Oxidative preconditioning and apoptosis in L-cells. Roles of protein kinase B and mitogen-activated protein kinases

Helicobacter pylori infection and Parkinson's Disease: etiology, pathogenesis and levodopa bioavailability

Parkinson's disease (PD), a neurodegenerative disorder with an unknown etiology, is primarily characterized by the degeneration of dopamine (DA) neurons. The prevalence of PD has experienced a significant surge in recent years. The unidentified etiology poses limitations to the development of effective therapeutic interventions for this condition. Helicobacter pylori (H. pylori) infection has affected approximately half of the global population. Mounting evidences suggest that H. pylori infection plays an important role in PD through various mechanisms. The autotoxin produced by H. pylori induces pro-inflammatory cytokines release, thereby facilitating the occurrence of central inflammation that leads to neuronal damage. Simultaneously, H. pylori disrupts the equilibrium of gastrointestinal microbiota with an overgrowth of bacteria in the small intestinal known as small intestinal bacterial overgrowth (SIBO). This dysbiosis of the gut flora influences the central nervous system (CNS) through microbiome-gut-brain axis. Moreover, SIBO hampers levodopa absorption and affects its therapeutic efficacy in the treatment of PD. Also, H. pylori promotes the production of defensins to regulate the permeability of the blood-brain barrier, facilitating the entry of harmful factors into the CNS. In addition, H. pylori has been found to induce gastroparesis, resulting in a prolonged transit time for levodopa to reach the small intestine. H. pylori may exploit levodopa to facilitate its own growth and proliferation, or it can inflict damage to the gastrointestinal mucosa, leading to gastrointestinal ulcers and impeding levodopa absorption. Here, this review focused on the role of H. pylori infection in PD from etiology, pathogenesis to levodopa bioavailability.

Development of a p38α-selective radioactive probe for qualitative diagnosis of cancer using SPECT

OBJECTIVE

p38 mitogen-activated protein (MAP) kinase (p38α) has drawn attention as a new target molecule for the treatment and diagnosis of cancer, and its overexpression and activation have been reported in various types of cancer. In this study, a single photon emission computed tomography (SPECT) imaging probe of p38α was developed to noninvasively image p38α activity for effective qualitative diagnosis of cancer.

METHODS

Pyrrolepyridine derivatives, m-YTM and p-YTM, were designed and synthesized based on the structure of the p38α-selective inhibitor. Radioactive iodine-labeled m-YTM, [¹²⁵I]m-YTM, was synthesized because m-YTM greatly inhibited the phosphorylation of p38α upon examining the inhibitory effects of the compounds. After investigating the binding affinity of [¹²⁵I]m-YTM to the recombinant p38α, a saturation binding experiment using activated p38α and inactive p38α was performed to determine the binding site. Uptake of [¹²⁵I]m-YTM into various cancer cell lines was investigated, and the pharmacokinetics was evaluated using tumor-bearing mice.

RESULTS

The inhibitory activity of m-YTM was approximately 13 times higher than that of SB203580, a p38α-selective inhibitor. The binding site of [¹²⁵I]m-YTM was estimated to be the p38α activating site, similar to that of SB203580, because the [¹²⁵I]m-YTM bound strongly to both activated p38α and inactive p38α. Various different cancer cells incorporated [¹²⁵I]m-YTM; however, its accumulation was significantly reduced by treatment with SB203580. Pharmacokinetics study of [¹²⁵I]m-YTM in B-16 tumor-bearing mice was examined which revealed high accumulation of radioactivity in tumor tissues. The ratios of radioactivity in the B-16 tumor to that in blood were 3.1 and 50 after 1 and 24 h, respectively. The ratio of radioactivity in the tumor to that in blood in the tumor-bearing mice generated using other cancer cell lines was also ≥ 1 at 1 h after the administration of the probe.

CONCLUSIONS

This study suggests that [¹²³I]m-YTM has potential as a p38α imaging probe effective for various cancer types.

Sex-related differences in oxidative stress and neurodegeneration

Oxidative stress has been implicated in a number of neurodegenerative diseases spanning various fields of research. Reactive oxygen species can be beneficial or harmful, depending on their concentration. High levels of reactive oxygen species can lead to oxidative stress, which is an imbalance between free radicals and antioxidants. Increased oxidative stress can result in cell loss. Interestingly, sex differences have been observed in oxidative stress generation, which may underlie sex differences observed in neurodegenerative disorders. An enhanced knowledge of the role of sex hormones on oxidative stress signaling and cell loss can yield valuable information, leading to sex-based mechanistic approaches to neurodegeneration.

Inhibition of p38 Mitogen-Activated Protein Kinase Enhances the Apoptosis Induced by Oxidized Low-Density Lipoprotein in Endothelial Progenitor Cells

Oxidized low-density lipoprotein (oxLDL) is an important risk factor in the development of atherosclerosis. oxLDL has been shown to decrease endothelial progenitor cell (EPC) number by inducing apoptosis. p38 mitogen-activated protein kinase (MAPK) was shown to be activated by oxLDL and participated in the regulation of EPC number and function. However, the role of p38 remains unknown. Here, we show that oxLDL-induced p38 phosphorylation in EPCs is time and dose dependent. Treatment with antioxidant N-acetyl cysteine restored oxLDL-induced p38 phosphorylation to basal levels. LOX-1-blocking antibody also significantly decreased oxLDL-induced p38 phosphorylation. Interestingly, TUNEL staining showed that pretreatment with the p38 inhibitor SB203580 further increased oxLDL-induced apoptosis in EPCs. In accordance with these findings, pretreatment with SB203580 further attenuated Akt phosphorylation in EPCs challenged with oxLDL, indicating an interaction between Akt and p38 MAPK pathways. In agreement, inhibition of p38 MAPK further attenuated Akt phosphorylation and increased apoptosis in EPCs isolated from hypercholesterolemic ApoE-/- mice. In conclusion, p38 MAPK serves as an anti-apoptotic pathway by supporting Akt activity when EPCs are challenged with oxLDL.

BDNF-TrkB pathway mediates neuroprotection of hydrogen sulfide against formaldehyde-induced toxicity to PC12 cells

Formaldehyde (FA) is a common environmental contaminant that has toxic effects on the central nervous system (CNS). Our previous data demonstrated that hydrogen sulfide (H2S), the third endogenous gaseous mediator, has protective effects against FA-induced neurotoxicity. As is known to all, Brain-derived neurotropic factor (BDNF), a member of the neurotrophin gene family, mediates its neuroprotective properties via various intracellular signaling pathways triggered by activating the tyrosine kinase receptor B (TrkB). Intriguingly, our previous data have illustrated the upregulatory role of H2S on BDNF protein expression in the hippocampus of rats. Therefore, in this study, we hypothesized that H2S provides neuroprotection against FA toxicity by regulating BDNF-TrkB pathway. In the present study, we found that NaHS, a donor of H2S, upregulated the level of BDNF protein in PC12 cells, and significantly rescued FA-induced downregulation of BDNF levels. Furthermore, we found that pretreatment of PC12 cells with K252a, an inhibitor of the BDNF receptor TrkB, markedly reversed the inhibition of NaHS on FA-induced cytotoxicity and ablated the protective effects of NaHS on FA-induced oxidative stress, including the accumulation of intracellular reactive oxygen species (ROS), 4-hydroxy-2-trans-nonenal (4-HNE), and malondialdehyde (MDA). We also showed that K252a abolished the inhibition of NaHS on FA-induced apoptosis, as well as the activation of caspase-3 in PC12 cells. In addition, K252a reversed the protection of H2S against FA-induced downregulation of Bcl-2 protein expression and upregulation of Bax protein expression in PC12 cells. These data indicate that the BDNF-TrkB pathway mediates the neuroprotection of H2S against FA-induced cytotoxicity, oxidative stress and apoptosis in PC12 cells. These findings provide a novel mechanism underlying the protection of H2S against FA-induced neurotoxicity.

