Paraquat Induces Apoptosis through Cytochrome C Release and ERK Activation

Regulation of macrophage polarization and glucose metabolism by the ERK/MAPK-HK1 signaling pathway in paraquat-induced acute lung injury

Acute lung injury is the leading cause of paraquat (PQ) poisoning-related mortality. The mechanism by which macrophages are involved in PQ-induced acute lung injury remains unclear. In recent years, the role of metabolic reprogramming in macrophage functional transformation has received significant attention. The current study aimed to identify the role of altered macrophage glucose metabolism and molecular mechanisms in PQ poisoning-induced acute lung injury. We established a model of acute lung injury in PQ-intoxicated mice via the intraperitoneal injection of PQ. PQ exposure induces macrophage M1 polarization and promotes the release of inflammatory factors, which causes the development of acute lung injury in mice. In vitro analysis revealed that PQ altered glucose metabolism, which could be reversed by siRNA transfection to silence the expression of HK1, a key enzyme in glucose metabolism. RNA sequencing revealed that the ERK/MAPK pathway was the crucial molecular mechanism of PQ pathogenesis. Further, U0126, an ERK inhibitor, could inhibit PQ-induced HK1 activation and macrophage M1 polarization. These findings provide novel insights into the previously unrecognized mechanism of ERK/MAPK-HK1 activation in PQ poisoning.

Roles of oxidative stress/JNK/ERK signals in paraquat-triggered hepatic apoptosis

Paraquat (PQ), a toxic and nonselective bipyridyl herbicide, is one of the most extensively used pesticides in agricultural countries. In addition to pneumotoxicity, the liver is an important target organ for PQ poisoning in humans. However, the mechanism of PQ in hepatotoxicity remains unclear. In this study, we found that exposure of rat hepatic H4IIE cells to PQ (0.1-2 mM) induced significant cytotoxicity and apoptosis, which was accompanied by mitochondria-dependent apoptotic signals, including loss of mitochondrial membrane potential (MMP), cytosolic cytochrome c release, and changes in the Bcl-2/Bax mRNA ratio. Moreover, PQ (0.5 mM) exposure markedly induced JNK and ERK1/2 activation, but not p38-MAPK. Blockade of JNK and ERK1/2 signaling by pretreatment with the specific pharmacological inhibitors SP600125 and PD98059, respectively, effectively prevented PQ-induced cytotoxicity, mitochondrial dysfunction, and apoptotic events. Additionally, PQ exposure stimulated significant oxidative stress-related signals, including reactive oxygen species (ROS) generation and intracellular glutathione (GSH) depletion, which could be reversed by the antioxidant N-Acetylcysteine (NAC). Buffering the oxidative stress response with NAC also effectively abrogated PQ-induced hepatotoxicity, MMP loss, apoptosis, and phosphorylation of JNK and ERK1/2 protein, however, the JNK or ERK inhibitors did not suppress ROS generation in PQ-treated cells. Collectively, these results demonstrate that PQ exposure induces hepatic cell toxicity and death via an oxidative stress-dependent JNK/ERK activation-mediated downstream mitochondria-regulated apoptotic pathway.

Paraquat and Parkinson's Disease: The Molecular Crosstalk of Upstream Signal Transduction Pathways Leading to Apoptosis

Parkinson's disease (PD) is a heterogeneous disease involving a complex interaction between genes and the environment that affects various cellular pathways and neural networks. Several studies have suggested that environmental factors such as exposure to herbicides, pesticides, heavy metals, and other organic pollutants are significant risk factors for the development of PD. Among the herbicides, paraquat has been commonly used, although it has been banned in many countries due to its acute toxicity. Although the direct causational relationship between paraquat exposure and PD has not been established, paraquat has been demonstrated to cause the degeneration of dopaminergic neurons in the substantia nigra pars compacta. The underlying mechanisms of the dopaminergic lesion are primarily driven by the generation of reactive oxygen species, decrease in antioxidant enzyme levels, neuroinflammation, mitochondrial dysfunction, and ER stress, leading to a cascade of molecular crosstalks that result in the initiation of apoptosis. This review critically analyses the crucial upstream molecular pathways of the apoptotic cascade involved in paraquat neurotoxicity, including mitogenactivated protein kinase (MAPK), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT, mammalian target of rapamycin (mTOR), and Wnt/β-catenin signaling pathways.

