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2.  Exposure to Electronic Cigarettes Impairs Pulmonary Anti-Bacterial and Anti-Viral Defenses in a Mouse Model 
PLoS ONE  2015;10(2):e0116861.
Electronic cigarettes (E-cigs) have experienced sharp increases in popularity over the past five years due to many factors, including aggressive marketing, increased restrictions on conventional cigarettes, and a perception that E-cigs are healthy alternatives to cigarettes. Despite this perception, studies on health effects in humans are extremely limited and in vivo animal models have not been generated. Presently, we determined that E-cig vapor contains 7x1011 free radicals per puff. To determine whether E-cig exposure impacts pulmonary responses in mice, we developed an inhalation chamber for E-cig exposure. Mice that were exposed to E-cig vapor contained serum cotinine concentrations that are comparable to human E-cig users. E-cig exposure for 2 weeks produced a significant increase in oxidative stress and moderate macrophage-mediated inflammation. Since, COPD patients are susceptible to bacterial and viral infections, we tested effects of E-cigs on immune response. Mice that were exposed to E-cig vapor showed significantly impaired pulmonary bacterial clearance, compared to air-exposed mice, following an intranasal infection with Streptococcus pneumonia. This defective bacterial clearance was partially due to reduced phagocytosis by alveolar macrophages from E-cig exposed mice. In response to Influenza A virus infection, E-cig exposed mice displayed increased lung viral titers and enhanced virus-induced illness and mortality. In summary, this study reports a murine model of E-cig exposure and demonstrates that E-cig exposure elicits impaired pulmonary anti-microbial defenses. Hence, E-cig exposure as an alternative to cigarette smoking must be rigorously tested in users for their effects on immune response and susceptibility to bacterial and viral infections.
PMCID: PMC4317176  PMID: 25651083
3.  Transcriptional responses of neonatal mouse lung to hyperoxia by Nrf2 status 
Cytokine  2013;65(1):10.1016/j.cyto.2013.09.021.
Hyperoxia exposure can inhibit alveolar growth in the neonatal lung through induction of p21/ p53 pathways and is a risk factor for the development of bronchopulmonary dysplasia (BPD) in preterm infants. We previously found that activation of nuclear factor erythroid 2 p45-related factor (Nrf2) improved survival in neonatal mice exposed to hyperoxia likely due to increased expression of anti-oxidant response genes. It is not known however, whether hyperoxic induced Nrf2 activation attenuates the growth impairment caused by hyperoxia in neonatal lung. To determine if Nrf2 activation modulates cell cycle regulatory pathway genes associated with growth arrest we examined the gene expression in the lungs of Nrf2−/− and Nrf2+/+ neonatal mice at one and three days of hyperoxia exposure.
Microarray analysis was performed in neonatal Nrf2+/+ and Nrf2−/− lungs exposed to one and three days of hyperoxia. Sulforaphane, an inducer of Nrf2 was given to timed pregnant mice to determine if in utero exposure attenuated p21 and IL-6 gene expression in wildtype neonatal mice exposed to hyperoxia.
Cell cycle regulatory genes were induced in Nrf2−/− lung at one day of hyperoxia. At 3 days of hyperoxia, induction of cell cycle regulatory genes was similar in Nrf2+/+ and Nrf2−/− lungs, despite higher inflammatory gene expression in Nrf2−/− lung.
p21/ p53 pathways gene expression was not attenuated by Nrf2 activation in neonatal lung. In utero SUL did not attenuate p21 expression in wildtype neonatal lung exposed to hyperoxia. These findings suggest that although Nrf2 activation induces expression of antioxidant genes, it does not attenuate alveolar growth arrest caused by exposure to hyperoxia.
PMCID: PMC3875154  PMID: 24139870
Alveolar growth inhibition; cell cycle regulatory genes; inflammation; hyperoxia; chronic lung disease of prematurity; bronchopulmonary dysplasia neonatal lung; nuclear factor erythroid 2 p45-related factor
4.  NRF2 plays a protective role in diabetic retinopathy in mice 
Diabetologia  2013;57(1):204-213.
Although much is known about the pathophysiological processes contributing to diabetic retinopathy (DR), the role of protective pathways has received less attention. The transcription factor nuclear factor erythroid-2-related factor 2 (also known as NFE2L2 or NRF2) is an important regulator of oxidative stress and also has anti-inflammatory effects. The objective of this study was to explore the potential role of NRF2 as a protective mechanism in DR.
Retinal expression of NRF2 was investigated in human donor and mouse eyes by immunohistochemistry. The effect of NRF2 modulation on oxidative stress was studied in the human Müller cell line MIO-M1. Non-diabetic and streptozotocin-induced diabetic wild-type and Nrf2 knockout mice were evaluated for multiple DR endpoints.
