series of National Bovine Functional Genomics Consortium (NBFGC) microarrays. LOWESS data normalization followed by mixture model analyses showed that 11.15% of the spotted NBFGC cDNAs (2,036/18,263) were expressed in 4-h (untreated) neutrophils. Subsequent two-step mixed-model analysis detected ( P ≤ 0.05) 1,109 differentially expressed genes, of which contrast analysis indicated those that were independently responsive to aging (1,064), Dex (502), RU486 + Dex (141), or RU486 (357). In silico analysis revealed that 416 of the differentially expressed genes are unknown, 59 did not cluster well based on known function, and 634 clustered into 20 ontological categories. Independent validation of differential expression was done for 14 of the putatively Dex-responsive genes across these categories. Results showed that Dex induced rapid translocation of GR into the neutrophil nucleus and signaled dramatic alterations in expression of genes that delay apoptosis, enhance bactericidal activity, and promote tissue remodeling without inflammation or fibrosis. Thus these findings revealed hitherto unappreciated plasticity of blood neutrophils and potentially novel anti-inflammatory/wound-healing actions of glucocorticoids.

Water-soluble genistin glycoside isoflavones up-regulate antioxidant metallothionein expression and scavenge free radicals

Genistin has antioxidant activities; however, its insolubility in water often limits its biological availability in vivo. Using a novel transglycosylation process, the solubility of genistin glycosides was increased 1000 to 10000-fold, but it was not known whether these modified genistin glycosides maintained antioxidant activity. We found that both genistin and its glycosides similarly up-regulated the transcription of several metallothionein (MT) antioxidant genes (MT1A, MT2A, MT1E, and MT1X), as well as the glucose 6-phosphate dehydrogenase (G6PD) gene in HepG2 cells. This gene induction was mediated by the sequestration of zinc in the cytosol, which up-regulated the metal-responsive transcription factor-1 (MTF-1) that induced MT gene expression. Although not as effective as ascorbic acid, genistin glycosides possessed slightly greater reducing power than genistin. We concluded that genistin and genistin glycosides have a direct antioxidant effect and an indirect antioxidant effect, perhaps via induction of MT by activity of MTF-1.

Induction of human metallothionein 1G promoter by VEGF and heavy metals: differential involvement of E2F and metal transcription factors

The E2F transcription factors induce the expression of many genes in response to specific extracellular stimuli. Here, we show that human metallothionein 1G (hMT1G) promoter is upregulated by E2F1 upon VEGF stimulation of human aortic endothelial cells. Analysis of the hMT1G promoter showed the presence of many potential E2F-binding sites flanked by potential SP1 sites and metal response elements (MREs). hMT1G promoter could be induced by E2F1 in transient transfections; further, deletion analysis suggested that the region spanning the E2F-binding sites was necessary for VEGF-mediated induction. E2Fs 1-5 could bind to the hMT1G promoter in a chromatin immunoprecipitation assay. VEGF stimulation led to an increased binding of E2Fs 1-3 to the endogenous hMT1G promoter; at the same time, the binding of Rb, p107 and p130 to the promoter was abolished. VEGF stimulation also led to the increased acetylation E2F1 as well as the histones in the hMT1G promoter region. Stimulation with metals or VEGF led to dissociation of histone deacetylase 1 (HDAC1) from the promoter, leading to acetylation of histones. Induction of the hMT1G promoter upon exposure to heavy metals such as Zn and Cd is mediated by the MRE. Interestingly, mutation of MRE affected the metal response, but not the VEGF response of the hMT1G promoter. In contrast, deletion of the E2F-binding sites did not affect the metal response. Based on these findings, we conclude that induction of the hMT1G promoter by VEGF and heavy metals occurs through the utilization of different transcription factors.