Over-expression of hypoxia-inducible factor-1 alpha in vitro protects the cardiac fibroblasts from hypoxia-induced apoptosis

OBJECTIVES

A great number of studies indicate that cardiac fibroblasts are essential for maintaining the structure and function of heart. Hypoxia-inducible factor-1 alpha (HIF-1α) is a central transcriptional regulator of hypoxic response. The present study examined whether over-expression of HIF-1α could prevent hypoxia-induced injury in neonatal rat cardiac fibroblasts and, if so, its possible molecular targets.

METHODS

Western blotting was used to detect protein level. MTT, electron microscopy, TUNEL staining and confocal microscopy were used to identify cell viability, cell apoptosis and intracellular calcium ([Ca]i) in cardiac fibroblasts, respectively.

RESULTS

When cardiac fibroblasts were exposed to hypoxia, HIF-1α protein in nuclei was transiently accumulated at 1 h, and then gradually degraded within 24 h of hypoxia exposure. Over-expression of HIF-1α enhanced nucleus expression of HIF-1α in cardiac fibroblasts, and significantly abolished the decrease of cell viability and cell apoptosis caused by 24-h hypoxia. Accordingly, hypoxia-induced Bax up-regulation, Bcl-2 down-regulation, caspase-3 activation and overload of [Ca]i in cardiac fibroblasts were reversed by HIF-1α over-expression, but were promoted by 30 μmol/l SC205346, a specific HIF-1α blocker.

CONCLUSIONS

Our results indicate that HIF-1α may act as a protective factor in the apoptotic process of cardiac fibroblasts and represent a potential therapeutic target for heart remodeling after hypoxia injury.

Oleanolic Acid enhances the beneficial effects of preconditioning on PC12 cells

Preconditioning triggers endogenous protection against subsequent exposure to higher concentrations of a neurotoxin. In this study, we investigated whether exposure to oleanolic acid (OA) enhances the protective effects of preconditioning on PC12 cells exposed to 6-hydroxydopamine (6-OHDA). A concentration response curve was constructed using 6-OHDA (50, 150, 300, and 600 μM). The experiment consisted of 6 groups: untreated, OA only, Group 1: cells treated with 6-OHDA (50 μM) for 1 hour, Group 2: cells treated with 6-OHDA (150 μM) for 1 hour, Group 3: cells treated with 6-OHDA (50 μM) for 30 minutes followed 6 hours later by treatment with 6-OHDA (150 μM) for 30 minutes, and Group 4: cells treated as in group 3 but also received OA immediately after the second 6-OHDA treatment. Cell viability and apoptotic ratio were assessed using the MTT and Annexin V staining tests, respectively. In preconditioned cells, we found that cell viability remained high following exposure to 6-OHDA (150 μM). OA treatment enhanced the protective effects of preconditioning. Similarly, with the annexin V apoptosis test, preconditioning protected the cell and this was enhanced by OA. Therefore, preexposure of PC12 cells to low 6-OHDA concentration can protect against subsequent toxic insults of 6-OHDA and OA enhances this protection.

Proteomic study on the protective mechanism of fibroblast growth factor 21 to ischemia-reperfusion injury

Fibroblast growth factor (FGF)-21 is a novel regulator of insulin-independent glucose transport in 3T3-L1 adipocytes and has glucose and triglyceride lowering effects in rodent models of diabetes. In this study, we found that FGF-21 can significantly attenuate ischemia-reperfusion (I/R) induced damage in H9c2 cells (rat heart). However, it is unclear which signal transduction pathway is involved in the cardioprotective effect of FGF-21. Thus, this study was designed to investigate the potential mechanism induced by FGF-21. The results showed that FGF-21 treatment prevented the oxidative stress and apoptosis associated with I/R damage by reducing the levels of superoxide anions, inhibiting glycogen synthase kinase (GSK) 3β by activating Akt phosphorylation, and recovering the levels of ATP synthase pyruvate kinase isozymes M1 and protein kinase C, thereby improving energy supply. In summary, we conclude that FGF-21 protects H9c2 cells against I/R injury mainly through the Akt-GSK-3β-caspase-3 dependent pathway, preventing oxidative stress, and recovery of the energy supply.

H2O2 preconditioning modulates phase II enzymes through p38 MAPK and PI3K/Akt activation

Ischemic preconditioning is a complex cardioprotective phenomenon that involves adaptive changes in cells and molecules and occurs in a biphasic pattern: an early phase after 1-2 h and a late phase after 12-24 h. While it is widely accepted that reactive oxygen species are strongly involved in triggering ischemic preconditiong, it is not clear if they play a major role in the early or late phase of preconditioning and which are the mechanisms involved. The present study was designed to investigate the mechanisms behind H(2)O(2)-induced cardioprotection in rat neonatal cardiomyocytes. We focused on antioxidant and phase II enzymes and their modulation by protein kinase signaling pathways and nuclear-factor-E(2)-related factor-1 (Nrf1) and Nrf2. H(2)O(2) preconditioning was able to counteract oxidative stress more effectively in the late than in the early phase of adaptation. In particular, H(2)O(2) preconditioning counteracted oxidative stress-induced apoptosis by decreasing caspase-3 activity, increasing Bcl2 expression and selectively increasing the expression and activity of antioxidant and phase II enzymes through Nrf1 and Nrf2 translocation to the nucleus. The downregulation of Nrf1 and Nrf2 by small interfering RNA reduced the expression level of phase II enzymes. Specific inhibitors of phosphatidylinositol 3-kinase/Akt and p38 MAPK activation partially reduced the cardioprotection elicited by H(2)O(2) preconditioning and the induction and activity of phase II enzymes. These findings demonstrate, for the first time, a key role for Nrf1, and not only for Nrf2, in the induction of phase II enzymes triggered by H(2)O(2) preconditioning.

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress.

MicroRNA: A matter of life or death

Progressive cell loss due to apoptosis is a pathological hallmark implicated in a wide spectrum of degenerative diseases such as heart disease, atherosclerotic arteries and hypertensive vessels, Alzheimer’s disease and other neurodegenerative disorders. Tremendous efforts have been made to improve our understanding of the molecular mechanisms and signaling pathways involved in apoptosistic cell death. Once ignored completely or overlooked as cellular detritus, microRNAs (miRNAs) that were discovered only a decade ago, have recently taken many by surprise. The importance of miRNAs has steadily gained appreciation and miRNA biology has exploded into a massive swell of interest with enormous range and potential in almost every biological discipline because of their widespread expression and diverse functions in both animals and humans. It has been established that miRNAs are critical regulators of apoptosis of various cell types. These small molecules act by repressing the expression of either the proapoptotic or antiapoptotic genes to produce antiapoptotic or proapoptotic effects. Appealing evidence has been accumulating for the involvement of miRNAs in human diseases associated with apoptotic cell death and the potential of miRNAs as novel therapeutic targets for the treatment of the diseases. This editorial aims to convey this message and to boost up the research interest by providing a timely, comprehensive overview on regulation of apoptosis by miRNAs and a synopsis on the pathophysiologic implications of this novel regulatory network based on the currently available data in the literature. It begins with a brief introduction to apoptosis and miRNAs, followed by the description of the fundamental aspects of miRNA biogenesis and action, and the role of miRNAs in regulating apoptosis of cancer cells and cardiovascular cells. Speculations on the development of miRNAs as potential therapeutic targets are also presented. Remarks are also provided to point out the unanswered questions and to outline the new directions for the future research of the field.

Low concentration of GA activates a preconditioning response in HepG2 cells during oxidative stress-roles of Hsp90 and vimentin

Oxidative stress can be a significant cause of cell death and apoptosis. We performed studies in HepG2 cells to explore whether prior exposure to oxidative stress ("oxidative preconditioning") and geldanamycin (GA) treatment can protect the cell from damage caused by subsequent oxidative insults. The cells were treated with 10 nM GA for 24 h before oxidative stress. Oxidative preconditioning was achieved by 2 h exposures to H(2)O(2) (50 microM) separated by a 10-h recovery period in normal culture medium. Oxidative stress was induced by exposure to 500 microM H(2)O(2) for 24 h. The effects of GA and oxidative preconditioning were investigated on the formation of Hsp90, vimentin, insoluble vimentin aggregates, and cleavage of vimentin in a cell culture model of oxidative stress. GA treatment leads to enhanced expression of Hsp90 and vimentin and to inhibition of vimentin protein aggregation. Similar results were obtained by oxidative preconditioning. It is confirmed that low concentrations of GA protected HepG2 cells from subsequent oxidative stress by increasing the levels of Hsp90 and by alleviating the extent of cell apoptosis induced by oxidative stress, which is similar to oxidative preconditioning. However, in contrast to preconditioning, GA treatment obviously changed binding activity of Hsp90 to vimentin cleavages. All the above indicated that low concentrations of GA treatment triggered cell protection from oxidative stress. Both the level of Hsp90 and its ability to bind with vimentin were changed by low concentrations of GA and might contribute to oxidative stress protection.

