高糖通过下调FoxO1磷酸化诱导β细胞去分化

胰岛β细胞发生去分化现象是导致其功能减退的机制之一。已有研究证明,FoxO1与β细胞去分化密切相关。然而,高糖是否可通过FoxO1诱导β细胞发生去分化目前尚未见报告。本研究通过不同浓度高糖干预MIN6细胞,采用葡萄糖刺激胰岛素分泌试验（GSIS）检测β细胞功能|实时荧光定量PCR及蛋白免疫印迹、免疫荧光方法检测高糖干预后β细胞内祖细胞标志基因、β细胞标志基因及FoxO1的表达变化。结果显示,不同浓度高糖干预β细胞后,当浓度达到35 mmol/L时,β细胞祖细胞标志基因表达明显增加。且在该浓度时,检测到β细胞标志基因表达明显降低,MIN6细胞葡萄糖刺激胰岛素分泌功能减退,磷酸化FoxO1表达减少。上述结果提示,高糖可诱导胰岛β细胞去分化的发生,其机制可能是通过FoxO1介导。     

Studies on hepatic oxidative stress and antioxidant defence systems during arteether treatment of Plasmodium yoelii nigeriensis infected mice

Reactive Oxygen species play an important role in pathology during malaria infection. The status of hepatic oxidative stress and antioxidant defence indices was studied during Plasmodium yoelii nigeriensis (P. y. nigeriensis) infection in mice and arteether treatment of P. y. nigeriensis infected mice. P. y. nigeriensis infection caused a significant increase in hepatic xanthine oxidase, rate of lipid peroxidation, reduced glutathione (GSH) and glutathione reductase with progressive rise in parasitemia. This was accompanied by a significant decrease in hepatic superoxide dismutase (SOD) and catalase with increase in parasitemia. Arteether treatment (10 mg/kg body weight of mice) of infected mice from day 2 of post infection resulted in complete clearance of parasitemia on day 4 of post infection which was accompanied by restoration of all the oxidative stress and antioxidant defence indices to normal levels.     

Effect of intravenous nitroglycerin therapy on erythrocyte antioxidant enzymes

Intravenous nitroglycerin (GTN) has been used as an anti-ischemic agent for the therapy of unstable and post-infarction angina. Nitric oxide (^?NO) and S-nitrosothiols constitute the biologically active species formed via nitroglycerin bioactivation. Increased levels of reactive oxygen species can diminish the therapeutic action of organic nitrates by scavenging donated ^?NO and oxidizing tissue thiols important in nitrate biotransformation. Studies reported here show that the red cell activity of antioxidant enzymes, catalase and glutathione peroxidase, are significantly decreased after intravenous nitroglycerin treatment. Catalase activity decreased to and after 1 and 24?hr GTN infusion, respectively. Similarly, glutathione peroxidase activity decreased to and after 1 and 24?hr GTN infusion, respectively. The reported decrease in antioxidant enzyme activities can lead to an oxidant milieu and contribute to the generation of nitrate tolerance.     

Effect of stress on the antioxidant enzymes and gastric ulceration

The effect of cold-restraint stress on the antioxidant enzymes of the rat gastric mucosa was studied with a view to finding out their role in stress induced gastric ulceration. Histological examination revealed stress induced extensive damage of the surface epithelial cell with lesions extending upto submucosa in some cases. Stress causes time-dependent increase in histamine and pepsin content but decrease in acid content of the gastric fluid with the progress of ulceration (ulcer index) for two hours. The tissue lipid peroxidation was significantly increased as evidenced by accumulation of malondialdehyde. Since lipid peroxidation results from the generation of reactive oxygen species, stress effect was studied on some antioxidant enzymes such as superoxide dismutase, peroxidases and prostaglandin synthetase as a function of time. The time dependent increase in stress ulcer correlates well with the concomitant increase in superoxide dismutase activity and decrease in peroxidase and prostaglandin synthetase activity. This creates a favourable condition for accumulation of endogenous H₂O₂ and more reactive hydroxyl radical (OH·). Administration of antioxidants such as reduced glutathione or sodium benzoate prior to stress causes significant decrease in ulcer index and lipid peroxidation and protection of gastric peroxidase activity suggesting the involvement of reactive oxygen species in stress induced gastric ulceration. This is supported by thein vitro observation that OH· can also inactivate peroxidase and induce lipid peroxidation. As prostaglandin is known to offer cytoprotection, stress-induced loss of prostaglandin synthetase activity appears to aggravate the oxidative damage caused by reactive oxygen species.Abbreviations ROS reactive oxygen species - GPO gastric peroxidase - SOD superoxide dismutase - MDA malondialdehyde - GSH reduced glutathione - TCA trichloroacetic acid     

