Induction of hepatic metallothionein synthesis by endoplasmic reticulum stress in mice

Ethyl Acetate Fraction of Amomum villosum var. xanthioides Attenuates Hepatic Endoplasmic Reticulum Stress-Induced Non-Alcoholic Steatohepatitis via Improvement of Antioxidant Capacities

Non-alcoholic fatty liver disease (NAFLD), including non-alcoholic steatohepatitis (NASH), affects 25% of the global population. Despite the prevalence of NAFLD worldwide, effective therapeutics are currently lacking. Amomum villosum var. xanthioides (Wall. ex Baker) T.L.Wu & S.J.Chen (AX) is a medicinal herb traditionally used for treating digestive tract disorders in countries across Asia. We aimed to examine the pharmacological effects of the ethyl acetate fraction of AX (AXEF) against tunicamycin (TM)-induced ER stress in a NASH mouse model using C57/BL6J male mice. Following TM injections (2 mg/kg), the mice were orally administrated AXEF (12.5, 25, or 50 mg/kg), silymarin (50 mg/kg), or distilled water daily for 5 days, and the outcomes for fatty liver, inflammation, and oxidative stress were measured in serum or liver tissue levels. AXEF drastically attenuated hepatic ER stress-induced NASH as indicated by decreases in lipid droplet accumulations, serum liver enzymes, hepatic inflammations, and cell death signals in the hepatic tissue and/or serum levels. Interestingly, AXEF showed potent antioxidant effects by quenching reactive oxidative stress and its final product lipid peroxide in the hepatic tissue, specifically an increase in metallothionein (MT). To confirm the underlying actions of AXEF, we observed that AXEF increases MT1 gene promoter activities in the physiological levels. Collectively, AXEF showed antioxidant properties on TM-induced ER stress in a NASH mice model through the improvement of MTs.

Zinc Supplementation Prevented Type 2 Diabetes-Induced Liver Injury Mediated by the Nrf2-MT Antioxidative Pathway

Zinc is an essential trace element that is often reduced under the type 1 diabetic condition. Previous studies demonstrated that zinc deficiency enhanced type 1 diabetes-induced liver injury and that zinc supplementation significantly helped to prevent this. Due to the differences in pathogenesis between type 1 and type 2 diabetes, it is unknown whether zinc supplementation can induce a beneficial effect on type 2 diabetes-induced liver injury. This possible protective mechanism was investigated in the present study. A high-fat diet, along with a one-time dose of streptozotocin, was applied to metallothionein (MT) knockout mice, nuclear factor-erythroid 2-related factor (Nrf) 2 knockout mice, and age-matched wild-type (WT) control mice, in order to induce type 2 diabetes. This was followed by zinc treatment at 5 mg/kg body weight given every other day for 3 months. Global metabolic disorders of both glucose and lipids were unaffected by zinc supplementation. This induced preventive effects on conditions caused by type 2 diabetes like oxidative stress, apoptosis, the subsequent hepatic inflammatory response, fibrosis, hypertrophy, and hepatic dysfunction. Additionally, we also observed that type 2 diabetes reduced hepatic MT expression, while zinc supplementation induced hepatic MT expression. This is a crucial antioxidant. A mechanistic study showed that MT deficiency blocked zinc supplementation-induced hepatic protection under the condition of type 2 diabetes. This suggested that endogenous MT is involved in the hepatic protection of zinc supplementation in type 2 diabetic mice. Furthermore, zinc supplementation-induced hepatic MT increase was unobserved once Nrf2 was deficient, indicating that Nrf2 mediated the upregulation of hepatic MT in response to zinc supplementation. Results of this study indicated that zinc supplementation prevented type 2 diabetes-induced liver injury through the activation of the Nrf2-MT-mediated antioxidative pathway.