Transgenic RFP-RPS-30UbL strain of the nematode Caenorhabditis elegans as a biomonitor for environmental pollutants

Environmental pollutants are recognized as one of the major concerns for public health. The free-living nematode Caenorhabditis elegans are widely used to evaluate the toxicity of environmental contaminants in biomonitoring researches. In the present study, a new transgenic strain, rps-30^-/- ;RFP-RPS-30^UbL was generated, with constitutively active rps-30 promoter used to control the expression of RFP-RPS-30^UbL fusion protein. We found RFP-RPS-30^UbL would accumulate to form 'rod-like' structures, when worms were exposed to environmental contaminants, including Cd, Hg, Pb, As, Paraquat and Dichlorvos. The number of the 'rod-like' structures was induced by environmental contaminants in a concentration- and time-dependent manner. The 'rod-like' structure formation could be detectable in response to the concentration of each contaminant as low as 24-h LC50 × 10^-7 , and the detectable time could be within 2 h. Detecting the transcription and expression levels of RFP-RPS-30^UbL in worms exposed to different kinds of environmental contaminants showed that the expression level of RFP-RPS-30^UbL was not regulated by environmental contaminants, and the number differences of 'rod-like' structures were just due to the morphological change of RFP-RPS-30^UbL from dispersion to accumulation induced by environmental contaminants. In addition, this transgenic strain was developed in rps-30^-/- homozygous worm, which was a longevity strain. Detection of lifespan and brood size showed that rps-30^-/- ;RFP-RPS-30^UbL transgenic worm was more suitable to be cultured and used further than N2;GFP-RPS-30^UbL , for expressing RPS-30^UbL in wild type N2 worms shortened the lifespan and deceased the brood size. Therefore, rps-30^-/- ;RFP-RPS-30^UbL transgenic worm might play a potential role in versatile environmental biomonitoring, with the advantage of not only the convenient and quick fluorescence-based reporter assay, but also the quantificational evaluation of the toxicities of environmental contaminants using 'rod-like' structures with high sensitivity, off-limited the expression level of the reporter protein.

Verbascoside inhibits paraquate-induced pulmonary toxicity via modulating oxidative stress, inflammation, apoptosis and DNA damage in A549 cell

Paraquat (PQ), one of the most frequently used herbicides, can cause serious health problems in an exposed individual. In the present study, we investigated the protective effect of verbascoside (VB), a phenylpropanoid glycoside from lemon verbena, against PQ-induced A549 cell injury with a particular focus on the possible molecular pathways involved. A549 cells were exposed to PQ (300 µM) and different concentrations of VB (12.5, 25, and 50 µM). Cell viability, ROS content, the level of antioxidant enzymes (SOD, CAT and GPx) and inflammatory markers (IL-6 and TNF-α), as well as 8-OHdG, were detected using MTT assay and an ELISA kit. Western blotting and qRT-PCR were performed to measure the levels of caspase3 and NF-κB mRNA and protein expression. Exposure of cells to PQ caused viability loss and ROS increase. PQ also increased the levels of IL-6, TNF-α and 8-OHdG and decreased the antioxidant enzymes content. PQ treatment resulted in cell death by increasing the gene and protein expression level of caspase 3 and NF-κB. Treatment with VB notably increased cell survival, antioxidant enzymes activity, which concomitantly attenuated ROS, NF-κB and inflammatory mediator production. VB also inhibited apoptosis expression markers. These results indicated that VB could protect A549 cells against PQ induced cell injury by attenuation of ROS and inflammatory marker production and modulation of antioxidant enzymes. VB efficiently suppressed increased NF-κB and caspase-3 activity and formation of 8-OHdG and ultimately improved cell viability. Therefore, VB may be useful in the development of a new therapy for PQ-induced pulmonary toxicity.

