Peroxisomal Catalase Research Articles

Silenced rice in both cytosolic ascorbate peroxidases displays pre-acclimation to cope with oxidative stress induced by 3-aminotriazole-inhibited catalase

The maintenance of H2O2 homeostasis and signaling mechanisms in plant subcellular compartments is greatly dependent on cytosolic ascorbate peroxidases (APX1 and APX2) and peroxisomal catalase (CAT) activities. APX1/2 knockdown plants were utilized in this study to clarify the role of increased cytosolic H2O2 levels as a signal to trigger the antioxidant defense system against oxidative stress generated in peroxisomes after 3-aminotriazole-inhibited catalase (CAT). Before supplying 3-AT, silenced APX1/2 plants showed marked changes in their oxidative and antioxidant profiles in comparison to NT plants. After supplying 3-AT, APX1/2 plants triggered up-expression of genes belonging to APX (OsAPX7 and OsAPX8) and GPX families (OsGPX1, OsGPX2, OsGPX3 and OsGPX5), but to a lower extent than in NT plants. In addition, APX1/2 exhibited lower glycolate oxidase (GO) activity, higher CO2 assimilation, higher cellular integrity and higher oxidation of GSH, whereas the H2O2 and lipid peroxidation levels remained unchanged. This evidence indicates that redox pre-acclimation displayed by silenced rice contributed to coping with oxidative stress generated by 3-AT. We suggest that APX1/2 plants were able to trigger alternative oxidative and antioxidant mechanisms involving signaling by H2O2, allowing these plants to display effective physiological responses for protection against oxidative damage generated by 3-AT, compared to non-transformed plants.

Species-specific differences in peroxisome proliferation, catalase, and SOD2 upregulation as well as toxicity in human, mouse, and rat hepatoma cells induced by the explosive and environmental pollutant 2,4,6-trinitrotoluene.

2,4,6-Trinitrotoluene (TNT) has been widely used as an explosive substance and its toxicity is still of interest as it persisted in polluted areas. TNT is metabolized in hepatocytes which are prone to its toxicity. Since analysis of the human liver or hepatocytes is restricted due to ethical reasons, we investigated the effects of TNT on cell viability, reactive oxygen species (ROS) production, peroxisome proliferation, and antioxidative enzymes in human (HepG2), mouse (Hepa 1-6), and rat (H4IIEC3) hepatoma cell lines. Under control conditions, hepatoma cells of all three species were highly comparable exhibiting identical proliferation rates and distribution of their cell cycle phases. However, we found strong differences in TNT toxicity with the lowest IC50 values (highest cell death rate) for rat cells, whereas human and mouse cells were three to sevenfold less sensitive. Moreover, a strong decrease in cellular dehydrogenase activity (MTT assay) and increased ROS levels were noted. TNT caused peroxisome proliferation with rat hepatoma cells being most responsive followed by those from mouse and human. Under control conditions, rat cells contained fivefold higher peroxisomal catalase and mitochondrial SOD2 activities and a twofold higher capacity to reduce MTT than human and mouse cells. TNT treatment caused an increase in catalase and SOD2 mRNA and protein levels in human and mouse, but not in rat cells. Similarly, human and mouse cells upregulated SOD2 activity, whereas rat cells failed therein. We conclude that TNT induced oxidative stress, peroxisome proliferation and mitochondrial damage which are highest in rat cells rendering them most susceptible toward TNT. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 989-1006, 2017.

Targeted Antioxidant, Catalase-SKL, Reduces Beta-Amyloid Toxicity in the Rat Brain.

Accumulation of beta-amyloid (Aβ) in the brain has been implicated as a major contributor to the cellular pathology and cognitive impairment observed in Alzheimer's disease. Beta-amyloid may exert its toxic effects by increasing reactive oxygen species and neuroinflammation in the brain. This study set out to investigate whether a genetically engineered derivative of the peroxisomal antioxidant enzyme catalase (CAT-SKL), is able to reduce the toxicity induced by intracerebroventricular injection of Aβ25-35 in the mature rat brain. Histopathological and immunohistochemical analyses were used to evaluate neuroinflammation, and neuronal loss. Spatial learning and reference memory was assessed using the Morris water maze. CAT-SKL treatment was able to reduce the pathology induced by Aβ25-35 toxicity by significantly decreasing microglia activation in the basal forebrain and thalamus, and reducing cholinergic loss in the basal forebrain. Aβ25-35 animals showed deficits in long-term reference memory in the Morris water maze, while Aβ25-35 animals treated with CAT-SKL did not demonstrate long-term memory impairments. This preclinical data provides support for the use of CAT-SKL in reducing neuroinflammation and long-term reference memory deficits induced by Aβ25-35.

