Oxidized proteins: intracellular distribution and recognition by the proteasome

Reactive oxygen species-scavenging nanomaterials for the prevention and treatment of age-related diseases

With increasing proportion of the elderly in the population, age-related diseases (ARD) lead to a considerable healthcare burden to society. Prevention and treatment of ARD can decrease the negative impact of aging and the burden of disease. The aging rate is closely associated with the production of high levels of reactive oxygen species (ROS). ROS-mediated oxidative stress in aging triggers aging-related changes through lipid peroxidation, protein oxidation, and DNA oxidation. Antioxidants can control autoxidation by scavenging free radicals or inhibiting their formation, thereby reducing oxidative stress. Benefiting from significant advances in nanotechnology, a large number of nanomaterials with ROS-scavenging capabilities have been developed. ROS-scavenging nanomaterials can be divided into two categories: nanomaterials as carriers for delivering ROS-scavenging drugs, and nanomaterials themselves with ROS-scavenging activity. This study summarizes the current advances in ROS-scavenging nanomaterials for prevention and treatment of ARD, highlights the potential mechanisms of the nanomaterials used and discusses the challenges and prospects for their applications.

Bacillus subtilis YtpP and Thioredoxin A Are New Players in the Coenzyme-A-Mediated Defense Mechanism against Cellular Stress

Coenzyme A (CoA) is an important cellular metabolite that is critical for metabolic processes and the regulation of gene expression. Recent discovery of the antioxidant function of CoA has highlighted its protective role that leads to the formation of a mixed disulfide bond with protein cysteines, which is termed protein CoAlation. To date, more than 2000 CoAlated bacterial and mammalian proteins have been identified in cellular responses to oxidative stress, with the majority being involved in metabolic pathways (60%). Studies have shown that protein CoAlation is a widespread post-translational modification which modulates the activity and conformation of the modified proteins. The induction of protein CoAlation by oxidative stress was found to be rapidly reversed after the removal of oxidizing agents from the medium of cultured cells. In this study, we developed an enzyme-linked immunosorbent assay (ELISA)-based deCoAlation assay to detect deCoAlation activity from Bacillus subtilis and Bacillus megaterium lysates. We then used a combination of ELISA-based assay and purification strategies to show that deCoAlation is an enzyme-driven mechanism. Using mass-spectrometry and deCoAlation assays, we identified B. subtilis YtpP (thioredoxin-like protein) and thioredoxin A (TrxA) as enzymes that can remove CoA from different substrates. With mutagenesis studies, we identified YtpP and TrxA catalytic cysteine residues and proposed a possible deCoAlation mechanism for CoAlated methionine sulfoxide reducatse A (MsrA) and peroxiredoxin 5 (PRDX5) proteins, which results in the release of both CoA and the reduced form of MsrA or PRDX5. Overall, this paper reveals the deCoAlation activity of YtpP and TrxA and opens doors to future studies on the CoA-mediated redox regulation of CoAlated proteins under various cellular stress conditions.

The MyoPulser field stimulator, a do it yourself programmable electronic pacemaker for contracting cells and tissues

After providing the free software MYOCYTER that analyzes a large amount of data from videos of contracting cells, tissues or organs, we now present an "Arduino"-based programmable, customizable and cost-effective electronic pacemaker ("MyoPulser") that triggers contraction by electric stimulation of the sample at arbitrary frequencies. In this work, construction, functions and application of the MyoPulser are explained in detail, the electronic pacemaker is also tested on isolated cardiomyocytes and HT22-cells to quantify biological effects of pacing. The device enables the user to select between different pulse types (monophasic, alternating, bi- and polyphasic) adjust the length of an applied pulse (1-200 ms), the gap between two consecutive pulses (20-2000 ms), application of irregular pulses with random length and gaps (simulation of arrhythmia) in a user-defined range, as well as manual pulsing, while extensive data are recorded for every single pulse during the experiment. Electrostimulation of isolated B6 cardiomyocytes showed very little deviation of the observed cellular contraction from the applied pulse settings of the device, while the carbon electrodes used proved to be biologically inert in long-term experiments. Due to the open source code and the expandable setup, the MyoPulser can be easily adapted to even highly specific requirements and together with the software MYOCYTER it represents a complete cardiomyophysiological measuring station.

High glucose leads to redistribution of the proteasomal system

The impact of high glucose on the cellular redox state, causing both induction of antioxidative systems and also enhanced protein oxidation is discussed for a long time. It is established that elevated glucose levels are disrupting the cellular proteostasis and influencing the proteasomal system. However, it is still unresolved whether this is due to a reaction of the cellular proteasomal system towards the high glucose or whether this is a secondary reaction to inflammatory stimuli. Therefore, we used a dermal fibroblast cell line exposed to high glucose in order to reveal whether a response of the proteasomal system takes place. We investigated the α4 and the inducible iβ5 subunits of the 20S proteasome, as well as the Rpn1-subunit of the 19S proteasomal regulator complex, measured activity of the 20S, 20S1, and 26S proteasome and detected as well changes in expression as a redistribution into the nucleus. Interestingly, while the activity of the proteasomal forms rather decreased under high glucose treatment; higher expression levels of components of the proteasomal system and higher concentrations of protein-bound 3-nitrotyrosine and Nrf2 (nuclear factor [erythroid-derived 2]-like 2) were detected. However, no change in the cytosol-nucleus distribution could be detected for most of the quantified parameters. We concluded that high glucose alone, without additional inflammatory stimuli, provokes a regulatory response on the ubiquitin-proteasomal system.

Autophagy Induced by Palmitic Acid Regulates Neutrophil Adhesion Through the Granule-Dependent Degradation of αMβ2 Integrin in Dairy Cows With Fatty Liver

β2 integrins are critical for neutrophil firm adhesion, trans-endothelial migration, and the recruitment to the inflamed tissue. Autophagy is implicated in cell migration and tumor metastasis through facilitating the turnover of β1 integrins; however, whether autophagy is able to control neutrophil migration by promoting the degradation of β2 integrins is unexplored. Here, we show that high blood levels of palmitic acid (PA) strongly triggered neutrophil autophagy activation, leading to adhesion deficiency in dairy cows with fatty liver. The three neutrophil granule subtypes, namely, azurophil granules (AGs), specific granules (SGs), and gelatinase granules (GGs), were engulfed by the autophagosomes for degradation, resulting in an increased vacuolation in fatty liver dairy cow neutrophils. Importantly, the adhesion-associated molecules CD11b and CD18 distributed on AGs, SGs, and GGs were degraded with the three granule subtypes by autophagy. Moreover, FGA, Hsc70, and TRIM21 mediated the degradation of cytosolic oxidized–ubiquitinated CD11b and CD18. Collectively, our results demonstrate that high blood PA triggers neutrophil autophagy-dependent vacuolation and granule-dependent adhesion deficiency, decreasing neutrophil mobility, and impairing the innate immune system of dairy cow with fatty liver. This theory extends the category of autophagy in maintaining granule homeostasis and provides a novel strategy to improve the immune of dairy cows with metabolic disease.