ERK: A Double-Edged Sword in Cancer. ERK-Dependent Apoptosis as a Potential Therapeutic Strategy for Cancer

The RAF/MEK/ERK signaling pathway regulates diverse cellular processes as exemplified by cell proliferation, differentiation, motility, and survival. Activation of ERK1/2 generally promotes cell proliferation, and its deregulated activity is a hallmark of many cancers. Therefore, components and regulators of the ERK pathway are considered potential therapeutic targets for cancer, and inhibitors of this pathway, including some MEK and BRAF inhibitors, are already being used in the clinic. Notably, ERK1/2 kinases also have pro-apoptotic functions under certain conditions and enhanced ERK1/2 signaling can cause tumor cell death. Although the repertoire of the compounds which mediate ERK activation and apoptosis is expanding, and various anti-cancer compounds induce ERK activation while exerting their anti-proliferative effects, the mechanisms underlying ERK1/2-mediated cell death are still vague. Recent studies highlight the importance of dual-specificity phosphatases (DUSPs) in determining the pro- versus anti-apoptotic function of ERK in cancer. In this review, we will summarize the recent major findings in understanding the role of ERK in apoptosis, focusing on the major compounds mediating ERK-dependent apoptosis. Studies that further define the molecular targets of these compounds relevant to cell death will be essential to harnessing these compounds for developing effective cancer treatments.

Comparison of Pancreatic Damage in Rats for Two Methods of Paraquat Administration

It is noted that elevated serum amylase levels suggesting pancreatic damage has an association with prognosis in PQ patients. This study aimed to determine whether PQ can cause pancreatic damage. The two conventional models (intragastric infusion (iG) and intraperitoneal injection (iP)) may exhibit different effects on the pancreas depending on whether or not they pass through the digestive tract. In this study, the rats were divided into four groups: the intragastric infusion group (PQ-iG, n = 45), intraperitoneal injection group (PQ-iP, n = 53), normal control group 1 (NC-iG, n = 6) and normal control group 2 (NC-iP, n = 6). Pancreatic damage was compared between groups using serum amylase activity assay, hematoxylin and eosin (H&E) staining, TUNEL assay, and transmission electron microscopy (TEM). Serum amylase levels in group PQ-iG were significantly higher than in group PQ-iP (p < 0.05). Examination of the H&E sections showed damage to the pancreas. Both experimental groups were displayed inflammatory infiltration within 9 h of PQ treatment. After 9 h, patchy necrosis was observed in group PQ-iP, when inflammatory infiltration was still the dominant pathology. Necrosis appeared and gradually worsened in group PQ-iG, in which necrosis was the dominant pathology. The TUNEL assay showed significantly higher numbers of apoptotic cells in the pancreas of PQ-groups than in the control NC- groups (p < 0.05). TEM showed expansive endoplasmic reticulum lumens and mitochondria swelling in the pancreas of the PQ-groups. It is concluded that both methods of modeling could cause pancreatic damage and the type and degree of damage would change over time. Note that pancreatic damage in group PQ-iG was more severe than that in group PQ-iP. Therefore, clinical practitioners should pay close attention to pancreatic damage caused by PQ, especially when the route of PQ administration was oral.

Cellular injury leading to oxidative stress in acute poisoning with potassium permanganate/oxalic acid, paraquat, and glyphosate surfactant herbicide

