The ATM cofactor ATMIN protects against oxidative stress and accumulation of DNA damage in the aging brain

Progressive accumulation of DNA damage is causally involved in cellular senescence and organismal aging. The DNA damage kinase ATM plays a central role in maintaining genomic stability. ATM mutations cause the genetic disorder ataxia telangiectasia, which is primarily characterized by progressive neurodegeneration and cancer susceptibility. Although the importance of ATM function to protect against oxidative DNA damage and during aging is well described, the mechanism of ATM activation by these stimuli is not known. Here we identify ATM interactor (ATMIN) as an essential component of the ATM signaling pathway in response to oxidative stress and aging. Embryos lacking ATMIN (atmin(Δ/Δ)) died in utero and showed increased numbers of cells positive for phosphorylated histone H2aX, indicative of increased DNA damage. atmin(Δ/Δ) mouse embryonic fibroblasts accumulated DNA damage and prematurely entered senescence when cultured at atmospheric oxygen levels (20%), but this defect was rescued by addition of an antioxidant and also by culturing cells at physiological oxygen levels (3%). In response to acute oxidative stress, atmin(Δ/Δ) mouse embryonic fibroblasts showed slightly lower levels of ATM phosphorylation and reduced ATM substrate phosphorylation. Conditional deletion of ATMIN in the murine nervous system (atmin(ΔN)) resulted in reduced numbers of dopaminergic neurons, as does ATM deficiency. ATM activity was observed in old, but not in young, control mice, but aging-induced ATM signaling was impaired by ATMIN deficiency. Consequently, old atmin(ΔN) mice showed accumulation of DNA damage in the cortex accompanied by gliosis, resulting in increased mortality of aging mutant mice. These results suggest that ATMIN mediates ATM activation by oxidative stress, and thereby ATMIN protects the aging brain by preventing accumulation of DNA damage.     

Oxidative stress and neurodegenerative disorders

Oxidative insults, whether over-excitation, excessive release of glutamate or ATP caused by stroke, ischemia or inflammation, exposure to ionizing radiation, heavy-metal ions or oxidized lipoproteins may initiate various signaling cascades leading to apoptotic cell death and neurodegenerative disorders. Among the various reactive oxygen species (ROS) generated in the living organism, hydroxyl and peroxynitrite are the most potent and can damage proteins, lipids and nucleic acids. It appears that some natural antioxidants (tocopherol, ascorbic acid and glutathione) and defense enzyme systems (superoxide dismutase, catalase and glutathione peroxidase) may provide some protection against oxidative damage. Recent findings indicate several polyphenols and antioxidant drugs (probucol, seligilline) are effective in protecting the cells from ROS attack. Further development of these antioxidant molecules may be of value in preventing the development of neurodegenerative diseases.     

Plasma membrane Ca-ATPases: Targets of oxidative stress in brain aging and neurodegeneration

The plasma membrane Ca(2+)-ATPase (PMCA) pumps play an important role in the maintenance of precise levels of intracellular Ca(2+) [Ca(2+)](i), essential to the functioning of neurons. In this article, we review evidence showing age-related changes of the PMCAs in synaptic plasma membranes (SPMs). PMCA activity and protein levels in SPMs diminish progressively with increasing age. The PMCAs are very sensitive to oxidative stress and undergo functional and structural changes when exposed to oxidants of physiological relevance. The major signatures of oxidative modification in the PMCAs are rapid inactivation, conformational changes, aggregation, internalization from the plasma membrane and proteolytic degradation. PMCA proteolysis appears to be mediated by both calpains and caspases. The predominance of one proteolytic pathway vs the other, the ensuing pattern of PMCA degradation and its consequence on pump activity depends largely on the type of insult, its intensity and duration. Experimental reduction of PMCA expression not only alters the dynamics of cellular Ca(2+) handling but also has a myriad of downstream consequences on various aspects of cell function, indicating a broad role of these pumps. Age- and oxidation-related down-regulation of the PMCAs may play an important role in compromised neuronal function in the aging brain and its several-fold increased susceptibility to neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and stroke. Therapeutic approaches that protect the PMCAs and stabilize [Ca(2+)](i) homeostasis may be capable of slowing and/or preventing neuronal degeneration. The PMCAs are therefore emerging as a new class of drug targets for therapeutic interventions in various chronic degenerative disorders.     