Differential oxidative stress responses and tobacco-specific nitrosamine accumulation in two burley varieties

Tobacco-specific nitrosamines (TSNAs) are carcinogens that accumulate in tobacco leaves during curing, storage, and processing, and their amounts in processed tobacco vary dependent on several intrinsic and extrinsic factors. Here, we assessed the hypothesis that there is a link between reactive oxygen species levels in leaves and TSNA formation during curing. First, we show that burley varieties KT 204LC and NCBH 129LC accumulate TSNAs to different levels but not as a result of a variety-specific abundance of TSNA precursors. Next, we measured the levels of reactive oxygen species, and we show that the variety that accumulates more TSNAs, NCBH 129LC, had significantly higher levels of hydrogen peroxide than KT 204LC. The NCBH 129LC also has more oxidatively damaged and glutathionylated proteins. Finally, we analyzed the antioxidant levels in KT 204LC and NCBH 129LC and their tolerance to oxidative stress. NCBH 129LC contained more of the essential antioxidant glutathione and was more tolerant to the oxidative stress-generating compound paraquat. Collectively, our data suggest that there is indeed a link between foliar oxidative stress parameters and the extent to which TSNAs accumulate in cured tobacco leaves.

Age-dependent altered redox homeostasis in the chronodisrupted rat model and moderation by melatonin administration

Circadian disruption or chronodisruption (CD) occurs when day-night cycles and other internal rhythms are not adjusted to environmental light-dark regimens and are unable to synchronize among each other. Artificial light-induced oxidative stress is a major concern as the circadian physiology of the cell is chronically altered due to suppression of the time-keeping hormone, melatonin. The relationship between age-related impaired redox status and disrupted circadian rhythms is still not fully understood. The present study evaluated the effect of artificial light at night (ALAN) with respect to aging and role of melatonin supplementation. This study was conducted on young (3 months) and old (24 months) male Wistar rats subdivided into four groups control (C), melatonin treated (MLT), artificial light at night (ALAN), and ALAN+MLT group. Pronounced changes were observed in the old compared to the young rats. Reactive oxygen species (ROS), malondialdehyde (MDA), plasma membrane redox system (PMRS), protein carbonyl (PCO), and sialic acid (SA) were significantly (p ≤ 0.05) increased, while ferric reducing ability of plasma (FRAP) and reduced glutathione (GSH) were significantly (p ≤ 0.05) suppressed in light-exposed young and old animals compared to their age-matched controls. Advanced oxidation protein products (AOPP) increased non-significantly in young rats of the ALAN group; however, significant (p ≤ 0.05) changes were observed in the old rats of the ALAN group compared to their respective controls. Advanced glycation end products (AGEs) increased and acetylcholinesterase (AChE) activity decreased, significantly (p ≤ 0.05) in young animals of the ALAN group, while nonsignificant changes of both parameters were recorded in the old animals of the ALAN groups compared with their age-matched controls. Melatonin supplementation resulted in maintenance of the normal redox homeostasis in both young and old animal groups. Our study suggests that aged rats are more susceptible to altered photoperiod as their circadian redox homeostasis is under stress subsequent to ALAN. Melatonin supplementation could be a promising means of alleviating age-related circadian disturbances, especially in light-polluted areas.

The Good, the Bad, and the Ugly of ROS: New Insights on Aging and Aging-Related Diseases from Eukaryotic and Prokaryotic Model Organisms

Aging is associated with the accumulation of cellular damage over the course of a lifetime. This process is promoted in large part by reactive oxygen species (ROS) generated via cellular metabolic and respiratory pathways. Pharmacological, nonpharmacological, and genetic interventions have been used to target cellular and mitochondrial networks in an effort to decipher aging and age-related disorders. While ROS historically have been viewed as a detrimental byproduct of normal metabolism and associated with several pathologies, recent research has revealed a more complex and beneficial role of ROS in regulating metabolism, development, and lifespan. In this review, we summarize the recent advances in ROS research, focusing on both the beneficial and harmful roles of ROS, many of which are conserved across species from bacteria to humans, in various aspects of cellular physiology. These studies provide a new context for our understanding of the parts ROS play in health and disease. Moreover, we highlight the utility of bacterial models to elucidate the molecular pathways by which ROS mediate aging and aging-related diseases.

Differential expression of NADPH oxidase-2 (Nox-2) and nuclear factor-erythroid 2-related factor 2 (Nrf2) transcripts in peripheral blood mononuclear cells isolated from dengue patients

The role of oxidative stress in the pathogenesis of dengue infection is not completely known. A recent study reveals the involvement of oxidative stress responsive molecules in the generation of host immune responses to dengue virus in vitro. Objective of the present study was to analyse the changes in the expression of oxidant-antioxidant genes Nox-2 (NADPH oxidase) and Nrf2 (nuclear factor-erythroid 2-related factor 2) in patients with dengue during the early phase of infection compared to other febrile illness (OFI) cases and healthy controls using Real-time qPCR assay. The study enrolled 88 dengue patients, 31 OFI cases, and 63 healthy individuals as controls. Out of 88 dengue cases, 32 were classified as severe dengue cases (SD) and remaining 56 patients as non-severe dengue (NSD). Blood samples were collected firstly at the time of admission and a second sampling was done from the available individuals (38 dengue and 13 OFI cases) at the time of defervescence. Total RNA was extracted from the Peripheral blood mononuclear cells and the transcripts level of Nox-2 and Nrf2 were analysed by qPCR. On DOA, both Nox-2 and Nrf2 expression was found to be down regulated in dengue and OFI cases (P < 0.05) compared to healthy controls. Interestingly at defervescence, the transcript levels were found to be significantly increased in dengue cases unlike OFI, where no such increment was evidenced. From DOA to DOD, the study observed a signficant increase in the levels of Nox-2 transcripts (P < 0.05) both in SD and NSD cases. But a significant Nrf2 activation was not observed in SD cases as we found in NSD cases. Thus  a steady and significant increase in Nox-2 transcript level in severe, non-severe and secondary dengue infected groups observed in the current study supports the earlier reports on the involvement of anti-oxidant response in dengue severity. However further studies on its protein levels and mechanistic action would decipher the exact role of these potential molecules in the disease virulence.

Metabolic Syndrome, Redox State, and the Proteasomal System

SIGNIFICANCE

Since the metabolic syndrome (MS) and pathologies associated with/resulting from metabolic dysregulations became a worldwide spreading and growing problem, the mechanisms mediating the according cellular changes got into a focus of interest. The ubiquitin-proteasomal system (UPS) is the main regulator of both the functional and dysfunctional protein pool of (not only) mammalian cells-thus, it is obvious that an impact on this system may also affect cellular functionality that directly depends on permanent regulation/adaption of the cell's proteostasis. However, the according research is still at the beginning. Recent Advances: It was also recently shown that maintaining a highly functional UPS positively correlates with increased health or even life span, thus modulation or restoration of UPS function may be an effective approach alleviating or even preventing MS detrimental consequences.

CRITICAL ISSUES

Even if many consequences of metabolic dysregulation such as a slight but chronic redox shift to a more oxidative state (i.e., a low-grade systemic inflammation that increases reactive oxygen species formation, lipid peroxidation, protein oxidation, formation of advanced glycation end products, glycosylation, S-glutathionylation, redox shifts, endoplasmic reticulum stress, unfolded protein response, expression of transcription factors, and release of cytokines) are already known to affect the highly redox-regulated UPS, experimental data about UPS changes that are directly mediated by glucotoxic and/or lipotoxic stress are still rarely published.

