Extracellular superoxide dismutase (EC-SOD) plays an important role in maintaining normal redox homeostasis in the lung. It is expressed at very high levels in pulmonary fibroblasts, alveolar type II epithelial cells and smooth muscle cells. The molecular mechanism(s) governing this cell-specific expression of EC-SOD are mostly unknown. In our previous studies we showed that EC-SOD cell specific expression was not attributed to differential transcriptional regulation, suggesting that other, possibly epigenetic, mechanisms are involved in regulation of its expression. In this paper, we found high levels of promoter methylation in A549 cells and correspondingly low levels of methylation in MRC5 cells. Inhibition of DNA methyltransferase activity by 5-azacytidine in A549 cells reactivated EC-SOD transcription (2.75±0.16 fold, p<0.001) demonstrating the importance of methylation in repression of EC-SOD expression. Furthermore, methylation of cytosines in the promoter markedly decreased Sp1/Sp3 driven promoter activity to 30.09±2.85% (p<0.001) compare to unmethylated promoter. This attenuation of transcription in the promoter-reporter construct was, at least in part, attributed to the binding of methyl-binding protein MeCP2 in the insect cells. However, no binding of MeCP2 or MBD2 proteins to EC-SOD promoter was detected in mammalian cells in vivo. We also found marked differences in the chromatin organization of the EC-SOD promoter between these two cell lines, further supporting the important role epigenetic modifications play in the regulation of EC-SOD expression.
reactive oxygen species; transcription; epigenetic regulation; DNA methylation; methyl-binding proteins; lung; chromatin organization
Prior studies indicate that superoxide (O2•−) is important in modulation of blood pressure, but have not specifically identified the cell types or organs involved. We created mice with loxP sites flanking the extracellular superoxide dismutase (SOD3) gene. These mice were crossed with mice expressing inducible Cre-recombinase driven by the smooth muscle myosin heavy chain promoter allowing tissue specific deletion of SOD3. Deletion of SOD3 increased vascular O2•− and reduced vascular NO levels as detected by ESR. Despite these changes in NO and O2•−, we did not observe increases in vascular inflammation caused by angiotensin II. Moreover, deletion of vascular SOD3 did not augment hypertension in response to angiotensin II. In additional studies, we also deleted SOD3 from the circumventricular organs by intracerebroventricular injection of an adenovirus encoding Cre-recombinase. While this raised blood pressure and augmented the hypertension caused by angiotensin II, these responses were not further increased by vascular deletion of SOD3. These data suggests that the extracellular superoxide dismutase in vascular smooth muscle is not involved in the genesis of angiotensin II-induced hypertension and further emphasize the role of central SOD3 in modulation of blood pressure.
Superoxide dismutase; blood pressure; inflammation; vasculature; central nervous system
Exposure of newborn calves to chronic hypoxia causes pulmonary artery (PA) hypertension and remodeling. Previous studies showed that the redox-sensitive transcription factor, early growth response-1 (Egr-1), is upregulated in the PA of chronically hypoxic calves and regulates cell proliferation. Furthermore, we established in mice a correlation between hypoxic induction of Egr-1 and reduced activity of extracellular superoxide dismutase (EC-SOD), an antioxidant that scavenges extracellular superoxide. We now hypothesize that loss of EC-SOD in chronically hypoxic calves leads to extracellular superoxide-mediated upregulation of Egr-1. To validate our hypothesis and identify the signaling pathways involved, we utilized PA tissue from normoxic and chronically hypoxic calves and cultured calf and human PA smooth muscle cells (PASMC). Total SOD activity was low in the PA tissue, and only the extracellular SOD component decreased with hypoxia. PA tissue of hypoxic calves showed increased oxidative stress and increased Egr-1 mRNA. To mimic the in vivo hypoxia-induced extracellular oxidant imbalance, cultured calf PASMC were treated with xanthine oxidase (XO), which generates extracellular superoxide and hydrogen peroxide. We found that 1) XO increased Egr-1 mRNA and protein, 2) XO induced the phosphorylation of ERK1/2 and, 3) pretreatment with an ERK1/2 inhibitor prevented induction of Egr-1 by XO. siRNA knock-down of EC-SOD in human PASMC also upregulated Egr-1 mRNA and protein, activated ERK1/2, and enhanced SMC proliferation and reduced apoptosis. We conclude that an oxidant/antioxidant imbalance arising from loss of EC-SOD in the PA with chronic hypoxia induces Egr-1 via activation of ERK1/2 and contributes to pulmonary vascular remodeling.