Autophagy, proteasomes, lipofuscin, and oxidative stress in the aging brain

In order to successfully respond to stress all cells rely on the ability of the proteasomal and lysosomal proteolytic pathways to continually maintain protein turnover. Increasing evidence suggests that as part of normal aging there are age-related impairments in protein turnover by the proteasomal proteolytic pathway, and perturbations of the lysosomal proteolytic pathway. Furthermore, with numerous studies suggest an elevated level of a specialized form of lysosomal proteolysis (autophagy or macroautophagy) occurs during the aging of multiple cell types. Age-related alterations in proteolysis are believed to contribute to a wide variety of neuropathological manifestations including elevations in protein oxidation, protein aggregation, and cytotoxicity. Within the brain altered protein turnover is believed to contribute to elevations in multiple forms of protein aggregation ranging from tangle and Lewy body formation, to lipofuscin-ceroid accumulation. In this review we discuss and summarize evidence for proteolytic alterations occurring in the aging brain, the contribution of oxidative stress to disruption of protein turnover during normal aging, the evidence for cross-talk between the proteasome and lysosomal proteolytic pathways in the brain, and explore the contribution of altered proteolysis as a mediator of oxidative stress, neuropathology, and neurotoxicity in the aging brain.     

Mitochondria as a primary target for vascular hypoperfusion and oxidative stress in Alzheimer's disease

It has been widely accepted that vascular hypoperfusion induces oxidative stress and the outcome of this misbalance is brain energy failure. This abnormality leads to neuronal death which manifests as cognitive impairment and the development of brain pathology as in Alzheimer's disease (AD). It has been demonstrated that the AD brain is characterized by impairments in energy metabolism. We theorize that hypoperfusion induced mitochondrial failure plays a key role in the generation of reactive oxygen species, resulting in oxidative damage to brain cellular compartments, especially in the vascular endothelium and in selective population of neurons with high metabolic activity in the AD brain. All of these abnormalities have been found to occur before classic AD pathology inducing neuronal degeneration and amyloid deposition during the progression of AD. Therefore, expanding investigations into both the mechanisms behind amyloid beta (Abeta) deposition and the possible accelerating effects of environmental factors such as chronic hypoxia/reperfusion may open a new avenue for effective treatments of AD. Future studies examining the importance of mitochondrial pathobiology in brain cellular compartments provide insight not only into the better understanding of the neurodegenerative and/or cerebrovascular disease but also provide targets for treating these conditions.     

Clinical aspects of neurodegenerative diseases - 15th HUPO BPP Workshop April 8-9, 2011, Bochum, Germany

The HUPO Brain Proteome Project (HUPO BPP) held its 15th workshop in Bochum, Germany, from April 8th to 9th, 2011 directly after the Proteomic Forum 2011 in Berlin. Like on every spring workshop, the focus was more on clinical aspects, so that especially clinicians participated in this workshop.     

Oxidative stress in primary glomerular diseases: a comparative study

Objective To evaluate the status of oxidative stress in patients with different primary glomerular diseases (PGD) which have differential predisposition to renal failure. Methods Seventy-three patients with PGD and 50 controls were enrolled in the study. They were sub-grouped into non-proliferative glomerulonephritis (NPGN) and proliferative glomerulonephritis (PGN). Levels of serum malondialdehyde (MDA), reactive nitrogen intermediates (RNI), plasma total homocysteine (tHcy), urine 8-isoprostane (8-IP), RBC thiols, glutathione-S-transferase (GST) and serum superoxide dismutase (SOD) were measured spectrophotometrically. Results PGD patients showed a significant increase in MDA, RNI, tHcy, 8-IP levels (P < 0.05) and decreased SOD, total thiols and protein bound thiol levels as compared to controls (P < 0.05). Significantly higher levels of tHcy, MDA and 8-IP (P < 0.05) and lower SOD enzyme activity (P < 0.05) were observed in PGN group as compared to NPGN and control groups. These changes remained significant even after adjustment was made for creatinine. Conclusions Oxidative stress in PGN is significantly higher than NPGN, indicating higher oxidative stress in these patients, independent of degree of renal dysfunction.     

