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Journal: Antioxidants & redox signaling

163

Aims: Here we develop a novel cancer treatment modality using mitochondria-targeting, high fluence low-power laser irradiation (HF-LPLI) in mouse tumor models and explore the mechanism of mitochondrial injury by HF-LPLI. Results: We demonstrated that the initial reaction after photon absorption was photosensitization of cytochrome c oxidase (COX), to inhibit enzymatic activity of COX in situ and cause respiratory chain superoxide anion (O2-•) burst. We also found that HF-LPLI exerted its main tumor killing effect through mitochondrial O2-• burst via electron transport chain (ETC). These phenomena were completely absent in the respiration-deficient cells and COX knockdown cells. With a carefully selected irradiation protocol, HF-LPLI could efficaciously destroy tumors. The inhibition of enzymatic activity of COX and generation of O2-• by HF-LPLI in vivo were also detected. Innovation: It is the first time that the mechanism involved in the interaction between light and its photoacceptor under HF-LPLI treatment is clarified. Our results clearly indicate that HF-LPLI initiates its effects via targeted COX photoinactivation and that the tumor-killing efficacy is dependent of the subsequent mitochondrial O2-• burst via ETC. Conclusion: Based on both in vitro and in vivo results, we conclude that HF-LPLI can selectively photoinactivate respiratory chain oxidase to trigger a fatal mitochondrial O2-• burst, producing oxidative damage on cancer cells. This study opens up the possibilities of applications of HF-LPLI as a mitochondria-targeting cancer phototherapy.

Concepts: Metabolism, Adenosine triphosphate, Mitochondrion, Oxidative phosphorylation, Cellular respiration, Electron transport chain, Cytochrome c, Cytochrome c oxidase

29

Abstract Aims: The sources of cytosolic superoxide in skeletal muscle have not been defined. This study examined the subcellular sites that contribute to cytosolic superoxide in mature single muscle fibers at rest and during contractile activity. Results: Isolated fibers from mouse flexor digitorum brevis loaded with superoxide and nitric-oxide-sensitive fluorescent probes, specific pathway inhibitors and immunolocalization techniques were used to identify subcellular sites contributing to cytosolic superoxide. Treatment with the electron transport chain complex III inhibitor, antimycin A, but not the complex I inhibitor, rotenone, caused increased cytosolic superoxide through release from the mitochondrial intermembrane space via voltage-dependent anion or Bax channels, but inhibition of these channels did not affect contraction-induced increases in cytosolic superoxide. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors decreased cytosolic superoxide at rest and following contractions. Protein and mRNA expression of NADPH oxidase subunits was demonstrated in single fibers. NOX2, NOX4, and p22(phox) subunits localized to the sarcolemma and transverse tubules; NOX4 was additionally expressed in mitochondria. Regulatory p40(phox) and p67(phox) proteins were found in the cytoplasm of resting fibers, but following contractions, p40(phox) appeared to translocate to the sarcolemma. Innovation: Superoxide and other reactive oxygen species generated by skeletal muscle are important regulators of muscle force production and adaptations to contractions. This study has defined the relative contribution of mitochondrial and cytosolic sources of superoxide within the cytosol of single muscle fibers at rest and during contractions. Conclusion: Muscle mitochondria do not modulate cytosolic superoxide in skeletal muscle but NADPH oxidase is a major contributor both at rest and during contractions. Antioxid. Redox Signal. 00, 000-000.

Concepts: Photosynthesis, Metabolism, Adenosine triphosphate, Mitochondrion, Oxidative phosphorylation, Cellular respiration, Nicotinamide adenine dinucleotide, Electron transport chain

29

The process of lipid peroxidation is emerging as an important mechanism that mediates the post-translational modification of proteins. Through advanced analytical techniques, lipidomics is now emerging as a critical factor in our understanding of the pathology of a broad range of diseases. RECENT ADVANCES: During enzymatic or nonenzymatic lipid peroxidation, the simple structure of an unsaturated fatty acid is converted to an oxylipidome, many members of which are electrophilic and form the reactive lipid species (RLS). This aspect of lipid biology is particularly important, as it directly connects lipidomics with proteomics through the post-translational modification of a sub-proteome in the cell. This arises, because the electrophilic members of the oxylipidome react with proteins at nucleophilic amino-acid residues and so change their structure and function to form electrophile-responsive proteomes (ERP).

Concepts: Protein, Amino acid, Metabolism, Fatty acid, Ketone, Biochemistry, Proteome, Unsaturated fat

28

Significance: Thioredoxin, glutaredoxin and peroxiredoxin systems play critical roles in a large number of redox sensitive cellular processes. These systems are linked to each other by coupled redox cycles and common reaction intermediates into a larger network. Given the scale and connectivity of this network, computational approaches are required to analyze its dynamics and organization. Recent Advances: Theoretical advances, as well as new redox proteomic methods, have led to the development of both top-down and bottom-up systems biology approaches to analyze the these systems and the network as a whole. Top-down approaches have been based on modifications to the Nernst equation or on graph theoretical approaches while bottom-up approaches have been based on kinetic or stoichiometric modeling techniques. Critical issues: This review will consider the rationale behind these approaches and focus on their advantages and limitations. Further, the review will discuss modeling standards to ensure model accuracy and availability. Future Directions: Top-down and bottom-up approaches have distinct strengths and limitations in describing cellular redoxin networks. The availability of methods to overcome these limitations, together with the adoption of common modeling standards, is expected to increase the pace of model-led discovery within the redox biology field.

