Expression of human Cu-Zn superoxide dismutase gene in transgenic mice: model for gene dosage effect in Down syndrome

Catalase overexpression fails to attenuate allergic airways disease in the mouse

Oxidative stress is a hallmark of asthma, and increased levels of oxidants are considered markers of the inflammatory process. Most studies to date addressing the role of oxidants in the etiology of asthma were based on the therapeutic administration of low m.w. antioxidants or antioxidant mimetic compounds. To directly address the function of endogenous hydrogen peroxide in the pathophysiology of allergic airway disease, we comparatively evaluated mice systemically overexpressing catalase, a major antioxidant enzyme that detoxifies hydrogen peroxide, and C57BL/6 strain matched controls in the OVA model of allergic airways disease. Catalase transgenic mice had 8-fold increases in catalase activity in lung tissue, and had lowered DCF oxidation in tracheal epithelial cells, compared with C57BL/6 controls. Despite these differences, both strains showed similar increases in OVA-specific IgE, IgG1, and IgG2a levels, comparable airway and tissue inflammation, and identical increases in procollagen 1 mRNA expression, following sensitization and challenge with OVA. Unexpectedly, mRNA expression of MUC5AC and CLCA3 genes were enhanced in catalase transgenic mice, compared with C57BL/6 mice subjected to Ag. Furthermore, when compared with control mice, catalase overexpression increased airway hyperresponsiveness to methacholine both in naive mice as well as in response to Ag. In contrast to the prevailing notion that hydrogen peroxide is positively associated with the etiology of allergic airways disease, the current findings suggest that endogenous hydrogen peroxide serves a role in suppressing both mucus production and airway hyperresponsiveness.

Oxidized SOD1 alters proteasome activities in vitro and in the cortex of SOD1 overexpressing mice

Premature ageing, one of the characteristics of Down syndrome (DS), may involve oxidative stress and impairment of proteasome activity. Transgenic mice overexpressing the human copper/zinc superoxide dismutase (SOD1) gene are one of the first murine models for DS and it has been shown that SOD1 overexpression might be either deleterious or beneficial. Here, we show a reduction in proteasome activities in the cortex of SOD1 transgenic mice and an associated increase in the content of oxidized SOD1 protein. As we demonstrate that in vitro oxidized SOD can inhibit purified proteasome peptidase activities, modified SOD1 might be partially responsible for proteasome inhibition shown in SOD1 transgenic mice.

Elevation of superoxide dismutase increases acoustic trauma from noise exposure

The generation of superoxide has been implicated as a cause of cochlear damage from excessive noise. Cu/Zn superoxide dismutase (SOD1) generally will protect against superoxide-mediated tissue injury but protection by this enzyme against noise trauma is controversial. This study assessed auditory function in C57BL/6 mice overexpressing SOD1 or treated with lecithinized SOD1 (PC-SOD1). Noise exposure caused significantly higher threshold shifts in PC-SOD1-treated animals than physiological saline-treated animals. Cochlear tissues of PC-SOD1-treated animals exhibited significant elevation of the levels in the SOD activity, not in the catalase activity, in comparison with those of saline-treated animals. Likewise, transgenic mice overexpressing SOD1 tended to suffer higher threshold shifts than nontransgenic littermates from noise exposure. The findings indicate that increasing SOD1 enhances auditory dysfunction following noise exposure.

Anti-oxidant gene expression imbalance, aging and Down syndrome

The expression of copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), glutathione peroxidase (GPx), and catalase (CAT) genes have been detected in human skin fibroblast cells for 2 year normal child (control), 50 year old normal male and female and a 1 year old Down Syndrome (DS) male and female with established trisomy karyotype using the RT-PCR technique. Differential expression of these genes is quantified individually against a beta-Actin gene that has been employed as an internal control. The immunoblotting of cell lysate proteins with polyclonal antibodies exhibit SOD1 (16 kD), SOD2 (40 kD), GPx (23 and 92 kD), CAT (64 kD), and Actin (43 kD) as translational products. The results demonstrate that the enhancement in the level of mRNAs encoding SOD1 in DS male and female, as well as aged male and female are 51, 21, 31 and 50% respectively compared to the normal child (control). In SOD2, DS male and female display higher (176%) and lower (26%) levels of expression whereas aged male and female exhibit enhanced levels of expression (66 and 119%) respectively compared to the control. This study demonstrates that DS affects the female less than the male whereas in the aging process, the female is more prone to oxidative damage than the male. These results not only indicate that the level of GPx mRNA is constant except in DS male, which shows a downward regulation but that even CAT mRNA is upward regulated in aged as well as in DS males and females. These disproportionate changes in anti-oxidant genes, which are incapable of coping with over expressed genes, may contribute towards the aging process, dementia and Down syndrome.