Oxidative stress in otosclerosis

Objectives: Otosclerosis is a disease involving abnormal bone turnover in the human otic capsule that results in hearing loss. Several hypotheses have been suggested for the etiopathogenesis of otosclerosis; however, its etiology remains unclear.

Methods: This study evaluated the correlation between otosclerosis and levels of paraoxonase-1 (PON1), arylesterase, total antioxidant status, total oxidant status (TOS), oxidative stress index (OSI), total sulfhydryl (-SH) groups, lipid hydroperoxide, and ceruloplasmin in the serum of otosclerosis patients and healthy subjects with respect to oxidative stress.

Results: In our study, TOS and OSI levels were higher in the otosclerosis patients than in the controls. The PON1 levels showed that oxidative stress was severe, and as a result, antioxidants were consumed and depleted.

Discussion: When an imbalance between oxygen free radical production and antioxidative defense mechanisms occurs, reactive oxygen species levels may increase, which in turn may damage cells and tissues through the peroxidation of phospholipid membrane structures. The body initially responds with increased antioxidant production, but if the oxidative stress is severe, decreased antioxidant levels may result. This study reports expression levels of oxidative stress species in otosclerosis patients.     

Evidence for an age-related attenuation of cerebral microvascular antioxidant response to oxidative stress

Effects of aging and oxidative stress were studied in cerebral microvessels and microvessel-depleted brain from 6-, 18-, and 24-month-old C57Bl/6J mice exposed to normoxia, 24 or 48 h hyperoxia, or 24 h hyperoxia followed by 24 h normoxia. Microvessels lacked smooth muscle and consisted predominantly of endothelium. Following exposure and isolation of microvessel and parenchymal proteins, Western blot analysis was performed for detection of cytosolic thioredoxin 1 (TRx 1) and mitochondrial thioredoxin 2 (TRx 2), protein carbonyl, and mitochondrial superoxide dismutase (MnSOD). Both microvessel and parenchymal TRx 1 levels were increased by hyperoxia; however, the microvascular response was limited and delayed in comparison to that of the parenchymal fraction. Whereas TRx 2 levels in microvessels were increased in older mice, irrespective of exposure condition, hyperoxia per se had little or no apparent effect. Parenchymal cells showed no age-related increase in TRx 2 level under normoxic conditions, but showed increased levels following hyperoxia. Microvessel MnSOD was lower than that in parenchymal cells, but increased with age under normoxia, and also was correlated with the duration of hyperoxia. Although hyperoxia augmented MnSOD levels in young (6 months) and middle-aged (18 months) animals, the response was less pronounced in microvessels from senescent, 24-month-old mice. Unlike microvessels, which showed a sustained age-related increase in MnSOD level under each exposure condition, parenchymal cells from normoxic mice showed no increase, and hyperoxia-induced elevations declined with prolonged 48 h exposure. These results indicate that the microvessel endothelium is (1) subjected to a more intense oxidative environment than neurons and glia and (2) is limited by aging in its ability to respond to oxidative insult.     

Oxidative and nitrosative stress in ammonia neurotoxicity

Increased ammonia accumulation in the brain due to liver dysfunction is a major contributor to the pathogenesis of hepatic encephalopathy (HE). Fatal outcome of rapidly progressing (acute) HE is mainly related to cytotoxic brain edema associated with astrocytic swelling. An increase of brain ammonia in experimental animals or treatment of cultured astrocytes with ammonia generates reactive oxygen and nitrogen species in the target tissues, leading to oxidative/nitrosative stress (ONS). In cultured astrocytes, ammonia-induced ONS is invariably associated with the increase of the astrocytic cell volume. Interrelated mechanisms underlying this response include increased nitric oxide (NO) synthesis which is partly coupled to the activation of NMDA receptors and increased generation of reactive oxygen species by NADPH oxidase. ONS and astrocytic swelling are further augmented by excessive synthesis of glutamine (Gln) which impairs mitochondrial function following its accumulation in there and degradation back to ammonia (“the Trojan horse” hypothesis). Ammonia also induces ONS in other cell types of the CNS: neurons, microglia and the brain capillary endothelial cells (BCEC). ONS in microglia contributes to the central inflammatory response, while its metabolic and pathophysiological consequences in the BCEC evolve to the vasogenic brain edema associated with HE. Ammonia-induced ONS results in the oxidation of mRNA and nitration/nitrosylation of proteins which impact intracellular metabolism and potentiate the neurotoxic effects. Simultaneously, ammonia facilitates the antioxidant response of the brain, by activating astrocytic transport and export of glutathione, in this way increasing the availability of precursors of neuronal glutathione synthesis.     

