Role of mitogen-activated protein kinases in 4-hydroxy-2-nonenal-induced actin remodeling and barrier function in endothelial cells

In vivo and in vitro studies indicate that 4-hydroxy-2-nonenal (4-HNE), generated by cellular lipid peroxidation or after oxidative stress, affects endothelial permeability and vascular tone. However, the mechanism(s) of 4-HNE-induced endothelial barrier function is not well defined. Here we provide evidence for the first time on the involvement of mitogen-activated protein kinases (MAPKs) in 4-HNE-mediated actin stress fiber formation and barrier function in lung endothelial cells. Treatment of bovine lung microvascular endothelial cells with hydrogen peroxide (H(2)O(2)), as a model oxidant, resulted in accumulation of 4-HNE as evidenced by the formation of 4-HNE-Michael protein adducts. Exposure of cells to 4-HNE, in a dose- and time-dependent manner, decreased endothelial cell permeability measured as transendothelial electrical resistance. The 4-HNE-induced permeability changes were not because of cytotoxicity or endothelial cell apoptosis, which occurred after prolonged treatment and at higher concentrations of 4-HNE. 4-HNE-induced changes in transendothelial electrical resistance were calcium independent, as 4-HNE did not alter intracellular free calcium levels as compared with H(2)O(2) or diperoxovanadate. Stimulation of quiescent cells with 4-HNE (1-100 microm) resulted in phosphorylation of ERK1/2, JNK, and p38 MAPKs, and actin cytoskeleton remodeling. Furthermore, pretreatment of bovine lung microvascular endothelial cells with PD 98059 (25 microm), an inhibitor of MEK1/2, or SP 600125 (25 microm), an inhibitor of JNK, or SB 202190 (25 microm), an inhibitor of p38 MAPK, partially attenuated 4-HNE-mediated barrier function and cytoskeletal remodeling. These results suggest that the activation of ERK, JNK, and p38 MAP kinases is involved in 4-HNE-mediated actin remodeling and endothelial barrier function.     

Luteolin, a flavonoid, inhibits AP-1 activation by basophils

Flavonoids including luteolin, apigenin, and fisetin are inhibitors of IL-4 synthesis and CD40 ligand expression by basophils. This study was done to search for compounds with greater inhibitory activity of IL-4 expression and to clarify the molecular mechanisms through which flavonoids inhibit their expression. Of the 37 flavonoids and related compounds examined, ayanin, luteolin, and apigenin were the strongest inhibitors of IL-4 production by purified basophils in response to anti-IgE antibody plus IL-3. Luteolin did not suppress Syk or Lyn phosphorylation in basophils, nor did suppress p54/46 SAPK/JNK, p38 MAPK, and p44/42 MAPK activation by a basophilic cell line, KU812 cells, stimulated with A23187 and PMA. However, luteolin did inhibit phosphorylation of c-Jun and DNA binding activity of AP-1 in nuclear lysates from stimulated KU812 cells. These results provide a fundamental structure of flavonoids for IL-4 inhibition and demonstrate a novel action of flavonoids that suppresses the activation of AP-1.     

Schisandrin B elicits a glutathione antioxidant response and protects against apoptosis via the redox-sensitive ERK/Nrf2 pathway in H9c2 cells

This study investigated the signal transduction pathway involved in the cytoprotective action of (-)schisandrin B [(-)Sch B, a stereoisomer of Sch B]. Using H9c2 cells, the authors examined the effects of (-)Sch B on MAPK and Nrf2 activation, as well as the subsequent eliciting of glutathione response and protection against apoptosis. Pharmacological tools, such as cytochrome P-450 (CYP) inhibitor, antioxidant, MAPK inhibitor, and Nrf2 RNAi, were used to delineate the signaling pathway. (-)Sch B caused a time-dependent activation of MAPK in H9c2 cells, with the degree of ERK activation being much larger than that of p38 or JNK. The MAPK activation was followed by an increase in the level of nuclear Nrf2, an indirect measure of Nrf2 activation, and the eliciting of a glutathione antioxidant response. The activation of MAPK and Nrf2 seemed to involve oxidants generated from a CYP-catalyzed reaction with (-)Sch B. Both ERK inhibition by U0126 and Nrf2 suppression by Nrf2 RNAi transfection largely abolished the cytoprotection against hypoxia/reoxygenation-induced apoptosis in (-)Sch B-pretreated cells. (-)Sch B pretreatment potentiated the reoxygenation-induced ERK activation, whereas both p38 and JNK activations were suppressed. Under the condition of ERK inhibition, Sch B treatment did not protect against ischemia/reperfusion injury in an ex vivo rat heart model. The results indicate that (-)Sch B triggers a redox-sensitive ERK/Nrf2 signaling, which then elicits a cellular glutathione antioxidant response and protects against hypoxia/reoxygenation-induced apoptosis in H9c2 cells. The ERK-mediated signaling is also likely involved in the cardioprotection afforded by Sch B in vivo.     