MicroRNAs and apoptosis: implications in the molecular therapy of human disease

1. MicroRNAs (miRNAs), the small non-coding RNAs of approximately 22 nucleotides, are now recognized as a very large family present throughout the genomes of plants and metazoans. These small transcripts modulate protein expression by binding to complementary or partially complementary target protein-coding mRNAs and targeting them for degradation or translational inhibition. 2. The discovery of miRNAs has revolutionized our understanding of the mechanisms that regulate gene expression, with the addition of an entirely novel level of regulatory control. Considerable information on miRNAs has been accumulated in this rapidly evolving research field. We now know that miRNAs play pivotal roles in diverse processes, such as development and differentiation, control of cell proliferation and death, stress response and metabolism. Indeed, aberrant miRNA expression has been documented in human disease as well as in animal models, with evidence for a causative role in tumourigenesis. 3. One of the most active fields of miRNA research is miRNA regulation of apoptosis, a programmed cell death implicated in many human diseases, such as cancer, Alzheimer's disease, hypertrophy and heart failure. Thus far, nearly 30 of 500 human miRNAs have been validated experimentally to regulate apoptosis; this number is likely to increase with future studies. 4. The present review provides a comprehensive summary and analysis of the currently available data, focusing on the transcriptional controls, target genes and signalling pathways linking the apoptosis-regulating miRNAs and apoptotic cell death.

Long-acting phosphodiesterase-5 inhibitor, tadalafil, induces sustained cardioprotection against lethal ischemic injury

The ability of pharmacological preconditioning mimetics to confer long-lasting and sustained cardioprotection may be a logical criterion to develop a drug that can be used clinically for cardioprotection. We propose here that the use of long-acting phosphodiesterase-5 inhibitor, tadalafil, may confer sustained cardioprotection against ischemia. Tadalafil (5 mg/kg) was administered orally to male C57B/6J mice (n = 6 in each treatment subgroup at each time point studied). Hearts were isolated and subjected to 40 min of ischemia and 30 min of reperfusion on Langendorff's apparatus at 1, 12, 24, 36, 48, 60, 72, and 108 h after tadalafil administration. In 1- to 48-h subgroups, tadalafil was given once at 0 h only. In 60- and 72-h subgroups, tadalafil was given twice at 0 and 36 h. Similarly, in the 108-h subgroup, tadalafil was administered at 0, 36, and 72 h. In the same subgroups, wortmannin (15 microg/kg ip), an inhibitor of phosphatidylinositol 3-kinase or 5-hydroxydecanoic acid (5 mg/kg ip), an inhibitor of mitochondrial ATP-sensitive K(+) channels, was given together with tadalafil, and the hearts were subjected to ischemia-reperfusion at 36 h to determine whether the effect of tadalafil on ischemia-reperfusion injury was abolished. As a result, tadalafil treatment reduced left ventricular end-diastolic pressure and increased left ventricular developed pressure as well as reduced lactate dehydrogenase release. This protection remained till 36-40 h, and thereafter it vanished. The readministration of tadalafil at 36 and 72 h restored the protection till 108 h. Tadalafil treatment accelerated Akt phosphorylation in cardiac tissue and decreased myocyte apoptosis. The administration of wortmannin abolished the beneficial effects of tadalafil on hemodynamic parameters and myocyte apoptosis, together with significantly reduced Akt phosphorylation. 5-Hydroxydecanoic acid also abolished the antiapoptotic effect of tadalafil. It is concluded that tadalafil treatment induces the long-term protection of ischemic myocardium via phosphatidylinositol 3-kinase/Akt signaling pathway.

Downregulation of miR-133 and miR-590 contributes to nicotine-induced atrial remodelling in canines

AIMS

The present study was designed to decipher molecular mechanisms underlying nicotine's promoting atrial fibrillation (AF) by inducing atrial structural remodelling.

METHODS AND RESULTS

The canine model of AF was successfully established by nicotine administration and rapid pacing. The atrial fibroblasts isolated from healthy dogs were treated with nicotine. The role of microRNAs (miRNAs) on the expression and regulation of transforming growth factor-beta1 (TGF-beta1), TGF-beta receptor type II (TGF-betaRII), and collagen production was evaluated in vivo and in vitro. Administration of nicotine for 30 days increased AF vulnerability by approximately eight- to 15-fold in dogs. Nicotine stimulated remarkable collagen production and atrial fibrosis both in vitro in cultured canine atrial fibroblasts and in vivo in atrial tissues. Nicotine produced significant upregulation of expression of TGF-beta1 and TGF-betaRII at the protein level, and a 60-70% decrease in the levels of miRNAs miR-133 and miR-590. This downregulation of miR-133 and miR-590 partly accounts for the upregulation of TGF-beta1 and TGF-betaRII, because our data established TGF-beta1 and TGF-betaRII as targets for miR-133 and miR-590 repression. Transfection of miR-133 or miR-590 into cultured atrial fibroblasts decreased TGF-beta1 and TGF-betaRII levels and collagen content. These effects were abolished by the antisense oligonucleotides against miR-133 or miR-590. The effects of nicotine were prevented by an alpha7 nicotinic acetylcholine receptor antagonist.

CONCLUSION

We conclude that the profibrotic response to nicotine in canine atrium is critically dependent upon downregulation of miR-133 and miR-590.

Acidic preconditioning protects endothelial cells against apoptosis through p38- and Akt-dependent Bcl-xL overexpression

To analyze the underlying cellular mechanisms of adaptation to ischemia-induced apoptosis through short acidic pretreatment, i.e. acidic preconditioning (APC), Wistar rat coronary endothelial cells (EC) were exposed for 40 min to acidosis (pH 6.4) followed by a 14 h recovery period (pH 7.4) and finally treated for 2 h with simulated in vitro ischemia (glucose-free anoxia at pH 6.4). APC led to a transient activation of p38 and Akt kinases, but not of JNK and ERK1/2 kinases, which was accompanied by significant reduction of the apoptotic cell number, caspase-12/-3 cleavage and Bcl-xL overexpression. These effects of APC were completely abolished by prevention of Akt- or p38-phosphorylation during APC. Furthermore, knock-down of Bcl-xL by siRNA-transfection also abolished the anti-apoptotic effect of APC. Therefore, APC leads to protection of EC against ischemic apoptosis by activation of Akt and p38 followed by overexpression of Bcl-xL, which is a key anti-apoptotic mechanism of APC.

Involvement of ERK1/2 and p38 MAPK in up-regulation of 14-3-3 protein induced by hydrogen peroxide preconditioning in PC12 cells

OBJECTIVE

To investigate the protective effects of hydrogen peroxide preconditioning (HPP) on the pheochromocytoma (PC12) cells treated with 1-methyl-4-phenylpyridinium (MPP(+)) and to explore the potential mechanisms.

METHODS

The viability and apoptosis of PC12 cells were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and 4',6'-diamidino-2-phenylindole (DAPI) staining, respectively. The expressions of 14-3-3 protein and phosphorylated p38 mitogen-activated protein kinase (MAPK) were determined by Western blot. Enzyme-linked immunosorbent assay (ELISA) was used to measure the activity of extracellular signal-regulated protein kinase 1/2 (ERK1/2).

RESULTS

The cell viability decreased and the number of apoptotic cells increased dramatically in MPP(+) group compared with that in Control group. HPP induced a significant increase in cell viability and a marked decrease in population of apoptotic cells of the MPP(+)-treated PC12 cells, accompanied with up-regulation of 14-3-3 protein and increase of ERK1/2 and p38 MAPK activities. The 14-3-3 protein expression was positively correlated with the phosphorylation of ERK1/2. Furthermore, inhibition of the ERK1/2 with PD98059 abolished the 14-3-3 protein up-regulation in PC12 cells induced by HPP.