Oxidative stress in rats induced by consumption of saxitoxin contaminated drink water

Saxitoxins (STXs) are neurotoxins produced by cyanobacteria such as Cylindrospermopsis raciborskii. During bloom events, the production of these compounds causes contamination on public water supply sources. STXs block voltage gated sodium channels and can lead to severe poisoning and death of organisms at different trophic levels. Other toxicity mechanism of STX is the generation of reactive oxygen species (ROS). The aim of this study was to investigate the effect of consumption of water contaminated with a C. raciborskii strain (producing variants of Neo-STX and STX) by rats during 30 days through the analysis of oxidative stress biochemical parameters. Total antioxidant capacity (ACAP) and oxidative stress parameters were analyzed at pre-frontal cortex, hippocampus and liver of adult Wistar rats (2–3 months old). Treated animals ingested concentrations of 3 and 9 μg/L of STX equivalents and were compared with a control group (culture medium ASM-1). At the concentration of 3 μg/L, a decrease in ROS production associated with lower ACAP at hippocampus was observed. Furthermore, a decrease of glutamate cysteine ligase (GCL) activity in the cortex and an increase of brain and liver glutathione concentration were also observed. At the highest concentration (9 μg/L), there was an ACAP increase in the hippocampus as well as in the activity GCL and glutathione-S-transferase in the cortex and hippocampus. At both concentrations, lipid peroxidation was registered in the liver. Therefore, chronic ingestion of STXs can alter the antioxidant defenses and induce oxidative stress in brain and liver. The present results point to the values adopted as threshold limit for STXs in potable waters (3 μg/L) shows already significant chronic effects that alter antioxidant defenses and induce oxidative stress at least in two of the organs studied.     

Oxidative stress in plants

Oxidative stress, defined as a shift of the balance between prooxidative and antioxidative reactions in favor of the former seems to be a common denominator of the action of various agents on living organisms. This review briefly presents the sources of reactive oxygen species and means of antioxidative defense in plants, means of assessment of oxidative stress and exemplary data on the induction of oxidative stress by various environmental and biological factors such as hyperoxia, light, drought, high salinity, cold, metal ions, pollutants, xenobiotics, toxins, reoxygenation after anoxia, experimental manipulations, pathogen infection and aging of plant organs.     

Proteasome and oxidative phoshorylation changes may explain why aging is a risk factor for neurodegenerative disorders

Neurodegenerative disorders (ND) belong to the most devastating diseases in the industrialized western world. Alzheimer disease (AD) is the most prevalent among these disorders followed by Parkinson disease (PD). Huntington disease (HD) is an autosomal dominantly inherited condition with a single mutation that causes disease in almost 100% of all cases. In this review we used previously published proteomics studies on AD, PD and HD to find cellular pathways changed similarly in ND and aging. All studies employed large gel two dimensional gel electrophoresis for protein separation and mass spectrometry for protein identification. Altered proteins were subjected to a KEGG pathway analysis and altered pathways determined for each disorder and aging. We found that besides the mitochondrial oxidative phosphorylation, the proteasome system are altered in aging and ND. The proteasome facilitates protein degradation which is commonly perturbed in ND which may link neurodegeneration to its largest risk factor—aging.     

Oxidative stress, osmotic stress and apoptosis: impacts on sperm function and preservation in the horse

Oxidative stress is an important component of the cytopathology of equine spermatozoa undergoing storage as liquid or frozen semen. Damage to chromatin, membranes and proteins of sperm are important components of oxidative damage to sperm. Similarly, sperm are exposed to a variety of osmotic stresses during storage that result from exposure to hypertonic media or result as a consequence of osmotic changes induced during freezing. A number of changes induced during processing and storage of equine sperm also appear to induce apoptotic-like changes which may adversely affect sperm survival and function. These processes appear in many cases to be interrelated, and this review will examine current understanding of these processes on the equine sperm function.     