Effect of Tff3 Deficiency and ER Stress in the Liver

Endoplasmic reticulum (ER) stress, a cellular condition caused by the accumulation of unfolded proteins inside the ER, has been recognized as a major pathological mechanism in a variety of conditions, including cancer, metabolic and neurodegenerative diseases. Trefoil factor family (TFFs) peptides are present in different epithelial organs, blood supply, neural tissues, as well as in the liver, and their deficiency has been linked to the ER function. Complete ablation of Tff3 expression is observed in steatosis, and as the most prominent change in the early phase of diabetes in multigenic mouse models of diabesity. To elucidate the role of Tff3 deficiency on different pathologically relevant pathways, we have developed a new congenic mouse model Tff3^−/−/C57BL6/N from a mixed background strain (C57BL6/N /SV129) by using a speed congenics approach. Acute ER stress was evoked by tunicamycin treatment, and mice were sacrificed after 24 h. Afterwards the effect of Tff3 deficiency was evaluated with regard to the expression of relevant oxidative and ER stress genes, relevant proinflammatory cytokines/chemokines, and the global protein content. The most dramatic change was noticed at the level of inflammation-related genes, while markers for unfolded protein response were not significantly affected. Ultrastructural analysis confirmed that the size of lipid vacuoles was affected as well. Since the liver acts as an important metabolic and immunological organ, the influence of Tff3 deficiency and physiological function possibly reflects on the whole organism.

Regulatory role of metallothionein-1/2 on development of sex differences in a high-fat diet-induced obesity

AIMS

To evaluate the role of metallothionein (MT) in sex differences of obesity, we examined the effect of MT on regulation of lipid accumulation in female and male wild type (WT) and MT1/MT2-null (MT-KO) mice.

MAIN METHODS

Male and female WT and MT-KO mice fed standard diet (SD) or high-fat diet (HFD) for 35 weeks. Surgical castration in male mice was also performed to examine the effects of androgen on fat accumulation under HFD condition.

KEY FINDINGS

The fat mass and size of adipocytes in white adipose tissue (WAT) was greater in adult MT-KO mice than in WT mice after 35 weeks of SD feeding without gender differences, suggesting a role of MT in limiting WAT development during normal growth in both sexes. In female mice fed HFD, weights of WAT and body were greater in MT-KO mice than in WT mice, indicating that MT had a preventive role against excess fat accumulation. In male mice fed HFD, WAT weight hardly increased in MT-KO mice compared to the increase in WT mice. Surgically castrated WT males fed HFD had lower WAT weight compared with sham-treated mice, although castrated MT-KO males fed HFD had greater increases in WAT weight compared with sham-treated mice and castrated WT males.

SIGNIFICANCE

These data suggest that MT could enhance the preventive action of estrogen against excess fat accumulation, on the contrary, MT augmented the ability of androgen to increase fat accumulation. MT may act to modify the susceptibility to obesity under sex hormones.

Zinc treatment prevents type 1 diabetes-induced hepatic oxidative damage, endoplasmic reticulum stress, and cell death, and even prevents possible steatohepatitis in the OVE26 mouse model: Important role of metallothionein

Whether zinc is able to improve diabetes-induced liver injury remains unknown. Transgenic type 1 diabetic (OVE26) mice develop hyperglycemia at 3 weeks old; therefore therapeutic effect of zinc on diabetes-induced liver injury was investigated in OVE26 mice. Three-month old OVE26 and age-matched wild-type mice were treated by gavage with saline or zinc at 5mg/kg body-weight every other day for 3 months. Hepatic injury was examined by serum alanine aminotransferase (ALT) level with liver histopathological and biochemical changes. OVE26 mice at 6 months old showed significant increases in serum ALT level and hepatic oxidative damage, endoplasmic reticulum stress and associated cell death, mild inflammation, and fibrosis. However, all these hepatic morphological and functional changes were significantly prevented in 3-month zinc-treated OVE26 mice. Mechanistically, zinc treatment significantly increased hepatic metallothionein, a protein with known antioxidant activity, in both wild-type and OVE26 mice. These results suggest that there were significantly functional, structural and biochemical abnormalities in the liver of OVE26 diabetic mice at 6 months old; however, all these changes could be prevented with zinc treatment, which was associated with the upregulation of hepatic metallothionein expression.