Cd and Zn uptake kinetics in Daphnia magna in relation to Cd exposure history

The uptake kinetics of Cd and Zn in a freshwater cladoceran Daphnia magna after exposure to different concentrations of Cd for various durations was quantified. The accumulated Cd concentrations increased with ambient Cd concentration and exposure duration. As a detoxification mechanism, metallothioneins (MTs) were induced when the Cd preexposure condition was beyond the noneffect threshold. The MT induction was dependent on both Cd concentration and duration of preexposure. Increasing the Cd exposure concentration to 20 microg L(-1) for 3 d caused a 44% reduction in Cd assimilation efficiency (AE, the fraction assimilated by the animals after digestion) by the daphnids from the dietary phase, but a 2.4-fold increase in Zn AE. Generally, the dissolved metal uptake rate was not significantly affected by the different Cd preexposure regimes, except at a much higher Cd concentration (20 microg L(-1)) when the Zn influx was enhanced. Significant effects from Cd exposure on the ingestion rate of the daphnids were also observed. When the MT synthesis was not coupled with the accumulated Cd tissue burden (e.g., a delay in MT synthesis), apparent Cd toxicity on the feeding behavior and the Cd AE was observed, thus highlighting the importance of MTs in modifying the metal uptake kinetics of D. magna. Overall, daphnids responded to acute Cd exposure by reducing their Cd AE and ingestion, whereas they developed a tolerance to Cd following chronic exposure. The bioavailability of Zn was enhanced as a result of Cd preexposure. This study highlights the important influences of Cd preexposure history on the biokinetics and potential toxicity of Cd and Zn to D. magna.

Chromium(VI) down-regulates heavy metal-induced metallothionein gene transcription by modifying transactivation potential of the key transcription factor, metal-responsive transcription factor 1

The robust induction of metallothionein-I and II (MT-I and MT-II) genes by several heavy metals such as zinc and cadmium requires the specific transcription factor metal-responsive transcription factor 1 (MTF1). Chromium (VI), a major environmental carcinogen, not only failed to activate these genes but also inhibited their induction by Zn2+ or Cd2+. The heavy metal-induced expression of another MTF1 target gene, zinc transporter 1 (ZnT-1), was also down-regulated by Cr6+. By contrast, the expression of two MTF1-independent Cd2+-inducible genes, heme oxygenase 1 (HO-1) and HSP-70, was not sensitive to Cr6+. Cr6+ did not also affect the expression of housekeeping genes such as GAPDH or beta-actin. Stable cell lines overexpressing variable levels of MTF1, the key transactivator of the MT genes, demonstrated differential resistance toward the inhibitory effect of Cr6+, indicating MTF1 as a target of chromium toxicity. The basal and inducible binding of MTF1 to metal response elements was not affected by treatment of cells with Cr6+. Transient transfection studies showed that the ability of MTF1 to transactivate the MT-I promoter was significantly compromised by Cr6+. The fusion protein consisting of a Gal-4 DNA binding domain and one or more of the three transactivation domains of MTF1, namely the acidic domain, proline-rich domain, and serine-threonine rich domain, activated the GAL-4-driven luciferase gene to different degrees, but all were sensitive to Cr6+. MTF1 null cells were prone to apoptosis after exposure to Zn2+ or Cd2+ that was augmented in presence Cr6+, whereas the onset of apoptosis was significantly delayed in cells overexpressing MTF1.

Age-related impairment of the transcriptional responses to oxidative stress in the mouse heart

To investigate the transcriptional response to oxidative stress in the heart and how it changes with age, we examined the cardiac gene expression profiles of young (5-mo-old), middle-aged (15-mo-old), and old (25-mo-old) C57BL/6 mice treated with a single intraperitoneal injection of paraquat (50 mg/kg). Mice were killed at 0, 1, 3, 5, and 7 h after paraquat treatment, and the gene expression profile was obtained with high-density oligonucleotide microarrays. Of 9,977 genes represented on the microarray, 249 transcripts in the young mice, 298 transcripts in the middle-aged mice, and 256 transcripts in the old mice displayed a significant change in mRNA levels (ANOVA, P < 0.01). Among these, a total of 55 transcripts were determined to be paraquat responsive for all age groups. Genes commonly induced in all age groups include those associated with stress, inflammatory, immune, and growth factor responses. Interestingly, only young mice displayed a significant increase in expression of all three isoforms of GADD45, a DNA damage-responsive gene. Additionally, the number of immediate early response genes (IEGs) found to be induced by paraquat was considerably higher in the younger animals. These results demonstrate that, at the transcriptional level, there is an age-related impairment of specific inducible pathways in the response to oxidative stress in the mouse heart.