CREB1 regulates glucose transport of glioma cell line U87 by targeting GLUT1

Chemical modification of chitosan is a promising method for the improvement of biological activity. In this study, chitosan-caffeic acid (CCA) was prepared and its in vitro hepatoprotective ability against hydrogen peroxide-induced hepatic damage in liver cells was evaluated. Treatment with CCA (50–400 µg/mL) did not show cytotoxicity and also significantly (p < 0.05) recovered cell viability against 650 µM hydrogen peroxide-induced hepatotoxicity. CCA treatment attenuated reactive oxygen species generation and lipid peroxidation in addition to increasing cellular glutathione level in cultured hepatocytes. To validate the underlying mechanism, antioxidant and phase II detoxifying enzyme expressions, which are mediated by NF-E2-related factor 2 (Nrf2) activation, were analyzed and CCA treatment was found to increase the expression of superoxide dismutase-1 (SOD-1), glutathione reductase (GR), heme oxygenase-1 (HO-1), and NAD(P)H:quinine oxidoreductase 1 (NQO1). CCA treatment resulted in increased Nrf2 nuclear translocation. The phosphorylation of extracellular regulated kinase (ERK), c-Jun NH₂-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) by CCA treatment contributed to Nrf2 activation. Pharmacological blockade of ERK, JNK, and p38 MAPK revealed that SP600125 (JNK inhibitor) and PD98059 (ERK inhibitor) treatment reduced Nrf2 translocation into the nucleus while SB203580 (p38 inhibitor) exhibited weak inhibition. Collectively, CCA protects liver cells against hydrogen peroxide-induced injury and this ability is attributed to the induction of antioxidants and phase II detoxifying enzymes that are mediated by Nrf2 translocation via JNK/ERK signaling.     

Suppression of ERK signaling evokes autocrine Fas‐mediated death in arachidonic acid‐treated human chronic myeloid leukemia K562 cells

Arachidonic acid (AA)‐induced apoptotic death of K562 cells (human chronic myeloid leukemic cells) was characteristic of reactive oxygen species (ROS) generation and mitochondrial depolarization. N‐Acetylcysteine pretreatment rescued viability of AA‐treated cells and abolished mitochondrial depolarization. In contrast to no significant changes in phospho‐JNK and phospho‐ERK levels, AA evoked notable activation of p38 MAPK. Unlike that of JNK and p38 MAPK, ERK suppression further reduced the viability of AA‐treated cells. Increases in Fas/FasL protein expression, caspase‐8 activation, the production of tBid and the loss of mitochondrial membrane potential were noted with K562 cells that were treated with a combination of U0126 and AA. Down‐regulation of FADD attenuated U0126‐evoked degradation of procaspase‐8 and Bid. Abolition of p38 MAPK activation abrogated U0126‐elicited Fas/FasL up‐regulation in AA‐treated cells. U0126 pretreatment suppressed c‐Fos phosphorylation but increased p38 MAPK‐mediated c‐Jun phosphorylation. Knock‐down of c‐Fos and c‐Jun protein expression by siRNA suggested that c‐Fos counteracted the effect of c‐Jun on Fas/FasL up‐regulation. Taken together, our data indicate that AA induces the ROS/mitochondria‐dependent death pathway and blocks the ERK pathway which enhances the cytotoxicity of AA through additionally evoking an autocrine Fas‐mediated apoptotic mechanism in K562 cells. J. Cell. Physiol. 222: 625–634, 2010. © 2009 Wiley‐Liss, Inc.     