Superoxide dismutases (SOD) convert superoxide radicals into less damaging hydrogen peroxide. The opportunistic human pathogen Candida albicans is known to express CuZnSOD (SOD1) and MnSOD (SOD3) in the cytosol and MnSOD (SOD2) in the mitochondria. We identified three additional CuZn-containing superoxide dismutases, SOD4, SOD5, and SOD6, within the sequence of the C. albicans genome. The transcription of SOD5 was up-regulated during the yeast to hyphal transition of C. albicans, and SOD5 was induced when C. albicans cells were challenged with osmotic or with oxidative stresses. SOD5 transcription was also increased when cells were grown on nonfermentable substrates as the only carbon source. The Rim101p transcription factor was required for all inductions observed, whereas the Efg1p transcription factor was specifically needed for serum-modulated expression. Deletion of SOD5 produced a viable mutant strain that showed sensitivity to hydrogen peroxide when cells were grown in nutrient-limited conditions. Sod5p was found to be necessary for the virulence of C. albicans in a mouse model of infection. However, the sod5 mutant strain showed the same resistance to macrophage attack as its parental strain, suggesting that the loss of virulence in not due to an increased sensitivity to macrophage attack.
Extracellular superoxide dismutase (EC-SOD, or SOD3) is the major extracellular antioxidant enzyme in the lung. To study the biologic role of EC-SOD in hyperoxic-induced pulmonary disease, we created transgenic (Tg) mice that specifically target overexpression of human EC-SOD (hEC-SOD) to alveolar type II and nonciliated bronchial epithelial cells. Mice heterozygous for the hEC-SOD transgene showed threefold higher EC-SOD levels in the lung compared with wild-type (Wt) littermate controls. A significant amount of hEC-SOD was present in the epithelial lining fluid layer. Both Tg and Wt mice were exposed to normobaric hyperoxia (>99% oxygen) for 48, 72, and 84 hours. Mice overexpressing hEC-SOD in the airways attenuated the hyperoxic lung injury response, showed decreased morphologic evidence of lung damage, had reduced numbers of recruited inflammatory cells, and had a reduced lung wet/dry ratio. To evaluate whether reduced numbers of neutrophil infiltration were directly responsible for the tolerance to oxygen toxicity observed in the Tg mice, we made Wt and Tg mice neutropenic using anti-neutrophil antibodies and subsequently exposed them to 72 hours of hyperoxia. Both Wt and Tg neutrophil-depleted (ND) mice have less severe lung injury compared with non-ND animals, thus providing direct evidence that neutrophils recruited to the lung during hyperoxia play a distinct role in the resultant acute lung injury. We conclude that oxidative and inflammatory processes in the extracellular lung compartment contribute to hyperoxic-induced lung damage and that overexpression of hEC-SOD mediates a protective response to hyperoxia, at least in part, by attenuating the neutrophil inflammatory response.
We previously demonstrated that superoxide and H2O2 promote pulmonary arterial vasoconstriction in a lamb model of persistent pulmonary hypertension of the newborn (PPHN). Because extracellular superoxide dismutase (ecSOD) augments vasodilation, we hypothesized that H2O2-mediated ecSOD inactivation contributes to pulmonary arterial vasoconstriction in PPHN lambs. ecSOD activity was decreased in pulmonary arterial smooth muscle cells (PASMCs) isolated from PPHN lambs relative to controls. Exposure to 95% O2 to mimic hyperoxic ventilation reduced ecSOD activity in control PASMCs. In both cases, these events were associated with increased protein thiol oxidation, as detected by the redox sensor roGFP. Accordingly, exogenous H2O2 decreased ecSOD activity in control PASMCs, and PEG-catalase restored ecSOD activity in PPHN PASMCs. In intact animal studies, ecSOD activity was decreased in fetal PPHN lambs, and in PPHN lambs ventilated with 100% O2 relative to controls. In ventilated PPHN lambs, administration of a single dose of intratracheal PEG-catalase enhanced ecSOD activity, reduced superoxide levels, and improved oxygenation. We propose that H2O2 generated by PPHN and hyperoxia inactivates ecSOD, and intratracheal catalase enhances enzyme function. The associated decrease in extracellular superoxide augments vasodilation, suggesting that H2O2 scavengers may represent an effective therapy in the clinical management of PPHN. Antioxid. Redox Signal. 15, 1497–1506.