Glucocorticoids aggravate hyperoxia-induced lung injury through decreased nuclear factor-kappa B activity

We previously reported that exposure of mice to hyperoxia is characterized by extensive lung cell necrosis and apoptosis, mild inflammatory response, and elevated circulating levels of corticosterone. Administration of hydroxycortisone acetate during hyperoxia aggravated lung injury. Using adrenalectomized (ADX) and sham-operated (sham) mice, we studied the role of the glucocorticoids in hyperoxia-induced lung injury. Lung damage was attenuated in ADX mice as measured by lung weight and protein and cell content in bronchoalveolar lavage and as seen by light microscopy. Mortality was delayed by 10 h. Nuclear factor-kappaB (NF-kappaB) activity was significantly decreased in lungs of sham mice exposed to hyperoxia but was preserved in ADX mice. There was a correlation between NF-kappaB activity in ADX mice and decreased levels of IkappaBalpha. In contrast, activator protein-1 activity increased similarly in both groups of mice. Levels of interleukin-6 (IL-6), a transcriptional target of NF-kappaB, were higher in bronchoalveolar lavage and serum of ADX than sham mice. However, the protective effect of ADX was not mediated by IL-6, because administration of recombinant human IL-6 to sham mice did not prevent lung damage. These results demonstrate that the adrenal response aggravates alveolar injury and is likely to be mediated by the decrease of NF-kappaB function involved in cell survival.

Inhibitors of histone deacetylase and DNA methyltransferase synergistically activate the methylated metallothionein I promoter by activating the transcription factor MTF-1 and forming an open chromatin structure

Inhibitors of DNA methyltransferase (Dnmt) and histone deacetylases (HDAC) synergistically activate the methylated metallothionein I gene (MT-I) promoter in mouse lymphosarcoma cells. The cooperative effect of these two classes of inhibitors on MT-I promoter activity was robust following demethylation of only a few CpG dinucleotides by brief exposure to 5-azacytidine (5-AzaC) but persisted even after prolonged treatment with the nucleoside analog. HDAC inhibitors (trichostatin A [TSA] and depsipeptide) either alone or in combination with 5-AzaC did not facilitate demethylation of the MT-I promoter. Treatment of cells with HDAC inhibitors increased accumulation of multiply acetylated forms of H3 and H4 histones that remained unaffected after treatment with 5-AzaC. Chromatin immunoprecipitation (ChIP) assay showed increased association of acetylated histone H4 and lysine 9 (K9)-acetyl H3 with the MT-I promoter after treatment with TSA, which was not affected following treatment with 5-AzaC. In contrast, the association of K9-methyl histone H3 with the MT-I promoter decreased significantly after treatment with 5-AzaC and TSA. ChIP assay with antibodies specific for methyl-CpG binding proteins (MBDs) demonstrated that only methyl-CpG binding protein 2 (MeCP2) was associated with the MT-I promoter, which was significantly enhanced after TSA treatment. Association of histone deacetylase 1 (HDAC1) with the promoter decreased after treatment with TSA or 5-AzaC and was abolished after treatment with both inhibitors. Among the DNA methyltransferases, both Dnmt1 and Dnmt3a were associated with the MT-I promoter in the lymphosarcoma cells, and association of Dnmt1 decreased with time after treatment with 5-AzaC. Treatment of these cells with HDAC inhibitors also increased expression of the MTF-1 (metal transcription factor-1) gene as well as its DNA binding activity. In vivo genomic footprinting studies demonstrated increased occupancy of MTF-1 to metal response elements of the MT-I promoter after treatment with both inhibitors. Analysis of the promoter by mapping with restriction enzymes in vivo showed that the MT-I promoter attained a more open chromatin structure after combined treatment with 5-AzaC and TSA as opposed to treatment with either agent alone. These results implicate involvement of multifarious factors including modified histones, MBDs, and Dnmts in silencing the methylated MT-I promoter in lymphosarcoma cells. The synergistic activation of this promoter by these two types of inhibitors is due to demethylation of the promoter and altered association of different factors that leads to reorganization of the chromatin and the resultant increase in accessibility of the promoter to the activated transcription factor MTF-1.