Mechanism of impaired microtubule-dependent peroxisome trafficking and oxidative stress in SPAST-mutated cells from patients with Hereditary Spastic Paraplegia.

Hereditary spastic paraplegia (HSP) is an inherited neurological condition that leads to progressive spasticity and gait abnormalities. Adult-onset HSP is most commonly caused by mutations in SPAST, which encodes spastin a microtubule severing protein. In olfactory stem cell lines derived from patients carrying different SPAST mutations, we investigated microtubule-dependent peroxisome movement with time-lapse imaging and automated image analysis. The average speed of peroxisomes in patient-cells was slower, with fewer fast moving peroxisomes than in cells from healthy controls. This was not because of impairment of peroxisome-microtubule interactions because the time-dependent saltatory dynamics of movement of individual peroxisomes was unaffected in patient-cells. Our observations indicate that average peroxisome speeds are less in patient-cells because of the lower probability of individual peroxisome interactions with the reduced numbers of stable microtubules: peroxisome speeds in patient cells are restored by epothilone D, a tubulin-binding drug that increases the number of stable microtubules to control levels. Patient-cells were under increased oxidative stress and were more sensitive than control-cells to hydrogen peroxide, which is primarily metabolised by peroxisomal catalase. Epothilone D also ameliorated patient-cell sensitivity to hydrogen-peroxide. Our findings suggest a mechanism for neurodegeneration whereby SPAST mutations indirectly lead to impaired peroxisome transport and oxidative stress.

Novel insights into renal d-amino acid oxidase accumulation: propiverine changes DAAO localization and peroxisomal size in vivo

Chronic exposure to propiverine, a frequently prescribed pharmaceutical for treatment of overactive bladder and incontinence, provokes massive protein accumulation in the cytosol and nucleus of renal proximal tubule epithelial cells in rats. Previously, the accumulating protein was identified as D-amino acid oxidase (DAAO), a peroxisomal flavoenzyme expressed in kidney, liver and brain. The cellular mechanism of propiverine-induced DAAO accumulation, however, remains unexplained and poorly characterized. Therefore, to further increase the understanding of DAAO accumulation in rat kidney, this study aimed to characterize DAAO accumulations using differential immunofluorescent staining of rat kidney sections as well as in vitro binding analyses and proteasomal activity studies. We demonstrated that propiverine is neither a ligand of DAAO nor an inhibitor of the proteasome in vitro. However, propiverine treatment resulted in a significant decrease of peroxisomal size in rat proximal tubule epithelial cells. Moreover, peroxisomal catalase also accumulated in the cytosol and nuclei of propiverine-treated rats concurrently with DAAO. Taken together, our study indicates that propiverine treatment affects the trafficking and/or degradation of peroxisomal proteins such as DAAO and catalase by a so far unique and unknown mechanism.

Oxidative and Non-Oxidative Metabolomics of Ethanol.

It is well known that ethanol can cause significant morbidity and mortality, and much of the related toxic effects can be explained by its metabolic profile. This work performs a complete review of the metabolism of ethanol focusing on both major and minor metabolites. An exhaustive literature search was carried out using textual and structural queries for ethanol and related known metabolizing enzymes and metabolites. The main pathway of metabolism is catalyzed by cytosolic alcohol dehydrogenase, which exhibits multiple isoenzymes and genetic polymorphisms with clinical and forensic implications. Another two oxidative routes, the highly inducible CYP2E1 system and peroxisomal catalase may acquire relevance under specific circumstances. In addition to oxidative metabolism, ethanol also originates minor metabolites such as ethyl glucuronide, ethyl sulfate, ethyl phosphate, ethyl nitrite, phosphatidylethanol and fatty acid ethyl esters. These metabolites represent alternative biomarkers since they can be detected several hours or days after ethanol exposure. It is expected that knowing the metabolomics of ethanol may provide additional insights to better understand the toxicological effects and the variability of dose response.