Differential expression of antioxidant enzymes in various hepatocellular carcinoma cell lines

Recent evidence suggests that reactive oxygen species (ROS) play an important role in the pathogenesis of various illnesses, and the ROS and antioxidant enzymes are highly associated with cell differentiation and diseases. In this study, we tested the hypothesis that specific antioxidant enzymes are differentially expressed in hepatocellular carcinoma (HCC) cell lines with various degrees of differentiation. We compared the expression of several antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GRx), and glutathione peroxidase (GPx) in five HCC cell lines with well (Hep G2 and Hep 3B) or poor (HA22T/VGH, HA55T/VGH, and SK-Hep-1) differentiation. Our results showed that both well-differentiated HCC cell lines expressed extremely higher CAT and GRx enzyme activities than all three poorly differentiated ones. Moreover, the protein and mRNA levels of CAT were much higher in two well-differentiated HCC cell lines than in all three poorly differentiated ones. Both well-differentiated HCC cell lines also showed a higher protein or mRNA expression of Cu/ZnSOD and MnSOD than three poorly differentiated ones. Our results demonstrate that specific antioxidant enzymes (especially, CAT and GRx) are differentially expressed in HCC cell lines with well or poor differentiation. These findings suggest that CAT and GRx are two potential differentiation markers for HCC.     

Bone marrow mesenchymal stem cells inhibit cardiac hypertrophy by enhancing FoxO1 transcription

Bone marrow–derived mesenchymal stem cells (BMSCs) have therapeutic potential for certain heart diseases. Previous studies have shown that stem cells inhibit cardiac hypertrophy; however, it is necessary to explore the mechanisms underlying this effect. This study aimed to investigate the possible mechanism underlying the inhibitory effect of BMSCs on cardiomyocyte hypertrophy. We induced cardiomyocyte hypertrophy in cultured rat cells through isoproterenol (ISO) treatment with or without BMSC coculture. A microarray was performed to analyze messenger RNA expression in response to ISO treatment and BMSC coculture. Pathway enrichment analysis showed that the expression of differential genes was closely related to the 5′-adenosine monophosphate-activated protein kinase (AMPK) signaling pathway and that the expression of forkhead box O 1 (FoxO1) was significantly increased in the presence of BMSCs. Furthermore, we determined the expression levels of p-AMPK/AMPK and p-FoxO1/FoxO1 by western blot analysis. The expression of p-AMPK/AMPK was upregulated, whereas that of p-FoxO1/FoxO1 was downregulated upon coculturing with BMSCs. The AMPK-specific antagonist Compound C inhibited the downregulation of p-FoxO1/FoxO1 induced by the BMSC coculture. Furthermore, treatment with the specific FoxO1 antagonist AS1842856 reduced the inhibitory effects of BMSCs on cardiomyocyte hypertrophy in vivo and in vitro. Our present study demonstrates the inhibition of cardiomyocyte hypertrophy by BMSCs, which occurs partly through the AMPK–FoxO1 signaling pathway.     

ROS leads to MnSOD upregulation through ERK2 translocation and p53 activation in selenite-induced apoptosis of NB4 cells

Following our previous finding that sodium selenite induces apoptosis in human leukemia NB4 cells, we now show that the expression of the critical antioxidant enzyme manganese superoxide dismutase (MnSOD) is remarkably elevated during this process. We further reveal that reactive oxygen species (ROS), especially superoxide radicals, play a crucial role in selenite-induced MnSOD upregulation, with extracellular regulated kinase (ERK) and p53 closely implicated. Specifically, ERK2 translocates into the nucleus driven by ROS, where it directly phosphorylates p53, leading to dissociation of p53 from its inhibitory protein mouse double minute 2 (MDM2). Active p53 directly mediates the expression of MnSOD, serving as the link between ERK2 translocation and MnSOD upregulation.     