CONCLUSION

HPP protects PC12 cells against MPP(+) toxicity by up-regulating 14-3-3 protein expression through the ERK1/2 and p38 MAPK signaling pathways.

The muscle-specific microRNAs miR-1 and miR-133 produce opposing effects on apoptosis by targeting HSP60, HSP70 and caspase-9 in cardiomyocytes

The microRNAs miR-1 and miR-133 are preferentially expressed in cardiac and skeletal muscles and have been shown to regulate differentiation and proliferation of these cells. We report here a novel aspect of cellular function of miR-1 and miR-133 regulation of cardiomyocyte apoptosis. miR-1 and miR-133 produced opposing effects on apoptosis, induced by oxidative stress in H9c2 rat ventricular cells, with miR-1 being pro-apoptotic and miR-133 being anti-apoptotic. miR-1 level was significantly increased in response to oxidative stress. We identified single target sites for miR-1 only, in the 3'-untranslated regions of the HSP60 and HSP70 genes, and multiple putative target sites for miR-133 throughout the sequence of the caspase-9 gene. miR-1 reduced the levels of HSP60 and HSP70 proteins without changing their transcript levels, whereas miR-133 did not affect HSP60 and HSP70 expression at all. By contrast, miR-133 repressed caspase-9 expression at both the protein and mRNA levels. The post-transcriptional repression of HSP60 and HSP70 and caspase-9 was further confirmed by luciferase reporter experiments. Our results indicate that miR-1 and miR-133 are involved in regulating cell fate with increased miR-1 and/or decreased miR-133 levels favoring apoptosis and decreased miR-1 and/or miR-133 levels favoring survival. Post-transcriptional repression of HSP60 and HSP70 by miR-1 and of caspase-9 by miR-133 contributes significantly to their opposing actions.

Role of the JAK-STAT pathway in protection of hydrogen peroxide preconditioning against apoptosis induced by oxidative stress in PC12 cells

The aim of this study was to investigate the role of JAK-STAT pathway in the cytoprotection afforded by preconditioning with H(2)O(2). It was shown that (1) Preconditioning with 100 micromol/L H(2)O(2) can markedly protect PC12 cells against apoptosis and cytotoxicity induced by 300 micromol/L H(2)O(2); (2) The expression and tyrosine phosphorylation of JAK2, not JAK1 were rapidly increased at 5 min after H(2)O(2) preconditioning; (3) The expression of STAT1 and STAT3 were significantly increased at 15 min after H(2)O(2) preconditioning, and the pTyr-STAT1 and pTyr-STAT3 were markedly increased at 60 min after H(2)O(2) preconditioning; (4) Pretreatment with the JAK inhibitor AG-490 (10 micromol/L) 20 min before H(2)O(2) preconditioning blocked not only the activation of JAK2, STAT1 and STAT3, but also the cytoprotection of H(2)O(2) preconditioning against apoptosis and cytotoxicity induced by oxidative stress. These findings suggested that preconditioning with H(2)O(2) activated the JAK-STAT pathway that played an important role in the cytoprotection induced by H(2)O(2) preconditioning.

Thermal sensitization through ROS modulation: a strategy to improve the efficacy of hyperthermic intraperitoneal chemotherapy

BACKGROUND

The purpose of this study was to investigate whether modulation of cellular reactive oxygen species (ROS) provides a synergistic effect with hyperthermia to induce tumor cell death in a colon cancer cell line.

MATERIALS AND METHODS

HT-29 colon cancer cells were exposed to heat (43 degrees C) in the presence of the ROS-generating drug, 2-2'-azobis-(2-amidinopropane) dihydrochloride (AAPH) for 1 h. Viable cell mass and apoptosis was measured by MTT and annexin V staining, respectively. Oxidative stress was evaluated by DCFH fluorescence. Protein levels were determined by Western blot analysis.

RESULTS

A synergistic effect on cell viability with AAPH was noted under hyperthermic conditions as compared with hyperthermia alone (P < .05). The number of nonviable cells after hyperthermia and AAPH exposure was also significantly increased compared with AAPH at 37 degrees C (42% vs 20%, P < .05). ROS levels were increased modestly with AAPH at 37 degrees C, whereas they increased significantly in a dose-dependent manner with AAPH at 43 degrees C. Transient increases of phosphorylated-p38 and ERK and decreases in phosphorylated-AKT were observed in the cells exposed to AAPH at 43 degrees C. Pretreatment of inhibitors of p38 yielded additional decreases in cell mass when used in combination with AAPH and hyperthermia (P < .05). Increased expression of HSP 27 observed at 43 degrees C was abrogated with AAPH exposure.

CONCLUSIONS

Oxidative stress increased the cytotoxic effects of hyperthermia in colon cancer cells. Thermal sensitization through modulation of cellular ROS may represent a novel approach to increase the efficacy of hyperthermia as an anticancer modality.

Androgen induces adaptation to oxidative stress in prostate cancer: implications for treatment with radiation therapy

Radiation therapy is a standard treatment for prostate cancer (PC). The postulated mechanism of action for radiation therapy is the generation of reactive oxygen species (ROS). Adjuvant androgen deprivation (AD) therapy has been shown to confer a survival advantage over radiation alone in high-risk localized PC. However, the mechanism of this interaction is unclear. We hypothesize that androgens modify the radioresponsiveness of PC through the regulation of cellular oxidative homeostasis. Using androgen receptor (AR)(+) 22rv1 and AR(-) PC3 human PC cell lines, we demonstrated that testosterone increased basal reactive oxygen species (bROS) levels, resulting in dose-dependent activation of phospho-p38 and pAKT, and increased expression of clusterin, catalase, and manganese superoxide dismutase. Similar data were obtained in three human PC xenografts; WISH-PC14, WISH-PC23, and CWR22, growing in testosterone-supplemented or castrated SCID mice. These effects were reversible through AD or through incubation with a reducing agent. Moreover, testosterone increased the activity of catalase, superoxide dismutases, and glutathione reductase. Consequently, AD significantly facilitated the response of AR(+) cells to oxidative stress challenge. Thus, testosterone induces a preset cellular adaptation to radiation through the generation of elevated bROS, which is modified by AD. These findings provide a rational for combined hormonal and radiation therapy for localized PC.

Carvedilol inhibits mitochondrial complex I and induces resistance to H2O2 -mediated oxidative insult in H9C2 myocardial cells

Carvedilol, a beta-adrenoreceptor antagonist with strong antioxidant activity, produces a high degree of cardioprotection in a variety of experimental models of ischemic cardiac injury. Although growing evidences suggest specific effects on mitochondrial metabolism, how carvedilol would exert its overall activity has not been completely disclosed. In the present work we have investigated the impact of carvedilol-treatment on mitochondrial bioenergetic functions and ROS metabolism in H9C2 cells. This analysis has revealed a dose-dependent decrease in respiratory fluxes by NAD-dependent substrates associated with a consistent decline of mitochondrial complex I activity. These changes were associated with an increase in mitochondrial H(2)O(2) production, total glutathione and protein thiols content. To evaluate the antioxidant activity of carvedilol, the effect of the exposure of control and carvedilol-pretreated H9C2 cells to H(2)O(2) were investigated. The H(2)O(2)-mediated oxidative insult resulted in a significant decrease of mitochondrial respiration, glutathione and protein thiol content and in an increased level of GSSG. These changes were prevented by carvedilol-pretreatment. A similar protective effect on mitochondrial respiration could be obtained by pre-treatment of the cells with a sub-saturating amount of rotenone, a complex I inhibitor. We therefore suggest that carvedilol exerts its protective antioxidant action both by a direct antioxidant effect and by a preconditioning-like mechanism, via inhibition of mitochondrial complex I.