The molecular mechanisms that govern the transcription of human extracellular superoxide dismutase (EC-SOD), the major extracellular antioxidant enzyme, are largely unknown. To elucidate the mechanisms involved in human EC-SOD gene regulation and expression, we localized multiple transcription start sites to a finite region located 3.9 kb upstream of the ATG initiation codon. Within this segment, we subcloned a 2.7-kb fragment upstream of a luciferase reporter gene; the resulting construct exhibited strong in vivo promoter activity in two lung-derived cell lines. Deletion analysis of the EC-SOD 5′-flanking sequences identified a minimal 0.3-kb region that had strong basal promoter activity. Computer sequence analysis revealed a putative Sp1-like binding site within the EC-SOD proximal promoter region that lacked a TATA-box and showed a high frequency of GC nucleotides. Binding of Sp1 and Sp3 transcription factors to the EC-SOD promoter was confirmed by DNase I footprint analysis, electophoretic mobility shift assay, and competition and supershift assays. Cotransfection of the EC-SOD promoter–luciferase reporter constructs with plasmids encoding Sp1 and Sp3 into Sp-deficient insect SL2 cells showed strong activation of luciferase gene expression. The occupancy of the EC-SOD promoter by Sp1/Sp3 and RNA polymerase II in vivo was determined by chromatin immunoprecipitation assay and correlated well with levels of EC-SOD expression in lung epithelial cells (A549) and pulmonary fibroblasts (MRC5). Collectively, our results demonstrate the important role Sp1 and Sp3 plays in regulating the expression of human EC-SOD in the lung.
extracellular superoxide dismutase; promoter; transcription; Sp1 gene family; antioxidant
Extracellular superoxide dismutase (EcSOD) is an important superoxide scavenger in the lung where its loss, sequence variation, or abnormal expression contributes to lung diseases; however, the role of EcSOD in lung cancer has yet to be studied. We hypothesized that EcSOD loss could affect malignant progression in lung, and could be either genetic or epigenetic in nature. To test this we analyzed EcSOD expression, gene copy number, promoter methylation and chromatin accessibility in normal lung and carcinoma cells. We found that normal airway epithelial cells expressed abundant EcSOD and had an unmethylated promoter, whereas EcSOD-negative lung cancer cells displayed aberrant promoter hypermethylation and decreased chromatin accessibility. 5-aza-dC induced EcSOD suggesting that cytosine methylation was causal, in part, to silencing. In 48/50 lung tumors EcSOD mRNA was significantly lower as early as stage I, and the EcSOD promoter was hypermethylated in 8/10 (80%) adenocarcinomas compared to 0/5 normal lung samples. In addition, 20% of the tumors showed LOH of EcSOD. Re-expression of EcSOD attenuated the malignant phenotype of lung carcinoma cells by significantly decreasing invasion and survival. Finally, EcSOD decreased heparanase and syndecan-1 mRNAs in part by reducing NF-κB. By contrast, MnSOD and CuZnSOD showed no significant changes in lung tumors and had no effect on heparanase expression. Taken together, the loss of EcSOD expression is unique among the superoxide dismutases in lung cancer and is the result of EcSOD promoter methylation and LOH, suggesting that its early loss may contribute to ECM remodeling and malignant progression.
SOD3; EcSOD; Heparanase; Syndecan-1; NF-κB; DNA methylation
Excessive proliferation and impaired apoptosis of pulmonary artery smooth muscle cells (PASMC) contributes to vascular obstruction in patients and fawn-hooded rats (FHR) with pulmonary arterial hypertension (PAH). Expression and activity of mitochondrial superoxide dismutase-2 (SOD2), the major generator of H2O2, is known to be reduced in PAH; however, the mechanism and therapeutic relevance of this is unknown.
Methods and Results
SOD2 expression in PASMC is decreased in PAH patients and FHR with PAH. FHR PASMC have higher proliferation and lower apoptosis rates than Sprague-Dawley PASMC. Moreover, FHR PASMC have hyperpolarized mitochondria, low H2O2 production and a reduced cytoplasmic and mitochondrial redox state. Administration of SOD2 siRNA to normal PASMC recapitulates the FHR-PAH phenotype, hyperpolarizing mitochondria, decreasing H2O2 and inhibiting caspase activity. Conversely, SOD2 over-expression in FHR PASMC, or therapy with the SOD-mimetic MnTBAP, reverses the hyperproliferative PAH phenotype. Importantly, SOD-mimetic therapy regresses PAH in vivo. Investigation of the SOD2 gene revealed no mutation, suggesting a possible epigenetic dysregulation. Genomic bisulfite sequencing demonstrates selective hypermethylation of a CpG island in an enhancer region of intron 2 and another in the promoter. Differential methylation occurs selectively in PA versus aortic SMC and is reversed by the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, restoring both SOD2 expression and the proliferation/apoptosis ratio. The expression of the enzymes that mediate gene methylation, DNA methyltransferases 1 and 3B, is upregulated in FHR lungs.
