Exendin-4 promotes extracellular-superoxide dismutase expression in A549 cells through DNA demethylation

Role of copper and SOD3-mediated extracellular redox regulation in tumor progression

Copper (Cu), an essential micronutrient, participates in several physiological processes, including cell proliferation and development. Notably, the disturbance of Cu homeostasis promotes tumor progression through the generation of oxidative stress. Chronic or excessive accumulation of reactive oxygen species (ROS) causes lipid peroxidation, protein denaturation, and enzyme inactivation, which leads to a breakdown of intracellular homeostasis and exacerbates tumor progression. The disruption of the ROS scavenging mechanism also reduces resistance to oxidative stress, leading to further deterioration in a disease state, and maintenance of redox homeostasis is thought to inhibit the onset and progression of various diseases. Superoxide dismutase 3 (SOD3), a Cu-containing secretory antioxidative enzyme, plays a key role in extracellular redox regulation, and the significant reduction in SOD3 facilitates tumor progression. Furthermore, the significant induction of SOD3 participates in tumor metastasis. This review focuses on the role of Cu homeostasis and antioxidative enzymes, including SOD3, in tumor progression, to help clarify the role of redox regulation.

Exendin-4 alleviates β-Amyloid peptide toxicity via DAF-16 in a Caenorhabditis elegans model of Alzheimer's disease

Epidemiological analyses indicate that type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD). They share common pathophysiological mechanisms. Thus, it has been increasingly suggested that several anti-T2DM drugs may have therapeutic potential in AD. Exendin-4, as a glucagon-like peptide-1 (GLP-1) receptor agonist, is an approved drug used to treat T2DM. In this research, the neuroprotective effect of Exendin-4 was investigated for the first time using transgenic Caenorhabditis elegans. Our results demonstrated that Exendin-4 attenuated the amyloid-β (1-42) (Aβ1-42) toxicity via multiple mechanisms, such as depressing its expression on protein and mRNA and reducing Aβ (1-42) accumulation. Exendin-4 at 0.5 mg/ml had been shown to extend life by 34.39% in CL4176 and delay the onset of paralysis in CL4176 and CL2006 which were increased by 8.18 and 8.02%, respectively. With the treatment of Exendin-4, the nuclear translocation of DAF-16 in the transgenic nematode TJ356 was enhanced. Superoxide dismutase-3 (SOD-3), as a downstream target gene regulated by DAF-16, was upregulated on mRNA level and activity. The reactive oxygen species (ROS) level was decreased. In contrast, we observed that the ability of Exendin-4 to regulate SOD was decreased in CL4176 worms with the DAF-16 gene silenced. The activity of SOD and the mRNA level of sod-3 were downregulated by 30.45 and 43.13%, respectively. Taken together, Exendin-4 attenuated Aβ (1-42) toxicity in the C. elegans model of AD via decreasing the expression and the accumulation of Aβ (1-42). Exendin-4 exhibited the ability of antioxidant stress through DAF-16. With continuous research, Exendin-4 would become a potential therapeutic strategy for treating AD.

Copper in the tumor microenvironment and tumor metastasis

Copper (Cu), an essential micronutrient, plays an essential role in several physiological processes, including cell proliferation and angiogenesis; however, its dysregulation induces oxidative stress and inflammatory responses. Significant Cu accumulation is observed in several tumor tissues. The bioavailability of intracellular Cu is tightly controlled by Cu transporters, including Cu transporter 1 (CTR1) and Cu-transporting P-type ATPase α and β (ATP7A and ATP7B), and Cu chaperones, including Cu chaperone for superoxide dismutase 1 (CCS) and antioxidant-1 (Atox-1). In several tumor tissues, these abnormalities that induce intra­cellular Cu accumulation are involved in tumor progression. In addition, functional disturbance in Cu-containing secretory enzymes, such as superoxide dismutase 3 (SOD3), and lysyl oxidase enzymes (LOX and LOXL1–4) with abnormal Cu dynamics plays a key role in tumor metastasis. For example, the loss of SOD3 in tumor tissues induces oxidative stress, which promotes neovascularization and epithelial-to-mesenchymal transition (EMT). LOX promotes collagen crosslinking, which functions in the metastatic niche formation. Accordingly, restricted Cu regulation may be a novel strategy for the inhibition of tumor metastasis. However, it is unclear how these Cu disturbances occur in tumor tissues and the exact molecular mechanisms underlying Cu secretory enzymes. In this review article, I discuss the role of Cu transporters, Cu chaperones, and Cu-containing secretory enzymes in tumor progression to better understand the role of Cu homeostasis in tumor tissues.