Olaquindox-induced apoptosis is suppressed through p38 MAPK and ROS-mediated JNK pathways in HepG2 cells

We investigated mitogen-activated protein kinase (MAPK) pathways as well as reactive oxygen species (ROS) in olaquindox-induced apoptosis. Exposure of HepG2 cells to olaquindox resulted in the phosphorylation of p38 MAPK and c-Jun N-terminal kinases (JNK). To confirm the role of p38 MAPK and JNK, HepG2 cells were pretreated with MAPKs-specific inhibitors prior to olaquindox treatment. Olaquindox-induced apoptosis was significantly potentiated by the JNK inhibitor (SP600125) or the p38 MAPK inhibitor (SB203580). Furthermore, we observed that olaquindox treatment led to ROS generation and that olaquindox-induced apoptosis and ROS generation were both significantly reduced by the antioxidants, superoxide dismutase and catalase. In addition, the levels of phosphorylation of JNK, but not p38 MAPK, were significantly suppressed after pretreatment of the antioxidants, while inhibition of the activations of JNK or p38 MAPK had no effect on ROS generation. This result suggested that ROS may be the upstream mediator for the activation of JNK. Conclusively, our results suggested that apoptosis in response to olaquindox treatment in HepG2 cells might be suppressed through p38 MAPK and ROS–JNK pathways.     

CYP2E1-mediated oxidative stress regulates HO-1 and GST expression in maneb- and paraquat-treated rat polymorphonuclear leukocytes

Cytochrome P4502E1 (CYP2E1), glutathione-S-transferase A4-4 (GSTA4-4), and inducible nitric oxide synthase (iNOS) are implicated in maneb- and paraquat-induced toxicity leading to various pathological conditions. The study aimed to investigate the role of CYP2E1 in maneb- and paraquat-induced oxidative stress in rat polymorphonuclear leukocytes (PMNs) and its crosstalk with iNOS-mediated nitrosative stress and GSTA4-4-linked protective effect, if any and their consequent links with the nuclear factor erythoid 2-related factor 2 (Nrf2) activation and heme oxygenase-1 (HO-1) expression. Rats were treated with/without maneb and/or paraquat for 1, 2, and 3 weeks along with vehicle controls. Subsets of rats were also treated with diallyl sulfide (DAS) or aminoguanidine (AG) along with the respective controls. Maneb and paraquat augmented the reactive oxygen species (ROS), lipid peroxidation (LPO) and 4-hydroxy nonenal (4-HNE) contents, and superoxide dismutase (SOD) activity in the PMNs. However, maneb and paraquat attenuated the reduced glutathione (GSH) level and the expression/activity of total GST and GST-pi. Maneb and paraquat increased the expression/activity of CYP2E1, GSTA4-4, iNOS, Nrf2 and HO-1, and nitrite content. CYP2E1 inhibitor, DAS noticeably alleviated maneb- and paraquat-induced ROS, LPO, 4-HNE, SOD, Nrf2 and HO-1, GST, GSH, and GST-pi while iNOS, nitrite content and GSTA4-4 levels were unchanged. Conversely, AG, an iNOS inhibitor, attenuated maneb- and paraquat-directed changes in nitrite, LPO, iNOS but it did not alter ROS, GSH, SOD, GST, GST-pi, Nrf2, HO-1, CYP2E1, and GSTA4-4. The results demonstrate that CYP2E1 induces iNOS-independent free radical generation and subsequently modulates the Nrf2-dependent HO-1 and 4-HNE-mediated GST expression in maneb- and paraquat-treated PMNs.     

The hierarchical relationship between MAPK signaling and ROS generation in human leukemia cells undergoing apoptosis in response to the proteasome inhibitor Bortezomib

The hierarchy of events accompanying induction of apoptosis by the proteasome inhibitor Bortezomib was investigated in Jurkat lymphoblastic and U937 myelomonocytic leukemia cells. Treatment of Jurkat or U937 cells with Bortezomib resulted in activation of c-Jun-N-terminal kinase (JNK) and p38 MAPK (mitogen-activated protein kinase), inactivation of extracellular signal-regulating kinase 1/2 (ERK1/2), cytochrome c release, caspase-9, -3, and -8 activation, and apoptosis. Bortezomib-mediated cytochrome c release and caspase activation were blocked by the pharmacologic JNK inhibitor SP600125, but lethality was not diminished by the p38 MAPK inhibitor SB203580. Inducible expression of a constitutively active MEK1 construct blocked Bortezomib-mediated ERK1/2 inactivation, significantly attenuated Bortezomib lethality, and unexpectedly prevented JNK activation. Conversely, pharmacologic MEK/ERK1/2 inhibition promoted Bortezomib-mediated JNK activation and apoptosis. Lastly, the antioxidant N-acetyl-l-cysteine (LNAC) attenuated Bortezomib-mediated reactive oxygen species (ROS) generation, ERK inactivation, JNK activation, mitochondrial dysfunction, and apoptosis. In contrast, enforced MEK1 and ERK1/2 activation or JNK inhibition did not modify Bortezomib-induced ROS production. Together, these findings suggest that in human leukemia cells, Bortezomib-induced oxidative injury operates at a proximal point in the cell death cascade to antagonize cytoprotective ERK1/2 signaling, promote activation of the stress-related JNK pathway, and to trigger mitochondrial dysfunction, caspase activation, and apoptosis. They also suggest the presence of a feedback loop wherein Bortezomib-mediated ERK1/2 inactivation contributes to JNK activation, thereby amplifying the cell death process.     