FUTURE DIRECTIONS

It may be taken into account that many MS-related pathologic changes result from UPS dysfunction or dysregulation. In this review, the main interface between MS effects and their impact on the UPS are highlighted since they may direct to new therapeutic approaches. Antioxid. Redox Signal. 25, 902-917.

Changes in cellular infrastructure after induced endoplasmic reticulum stress in Moniliophthora perniciosa

Moniliophthora perniciosa is a basidiomycete fungus that causes witches' broom disease in Theobroma cacao We analyzed the morphology and survival of fungal hyphae and endoplasmic reticulum (ER) remodeling in either glucose- or glycerol-grown M. perniciosa after treatment with ER stress-inducing chemicals dithiothreitol (DTT) or tunicamycin (TM). Changes in intracellular redox potential can cause endoplasmic reticulum (ER) stress due to diminished efficiency in protein folding that could in turn reduce cell survival. Such stress diminishes protein-folding efficiency that could in turn reduce cell survival. Light microscopy revealed morphological changes in hyphae after TM but not after DTT treatment, regardless of the media carbon source. Decrease in fungal survival, after both TM and DTT treatments, was dose-dependent and glycerol-grown cells showed a higher resistance to both chemicals compared to glucose-grown cells. Electron microscopy showed TM and DDT-induced ER stress in M. perniciosa as evidenced by structural alterations of the organelle. The volume of ER structures increased as a typical consequence of unfolded protein stress, and the number of autophagosomes was higher. In glycerol-grown fungus DTT treatment slightly induced expression of molecular chaperone BiP. The TM exposure-induced expression of gene MpIRE1, involved in signaling of the unfolded protein response, was higher in glycerol than glucose-grown cells. Such difference was not observable with expression of gene MpATG8, encoding a key protein in autosome formation, that was induced 1.4-fold and 1.2-fold in glucose or glycerol-grown cells, respectively. DHE-based fluorescence assay showed M. perniciosa oxidative stress induced by H₂O₂, and treated cells had a higher level of oxidative stress compared to control. A comprehensive study of remodeling of ER is important in understanding M. perniciosa fungus resistance to oxidative stress and its ability to implement a successful infection in T. cacao.

Canavanine Alters ROS/RNS Level and Leads to Post-translational Modification of Proteins in Roots of Tomato Seedlings

Canavanine (CAN), a structural analog of arginine (Arg), is used as a selective inhibitor of inducible NOS in mammals. CAN is incorporated into proteins' structure in the place of Arg, leading to the formation of aberrant compounds. This non-protein amino acid is found in legumes, e.g., Canavalia ensiformis (L.) DC. or Sutherlandia frutescens (L.) R.Br. and acts as a strong toxin against herbivores or plants. Tomato (Solanum lycopersicum L.) seedlings were treated for 24-72 h with CAN (10 or 50 μM) inhibiting root growth by 50 or 100%, without lethal effect. We determined ROS level/production in root extracts, fluorescence of DAF-FM and APF derivatives corresponding to RNS level in roots of tomato seedlings and linked CAN-induced restriction of root growth to the post-translational modifications (PTMs) of proteins: carbonylation and nitration. Both PTMs are stable markers of nitro-oxidative stress, regarded as the plant's secondary response to phytotoxins. CAN enhanced H2O2 content and superoxide radicals generation in extracts of tomato roots and stimulated formation of protein carbonyl groups. An elevated level of carbonylated proteins was characteristic for the plants after 72 h of the culture, mainly for the roots exposed to 10 μM CAN. The proteolytic activity was stimulated by tested non-protein amino acid. CAN treatment led to decline of fluorescence of DAF-FM derivatives, and transiently stimulated fluorescence of APF derivatives. Short-term exposure of tomato seedlings to CAN lowered the protein nitration level. Activity of peroxidase, polyamine oxidase and NADPH oxidase, enzymes acting as modulators of H2O2 concentration and governing root architecture and growth were determined. Activities of all enzymes were stimulated by CAN, but no strict CAN concentration dependence was observed. We conclude, that although CAN treatment led to a decline in the nitric oxide level, PTMs observed in roots of plants exposed to CAN are linked rather to the formation of carbonyl groups than to nitration, and are detected particularly after 24 h. Thus, oxidative stress and oxidative modifications of proteins seems to be of significant importance in the rapid response of plants to CAN.

Oxidation events and skin aging

The rate of skin aging, or that of tissue in general, is determined by a variable predominance of tissue degeneration over tissue regeneration. This review discusses the role of oxidative events of tissue degeneration and aging in general, and for the skin in particular. The mechanisms involved in intrinsic and extrinsic (photo-) aging are described. Since photoaging is recognized as an important extrinsic aging factor, we put special emphasize on the effects of UV exposure on aging, and its variable influence according to global location and skin type. We here summarise direct photochemical effects of UV on DNA, RNA, proteins and vitamin D, the factors contributing to UV-induced immunosuppression, which may delay aging, the nature and origin of reactive oxygen species (ROS) and reactive nitrogen species (RNS) as indirect contributors for aging, and the consequences of oxidative events for extracellular matrix (ECM) degradation, such as that of collagen. We conclude that conflicting data on studies investigating the validity of the free radical damage theory of aging may reflect variations in the level of ROS induction which is difficult to quantify in vivo, and the lack of targeting of experimental ROS to the relevant cellular compartment. Also mitohormesis, an adaptive response, may arise in vivo to moderate ROS levels, further complicating interpretation of in vivo results. We here describes how skin aging is mediated both directly and indirectly by oxidative degeneration.This review indicates that skin aging events are initiated and often propagated by oxidation events, despite recently recognized adaptive responses to oxidative stress.

Arsenic trioxide and all-trans retinoic acid target NPM1 mutant oncoprotein levels and induce apoptosis in NPM1-mutated AML cells

Nucleophosmin (NPM1) mutations represent an attractive therapeutic target in acute myeloid leukemia (AML) because they are common (∼30% AML), stable, and behave as a founder genetic lesion. Oncoprotein targeting can be a successful strategy to treat AML, as proved in acute promyelocytic leukemia by treatment with all-trans retinoic acid (ATRA) plus arsenic trioxide (ATO), which degrade the promyelocytic leukemia (PML)-retinoic acid receptor fusion protein. Adjunct of ATRA to chemotherapy was reported to be beneficial for NPM1-mutated AML patients. Leukemic cells with NPM1 mutation also showed sensibility to ATO in vitro. Here, we explore the mechanisms underlying these observations and show that ATO/ATRA induce proteasome-dependent degradation of NPM1 leukemic protein and apoptosis in NPM1-mutated AML cell lines and primary patients' cells. We also show that PML intracellular distribution is altered in NPM1-mutated AML cells and reverted by arsenic through oxidative stress induction. Interestingly, similarly to what was described for PML, oxidative stress also mediates ATO-induced degradation of the NPM1 mutant oncoprotein. Strikingly, NPM1 mutant downregulation by ATO/ATRA was shown to potentiate response to the anthracyclin daunorubicin. These findings provide experimental evidence for further exploring ATO/ATRA in preclinical NPM1-mutated AML in vivo models and a rationale for exploiting these compounds in chemotherapeutic regimens in clinics.