NRF2 was expressed prominently in Müller glial cells and astrocytes in both human and mouse retinas. In cultured MIO-M1 cells, NRF2 inhibition significantly decreased antioxidant gene expression and exacerbated tert-butyl hydroperoxide- and hydrogen peroxide-induced oxidative stress. NRF2 activation strongly increased NRF2 target gene expression and suppressed oxidant-induced reactive oxygen species. Diabetic mice exhibited retinal NRF2 activation, indicated by nuclear translocation. Superoxide levels were significantly increased by diabetes in Nrf2 knockout mice as compared with wild-type mice. Diabetic Nrf2 knockout mice exhibited a reduction in retinal glutathione and an increase in TNF-α protein compared with wild-type mice. Nrf2 knockout mice exhibited early onset of blood–retina barrier dysfunction and exacerbation of neuronal dysfunction in diabetes.
These results indicate that NRF2 is an important protective mechanism regulating the progression of DR and suggest enhancement of the NRF2 pathway as a potential therapeutic strategy.
PMCID: PMC4039644  PMID: 24186494
Diabetic retinopathy; Inflammation; Müller glial cells; Neuronal dysfunction; NF-E2-related factor-2; Reactive oxygen species; Transcription factor; Vascular permeability
6.  The Twist Box Domain is Required for Twist1-induced Prostate Cancer Metastasis 
Molecular cancer research : MCR  2013;11(11):10.1158/1541-7786.MCR-13-0218-T.
Twist1, a basic helix-loop-helix transcription factor, plays a key role during development and is a master regulator of the epithelial-mesenchymal transition (EMT) that promotes cancer metastasis. Structure-function relationships of Twist1 to cancer-related phenotypes are underappreciated, so we studied the requirement of the conserved Twist box domain for metastatic phenotypes in prostate cancer (PCa). Evidence suggests that Twist1 is overexpressed in clinical specimens and correlated with aggressive/metastatic disease. Therefore, we examined a transactivation mutant, Twist1-F191G, in PCa cells using in vitro assays which mimic various stages of metastasis. Twist1 overexpression led to elevated cytoskeletal stiffness and cell traction forces at the migratory edge of cells based on biophysical single-cell measurements. Twist1 conferred additional cellular properties associated with cancer cell metastasis including increased migration, invasion, anoikis resistance, and anchorage-independent growth. The Twist box mutant was defective for these Twist1 phenotypes in vitro. Importantly, we observed a high frequency of Twist1-induced metastatic lung tumors and extra-thoracic metastases in vivo using the experimental lung metastasis assay. The Twist box was required for PCa cells to colonize metastatic lung lesions and extra-thoracic metastases. Comparative genomic profiling revealed transcriptional programs directed by the Twist box that were associated with cancer progression, such as Hoxa9. Mechanistically, Twist1 bound to the Hoxa9 promoter and positively regulated Hoxa9 expression in PCa cells. Finally, Hoxa9 was important for Twist1-induced cellular phenotypes associated with metastasis. These data suggest that the Twist box domain is required for Twist1 transcriptional programs and PCa metastasis.
PMCID: PMC3833995  PMID: 23982216
Twist1; Twist box; epithelial-mesenchymal transition; prostate cancer; metastasis; Hoxa9
7.  Sildenafil Inhibits Superoxide Formation and Prevents Endothelial Dysfunction in a Mouse Model of Secondhand Smoke Induced Erectile Dysfunction 
The Journal of urology  2008;181(2):899-906.
We determined the effect of passive secondhand cigarette smoke on 1) erectile function in vivo, 2) molecular mechanisms involved in penile vascular function, and 3) erectile function and penile molecular signaling in the presence of phosphodiesterase type 5 inhibitor therapy.
Materials and Methods
Four groups of mice were used, including group 1—controls, group 2—mice exposed to 3 weeks of secondhand smoke (5 hours per day for 5 days per week), group 3—control plus sildenafil (100 mg/kg per day) and group 4—smoke exposed plus sildenafil (100 mg/kg per day). Cavernous nerve electrical stimulation and intracavernous injection of acetylcholine were done to assess erectile function. Constitutive and inducible nitric oxide synthase activity, reactive oxygen species generation, nitrotyrosine formation and superoxide anion levels were assessed.
Decreased erectile responses to cavernous nerve electrical stimulation and impaired endothelium dependent erectile responses to ACh in mice exposed to secondhand smoke were observed. Superoxide anion was increased in endothelial and corporeal smooth muscle cells of smoking mouse penises. In mice exposed to secondhand smoke constitutive nitric oxide synthase activity was decreased, and inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation increased. Sildenafil therapy restored constitutive nitric oxide synthase activity in the penis of smoking mice, decreased inducible nitric oxide synthase activity, reactive oxygen species generation and nitrotyrosine formation, and improved erectile responses to cavernous nerve electrical stimulation and acetylcholine.