Unravelling mitochondrial retrograde regulation in the abiotic stress induction of rice ALTERNATIVE OXIDASE 1 genes

Mitochondrial retrograde regulation (MRR) is the transduction of mitochondrial signals to mediate nuclear gene expression. It is not clear whether MRR is a common regulation mechanism in plant abiotic stress response. In this study, we analysed the early abiotic stress response of the rice OsAOX1 genes, and the induction of OsAOX1a and OsAOX1b (OsAOX1a/b) was selected as a working model for the stress‐induced MRR studies. We found that the induction mediated by the superoxide ion (O_2·^‐)‐generating chemical methyl viologen was stronger than that of hydrogen peroxide (H₂O₂). The addition of reactive oxygen species (ROS) scavengers demonstrated that the stress induction was reduced by eliminating O_2·^‐. Furthermore, the stress induction did not rely on chloroplast‐ or cytosol‐derived O_2·^‐. Next, we generated transgenic plants overexpressing the superoxide dismutase (SOD) gene at different subcellular locations. The results suggest that only the mitochondrial SOD, OsMSD, attenuated the stress induction of OsAOX1a/b specifically. Therefore, our findings demonstrate that abiotic stress initiates the MRR on OsAOX1a/b and that mitochondrial O_2·^– is involved in the process.     

In vitro evaluation of the antioxidant activity of calcium fructoborate

Although increasing evidence shows the nutritional benefits of calcium fructoborate (CF) on animals and humans, its action mechanism has not been clearly identified. The present study aims to investigate the possible antioxidant function of CF. Based on its efficiency in skin wound healing, the authors tested whether CF possesses antioxidant properties on human keratinocytes cultures, in a complete serum-free medium (KMK-2; Sigma). The cells treated with CF (0–450 nmol/culture medium) were exposed to exogenous 100 μmol of hydrogen peroxide to mimic the oxidative stress. The changes in general cell oxidant production evaluated with dihydrorhodamine-123 showed that the intracellular reactive oxygen species (ROS) were markedly reduced by preincubation with CF. The maximum antioxidant activity was notice at 90 nmol CF. To assess the reactivity of CF on ROS, we analyzed its ability to inhibit the superoxide-dependent auto-oxidation of pyrogallol. The CF inhibited the pyrogallol auto-oxidation depending on time and concentration, which suggests its possible role as a superoxide radical scavenger. Taken together, our results indicate that CF has antioxidant activity, which could have clinical significance in protecting cells from oxidant-induced injury. A hypothetic mechanism for the antioxidant activity of CF is proposed.     

Studies on hepatic oxidative stress and antioxidant defence system during chloroquine/poly ICLC treatment of Plasmodium yoelii nigeriensis infected mice

Reactive oxygen species are important mediators of tissue injury during malaria infection. The status of hepatic oxidative stress and antioxidant defence indices were studied during Plasmodium yoelii nigeriensis (P. y. nigeriensis) infection and chloroquine/polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly ICLC) treatment of infected mice. P. y. nigeriensis infection resulted in a significant increase in oxidative stress indices viz., xanthine oxidase and rate of lipid peroxidation (LPO). This was accompanied by a highly significant increase in antioxidant defence indices viz., reduced glutathione (GSH) and glutathione reductase while superoxide dismutase (SOD) and catalase showed a highly significant decrease with respect to normal mice. Chloroquine treatment of infected mice caused a decrease in parasitaemia which was associated with restoration of indices altered during infection towards normalization. Poly ICLC treatment of infected mice caused no change in blood parasitaemia but resulted in a significant increase in GSH, glutathione reductase, SOD and catalase with respect to infected mice. Combination therapy of chloroquine and poly ICLC resulted in clearance of parasitaemia and restoration of all oxidative stress and antioxidant defence indices to normal levels.     

Attenuation of hydrogen peroxide-mediated oxidative stress by Brassica juncea annexin-3 counteracts thiol-specific antioxidant (TSA1) deficiency in Saccharomyces cerevisiae

Brassica juncea annexin-3 (BjAnn3) was functionally characterized for its ability to modulate H₂O₂-mediated oxidative stress in Saccharomyces cerevisiae. BjAnn3 showed a significant protective role in cellular-defense against oxidative stress and partially alleviated inhibition of mitochondrial respiration in presence of exogenously applied H₂O₂. Heterologous expression of BjAnn3 protected membranes from oxidative stress-mediated damage and positively regulated antioxidant gene expression for ROS detoxification. We conclude that, BjAnn3 partially counteracts the effects of thioredoxin peroxidase 1 (TSA1) deficiency and aids in cellular-protection across kingdoms. Despite partial compensation of TSA1 by BjAnn3 in cell-viability tests, the over-complementation in ROS-related features suggests the existence of both redundant (e.g. ROS detoxification) and distinct features (e.g. membrane protection versus proximity-based redox regulator) of both proteins.     