Preventive effects of metallothionein against DNA and lipid metabolic damages in dyslipidemic mice under repeated mild stress

The effects of repeated mild stress on DNA and lipid metabolic damages in multiple organs of dyslipidemic mice, and the preventive role of metallothionein (MT) were investigated. Female adult wild-type and MT-null mice fed high-fat diet (HFD) or standard diet (STD) were repeatedly subjected to fasting or restraint for three weeks. The liver, pancreas, spleen, bone marrow and serum samples were taken for evaluating DNA damage, MT, glutathione (GSH), corticosterone, carnitine and adiponectin. Body weights of restraint groups were reduced with the intensity of stress increased, even if the energy intakes were higher than those of STD group. Hepatic GSH levels were reduced in HFD control group and were further reduced in stress groups, especially in restraint groups, while the hepatic MT and serum corticosterone levels were increased in concert with the intensity of stress. Cellular DNA damages were generally increased by the restraint stress, especially in MT-null mice. Hepatic carnitine levels of MT-null mice were markedly lower than those of wild-type mice. The data suggest that MT plays a preventive role by acting as an antioxidant in corporation with GSH decreased by repeated stress and that MT may be an essential factor for inducing carnitine under the stress.

Metallothionein prevents intermittent hypoxia-induced cardiac endoplasmic reticulum stress and cell death likely via activation of Akt signaling pathway in mice

Endoplasmic reticulum (ER) stress, an adaptive response normally, causes apoptotic cell death under pathological conditions. Cardiac ER stress and associated cell death involve in the inflammatory responses that often cause cardiac remodeling and dysfunction. Here we examined whether chronic intermittent hypoxia (IH) induces cardiac ER stress and associated cell death along with inflammatory response and if so, whether these effects can be affected by transgenic overexpression or deletion of metallothionein gene (MT-TG or MT-KO). IH exposures for 3 days to 4 weeks significantly increased cardiac ER stress and apoptosis, shown by the increased expression of GRP78, ATF6 and CHOP, the activation of caspase-12 and capase-3, and the decreased Bcl2/Bax expression ratio, predominantly in the 3rd week of IH exposures. These effects were significantly exacerbated in MT-KO mice, but completely prevented in MT-TG mice. In vitro mechanistic study with H9c2 cardiac and primary neonatal cardiomyocytes showed that MT protection from ER stress-induced apoptosis was mediated by up-regulating Akt phosphorylation since inhibition of Akt phosphorylation abolished MT's protection MT from ER stress and apoptosis. These findings suggest that chronic IH is able to induce cardiac ER stress, cell death and inflammation can be prevented by MT, probably via up-regulation of Akt function.

Endoplasmic reticulum stress preconditioning attenuates methylmercury-induced cellular damage by inducing favorable stress responses

We demonstrate that methylmercury (MeHg)-susceptible cells preconditioned with an inhibitor of endoplasmic reticulum (ER) Ca(2+)-ATPase, thapsigargin, showed resistance to MeHg cytotoxicity through favorable stress responses, which included phosphorylation of eukaryotic initiation factor 2 alpha (Eif2α), accumulation of activating transcription factor 4 (Atf4), upregulation of stress-related proteins, and activation of extracellular signal regulated kinase pathway. In addition, ER stress preconditioning induced suppression of nonsense-mediated mRNA decay (NMD) mainly through the phospho-Eif2α-mediated general suppression of translation initiation and possible combined effects of decreased several NMD components expression. Atf4 accumulation was not mediated by NMD inhibition but translation inhibition of its upstream open reading frame (uORF) and translation facilitation of its protein-coding ORF by the phospho-Eif2α. These results suggested that ER stress plays an important role in MeHg cytotoxicity and that the modulation of ER stress has therapeutic potential to attenuate MeHg cytotoxicity, the underlying mechanism being the induction of integrated stress responses.