Inhibition of myocardial apoptosis by ischaemic and beta-adrenergic preconditioning is dependent on p38 MAPK

INTRODUCTION

Apoptosis occurring during ischaemia /reperfusion contributes independently to tissue damage, and involves activation of the stress-kinase, p38 MAPK during reperfusion. Ischaemic preconditioning (IPC) protects against ischaemia/reperfusion mediated necrosis and apoptosis. The role of p38 MAPK in the protective effect of preconditioning against apoptosis is unknown. Pharmacologic preconditioning with isoproterenol (beta-PC) also protects against necrosis, but it is not known whether it protects against apoptosis.

AIM

The aim of the study was to investigate whether the protective effect of IPC against apoptosis is related to activation of p38 MAPK and whether beta-PC also protects against apoptosis.

MATERIALS AND METHODS

Isolated perfused rat hearts were used to study the effect of ischaemia and reperfusion on apoptosis and infarct size. Ischaemic preconditioning was elicited by 3 x 5 min global ischaemia, and beta-PC by 5 min isoproterenol 10(-7) M. For infarct size hearts were subjected to regional ischaemia for 35 min followed by 120 min reperfusion. Infarct size was determined by the tetrazolium staining technique, and expressed as percentage of area at risk. For markers of apoptosis hearts were subjected to global ischaemia of 25 min plus 30 min reperfusion. Apoptosis was determined by Western blot using antibodies against caspase-3 and PARP. p38 MAPK activation was inhibited by SB203580 (1 microM) administration 10 min prior to commencing ischaemia, and bracketing the IPC and beta-PC preconditioning protocols. p38 MAPK was activated by administration of anisomycin (5 microM) 10 min prior to index ischaemia in one protocol, and 10 min during reperfusion in non-preconditioned as well as IPC and beta-PC hearts. Results were analysed using ANOVA and a Newman-Keuls post-hoc test.

RESULTS

In the apoptosis model using global ischaemia, IPC and beta-PC both resulted in a significant decrease in p38 MAPK activation at the end of reperfusion when compared to non-preconditioned hearts. This was accompanied by a significant decrease in apoptosis as measured with both caspase-3 activation and PARP cleavage. Inhibiting p38 MAPK by administration of SB203580 10 min prior to ischaemia resulted in a significant reduction in both markers of apoptosis. Bracketing the triggering phase of either IPC or beta-PC with SB203580 resulted in attenuated p38 MAPK activation during reperfusion and did not abolish the protective effect of IPC or beta-PC against apoptosis. Activating p38 MAPK with anisomycin prior to ischaemia resulted in a reduction of markers of apoptosis, whereas activation of p38 MAPK with anisomycin during reperfusion did not exacerbate apoptosis in any groups, exept for an increase in PARP cleavage in IPC hearts. In the model of regional ischaemia, IPC and beta-PC reduced infarct size significantly, and to the same extent as inhibition of p38 MAPK by administration of SB203580 10 min prior to ischaemia. Bracketing the triggering phase of either IPC or beta-PC did not abolish the reduction in infarct size. Activating p38 MAPK during reperfusion was accompanied by an increase in infarct size only in IPC hearts, but not in beta-PC hearts.

CONCLUSION

These results indicate that (1) Both IPC and beta-PC elicit protection against apoptosis and necrosis, (2) activation of p38 MAPK is not a trigger of preconditioning against apoptosis and necrosis and (3) activation of p38 MAPK during reperfusion increases necrosis only if ischaemia is used to precondition hearts, but not with pharmacologic preconditioning with isoproterenol.

Peroxynitrite is a major trigger of cardiomyocyte apoptosis in vitro and in vivo

Recent evidence indicates that peroxynitrite represents a major cytotoxic effector in heart diseases, but its mechanisms of action are still not known exactly. Notably, the ability of peroxynitrite to trigger cardiomyocyte apoptosis, a crucial mode of cell death in many cardiac conditions, remains poorly defined. We evaluated apoptotic and necrotic cell death in cultured H9C2 cardiomyocytes, following a brief (20 min) exposure to peroxynitrite (50-500 microM). Peroxynitrite-dependent myocardial toxicity was then investigated in a rat model of myocardial ischemia-reperfusion (MIR), where the effects of peroxynitrite were blocked by the superoxide dismutase mimetics and peroxynitrite scavenger Mn(III)-tetrakis(4-benzoic acid) porphyrin (MnTBAP). In vitro, peroxynitrite killed cardiomyocytes mostly through apoptosis (DNA fragmentation, apoptotic nuclear alterations, caspase-3 activation, and PARP cleavage), but not necrosis (propidium iodide staining and LDH release). In vivo, MIR triggered myocardial oxidative stress (malondialdehyde generation), nitrotyrosine formation, neutrophil accumulation, and the cleavage of caspase-3 and PARP, indicating ongoing myocardial apoptosis. MnTBAP suppressed these alterations, allowing a considerable reduction of myocardial injury. Thus, peroxynitrite triggers apoptosis in cardiomyocytes in vitro and in the myocardium in vivo, through a pathway involving caspase-3 activation and the cleavage of PARP. These results provide important novel information on the mechanisms of myocardial toxicity of peroxynitrite.

Effect of sublethal 6-hydroxydopamine on the response to subsequent oxidative stress in dopaminergic cells: evidence for preconditioning

Exposure to sublethal stress can trigger endogenous protection against subsequent, higher levels of stress. We tested for this preconditioning phenomenon in a model of Parkinson's disease by applying 6-hydroxydopamine to the dopaminergic MN9D cell line. Exposure to sublethal concentrations of 6-hydroxydopamine (5-10 microM) protected against the toxic effects of a subsequent exposure to a higher concentration (50 microM), as measured by the Hoechst assay for nuclear viability. This was accompanied by little or no protection against 6-hydroxydopamine-induced lactate dehydrogenase release, decline in ATP, or reduction in (3)H-dopamine uptake. The antioxidant, N-acetyl cysteine (20 mM), when applied during preconditioning, abolished protection, as did the protein synthesis inhibitor, cycloheximide (0.2 microM). Preconditioning did not affect superoxide dismutase or glutathione peroxidase enzymes, or levels of heat shock protein-72. However, Bcl-2 protein levels rose with preconditioning. Preconditioning rapidly increased phosphorylation of kinases ERK1/2, Akt and JNK, and was abolished by pharmacological inhibitors of their activity. Finally, sublethal 6-hydroxydopamine preconditioned against the toxicity of proteasome inhibitor, MG-132 (1 microM). Thus, exposure of a dopaminergic cell line to sublethal oxidative stress can protect against additional oxidative stress due to translational and post-translational modifications, as well as confer 'cross-tolerance' against a different insult, proteasome inhibition.

Stat3 is required for cytoprotection of the respiratory epithelium during adenoviral infection

The role of Stat3 in the maintenance of pulmonary homeostasis following adenoviral-mediated lung injury was assessed in vivo. Stat3 was selectively deleted from bronchiolar and alveolar epithelial cells in Stat3(DeltaDelta) mice. Although lung histology and function were unaltered by deletion of Stat3 in vivo, Stat3(DeltaDelta) mice were highly susceptible to lung injury caused by intratracheal administration of AV1-GFP, an early (E) region 1- and E3-deleted, nonproliferative adenovirus. Severe airspace enlargement, loss of alveolar septae, and sloughing of the bronchiolar epithelium were observed in Stat3(DeltaDelta) mice as early as 1 day after exposure to the virus. Although surfactant protein A, B, and C content and surfactant protein-B mRNA expression in Stat3(DeltaDelta) mice were similar, TUNEL staining and caspase-3 were increased in alveolar type II epithelial cells of Stat3(DeltaDelta) mice after exposure to virus. RNA microarray analysis of type II epithelial cells isolated from Stat3(DeltaDelta) mice demonstrated significant changes in expression of numerous genes, including those genes regulating apoptosis, supporting the concept that the susceptibility of Stat3-deficient mice to adenovirus was related to the role of Stat3 in the regulation of cell survival. AV1-Bcl-x(L), an E1- and E3-deleted, nonproliferative adenovirus expressing the antiapoptotic protein Bcl-x(L), protected Stat3(DeltaDelta) mice from adenoviral-induced lung injury. Adenoviral infection of the lungs of Stat3-deficient mice was associated with severe injury of the alveolar and bronchiolar epithelium. Thus, Stat3 plays a critical cytoprotective role that is required for epithelial cell survival and maintenance of alveolar structures during the early phases of pulmonary adenoviral infection.