Tissue-specific, epigenetic SOD2 deficiency initiates and sustains a heritable form of PAH by impairing redox signaling and creating a proliferative, apoptosis-resistant PASMC. SOD augmentation regresses experimental PAH. The discovery of an epigenetic component to PAH may offer new therapeutic targets.
Pulmonary arterial hypertension; Voltage-gated potassium channels (Kv1.5); Hypoxia-inducible factor-1α (HIF-1α); Epigenetic gene methylation; DNA methyltransferase
Bacillus subtilis was found to possess one detectable superoxide dismutase (Sod) in both vegetative cells and spores. The Sod activity in vegetative cells was maximal at stationary phase. Manganese was necessary to sustain Sod activity at stationary phase, but paraquat, a superoxide generator, did not induce the expression of Sod. The specific activity of purified Sod was approximately 2,600 U/mg of protein, and the enzyme was a homodimer protein with a molecular mass of approximately 25,000 per monomer. The gene encoding Sod, designated sodA, was cloned by the combination of several PCR methods and the Southern hybridization method. DNA sequence analysis revealed the presence of one open reading frame consisting of 606 bp. Several putative promoter sites were located in the upstream region of sodA. The deduced amino acid sequence showed high homology with other bacterial manganese Sods. Conserved regions in bacterial manganese Sod could also be seen. The phenotype of double mutant Escherichia coli sodA sodB, which could not grow in minimal medium without supplemental amino acids, was complemented by the expression of B. subtilis sodA.
The extracellular matrix is a complex system that regulates cell function within a tissue. The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is bound to the matrix and previous studies show that a lack of EC-SOD results in increased cardiac injury, fibrosis, and loss of cardiac function. This study tests the hypothesis that EC-SOD protects against cardiac fibrosis mechanistically by limiting oxidative stress and oxidant-induced shedding of syndecan-1 in the extracellular matrix.
Wild type and EC-SOD null mice were treated with a single dose of doxorubicin, 15 mg/kg, and evaluated on day 15. Serum and left ventricle tissue were collected for biochemical assays, including western blot, mRNA expression, and immunohistochemical staining for syndecan-1.
The loss of EC-SOD and doxorubicin-induced oxidative injury lead to increases in shed syndecan-1 in the serum, which originates from the endothelium of the vasculature. The shed syndecan-1 ectodomain induces proliferation of primary mouse cardiac fibroblasts.
This study suggests that one mechanism through which EC-SOD protects the heart against cardiac fibrosis is by preventing oxidative shedding of cardiovascular syndecan-1 and its subsequent induction of fibroblast proliferation. This study provides potential new targets for understanding and altering fibrosis progression in the heart.
Extracellular Superoxide dismutase; doxorubicin; syndecan-1; fibrosis
Pulmonary vascular remodeling and oxidative stress are common to many adult lung diseases. However, little is known about the relevance of lung mesenchymal stem cells (MSCs) in these processes. We tested the hypothesis that dysfunctional lung MSCs directly participate in remodeling of the microcirculation. We employed a genetic model to deplete extracellular superoxide dismutase (EC-SOD) in lung MSCs coupled with lineage tracing analysis. We crossed floxpsod3 and mT/mG reporter mice to a strain expressing Cre recombinase under the control of the ABCG2 promoter. We demonstrated In vivo that depletion of EC-SOD in lung MSCs resulted in their contribution to microvascular remodeling in the smooth muscle actin positive layer. We further characterized lung MSCs to be multipotent vascular precursors, capable of myofibroblast, endothelial and pericyte differentiation in vitro. EC-SOD deficiency in cultured lung MSCs accelerated proliferation and apoptosis, restricted colony-forming ability, multilineage differentiation potential and promoted the transition to a contractile phenotype. Further studies correlated cell dysfunction to alterations in canonical Wnt/β-catenin signaling, which were more evident under conditions of oxidative stress. Our data establish that lung MSCs are a multipotent vascular precursor population, a population which has the capacity to participate in vascular remodeling and their function is likely regulated in part by the Wnt/β-catenin signaling pathway. These studies highlight an important role for microenviromental regulation of multipotent MSC function as well as their potential to contribute to tissue remodeling.