Altered cross-bridge properties in skeletal muscle dystrophies

Force and motion generated by skeletal muscle ultimately depends on the cyclical interaction of actin with myosin. This mechanical process is regulated by intracellular Ca²⁺ through the thin filament-associated regulatory proteins i.e.; troponins and tropomyosin. Muscular dystrophies are a group of heterogeneous genetic affections characterized by progressive degeneration and weakness of the skeletal muscle as a consequence of loss of muscle tissue which directly reduces the number of potential myosin cross-bridges involved in force production. Mutations in genes responsible for skeletal muscle dystrophies (MDs) have been shown to modify the function of contractile proteins and cross-bridge interactions. Altered gene expression or RNA splicing or post-translational modifications of contractile proteins such as those related to oxidative stress, may affect cross-bridge function by modifying key proteins of the excitation-contraction coupling. Micro-architectural change in myofilament is another mechanism of altered cross-bridge performance. In this review, we provide an overview about changes in cross-bridge performance in skeletal MDs and discuss their ultimate impacts on striated muscle function.

Hepatic transcriptome profiles differ among maturing beef heifers supplemented with inorganic, organic, or mixed (50% inorganic:50% organic) forms of dietary selenium

Selenium (Se) is an important trace mineral that, due to deficiencies in the soil in many parts of the USA, must be supplemented directly to the diet of foraging cattle. Both organic and inorganic forms of dietary Se supplements are available and commonly used, and it is known that Se form affects tissue assimilation, bioavailability, and physiological responses. However, little is known about the effects of form of dietary Se supplements on gene expression profiles, which ostensibly account for Se form-dependent physiological processes. To determine if hepatic transcriptomes of growing beef (Angus-cross) heifers (0.5 kg gain/day) was altered by form of dietary supplemental Se, none (Control), or 3 mg Se/day as inorganic Se (ISe, sodium selenite), organic (OSe, Sel-Plex®), or a blend of ISe and OSe (1.5 mg:1.5 mg, Mix) Se was fed for 168 days, and the RNA expression profiles from biopsied liver tissues was compared by microarray analysis. The relative abundance of 139 RNA transcripts was affected by Se treatment, with 86 of these with complete gene annotations. Statistical and bioinformatic analysis of the annotated RNA transcripts revealed clear differences among the four Se treatment groups in their hepatic expression profiles, including (1) solely and commonly affected transcripts; (2) Control and OSe profiles being more similar than Mix and ISe treatments; (3) distinct OSe-, Mix-, and ISe-Se treatment-induced "phenotypes" that possessed both common and unique predicted physiological capacities; and (4) expression of three microRNAs were uniquely sensitive to OSe, ISe, or Mix treatments, including increased capacity for redox potential induced by OSe and Mix Se treatments resulting from decreased expression of MiR2300b messenger RNA. These findings indicate that the form of supplemental dietary Se consumed by cattle will affect the composition of liver transcriptomes resulting, presumably, in different physiological capacities.

The proteasome and the degradation of oxidized proteins: part III-Redox regulation of the proteasomal system

Here, we review shortly the current knowledge on the regulation of the proteasomal system during and after oxidative stress. After addressing the components of the proteasomal system and the degradation of oxidatively damaged proteins in part I and II of this series, we address here which changes in activity undergo the proteasome and the ubiquitin-proteasomal system itself under oxidative conditions. While several components of the proteasomal system undergo direct oxidative modification, a number of redox-regulated events are modulating the proteasomal activity in a way it can address the major tasks in an oxidative stress situation: the removal of oxidized proteins and the adaptation of the cellular metabolism to the stress situation.

Nitrite and catalase levels rule oxidative stability and safety properties of milk: a review

This review focuses on recent evidence showing that various types of udder inflammation (mastitis) are associated with increased concentration of NO˙-derived metabolites, nitrite and nitrate, and oxidatively modified organic components under commercial farming and experimental conditions.

The proteasome and the degradation of oxidized proteins: Part II - protein oxidation and proteasomal degradation

Here, we review the role of oxidative protein modification as a signal for recognition and degradation of proteins. It was clearly demonstrated that the ATP- and ubiquitin-independent 20S proteasome is playing a key role in the selective removal of oxidized proteins. Furthermore, the current knowledge of the substrate susceptibility on the degradation of oxidized proteins and the role of the immunoproteasome will be highlighted.

Nrf2 deficiency prevents reductive stress-induced hypertrophic cardiomyopathy

AIMS

Mutant protein aggregation (PA) cardiomyopathy (MPAC) is characterized by reductive stress (RS), PA (of chaperones and cytoskeletal components), and ventricular dysfunction in transgenic mice expressing human mutant CryAB (hmCryAB). Sustained activation of nuclear erythroid-2 like factor-2 (Nrf2) causes RS, which contributes to proteotoxic cardiac disease. The goals of this pre-clinical study were to (i) investigate whether disrupting Nrf2-antioxidant signalling prevents RS and rescues redox homeostasis in hearts expressing the mutant chaperone and (ii) elucidate mechanisms that could delay proteotoxic cardiac disease.

METHODS AND RESULTS

Non-transgenic (NTG), transgenic (TG) with MPAC and MPAC-TG:Nrf2-deficient (Nrf2-def) mice were used in this study. The effects of Nrf2 diminution (Nrf2±) on RS mediated MPAC in TG mice were assessed at 6-7 and 10 months of age. The diminution of Nrf2 prevented RS and prolonged the survival of TG mice (∼50 weeks) by an additional 20-25 weeks. The TG:Nrf2-def mice did not exhibit cardiac hypertrophy at even 60 weeks, while the MPAC-TG mice developed pathological hypertrophy and heart failure starting at 24-28 weeks of age. Aggregation of cardiac proteins was significantly reduced in TG:Nrf2-def when compared with TG mice at 7 months. Preventing RS and maintaining redox homeostasis in the TG:Nrf2-def mice ameliorated PA, leading to decreased ubiquitination of proteins.

CONCLUSION

Nrf2 deficiency rescues redox homeostasis, which reduces aggregation of mutant proteins, thereby delaying the proteotoxic pathological cardiac remodelling caused by RS and toxic protein aggregates.

Interaction between misfolded PrP and the ubiquitin-proteasome system in prion-mediated neurodegeneration

Prion diseases are associated with the conformational conversion of cellular prion protein (PrP(C)) to pathological β-sheet isoforms (PrP(Sc)), which is the infectious agent beyond comprehension. Increasing evidence indicated that an unknown toxic gain of function of PrP(sc) underlies neuronal death. Conversely, strong evidence indicated that cellular prion protein might be directly cytotoxic by mediating neurotoxic signaling of β-sheet-rich conformers independent of prion replication. Furthermore, the common properties of β-sheet-rich isoform such as PrP(Sc) and β amyloid protein become the lynchpin that interprets the general pathological mechanism of protein misfolding diseases. Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in various protein misfolding diseases. However, the mechanisms of this impairment remain unknown in many cases. In prion disease, prion-infected mouse brains have increased levels of ubiquitin conjugates, which correlate with decreased proteasome function. Both PrP(C) and PrP(Sc) accumulate in cells after proteasome inhibition, which leads to increased cell death. A direct interaction between 20S core particle and PrP isoforms was demonstrated. Here we review the ability of misfolded PrP and UPS to affect each other, which might contribute to the pathological features of prion-mediated neurodegeneration.