Incretin drugs effect on epigenetic machinery: New potential therapeutic implications in preventing vascular diabetic complications

The effect of GLP-1R agonists on DNA methylation levels of NF-κB and SOD2 genes in human aortic endothelial cells exposed to high glucose and in diabetic patients treated and not with incretin-based drugs, was evaluated. Methylation levels, mRNA and protein expression of NF-κB and SOD2 genes were measured in human endothelial cells exposed to high glucose for 7 days and treated with GLP-1R agonists. Methylation status of NF-κB and SOD2 promoter was also analyzed in 128 diabetics and 116 nondiabetics and correlated with intima media thickness (ITM), an early marker of atherosclerotic process. Cells exposed to high glucose showed lower NF-κB and SOD2 methylation levels, increased NF-κB and reduced SOD2 expression compared to normal glucose cells. Co-treatment with GLP-1 agonists prevented methylation and genes expression changes induced by high glucose. Both high glucose and incretins exposure increased DNA methyltransferases and demethylases levels. In diabetics, incretin treatment resulted a significant predictor of NF-κB DNA methylation, independently of age, sex, body mass index (BMI), glucose and plasma lipid levels. NF-κB DNA methylation inversely correlated with IMT after adjusting for multiple covariates. Our results firstly provide new evidences of an additional mechanism by which incretin drugs could prevent vascular diabetic complications.

[Regulation of Extracellular Redox Homeostasis in Tumor Microenvironment]

Excessive generation of reactive oxygen species (ROS) has been implicated in the progression of tumors. Superoxide dismutase 3 (SOD3) is a copper-containing secretory antioxidative enzyme that plays a critical role in redox homeostasis, particularly in extracellular spaces. Considerable evidence suggests that SOD3 protein expression is significantly decreased or lost in several tumor tissues, and this loss results in tumor metastasis. On the other hand, epigenetic disturbances, including DNA hyper-/hypomethylation, histone de/acetylation, and histone de/methylation, may be involved in tumorigenesis and the progression of metastasis. However, regulation of SOD3 in the tumor microenvironment and the involvement of epigenetics in its expression remain unclear. To elucidate the molecular mechanisms underlying SOD3 expression, we investigated the involvement of epigenetics, including DNA methylation and histone modifications, in its regulation in tumor cells and macrophages. SOD3 expression in human monocytic THP-1 cells and human lung cancer A549 cells was silenced by DNA hypermethylation within the SOD3 promoter region. Furthermore, the DNA demethylase, ten-eleven translocation 1, was shown for the first time to play a key role in regulation of DNA methylation within that region. We also demonstrated that myocyte enhancer factor 2 functioned as one of the transcription factors of SOD3 expression in THP-1 cells. Collectively, these novel results will contribute to the elucidation of epigenetic redox regulation, and may provide important insights into tumorigenesis and tumor metastasis.

Ten-eleven translocation 1 functions as a mediator of SOD3 expression in human lung cancer A549 cells

Superoxide dismutase (SOD) 3, one of the SOD isozymes, plays a pivotal role in extracellular redox homeostasis. The expression of SOD3 is regulated by epigenetics in human lung cancer A549 cells and human monocytic THP-1 cells; however, the molecular mechanisms governing SOD3 expression have not been elucidated in detail. Ten-eleven translocation (TET), a dioxygenase of 5-methylcytosine (5mC), plays a central role in DNA demethylation processes and induces target gene expression. In the present study, TET1 expression was abundant in U937 cells, but its expression was weakly expressed in A549 and THP-1 cells. These results are consistent with the expression pattern of SOD3 and its DNA methylation status in these cells. Moreover, above relationship was also observed in human breast cancer cells, human prostate cancer cells, and human skin fibroblasts. The overexpression of TET1-catalytic domain (TET1-CD) induced the expression of SOD3 in A549 cells, and this was accompanied by the direct binding of TET1-CD to the SOD3 promoter region. Furthermore, in TET1-CD-transfected A549 cells, the level of 5-hydroxymethylcytosine within that region was significantly increased, whereas the level of 5mC was decreased. The results of the present study demonstrate that TET1 might function as one of the key molecules in SOD3 expression through its 5mC hydroxylation in A549 cells.