Short-term exposure to secondhand smoke impairs erectile function through excessive penile reactive oxygen species signaling and inducible nitric oxide synthase activity. Decreased penile constitutive nitric oxide synthase activity may be attributable to the decreased endothelial nitric oxide synthase activity resulting from increased oxidative stress. Sildenafil therapy restored nitric oxide synthase activity and decreased reactive oxygen species signaling, resulting in improved erectile function.
PMCID: PMC4124638  PMID: 19095260
penis; erectile dysfunction; smoking; sildenafil; mice
8.  Notch-Nrf2 Axis: Regulation of Nrf2 Gene Expression and Cytoprotection by Notch Signaling 
Molecular and Cellular Biology  2014;34(4):653-663.
The Notch signaling pathway enables regulation and control of development, differentiation, and homeostasis through cell-cell communication. Our investigation shows that Notch signaling directly activates the Nrf2 stress adaptive response pathway through recruitment of the Notch intracellular domain (NICD) transcriptosome to a conserved Rbpjκ site in the promoter of Nrf2. Stimulation of Notch signaling through Notch ligand expression in cells and by overexpression of the NICD in RosaNICD/−::AlbCre mice in vivo induces expression of Nrf2 and its target genes. Continuous and transient NICD expression in the liver produces a Notch-dependent cytoprotective response through direct transcriptional activation of Nrf2 signaling to rescue mice from acute acetaminophen toxicity. This response can be reversed upon genetic disruption of Nrf2. Morphological studies showed that the characteristic phenotype of high-density intrahepatic bile ducts and enlarged liver in RosaNICD/−::AlbCre mice could be at least partially reversed after Nrf2 disruption. Furthermore, the liver and bile duct phenotypes could be recapitulated with constitutive activation of Nrf2 signaling in Keap1F/F::AlbCre mice. It appears that Notch-to-Nrf2 signaling is another important determinant in liver development and function and promotes cell-cell cytoprotective signaling responses.
PMCID: PMC3911489  PMID: 24298019
9.  Rtp801, a suppressor of mTOR signaling, is an essential mediator of cigarette smoke – induced pulmonary injury and emphysema 
Nature medicine  2010;16(7):767-773.
Rtp801, a stress – related protein triggered by adverse environmental conditions, inhibits mTOR and enhances oxidative stress – dependent cell death. We postulated that Rtp801 acts as potential amplifying switch in the development of cigarette smoke – induced lung injury, leading to emphysema. Rtp801 was overexpressed in human emphysematous lungs and in lungs of mice exposed to cigarette smoke. The upregulation of Rtp801 expression by cigarette smoke in the lung relied on oxidative stress – dependent activation of the CCAAT response element. Rtp801 was necessary and sufficient for NF – κ B activation in cultured cells and, when forcefully expressed in mouse lungs, it promoted NF – kB activation, alveolar inflammation, oxidative stress, and apoptosis of alveolar septal cells. On the other hand, Rtp801 − / − mice were markedly protected against acute cigarette smoke – induced lung injury, partly via increased mTOR signaling, and, when exposed chronically, against emphysema. Our data support the notion that Rtp801 may represent an important molecular sensor and mediator of lung injury to cigarette smoke.
PMCID: PMC3956129  PMID: 20473305
Rtp801; cigarette smoke; oxidative stress; apoptosis; inflammation; NF –κB; rapamycin
10.  Genetic silencing of Nrf2 enhances X-ROS in dysferlin-deficient muscle 
Oxidative stress is a critical disease modifier in the muscular dystrophies. Recently, we discovered a pathway by which mechanical stretch activates NADPH Oxidase 2 (Nox2) dependent ROS generation (X-ROS). Our work in dystrophic skeletal muscle revealed that X-ROS is excessive in dystrophin-deficient (mdx) skeletal muscle and contributes to muscle injury susceptibility, a hallmark of the dystrophic process. We also observed widespread alterations in the expression of genes associated with the X-ROS pathway and redox homeostasis in muscles from both Duchenne muscular dystrophy patients and mdx mice. As nuclear factor erythroid 2-related factor 2 (Nrf2) plays an essential role in the transcriptional regulation of genes involved in redox homeostasis, we hypothesized that Nrf2 deficiency may contribute to enhanced X-ROS signaling by reducing redox buffering. To directly test the effect of diminished Nrf2 activity, Nrf2 was genetically silenced in the A/J model of dysferlinopathy—a model with a mild histopathologic and functional phenotype. Nrf2-deficient A/J mice exhibited significant muscle-specific functional deficits, histopathologic abnormalities, and dramatically enhanced X-ROS compared to control A/J and WT mice, both with functional Nrf2. Having identified that reduced Nrf2 activity is a negative disease modifier, we propose that strategies targeting Nrf2 activation may address the generalized reduction in redox homeostasis to halt or slow dystrophic progression.