Extracellular superoxide dismutase attenuates release of pulmonary hyaluronan from the extracellular matrix following bleomycin exposure

The major pulmonary antioxidant enzyme involved in the protection of the lung interstitium from oxidative stress is extracellular superoxide dismutase (EC-SOD). It has been previously shown that EC-SOD knock-out mice are more susceptible to bleomycin-induced lung injury, however, the molecular mechanism(s) remains unclear. We report here that bleomycin-induced lung damage, in EC-SOD KO mice, is associated with increased hyaluronan release into alveolar fluid. Analysis of hyaluronan synthase gene expression and hyaluronan molecular weight distribution suggested that elevated levels of hyaluronan in the alveolar fluid are mostly due to its release from the interstitium. Our results indicate that EC-SOD attenuates bleomycin-induced pulmonary injury, at least in part, by preventing superoxide-mediated release of hyaluronan into alveolar space.     

Hepatic insulin resistance in ob/ob mice involves increases in ceramide,aPKC activity,and selective impairment of Akt-dependent FoxO1 phosphorylation

Pathogenesis of insulin resistance in leptin-deficient ob/ob mice is obscure. In another form of diet-dependent obesity, high-fat-fed mice, hepatic insulin resistance involves ceramide-induced activation of atypical protein kinase C (aPKC), which selectively impairs protein kinase B (Akt)-dependent forkhead box O1 protein (FoxO1) phosphorylation on scaffolding protein, 40 kDa WD(tryp-x-x-asp)-repeat propeller/FYVE protein (WD40/ProF), thereby increasing gluconeogenesis. Resultant hyperinsulinemia activates hepatic Akt and mammalian target of rapamycin C1, and further activates aPKC; consequently, lipogenic enzyme expression increases, and insulin signaling in muscle is secondarily impaired. Here, in obese minimally-diabetic ob/ob mice, hepatic ceramide and aPKC activity and its association with WD40/ProF were increased. Hepatic Akt activity was also increased, but Akt associated with WD40/ProF was diminished and accounted for reduced FoxO1 phosphorylation and increased gluconeogenic enzyme expression. Most importantly, liver-selective inhibition of aPKC decreased aPKC and increased Akt association with WD40/ProF, thereby restoring FoxO1 phosphorylation and reducing gluconeogenic enzyme expression. Additionally, lipogenic enzyme expression diminished, and insulin signaling in muscle, glucose tolerance, obesity, hepatosteatosis, and hyperlipidemia improved. In conclusion, hepatic ceramide accumulates in response to CNS-dependent dietary excess irrespective of fat content; hepatic insulin resistance is prominent in ob/ob mice and involves aPKC-dependent displacement of Akt fromWD40/ProF and subsequent impairment of FoxO1 phosphorylation and increased expression of hepatic gluconeogenic and lipogenic enzymes; and hepatic alterations diminish insulin signaling in muscle.     

Phosphorylation of the Arabidopsis AtrbohF NADPH oxidase by OST1 protein kinase

The plant hormone abscisic acid (ABA) triggers production of reactive oxygen species (ROS) in guard cells via the AtrbohD and AtrbohF NADPH oxidases, leading to stomatal closure. The ABA-activated SnRK2 protein kinase open stomata 1 (OST1) (SRK2E/SnRK2.6) acts upstream of ROS in guard cell ABA signaling. Here, we report that OST1 phosphorylates Ser13 and Ser174 on AtrbohF. In addition, substitution of Ser174 to Ala results in a ∼40% reduction in the phosphorylation of AtrbohF by OST1. We also show that OST1 physically interacts with AtrbohF. These results provide biochemical evidence suggesting that OST1 regulates AtrbohF activity.

Structured summary

MINT-7260179, MINT-7260147, MINT-7260165: OST1 (uniprotkb:Q940H6) phosphorylates (MI:0217) ATRBOHF (uniprotkb:O48538) by protein kinase assay (MI:0424)MINT-7260208: OST1 (uniprotkb:Q940H6) and ATRBOHF (uniprotkb:O48538) physically interact (MI:0915) by bimolecular fluorescence complementation (MI:0809)