endothelial cell; extracellular superoxide dismutase; myofibroblast; niche; pericytes; pulmonary arterial hypertension; resident lung mesenchymal stem cells
Superoxide anion is elevated during neointima development and is essential for neointimal vascular smooth muscle cell (VSMC) proliferation. However, little is known about the role of manganese superoxide dismutase (MnSOD, SOD2) in the neointima formation following vascular injury. SOD2 in the mitochondria plays an important role in cellular defense against oxidative damage. Because of its subcellular localization, SOD2 is considered the first line of defense against oxidative stress and plays a central role in metabolizing superoxide. Because mitochondria are the most important sources of superoxide anion, we speculated that SOD2 may have therapeutic benefits in preventing vascular remodeling. In this study, we used a rat carotid artery balloon-injury model and an adenoviral gene delivery approach to test the hypothesis that SOD2 suppresses vascular lesion formation. SOD2 was activated along with the progression of neointima formation in balloon-injured rat carotid arteries. Depletion of SOD2 by RNA interference markedly promoted the lesion formation, whereas SOD2 overexpression suppressed the injury-induced neointima formation via attenuation of migration and proliferation of VSMCs. SOD2 exerts its inhibitory effect on VSMC migration induced by angiotensin II by scavenging superoxide anion and suppressing the phosphorylation of Akt. Our data indicate that SOD2 is a negative modulator of vascular lesion formation after injury. Therefore, SOD2 augmentation may be a promising therapeutic strategy for the prevention of lesion formation in proliferative vascular diseases such as restenosis.
Manganese superoxide dismutase; Oxidative stress; Neointima; Migration; Proliferation; Vascular smooth muscle cells; Signal transduction; Free radicals
Normal cells require adhesion to extracellular matrix for survival. Cell detachment causes a drastic increase in reactive oxygen species (ROS) that promotes anoikis. In the present study, we observed that upon detachment from matrix, human mammary epithelial cells strongly upregulate manganese superoxide dismutase (MnSOD, or SOD2), a principal mitochondrial antioxidant enzyme that detoxifies ROS through dismutation of superoxide. Induction of MnSOD by cell detachment is dependent on the NFκB transcription factor. Detachment of mammary epithelial cells potently increases mitochondrial superoxide levels, which are further elevated by depletion of MnSOD in suspended cells. Consequently, cells depleted of MnSOD are hypersensitive to matrix detachment and exhibit increased anoikis. These results suggest that detachment-induced MnSOD counters mitochondrial superoxide accumulation and confers anoikis resistance. Taken together with our previous finding that detached cells evade excessive ROS production by attenuating oxidative metabolism of glucose, we conclude that mammary epithelial cells coordinate their responses to detachment through increasing MnSOD and decreasing ROS generation from mitochondrial glucose oxidation, thereby mitigating anoikis. Anoikis is a barrier to tumor metastasis. Indeed, MnSOD expression is elevated in human breast cancer metastases compared with primary tumors. Expression of MnSOD correlates with histologic tumor grades in human cancer and contributes to cancer cell's resistance to anoikis. Our study suggests that inhibition of ROS detoxification coupled with stimulation of glucose oxidative metabolism may be an efficient strategy to enhance anoikis and block metastasis.
anoikis; ROS; MnSOD; NFκB; metastasis; NRF2
Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.
The bioactivity of endothelium-derived nitric oxide (NO) reflects its rates of production and of inactivation by superoxide (O2•–), a reactive species dismutated by extracellular superoxide dismutase (ecSOD). We have now examined the complementary hypothesis, namely that NO modulates ecSOD expression. The NO donor DETA-NO increased ecSOD expression in a time- and dose-dependent manner in human aortic smooth muscle cells. This effect was prevented by the guanylate cyclase inhibitor ODQ and by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMP. Expression of ecSOD was also increased by 8-bromo-cGMP, but not by 8-bromo-cAMP. Interestingly, the effect of NO on ecSOD expression was prevented by inhibition of the MAP kinase p38 but not of the MAP kinase kinase p42/44, suggesting that NO modulates ecSOD expression via cGMP/PKG and p38MAP kinase–dependent pathways, but not through p42/44MAP kinase. In aortas from mice lacking the endothelial nitric oxide synthase (eNOS), ecSOD was reduced more than twofold compared to controls. Treadmill exercise training increased eNOS and ecSOD expression in wild-type mice but had no effect on ecSOD expression in mice lacking eNOS, suggesting that this effect of exercise is meditated by endothelium-derived NO. Upregulation of ecSOD expression by NO may represent an important feed-forward mechanism whereby endothelial NO stimulates ecSOD expression in adjacent smooth muscle cells, thus preventing O2•–-mediated degradation of NO as it traverses between the two cell types.