Oxidative stress, metabolism of ethanol and alcohol-related diseases

Alcohol-induced oxidative stress is linked to the metabolism of ethanol. Three metabolic pathways of ethanol have been described in the human body so far. They involve the following enzymes: alcohol dehydrogenase, microsomal ethanol oxidation system (MEOS) and catalase. Each of these pathways could produce free radicals which affect the antioxidant system. Ethanol per se, hyperlactacidemia and elevated NADH increase xanthine oxidase activity, which results in the production of superoxide. Lipid peroxidation and superoxide production correlate with the amount of cytochrome P450 2E1. MEOS aggravates the oxidative stress directly as well as indirectly by impairing the defense systems. Hydroxyethyl radicals are probably involved in the alkylation of hepatic proteins. Nitric oxide (NO) is one of the key factors contributing to the vessel wall homeostasis, an important mediator of the vascular tone and neuronal transduction, and has cytotoxic effects. Stable metabolites--nitrites and nitrates--were increased in alcoholics (34.3 +/- 2.6 vs. 22.7 +/- 1.2 micromol/l, p < 0.001). High NO concentration could be discussed for its excitotoxicity and may be linked to cytotoxicity in neurons, glia and myelin. Formation of NO has been linked to an increased preference for and tolerance to alcohol in recent studies. Increased NO biosynthesis also via inducible NO synthase (NOS, chronic stimulation) may contribute to platelet and endothelial dysfunctions. Comparison of chronically ethanol-fed rats and controls demonstrates that exposure to ethanol causes a decrease in NADPH diaphorase activity (neuronal NOS) in neurons and fibers of the cerebellar cortex and superior colliculus (stratum griseum superficiale and intermedium) in rats. These changes in the highly organized structure contribute to the motor disturbances, which are associated with alcohol abuse. Antiphospholipid antibodies (APA) in alcoholic patients seem to reflect membrane lesions, impairment of immunological reactivity, liver disease progression, and they correlate significantly with the disease severity. The low-density lipoprotein (LDL) oxidation is supposed to be one of the most important pathogenic mechanisms of atherogenesis, and antibodies against oxidized LDL (oxLDL) are some kind of epiphenomenon of this process. We studied IgG oxLDL and four APA (anticardiolipin, antiphosphatidylserine, antiphosphatidylethanolamine and antiphosphatidylcholine antibodies). The IgG oxLDL (406.4 +/- 52.5 vs. 499.9 +/- 52.5 mU/ml) was not affected in alcoholic patients, but oxLDL was higher (71.6 +/- 4.1 vs. 44.2 +/- 2.7 micromol/l, p < 0.001). The prevalence of studied APA in alcoholics with mildly affected liver function was higher than in controls, but not significantly. On the contrary, changes of autoantibodies to IgG oxLDL revealed a wide range of IgG oxLDL titers in a healthy population. These parameters do not appear to be very promising for the evaluation of the risk of atherosclerosis. Free radicals increase the oxidative modification of LDL. This is one of the most important mechanisms, which increases cardiovascular risk in chronic alcoholic patients. Important enzymatic antioxidant systems - superoxide dismutase and glutathione peroxidase - are decreased in alcoholics. We did not find any changes of serum retinol and tocopherol concentrations in alcoholics, and blood and plasma selenium and copper levels were unchanged as well. Only the zinc concentration was decreased in plasma. It could be related to the impairment of the immune system in alcoholics. Measurement of these parameters in blood compartments does not seem to indicate a possible organ, e.g. liver deficiency.     