Impaired autophagy, chaperone expression, and protein synthesis in response to critical illness interventions in porcine skeletal muscle

Critical illness myopathy (CIM) is characterized by a preferential loss of the motor protein myosin, muscle wasting, and impaired muscle function in critically ill intensive care unit (ICU) patients. CIM is associated with severe morbidity and mortality and has a significant negative socioeconomic effect. Neuromuscular blocking agents, corticosteroids, sepsis, mechanical ventilation, and immobilization have been implicated as important risk factors, but the causal relationship between CIM and the risk factors has not been established. A porcine ICU model has been used to determine the immediate molecular and cellular cascades that may contribute to the pathogenesis prior to myosin loss and extensive muscle wasting. Expression profiles have been compared between pigs exposed to the ICU interventions, i.e., mechanically ventilated, sedated, and immobilized for 5 days, with pigs exposed to critical illness interventions, i.e., neuromuscular blocking agents, corticosteroids, and induced sepsis in addition to the ICU interventions for 5 days. Impaired autophagy as well as impaired chaperone expression and protein synthesis were observed in the skeletal muscle in response to critical illness interventions. A novel finding in this study is impaired core autophagy machinery in response to critical illness interventions, which when in concert with downregulated chaperone expression and protein synthesis may collectively affect the proteostasis in skeletal muscle and may exacerbate the disease progression in CIM.

Protein oxidation in aging and the removal of oxidized proteins

Reactive oxygen species (ROS) are generated constantly within cells at low concentrations even under physiological conditions. During aging the levels of ROS can increase due to a limited capacity of antioxidant systems and repair mechanisms. Proteins are among the main targets for oxidants due to their high rate constants for several reactions with ROS and their abundance in biological systems. Protein damage has an important influence on cellular viability since most protein damage is non-repairable, and has deleterious consequences on protein structure and function. In addition, damaged and modified proteins can form cross-links and provide a basis for many senescence-associated alterations and may contribute to a range of human pathologies. Two proteolytic systems are responsible to ensure the maintenance of cellular functions: the proteasomal (UPS) and the lysosomal system. Those degrading systems provide a last line of antioxidative protection, removing irreversible damaged proteins and recycling amino acids for the continuous protein synthesis. But during aging, both systems are affected and their proteolytic activity declines significantly. Here we highlight the recent advantages in the understanding of protein oxidation and the fate of these damaged proteins during aging. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Murraya koenigii leaf extract inhibits proteasome activity and induces cell death in breast cancer cells

Background

Inhibition of the proteolytic activity of 26S proteasome, the protein-degrading machine, is now considered a novel and promising approach for cancer therapy. Interestingly, proteasome inhibitors have been demonstrated to selectively kill cancer cells and also enhance the sensitivity of tumor cells to chemotherapeutic agents. Recently, polyphenols/flavonoids have been reported to inhibit proteasome activity. Murraya koenigii Spreng, a medicinally important herb of Indian origin, has been used for centuries in the Ayurvedic system of medicine. Here we show that Murraya koenigii leaves (curry leaves), a rich source of polyphenols, inhibit the proteolytic activity of the cancer cell proteasome, and cause cell death.

Methods

Hydro-methanolic extract of curry leaves (CLE) was prepared and its total phenolic content [TPC] determined by, the Folin-Ciocalteau’s method. Two human breast carcinoma cell lines: MCF-7 and MDA-MB-231 and a normal human lung fibroblast cell line, WI-38 were used for the studies. Cytotoxicity of the CLE was assessed by the MTT assay. We studied the effect of CLE on growth kinetics using colony formation assay. Growth arrest was assessed by cell cycle analysis and apoptosis by Annexin-V binding using flow cytometry. Inhibition of the endogenous 26S proteasome was studied in intact cells and cell extracts using substrates specific to 20S proteasomal enzymes.

Results

CLE decreased cell viability and altered the growth kinetics in both the breast cancer cell lines in a dose-dependent manner. It showed a significant arrest of cells in the S phase albeit in cancer cells only. Annexin V binding data suggests that cell death was via the apoptotic pathway in both the cancer cell lines. CLE treatment significantly decreased the activity of the 26S proteasome in the cancer but not normal cells.

Conclusions

Our study suggests M. koenigii leaves to be a potent source of proteasome inhibitors that lead to cancer cell death. Therefore, identification of active component(s) from the leaf extract could lead to the development of anti-cancer agents which could be useful in the treatment of different types of cancers.

Carbonylation of the cytoskeletal protein actin leads to aggregate formation

Protein carbonylation is a common feature in cells exposed to oxidants, leading to protein dysfunction and protein aggregates. Actin, which is involved in manifold cellular processes, is a sensitive target protein to this oxidative modification. T-cell proteins have been widely described to be sensitive targets to oxidative modifications. The aim of this work was to test whether the formation of protein aggregates contributes to the impaired proliferation of Jurkat cells after oxidative stress and to test whether actin as a major oxidation-prone cytoskeletal protein is an integral part of such protein aggregates. We used Jurkat cells, an established T-cell model, showing the formation of actin aggregates along with the decrease of proteasome activity. The presence of these protein aggregates inhibits Jurkat proliferation even under conditions not influencing viability. As a conclusion, we propose that an oxidative environment leads to actin aggregates contributing to T-cell cellular functional impairment.

Free radical-operated proteotoxic stress in macrophages primed with lipopolysaccharide

The free-radical-operated mechanism of death of activated macrophages at sites of inflammation is unclear, but it is important to define it in order to find targets to prevent further tissue dysfunction. A well-defined model of macrophage activation at sites of inflammation is the treatment of RAW 264.7 cells with lipopolysaccharide (LPS), with the resulting production of reactive oxygen species (ROS). ROS and other free radicals can be trapped with the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), a cell-permeable probe with antioxidant properties, which thus interferes with free-radical-operated oxidation processes. Here we have used immuno-spin trapping to investigate the role of free-radical-operated protein oxidation in LPS-induced cytotoxicity in macrophages. Treatment of RAW 264.7 cells with LPS resulted in increased ROS production, oxidation of proteins, cell morphological changes and cytotoxicity. DMPO was found to trap protein radicals to form protein-DMPO nitrone adducts, to reduce protein carbonyls, and to block LPS-induced cell death. N-Acetylcysteine (a source of reduced glutathione), diphenyleneiodonium (an inhibitor of NADPH oxidase), and 2,2'-dipyridyl (a chelator of Fe(2+)) prevented LPS-induced oxidative stress and cell death and reduced DMPO-nitrone adduct formation, suggesting a critical role of ROS, metals, and protein-radical formation in LPS-induced cell cytotoxicity. We also determined the subcellular localization of protein-DMPO nitrone adducts and identified some candidate proteins for DMPO attachment by LC-MS/MS. The LC-MS/MS data are consistent with glyceraldehyde-3-phosphate dehydrogenase, one of the most abundant, sensitive, and ubiquitous proteins in the cell, becoming labeled with DMPO when the cell is primed with LPS. This information will help find strategies to treat inflammation-associated tissue dysfunction by focusing on preventing free radical-operated proteotoxic stress and death of macrophages.