Mechanisms of electron transfer between a styrylquinolinium dye and yeast in biofuel cell

In the present study, the influence of the recently synthesized styrylquinolinium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide (DANSQI) on the intracellular processes as well as the electrical outputs of Candida melibiosica 2491 yeast-based biofuel cell was investigated. The addition of nanomolar quantities of DANSQI to the yeast suspension results in an increase of the current outputs right after the startup of the biofuel cells, associated with an electrooxidation of the dye on the anode. After that, the formed cation radical of the dye penetrates the yeast cells, provoking a set of intracellular changes. Studies of the subcellular anolyte fractions show that 1μM dye increased the peroxisomal catalase activity 30-times (1.15±0.06Unit/mg protein) and over twice the mitochondrial cytochrome c oxidase activity (92±5Unit/mg protein). The results obtained by electrochemical and spectrophotometric analyses let to the supposition that the dye acts as subcellular shuttle, on account of its specific intramolecular charge transfer properties. The transition between its benzoid, quinolyl radical and ion forms and their putative role for the extracellular and intracellular charge transfer mechanisms are discussed.

Maladies peroxysomales

Peroxisomes are small intracellular organelles that catalyse key metabolic reactions such as the beta-oxidation of some straight-chain or branched-chain fatty acids and the alpha-oxidation of phytanic acid. These enzyme reactions produce hydrogen peroxide, which is subsequently neutralized by the peroxisomal catalase. Peroxisomes also metabolize glyoxylate to glycine, and catalyze the first steps of plasmalogen biosynthesis. There are more than a dozen inherited peroxisomal disorders in humans. These metabolic diseases are due to monogenic defects that affect either a single function (such as enzyme or a transporter) or more than two distinct functions because of the impairment of several aspects of peroxisome biogenesis. With the notable exception of X-linked adrenoleucodystrophy, these inborn disorders are transmitted as autosomal recessive traits. Their clinical presentation can be very heterogeneous, and include neonatal, infantile or adult forms. The present review describes the symptomatology of these genetic diseases, the underlying genetic and biochemical alterations, and summarizes their diagnostic approach.

A genetic framework for H2O2 induced cell death in Arabidopsis thaliana.

BackgroundTo survive in a changing environment plants constantly monitor their surroundings. In response to several stresses and during photorespiration plants use reactive oxygen species as signaling molecules. The Arabidopsis thaliana catalase2 (cat2) mutant lacks a peroxisomal catalase and under photorespiratory conditions accumulates H2O2, which leads to activation of cell death.MethodsA cat2 double mutant collection was generated through crossing and scored for cell death in different assays. Selected double mutants were further analyzed for photosynthetic performance and H2O2 accumulation.ResultsWe used a targeted mutant analysis with more than 50 cat2 double mutants to investigate the role of stress hormones and other defense regulators in H2O2-mediated cell death. Several transcription factors (AS1, MYB30, MYC2, WRKY70), cell death regulators (RCD1, DND1) and hormone regulators (AXR1, ERA1, SID2, EDS1, SGT1b) were essential for execution of cell death in cat2. Genetic loci required for cell death in cat2 was compared with regulators of cell death in spontaneous lesion mimic mutants and led to the identification of a core set of plant cell death regulators. Analysis of gene expression data from cat2 and plants undergoing cell death revealed similar gene expression profiles, further supporting the existence of a common program for regulation of plant cell death.ConclusionsOur results provide a genetic framework for further study on the role of H2O2 in regulation of cell death. The hormones salicylic acid, jasmonic acid and auxin, as well as their interaction, are crucial determinants of cell death regulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1964-8) contains supplementary material, which is available to authorized users.