Heavy metal scavenger metallothionein attenuates ER stress-induced myocardial contractile anomalies: role of autophagy

Endoplasmic reticulum (ER) stress increases the risk of cardiovascular morbidity and mortality although the underlying mechanism remains elusive. This study was designed to examine the impact of cardiac over-expression of metallothionein, a cysteine-rich heavy metal scavenger, on ER stress-induced changes in myocardial function and underlying mechanism involved with a focus on autophagy. Wild-type friendly virus B (FVB) and metallothionein transgenic mice were subjected to the ER stress inducer tunicamycin (1 mg/kg). Our results showed that ER stress led to compromised echocardiographic and cardiomyocyte contractile function, intracellular Ca(2+) mishandling. Tunicamycin promoted ER stress and oxidative stress, increased left ventricular end systolic and diastolic diameter, as well as suppressed fractional shortening and whole heart contractility, the effects of which were significantly attenuated or ablated by metallothionein. Levels of the autophagy markers such as phosphorylated ULK1, Atg5, Atg7, LC3B and the autophagy adaptor p62 were significantly upregulated. These ER stress-induced changes in myocardial function, autophagy and autophagy signaling were distinctly mitigated or alleviated by metallothionein. Inhibition of autophagy using 3-methyladenine in vitro reversed ER stress-induced cardiomyocyte contractile defects. Meanwhile, ER stress-induced cardiomyocyte dysfunction was attenuated by the antioxidant N-acetylcysteine. Collectively, these findings suggested that metallothionein protects against ER stress-induced cardiac anomalies possibly through attenuation of cardiac autophagy.

Calcium and zinc dyshomeostasis during isoproterenol-induced acute stressor state

Acute hyperadrenergic stressor states are accompanied by cation dyshomeostasis, together with the release of cardiac troponins predictive of necrosis. The signal-transducer-effector pathway accounting for this pathophysiological scenario remains unclear. We hypothesized that a dyshomeostasis of extra- and intracellular Ca2+ and Zn2+ occurs in rats in response to isoproterenol (Isop) including excessive intracellular Ca2+ accumulation (EICA) and mitochondrial [Ca2+]m-induced oxidative stress. Contemporaneously, the selective translocation of Ca2+ and Zn2+ to tissues contributes to their fallen plasma levels. Rats received a single subcutaneous injection of Isop (1 mg/kg body wt). Other groups of rats received pretreatment for 10 days with either carvedilol (C), a β-adrenergic receptor antagonist with mitochondrial Ca2+ uniporter-inhibiting properties, or quercetin (Q), a flavonoid with mitochondrial-targeted antioxidant properties, before Isop. We monitored temporal responses in the following: [Ca2+] and [Zn2+] in plasma, left ventricular (LV) apex, equator and base, skeletal muscle, liver, spleen, and peripheral blood mononuclear cells (PBMC), indices of oxidative stress and antioxidant defenses, mitochondrial permeability transition pore (mPTP) opening, and myocardial fibrosis. We found ionized hypocalcemia and hypozincemia attributable to their tissue translocation and also a heterogeneous distribution of these cations among tissues with a preferential Ca2+ accumulation in the LV apex, muscle, and PBMC, whereas Zn2+ declined except in liver, where it increased corresponding with upregulation of metallothionein, a Zn2+-binding protein. EICA was associated with a simultaneous increase in tissue 8-isoprostane and increased [Ca2+]m accompanied by a rise in H2O2 generation, mPTP opening, and scarring, each of which were prevented by either C or Q. Thus excessive [Ca2+]m, coupled with the induction of oxidative stress and increased mPTP opening, suggests that this signal-transducer-effector pathway is responsible for Isop-induced cardiomyocyte necrosis at the LV apex.