PMCID: PMC3928547  PMID: 24600403
Nrf2; X-ROS; ROS; dysferlin; dystrophy
11.  NRF2-mediated Notch pathway activation enhances hematopoietic reconstitution following myelosuppressive radiation 
A nuclear disaster may result in exposure to potentially lethal doses of ionizing radiation (IR). Hematopoietic acute radiation syndrome (H-ARS) is characterized by severe myelosuppression, which increases the risk of infection, bleeding, and mortality. Here, we determined that activation of nuclear factor erythroid-2–related factor 2 (NRF2) signaling enhances hematopoietic stem progenitor cell (HSPC) function and mitigates IR-induced myelosuppression and mortality. Augmenting NRF2 signaling in mice, either by genetic deletion of the NRF2 inhibitor Keap1 or by pharmacological NRF2 activation with 2-trifluoromethyl-2′-methoxychalone (TMC), enhanced hematopoietic reconstitution following bone marrow transplantation (BMT). Strikingly, even 24 hours after lethal IR exposure, oral administration of TMC mitigated myelosuppression and mortality in mice. Furthermore, TMC administration to irradiated transgenic Notch reporter mice revealed activation of Notch signaling in HSPCs and enhanced HSPC expansion by increasing Jagged1 expression in BM stromal cells. Administration of a Notch inhibitor ablated the effects of TMC on hematopoietic reconstitution. Taken together, we identified a mechanism by which NRF2-mediated Notch signaling improves HSPC function and myelosuppression following IR exposure. Our data indicate that targeting this pathway may provide a countermeasure against the damaging effects of IR exposure.
PMCID: PMC3904618  PMID: 24463449
12.  Histone deacetylase 6–mediated selective autophagy regulates COPD-associated cilia dysfunction 
The Journal of Clinical Investigation  2013;123(12):5212-5230.
Chronic obstructive pulmonary disease (COPD) involves aberrant airway inflammatory responses to cigarette smoke (CS) that are associated with epithelial cell dysfunction, cilia shortening, and mucociliary clearance disruption. Exposure to CS reduced cilia length and induced autophagy in vivo and in differentiated mouse tracheal epithelial cells (MTECs). Autophagy-impaired (Becn1+/– or Map1lc3B–/–) mice and MTECs resisted CS-induced cilia shortening. Furthermore, CS increased the autophagic turnover of ciliary proteins, indicating that autophagy may regulate cilia homeostasis. We identified cytosolic deacetylase HDAC6 as a critical regulator of autophagy-mediated cilia shortening during CS exposure. Mice bearing an X chromosome deletion of Hdac6 (Hdac6–/Y) and MTECs from these mice had reduced autophagy and were protected from CS-induced cilia shortening. Autophagy-impaired Becn1–/–, Map1lc3B–/–, and Hdac6–/Y mice or mice injected with an HDAC6 inhibitor were protected from CS-induced mucociliary clearance (MCC) disruption. MCC was preserved in mice given the chemical chaperone 4-phenylbutyric acid, but was disrupted in mice lacking the transcription factor NRF2, suggesting that oxidative stress and altered proteostasis contribute to the disruption of MCC. Analysis of human COPD specimens revealed epigenetic deregulation of HDAC6 by hypomethylation and increased protein expression in the airways. We conclude that an autophagy-dependent pathway regulates cilia length during CS exposure and has potential as a therapeutic target for COPD.
PMCID: PMC3859407  PMID: 24200693
13.  Oxidized phospholipids impair pulmonary antibacterial defenses: Evidence in mice exposed to cigarette smoke 
Patients with COPD are associated with poor pulmonary anti-bacterial innate defenses, which increase the risk for frequent acute exacerbations caused by bacterial infection. Despite elevated numbers of phagocytes (macrophages and neutrophils), airways of patients with COPD show stable bacterial colonization. A defect in the phagocytic ability of alveolar macrophages (AMs) is one of the primary reasons for failure to clear the invading bacteria in airways of smokers and COPD patients and also in mice exposed to cigarette smoke (CS). Oxidative stress, as a result of CS exposure is implicated; however, the factors or mediators that inhibit phagocytic activity of AMs in lungs of smokers remain unclear. In the current study, we provide evidence that accumulation of oxidized phospholipids (Ox-PLs) mediate inhibition of phagocytic function of AMs in CS-exposed mice. Mice exposed to 6 months of CS showed impaired bacterial phagocytosis and clearance by AMs and elevated levels of Ox-PLs in bronchoalveolar lavage fluid (BALF), compared to mice exposed to room air. Intratracheal instillation of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OX-PAPC) inhibited phagocytic activity of AMs and impaired pulmonary bacterial clearance in mice. In vitro studies demonstrated that exposure of J774 macrophages to OX-PAPC inhibited bacterial phagocytosis and clearance. However, pre-treatment of OX-PAPC with the monoclonal antibody EO6, which specifically binds to oxidized phospholipid but not native phospholipid, abolished OX-PAPC induced inhibition of bacterial phagocytosis and clearance. Incubation of BALF retrieved from CS-exposed mice impaired bacterial phagocytosis by J774 macrophages, which was abolished by pre-treatment of BALF with the EO6 antibody. In conclusion, our study shows that Ox-PLs generated following chronic CS exposure could play a crucial role in inhibiting phagocytic function of AMs and thus impair pulmonary anti-bacterial innate defenses in CS-exposed mice. Therapeutic approaches that augment pulmonary antioxidant defenses could be beneficial in reducing oxidative stress-driven impairment of phagocytosis by AMs in smokers and COPD patients.