PP37 - Discovery of novel photorespiratory players by forward chemical and genetic approaches

The high metabolic flux through photorespiration constitutes a significant part of the carbon cycle. Although the major enzymatic steps of the photorespiratory pathway are well characterized, little information is available on the functional significance of photorespiration beyond carbon recycling. Particularly important in this respect is the peroxisomal catalase activity which removes photorespiratory H 2 O 2 generated during the oxidation of glycolate to glyoxylate, thus maintaining the cellular redox homeostasis governing the perception, integration and execution of stress responses. We have previously performed a chemical screen that led to the identification of 34 small molecules that alleviate the negative effects of photorespiration in Arabidopsis thaliana mutants lacking peroxisomal catalase ( cat2 ). In parallel, we screened a mutagenized cat2 population and looked for second-site mutations that similarly attenuate the effects of photorespiratory conditions in cat2 plants. Currently, we characterize putative protein targets of some of the chemical hits and investigate the fine-tuning roles of the confirmed mutations on the photorespiratory phenotype of cat2 .

Subunits B'γ and B'ζ of protein phosphatase 2A regulate photo-oxidative stress responses and growth in Arabidopsis thaliana.

Plants survive periods of unfavourable conditions with the help of sensory mechanisms that respond to reactive oxygen species (ROS) as signalling molecules in different cellular compartments. We have previously demonstrated that protein phosphatase 2A (PP2A) impacts on organellar cross-talk and associated pathogenesis responses in Arabidopsis thaliana. This was evidenced by drastically enhanced pathogenesis responses and cell death in cat2 pp2a-b'γ double mutants, deficient in the main peroxisomal antioxidant enzyme CATALASE 2 and PP2A regulatory subunit B'γ (PP2A-B'γ). In the present paper, we explored the impacts of PP2A-B'γ and a highly similar regulatory subunit PP2A-B'ζ in growth regulation and light stress tolerance in Arabidopsis. PP2A-B'γ and PP2A-B'ζ display high promoter activities in rapidly growing tissues and are required for optimal growth under favourable conditions. Upon acclimation to a combination of high light, elevated temperature and reduced availability of water, however, pp2a-b'γζ double mutants grow similarly to the wild type and show enhanced tolerance against photo-oxidative stress. We conclude that by controlling ROS homeostasis and signalling, PP2A-B'γ and PP2A-B'ζ may direct acclimation strategies upon environmental perturbations, hence acting as important determinants of defence responses and light acclimation in plants.

Catalase therapy corrects oxidative stress-induced pathophysiology in incipient diabetic retinopathy.

Preclinical studies have highlighted retinal oxidative stress in the pathogenesis of diabetic retinopathy. We evaluated whether a treatment designed to enhance cellular catalase reduces oxidative stress in retinal cells cultured in high glucose and in diabetic mice corrects an imaging biomarker responsive to antioxidant therapy (manganese-enhanced magnetic resonance imaging [MEMRI]). Human retinal Müller and pigment epithelial cells were chronically exposed to normal or high glucose levels and treated with a cell-penetrating derivative of the peroxisomal enzyme catalase (called CAT-SKL). Hydrogen peroxide (H2O2) levels were measured using a quantitative fluorescence-based assay. For in vivo studies, streptozotocin (STZ)-induced diabetic C57Bl/6 mice were treated subcutaneously once a week for 3 to 4 months with CAT-SKL; untreated age-matched nondiabetic controls and untreated diabetic mice also were studied. MEMRI was used to analytically assess the efficacy of CAT-SKL treatment on diabetes-evoked oxidative stress-related pathophysiology in vivo. Similar analyses were performed with difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase. After catalase transduction, high glucose-induced peroxide production was significantly lowered in both human retinal cell lines. In diabetic mice in vivo, subnormal intraretinal uptake of manganese was significantly improved by catalase supplementation. In addition, in the peroxisome-rich liver of treated mice catalase enzyme activity increased and oxidative damage (as measured by lipid peroxidation) declined. On the other hand, DFMO was largely without effect in these in vitro or in vivo assays. This proof-of-concept study raises the possibility that augmentation of catalase is a therapy for treating the retinal oxidative stress associated with diabetic retinopathy.

Modulatory effects of Acanthopanax koreanum Nakai on oxidative stress induced by combination of alcohol and high‐fat diet in C57BL/6j mice.