Diabetes- and angiotensin II-induced cardiac endoplasmic reticulum stress and cell death: metallothionein protection

We have shown cardiac protection by metallothionein (MT) in the development of diabetic cardiomyopathy (DCM) via suppression of cardiac cell death in cardiac-specific MT-overexpressing transgenic (MT-TG) mice. The present study was undertaken to define whether diabetes can induce cardiac endoplasmic reticulum (ER) stress and whether MT can prevent cardiac cell death via attenuating ER stress. Diabetes was induced by streptozotocin in both MT-TG and wild-type (WT) mice. Two weeks, and 2 and 5 months after diabetes onset, cardiac ER stress was detected by expression of ER chaperones, and apoptosis was detected by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3 and caspase-12. Cardiac apoptosis in the WT diabetic mice, but not in MT-TG diabetic mice, was significantly increased 2 weeks after diabetes onset. In parallel with apoptotic effect, significant up-regulation of the ER chaperones, including glucose-regulated protein (GRP)78 and GRP94, cleaved ATF6 and phosporylated eIF2alpha, in the hearts of WT, but not MT-TG diabetic mice. Infusion of angiotensin II (Ang II) also significantly induced ER stress and apoptosis in the hearts of WT, but not in MT-TG mice. Direct administration of chemical ER stress activator tunicamycin significantly increased cardiac cell death only in WT mice. Pre-treatment with antioxidants completely prevented Ang II-induced ER stress and apoptosis in the cultured cardiac cells. These results suggest that ER stress exists in the diabetic heart, which may cause the cardiac cell death. MT prevents both diabetes- and Ang II-induced cardiac ER stress and associated cell death most likely via its antioxidant action, which may be responsible for MT's prevention of DCM.

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.

The protective effect of a newly developed molecular chaperone-inducer against mouse ischemic acute kidney injury

Activation of the unfolded protein response (UPR) has been suggested to attenuate renal ischemia-reperfusion (I/R) injury. We recently found a compound, namely BIX, that activated the UPR selectively through the activating transcription factor 6 pathway. This study examined the effect of BIX on renal I/R injury in mice. BIX selectively up-regulated renal BiP mRNA and protein. Pretreatment with BIX significantly ameliorated renal I/R injury. Co-administration of BIX and tunicamycin, a non-selective UPR inducer, provided no additional protection. Our results suggest that the UPR activation by BIX leads to a novel drug therapy against renal I/R injury.

A protective role of unfolded protein response in mouse ischemic acute kidney injury

Although renal ischemia-reperfusion is known to activate the unfolded protein response, the renal site and role of activation of this response following the insult in vivo remains largely unknown. Here we studied the renal spatio-temporal expression pattern of glucose-regulated protein (GRP) 78, a central regulator of the unfolded protein response network, following renal ischemia-reperfusion and the effects of the specific chemical unfolded protein response inducers, tunicamycin and thapsigargin, on renal ischemia-reperfusion injury in mice. Renal ischemia-reperfusion resulted in expression of the spliced form of the X-box binding protein-1 (XBP-1s) transcript, an unfolded protein response target, at 1 and 2 h after the insult. This response was followed by an increase in the GRP78 transcript and protein. The increased amount of GRP78 protein after ischemia-reperfusion was largely localized in proximal tubule cells. Pretreatment with tunicamycin or thapsigargin significantly ameliorated renal dysfunction and injury after ischemia-reperfusion. Taken together with these results, the unfolded protein response was activated following renal ischemia-reperfusion at sites that are susceptible to ischemia-reperfusion injury, and this activation had a protective effect against renal ischemia-reperfusion injury in vivo. Molecules involved in the unfolded protein response may offer new opportunities for pharmacological intervention against renal ischemia-reperfusion injury, which is an important cause of acute kidney injury.