PMCID: PMC3495329  PMID: 22935414
COPD; macrophages; oxidized phospholipids; bacteria; phagocytosis; cigarette smoke
14.  Transcription factor NRF2 regulates miR-1 and miR-206 to drive tumorigenesis 
The Journal of Clinical Investigation  2013;123(7):2921-2934.
The mechanisms by which deregulated nuclear factor erythroid-2–related factor 2 (NRF2) and kelch-like ECH-associated protein 1 (KEAP1) signaling promote cellular proliferation and tumorigenesis are poorly understood. Using an integrated genomics and 13C-based targeted tracer fate association (TTFA) study, we found that NRF2 regulates miR-1 and miR-206 to direct carbon flux toward the pentose phosphate pathway (PPP) and the tricarboxylic acid (TCA) cycle, reprogramming glucose metabolism. Sustained activation of NRF2 signaling in cancer cells attenuated miR-1 and miR-206 expression, leading to enhanced expression of PPP genes. Conversely, overexpression of miR-1 and miR-206 decreased the expression of metabolic genes and dramatically impaired NADPH production, ribose synthesis, and in vivo tumor growth in mice. Loss of NRF2 decreased the expression of the redox-sensitive histone deacetylase, HDAC4, resulting in increased expression of miR-1 and miR-206, and not only inhibiting PPP expression and activity but functioning as a regulatory feedback loop that repressed HDAC4 expression. In primary tumor samples, the expression of miR-1 and miR-206 was inversely correlated with PPP gene expression, and increased expression of NRF2-dependent genes was associated with poor prognosis. Our results demonstrate that microRNA-dependent (miRNA-dependent) regulation of the PPP via NRF2 and HDAC4 represents a novel link between miRNA regulation, glucose metabolism, and ROS homeostasis in cancer cells.
PMCID: PMC3696551  PMID: 23921124
15.  Aquaporin 5 regulates cigarette smoke induced emphysema by modulating barrier and immune properties of the epithelium 
Tissue Barriers  2013;1(4):e25248.
Chronic obstructive pulmonary disease (COPD) causes significant morbidity and mortality. Cigarette smoke, the most common risk factor for COPD, induces airway and alveolar epithelial barrier permeability and initiates an innate immune response. Changes in abundance of aquaporin 5 (AQP5), a water channel, can affect epithelial permeability and immune response after cigarette smoke exposure. To determine how AQP5-derived epithelial barrier modulation affects epithelial immune response to cigarette smoke and development of emphysema, WT and AQP5−/− mice were exposed to cigarette smoke (CS). We measured alveolar cell counts and differentials, and assessed histology, mean-linear intercept (MLI), and surface-to-volume ratio (S/V) to determine severity of emphysema. We quantified epithelial-derived signaling proteins for neutrophil trafficking, and manipulated AQP5 levels in an alveolar epithelial cell line to determine specific effects on neutrophil transmigration after CS exposure. We assessed paracellular permeability and epithelial turnover in response to CS. In contrast to WT mice, AQP5−/− mice exposed to 6 months of CS did not demonstrate a significant increase in MLI or a significant decrease in S/V compared with air-exposed mice, conferring protection against emphysema. After sub-acute (4 weeks) and chronic (6 mo) CS exposure, AQP5−/− mice had fewer alveolar neutrophil but similar lung neutrophil numbers as WT mice. The presence of AQP5 in A549 cells, an alveolar epithelial cell line, was associated with increase neutrophil migration after CS exposure. Compared with CS-exposed WT mice, neutrophil ligand (CD11b) and epithelial receptor (ICAM-1) expression were reduced in CS-exposed AQP5−/− mice, as was secreted LPS-induced chemokine (LIX), an epithelial-derived neutrophil chemoattractant. CS-exposed AQP5−/− mice demonstrated decreased type I pneumocytes and increased type II pneumocytes compared with CS-exposed WT mice suggestive of enhanced epithelial repair. Absence of AQP5 protected against CS-induced emphysema with reduced epithelial permeability, neutrophil migration, and altered epithelial cell turnover which may enhance repair.