Excess alcohol consumption is liked to a high risk of liver problem, which can develop into steatohepatitis and liver cirrhosis in modern society. A high‐fat (HF) diet can also lead to the progression of fatty liver. Therefore the role of alcohol as a risk factor for liver damage may be clearly demonstrated by a combination of both alcohol and HF diet. We tested this hypothesis by using Acanthopanax koreanum Nakai (AK) as a model compound. C57BL/6j mice (8‐week‐old; n=56) were randomly divided into seven groups for four weeks; normal control (NC), ethanol control (EC), EC + high fat diet (EF), EC + 1% AK (ECL), EC + 3% AK (ECH), EF + 1% AK (EFL), and EF + 3% AK (EFH). AK was provided in the diet and 50% (v/v) ethanol was provided by gavage. ADH had no significant difference among all groups. Hepatic ALDH activities were significantly increased in the EH compared with the NC, whereas the ECH showed a tendency of increase in ALDH activity compared with the EC. CYP2E1 was significantly increased in both the EC and the EF compared with the NC. ECH tended to decrease CYP2E1 protein expression compared with the EC and the EFL and EFH showed a tendency to decrease compared with the EF. Peroxisomal catalase (CAT) and glutathione reductase (GR) had a tendency to decrease in the EC; CAT and GR decreased significantly in the HF than in the NC. The AK treatment groups (ECH and EFH) showed a tendency to increase in CAT and GR. Taken together, the results support the hypothesis that combination of alcohol and high‐fat diet provide better animal model for testing the alcohol‐induced oxidative stress. Based on this animal model, the results suggest that AK administration in particularly at a high dose may have protective effects against hepatic injury via anti‐oxidative function.

Peroxisomal biogenesis in ischemic brain.

Peroxisomes are highly adaptable and dynamic organelles, adjusting their size, number, and enzyme composition to changing environmental and metabolic demands. We determined whether peroxisomes respond to ischemia, and whether peroxisomal biogenesis is an adaptive response to cerebral ischemia. Focal cerebral ischemia induced peroxisomal biogenesis in peri-infarct neurons, which was associated with a corresponding increase in peroxisomal antioxidant enzyme catalase. Peroxisomal biogenesis was also observed in primary cultured cortical neurons subjected to ischemic insult induced by oxygen-glucose deprivation (OGD). A catalase inhibitor increased OGD-induced neuronal death. Moreover, preventing peroxisomal proliferation by knocking down dynamin-related protein 1 (Drp1) exacerbated neuronal death induced by OGD, whereas enhancing peroxisomal biogenesis pharmacologically using a peroxisome proliferator-activated receptor-alpha agonist protected against neuronal death induced by OGD. This is the first documentation of ischemia-induced peroxisomal biogenesis in mammalian brain using a combined in vivo and in vitro approach, electron microscopy, high-resolution laser-scanning confocal microscopy, and super-resolution structured illumination microscopy. Our findings suggest that neurons respond to ischemic injury by increasing peroxisome biogenesis, which serves a protective function, likely mediated by enhanced antioxidant capacity of neurons.

Expression of turtle riboflavin-binding protein represses mitochondrial electron transport gene expression and promotes flowering in Arabidopsis.

BackgroundRecently we showed that de novo expression of a turtle riboflavin-binding protein (RfBP) in transgenic Arabidopsis increased H2O2 concentrations inside leaf cells, enhanced the expression of floral regulatory gene FD and floral meristem identity gene AP1 at the shoot apex, and induced early flowering. Here we report that RfBP-induced H2O2 presumably results from electron leakage at the mitochondrial electron transport chain (METC) and this source of H2O2 contributes to the early flowering phenotype.ResultsWhile enhanced expression of FD and AP1 at the shoot apex was correlated with early flowering, the foliar expression of 13 of 19 METC genes was repressed in RfBP-expressing (RfBP+) plants. Inside RfBP+ leaf cells, cytosolic H2O2 concentrations were increased possibly through electron leakage because similar responses were also induced by a known inducer of electron leakage from METC. Early flowering no longer occurred when the repression on METC genes was eliminated by RfBP gene silencing, which restored RfBP+ to wild type in levels of FD and AP1 expression, H2O2, and flavins. Flowering was delayed by the external riboflavin application, which brought gene expression and flavins back to the steady-state levels but only caused 55% reduction of H2O2 concentrations in RfBP+ plants. RfBP-repressed METC gene expression remedied the cytosolic H2O2 diminution by genetic disruption of transcription factor NFXLl and compensated for compromises in FD and AP1 expression and flowering time. By contrast, RfBP resembled a peroxisomal catalase mutation, which augments the cytosolic H2O2, to enhance FD and AP1 expression and induce early flowering.ConclusionsRfBP-repressed METC gene expression potentially causes electron leakage as one of cellular sources for the generation of H2O2 with the promoting effect on flowering. The repressive effect on METC gene expression is not the only way by which RfBP induces H2O2 and currently unappreciated factors may also function under RfBP+ background.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0381-5) contains supplementary material, which is available to authorized users.

