Gonadotropin regulation of glutathione synthesis in the rat ovary.

Glutathione (GSH), an antioxidant and conjugator of electrophilic toxicants, prevents toxicant-mediated destruction of ovarian follicles and oocytes. Ovarian GSH has previously been shown to change with estrous cycle stage in rats, suggesting that the gonadotropin hormones may regulate ovarian GSH synthesis. The present studies tested the hypotheses that [1] estrous cycle-related changes in ovarian GSH result from cyclic changes in protein and mRNA expression of the rate-limiting enzyme in GSH synthesis, glutamate cysteine ligase (GCL, also called gamma-glutamylcysteine synthetase), and [2] that these changes result from gonadotropin-mediated regulation of GCL subunit expression. In the first experiment, ovaries were harvested from cycling adult female rats on each stage of the estrous cycle. In the second experiment immature female rats were injected with pregnant mare's serum gonadotropin (PMSG) to stimulate follicular development or with vehicle and killed 8, 24, or 48 h later. In both experiments the ovaries were harvested for [1] total GSH assay, [2] Western analysis for GCL catalytic (GCLc) and regulatory (GCLm) subunit protein levels, or [3] Northern analysis for Gclc and Gclm mRNA levels. Ovarian GSH concentrations and Gclc and Gclm mRNA levels, but not GCL subunit protein levels, varied significantly with estrous cycle stage. PMSG administration significantly increased ovarian GSH concentrations 24 and 48 h later. GCLm protein levels increased significantly at 24 h and 48 h following PMSG. GCLc protein levels did not increase significantly following PMSG. Gcl subunit mRNA levels were not significantly increased at any time point by the planned ANOVA; however, an increase in Gelc at 48 h was identified by t-testing. These results support the hypothesis that gonadotropins regulate ovarian GSH synthesis by modulating GCL subunit expression.     

Modulation of stellate cell proliferation and gene expression by rat hepatocytes: effect of toxic iron overload

Mechanisms by which hepatocytes and transdifferentiated hepatic stellate cells (HSC) initiate liver fibrosis in chronic iron toxicity are unknown. This study was to determine if factors in media from control and iron-loaded rat hepatocyte cultures modulate HSC gene expression and proliferation. Conditioned medium (CM) from both control and iron-loaded hepatocytes increased serum-stimulated DNA synthesis by HSC to 140% of control values (P<0.05). Heating CM (15 min, 80 degrees C) caused a suppression of DNA synthesis that was partially reversed by a TGF-beta-neutralizing antibody. Addition of TGF-beta1 reproduced the suppression. Levels in HSC of mRNA for collagen type I, collagen type IV, TGF-beta, and plasminogen activator inhibitor-1 were unaffected by exposure to CM but increased significantly when CM from iron-loaded hepatocytes was heat-treated. In HepG2 cell cultures, iron loading increased total (but not activated) TGF-beta secretion into the medium approximately 2-fold. We conclude that increased secretion of latent TGF-beta by hepatocytes injured by iron is a potential factor influencing fibrogenic behavior of HSC.     

The age-related change of glutathione antioxidant system in mice liver

Abstract

Cellular glutathione (GSH) antioxidant system is an important defensive system of the body, which is crucial in the protection against oxidative stress-induced liver injury. The present study was designed to observe the difference of this system in the liver of mice with 1-month- and 12-month-old. Liver reduced GSH level was showed no difference between these two groups of mice. Next, the results showed that liver glutamate-cysteine ligase (GCL) activity was higher in mice of 1-month- than 12-month-old, while glutathione-S-transferase (GST) activity was higher in mice of 12-month- than 1-month-old. Further results showed that the higher activity of liver GCL in 1-month-old mice was due to the higher expression of catalytic subunit of GCL (GCLc) mRNA, while the higher activity of liver GST in 12-month-old mice might be due to the higher expression of GSTA1, GSTA2, GSTP1 and GSTP2 mRNA. Taken together, our results revealed the age-related change of liver GSH antioxidant system in mice, which may be helpful for elucidating some age-related liver injury or diseases.     