Concepts: Electrochemistry, The Network, Proteomics, Galvanic cell, Equations, Nernst equation, Walther Nernst, Top-down and bottom-up design

28

Abstract Aims: The signaling molecule hydrogen sulfide (H(2)S) protects cells against oxidative stress and activates NF-E2 p45-related factor 2 (Nrf2), a transcription factor that regulates antioxidant genes. We sought to establish whether H(2)S requires Nrf2 to protect against oxidative stress, and whether activation of Nrf2 by H(2)S involves antagonism of Kelch-like ECH-associated protein-1 (Keap1), a redox-sensitive ubiquitin ligase substrate adaptor that represses Nrf2 under normal homeostatic conditions. Results: H(2)S stabilizes Nrf2 protein and induces Nrf2-target genes via an antioxidant-/electrophile-response element. In mouse embryonic fibroblasts, the ability of H(2)S to protect against cell death caused by the redox-cycling agent menadione is dependent on Nrf2. Moreover, Nrf2 regulates murine genes involved in the production of H(2)S (Cystathionine-beta-synthase [Cbs] and Cystathionine-gamma-lyase [Cse]) and the degradation of H(2)S (Sulfide:quinone reductase-like [yeast] [Sqrdl]). We found that H(2)S stabilizes Nrf2 through inhibition of Keap1, an event that requires covalent modification of amino acids C226 and C613 in the substrate adaptor. Upregulation of Nrf2 by H(2)S partially involves the production of H(2)O(2), which inhibits Keap1 by stimulating the formation of an intramolecular disulfide bond between C226 and C613. The Keap1 C226 and C613 residues are also S-sulfhydrated by H(2)S, and this may entail reduction of the C226-C613 disulfide bridge formed by H(2)O(2). Innovation: Upregulation of Nrf2 by H(2)S and H(2)O(2) involves inactivation of Keap1 through modification of C226 and C613. Conclusion: Inhibition of Keap1 by H(2)S leads to Nrf2-mediated induction of cytoprotective genes. Nrf2 controls Cbs, Cse, and Sqrdl, suggesting that a feedback loop exists between Nrf2 and H(2)S. Antioxid. Redox Signal. 00, 000-000.

Concepts: Protein, Protein structure, Enzyme, Hydrogen, Disulfide bond, Glutathione, Sulfur, Cysteine

27

Aims: Free iron plays an important role in the pathogenesis of acute kidney injury (AKI) via the formation of hydroxyl radicals. Systemic iron homeostasis is controlled by the hemojuvelin-hepcidin-ferroportin axis in the liver, but less is known about this role in AKI. Results: By proteomics, we identified a 42 kDa soluble hemojuvelin (sHJV), processed by furin protease from membrane-bound hemojuvelin (mHJV), in the urine during AKI after cardiac surgery. Biopsies from human and mouse specimens with AKI confirm that HJV is extensively increased in renal tubules. Iron overload enhanced the expression of hemojuvelin-hepcidin signaling pathway. The furin inhibitor decreases furin mediated proteolytic cleavage of mHJV into sHJV and augments the mHJV/sHJV ratio after iron overload with hypoxia condition. The furin inhibitor could reduce renal tubule apoptosis, stabilize hypoxic induced factor-1 (HIF-1), prevent the accumulation of iron in the kidney and further ameliorate ischemic-reperfusion injury. mHJV is associated with decreasing total kidney iron, secreting hepcidin, and promoting the degradation of ferroportin at AKI, whereas sHJV does the opposite. Innovation: This study suggests the ratio of mHJV/sHJV affects the iron deposition during acute kidney injury and sHJV could be an early biomarker of AKI. Conclusion: Our findings link endogenous HJV inextricably with renal iron homeostasis for the first time, add new significance to early predict AKI, and identify novel therapeutic targets to reduce the severity of AKI using the furin inhibitor.

Concepts: Renal failure, Kidney, Iron, Urine, Nephron, Ureter, Human iron metabolism, Hepcidin