Cytokinin oxidase/dehydrogenase overexpression modifies antioxidant defense against heat, drought and their combination in Nicotiana tabacum plants

Cytokinins (CKs) as well as the antioxidant enzyme system (AES) play important roles in plant stress responses. The expression and activity of antioxidant enzymes (AE) were determined in drought, heat and combination of both stresses, comparing the response of tobacco plants overexpressing the main cytokinin degrading enzyme, cytokinin oxidase/dehydrogenase, under the control of root-specific WRKY6 promoter (W6:CKX1 plants) or constitutive promoter (35S:CKX1 plants) and the corresponding wild-type (WT). Expression levels as well as activities of cytosolic ascorbate peroxidase, catalase 3, and cytosolic superoxide dismutase were low under optimal conditions and increased after heat and combined stress in all genotypes. Unlike catalase 3, two other peroxisomal enzymes, catalase 1 and catalase 2, were transcribed extensively under control conditions. Heat stress, in contrast to drought or combined stress, increased catalase 1 and reduced catalase 2 expression in WT and W6:CKX1 plants. In 35S:CKX1, catalase 1 expression was enhanced by heat or drought, but not under combined stress conditions. Mitochondrial superoxide dismutase expression was generally higher in 35S:CKX1 plants than in WT. Genes encoding for chloroplastic AEs, stromatal ascorbate peroxidase, thylakoidal ascorbate peroxidase and chloroplastic superoxide dismutase, were strongly transcribed under control conditions. All stresses down-regulated their expression in WT and W6:CKX1, whereas more stress-tolerant 35S:CKX1 plants maintained high expression during drought and heat. The achieved data show that the effect of down-regulation of CK levels on AES may be mediated by altered habit, resulting in improved stress tolerance, which is associated with diminished stress impact on photosynthesis, and changes in source/sink relations.

Spatial H2O2 Signaling Specificity: H2O2 from Chloroplasts and Peroxisomes Modulates the Plant Transcriptome Differentially

Hydrogen peroxide (H2O2) operates as a signaling molecule in eukaryotes, but the specificity of its signaling capacities remains largely unrevealed. Here, we analyzed whether a moderate production of H2O2 from two different plant cellular compartments has divergent effects on the plant transcriptome. Arabidopsis thaliana overexpressing glycolate oxidase in the chloroplast (Fahnenstich et al., 2008; Balazadeh et al., 2012) and plants deficient in peroxisomal catalase (Queval et al., 2007; Inzé et al., 2012) were grown under non-photorespiratory conditions and then transferred to photorespiratory conditions to foster the production of H2O2 in both organelles. We show that H2O2 originating in a specific organelle induces two types of responses: one that integrates signals independently from the subcellular site of H2O2 production and another that is dependent on the H2O2 production site. H2O2 produced in peroxisomes induces transcripts involved in protein repair responses, while H2O2 produced in chloroplasts induces early signaling responses, including transcription factors and biosynthetic genes involved in production of secondary signaling messengers. There is a significant bias towards the induction of genes involved in responses to wounding and pathogen attack by chloroplastic-produced H2O2, including indolic glucosinolates-, camalexin-, and stigmasterol-biosynthetic genes. These transcriptional responses were accompanied by the accumulation of 4-methoxy-indol-3-ylmethyl glucosinolate and stigmasterol.