Previous studies on human acute kidney injury (AKI) following poisoning with potassium permanganate/oxalic acid (KMnO4/H2C2O4), paraquat, and glyphosate surfactant herbicide (GPSH) have shown rapid and large increases in serum creatinine (sCr) that cannot be entirely explained by direct nephrotoxicity. One plausible mechanism for a rapid increase in sCr is oxidative stress. Thus, we aimed to explore biomarkers of oxidative stress, cellular injury, and their relationship with sCr, after acute KMnO4/H2C2O4, paraquat, and GPSH poisonings. Serum biomarkers [sCr, creatine (sCn), cystatin C (sCysC)] and urinary biomarkers [cytochrome C (CytoC), 8-isoprostane (8-IsoPs)] were evaluated in 105 patients [H2C2O4/KMnO4 (N = 57), paraquat, (N = 21), GPSH (N = 27)] recruited to a multicenter cohort study. We used area under the receiver operating characteristics curve (AUC-ROC) to quantify the extent of prediction of moderate to severe AKI (acute kidney injury network stage 2/3 (AKIN2/3)). Patients with AKIN2/3 showed increased levels of CytoC. Early high CytoC predicted AKIN2/3 in poisoning with KMnO4/H2C2O4 (AUC-ROC4-8h: 0.81), paraquat (AUC-ROC4-8h: 1.00), and GPSH (AUC-ROC4-8h: 0.91). 8-Isoprostane levels were not significantly elevated. Reduced sCn and increased sCr/sCn ratios were observed for 48 h post KMnO4/H2C2O4 ingestion. Paraquat exhibited a similar pattern (N = 11), however only 3 were included in our study. Increased CytoC suggests there is mitochondrial injury coupled with energy depletion. The increased sCr within 24 h could be due to increased conversion of cellular creatine to creatinine during the process of adenosine triphosphate (ATP) generation and then efflux from cells. Later increases of sCr are more likely to represent a true decrease in kidney function.

High-Dose Paraquat Induces Human Bronchial 16HBE Cell Death and Aggravates Acute Lung Intoxication in Mice by Regulating Keap1/p65/Nrf2 Signal Pathway

Paraquat (PQ) intoxication seriously endangers human beings’ health, however, the underlying mechanisms are still unclear. Here we found that PQ inhibits human bronchial 16HBE cell proliferation and promotes cell apoptosis, necrosis as well as ROS generation in a dose dependent manner. Of note, low-dose PQ (50 μM) induces cell autophagy, increases Nrf2 as well as p65 levels and has little impacts on Keap1, while high-dose PQ (500 μM) inhibits autophagy, upregulates Keap1 as well as downregulates p65 and Nrf2. In addition, we verified that p65 overexpression increases Nrf2 and its downstream targets in 16HBE cells, which are reversed by synergistically knocking down Nrf2. Our further results showed that high-dose PQ’s effects on cell proliferation, apoptosis, ROS levels and autophagy are reversed by p65 overexpression. Besides, the protective effects of overexpressed p65 on high-dose PQ (500 μM) treated 16HBE cells are abrogated by synergistically knocking down Nrf2. In vivo experiments also showed that high-dose PQ promotes inflammatory cytokines secretion, lung fibrosis and cell apoptosis, inhibits cell proliferation in mice models by regulating Keap1/p65/Nrf2 signal pathway. Therefore, we concluded that high-dose PQ (500 μM) inhibits 16HBE cell proliferation and autophagy, promotes cell death and mice lung fibrosis by regulating Keap1/p65/Nrf2 signal pathway.

The protective effects of bone mesenchymal stem cells on paraquat-induced acute lung injury via the muc5b and ERK/MAPK signaling pathways

OBJECTIVE

To evaluate the protective effect of bone mesenchymal stem cells (BMSCs) on paraquat (PQ)-induced acute lung injury (ALI) and investigate the possible underlying mechanisms.

METHODS

Male Sprague Dawley rats were treated with BMSCs (3 × 10⁶) 1 h after intraperitoneal injection of PQ. The cell apoptosis rate and mitochondrial membrane potential in rat pulmonary alveolar type II epithelial (ATII) cells were quantitated by flow cytometry. IL-17, IL-6, and MUC5B levels in bronchoalveolar lavage fluid (BALF) and ATII culture medium were measured. Lung tissues were collected to determine the wet-to-dry (W/D) ratios and lung injury scores, in addition to the protein and mRNA expression levels of ERK1/2, Bcl-2, Bax, and muc5b.

RESULTS

BMSCs had decreased mRNA expression of Muc5b in lung tissue of rats with PQ-induced ALI as shown by RNA-seq. Treatment with BMSCs also alleviated the PQ-induced increases in protein expression in the BALF and reduced the concentration of IL-17, IL-6, and Muc5b in both the BALF and ATII culture medium. In addition, the ATII cell apoptosis rate and mitochondrial membrane potential, as well as the W/D ratios, were decreased by BMSC treatment. Moreover, BMSCs ameliorated the expression levels of Bax mRNA and active caspase-3 proteins and increased Bcl-2 mRNA expression. Furthermore, BMSCs attenuated ERK1/2 activation upon PQ-induced ALI in lung tissue.