Modulating GSH Synthesis Using Glutamate Cysteine Ligase Transgenic and Gene-Targeted Mice

Glutathione (GSH) is an important antioxidant and cofactor for glutathione S-transferase conjugation. GSH synthesis is catalyzed by glutamate cysteine ligase (GCL), composed of catalytic (GCLC) and modifier (GCLM) subunits. Transgenic mice that conditionally over express GCL subunits are protected from acetaminophen induced liver injury. Gclm null mice exhibit low GSH levels and enhanced sensitivity to acetaminophen. When Gclm expression and GCL activity are restored in Gclm conditional transgenic X Gclm null mice, they become resistant to APAP-induced liver damage. These animal models are a valuable resource for investigating the role of GSH synthesis in modulating oxidative damage and drug-induced hepatotoxicity.     

Modulating GSH synthesis using glutamate cysteine ligase transgenic and gene-targeted mice

Glutathione (GSH) is an important antioxidant and cofactor for glutathione S-transferase conjugation. GSH synthesis is catalyzed by glutamate cysteine ligase (GCL), composed of catalytic (GCLC) and modifier (GCLM) subunits. Transgenic mice that conditionally over express GCL subunits are protected from acetaminophen induced liver injury. Gclm null mice exhibit low GSH levels and enhanced sensitivity to acetaminophen. When Gclm expression and GCL activity are restored in Gclm conditional transgenic X Gclm null mice, they become resistant to APAP-induced liver damage. These animal models are a valuable resource for investigating the role of GSH synthesis in modulating oxidative damage and drug-induced hepatotoxicity.     

Pro-oxidant shift in glutathione redox state during aging

The GSH:GSSG ratio, which is the primary determinant of the cellular redox state, becomes progressively more pro-oxidizing during the aging process due to an elevation in the GSSG content and a decline in the ability for de novo GSH biosynthesis. The K(m) of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in de novo GSH biosynthesis, significantly increases during aging, which would adversely affect the ability for rapid GSH biosynthesis, especially under stressful conditions. Experimental studies suggest that age-related accumulation of homocysteine, an intermediate in the trans-sulfuration pathway, may be responsible for causing the loss of affinity between GCL and its substrates. Over-expression of GCL has been shown to prolong the life span of Drosophila by up to 50%, suggesting that perturbations in glutathione metabolism play a causal role in the aging process.     

Effect of methylmercury on glutamate-cysteine ligase expression in the placenta and yolk sac during mouse development

The placenta and the yolk sac play critical roles in fetal development, including protection from oxidative stress through the presence of detoxifying enzymes. Glutathione (GSH; gamma-glutamylcysteinylglycine), a crucial molecule in the maintenance of cellular redox status, plays a critical role in development, and it is also protective against methylmercury toxicity. Glutamate-cysteine ligase (GCL), the enzyme that catalyzes the rate-limiting step in GSH synthesis, is widely expressed in the mouse embryo and extraembryonic membranes throughout development. The aim of this study was to investigate the effect of low-level subchronic methylmercury exposure on GCL expression in the mouse placenta and yolk sac, after describing the basal developmental expression of the enzyme in these tissues. We found that basal mRNA expression levels increased dramatically in the placenta and the yolk sac at gd 18, whereas protein levels did not increase in parallel with the mRNA. We also found that methylmercury induced GCLc mRNA expression in the placenta at gd 18 in a dose-dependent manner, suggesting an important role for this enzyme in the response of the placenta to toxicants. These changes in expression may be useful as a biomarker of MeHg exposure during development.     

Elevated glutathione levels confer cellular sensitization to cisplatin toxicity by up-regulation of copper transporter hCtr1

Previous studies have demonstrated that treating cultured cells with cisplatin (CDDP) up-regulated the expression of glutathione (GSH) and its de novo rate-limiting enzyme glutamate-cysteine ligase (GCL), which consists of a catalytic (GCLC) and a modifier (GCLM) subunit. It has also been shown that many CDDP-resistant cell lines exhibit high levels of GCLC/GCLM and GSH. Because the GSH system is the major intracellular regulator of redox conditions that serve as an important detoxification cytoprotector, these results have been taken into consideration that elevated levels of GCL/GSH are responsible for the CDDP resistance. In contrast to this context, we demonstrated here that overexpression of GSH by transfection with an expression plasmid containing the GCLC cDNA conferred sensitization to CDDP through up-regulation of human copper transporter (hCtr) 1, which is also a transporter for CDDP. Depleting GSH levels in these transfected cells reversed CDDP sensitivity with concomitant reduction of hCtr1 expression. Although rates of copper transport were also up-regulated in the transfected cells, these cells exhibited biochemical signature of copper deficiency, suggesting that GSH functions as an intracellular copper-chelator and that overexpression of GSH can alter copper metabolism. More importantly, our results reveal a new role of GSH in the regulation of CDDP sensitivity. Overproduction of GSH depletes the bioavailable copper pool, leading to up-regulation of hCtr1 and sensitization of CDDP transport and cell killing. These findings also have important implications in that modulation of the intracellular copper pool may be a novel strategy for improving chemotherapeutic efficacy of platinum-based antitumor agents.     