Ceramide attenuates hypoxic cell death via reactive oxygen species signaling

We have previously demonstrated that tumor necrosis factor alpha (TNFalpha), a cytokine known to be induced by ischemia, independently promotes preconditioning in part via ceramide generation. As reactive oxygen species (ROS) signaling is evoked by ischemic preconditioning, by TNFalpha and by ceramide we reasoned that ceramide-induced preconditioning is ROS-mediated. Fibroblastic L-cells were subjected to 8 hours simulated ischemia and were preconditioned by pretreatment with cell permeable c2 ceramide (1 microM) with or without the antioxidant N-mercaptopropionyl glycine (MPG; 1 mM). Pretreatment with ceramide reduced lactate dehydrogenase release at the end of the simulated ischemia but this cytoprotective effect was lost in the presence of MPG. Concurrent temporal ROS generation was measured using confocal microscopy on cells stained with dichlorofluorescein diacetate (DCF-DA). Ceramide increased ROS production after 30 minutes and this induction was decreased by MPG. Incubation of ceramide with cyclooxygenase-2 inhibitor, NS 398 (10 microM), or with a mitochondrial respiratory chain inhibitor, rotenone (10 microM) reduced the cytoprotective effect of ceramide in parallel with a partial diminution in ROS generation. In contrast, inhibition of other ROS-producing systems including nitric oxide synthase, xanthine oxidase, or NADPH oxidase failed to modulate ceramide-induced cytoprotection. Collectively, these data demonstrate that ceramide induces a cell survival program through ROS signaling activated, in part, via cyclooxygenase and the mitochondrial respiratory chain.

Human Alveolar Macrophages Are Deficient in PTEN

Human alveolar macrophages play a critical role in host defense and in the development of inflammation and fibrosis in the lung. Unlike their precursor cells, blood monocytes, alveolar macrophages are long-lived and tend to be resistant to apoptotic stimuli. In this study, we examined the role of differentiation in altering baseline phosphatidylinositol (PI) 3-kinase/Akt activity. We found that differentiation increased activity of pro-survival PI 3-kinase/Akt while decreasing amounts of the negative PI 3-kinase regulator, PTEN. PTEN is a lipid phosphatase with activity against phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3), the major bioactive product of PI 3-kinase. Examining in vivo differentiation of alveolar macrophages (by comparing blood monocytes to alveolar macrophages from single donors), we found that differentiation resulted in increased baseline reactive oxygen species (ROS) in the alveolar macrophages. This led to a deficiency in PTEN, increased activity of Akt, and prolonged survival of alveolar macrophages. These data support the hypothesis that alterations in ROS levels contribute to macrophage homeostasis by altering the balance between PI 3-kinase/Akt and the phosphatase, PTEN.

Choline produces cytoprotective effects against ischemic myocardial injuries: evidence for the role of cardiac m3 subtype muscarinic acetylcholine receptors

BACKGROUND/AIMS

Accumulating evidence indicates the presence of functional M3 subtype of acetylcholine muscarinic receptors (M(3)-mAChR), in addition to the well-recognized M(2)-mAChR, in the heart of various species including man. However, the pathophysiological role of the cardiac M(3)-mAChR remain undefined. This study was designed to explore the possible role of M(3)-mAChR in cytoprotection of myocardial infarction and several related signaling pathways as potential mechanisms.

METHODS

Studies were performed in a rat model of myocardial infarction and in isolated myocytes.

RESULTS

We found that choline relieved myocardial injuries during ischemia or under oxidative stress, which was achieved by correcting hemodynamic impairment, diminishing ventricular arrhythmias and protecting cardiomyocytes from apoptotic death. The beneficial effects of choline were reversed by the M(3)-selective antagonists but not by the M(2)-selective antagonist. Choline/M(3)-mAChR activated several survival signaling molecules (antiapoptotic proteins Bcl-2 and ERKs), increased endogenous antioxidant reserve (SOD), and reduced apoptotic mediators (proapoptotic proteins Fas and p38 MAPK) and intracellular Ca2+ overload.

CONCLUSION

Choline improves cardiac function and reduces ischemic myocardial injuries via stimulating the cardiac M(3)-mAChRs which in turn result in alterations of multiple signaling pathways leading to cytoprotection. The findings suggest M(3)-mAChR as a new target for drug development for improving cardiac function and preventing cardiac injuries during ischemia/reperfusion.

Protection of oxidative preconditioning against apoptosis induced by H2O2 in PC12 cells: mechanisms via MMP, ROS, and Bcl-2

The present study is designed to investigate the effects of preconditioning with different doses of hydrogen peroxide (H2O2) on oxidative stress-induced apoptosis and the changes in mitochondrial membrane potential (MMP), intracellular reactive oxygen species (ROS) level, and expression of Bcl-2 during H2O2 preconditioning in rat pheochromocytoma (PC12) cells. It was shown that (1) H2O2 induced apoptosis in PC12 cells in a dose-dependent manner; (2) the preconditioning with 10 micromol L(-1) or 20 micromol L(-1) H2O2 can significantly protect PC12 cells against apoptosis induced by 50 or 100 micromol L(-1) H2O2, low (5 micromol L(-1)) and higher (30 micromol L(-1)) concentrations of H2O2 had no cytoprotections; (3) high concentration (100 micromol L(-1)) of H2O2 reduced MMP and expression of Bcl-2, and increased ROS level, but these effects were blocked by preconditioning with 10 micromol L(-1) H2O2; (4) the preconditioning with 10 micromol L(-1) H2O2 induced overexpression of Bcl-2. These results suggested that the preconditioning with low dose of H2O2 could protect the oxidative stress-induced PC12 cells apoptosis not only by preventing the reduction of MMP and expression of Bcl-2 as well as increase in ROS level, but also through overexpression of Bcl-2. It was indicated that overexpression of Bcl-2 may play a key role in the cytoprotection induced by preconditioning with low dose of H2O2 in PC12 cells.

Differential regulation of c-jun and CREB by acrolein and 4-hydroxynonenal

In Alzheimer's disease (AD), oxidative stress-induced lipid peroxidation leads to accumulation of unsaturated aldehydes including acrolein and 4-hydroxynonenal (4HNE) in brain. In this study, we examined the effects of these lipid peroxidation products on apoptotic pathways in cultured neurons. Acrolein and 4HNE increased the levels of active phosphorylated forms of c-jun and CREB, the transcription factors that promote apoptosis and cell survival, respectively. However, they decreased the activity of CREB-dependent BDNF promoter while they increased the activity of promoters responsive to c-jun. We hypothesized that this differential regulation could be due to competition between proapoptotic c-jun and cytoprotective CREB for CBP (CREB-binding protein), a coactivator shared by several transcription factors. In support of this hypothesis, we demonstrate that the decrease of BDNF promoter activity by acrolein and 4HNE could be restored (i) by cotransfection with CBP, (ii) by cotransfection with VP 16-CREB, a constitutively active form of CREB that does not depend on CBP for its activation, or (iii) by inhibiting JNK-mediated c-jun activation. Finally, adenoviral transduction of hippocampal neurons with VP 16-CREB resulted in significant reduction in caspase-3 activation by acrolein and 4HNE. These observations suggest that lipid peroxidation-induced differential regulation of CREB and c-jun might play a role in neurodegeneration in AD.

Hydrogen peroxide preconditioning protects PC12 cells against apoptosis induced by dopamine

Dopamine (DA), one of the major sources of reactive oxygen species (ROS), is implicated in neuronal death associated with Parkinson's disease (PD). Preconditioning with oxidative stress has been shown to provide cytoprotection similar to ischemic preconditioning (IPC), against cell apoptosis. In this study, using the model neurosecretory cell line, PC12, we investigated whether hydrogen peroxide (H(2)O(2)) at low concentration (10 microM) can protect PC12 cells against apoptosis induced by DA. PC12 cells were preconditioned with 10 microM H(2)O(2) for 90 min, followed by 24-h recovery and subsequent exposures to different concentrations (20, 50, 100 and 200 microM) of DA for 24-h, respectively. DA induced apoptotic cell death with significant morphological nuclear changes and DNA fragmentation as well as the dysfunction of mitochondria. Preconditioning with H(2)O(2) at 10 microM significantly reduced the percentage of apoptotic cells and partly blocked the decreases in 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) reduction and mitochondrial membrane potential (MMP) induced by DA. These results suggest that preconditioning with low concentration of H(2)O(2) protected PC12 cells against DA-induced apoptosis, the part restoration of the damaged mitochondrial functions might be one of the underlying mechanisms of this cytoprotection.