Cytosolic H2O2 mediates hypertrophy, apoptosis, and decreased SERCA activity in mice with chronic hemodynamic overload

Oxidative stress in the myocardium plays an important role in the pathophysiology of hemodynamic overload. The mechanism by which reactive oxygen species (ROS) in the cardiac myocyte mediate myocardial failure in hemodynamic overload is not known. Accordingly, our goals were to test whether myocyte-specific overexpression of peroxisomal catalase (pCAT) that localizes in the sarcoplasm protects mice from hemodynamic overload-induced failure and prevents oxidation and inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), an important sarcoplasmic protein. Chronic hemodynamic overload was caused by ascending aortic constriction (AAC) for 12 wk in mice with myocyte-specific transgenic expression of pCAT. AAC caused left ventricular hypertrophy and failure associated with a generalized increase in myocardial oxidative stress and specific oxidative modifications of SERCA at cysteine 674 and tyrosine 294/5. pCAT overexpression ameliorated myocardial hypertrophy and apoptosis, decreased pathological remodeling, and prevented the progression to heart failure. Likewise, pCAT prevented oxidative modifications of SERCA and increased SERCA activity without changing SERCA expression. Thus cardiac myocyte-restricted expression of pCAT effectively ameliorated the structural and functional consequences of chronic hemodynamic overload and increased SERCA activity via a post-translational mechanism, most likely by decreasing inhibitory oxidative modifications. In pressure overload-induced heart failure cardiac myocyte cytosolic ROS play a pivotal role in mediating key pathophysiologic events including hypertrophy, apoptosis, and decreased SERCA activity.

Activation of auxin signalling counteracts photorespiratory H2O2-dependent cell death.

The high metabolic flux through photorespiration constitutes a significant part of the carbon cycle. Although the major enzymatic steps of the photorespiratory pathway are well characterized, little information is available on the functional significance of photorespiration beyond carbon recycling. Particularly important in this respect is the peroxisomal catalase activity which removes photorespiratory H2O2 generated during the oxidation of glycolate to glyoxylate, thus maintaining the cellular redox homeostasis governing the perception, integration and execution of stress responses. By performing a chemical screen, we identified 34 small molecules that alleviate the negative effects of photorespiration in Arabidopsis thaliana mutants lacking photorespiratory catalase (cat2). The chlorophyll fluorescence parameter photosystem II maximum efficiency (Fv′/Fm′) was used as a high-throughput readout. The most potent chemical that could rescue the photorespiratory phenotype of cat2 is a pro-auxin that contains a synthetic auxin-like substructure belonging to the phenoxy herbicide family, which can be released in planta. The naturally occurring indole-3-acetic acid (IAA) and other chemically distinct synthetic auxins also inhibited the photorespiratory-dependent cell death in cat2 mutants, implying a role for auxin signalling in stress tolerance.

Isolation of a Novel Peroxisomal Catalase Gene from Sugarcane, Which Is Responsive to Biotic and Abiotic Stresses

Catalase is an iron porphyrin enzyme, which serves as an efficient scavenger of reactive oxygen species (ROS) to avoid oxidative damage. In sugarcane, the enzymatic activity of catalase in a variety (Yacheng05–179) resistant to the smut pathogen Sporisorium scitamineum was always higher than that of the susceptible variety (Liucheng03–182), suggesting that catalase activity may have a positive correlation with smut resistance in sugarcane. To understand the function of catalase at the molecular level, a cDNA sequence of ScCAT1 (GenBank Accession No. KF664183), was isolated from sugarcane infected by S. scitamineum. ScCAT1 was predicted to encode 492 amino acid residues, and its deduced amino acid sequence shared a high degree of homology with other plant catalases. Enhanced growth of ScCAT1 in recombinant Escherichia coli Rosetta cells under the stresses of CuCl2, CdCl2 and NaCl indicated its high tolerance. Q-PCR results showed that ScCAT1 was expressed at relatively high levels in the bud, whereas expression was moderate in stem epidermis and stem pith. Different kinds of stresses, including S. scitamineum challenge, plant hormones (SA, MeJA and ABA) treatments, oxidative (H2O2) stress, heavy metal (CuCl2) and hyper-osmotic (PEG and NaCl) stresses, triggered a significant induction of ScCAT1. The ScCAT1 protein appeared to localize in plasma membrane and cytoplasm. Furthermore, histochemical assays using DAB and trypan blue staining, as well as conductivity measurement, indicated that ScCAT1 may confer the sugarcane immunity. In conclusion, the positive response of ScCAT1 to biotic and abiotic stresses suggests that ScCAT1 is involved in protection of sugarcane against reactive oxidant-related environmental stimuli.