Release of mitochondrial apoptogenic factors and cell death are mediated by CK2 and NADPH oxidase

Activation of the NADPH oxidase subunit, NOX2, and increased oxidative stress are associated with neuronal death after cerebral ischemia and reperfusion. Inhibition of NOX2 by casein kinase 2 (CK2) leads to neuronal survival, but the mechanism is unknown. In this study, we show that in copper/zinc-superoxide dismutase transgenic (SOD1 Tg) mice, degradation of CK2α and CK2α' and dephosphorylation of CK2β against oxidative stress were markedly reduced compared with wild-type (WT) mice that underwent middle cerebral artery occlusion. Inhibition of CK2 pharmacologically or by ischemic reperfusion facilitated accumulation of poly(ADP-ribose) polymers, the translocation of apoptosis-inducing factor (AIF), and cytochrome c release from mitochondria after ischemic injury. The eventual enhancement of CK2 inhibition under ischemic injury strongly increased 8-hydroxy-2'-deoxyguanosine and phosphorylation of H2A.X. Furthermore, CK2 inhibition by tetrabromocinnamic acid (TBCA) in SOD1 Tg and gp91 knockout (KO) mice after ischemia reperfusion induced less release of AIF and cytochrome c than in TBCA-treated WT mice. Inhibition of CK2 in gp91 KO mice subjected to ischemia reperfusion did not increase brain infarction compared with TBCA-treated WT mice. These results strongly suggest that NOX2 activation releases reactive oxygen species after CK2 inhibition, triggering release of apoptogenic factors from mitochondria and inducing DNA damage after ischemic brain injury.

Specific nitration of tyrosines 46 and 48 makes cytochrome c assemble a non-functional apoptosome

Under nitroxidative stress, a minor fraction of cytochrome c can be modified by tyrosine nitration. Here we analyze the specific effect of nitration of tyrosines 46 and 48 on the dual role of cytochrome c in cell survival and cell death. Our findings reveal that nitration of these two solvent-exposed residues has a negligible effect on the rate of electron transfer from cytochrome c to cytochrome c oxidase, but impairs the ability of the heme protein to activate caspase-9 by assembling a non-functional apoptosome. It seems that cytochrome c nitration under cellular stress counteracts apoptosis in light of the small amount of modified protein. We conclude that other changes such as increased peroxidase activity prevail and allow the execution of apoptosis.

BLENX MODELS OF α-SYNUCLEIN AND PARKIN KINETICS IN NEUROPATHOLOGY OF PARKINSON'S DISEASE

In this paper two stochastic kinetic models of a faulty ubiquitin–proteasome are presented. In the first model, mutant variants of the α-synuclein, induced by environmental stress factors, inhibit the ubiquitin–proteasome pathway that is in charge to start the degradation of misfolded proteins. In the second model mutant variants of parkin proteins are not able to transfer the ubiquitin molecules on the faulty proteins, so that they are not targeted and recognized as toxic products. The models are specified in BlenX and simulated with Beta Workbench (Beta WB) simulator. BlenX is a new programming language that has been recently designed by the CoSBi team of researchers to describe components and interactions among components of a biochemical system. It implements a process calculus in which the communication and synchronization between computational processes abstract the biochemical interaction and reactions between molecules, proteins and functional complexes. The aim of this study is twofold: (i) to move the current focus on the structural studies of the components of the protein ubiquitination and degradation to the dynamics of such components in a typical systems biology perspective; (ii) to provide first stochastic models in a new language suitable to systemic approach to the modelling of biochemical kinetics. This tool makes it possible for biologists and medical researchers a high-level modeling of molecular mechanisms underlying the pathogenesis of the disease. Consequently, the suitable abstraction provided by the language makes possible the elucidation of important and still elusive aspects of the involved biochemical interactions. The agreement of the simulations of our models with the available qualitative experimental observations and previous theoretical studies supports the confidence in the model validity.

Nitration of tyrosines 46 and 48 induces the specific degradation of cytochrome c upon change of the heme iron state to high-spin

The Reactive Nitrogen and Oxygen Species (the so-called RNOS), which are well-known radicals formed in the mitochondria under nitro-oxidative cell stress, are responsible for nitration of tyrosines in a wide variety of proteins and, in particular, in cytochrome c (Cc). Only three out of the five tyrosine residues of human Cc, namely those at positions 67, 74 and 97, have been detected in vivo as nitrotyrosines. However, nitration of the two other tyrosines, namely those at positions 46 and 48, has never been detected in vivo despite they are both well-exposed to solvent. Here we investigate the changes in heme coordination and alkaline transition, along with the peroxidase activity and in cell degradation of Cc mutants in which all their tyrosine residues - with the only exception of that at position 46 or 48 - are replaced by phenylalanines. In Jurkat cell extracts devoid of proteases inhibitors, only the high-spin iron nitrated forms of these monotyrosine mutants are degraded. Altogether the resulting data suggest that nitration of tyrosines 46 and 48 makes Cc easily degradable upon turning the heme iron state to high-spin.

N-terminal ataxin-3 causes neurological symptoms with inclusions, endoplasmic reticulum stress and ribosomal dislocation

Mutant ataxin-3 is aberrantly folded and proteolytically cleaved in spinocerebellar ataxia type 3. The C-terminal region of the protein includes a polyglutamine stretch that is expanded in spinocerebellar ataxia type 3. Here, we report on the analysis of an ataxin-3 mutant mouse that has been obtained by gene trap integration. The ataxin-3 fusion protein encompasses 259 N-terminal amino acids including the Josephin domain and an ubiquitin-interacting motif but lacks the C-terminus with the polyglutamine stretch, the valosin-containing protein binding region and part of the ubiquitin-interacting motif 2. Homozygous ataxin-3 mutant mice were viable and showed no apparent anatomical defects at birth. However, at the age of 9 months, homozygous and heterozygous mutant mice revealed significantly altered behaviour and progressing deficits of motor coordination followed by premature death at ∼12 months. At this time, prominent extranuclear protein aggregates and neuronal cell death was found in mutant mice. This was associated with disturbances of the endoplasmic reticulum-mediated unfolded protein response, consistent with the normal role of ataxin-3 in endoplasmic reticulum homeostasis. Thus, the ataxin-3 gene trap model provides evidence for a contribution of the non-polyglutamine containing ataxin-3 N-terminus, which mimics a calpain fragment that has been observed in spinocerebellar ataxia type 3. Consistent with the disease in humans, gene trap mice develop cytoplasmic inclusion bodies and implicate impaired unfolded protein response in the pathogenesis of spinocerebellar ataxia type 3.

Combination of PDT and inhibitor treatment affects melanoma cells and spares keratinocytes

Photodynamic therapy (PDT) is a potential tool in cancer treatment. Today this therapy is established among others for the treatment of nonmelanoma skin cancer. However, the more dangerous skin cancer--the melanoma--still has to be removed by surgery. Therefore, we investigated the effects of PDT and additional administration of heme oxygenase I (HO-I) and poly(ADP-ribose) polymerase (PARP) inhibitors on the treatment of melanoma cells in comparison to nonmalignant keratinocytes. Therefore, cocultures were established with WM451LU melanoma cells and HaCaT keratinocytes. In the coculture some 65% melanoma cells and 35% HaCaT cells were present before PDT, whereas after PDT the proportion was 41% melanoma cells and 59% HaCaT cells. Combination of both inhibitors improves these results to only 16% melanoma cells and 84% HaCaT cells. PDT is, therefore, a potent skin cancer treatment, which might also be interesting for melanoma treatment. The cytotoxic effects of PDT are largely mediated by ROS. Addition of HO-I and PARP inhibitors could improve the efficiency of photodynamic treatment.