Calcium‐stimulated mitogen‐activated protein kinase activation elicits Bcl‐xL downregulation and Bak upregulation in notexin‐treated human neuroblastoma SK‐N‐SH cells

Notechis scutatus scutatus notexin induced apoptotic death of SK‐N‐SH cells accompanied with downregulation of Bcl‐xL, upregulation of Bak, mitochondrial depolarization, and ROS generation. Upon exposure to notexin, Ca²⁺‐mediated JNK and p38 MAPK activation were observed in SK‐N‐SH cells. Production of ROS was a downstream event followed by Ca²⁺‐mediated mitochondrial alteration. Notexin‐induced cell death, mitochondrial depolarization, and ROS generation were suppressed by SB202190 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor). Moreover, phospho‐p38 MAPK and phospho‐JNK were proved to be involved in Bcl‐xL degradation, and overexpression of Bcl‐xL attenuated the cytotoxic effect of notexin. Bak upregulation was elicited by p38 MAPK‐mediated ATF‐2 activation and JNK‐mediated c‐Jun activation. Suppression of Bak upregulation by ATF‐2 siRNA or c‐Jun siRNA attenuated notexin‐evoked mitochondrial depolarization and rescued viability of notexin‐treated cells. Taken together, our data indicate that notexin‐induced apoptotic death of SK‐N‐SH cells is mediated through mitochondrial alteration triggering by Ca²⁺‐evoked p38 MAPK/ATF‐2 and JNK/c‐Jun signaling pathways. J. Cell. Physiol. 222:177–186, 2010. © 2009 Wiley‐Liss, Inc.     

Advanced Glycation End Products Induce Human Corneal Epithelial Cells Apoptosis through Generation of Reactive Oxygen Species and Activation of JNK and p38 MAPK Pathways

Advanced Glycation End Products (AGEs) has been implicated in the progression of diabetic keratopathy. However, details regarding their function are not well understood. In the present study, we investigated the effects of intracellular reactive oxygen species (ROS) and JNK, p38 MAPK on AGE-modified bovine serum albumin (BSA) induced Human telomerase-immortalized corneal epithelial cells (HUCLs) apoptosis. We found that AGE-BSA induced HUCLs apoptosis and increased Bax protein expression, decreased Bcl-2 protein expression. AGE-BSA also induced the expression of receptor for advanced glycation end product (RAGE). AGE-BSA-RAGE interaction induced intracellular ROS generation through activated NADPH oxidase and increased the phosphorylation of p47phox. AGE-BSA induced HUCLs apoptosis was inhibited by pretreatment with NADPH oxidase inhibitors, ROS quencher N-acetylcysteine (NAC) or neutralizing anti-RAGE antibodies. We also found that AGE-BSA induced JNK and p38 MAPK phosphorylation. JNK and p38 MAPK inhibitor effectively blocked AGE-BSA-induced HUCLs apoptosis. In addition, NAC completely blocked phosphorylation of JNK and p38 MAPK induced by AGE-BSA. Our results indicate that AGE-BSA induced HUCLs apoptosis through generation of intracellular ROS and activation of JNK and p38 MAPK pathways.     

Long-term blue light exposure induces RGC-5 cell death in vitro: involvement of mitochondria-dependent apoptosis,oxidative stress,and MAPK signaling pathways