Delivery of recombinant superoxide dismutase to lung is limited by its short half life and poor tissue penetration. We hypothesized that a chimeric protein, SOD2/3, containing the enzymatic domain of manganese superoxide dismutase (SOD2) and the heparan binding domain of extracellular superoxide dismutase (SOD3) would allow for the delivery of more sustained lung and pulmonary vascular antioxidant activity compared to SOD2. We administered SOD2/3 to rats by intratracheal, (IT) intraperitoneal (IP), or intravenous (IV) routes and evaluated the presence, localization and activity of lung SOD2/3 1 day later using Western blot, immunohistochemistry and SOD activity gel. The effect of IT SOD2/3 on the pulmonary and systemic circulation was studied in vivo in chronically catheterized rats exposed to acute hypoxia. Active SOD2/3 was detected in lung 1 day following IT administration but not detected following IP or IV SOD2/3 administration or IT SOD2. The physiologic response to acute hypoxia, vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation, was enhanced in rats treated 1 day earlier with IT SOD2/3. These findings indicate that IT administration of SOD2/3 effectively delivers sustained enzyme activity to the lung as well as pulmonary circulation and has a longer tissue half-life compared to native SOD2. Further testing in models of chronic lung or pulmonary vascular diseases mediated by excess superoxide should consider the longer tissue half-life of SOD2/3 as well as its potential systemic vascular effects.
superoxide dismutase; acute hypoxic pulmonary vasoconstriction; SOD2/3
Oxidative stress is proposed as an important factor in osteoarthritis (OA). We therefore investigated the expression of the three superoxide dismutase (SOD) antioxidant enzymes in OA.
SOD expression was determined by real-time polymerase chain reaction and immunohistochemistry using human femoral head cartilage. SOD2 expression in Dunkin Hartley guinea pig knee articular cartilage was determined by immunohistochemistry. The DNA methylation status of the SOD2 promoter was determined using bisulfite sequencing. RNA interference was used to determine the consequence of SOD2 depletion on the levels of reactive oxygen species (ROS) using MitoSOX™ and collagenases, matrix metalloproteinase 1 (MMP-1) and MMP-13, gene expression.
All three SOD were abundantly expressed in human cartilage but were markedly down-regulated in end-stage OA cartilage, especially SOD2. In the Dunkin Hartley guinea pig spontaneous OA model SOD2 expression was decreased in the medial tibial chondyle cartilage prior to, and following, the development of OA-like lesions. The SOD2 promoter had significant DNA methylation alterations in OA cartilage. Depletion of SOD2 in chondrocytes gave an increase in ROS but a decrease in collagenase expression.
This is the first comprehensive expression profile of all SOD genes in cartilage and importantly, using an animal model, we show that a reduction in SOD2 is associated with the earliest stages of OA. We found that a decrease in SOD2 associates with an increase in ROS and but a reduction of collagenase gene expression, demonstrating the complexities of ROS function.
Osteoarthritis; chondrocytes; superoxide dismutase; gene expression
Studies have demonstrated that increased oxidative stress contributes to the pathogenesis and the development of pulmonary artery hypertension (PAH). Extracellular superoxide dismutase (SOD3) is essential for removing extracellular superoxide anions and it is highly expressed in lung tissue. However, it is not clear whether endogenous SOD3 can influence the development of PAH. Here we examined the effect of SOD3 knockout on hypoxia-induced PAH in mice and a loss-of-function SOD3 gene mutation (SOD3E124D) on monocrotaline (40 mg/kg)-induced PAH in rats. SOD3 knockout significantly exacerbated 2 weeks hypoxia-induced right ventricular (RV) pressure and RV hypertrophy, while RV pressure in SOD3 KO mice under normoxic conditions is similar to wild type controls. In untreated control rats at age of 8 weeks, there was no significant difference between wild type and SOD3E124D rats in RV pressure and the ratio of RV weight to left ventricular weight (0.25±0.02 in wild type rats vs. 0.25±0.01 in SOD3E124D rats). However, monocrotaline caused significantly greater increases of RV pressure in SOD3E124D rats (48.6±1.8 mmHg in wild type vs. 57.5±3.1 mmHg in SOD3E124D rats), of the ratio of RV weight to left ventricular weight (0.41±0.01 vs. 0.50±0.09, p<0.05), and of the percentage of fully muscularized small arterioles in SOD3E124D rats (55.2±2.3 % vs. 69.9 ±2.6 %, p<0.05). Together, these findings indicate that the endogenous SOD3 has no role in the development of PAH under control conditions, but plays an important role in protecting the lung from the development of PAH under stress conditions.