Glutathione-deficient mice are susceptible to TCDD-Induced hepatocellular toxicity but resistant to steatosis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) generates both hepatocellular injury and steatosis, processes that involve oxidative stress. Herein, we evaluated the role of the antioxidant glutathione (GSH) in TCDD-induced hepatotoxicity. Glutamate-cysteine ligase (GCL), comprising catalytic (GCLC) and modifier (GCLM) subunits, is rate limiting in de novo GSH biosynthesis; GCLM maintains GSH homeostasis by optimizing the catalytic efficiency of GCL holoenzyme. Gclm(-/-) transgenic mice exhibit 10-20% of normal tissue GSH levels. Gclm(-/-) and Gclm(+/+) wild-type (WT) female mice received TCDD for 3 consecutive days and were then examined 21 days later. As compared with WT littermates, Gclm(-/-) mice were more sensitive to TCDD-induced hepatocellular toxicity, exhibiting lower reduction potentials for GSH, lower ATP levels, and elevated levels of plasma glutamic oxaloacetic transaminase (GOT) and γ-glutamyl transferase (GGT). However, the histopathology showed that TCDD-mediated steatosis, which occurs in WT mice, was absent in Gclm(-/-) mice. This finding was consistent with cDNA microarray expression analysis, revealing striking deficiencies in lipid biosynthesis pathways in Gclm(-/-) mice; qrt-PCR analysis confirmed that Gclm(-/-) mice are deficient in expression of several lipid metabolism genes including Srebp2, Elovl6, Fasn, Scd1/2, Ppargc1a, and Ppara. We suggest that whereas GSH protects against TCDD-mediated hepatocellular damage, GSH deficiency confers resistance to TCDD-induced steatosis due to impaired lipid metabolism.     

Green tea polyphenol epigallocatechin-3-gallate suppresses rat hepatic stellate cell invasion by inhibition of MMP-2 expression and its activation

AIM: Epigallocatechin-3-gallate (EGCG) is the major component of green tea polyphenols, whose wide range of biological properties includes anti-fibrogenic activity. Matrix metalloproteinases (MMP) that participate in extracellular matrix degradation are involved in the development of hepatic fibrosis. The present study investigates whether EGCG inhibits activation of the major gelatinase matrix metalloproteinase-2 (MMP-2) in rat hepatic stellate cells (HSC). METHODS: The expression of MMP-2, tissue inhibitors of metalloproteinases-2 (TIMP-2), and membrane-type 1-MMP (MT1-MMP) was assessed by RT-PCR and Western blot analyses. MMP-2 activity was evaluated by zymography and MT1-MMP activity was assessed by an enzymatic assay. HSC migration was measured by a wound healing assay and cell invasion was performed using Transwell cell culture chambers. RESULTS: The expression of MMP-2 mRNA and protein in HSC was substantially reduced by EGCG treatment. EGCG treatment also reduced concanavalin A (ConA)-induced activation of secreted MMP-2 and reduced MT1-MMP activity in a dose-dependent manner. In addition, EGCG inhibited either HSC migration or invasion. CONCLUSION: The abilities of EGCG to suppress MMP-2 activation and HSC invasiveness suggest that EGCG may be useful in the treatment and prevention of hepatic fibrosis.     

Minimal ovarian upregulation of glutamate cysteine ligase expression in response to suppression of glutathione by buthionine sulfoximine