PMCID: PMC3783223  PMID: 24665410
Aquaporin 5; epithelial permeability; barrier function; epithelial immune response
16.  Experimental Therapeutics of Nrf2 as a Target for Prevention of Bacterial Exacerbations in COPD 
A growing body of evidence indicates that oxidative stress plays a central role in the progression of chronic obstructive pulmonary disease (COPD). Chronic oxidative stress caused by cigarette smoke generates damage-associated molecular patterns (DAMPs), such as oxidatively or nitrosatively modified proteins and extracellular matrix fragments, which induce abnormal airway inflammation by activating innate and adaptive immune responses. Furthermore, oxidative stress–induced histone deacetylase 2 (HDAC2) inactivity is implicated in amplifying inflammatory responses and corticosteroid resistance in COPD. Oxidative stress also mediates disruption of innate immune defenses, which is associated with acute exacerbation of COPD. Host defense transcription factor Nuclear factor erythroid 2–related factor 2 (Nrf2) regulates a multifaceted cytoprotective response to counteract oxidative stress–induced pathological injuries. A decrease in Nrf2 signaling is associated with the progression of diseases. Recent evidence indicates that targeting Nrf2 can be a novel therapy to mitigate inflammation, improve innate antibacterial defenses, and restore corticosteroid responses in patients with COPD.
PMCID: PMC3359107  PMID: 22550241
COPD; Nrf2; bacteria; exacerbation; therapeutics
17.  Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis 
A number of factors have been identified that increase the risk of HCC. Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first line therapy for the treatment of type II diabetes where it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. While a number of preclinical studies demonstrate the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. Additionally, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC where increased lipid synthesis is observed. As a whole these studies demonstrate that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at risk patients.
PMCID: PMC3324649  PMID: 22467080
Metformin; HCC; Tumor growth; lipogenesis; chemoprevention
18.  12/15-lipoxygenase expressed in non-epithelial cells causes airway epithelial injury in asthma 
Scientific Reports  2013;3:1540.
The mechanisms underlying asthmatic airway epithelial injury are not clear. 12/15-lipoxygenase (an ortholog of human 15-LOX-1), which is induced by IL-13, is associated with mitochondrial degradation in reticulocytes at physiological conditions. In this study, we showed that 12/15-LOX expressed in nonepithelial cells caused epithelial injury in asthma pathogenesis. While 12/15-LOX overexpression or IL-13 administration to naïve mice showed airway epithelial injury, 12/15-LOX knockout/knockdown in allergic mice reduced airway epithelial injury. The constitutive expression of 15-LOX-1 in bronchial epithelia of normal human lungs further indicated that epithelial 15-LOX-1 may not cause epithelial injury. 12/15-LOX expression is increased in various inflammatory cells in allergic mice. Though non-epithelial cells such as macrophages or fibroblasts released 12/15-LOX metabolites upon IL-13 induction, bronchial epithelia didn't release. Further 12-S-HETE, arachidonic acid metabolite of 12/15-LOX leads to epithelial injury. These findings suggested 12/15-LOX expressed in non-epithelial cells such as macrophages and fibroblasts leads to bronchial epithelial injury.
PMCID: PMC3607899  PMID: 23528921
19.  Linoleic acid metabolite drives severe asthma by causing airway epithelial injury 
Scientific Reports  2013;3:1349.
Airway epithelial injury is the hallmark of various respiratory diseases, but its mechanisms remain poorly understood. While 13-S-hydroxyoctadecadienoic acid (13-S-HODE) is produced in high concentration during mitochondrial degradation in reticulocytes little is known about its role in asthma pathogenesis. Here, we show that extracellular 13-S-HODE induces mitochondrial dysfunction and airway epithelial apoptosis. This is associated with features of severe airway obstruction, lung remodeling, increase in epithelial stress related proinflammatory cytokines and drastic airway neutrophilia in mouse. Further, 13-S-HODE induced features are attenuated by inhibiting Transient Receptor Potential Cation Channel, Vanilloid-type 1 (TRPV1) both in mouse model and human bronchial epithelial cells. These findings are relevant to human asthma, as 13-S-HODE levels are increased in human asthmatic airways. Blocking of 13-S-HODE activity or disruption of TRPV1 activity attenuated airway injury and asthma mimicking features in murine allergic airway inflammation. These findings indicate that 13-S-HODE induces mitochondrial dysfunction and airway epithelial injury.
PMCID: PMC3583002  PMID: 23443229
20.  Cigarette smoking, oxidative stress, the anti-oxidant response through Nrf2 signaling, and Age-related Macular Degeneration 
Vision research  2009;50(7):652-664.