Death mechanisms in status epilepticus-generated neurons and effects of additional seizures on their survival

Status epilepticus (SE) increases neurogenesis in the subgranular zone (SGZ) of the adult dentate gyrus, but many of the newborn cells die, partly through caspase-induced apoptosis. Here we provide immunohistochemical evidence indicating that the caspase-evoked death of the new neurons involves the mitochondrial but not the death-receptor-mediated pathway. Cytochrome c released from mitochondria was found in a subset of progenitor cell progeny, while Fas ligand and tumor necrosis factor 1 receptor-associated domain as well as the mitochondria-related, caspase-independent apoptosis-inducing factor were not detected. We also show that additional seizures, induced at different stages during neuronal differentiation of progenitor cell progeny following SE, neither potentiate cell death mechanisms in the SGZ nor compromise the survival of the new cells. Thus, we found similar expression of cytochrome c, active caspase-3, caspase-cleaved PARP, and TUNEL/Hoechst-positive DNA fragmentation, as well as numbers of new cells in the SGZ in rats exposed to additional seizures at days 6 and 7 or days 33 and 34 following SE as in control animals only subjected to SE. We propose that the degree of survival of newly generated neurons is determined primarily by the initial SE insult and the ensuing pathology in the tissue environment, whereas spontaneous seizures play a minor role.

Impact of brief oxidant stress on primary adult cardiac fibroblasts

Reperfusion of ischemic myocardium (I/R) is associated with local release of a brief pulse of reactive oxygen species. The purpose of this study was to determine the effects of brief H2O2 stimulation on primary adult cardiac fibroblast phenotype. We demonstrate that brief H2O2 exposure results in transient phosphorylations of p38 and ERK which peaked by 15 min. Proliferation was minimally affected by either H2O2 or MAPK inhibition. Pretreatment with SB203580 or U0126 revealed that p38 enhances or maintains migration rates while ERK retarded migration. Peroxide exposure increased necrosis from 4% at baseline to >12% while reducing apoptosis by 3.5-fold. p38 inhibition resulted in increased necrosis and apoptosis while ERK inhibition had minimal effects. In conclusion, primary adult cardiac fibroblasts exposed to brief H2O2 exhibit an altered phenotype characterized by reduced migration and apoptosis and increased necrosis resulting, in part, from the differential effects of p38 and ERK signaling.

Progressive apoptotic cell death triggered by transient oxidative insult in H9c2 rat ventricular cells: a novel pattern of apoptosis and the mechanisms

Many pathophysiological processes are associated with oxidative stress and progressive cell death. Oxidative stress is an apoptotic inducer that is known to cause rapid cell death. Here we show that a brief oxidative insult (5-min exposure to 400 microM H(2)O(2)), although it did not kill H9c2 rat ventricular cells during the exposure, triggered an intracellular death cascade leading to delayed time-dependent cell death starting from 1 h after the insult had been withdrawn, and this post-H(2)O(2) cell death cumulated gradually, reaching a maximum level 8 h after H(2)O(2) withdrawal. By comparison, sustained exposure to H(2)O(2) caused complete cell death within a narrow time frame (2 h). The time-dependent post-H(2)O(2) cell death was typical of apoptosis, both morphologically (cell shrinkage and nuclear condensation) and biochemically (DNA fragmentation, extracellular exposure of phosphatidylserines, and caspase-3 activation). A dichlorofluorescein fluorescent signal showed a time-dependent endogenous increase of reactive oxygen species (ROS) production, which was almost abolished by inhibition of the mitochondrial electron transport chain. Application of antioxidants (vitamin E or DTT) before H(2)O(2) addition or after H(2)O(2) withdrawal prevented the H(2)O(2)-triggered progressive ROS production and apoptosis. Sequential appearance of events associated with activation of the mitochondrial death pathway was found, including progressive dissipation of mitochondrial membrane potential, cytochrome c release, and late activation of caspase-3. In conclusion, transient oxidative stress triggers an intrinsic program leading to self-sustained apoptosis in H9c2 cells via cumulative production of mitochondrial ROS and subsequent activation of the mitochondrial death pathway. This pattern of apoptosis may contribute to the progressive and long-lasting cell loss in some degenerative diseases.

Signals for death and differentiation: a two-step mechanism for in vitro transformation of adult islets of Langerhans to duct epithelial structures

Phenotypic change of adult pancreatic islets has been implicated in the development of certain pancreatic cancers and in islet transplant failure. The aim of this study was to characterize intracellular events that mediate changes in adult islet phenotype. Using an in vitro islet-to-duct transformation model, canine islets were induced to undergo phenotypic transformation to duct-like epithelial structures through a two-stage process. Stage one was characterized by widespread islet cell apoptosis associated with the formation of cavitary spaces within the islets. During this stage, c-Jun N-terminal regulated kinase (JNK) and caspase-3 activities were elevated, while extracellular signal-regulated kinase (ERK) and Akt activities were decreased. The second stage of the process was characterized by an inversion in the balance in activity between these signal transduction pathways and by a concomitant decrease in apoptosis. The transformed islets were no longer immunoreactive for islet cell hormones, but expressed the duct epithelial cell marker CK-AE1/AE3. In contrast to islet cells, these duct epithelial cells were highly proliferative. To clarify the role of the identified changes in signal transduction events, we performed additional studies using pharmacological inhibitors of enzyme activity and demonstrated that inhibition of JNK and caspase-3 activity prevented cystic transformation. Our results indicate that the balance in signaling activity between ERK/Akt and JNK/caspase-3 appears to be an important regulator of islet cell death and differentiation.

Oxidant preconditioning protects human proximal tubular cells against lethal oxidant injury via p38 MAPK and heme oxygenase-1

Ischemic preconditioning protects the kidney from subsequent ischemic injury but the signal transduction pathways involved are unknown. Human proximal tubular (HK-2) cells were protected from injury with 2.5 mM H(2)O(2) by preconditioning with a single 15-min exposure to 500 microM H(2)O(2) followed by 16 h of recovery (oxidant preconditioning). To identify the signaling pathways involved in oxidant preconditioning, we utilized inhibitors of several signaling intermediates (MAPK/ERK kinase I, p38 mitogen-activated protein kinase (MAPK), protein kinase C and tyrosine kinase). A rapid but transient increase in p38 MAPK was observed following oxidant preconditioning and an inhibitor of p38 MAPK (SB203580) abolished the protection provided by oxidant preconditioning. Oxidant preconditioning was also associated with heat shock protein-27 phosphorylation (by p38 MAPK) and an increased synthesis of heme oxygenase-1 (HO-1). Stimulation or inhibition of HO-1 with hemin or Zn(II) protoporphyrin IX, respectively, mimicked or abolished oxidant preconditioning-mediated cytoprotection. Inhibitors of new protein synthesis (cycloheximide) and gene transcription (actinomycin D) also blocked the cytoprotection by oxidant preconditioning. We conclude that oxidant preconditioning protects HK-2 cells against more severe oxidant injury via activation of signaling pathways that include p38 MAPK and increased synthesis of HO-1.