pulmonary artery hypertension; right ventricular hypertrophy; oxidative stress; extracellular SOD
Extracellular superoxide dismutase (EC-SOD) is expressed at high levels in lungs. EC-SOD has a polycationic matrix-binding domain that binds to polyanionic constituents in the matrix. Previous studies indicate that EC-SOD protects the lung in both bleomycin- and asbestos-induced models of pulmonary fibrosis. Although the mechanism of EC-SOD protection is not fully understood, these studies indicate that EC-SOD plays an important role in regulating inflammatory responses to pulmonary injury. Hyaluronan is a polyanionic high molecular mass polysaccharide found in the extracellular matrix that is sensitive to oxidant-mediated fragmentation. Recent studies found that elevated levels of low molecular mass hyaluronan are associated with inflammatory conditions. We hypothesize that EC-SOD may inhibit pulmonary inflammation in part by preventing superoxide-mediated fragmentation of hyaluronan to low molecular mass fragments. We found that EC-SOD directly binds to hyaluronan and significantly inhibits oxidant-induced degradation of this glycosaminoglycan. In vitro human polymorphic neutrophil chemotaxis studies indicate that oxidative fragmentation of hyaluronan results in polymorphic neutrophil chemotaxis and that EC-SOD can completely prevent this response. Intratracheal injection of crocidolite asbestos in mice leads to pulmonary inflammation and injury that is enhanced in EC-SOD knock-out mice. Notably, hyaluronan levels are increased in the bronchoalveolar lavage fluid after asbestos-induced pulmonary injury, and this response is markedly enhanced in EC-SOD knock-out mice. These data indicate that inhibition of oxidative hyaluronan fragmentation probably represents one mechanism by which EC-SOD inhibits inflammation in response to lung injury.
Human extracellular superoxide dismutase (EC-SOD) is involved in the defence against oxidative stress induced by the superoxide radical. The protein is a homotetramer stabilised by hydrophobic interactions within the N-terminal region. During the purification of EC-SOD from human aorta, we noticed that material with high affinity for heparin–Sepharose formed not only a tetramer but also an octamer. Analysis of the thermodynamic stability of the octamer suggested that the C-terminal region is involved in formation of the quaternary structure. In addition, we show that the octamer is composed of both aEC-SOD and iEC-SOD folding variants. The presence of the EC-SOD octamer with high affinity may represent a way to influence the local concentration of EC-SOD to protect tissues specifically sensitive to oxidative damage.
Superoxide dismutase; Quaternary structure; Tissue distribution; Oxidative stress
Many breast cancer cells typically exhibit lower expression of manganese superoxide dismutase (MnSOD) compared to the normal cells from which they arise. This decrease can often be attributed to a defect in the transcription of SOD2, the gene encoding MnSOD; however, the mechanism responsible for this change remains unclear. Here, we describe how altered histone modifications and a repressive chromatin structure constitute an epigenetic process to down regulate SOD2 in human breast carcinoma cell lines. Utilizing chromatin immunoprecipitation (ChIP) we observed decreased levels of dimethyl H3K4 and acetylated H3K9 at key regulatory elements of the SOD2 gene. Consistent with these results, we show that loss of these histone modifications creates a repressive chromatin structure at SOD2. Transcription factor ChIP experiments revealed that this repressive chromatin structure influences the binding of SP-1, AP-1, and NFκB to SOD2 regulatory cis-elements in vivo. Lastly, we show that treatment with the histone deacetylase inhibitors trichostatin A and sodium butyrate can reactivate SOD2 expression in breast cancer cell lines. Taken together, these results indicate that epigenetic silencing of SOD2 could be facilitated by changes in histone modifications and represent one mechanism leading to the altered expression of MnSOD observed in many breast cancers.
methylation; chromatin; mammary; carcinoma; antioxidant
Tumour suppressor SIRT3 deacetylates and activates manganese superoxide dismutase to scavenge ROS
Mitochondria manganese superoxide dismutase (SOD2) is a major antioxidant enzyme associated with several diseases. This study shows that SOD2 is inhibited by acetylation and activated by SIRT3-mediated deacetylation in response to reactive oxygen species (ROS).