Age-related Macular Degeneration (AMD) is the leading cause of blindness among the elderly. While excellent treatment has emerged for neovascular disease, treatment for early AMD is lacking due to an incomplete understanding of the early molecular events. Cigarette smoking is the strongest epidemiologic risk factor, yet we do not understand how smoking contributes to AMD. Smoking related oxidative damage during the early phases of AMD may play an important role. This review explores how cigarette smoking and oxidative stress to the retinal pigmented epithelium (RPE) might contribute to AMD, and how the transcription factor Nrf2 can activate a cytoprotective response.
PMCID: PMC3575185  PMID: 19703486
Age-related Macular Degeneration; Cigarette smoking; Nrf2; Oxidative stress; Retinal pigmented epithelium
21.  Conditional Deletion of Nrf2 in Airway Epithelium Exacerbates Acute Lung Injury and Impairs the Resolution of Inflammation 
Oxidant stress, resulting from an excess of reactive electrophiles produced in the lung by both resident (epithelial and endothelial) and infiltrated leukocytes, is thought to play an obligatory role in tissue injury and abnormal repair. Previously, using a conventional (whole-body) knockout model, we showed that antioxidative gene induction regulated by the transcription factor Nrf2 is critical for mitigating oxidant-induced (hyperoxic) stress, as well as for preventing and resolving tissue injury and inflammation in vivo. However, the contribution to pathogenic acute lung injury (ALI) of the cellular stress produced by resident versus infiltrated leukocytes remains largely undefined in vivo. To address this critical gap in our knowledge, we generated mice with a conditional deletion of Nrf2 specifically in Clara cells, subjected these mice to hyperoxic insult, and allowed them to recover. We report that a deficiency of Nrf2 in airway epithelia alone is sufficient to contribute to the development and progression of ALI. When exposed to hyperoxia, mice lacking Nrf2 in Clara cells showed exacerbated lung injury, accompanied by greater levels of cell death and epithelial sloughing than in their wild-type littermates. In addition, we found that an Nrf2 deficiency in Clara cells is associated with a persistent inflammatory response and epithelial sloughing in the lungs during recovery from sublethal hyperoxic insult. Our results demonstrate (for the first time, to the best of our knowledge) that Nrf2 signaling in Clara cells is critical for conferring protection from hyperoxic lung injury and for resolving inflammation during the repair process.
PMCID: PMC3262666  PMID: 21659655
oxidative stress; lung injury and repair; inflammation
22.  Telomere Length Is a Determinant of Emphysema Susceptibility 
Rationale: Germline mutations in the enzyme telomerase cause telomere shortening, and have their most common clinical manifestation in age-related lung disease that manifests as idiopathic pulmonary fibrosis. Short telomeres are also a unique heritable trait that is acquired with age.
Objectives: We sought to understand the mechanisms by which telomerase deficiency contributes to lung disease.
Methods: We studied telomerase null mice with short telomeres.
Measurements and Main Results: Although they have no baseline histologic defects, when mice with short telomeres are exposed to chronic cigarette smoke, in contrast with controls, they develop emphysematous air space enlargement. The emphysema susceptibility did not depend on circulating cell genotype, because mice with short telomeres developed emphysema even when transplanted with wild-type bone marrow. In lung epithelium, cigarette smoke exposure caused additive DNA damage to telomere dysfunction, which limited their proliferative recovery, and coincided with a failure to down-regulate p21, a mediator of cellular senescence, and we show here, a determinant of alveolar epithelial cell cycle progression. We also report early onset of emphysema, in addition to pulmonary fibrosis, in a family with a germline deletion in the Box H domain of the RNA component of telomerase.
Conclusions: Our data indicate that short telomeres lower the threshold of cigarette smoke–induced damage, and implicate telomere length as a genetic susceptibility factor in emphysema, potentially contributing to its age-related onset in humans.
PMCID: PMC3208661  PMID: 21757622
telomerase; chronic obstructive pulmonary disease; dyskeratosis congenita; interstitial lung disease
23.  Enhancing Nrf2 Pathway by Disruption of Keap1 in Myeloid Leukocytes Protects against Sepsis 
Rationale: Sepsis syndrome is characterized by inappropriate amplified systemic inflammatory response and bacteremia that promote multiorgan failure and mortality. Nuclear factor–erythroid 2 p45-related factor 2 (Nrf2) regulates a pleiotropic cytoprotective defense program including antioxidants and protects against several inflammatory disorders by inhibiting oxidative tissue injuries. However, the role of enhanced Nrf2 activity in modulating innate immune responses to microbial infection and pathogenesis of sepsis is unclear.
Objectives: To determine whether Nrf2 in myeloid leukocytes alters inflammatory response and protects against sepsis.
Methods: Mice with deletion of Nrf2 or kelch-like ECH-associated protein (Keap1) in myeloid leukocyte cells and respective floxed controls were subjected to cecal ligation and puncture–induced sepsis and were assessed for survival, organ injury, systemic inflammation, and bacteremia. Using LPS-stimulated peritoneal macrophages, Toll-like receptor (TLR) 4 surface trafficking and downstream signaling events were analyzed.