CONCLUSION

BMSC therapy can protect against PQ-induced ALI in rats. A possible mechanism is the suppression of the muc5b and ERK/MAPK signaling pathways, resulting in an improvement in the endothelial permeability and a decrease in inflammation and cell apoptosis.

Chlorogenic acid prevents paraquat-induced apoptosis via Sirt1-mediated regulation of redox and mitochondrial function

Paraquat (PQ) is a widely used agro-chemical in agriculture and highly toxic to humans. Although the mechanism of PQ poisoning is not clear, it has been well documented that reactive oxygen species (ROS) generation and apoptosis play pivotal roles. Alternatively, chlorogenic acid (CA) is a biologically active dietary polyphenol, playing several therapeutic roles. However, it is not known whether CA has protective effect on PQ-induced apoptosis. Here, we investigated the effect of CA in preventing PQ-induced apoptosis and explored the underlying mechanisms. A549 cells were pretreated with 100 µM CA for 24 h and then exposed to 160 µM PQ for 24 h. We found that CA was effective in preventing PQ-induced apoptotic features, including the release of cytochrome c from the mitochondria to cytoplasm, the cleavages of caspase 3 and caspase 9, and the increases in levels of Bcl-2-associated X protein (Bax) and intracellular calcium ions. CA alleviated ROS production and prevented the reduction of antioxidant capacity in cells exposed to PQ by increasing NF-E2-related factor 2 (Nrf2), superoxide dismutase 2 (SOD2) and glutathione levels. In addition, CA also attenuated PQ-induced alterations of mitochondrial structure and function (such as the decreases in membrane potential and adenosine triphosphate level), and the impaired autophagic flux was improved by CA. Down-regulation of sirtuin 1 (Sirt1) by short hairpin RNA reversed the protective effects of CA. Thus, CA may be viewed as a potential drug to treat PQ-induced lung epithelial cell apoptosis and other disorders with similar pathologic mechanisms.

Melatonin protects against paraquat-induced damage during in vitro maturation of bovine oocytes

Paraquat (PQ), a broad-spectrum agricultural pesticide, causes cellular toxicity by increasing oxidative stress levels in various biological systems, including the reproductive system. PQ exposure causes embryotoxicity and reduces the developmental abilities of embryos. However, there is little information regarding the toxic effects of PQ on oocyte maturation. In this study, we studied the toxic effects of PQ exposure and the effects of melatonin on PQ-induced damage in bovine oocytes. PQ exposure disrupted nuclear and cytoplasmic maturation, which was manifested as decreased cumulus cell expansion, reduced first polar body extrusion, and abnormal distribution patterns of cortical granules and mitochondria. In addition, PQ treatment severely disrupted the ability of the resulted in vitro-produced embryos to develop to the blastocyst stage. Moreover, PQ exposure significantly increased the intracellular reactive oxygen species (ROS) level and early apoptotic rate, and decreased the glutathione (GSH) level, antioxidative CAT and GPx4 mRNA, and apoptotic-related Bcl-2/Bax mRNA ratio. These results indicated that PQ causes reproductive toxicity in bovine oocytes. Melatonin application resulted in significant protection against the toxic effects of PQ in PQ-exposed oocytes. The mechanisms underlying the role of melatonin included the inhibition of PQ-induced p38 mitogen-activated protein kinase (MAPK) activation, and restoration of abnormal trimethyl-histone H3 lysine 4 (H3K4me3) and trimethyl-histone H3 lysine 9 (H3K9me3) levels. These results reveal that melatonin serves as a powerful agent against experimental PQ-induced toxicity during bovine oocyte maturation and could form a basis for further studies to develop therapeutic strategies against PQ poisoning.