Glutathione and thioredoxin dependent systems in neurodegenerative disease: What can be learned from reverse genetics in mice

Oxidative stress is a major common hallmark of many neurodegenerative disease such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and stroke. Novel concepts in our understanding of oxidative stress indicate that a perturbed redox circuitry could be strongly linked with the onset of such diseases. In this respect, glutathione and thioredoxin dependent antioxidant enzymes play a central role as key regulators due to the fact that a slight dysfunction of any of these enzymes leads to sustained reactive oxygen species (ROS) production. Apart from their classical role as ROS scavengers, some of these enzymes are also able to control post-translational modifications. Therefore, efficient control of ROS production and reversibility of post-translational modifications are critical as improper control of such events may lead to the activation of pathological redox circuits that eventually culminate in neuronal cell death. To dissect the apparently opposing functions of ROS in cell physiology and pathophysiology, a proper working toolkit is mandatory. In vivo modeling is an absolute requirement due to the complexity of redox signaling systems that often contradict data obtained from in vitro approaches. Hence, inducible/conditional knockout mouse models for key redox enzymes are emerging as powerful tools to perturb redox circuitries in a temporal and spatial manner. In this review we address the basics of ROS generation, chemistry and detoxification as well as examples in where applications of mouse models of important enzymes have been successfully applied in the study of neurodegenerative processes. We also highlight the importance of new models to overcome present technical limitations in order to advance in the study of redox processes in the role of neurodegeneration.     

Oxidative and nitrative stress markers in glaucoma

Glaucoma is a progressive optic neuropathy and is the leading cause of blindness in the United States and other industrialized countries. Elevated pressure in the eye is a risk factor for glaucoma and indeed experimental studies of induced pressure elevation in nonhuman primate's results in typical glaucomatous optic nerve damage. However, normal intraocular pressure can also lead to loss of vision in glaucoma. Although the initiating causes leading to glaucoma are unknown, oxidative and nitrative stress appears to play a role in the progressive neuronal death that is characteristic of glaucomatous optic nerve damage. Increased markers of oxidative stress that have been reported in glaucoma include protein nitrotyrosine, carbonyls in proteins, lipid oxidation products and oxidized DNA bases. Studies have also highlighted the role of nitric oxide in glaucoma by reporting the presence of inducible nitric oxide synthase in the iris-ciliary body, retina and in the glaucomatous optic nerve head of experimental rat models. This review discusses the role of reactive oxygen and nitrogen species in the pathogenesis of glaucoma and examines the relevance of antioxidants in neurodegeneration associated with the disease. It is concluded that oxidative and nitrative stress have a pathogenic role in glaucoma.     

Oxidative stress and aging: beyond correlation

The oxidative stress theory of aging has become increasingly accepted as playing a role in the aging process, based primarily on a substantial accumulation of circumstantial evidence. In recent years, the hypothesis that mitochondrially generated reactive oxygen species play a role in organismal aging has been directly tested in both invertebrate and mammalian model systems. Initial results imply that oxidative damage, specifically the level of superoxide, does play a role in limiting the lifespans of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. In mammalian model systems, the effect of oxidative stress on lifespan is less clear, but there is evidence that antioxidant treatment protects against age-related dysfunction, including cognitive decline.     

The importance of neuromuscular rate of force development for physical function in aging and common neurodegenerative disorders – a systematic review

We systematically reviewed existing literature regarding lower extremity neuromuscular rate of force development (RFD), maximal muscle strength (Fmax), and physical function in neurodegenerative populations, and to what extent these outcomes are affected and/or associated. Following PRISMA guidelines, 4 databases (Pubmed, Embase, SPORTDiscus, Web of Science) were searched. Across aging, Parkinson Disease (PD), Alzheimer’s Disease (AD), Multiple Sclerosis (MS), or Stroke, included studies should report (Part 1) deficits in lower extremity RFD, Fmax, and physical function (~ individuals having inferior vs. superior physical function), and/or (Part 2) associations between RFD (or Fmax) and physical function. A total of N=32 studies (n=1087 participants) were included. Part 1: deficits in RFD (-31%, mean; N=22) were comparable to deficits in physical function (-26%; N=7), yet both deficits exceeded that of Fmax (-21%; N=20). Part 2: associations between RFD and physical function (r²=0.13, mean; N=16) were comparable to associations between Fmax and physical function (r²=0.15; N=12). Lower extremity RFD is (1) particularly sensitive (i.e. adapts earlier and/or more extensively) towards neurodegeneration, and more so than Fmax, and (2) of importance for physical function but apparently not superior to Fmax. RFD could serve as a useful indicator/biomarker of changes in neuromuscular function elicited by neurodegeneration.