The mechanism of blue light-induced retinal ganglion cell (RGC) injury is poorly understood. In this study, we established a patented light-emitting diode-based system to study the effects of long-term blue light exposure under culture conditions on RGC-5 cells. Long-term blue light exposure significantly reduced cell viability in a time-dependent manner and induced apoptosis and necrosis in RGC-5 cells. Long-term blue light exposure marked an increase in the expression of Bax and active Caspase-3 (p17), which was accompanied by Bcl-2 down-regulation, and displayed features of the mitochondria-dependent apoptosis pathway. Blue light exposure also increased the generation of reactive oxygen species (ROS), and was a strong inducer of ROS-sensitive protein nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expression. Moreover, blue light exposure constitutively activated p38 mitogen-activated protein kinases and c-Jun NH2-terminal kinase (JNK), as well as induced the phosphorylation of extracellular signal-regulated kinase in the early phase, in blue light-exposed RGC-5 cells. The protein expression of c-jun and c-fos was further enhanced after RGC-5 cells were exposed to blue light. Taken together, these findings indicated that blue light induced RGC-5 cell line death in dependence upon exposure duration. The potential mechanisms for this phenomenon might be via activated mitochondria-dependent apoptosis, increased ROS production and protein expressions of Nrf2 and HO-1, and activated JNK/p38 MAPK signaling pathways.     

Upregulation of thioredoxin system via Nrf2-antioxidant responsive element pathway in adaptive-retinal neuroprotection in vivo and in vitro

We tested the hypothesis that stress responses mediated by the Nrf2-antioxidant responsive element (ARE) pathway are involved in the initiation of retinal neuroprotection provided by bright-cyclic-light rearing. Albino rats born and raised in dim (5 lux) or bright (400 lux) cyclic light were exposed to damaging light (3000 lux, 6 h). After exposure, the outer nuclear layer thickness and area and the electroretinogram a- and b-wave amplitudes were significantly reduced in the dim-light-reared rats compared to the bright-light-reared rats, demonstrating a light adaptation neuroprotection phenomenon. In bright-cyclic-light-reared rats, the retinal levels of thioredoxin (Trx) (2.4-fold), Trx reductase (TrxR) (2.9-fold), and proteins modified by 4-hydroxynonenal (4-HNE) (1.5-fold) were upregulated by Western blot analyses, and the nuclear translocation of Nrf2 (2.2-fold) and the DNA binding activity of Nrf2, small Maf, and cJun to the ARE were increased as determined by electrophoretic mobility shift assays. In mouse photoreceptor-derived 661W cells, pretreatment with a sublethal dose of 4-HNE protected against H₂O₂-induced cell damage. Treatment with 4-HNE upregulated cellular Trx, TrxR, and heme oxygenase-1 (HO-1) levels in addition to DNA binding activity of Nrf2, small Maf, and cJun to the ARE. Downregulation of Nrf2 using RNA interference technology diminished 4-HNE-mediated upregulation of Trx and Trx reductase but did not affect the upregulation of HO-1 by 4-HNE. Cytoprotection by 4-HNE pretreatment against H₂O₂-induced cell damage was not observed in 661W cells with a silenced Nrf2 gene. The results suggest that upregulation of the Trx system by 4-HNE via the Nrf2–ARE pathway may be involved in the molecular mechanism of the retinal neuroprotection phenomenon.     

Estradiol-17beta protects against hypoxia-induced hepatocyte injury through ER-mediated upregulation of Bcl-2 as well as ER-independent antioxidant effects

Although many previous studies have suggested that estrogen functions as a cytoprotective agent under oxidative stress conditions, the underlying mechanism by which this effect is exerted remains to be elucidated. This study assessed the effects of estradiol-17β （E2） （10^-8s M） on hypoxia-induced cell injury and its related signaling in primary cultured chicken hepatocytes. Hypoxic conditions were found to augment the level of DNA damage and to reduce cell viability and the level of [^3H]-thymidine incorporation, and these phenomena were prevented through treatment with E2. Hypoxia also increased caspase-3 expression, but showed no evidence of an influence on the expression of Bcl-2. However, E2 induced an increase in the level of Bcl-2 expression under hypoxic conditions and reduced the level of caspase-3 expression. The effects of E2 on Bcl-2 and caspase expression were blocked by ICI 182780 （E2 receptor （ER） antagonist, 10＂7 M）. In addition, hypoxia resulted in an increase in the intracellular reactive oxygen species （ROS） generated. These effects were blocked by E2, but not by E2-BSA and ICI 182780. Hypoxia also activated p38 mitogen-activated protein kinase （MAPK）, c-JUN N-terminal kinase/stress-activated protein kinase （JNK/SAPK） and nuclear factor-kB （NF-kB）. These effects were blocked by E2, but not by ICI 182780. The inhibition of p38 MAPK and JNK/SAPK blocked NF-kB activation. In conclusion, E2 was found to protect against hypoxia-induced cell injury in chicken hepatocytes through ER-mediated upregulation of Bcl-2 expression and through reducing the activity of ROS-dependent p38 MAPK, JNK/ SAPK and NF-kB.