The antioxidant tripeptide glutathione (GSH) protects ovarian follicles against oxidative damage that may lead to apoptotic death. The rate-limiting step in synthesis of GSH is catalyzed by glutamate cysteine ligase (GCL), a heterodimer composed of a catalytic subunit (GCLC), and a modifier subunit (GCLM). We hypothesized that GSH depletion in vivo or in vitro with buthionine sulfoximine (BSO), a specific inhibitor of GCL activity, would increase ovarian and granulosa cell GCL subunit expression. Ovarian glutathione levels are lowest on proestrous morning and increase to their highest levels on estrus and metestrus. Therefore, we treated rats on proestrous morning or on proestrous morning and again 12h later to prevent the normal increase in ovarian glutathione between proestrus and estrus. Ovarian Gclc and Gclm mRNA levels and GCLC protein levels increased transiently by 1.4-1.5-fold at 8 h, but not at 12 or 24 h, after a single dose of BSO administered to adult rats on the morning of proestrus. GCLC protein levels were also modestly increased 1.4-fold at 12 h after a second dose of BSO. GCLM protein levels increased 1.4-fold at 24 h after a single dose of BSO, but not at other time points. BSO treatment did not significantly alter ovarian GCL enzymatic activity or the intraovarian localization of either GCL subunit mRNA. Treatment of a human granulosa cell line or primary rat granulosa cells with BSO suppressed intracellular GSH; however, there was no compensatory upregulation of GCL subunit protein or mRNA levels. These results demonstrate that ovarian follicles and granulosa cells are minimally able to respond to acute GSH depletion by upregulating expression of GCL.     

Regulation of gamma-glutamate-cysteine ligase expression by oxidative stress in the mouse preimplantation embryo

The present study examined expression of gamma-glutamate-cysteine ligase (GLCL; also known as gamma-glutamylcysteine synthetase), the rate-limiting enzyme for de novo synthesis of glutathione, in the preimplantation mouse embryo. Previous studies indicated that the cleavage stage embryo is unable to synthesize glutathione de novo. It is hypothesized that GLCL mRNA and protein are not normally expressed in the cleavage stage embryo, but either glutathione depletion or oxidation may induce their expression. In untreated embryos, RT-PCR and Western blotting revealed GLCL heavy subunit (GLCL-H) mRNA and protein only at the blastocyst stage of development. Furthermore, while diethyl maleate (DEM) exposure to deplete cellular glutathione did not induce expression of GLCL-H, exposure to tertiary-butyl hydroperoxide (tBH), an oxidizing agent, resulted in significant upregulation of GLCL-H expression in two-cell embryos. Neither treatment affected expression in blastocysts. Finally, HPLC analysis confirmed that tBH-treated embryos experienced oxidative stress, as indicated by an increase in the ratio of oxidized to reduced glutathione. This oxidative stress induced de novo glutathione synthesis in the cleavage stage embryo, as demonstrated by the subsequent recovery of reduced glutathione levels following DEM-induced depletion. In the absence of tBH treatment, however, cleavage stage embryos could not recover GSH after DEM-mediated depletion. This study demonstrates that the preimplantation embryo has the capacity to upregulate glutathione synthesis in response to oxidative stress but not GSH depletion. These results suggest that, while the preimplantation embryo is well adapted to dealing with oxidative stress, it may be poorly protected from GSH-depleting toxicants.     

丹酚酸B对大鼠肝星状细胞胶原生成与丝裂原激活蛋白激酶活性的影响

目的:研究丹酚酸B影响肝星状细胞活化与转化生长因子β1胞内信号转导的抗肝纤维化作用机制.方法:正常大鼠肝脏链酶蛋白酶原位灌流消化与11％nycondenz密度梯度离心分离肝星状细胞,传一代培养.[~3H]TdR掺入法测定细胞增殖,丽春红染色、图像分析半定量细胞胶原沉积量,ELISA法测定细胞培养上清Ⅰ型胶原分泌量,培养上清酸化处理后,ELISA法测定活性TGF-β1含量.RT-PCR法分析细胞前胶原α_1(Ⅰ)基因的表达,免疫沉淀与蛋白印迹法分析丝裂原激活蛋白激酶(MAPK)活性.结果:丹酚酸B 0.1-100 μmol/L浓度依赖性抑制星状细胞增殖,丹酚酸B 1-100 μmol/L浓度依赖性抑制细胞的Ⅰ型胶原分泌量与总胶原的沉积.丹酚酸B 1-10 μmol/L抑制TGF-β1自分泌量,下调α_1(Ⅰ)前胶原的基因表达.而且丹酚酸B 1-PffiO卫几明显抑制TGF-β1刺激的MAPK活性.结论:丹酚酸B可抑制肝星状细胞的增殖与胶原生成,抑制TGF-β1的自分泌与MAKP活性,这些作用是丹酚酸B抗肝纤维化的主要作用机制.     