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Clinical relevance of epigenetics in the onset and management of type 2 diabetes mellitus

Epigenetics is involved in the altered expression of gene networks that underlie insulin resistance and insufficiency. Major genes controlling β-cell differentiation and function, such as PAX4, PDX1, and GLP1 receptor, are epigenetically controlled. Epigenetics can cause insulin resistance through immunomediated pro-inflammatory actions related to several factors, such as NF-kB, osteopontin, and Toll-like receptors. Hereafter, we provide a critical and comprehensive summary on this topic with a particular emphasis on translational and clinical aspects. We discuss the effect of epigenetics on β-cell regeneration for cell replacement therapy, the emerging bioinformatics approaches for analyzing the epigenetic contribution to type 2 diabetes mellitus (T2DM), the epigenetic core of the transgenerational inheritance hypothesis in T2DM, and the epigenetic clinical trials on T2DM. Therefore, prevention or reversion of the epigenetic changes occurring during T2DM development may reduce the individual and societal burden of the disease.

Exendin-4 induces extracellular-superoxide dismutase through histone H3 acetylation in human retinal endothelial cells

Extracellular-superoxide dismutase (genetic name SOD3) is a secreted anti-oxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. Oxidative stress has been implicated in the pathogenesis of diabetic retinopathy; therefore, increases in extracellular-superoxide dismutase have been suggested to inhibit the progression of diabetic retinopathy. Incretin-based drugs such as glucagon-like peptide-1 receptor agonists are used in the treatment of type 2 diabetes. Glucagon-like peptide-1 receptor agonists are expected to function as extrapancreatic agents because the glucagon-like peptide-1 receptor is expressed not only in pancreatic tissues, but also in many other tissue types. We herein demonstrated that exendin-4, a glucagon-like peptide-1 receptor agonist, induced the expression of extracellular-superoxide dismutase in human retinal microvascular endothelial cells through epigenetic regulation. The results of the present study demonstrated that exendin-4 induced the expression of extracellular-superoxide dismutase through histone H3 acetylation at the SOD3 proximal promoter region. Moreover, plasma extracellular-superoxide dismutase concentrations in diabetic patients were elevated by incretin-based therapies. Therefore, incretin-based therapies may exert direct extrapancreatic effects in order to protect blood vessels by enhancing anti-oxidative activity.

Reduced endogenous urinary total antioxidant power and its relation of plasma antioxidant activity of superoxide dismutase in individuals with autism spectrum disorder

Individuals with autism spectrum disorders (ASD) have impaired detoxification capacity. Investigating　the neurobiological bases of　impaired antioxidant capacity is thus a research priority in the pathophysiology of ASD.　We measured　the urinary levels of hexanoyl-lysine (HEL) which is a new oxidative stress　biomarker, total antioxidant power (TAP) and DNA methylation biomarker 8-hydroxy-2'-deoxyguanosine (8-OHdG), and the plasma levels of superoxide dismutase (SOD), which is a major antioxidant enzyme. We examined whether the urinary levels of these enzymes and biomarkers may be related to symptoms of social impairment in 20 individuals with ASD (meanage,11.1±5.2years) and 12 age- and gender-matched healthy controls (meanage,14.3±6.2years). Symptoms of social impairment were　assessed using the Social Responsiveness Scale (SRS). The dietary TAP of the fruit juice, chocolate, cookies, biscuits, jam and marmalade were significantly higher in the ASD group than in the control group, although the intake of nutrients was not significantly different between the groups. The urinary TAP levels were significantly lower in the ASD group than in the control group. There were no significantly differences in urinary HEL and 8-OHdG levels between the ASD and control groups. The SRS scores were significantly higher in the ASD group than in the control group. Stepwise regression analysis revealed that urinary TAP levels and plasma SOD levels can differences in the biomarkers and the SRS scores between the ASD group and the control group. The endogenous antioxidant capacity may be deficient without altered urinary HEL and 8-OHdG levels in individuals with ASD. The plasma SOD levels may be related to reduced endogenous antioxidant capacity.