Involvement of MEK/ERK pathway in cephaloridine-induced injury in rat renal cortical slices

We have previously reported that free radical-mediated injury induced by cephaloridine (CER) is enhanced by phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, in rat renal cortical slices. We have also shown that PKC activation in mitochondria is involved in CER-induced nephrotoxicity in rats. We investigated the role of a downstream PKC pathway, a MEK/ERK pathway, in free radical-induced injury in rat renal cortical slices exposed to CER. Immediately after preparing slices from rat renal cortex, the slices were incubated in the medium containing MEK inhibitors. ERK1/2 activation was determined by Western blot analysis for phosphorylated ERK (pERK) 1/2 protein in nucleus fraction prepared from the slices exposed to CER. Prominently, CER caused not only increases in lipid peroxidation as an index of free radical generation and in LDH leakage as that of cell injury in the slices, but also marked activation of ERK1/2 in nucleus fraction. PD98059 and U0126, MEK1/2 inhibitors, significantly attenuated CER-induced increases in lipid peroxidation and LDH leakage in the slices. PD98059 also suppressed ERK1/2 activation in nucleus fraction prepared from the slices treated with CER. Inhibition of other MAP kinase pathways, p38 MAP kinase and c-Jun N-terminal kinase (JNK) had no effect on CER-induced increases in lipid peroxidation level and LDH leakage in the slices. The present results suggest that a MEK/ERK pathway down stream of a PKC pathway is probably involved in free radical-induced injury in rat renal cortical slices exposed to CER.

Pro-apoptotic signaling in neuronal cells following iron and amyloid beta peptide neurotoxicity

In a previous report, we characterized several oxidative stress parameters during the course of amyloid beta (Abeta) peptide/Fe2+-induced apoptotic death in neuronal cells. In extending these findings, we now report a marked decrease in protein kinase C (PKC) isoforms, reduced Akt serine/threonine kinase activity, Bcl 2-associated death promoter (BAD) phosphorylation and enhanced p38 mitogen-activated protein kinase (MAPK) and caspase-9 and -3 activation, 12 h after addition of both 5 micro m Abeta and 5 micro m Fe2+. These activities reminiscent for a pro-apoptotic cellular course were blocked in the presence of the iron chelator deferroxamine. Abeta alone, increased PKC isoform levels between three- and four-fold after 12 h, enhanced Akt activity approximately eight-fold and Ser136 BAD phosphorylation two-fold, suggesting that by itself is not toxic. Fe2+ alone transiently enhanced p38 MAPK and caspase-9 and -3 enzymes indicative for cell damage, but was not sufficient to cause cell death as previously indicated. GF, a PKC inhibitor or wortmannin, a blocker of the Akt pathway enhanced Abeta/Fe2+-induced toxicity, while SB, a p38 MAPK inhibitor, prevented cell damage and apoptosis. These findings further support the hypothesis that metal ion chelation and inhibitors of pro-apoptotic kinase cascades may be beneficial for Alzheimer's disease therapy.

H2O2 and 4-hydroxynonenal mediate amyloid beta-induced neuronal apoptosis by activating JNKs and p38MAPK

Amyloid beta peptides (Abeta) may be neurotoxic during the progression of Alzheimer's disease by eliciting oxidative stress. Exposure of neuronally differentiated SK-N-BE cells to Abeta(25-35) fragment as well as to full-length Abeta(1-40) and Abeta(1-42) induces early and time-dependent generation of oxidative stress that has been evaluated by carefully monitoring generation of hydrogen peroxide (H(2)O(2)), 4-hydroxynonenal (HNE), thiobarbituric acid reactive substances (TBARS), and fluorescent chromolipids. Abeta treatment also results in the activation of c-Jun aminoterminal kinases (JNKs) and p38(MAPK) and is followed by characteristic nuclear changes of apoptosis as evaluated by DAPI staining and TUNEL technique. To reproduce the relationships between oxidative stress and Abeta apoptosis we found that only the simultaneous administration of HNE and H(2)O(2), at concentrations similar to those generated within the first 3 h of Abeta exposure, can fully mimic Abeta-dependent activation of JNKs and p38(MAPK) and occurrence of apoptosis. Antioxidants such as alpha-tocopherol and N-acetylcysteine prevent completely either neuronal apoptosis or activation of JNKs and p38(MAPK) elicited by Abeta or by simultaneous HNE and H(2)O(2) addition. Finally, direct evidence that activation of these kinases is required for cell death induced by Abeta has been obtained by pretreating cell with specific inhibitors of JNKs and p38(MAPK). These results suggest the existence of a sequence of events in Abeta-induced apoptosis involving simultaneous generation of HNE and H(2)O(2) and oxidative stress-dependent activation of JNKs and p38(MAPK).

Normal function of HERG K+ channels expressed in HEK293 cells requires basal protein kinase B activity

The potential role of protein kinase B (PKB), a serine/threonine protein kinase, in regulating HERG (human ether-a-go-go related gene) K(+) channel function was investigated. Wortmannin (a phosphoinositide 3-kinase (PI3K) inhibitor) caused approximately 30% reduction of HERG current (I(HERG)) stably expressed in HEK293 cells. Transient transfection with the constitutively active PI3K in HERG-expressing HEK293 cells slightly increased ( approximately 7%) I(HERG) while a dominant negative PI3K significantly reduced I(HERG) ( approximately 25%) relative to results in vehicle-transfected cells. I(HERG) was approximately 35% greater in cells transfected with the constitutively activated PKB (caPKB), whereas it was approximately 47% smaller in cells transfected with dominant negative PKB (dnPKB). Basal activation of PKB was detected by immunocytochemistry. PKB activity was significantly enhanced in caPKB-transfected cells and nearly abolished in dnPKB-transfected cells. We conclude that normal HERG function in HEK293 cells requires basal activity of PKB. Our data represent the first evidence that PKB phosphorylation regulates K(+) channels.

Carbon monoxide inhibition of apoptosis during ischemia-reperfusion lung injury is dependent on the p38 mitogen-activated protein kinase pathway and involves caspase 3

Carbon monoxide (CO), a reaction product of the cytoprotective gene heme oxygenase, has been shown to be protective against organ injury in a variety of models. One potential mechanism whereby CO affords cytoprotection is through its anti-apoptotic properties. Our studies show that low level, exogenous CO attenuates anoxia-reoxygenation (A-R)-induced lung endothelial cell apoptosis. Exposure of primary rat pulmonary artery endothelial cells to minimal levels of CO inhibits apoptosis and enhances phospho-p38 mitogen-activated protein kinase (MAPK) activation in A-R. Transfection of p38alpha dominant negative mutant or inhibition of p38 MAPK activity with SB203580 ablates the anti-apoptotic effects of CO in A-R. CO, through p38 MAPK, indirectly modulates caspase 3. Furthermore, we correlate our in vitro apoptosis model with an in vivo model of A-R by showing that CO can attenuate I-R injury of the lung. Taken together, our data are the first to demonstrate in models of A-R that the anti-apoptotic effects of CO are via modulation of p38 MAPK and caspase 3.

Caspase-mediated death of newly formed neurons in the adult rat dentate gyrus following status epilepticus

A large proportion of cells that proliferate in the adult dentate gyrus under normal conditions or in response to brain insults exhibit only short-term survival. Here, we sought to determine which cell death pathways are involved in the degeneration of newly formed neurons in the rat dentate gyrus following 2 h of electrically induced status epilepticus. We investigated the role of three families of cysteine proteases, caspases, calpains, and cathepsins, which can all participate in apoptotic cell death. Status epilepticus increased the number of bromodeoxyuridine (BrdU)-positive proliferated cells in the subgranular zone of the dentate gyrus. At the time of maximum cell proliferation, immunohistochemical analyses revealed protein expression of active caspase-cleaved poly (ADP-ribose) polymerase (PARP) in approximately 66% of the BrdU-positive cells, while none of them expressed cathepsin B or the 150-kDa calpain-produced fodrin breakdown product. To evaluate the importance of cysteine proteases in regulating survival of the newly formed neurons, we administered intracerebroventricular infusions of a caspase inhibitor cocktail (zVAD-fmk, zDEVD-fmk and zLEHD-fmk) over a 2-week period, sufficient to allow for neuronal differentiation, starting 1 week after the epileptic insult. Increased numbers of cells double-labelled with BrdU and neuron-specific nuclear protein (NeuN) marker were detected in the subgranular zone and granule cell layer of the caspase inhibitor-treated rats. Our data indicate that caspase-mediated cell death pathways are active in progenitor cell progeny generated by status epilepticus and compromise survival during neuronal differentiation.