JNK Inhibitor SP600125 Attenuates Paraquat-Induced Acute Lung Injury: an In Vivo and In Vitro Study

Acute lung injury (ALI) is a major complication soon after paraquat poisoning and rapidly progresses with high mortality. However, the specific mechanism underlying paraquat-induced ALI is still unclear. In this study, the mechanism underlying the protective effects of SP600125 on paraquat-induced ALI was investigated according to oxidative stress, inflammation, and apoptosis. The rats were randomly assigned into the control group (CON), the paraquat poisoning group (PQ), and the PQ + SP600125 group (SP). A549 cells were divided into the Con group, Pq group, and Sp group. H&E staining and detection of lung wet/dry ratio were employed to evaluate lung injury. Annexin V-PI staining was done to evaluate A549 cell apoptosis. Dihydroethidium fluorescence was used to measure reactive oxygen species (ROS) in the lungs and A549 cells. ELISA was performed to detect TNF-α and IL-6 in the supernatant of bronchoalveolar lavage fluid (BALF) and A549 cells. RT-qPCR was done to measure the messenger RNA (mRNA) expression of TNF-α and IL-6 in the lungs and A549 cells. Western blotting assay was performed to detect the protein expression of phospho-JNK, total JNK, and cleaved caspase-3. Electrophoretic mobility shift assay was employed to detect the DNA binding activities of AP-1 and P-p65. JNK inhibitor SP600125 reduced JNK phosphorylation, downregulated cleaved caspase-3 protein level, decreased AP-1 transcriptional activity and ROS level, and reduced the transcription and expression of TNF-α and IL-6, which improved ALI and cell apoptosis after paraquat poisoning. Our results indicate that JNK/AP-1 mediates ALI as well as oxidative stress and inflammation deterioration secondary to paraquat poisoning.

Heparan Sulfate Induces Necroptosis in Murine Cardiomyocytes: A Medical-In silico Approach Combining In vitro Experiments and Machine Learning

Life-threatening cardiomyopathy is a severe, but common, complication associated with severe trauma or sepsis. Several signaling pathways involved in apoptosis and necroptosis are linked to trauma- or sepsis-associated cardiomyopathy. However, the underling causative factors are still debatable. Heparan sulfate (HS) fragments belong to the class of danger/damage-associated molecular patterns liberated from endothelial-bound proteoglycans by heparanase during tissue injury associated with trauma or sepsis. We hypothesized that HS induces apoptosis or necroptosis in murine cardiomyocytes. By using a novel Medical-In silico approach that combines conventional cell culture experiments with machine learning algorithms, we aimed to reduce a significant part of the expensive and time-consuming cell culture experiments and data generation by using computational intelligence (refinement and replacement). Cardiomyocytes exposed to HS showed an activation of the intrinsic apoptosis signal pathway via cytochrome C and the activation of caspase 3 (both p < 0.001). Notably, the exposure of HS resulted in the induction of necroptosis by tumor necrosis factor α and receptor interaction protein 3 (p < 0.05; p < 0.01) and, hence, an increased level of necrotic cardiomyocytes. In conclusion, using this novel Medical-In silico approach, our data suggest (i) that HS induces necroptosis in cardiomyocytes by phosphorylation (activation) of receptor-interacting protein 3, (ii) that HS is a therapeutic target in trauma- or sepsis-associated cardiomyopathy, and (iii) indicate that this proof-of-concept is a first step toward simulating the extent of activated components in the pro-apoptotic pathway induced by HS with only a small data set gained from the in vitro experiments by using machine learning algorithms.

Diepoxybutane-induced apoptosis is mediated through the ERK1/2 pathway

Diepoxybutane (DEB) is the most potent active metabolite of butadiene, a regulated air pollutant. We previously reported the occurrence of DEB-induced, p53-dependent, mitochondrial-mediated apoptosis in human lymphoblasts. The present study investigated the role of the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathway in DEB-induced apoptotic signaling in exposed human lymphoblasts. Activated ERK1/2 and mitogen-activated protein (MAP) kinase/ERK1/2 kinase (MEK) levels were significantly upregulated in DEB-exposed human lymphoblasts. The MEK inhibitor PD98059 and ERK1/2 siRNA significantly inhibited apoptosis, ERK1/2 activation, as well as p53 and phospho-p53 (serine-15) levels in human lymphoblasts undergoing DEB-induced apoptosis. Collectively, these results demonstrate that DEB induces apoptotic signaling through the MEK-ERK1/2-p53 pathway in human lymphoblasts. This is the first report implicating the activation of the ERK1/2 pathway and its subsequent role in mediating DEB-induced apoptotic signaling in human lymphoblasts. These findings contribute towards the understanding of DEB toxicity, as well as the signaling pathways mediating DEB-induced apoptosis in human lymphoblasts.