Enhancement of MT synthesis by leptin in fasted mice

It is known that metallothionein (MT) synthesis occurs in the liver in various stressful situations such as immobilization and fasting. However, the mechanism of MT synthesis in stressful situations is not fully understood. In this study, we examined the involvement of leptin, the obese gene product, in MT synthesis induced by fasting stress. Despite an increase in hepatic MT levels induced by 24-hr fasting in wild-type mice, both wild-type and MT-null mice showed decreases in plasma leptin levels after 24 hr of fasting. Hepatic MT levels increased to levels comparable with that in control mice in ICR, C3H, 129Sv and Balb/c mice fasted for 24 hr, and plasma leptin levels decreased significantly. Repetition of fasting and feeding in turn every 24 hr caused a gradual decrease in hepatic MT levels after the fasting period. In contrast, the reduced plasma leptin levels increased after the fasting period with repetition of fasting-feeding cycles. The findings indicate that there is an adaptation to starvation. On the other hand, subcutaneous leptin infusion in fasted mice via an osmotic pump resulted in increases in hepatic MT levels compared to the levels in vehicle-treated mice after 24 hr of fasting. Only leptin infusion had no effect on hepatic MT levels. These results suggest that MT synthesis in fasting stress is not correlated with decrease in plasma leptin levels but that leptin itself is a potent inducer of MT in a fasting situation.

Induction of metallothionein by zinc protects from daunorubicin toxicity in rats

Daunorubicin (DNR) is an anthracyline antibiotic used in the treatment of a variety of human cancers. Reactive oxygen species (ROS) produced in the metabolism of DNR have severe cardiotoxicity which consequently compromises its clinical use as anticancer drug. This study aimed to investigate the effect of DNR administration on both cardiac and hepatic tissues, and the possible protective role of zinc on the cardiotoxicity and hepatotoxicity produced by DNR. Administration of 10 or 20 mg/kg DNR to Sprague-Dawley rats, increases serum creatine kinase activity, and blood troponin T levels (as cardiotoxicity indices), alanine aminotransferase activity (as hepatotoxicity index), as well as cardiac and hepatic 2-thiobarbituric acid reactive substances (as an index of lipid peroxidation). Treatment with 20 mg/kg Zn prior to DNR, dramatically induced metallothionein-1 (MT-1) mRNA and MT protein in both heart and liver while DNR alone induced MT, but to a much lower degree than Zn. The analysis of MT protein isoforms revealed that MT-1 was the form induced, while metallothionein-2 (MT-2) levels remained practically unchanged. The increases in both MT protein and MT-1 mRNA ran parallel with the reduction of cardiac and hepatic toxicities. Our results indicate that MT induction by Zn is a highly effective approach in preventing cardiotoxicity and hepatotoxicity caused by DNR. These animal data suggest the use of Zn to reduce DNR-induced cardiotoxicity and hepatotoxicity in the chemotherapy of cancer patients.

Role of de novo DNA methyltransferases and methyl CpG-binding proteins in gene silencing in a rat hepatoma