Beta-amyloid (1-42)-induced learning and memory deficits in mice: involvement of oxidative burdens in the hippocampus and cerebral cortex

We have demonstrated that oxidative stress is involved, at least in part, in beta-amyloid protein (Abeta)-induced neurotoxicity in vivo [Eur. J. Neurosci. 1999;11:83-90; Neuroscience 2003;119:399-419]. However, mechanistic links between oxidative stress and memory loss in response to Abeta remain elusive. In the present study, we examined whether oxidative stress contributes to the memory deficits induced by intracerebroventricular injection of Abeta (1-42) in mice. Abeta (1-42)-induced memory impairments were observed, as measured by the water maze and passive avoidance tests, although these impairments were not found in Abeta (40-1)-treated mice. Treatment with antioxidant alpha-tocopherol significantly prevented memory impairment induced by Abeta (1-42). Increased activities of the cytosolic Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and mitochondrial Mn-superoxide dismutase (Mn-SOD) were observed in the hippocampus and cerebral cortex of Abeta (1-42)-treated animals, as compared with Abeta (40-1)-treated mice. The induction of Cu,Zn-SOD was more pronounced than that of Mn-SOD after Abeta (1-42) insult. However, the concomitant induction of glutathione peroxidase (GPX) in response to significant increases in SOD activity was not seen in animals treated with Abeta (1-42). Furthermore, glutathione reductase (GRX) activity was only increased at 2h after Abeta (1-42) injection. Production of malondialdehyde (lipid peroxidation) and protein carbonyl (protein oxidation) remained elevated at 10 days post-Abeta (1-42), but the antioxidant alpha-tocopherol significantly prevented these oxidative stresses. Therefore, our results suggest that the oxidative stress contributes to the Abeta (1-42)-induced learning and memory deficits in mice.

Overexpression of Phospholipid-hydroperoxide Glutathione Peroxidase in Human Dermal Fibroblasts Abrogates UVA Irradiation-induced Expression of Interstitial Collagenase/Matrix Metalloproteinase-1 by Suppression of Phosphatidylcholine Hydroperoxide-mediated NFκB Activation and Interleukin-6 Release

Phospholipid-hydroperoxide glutathione peroxidase (PHGPx) exhibits high specific activity in reducing phosphatidylcholine hydroperoxides (PCOOHs) and thus may play a central role in protecting the skin against UV irradiation-triggered detrimental long term effects like cancer formation and premature skin aging. Here we addressed the role of PHGPx in the protection against UV irradiation-induced expression of matrix metalloproteinase-1 (MMP-1). For this purpose, we created human dermal fibroblast cell lines overexpressing human PHGPx. Overexpression led to a significant increase in PHGPx activity. In contrast to a maximal 4.5-fold induction of specific MMP-1 mRNA levels in vector-transfected cells at 24 h after UVA irradiation, no MMP-1 induction occurred at any studied time point after UVA treatment of PHGPx-overexpressing fibroblasts. As interleukin-6 (IL-6) was earlier shown to mediate the UVA induction of MMP-1, we studied whether PHGPx overexpression might interfere with the NFkappaB-mediated IL-6 induction and downstream signaling. Using transient transfections of IL-6 promoter constructs containing NFkappaB binding sites, we observed a high induction of the reporter gene luciferase in vector-transfected control cells and a significantly lower induction in PHGPx-overexpressing fibroblasts following UVA irradiation. Consistently both UVA irradiation and treatment of fibroblasts with PCOOHs led to phosphorylation and nuclear translocation of the p65 subunit, whereas cells overexpressing PHGPx exhibited impaired NFkappaB activation, p65 phosphorylation, and nuclear translocation. In line with this, the PHGPx-overexpressing fibroblasts showed a reduced constitutive and UVA irradiation-induced IL-6 release. After incubating PHGPx-overexpressing cells with PCOOHs a reduced induction of IL-6 was observed. This together with the suppression of UVA irradiation-induced IL-6 release in the presence of Trolox, a chain breaker of PCOOH-initiated lipid peroxidation, indicates that UVA irradiation-induced PCOOHs and subsequent lipid peroxides initiate the NFkappaB-mediated induction of IL-6, which mediates the induction of MMP-1. Our finding is particularly relevant in light of the already available small molecule mimetics of PHGPx.