Hepatitis C virus impairs the induction of cytoprotective Nrf2 target genes by delocalization of small Maf proteins

The expression of a variety of cytoprotective genes is regulated by short cis-acting elements in their promoters, called antioxidant response elements (AREs). A central regulator of ARE-mediated gene expression is the NF-E2-related factor 2 (Nrf2). Nrf2/ARE-regulated genes are crucial for the maintenance of cellular integrity. Hepatitis C virus inhibits the induction of ARE-regulated genes, but neither induction nor inhibition of ARE-regulated gene expression affects HCV replication directly. In HCV-replicating cells the core protein triggers the delocalization of sMaf proteins from the nucleus to the replicon complex. Here sMafs bind to NS3. The extranuclear sMaf proteins prevent Nrf2 from entry in the nucleus and thereby inhibit the induction of Nrf2/ARE-regulated genes. This results in the decreased expression of cytoprotective genes. Consistent with this finding, the elimination of ROI is impaired in HCV-replicating cells as demonstrated by elevated protein oxidation or 8-OH-dG formation, reflecting DNA damage. In conclusion, these data identified a novel mechanism of Nrf2 regulation and suggest that the HCV-dependent inhibition of Nrf2/ARE-regulated genes confers to the HCV-associated pathogenesis by elevation of intracellular ROI that affect integrity of the host genome and regenerative processes.

The outcome of 5-ALA-mediated photodynamic treatment in melanoma cells is influenced by vitamin C and heme oxygenase-1

Photodynamic therapy (PDT) is an important clinical approach for cancer treatment. It involves the administration of a photosensitizer, followed by its activation with light and induction of cell death. The underlying mechanism is an increased production of reactive oxygen species (ROS) leading to oxidative stress, which is followed by cell death. However, effectiveness of PDT is limited due to an initiation of endogenous rescue response systems like heme oxygenase-1 (HO-1) in tumor cells. In recent years, consuming of antioxidant supplements has become widespread, but the effect of exogenously applied antioxidants on cancer therapy outcome remains unclear. Thus, this study was aimed to investigate if exogenous antioxidants might decrease ROS-induced cytotoxicity in photodynamic treatment. Lycopene, β-carotene, vitamin C, N-acetylcysteine, trolox, and N-tert-butyl-α-phenylnitrone in different doses were administered to human melanoma cells prior exposure to photodynamic treatment. Supplementation with vitamin C resulted in a significant decrease of the cell death rate, whereas the other tested antioxidants had no effect on cell viability and oxidative stress markers. The simultaneous application of vitamin C with the HO-1 activity inhibitor zinc protoporphyrine IX (ZnPPIX) caused a considerable decrease of photodynamic treatment-induced cytotoxicity compared to ZnPPIX alone. It can be summarized that exogenously applied antioxidants do not have a leading role in the protective response against photodynamic treatment. However, further studies are necessary to investigate more antioxidants and other substances, which might affect the outcome of photodynamic treatment in cancer therapy.

Pharmacological preconditioning by diazoxide downregulates cardiac L-type Ca(2+) channels

BACKGROUND AND PURPOSE

Pharmacological preconditioning (PPC) with mitochondrial ATP-sensitive K(+) (mitoK(ATP) ) channel openers such as diazoxide, leads to cardioprotection against ischaemia. However, effects on Ca(2+) homeostasis during PPC, particularly changes in Ca(2+) channel activity, are poorly understood. We investigated the effects of PPC on cardiac L-type Ca(2+) channels.

EXPERIMENTAL APPROACH

PPC was induced in isolated hearts and enzymatically dissociated cardiomyocytes from adult rats by preincubation with diazoxide. We measured reactive oxygen species (ROS) production and Ca(2+) signals associated with action potentials using fluorescent probes, and L-type currents using a whole-cell patch-clamp technique. Levels of the α(1c) subunit of L-type channels in the cellular membrane were measured by Western blot.

KEY RESULTS

PPC was accompanied by a 50% reduction in α(1c) subunit levels, and by a reversible fall in L-type current amplitude and Ca(2+) transients. These effects were prevented by the ROS scavenger N-acetyl-L-cysteine (NAC), or by the mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD). PPC significantly reduced infarct size, an effect blocked by NAC and 5-HD. Nifedipine also conferred protection against infarction when applied during the reperfusion period. Downregulation of the α(1c) subunit and Ca(2+) channel function were prevented in part by the protease inhibitor leupeptin.

CONCLUSIONS AND IMPLICATIONS

PPC downregulated the α(1c) subunit, possibly through ROS. Downregulation involved increased degradation of the Ca(2+) channel, which in turn reduced Ca(2+) influx, which may attenuate Ca(2+) overload during reperfusion.

Vitamin C inhibits NO-induced stabilization of HIF-1alpha in HUVECs

HIF-1alpha represents the oxygen-regulated sub-unit of the transcription factor HIF-1, which regulates the transcription of numerous genes involved in cellular response to hypoxia and oxidative stress. It is shown here that nitric oxide (NO) induces HIF-1alpha stabilization in human endothelial cells from umbilical cords (HUVECs) under normoxic conditions. HIF-1alpha protein was increased approximately 36-fold after incubation with 500 microM DETA-NO, which releases a steady state NO concentration of roughly one thousandth of the initial concentration of the donor. Loading of the cells with vitamin C counteracted NO-induced HIF-1alpha accumulation. Based on the observations that oxidative and nitrosative stress can influence the activity of the proteasomal system, which is responsible for the non-lysosomal degradation of proteins, among them HIF-1alpha, it was investigated whether NO-induced stabilization of HIF-1alpha might be due to reduced 20S proteasomal activity. This hypothesis could not be proved, because NO concentrations to inhibit 20S proteasomal activity were about one order of magnitude higher than that to inhibit HIF-1alpha degradation.

Meta-analysis of kindling-induced gene expression changes in the rat hippocampus

Numerous studies have been performed to examine gene expression patterns in the rodent hippocampus in the kindling model of epilepsy. However, recent reviews of this literature have revealed limited agreement among studies. Because this conclusion was based on retrospective comparison of reported “hit lists” from individual studies, we hypothesized that re-analysis of the original expression data would help address this concern. In this paper, we reanalyzed four genome-wide expression studies of excitotoxin-induced kindling in rat and performed a statistical meta-analysis. The meta-analysis revealed over 800 genes which show significant change in expression 24 h after initial seizure induction, and 59 genes altered after 10 days. To evaluate our results in light of previous work, we assembled a reference list of genes formed from a consensus of the published literature. Our profiles include most of the genes in this reference list, and most of the additional genes are from pathways or biological processes previously recognized to be altered in kindling. In addition our results emphasized expression changes in lipid metabolism and protein degradation pathways. We conclude that a cautious re-analysis of published expression data can help illuminate genes and pathways underling kindling. Supplementary Material is available at http://www.chibi.ubc.ca/faculty/pavlidis/meta-analysis-of-brain-kindling/

Metabolism-induced oxidative stress is a mediator of glucose toxicity in HT22 neuronal cells

Oxidative stress has been widely considered as a key player in the adverse effects of hyperglycaemia to various tissues, including neuronal cells. This study examined the participation of oxidative stress in injurious effects of high glucose on HT22 cells along with the activity of proteasome, a proteolytic system responsible for degradation of oxidized proteins. Although 10-fold glucose concentration caused non-significant viability changes, a significant reduction of cell proliferation was found. Moreover, the cell morphology was also altered. These changes were followed by an enhancement of intracellular ROS generation, however without any significant boost of the carbonyl group concentration in proteins. Correspondingly, only a slight decline in the 20S proteasome activity was found in high-glucose-treated cells. On the other hand, substances affecting glucose metabolism or antioxidants partially preserved the oxidative stress in high glucose treated cells. In summary, these results highlight the role of metabolic oxidative stress in hyperglycaemia affecting neurons.