The expression of metallothionein-I (MT-I), a known antioxidant, was suppressed in a transplanted rat hepatoma because of promoter methylation and was induced by heavy metals only after demethylation by 5-azacytidine (5-AzaC). Treatment of the tumor-bearing rats with 5-AzaC resulted in significant regression of the hepatoma. When the inhibitor-treated tumor was allowed to grow in a new host, MT-I promoter was remethylated, which suggested de novo methylation. The activities of both de novo (3-fold) and maintenance DNA methyltransferases (DNMT) (5-fold) were higher in the hepatoma than in the host liver. The mRNA levels of the de novo methyltransferases DNMT3a and DNMT3b were 3- and 6-fold higher, respectively, in the tumor implicating transcriptional up-regulation of these two genes in this tissue. Immunohistochemical analysis showed exclusive localization of DNMT3a in the nuclei of both the liver and hepatoma, whereas DNMT3b was detected in the nuclei as well as the cytoplasm. Immunoblot assay showed that the levels of DNMT1, DNMT3a, and DNMT3b proteins in the hepatoma were 5-, 10-, and 4-fold higher, respectively, than in the liver. The mRNA level of the major methyl CpG-binding protein (MeCP2) was 8-fold higher in the tumor compared with the liver. Immunohistochemical studies showed that MeCP2 is localized exclusively in the nuclei of both tissues. A chromatin immunoprecipitation assay demonstrated that MeCP2 was associated with the MT-I promoter in the hepatoma implicating its involvement in repressing the methylated promoter. Analysis of the DNA isolated from the liver and hepatoma by RLGS-M (restriction landmark genomic scanning with methylation-sensitive enzyme) (NotI) showed that many genes in addition to MT-I were methylated in the hepatoma. These data demonstrate suppression of the MT-I gene and probably other genes in a solid tumor by promoter methylation and have provided potential molecular mechanisms for the altered methylation profile of the genes in this tumor.

Restraint stress and protection from acoustic injury in mice

The phenomenon of 'conditioning', whereby prior exposure to moderate-level non-traumatic sound reduces the permanent injury to subsequent high-level sound exposures, is suggestive of protective effects mediated by stress-induced gene expression in other systems. To test the role of stress pathways in acoustic injury, this study investigated the effect of mild physical restraint, a classic non-acoustic elicitor of stress, on vulnerability to subsequent noise-induced hearing loss. CBA/CaJ mice were divided into groups (control, restraint-only, restraint pre-trauma, and trauma-only), and cochlear sensitivity was assessed via compound action potentials and distortion product otoacoustic emissions. Results showed that two 12-h epochs of mild physical restraint significantly reduced permanent threshold shifts from a subsequent acoustic overexposure, as long as the treatment-trauma interval was short (2 h). Concurrent measures of circulating glucocorticoids showed that the period of protection coincided with the period of elevated corticosterone. Results are consistent with the idea that cochlear protective effects may be mediated by stress pathways and that glucocorticoid levels may be an important upstream regulator of these effects.

Isothermal titration calorimetry reveals a zinc ion as an atomic switch in the diadenosine polyphosphates

Diadenosine polyphosphates (diadenosine 5',5'''-P(1),P(n)-polyphosphate (Ap(n)A)) are 5'-5'''-phosphate-bridged dinucleosides that have been proposed to act as signaling molecules in a variety of biological systems. Isothermal titration calorimetry was used to measure the affinities of a variety of metal cations for ATP, diadenosine 5',5'''-P(1),P(3)-triphosphate (Ap(3)A), diadenosine 5',5'''-P(1),P(4)-tetraphosphate (Ap(4)A), and diadenosine 5',5'''-P(1),P(5)-pentaphosphate (Ap(5)A). The binding of Mg(2+), Ca(2+), and Mn(2+) to ATP is shown to take place with the beta,gamma-phosphates (primary site) and be endothermic in character. The binding of Ni(2+), Cd(2+), and Zn(2+) to ATP is found to take place at both the primary site and at a secondary site identified as N-7 of the adenine ring. Binding to this second site is exothermic in character. Generally, the binding of metal cations to diadenosine polyphosphates involves a similar primary site to ATP. No exothermic binding events are identified. Critically, the binding of Zn(2+) to diadenosine polyphosphates proves to be exceptional. This appears to involve a very high affinity association involving the N-7 atoms of both adenine rings in each Ap(n)A, as well as the more usual endothermic association with the phosphate chain. The high affinity association is also endothermic in character. A combination of NMR and CD evidence is provided in support of the calorimetry data demonstrating chemical shift changes and base stacking disruptions entirely consistent with N-7 bridging interactions. N-7 bridging interactions are entirely reversible, as demonstrated by EDTA titration. Considering the effects of Zn(2+) on a wide variety of dinucleoside polyphosphate-metabolizing enzymes, we examine the possibility of Zn(2+) acting as an atomic switch to control the biological function of the diadenosine polyphosphates.