Measurements and Main Results: Mortality, organ injury, circulating levels of inflammatory mediators, and bacteremia were markedly reduced in LysM-Keap1−/− compared with respective floxed controls (Keap1f/f or Nrf2f/f) and significantly elevated in LysM-Nrf2−/− mice after cecal ligation and puncture. Peritoneal macrophages from septic LysM-Keap1−/− mice showed a greater bacterial phagocytic activity compared with LysM-Nrf2−/− and floxed controls. LPS stimulation resulted in greater reactive oxygen species–induced cell surface transport of TLR4 from trans-Golgi network and subsequent TLR4 downstream signaling (recruitment of MYD88 and TRIF, phosphorylation of IkB and IRF3, and cytokine expression) in macrophages of LysM-Nrf2−/− compared with LysM-Keap1−/− mice and floxed controls.
Conclusions: Our study shows that Nrf2 acts as a critical immunomodulator in leukocytes, controls host inflammatory response to bacterial infection, and protects against sepsis.
PMCID: PMC3208662  PMID: 21799073
Nrf2; Keap1; sepsis; antioxidants; inflammation
24.  Neonatal Hyperoxia Contributes Additively to Cigarette Smoke–Induced Chronic Obstructive Pulmonary Disease Changes in Adult Mice 
The extent by which early postnatal lung injury contributes to the development of chronic obstructive pulmonary disease (COPD) in the adult is unclear. We hypothesized that exposure to hyperoxia during early postnatal life can augment lung changes caused by adult chronic cigarette smoke (CS) exposure. C57BL/6J mice (1 d old) were exposed to hyperoxia (O2) for 5 days. At 1 month of age, half of the O2–exposed mice and half of the control mice were placed in a CS chamber for 6 months. After exposure to CS, mice underwent quasi-static pressure–volume curve and mean chord length measurements; quantification of pro–Sp-c expression; and measurement of lung IL-8/ KC, CXCR2/IL8Rα, TNF-α, and IL-6 mRNA by real-time PCR. Adult mice exposed to O2+CS had significantly larger chord length measurements (P < 0.02) and lung volumes at 35 cm H2O (P < 0.05) compared with all other groups. They also had significantly less pro–Sp-c protein and surfactant protein C mRNA expression (P < 0.003). Mice exposed to O2+CS and CS-only mice had significantly higher lung resistance and longer mean time constants (P < 0.01), significantly more inflammatory cells in the bronchoalveolar lavage fluid (P < 0.03), and significantly higher levels of lung CXCR2/IL8Rα mRNA compared with mice not exposed to smoke (P < 0.02). We conclude that exposure to early postnatal hyperoxia contributed additively to CS-induced COPD changes in adult mice. These results may be relevant to a growing population of preterm children who sustained lung injury in the newborn period and may be exposed to CS in later life.
PMCID: PMC3175575  PMID: 21239606
early postnatal hyperoxia; airspace abnormalities; chronic cigarette smoke exposure; chronic obstructive pulmonary disease
25.  Carbon monoxide-activated Nrf2 pathway leads to protection against permanent focal cerebral ischemia 
Background and Purpose
Carbon monoxide (CO) is a gaseous second messenger produced when heme oxygenase (HO) enzymes catabolize heme. We have demonstrated that CO can be therapeutic in ischemia-reperfusion brain injury; however, it is unclear whether CO can also offer protection in permanent ischemic stroke or what mechanism(s) underlies the effect. HO1 neuroprotection was shown to be regulated by Nrf2; therefore, we investigated whether CO might partially exert neuroprotection by modulating the Nrf2 pathway.
To evaluate potential protective effects of CO, we exposed male wildtype and Nrf2 knockout mice to 250 ppm CO or control air for 18 hours immediately after permanent middle cerebral artery occlusion. Infarct volume and neurological deficits were assessed on day 7. Molecular mechanisms of Nrf2 pathway activation by CO were also investigated.
Mice exposed to CO after permanent ischemia had 29.6±12.6% less brain damage than did controls at 7 days, though amelioration in neurological deficits did not reach significance. Additionally, 18-hour CO treatment led to Nrf2 dissociation from Keap1, nuclear translocation, increased binding activity of Nrf2 to HO1 antioxidant response elements, and elevated HO1 expression 6–48 hours after CO exposure. The CO neuroprotection was completely abolished in Nrf2 knockout mice.
Low-concentration CO represent a neuroprotective agent for combination treatment of ischemic stroke, and its beneficial effect would be at least partially mediated by activation of the Nrf2 pathway.
PMCID: PMC3278075  PMID: 21852618
carboxyhemoglobin; heme oxygenase; mouse; neuroprotection; stroke

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