Increased level of cellular Bip critically determines estrogenic potency for a xenoestrogen kepone in the mouse uterus

Xenoestrogen mimics estrogen-like activities primarily based on alterations of gene expression and interactions with estrogen receptor (ER)-alpha and -beta. However, the requirement for large concentrations to induce estrogenic phenotypes and low affinity for ERs has challenged the notion that prevailing xenoestrogens are significant health hazards. Here in this study, we show that under certain conditions, exposure of xenoestrogen could be potentially harmful in respect to enhanced uterine estrogenicity. Previously, we have demonstrated that estradiol-17beta up-regulates uterine Bip, a stress-related endoplasmic reticulum protein, via an ER-independent mechanism in mice. Moreover, this protein essentially involves in estradiol-17beta-mediated uterine growth response and ERalpha-dependent gene transcription. Here, we demonstrate that among three tested xenoestrogens, only kepone (>15-30 mg/kg) exerts sustained inductive response for uterine Bip expression. Interestingly, this kepone-induced Bip strongly correlates with ERalpha-dependent growth and gene expressional responses in the mouse uterus. Furthermore, these effects were strongly suppressed after knockdown of uterine Bip, via the adenovirus approach. Although kepone at 7.5 mg/kg was not effective, it was strongly stimulatory by the adenovirus-driven forced expression of uterine Bip. In contrast, the control green fluorescence protein virus was not effective in the aforementioned responses. Furthermore, the induction of uterine Bip by stress-related signals also revealed the onset of uterine growth in mice when exposed to a sublethal dose of kepone. Collectively, studies provide novel molecular evidence that Bip acts as a critical regulator to amplify estrogenic potency for a weak xenoestrogen kepone.

[Endoplasmic reticulum stress and metallothionein]

Much attention has been paid to lifestyle-related diseases including type 2 diabetes mellitus, cardiovascular disease, hypertension, and hyperlipidemia because the incidence rates of these diseases are increasing in developed countries. Elucidation of factors contributing to the development of obesity and insulin resistance is needed. Metallothionein (MT), a ubiquitous metal-binding protein, is induced not only by heavy metals but also by various kinds of stresses. Endoplasmic reticulum (ER) stress is caused by accumulation of misfolded proteins in ER. Recently, increased ER stress by obesity and impairment of insulin action by ER stress have been reported. Exposure to ER stress increased induction of MT synthesis, and an enhanced response to ER stress evaluated as expression of Bip/GRP78mRNA was observed in the liver of MT-null mice, suggesting that MT attenuates expression of ER stress. MT may prevent ER stress and thereby modulate the development of obesity and insulin resistance. A possible role of metallothionein in response reaction for ER stress is discussed.

Toxicity assays in nanodrops combining bioassay and morphometric endpoints

BACKGROUND

Improved chemical hazard management such as REACH policy objective as well as drug ADMETOX prediction, while limiting the extent of animal testing, requires the development of increasingly high throughput as well as highly pertinent in vitro toxicity assays.

METHODOLOGY

This report describes a new in vitro method for toxicity testing, combining cell-based assays in nanodrop Cell-on-Chip format with the use of a genetically engineered stress sensitive hepatic cell line. We tested the behavior of a stress inducible fluorescent HepG2 model in which Heat Shock Protein promoters controlled Enhanced-Green Fluorescent Protein expression upon exposure to Cadmium Chloride (CdCl2), Sodium Arsenate (NaAsO2) and Paraquat. In agreement with previous studies based on a micro-well format, we could observe a chemical-specific response, identified through differences in dynamics and amplitude. We especially determined IC50 values for CdCl2 and NaAsO2, in agreement with published data. Individual cell identification via image-based screening allowed us to perform multiparametric analyses.

CONCLUSIONS

Using pre/sub lethal cell stress instead of cell mortality, we highlighted the high significance and the superior sensitivity of both stress promoter activation reporting and cell morphology parameters in measuring the cell response to a toxicant. These results demonstrate the first generation of high-throughput and high-content assays, capable of assessing chemical hazards in vitro within the REACH policy framework.