Influenza virus infection induces metallothionein gene expression in the mouse liver and lung by overlapping but distinct molecular mechanisms

Metallothionein I (MT-I) and MT-II have been implicated in the protection of cells against reactive oxygen species (ROS), heavy metals, and a variety of pathological and environmental stressors. Here, we show a robust increase in MT-I/MT-II mRNA level and MT proteins in the livers and lungs of C57BL/6 mice exposed to the influenza A/PR8 virus that infects the upper respiratory tract and lungs. Interleukin-6 (IL-6) had a pronounced effect on the induction of these genes in the liver but not the lung. Treatment of the animals with RU-486, a glucocorticoid receptor antagonist, inhibited induction of MT-I/MT-II in both liver and lung, revealing a direct role of glucocorticoid that is increased upon infection in this induction process. In vivo genomic footprinting (IVGF) analysis demonstrated involvement of almost all metal response elements, major late transcription factor/antioxidant response element (MLTF/ARE), the STAT3 binding site on the MT-I upstream promoter, and the glucocorticoid responsive element (GRE1), located upstream of the MT-II gene, in the induction process in the liver and lung. In the lung, inducible footprinting was also identified at a unique gamma interferon (IFN-gamma) response element (gamma-IRE) and at Sp1 sites. The mobility shift analysis showed activation of STAT3 and the glucocorticoid receptor in the liver and lung nuclear extracts, which was consistent with the IVGF data. Analysis of the newly synthesized mRNA for cytokines in the infected lung by real-time PCR showed a robust increase in the levels of IL-10 and IFN-gamma mRNA that can activate STAT3 and STAT1, respectively. A STAT1-containing complex that binds to the gamma-IRE in vitro was activated in the infected lung. No major change in MLTF/ARE DNA binding activity in the liver and lung occurred after infection. These results have demonstrated that MT-I and MT-II can be induced robustly in the liver and lung following experimental influenza virus infection by overlapping but distinct molecular mechanisms.

Hyperoxia increases leptin production: a mechanism mediated through endogenous elevation of corticosterone

Leptin, a cytokine involved in the regulation of food intake, has been reported to be decreased in lung diseases such as chronic obstructive pulmonary disease and cystic fibrosis and increased in critically ill patients with sepsis. We investigated the role of leptin during hyperoxia in mice, which results in alveolar edema, severe weight loss, and death within 3-4 days. In oxygen-breathing mice, serum leptin was increased six- to sevenfold and its mRNA was upregulated in white adipose tissue. Leptin elevation could not be attributed to changes in circulating tumor necrosis factor-alpha but was completely dependent on endogenous corticosterone elevation because adrenalectomized mice did not exhibit any increase in leptin levels. Using leptin-deficient mice and wild-type mice treated with anti-leptin antibody, we demonstrate that weight loss was leptin independent. Lung damage was moderately attenuated in leptin-deficient mice but was not modified by anti-leptin antibody or leptin administration, suggesting that leptin does not play an essential role in the direct and short-term effects of oxygen-induced injury.

Microbial metallothioneins

Bacterial metallothioneins bind, sequester and buffer excess intracellular zinc. At present, the vast majority of the available experimental data relate to cyanobacterial metallothionein, SmtA, from Synechococcus PCC 7942. SmtA is required for normal resistance to zinc and smtA-mediated zinc resistance has been used as a selectable marker. The imidazole groups of histidine residues, in addition to the thiol groups of cysteine residues, co-ordinate zinc in bacterial metallothioneins. The structure of bacterial metallothionein must facilitate some discrimination between 'adventitious' and 'adventageous' zinc-binding sites such that under excess zinc conditions metal is predominantly scavenged from the former. It remains unclear whether or not bacterial metallothionein also acts as a zinc store that supplies zinc-requiring proteins or if under some conditions it deactivates a subset of proteins via zinc removal. Expression of smtA is induced in response to elevated concentrations of zinc via the action of SmtB. SmtB has some sequence similarity to the arsenic responsive repressor ArsR and genes encoding related proteins are present in many bacterial genomes. Metal perception by SmtB differs from ArsR. The latter contains a characteristic Cys-Val-Cys motif associated with a DNA-binding helix-turn-helix (the ArsR motif), while the former contains metal-binding motifs associated with a carboxyl-terminal alpha-helix that forms the interface between SmtB dimers (the SmtB motif). Some SmtB-ArsR family proteins, including the zinc sensor ZiaR from the cyanobacterium Synechocystis PCC 6803, have the metal-sensory motifs of both SmtB and ArsR. The mechanisms of action, and the features that allow discrimination between different metal ions by these sensors, are discussed.