Impact of Magnetic Labeling on Human and Mouse Stem Cells and Their Long-Term Magnetic Resonance Tracking in a Rat Model of Parkinson Disease

Magnetic resonance imaging (MRI) of magnetically labeled stem cells has become a valuable tool in the understanding and evaluation of experimental stem cell–based therapies of degenerative central nervous system disorders. This comprehensive study assesses the impact of magnetic labeling of both human and rodent stem cell–containing populations on multiple biologic parameters as maintenance of stemness and oxidative stress levels. Cells were efficiently magnetically labeled with very small superparamagnetic iron oxide particles. Only under the condition of tailored labeling strategies can the impact of magnetic labeling on vitality, proliferation, pluripotency, and oxidative stress levels be minimized. In a rat model of Parkinson disease, magnetically labeled mouse embryonic stem cells were tracked by high-field MRI for 6 months. Significant interindividual differences concerning the spatial distribution of cells became evident. Histologically, transplanted green fluorescent protein–positive iron oxide–labeled cells were clearly identified. No significant increase in oxidative stress levels at the implantation site and no secondary uptake of magnetic label by host phagocytotic cells were observed. Our study strongly suggests that molecular MRI approaches must be carefully tailored to the respective cell population to exert minimal physiologic impact, ensuring the feasibility of this imaging approach for clinical applications.

Protein stability and resistance to oxidative stress are determinants of longevity in the longest-living rodent, the naked mole-rat

The widely accepted oxidative stress theory of aging postulates that aging results from accumulation of oxidative damage. Surprisingly, data from the longest-living rodent known, naked mole-rats [MRs; mass 35 g; maximum lifespan (MLSP) > 28.3 years], when compared with mice (MLSP 3.5 years) exhibit higher levels of lipid peroxidation, protein carbonylation, and DNA oxidative damage even at a young age. We hypothesize that age-related changes in protein structural stability, oxidation, and degradation are abrogated over the lifespan of the MR. We performed a comprehensive study of oxidation states of protein cysteines [both reversible (sulfenic, disulfide) and indirectly irreversible (sulfinic/sulfonic acids)] in liver from young and old C57BL/6 mice (6 and 28 months) and MRs (2 and >24 years). Furthermore, we compared interspecific differences in urea-induced protein unfolding and ubiquitination and proteasomal activity. Compared with data from young mice, young MRs have 1.6 times as much free protein thiol groups and similar amounts of reversible oxidative damage to cysteine. In addition, they show less urea-induced protein unfolding, less protein ubiquitination, and higher proteasome activity. Mice show a significant age-related increase in cysteine oxidation and higher levels of ubiquitination. In contrast, none of these parameters were significantly altered over 2 decades in MRs. Clearly MRs have markedly attenuated age-related accrual of oxidation damage to thiol groups and age-associated up-regulation of homeostatic proteolytic activity. These pivotal mechanistic interspecies differences may contribute to the divergent aging profiles and strongly implicate maintenance of protein stability and integrity in successful aging.

The proteasome and its role in the degradation of oxidized proteins

The generation of free radicals and the resulting oxidative modification of cell structures are omnipresent in mammalian cells. This includes the permanent oxidation of proteins leading to the disruption of the protein structure and an impaired functionality. In consequence, these oxidized proteins have to be removed in order to prevent serious metabolic disturbances. The most important cellular proteolytic system responsible for the removal of oxidized proteins is the proteasomal system. For normal functioning, the proteasomal system needs the coordinated interaction of numerous components. This review describes the fundamental functions of the 20S "core" proteasome, its regulators, and the roles of the proteasomal system beyond the removal of oxidized proteins in mammalian cells.

Age-related differences in oxidative protein-damage in young and senescent fibroblasts

Aging is accompanied by an accumulation of oxidized proteins and cross-linked modified protein material. The intracellular formation and accumulation of highly oxidized and cross-linked proteins, the so-called lipofuscin, is a typical sign of senescence. However, little is known whether the lipofuscin accumulation during aging is related to environmental conditions, as oxidative stress, and whether the accumulation of oxidized proteins and lipofuscin is preferentially taking place in the cytosol or the nucleus and finally, what is the role of lysosomes in this process. Therefore, we investigated human skin fibroblasts in an early stage of proliferation ("young cells") and in a late stage ("senescent cells"). Such cells were compared for the amount of protein carbonyls and lipofuscin and their distribution within the cytosol and the nucleus. Furthermore, cells were exposed to single and repeated doses of hydrogen peroxide and paraquat, measuring the same set of parameters. In addition to that the role of the proteasome to degrade oxidized proteins in young and senescent cells was tested. Furthermore, detailed microscopic analysis was performed testing the intracellular distribution of lipofuscin. The results clearly demonstrated that repeated/chronic oxidative stress induces a senescence-like phenotype of the distribution of oxidized proteins as well as of lipofuscin. It could be demonstrated that most of the lipofuscin is located in lysosomes and that senescent cells contain less lysosomes not lipofuscin-laden in comparison to young cells.

A philosophy of anti-infectives as a guide in the search for new drugs for tuberculosis

How we develop antibiotics is shaped by how we view infectious disease. Given the urgent need for new chemotherapeutics for tuberculosis and other infectious diseases, it is timely to reconsider a view of infectious disease that is strongly supported by contemporary evidence but that has rarely been applied in antibiotic development. This view recognizes the importance of nonreplicating bacteria in persistent infections, acknowledges the heterogeneity and stringency of chemical environments encountered by the pathogen in the host, and emphasizes metabolic adaptation of the host and the pathogen during their competition. For example, efforts in our lab are guided by the perspective that Mycobacterium tuberculosis (Mtb) has co-evolved with the human immune response, with the result that Mtb turns host-imposed metabolic adversity to its own advantage. We seek chemotherapeutics that turn Mtb's adversity to the host's advantage.

The role of proteolytic cellular systems in trabecular meshwork homeostasis

The molecular mechanisms contributing to the progressive malfunction of the trabecular meshwork (TM)/Schlemm's canal (SC) conventional outflow pathway during aging and in Primary Open Angle Glaucoma (POAG) are still poorly understood. Progressive accumulation of damaged and cross-linked proteins is a hallmark of aging tissues and has been proposed to play a major role in the tissue abnormalities associated with organismal aging and many age-related diseases. Such progressive accumulation of damaged proteins with age is believed to result from both, increased oxidative stress that results in faster rates of protein damage, as well as from a functional decline in the cellular proteolytic machinery that eliminates misfolded and damaged proteins. Here, we review the reported data that supports the occurrence of oxidative damage and the alterations in the intracellular proteolytic systems in the TM in aging and POAG. Finally, we discuss how the functional decline of the cellular proteolytic machinery in the TM might lead to the observed physiologic alterations of the outflow pathway in glaucoma.