Cataract: Window for systemic disorders

Cataract is the leading cause of visual handicap throughout the world, and almost all elderly individuals develop lens opacities. Epidemiological studies have shown that nuclear cataracts in young adults are associated with higher mortality. Many cataractogenic stressors induce endoplasmic reticulum (ER) stress, which in turn induces the unfolded protein response (UPR). The UPR can damage or kill a wide range of cell types and may be involved in many human diseases. We hypothesize that a cataract can be considered a window that can indicate the presence of systemic disorders. This is important because cataract is easily detected during a routine ocular examination. The slightest opacity in any region of the lenses, especially in younger patients, may be a sign of systemic disorders. Earlier detection of systemic disorders can save the lives of patients. If our hypothesis is correct, then elimination of known ER/cataractogenic stressors from individuals with cataracts should be the one of the first steps for treatments of the systemic disorders. We discuss the potential risk factors and beneficial effects of removal of such risk factors in patients with early cataracts. All patients with cataract should be referred for comprehensive medical examination.

Real-time detection and continuous monitoring of ER stress in vitro and in vivo by ES-TRAP: evidence for systemic, transient ER stress during endotoxemia

Activity of secreted alkaline phosphatase (SEAP) produced by transfected cells is rapidly down-regulated by endoplasmic reticulum (ER) stress independent of transcriptional regulation. This phenomenon was observed in a wide range of cell types triggered by various ER stress inducers. The magnitude of the decrease in SEAP was proportional to the extent of ER stress and inversely correlated with the induction of endogenous ER stress markers grp78 and grp94. In contrast to SEAP, activity of secreted luciferase was less susceptible to ER stress. The decrease in SEAP activity by ER stress was caused by abnormal post-translational modification, accelerated degradation and reduced secretion of SEAP protein. In transgenic mice constitutively producing SEAP, systemic induction of ER stress led to reduction in serum SEAP. In these mice, administration with lipopolysaccharide caused rapid, transient decrease in serum SEAP activity, and it was correlated with up-regulation of grp78 in several organs including the spleen, lung, kidney, liver and heart. These results elucidated for the first time a possible involvement of transient, systemic ER stress in endotoxemia and provided evidence for usefulness of ER stress responsive alkaline phosphatase for real-time monitoring of ER stress in vitro and in vivo.

Xenobiotic-induced alterations in thymocyte development

The thymus is a very sensitive target for environmental pollutants, which can affect this organ as well as thymocyte differentiation. A failure in thymocyte development can be due to the exacerbation of apoptosis, arrest of thymocyte maturation, generation of autoreactive T cells, and inhibition or stimulation of the output of recent thymic emigrants to the periphery. Recent data demonstrate that the immune system has the potential to maintain homeostasis under conditions of elevated risk, and the thymus plays a crucial role in this process. Environmental xenobiotics can exert their effects through receptor-mediated interactions or independently on receptor involvement. Under natural conditions organisms are exposed to a variety of xenobiotics. The final effect of such exposure is not related to the action of a single chemical, but to the action of a mixture of chemicals. The toxic effect of environmental xenobiotics on the generation and functions of immune cells may result in suppression or stimulation of the immune response. The most intensive studies have been done on halogenated aromatic hydrocarbons, heavy metals and various chemicals acting as endocrine disrupters. Recently, special interest has focused on the action of air particulate matter.

Cataracts: role of the unfolded protein response

Many cataracts are caused by unfolded protein aggregates in highly oxidized lenses, but the underlying mechanisms of their formation are poorly understood. A literature search has shown that many cataractogenic stressors are also endoplasmic reticulum (ER) stressors, which induce the unfolded protein response (UPR) in a wide range of cell types. Since the lumen of the ER is highly oxidized, ER stressors might generate unfolded protein aggregates, which activate the UPR leading to the production of reactive oxygen species (ROS) in lens epithelial cells (LECs). ROS decrease the amount of free glutathione from whole lenses and elicit a more oxidized environment, where unfolded protein aggregates are formed and grown to large protein aggregate particles to scatter light. Recently, we have shown that ER stressors, homocysteine, tunicamycin, Ca(2+) ionophore (A23187), and glucose deprivation induce the UPR in LECs. Here we hypothesize the cataractogenic stressors induce ER stress, initiate the UPR and ROS production in LECs with or without apoptosis and eventually resulted in cataracts.