Stress-induced sickness behaviors: an alternative hypothesis for responses during maternal separation

During maternal separation, some primate and nonprimate species show a biphasic (active/passive) response. The second stage is characterized by reduced activity, a hunched body posture, and other behaviors. Traditionally, the second stage has been referred to as "despair" and is considered an animal model for human depression. Recent research in psychoneuroimmunology suggests an alternative hypothesis--that behaviors occurring during the second passive phase represent stress-induced "sickness behaviors." This perspective more readily accounts for findings in widely divergent species, does not require assumptions regarding the ability to express complex emotional states, is empirically testable, and aligns the separation model with recent hypotheses regarding the nature and ontogeny of depressive illness.

Regulation of metallothionein gene expression

The rapid and robust induction of metallothioneins (MT)-I and II by a variety of inducers that include heavy toxic metals, reactive oxygen species, and different types of stress provide a useful system to study the molecular mechanisms of this unique induction process. The specific expression of MT-III in the brain and of MT-IV in the squamous epithelium of skin and tongue offers a unique opportunity to identify and characterize the tissue-specific factors involved in their expression. Studies using transgenic mice that overexpress MTs or MT null mice have revealed the role of MT in the protection of cells against numerous tissue-damaging agents such as reactive oxygen species. The primary physiological function of these proteins, however, remains an enigma. Considerable advances have been made in the identification of the cis-acting elements that are involved in the constitutive and induced expression of MT-I and MT-II. By contrast, only one key trans-activating factor, namely MTF-1, has been extensively characterized. Studies on the epigenetic silencing of MT-I and MT-II by promoter hypermethylation in some cancer cells have posed interesting questions concerning the functional relevance of MT gene silencing, the molecular mechanisms of MT suppression in these cells, particularly chromatin modifications, and the characteristics of the repressors.

Metallothionein induction by restraint stress: role of glucocorticoids and IL-6

Restraint stress increased liver metallothionein-I (MT-I) mRNA and MT-I+II protein levels. The glucocorticoid receptor antagonist RU 486 decreased this response. In contrast, adrenalectomy only decreased MT-I+II protein levels. Moreover, corticosterone or progesterone did not reverse the effect of RU 486. These results suggest that glucocorticoids are important for MT-I+II protein synthesis but not for MT-I mRNA accumulation during restraint stress, and that other factors must be involved in this process. Interleukin-6 (IL-6) deficient mice showed a significant decrease of restraint stress-induced liver MT-I mRNA levels (approximately 30% of IL-6+/+ mice) up to approximately 4-5 hours after the onset of stress. Western blotting of hepatic nuclear proteins showed that the IL-6 responsive transcription factor Stat3, which has been shown to mediate MT induction by inflammation, was also activated by restraint stress. Results after extended periods of restraint stress indicate that IL-6 participates early and transiently in the process. The analysis of the expression of the acute phase plasma protein serum amyloid A suggests that restraint stress elicits an acute phase response similar to that caused by inflammation.