Paraquat affects mitochondrial bioenergetics, dopamine system expression, and locomotor activity in zebrafish (Danio rerio)

The dipyridyl herbicide paraquat induces oxidative stress in cells and is implicated in adult neurodegenerative diseases. However, less is known about paraquat toxicity in early stages of vertebrate development. To address this gap, zebrafish (Danio rerio) embryos were exposed to 1, 10 and 100 μM paraquat for 96 h. Paraquat did not induce significant mortality nor deformity in embryos and larvae, but it did accelerate time to hatch. To evaluate whether mitochondrial respiration was related to earlier hatch times, oxygen consumption rate was measured in whole embryos. Maximal respiration of embryos exposed to 100 μM paraquat for 24 h was reduced by more than 70%, suggesting that paraquat negatively impacts mitochondrial bioenergetics in early development. Based upon this evidence for mitochondrial dysfunction, transcriptional responses of oxidative stress- and apoptosis-related genes were measured. Fish exposed to 1 μM paraquat showed higher expression levels of superoxide dismutase 2, heat shock protein 70, Bcl-2-associated X protein, and B-cell CLL/lymphoma 2a compared to control fish. No differences among groups were detected in larvae exposed to 10 and 100 μM paraquat, suggesting a non-monotonic response. We also measured endpoints related to larval behavior and dopaminergic signaling as paraquat is associated with degeneration of dopamine neurons. Locomotor activity was stimulated with 100 μM paraquat and dopamine transporter and dopamine receptor 3 mRNA levels were increased in larvae exposed to 1 μM paraquat, interpreted to be a compensatory response at lower concentrations. This study improves mechanistic understanding into the toxic actions of paraquat on early developmental stages.

Sulforaphane Induced Apoptosis via Promotion of Mitochondrial Fusion and ERK1/2-Mediated 26S Proteasome Degradation of Novel Pro-survival Bim and Upregulation of Bax in Human Non-Small Cell Lung Cancer Cells

Previous studies in our laboratory showed that sulforaphane (SFN) induced apoptosis by sustained activation of extracellular regulated protein kinases 1/2 (ERK1/2). However, the underlying mechanisms associated with SFN-induced apoptosis and downstream cascades which are modulated by ERK1/2 were not elucidated. Herein we demonstrated for the first time that alteration of mitochondrial dynamics contributed to SFN-induced apoptosis in human non-small cell lung cancer (NSCLC) cells. Reports showed that protein Bim not only induced apoptosis but also promoted proliferation under certain circumstances. We found that Bim was related to cell growth in NSCLC cells. Pro-survival Bim downregulation was shown to induce apoptosis in response to SFN. Further, Using the ERK1/2 inhibitor, PD98059, we found that SFN upregulated Bax and downregulated Bim through the ERK1/2-dependent signaling pathway. Furthermore, SFN activated ERK1/2 to increase 26S proteasome activity to degrade Bim, while the proteasome inhibitor MG132 reversed this effect. Therefore, SFN phosphorylated ERK1/2 and activated the proteasome system leading to the degradation of Bim, which contributed to apoptosis in NSCLC cells. These findings provided a novel insight into SFN-related therapeutics in cancer treatment.