Neuroprotective effect of epigallocatechin-3-gallate against β-amyloid-induced oxidative and nitrosative cell death via augmentation of antioxidant defense capacity

β-Amyloid (Aβ) peptide, a major component of senile plaques has been regarded to play a crucial role in the development and neuropathogenesis of Alzheimer’s disease (AD). Increasing data from in vitro and in vivo studies indicate that Aβ-induced damages in neurons and glia are mediated via nitrosative as well as oxidative stress. Therefore, recent researches have been focused on searching for dietary and herbal manipulations to protect against the Aβ-induced oxidative and/or nitrosative cell death. Epigallocatechin-3-gallate (EGCG), one of these candidates is a major polyphenolic compound present in green tea and has been reported to exhibit potent antioxidant and anti-inflammatory properties. In the present study, we have investigated the effect of EGCG against Aβ-induced oxidative and/or nitrosative cell death in BV2 microglia. Aβ treatment led to apoptosis in BV2 cells as revealed by DNA fragmentation, perturbation of mitochondrial transmembrane potential, and alterations in the expression of apoptosis-regulator Bcl-2 family proteins. EGCG pretreatment effectively ameliorated Aβ-induced cytotoxicity and manifestation of proapoptotic signals. Furthermore, BV2 cells exposed to Aβ underwent nitrosative stress as shown by the increased expression of inducible nitric oxide synthase (iNOS) and subsequent production of nitric oxide (NO) and peroxynitrite, which were effectively suppressed by EGCG pretreatment. To elucidate a molecular mechanism underlying the neuroprotective effect of EGCG, we have examined the cellular metabolism of reduced glutathione (GSH) with antioxidant properties. EGCG treatment fortified cellular GSH pool through elevated mRNA expression of γ-glutamylcysteine ligase (GCL), the rate limiting enzyme in the glutathione biosynthesis. These results suggest that EGCG may have preventive and/or therapeutic potential in AD patients by augmenting cellular antioxidant defense capacity and attenuating Aβ-mediated oxidative and/or nitrosative cell death.     

miRNA 与胆道闭锁肝纤维化

胆道闭锁(BA)是婴儿期引起梗阻性黄疸的主要病因之一, 以肝内外胆管进行性炎症和纤维性梗阻为主要特征, 导致胆汁淤积和肝纤维化及肝硬化。肝纤维化中最重要的是肝星状细胞(HSC)的活化, 这一过程受到多种机制的调节, 其中 miRNA 家族成员可通过调控靶基因的表达, 进而作用于多种信号通路促进 HSC 的活化, 在细胞外基质(ECM)的合成和降解中发挥调节作用。大量文献表明 PI3K/Akt 信号通路与肝纤维化的发生、 发展密切相关, 参与了活化 HSC 增殖、 凋亡的调控, miRNA 通过各种靶基因激活 PI3K/Akt 信号通路, 进而激活 HSC, 促进肝纤维化的发展。本文就胆道闭锁肝纤维化相关的 miRNA综述如下。     

Curcumin inhibits connective tissue growth factor gene expression in activated hepatic stellate cells in vitro by blocking NF-kappaB and ERK signalling

BACKGROUND AND PURPOSE: Gene expression of connective tissue growth factor (CTGF) is induced in activated hepatic stellate cells (HSC), the major effectors in hepatic fibrosis, and production of extracellular matrix (ECM) is consequently increased. We previously reported that curcumin, the yellow pigment in curry, suppressed ctgf expression, leading to decreased production of ECM by HSC. The purpose of this study is to evaluate signal transduction pathways involved in the curcumin suppression of ctgf expression in HSC. EXPERIMENTAL APPROACHES: Transient transfection assays were performed to evaluate effects of activation of signalling pathways on the ctgf promoter activity. Real-time PCR and Western blotting analyses were conducted to determine expression of genes. RESULTS: Suppression of ctgf expression by curcumin was dose-dependently reversed by lipopolysaccharide (LPS), an NF-kappaB activator. LPS increased the abundance of CTGF and type I collagen in HSC in vitro. Activation of NF-kappaB by dominant active IkappaB kinase (IKK), or inhibition of NF-kappaB by dominant negative IkappaBalpha, caused the stimulation, or suppression of the ctgf promoter activity, respectively. Curcumin suppressed gene expression of Toll-like receptor-4, leading to the inhibition of NF-kappaB. On the other hand, interruption of ERK signalling by inhibitors or dominant negative ERK, like curcumin, reduced NF-kappaB activity and in ctgf expression. In contrast, the stimulation of ERK signalling by constitutively active ERK prevented the inhibitory effects of curcumin. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that the interruption of NF-kappaB and ERK signalling by curcumin results in the suppression of ctgf expression in activated HSC in vitro.