Suppression of metallothionein gene expression in a rat hepatoma because of promoter-specific DNA methylation

Metallothionein I can be induced in response to a variety of agents that include heavy metals and oxidative stress. On the contrary, its induction was suppressed in some lymphoid-derived cancer cells. The mechanism of this repression has not been elucidated. Here, we show silencing of MT-I gene in a solid transplanted rat tumor as a result of promoter methylation at all the 21 CpG dinucleotides that span the region from -225 bp to +1 bp. By contrast, none of these CpG dinucleotides were methylated in the livers from the rats bearing the tumor, which was consistent with the efficient induction of the gene in this tissue by zinc sulfate. Genomic footprinting revealed lack of access of the transcriptional activators to the respective cis-acting elements of the methylated MT-I promoter in the hepatoma. The absence of footprinting was not due to inactivation of the metal regulatory transcription factor MTF-1, because it was highly active in the hepatoma. Treatment of the hepatoma bearing rats with 5-azacytidine, a demethylating agent, induced basal as well as heavy metal-activated MT-I gene expression in the hepatoma, implying that methylation was indeed responsible for silencing the gene. Bisulfite genomic sequencing showed significant (>90%) demethylation of CpG dinucleotides spanning MT-I promoter in the hepatoma following treatment with 5-AzaC. The hypermethylation of MT-I promoter was probably caused by significantly higher (as much as 7-fold) level of DNA methyl transferase activity as well as enhanced expression of its gene in the hepatoma relative to the host liver. These data elucidated for the first time the molecular mechanism for the silencing of a highly inducible gene in a solid tumor transplanted in an animal, as compared with the robust induction in the corresponding parental tissue and have discussed the probable reasons for the suppression of this gene in some tumors.

Chromium increases pancreatic metallothionein in the rat

The ability of chromium (Cr) salts to increase metallothionein (MT) levels in rat liver, kidney and pancreas, and its relationship with the presence of toxic effects are reported here. Rats were injected subcutaneously with 0, 10, 20, 30, 40, or 50 mg K2Cr2O7/kg and sacrificed 24 h later. Total Cr accumulation followed a dose-dependent pattern, levels in kidney being higher than those in liver or pancreas, suggesting different tissue bioavailabilities and accumulation patterns. Cr(IV) administration resulted in a tissue-specific MT induction: pancreas and liver showed five- and 3.5-fold MT increases, respectively; no increase was observed in the kidney. A positive correlation was observed between zinc and MT concentrations in liver, and between total Cr and MT concentrations in pancreas. Serum alpha-amylase activity showed a dose-dependent increase starting from 20 mg/kg, whereas serum glucose levels increased at doses higher than 30 mg/kg. Serum aspartate aminotransferase and alanine aminotransferase activities were increased in a dose-dependent manner, from 20 and 30 mg/kg, respectively. Our results showed that treatment with Cr(VI) can induce MT synthesis in pancreas and suggests a subsequent binding of Cr to MT. Also, pancreas is a target organ for Cr toxicity, and the usefulness of alpha-amylase activity as a sensitive biomarker of Cr toxicity in human exposed populations merits further study.

Heat stress and protection from permanent acoustic injury in mice

The inner ear can be permanently damaged by overexposure to high-level noise; however, damage can be decreased by previous exposure to moderate level, nontraumatic noise (). The mechanism of this "protective" effect is unclear, but a role for heat shock proteins has been suggested. The aim of the present study was to directly test protective effects of heat stress in the ear. For physiological experiments, CBA/CaJ mice were exposed to an intense octave band of noise (8-16 kHz) at 100 dB SPL for 2 hr, either with or without previous whole-body heat stress (rectal temperature to 41. 5 degrees C for 15 min). The interval between heat stress and sound exposure varied in different groups from 6 to 96 hr. One week later, inner ear function was assessed in each animal via comparison of compound action potential thresholds to mean values from unexposed controls. Permanent threshold shifts (PTSs) were approximately 40 dB in the group sound-exposed without previous heat stress. Heat-stressed animals were protected from acoustic injury: mean PTS in the group with 6 hr heat-stress-trauma interval was reduced to approximately 10 dB. This heat stress protection disappeared when the treatment-trauma interval surpassed 24 hr. A parallel set of quantitative PCR experiments measured heat-shock protein mRNA in the cochlea and showed 100- to 200-fold increase over control 30 min after heat treatment, with levels returning to baseline at 6 hr after treatment. Results are consistent with the idea that upregulation of heat shock proteins protects the ear from acoustic injury.