Paraquat induces extrinsic pathway of apoptosis in A549 cells by induction of DR5 and repression of anti-apoptotic proteins, DDX3 and GSK3 expression

Paraquat (PQ) is a bipyridyl derivative herbicide known to cause lung toxicity partly through induction of apoptosis. Here we demonstrated that PQ caused apoptosis in A549 cells. PQ increased cleavage of caspase-8 and Bid, indicating caspase-8 activation and truncated Bid, the two key mediators of extrinsic apoptosis. Additionally, PQ treatment caused an increase in DR5 (death receptor-5) and caspase-8 interaction, indicating formation of DISC (death-inducing signaling complex). These results indicate that PQ induces apoptosis through extrinsic pathway in A549 cells. Moreover, PQ drastically increased DR5 expression and membrane localization. Furthermore, PQ caused prominent concentration dependent reductions of DDX3 (the DEAD box protein-3) and GSK3 (glycogen synthase kinase-3) which can associate with DR5 and prevent DISC formation. Additionally, PQ decreased DR5-DDX3 interaction, suggesting a reduction of DDX3/GSK3 anti-apoptotic complex. Inhibition of GSK3, which is known to promote extrinsic apoptosis by its pharmacological inhibitor, BIO accentuated PQ-induced apoptosis. Moreover, GSK3 inhibition caused a further decrease in PQ-reduced DR5-DDX3 interaction. Taken together, these results suggest that PQ may induce extrinsic pathway of apoptosis in A549 cells through upregulation of DR5 and repression of anti-apoptotic proteins, DDX3/GSK3 leading to reduction of anti-apoptotic complex.

Identification of apoptosis and macrophage migration events in paraquat-induced oxidative stress using a zebrafish model

AIMS

Paraquat (PQ) is a pesticide highly toxic to human beings, and a well-known trigger of oxidative stress. Although several animal models of PQ poisoning have been developed, some disadvantages limit their application in vivo. A zebrafish model was used in the present study to better define mechanisms of oxidative stress injury induced by PQ.

MAIN METHODS

The toxicity of PQ was evaluated in the AB strain of zebrafish, and apoptosis was assessed by acridine orange staining. Macrophage migration was identified using the TG (zlyz:EGFP) transgenic strain, and angiogenesis was observed using the fli1a-EGFP casper strain. Following the validation of gene changes by zebrafish-based in vivo quantitative real-time PCR, network analysis was performed using the Ingenuity Pathway Analysis software.

KEY FINDINGS

We first established the LC50 of PQ in the zebrafish model, and then found that robust oxidative stress and antioxidant genes were activated after PQ exposure. Moreover, apoptosis and distinct macrophage activation and migration were identified for the first time in PQ-exposed zebrafish. Utilizing this model, both extrinsic and intrinsic pathways involved in PQ-induced apoptosis were elucidated. We further demonstrated that macrophage migration was specifically induced by PQ, and that Rho family members and JNK-MMP13 signaling participated in this process.

SIGNIFICANCE

Zebrafish is a promising tool for investigating the mechanisms of oxidative stress injury induced by PQ, and for screening effective anti-oxidant drugs.

The Neuroprotective Role of Insulin Against MPP(+) -Induced Parkinson's Disease in Differentiated SH-SY5Y Cells

Parkinson's disease (PD) is a common chronic neurodegenerative disorder associated with aging that primarily caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SN). Retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells (SH-SY5Y+RA) have been broadly utilized in studies of mechanisms of the pathogenesis underlying 1-Methyl-4-phenyl pyridinium (MPP(+))-induced PD models. Here, we investigated the neuroprotective mechanisms of insulin on MPP(+)-induced neurotoxicity on SH-SY5Y+RA cells. Recent studies suggest that insulin has a protective effect against oxidative stress but not been elucidated for PD. In this study, pretreatment of insulin prevented the cell death in a dose dependent manner and lowered nitric oxide (NO) release, reactive oxygen species (ROS), and calcium ion (Ca(2+)) influx induced by MPP(+). Insulin also elevated tyrosine hydroxylase (TH) and insulin signaling pathways in dopaminergic neuron through activating PI3K/Akt/GSK-3 survival pathways which in turn inhibits MPP(+)-induced iNOS and ERK activation, and Bax to Bcl-2 ratio. These results suggest that insulin has a protective effect on MPP(+)-neurotoxicity in SH-SY5Y+RA cells.