Mitochondria manganese superoxide dismutase (SOD2) is an important antioxidant enzyme, deficiency of which is associated with various human diseases. The known primary regulation of SOD2 is through transcriptional activation. Here, we report that SOD2 is acetylated at Lys 68 and that this acetylation decreases SOD2 activity. Mitochondrial deacetylase SIRT3 binds to, deacetylates and activates SOD2. Increase of reactive oxygen species (ROS) levels stimulates SIRT3 transcription, leading to SOD2 deacetylation and activation. SOD2-mediated ROS reduction is synergistically increased by SIRT3 co-expression, but is cancelled by SIRT3 depletion. These results reveal a new post-translational regulation of SOD2 by means of acetylation and SIRT3-dependent deacetylation in response to oxidative stress.
acetylation; ROS; SIRT3; SOD2
Extracellular superoxide dismutase (SOD3), a secretory copper-containing antioxidant enzyme, plays an important role in various oxidative stress-dependent cardiovascular diseases. Although cofactor copper is required for SOD3 activity, it remains unknown whether it can regulate SOD3 transcription. We previously demonstrated that SOD3 activity requires the copper chaperone Antioxidant-1 (Atox1) involved in copper delivery to SOD3 at the trans-Golgi network (TGN). Here we show that copper treatment in mouse fibroblasts significantly increases mRNA and protein levels of SOD3, but not SOD1, which is abolished in Atox1-deficient cells. Copper promotes Atox1 translocation to the nucleus. Promoter deletion analysis identifies copper- and Atox1-response element (RE) at the SOD3 promoter. Gel shift and ChIP assays reveal that Atox1 directly binds to the Atox1-RE in a copper-dependent manner in vitro and in vivo. Adenovirus-mediated re-expression in Atox1-/- cells with nucleus-targeted Atox1 (Atox1-NLS), but not TGN-targeted Atox1 (Atox1-TGN), increases SOD3 transcription without affecting SOD3 activity. Importantly, re-expression of both Atox1-NLS and Atox1-TGN together, but not either alone, in Atox1-/- cells increases SOD3 activity. SOD3 transcription is positively regulated by copper through transcription factor function of Atox1, while full activity of SOD3 requires both copper chaperone and transcription factor function of Atox1. Thus, Atox1 is a potential therapeutic target for oxidant stress-dependent cardiovascular disease.
Antioxidant-1; SOD3; Copper; Transcription Factor; Copper Chaperone
Neovascularization is a physiological repair process that is partly dependent on nitric oxide. Extracellular superoxide dismutase (EcSOD) is the major scavenger of superoxide and thus is an important regulator of nitric oxide bioavailability and thus protects against vascular dysfunction. We hypothesized that overexpression of EcSOD in skeletal muscle would improve recovery from hind-limb ischemia.
Adeno associated virus (AAV) vectors expressing EcSOD or luciferase (control) from the Cytomegalovirus (CMV) promoter were cross-packaged into AAV9 capsids and injected IM into hind-limb muscles (1×1011 viral genomes(vg)/limb) of 12 wk-old mice. Ischemia was then induced after IM injections. Limb perfusion was serially measured by laser Doppler on days 0, 7 & 14 post-injection and values were expressed as a ratio relative to the non-ischemic limb. EcSOD expression was measured by Western blotting. Capillary density was documented by immunohistochemical staining for platelet endothelial cell adhesion molecule (PECAM). Apoptosis was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and necrosis was visually evaluated daily.
EcSOD expression was 2-fold up-regulated in EcSOD treated vs. control ischemic muscles at day 14. Capillary density was 1.9-fold higher in treated (1.65±0.02 capillaries/fiber) vs. control muscle (0.78±0.17 capillaries/fiber, p<0.05). Recovery of perfusion ratio at day 14 post-ischemia was 1.5-fold greater in EcSOD vs. control mice (p<0.05). The percentage of apoptotic nuclei was 1.3 ± 0.4% in EcSOD treated mice as compared to 4.2± 0.2% in controls (p<0.001). Limb necrosis was also significantly lower in EcSOD vs. control mice.
AAV9-mediated overexpression of EcSOD in skeletal muscle significantly improves recovery from hind-limb ischemia in mice, consistent with improved capillary density and perfusion ratios in treated mice.
Extracellular superoxide dismutase; AAV-9; hind-limb ischemia; nitric oxide