27

Aims. We asked whether the neuroprotective effect of cholinergic microglia stimulation during an ischemic event acts via a mechanism involving the activation of nuclear factor erythroid 2 related factor 2 (Nrf2) and/or the expression of its target cytoprotective gene, heme oxygenase-1 (HO-1). Specifically, the protective effect of the pharmacologic alpha-7 nicotinic receptor (α7 nAChR) agonist PNU282987 was analyzed in organotypic hippocampal cultures (OHCs) subjected to oxygen and glucose deprivation in vitro as well as in photothrombotic stroke in vivo. Results. OHCs exposed to oxygen and glucose deprivation (OGD) followed by re-oxygenation, elicited cell death, measured by propidium iodide and MTT staining. Activation of α7 nAChR by PNU282987, after OGD, reduced cell death, ROS production and TNF release. This was associated with induction of HO-1 expression; an effect reversed by the α-bungarotoxin and by tin protoporhyrin IX (SnPP). The protective effect of PNU282987 was lost in microglia-depleted OHCs as well as in OHCs from Nrf2 deficient vs. wild type mice, an effect associated with suppression of HO-1 expression in microglia. Administration of PNU282987 1 h after induction of photothrombotic stroke in vivo reduced infarct size and improved motor skills in Hmox1lox/lox mice, that express normal levels of HO-1 but not in LysMCreHmox1∆/∆ in which HO-1 expression is inhibited in myeloid cells, including the microglia. Innovation. This study suggests the participation of the microglial α7 nAChR in the “brain cholinergic anti-inflammatory pathway”. Conclusion. Activation of the α7 nAChR/Nrf2/HO-1 axis in microglia regulates neuroinflammation and oxidative stress affording neuroprotection under brain ischemic conditions.

Concepts: Gene, Acetylcholine, Nicotinic acetylcholine receptor, Alpha-7 nicotinic receptor

26

Significance Fetal lung development takes place in hypoxia meaning that premature birth is hyperoxia for the prematurely born infant. The most common respiratory morbidity afflicting premature infants is bronchopulmonary dysplasia (BPD). Pathophysiologically, BPD represents the impact of injury, including O2 toxicity, to the immature developing lung that causes arrested lung development. Recent Advances The Trx system, which is predominantly expressed in pulmonary epithelia in the newborn lung, acts as an antioxidant system; however, it is increasingly recognized as a key redox regulator of signal transduction and gene expression via thiol-disulfide exchange reactions. Critical Issues This review focuses on the contribution of Trx family proteins toward normal and aberrant lung development. In particular, the roles of the Trx system in hyperoxic responses of alveolar epithelial cells, aberrant lung development in animal models of BPD, O2-dependent signaling processes, and possible therapeutic efficacy in preventing O2-mediated lung injury. Future Directions The significant contribution of the Trx system toward redox regulation of key developmental pathways necessary for proper lung development suggests that therapeutic strategies focused on preserving pulmonary Trx function could significantly improve the outcomes of prematurely born human infants.

Concepts: Childbirth, Infant, Gene expression, Pulmonology, Lung, Fetus, Epithelium, Cervix

24

Both acute kidney injury (AKI) and chronic kidney disease (CKD) are major causes of renal failure in humans and are associated with high incidences of morbidity and mortality. AKI and CKD are closely interconnected and fueled by the obesity and diabetes epidemic their prevalence is alarmingly increasing to the point that it currently represents a major heath issue worldwide. The kidney is an organ that is particularly sensitive to redox imbalance resulting in excessive production of reactive oxygen species (ROS). Oxidative stress is viewed as a critical pathogenic factor implicated in the initiation, development and progression of most renal diseases. This Forum discusses the redox-dependent factors and mechanisms accounting for the perturbation of renal function and circulation in the context of the major kidney pathologies linked to hypertension, diabetes and cancer.

Concepts: Renal failure, Chronic kidney disease, Kidney, Nephrology, Hypertension, Oxidative phosphorylation, Reactive oxygen species, Hydrogen peroxide

24

Angiotensin II (Ang II) aggravates hepatic fibrosis by inducing NADPH oxidase (NOX)-dependent oxidative stress. Angiotensin-(1-7) (Ang-(1-7)), which counter-regulates Ang II, has been evidenced to protect against hepatic fibrosis. The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome, being activated by reactive oxygen species (ROS), is identified as a novel mechanism of liver fibrosis. However, whether the NLRP3 inflammasome involves in regulation of Ang II-induced hepatic fibrosis remains unclear. Aims To investigate the different effects of the Ang II and Ang-(1-7) on collagen synthesis by regulating the NLRP3 inflammasome/Smad pathway via redox balance modulation. Results In vivo, Ang-(1-7) improved bile duct ligation (BDL) induced-hepatic fibrosis, reduced H2O2 content, protein levels of NOX4 and the NLRP3-inflammasome, whereas increased glutathione (GSH) and nuclear erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE). In vitro, Ang II treatment elevated NOX4 protein expression and ROS production in hepatic stellate cells (HSCs), whereas inhibited GSH and Nrf2-ARE, resulting in the activation of the NLRP3 inflammasome in the mitochondria of HSCs. NLRP3 depletion inhibited Ang II-induced collagen synthesis. Furthermore, Ang II increased NLRP3 and pro-IL-1β levels by activating the TLR4/MyD88/NF-κB pathway. Treatment with antioxidants, NOX4 siRNA, or Nrf2 activator inhibited Ang II induced NLRP3 inflammasome activation and collagen synthesis. In contrast, the action of Ang-(1-7) opposed the effects of Ang II. Innovation and Conclusions Ang-(1-7) improved liver fibrosis by regulating NLRP3 inflammasome activation induced by Ang II-mediated ROS via redox balance modulation.

Concepts: Oxygen, Antioxidant, Oxidative stress, Oxidative phosphorylation, Reactive oxygen species, Liver, Hydrogen peroxide, Glutathione