Aberrant neuronal and mitochondrial proteins in hippocampus of transgenic mice overexpressing human Cu/Zn superoxide dismutase 1

Mutations of Cu/Zn superoxide dismutase 1 (SOD1), a metalloenzyme catalyzing the conversion of superoxide anion to hydrogen peroxide (H(2)O(2)), are linked to motor neuron degeneration. Transgenic mouse strains overexpressing wild-type human SOD1 (Tg-SOD1) were shown to have mitochondrial swelling, vacuolization, or learning and memory deficits and are widely used for biochemical, genetic, and cognitive studies; this, along with the advent of advanced proteomic methods, made us investigate protein expression in hippocampus. Hippocampal tissues of wild-type, hemizygous, and homozygous Tg-SOD1 mice were isolated and used for two-dimensional gel electrophoresis with subsequent matrix-assisted laser desorption/ionization-time of flight identification. We identified several synaptosomal, neuronal, antioxidant, and mitochondrial proteins in hippocampus, and expression levels of syntaxin-binding protein 1, N-ethylmaleimide-sensitive factor, synaptosomal-associated protein 25, dynamin-1, neurofilament triplet L protein, neurofilament triplet M protein, neuronal tropomodulin, and neuronal protein 25 were significantly decreased in Tg-SOD1. None of the antioxidant proteins were altered except mouse SOD1. Mitochondrial ATP synthase alpha/beta chain and elongation factor Tu were aberrant in Tg-SOD1. We conclude that derangement of neuronal and mitochondrial proteins may indicate synaptosomal and neuronal loss in Tg-SOD1 hippocampus, already reported in morphological terms. This observation is of relevance to understanding brain deficits in Down syndrome, as SOD1 is encoded on chromosome 21.

An altered antioxidant balance occurs in Down syndrome fetal organs: Implications for the “gene dosage effect” hypothesis

Down syndrome (DS) is the congenital birth defect responsible for the greatest number of individuals with mental retardation. It arises due to trisomy of human chromosome 21 (HSA21) or part thereof. To date there have been limited studies of HSA21 gene expression in trisomy 21 conceptuses. In this study we investigate the expression of the HSA21 antioxidant gene, Cu/Zn-superoxide dismutase-1 (SOD1) in various organs of control and DS aborted conceptuses. We show that SOD1 mRNA levels are elevated in DS brain, lung, heart and thymus. DS livers show decreased SOD1 mRNA expression compared with controls. Since non-HSA21 antioxidant genes are reported to be concomitantly upregulated in certain DS tissues, we examined the expression of glutathione peroxidase-1 (GPX1) in control and DS fetal organs. Interestingly, GPX1 expression was unchanged in the majority of DS organs and decreased in DS livers. We examined the SOD1 to GPX1 mRNA ratio in individual organs, as both enzymes form part of the body's defense against oxidative stress, and because a disproportionate increase of SOD1 to GPX1 results in noxious hydroxyl radical damage. All organs investigated show an approximately 2-fold increase in the SOD1 to GPX1 mRNA ratio. We propose that it is the altered antioxidant ratio that contributes to certain aspects of the DS phenotype.

cDNA cloning, high-level expression, purification, and characterization of an avian Cu,Zn superoxide dismutase from Peking duck

As a special species of avian, Peking duck is often used as a model for exploring effective factors against cardio-cerebrovascular diseases, and therefore investigations of antioxidant enzymes including superoxide dismutase are intriguing. By using 3(')-RACE with a gene-specific primer, a cDNA encoding duck Cu,Zn SOD was amplified from the total RNA extracted from Peking duck liver. Three free cysteine residues are found in the deduced amino acid sequence of duck SOD, among which Cys153 at the carbonyl-terminal is a distinctive feature. Production with a high yield of recombinant duck Cu,Zn SOD was achieved in Escherichia coli after the reconstituted expression vector pET-3a-dSOD was transformed into the bacterial strain BL21(DE3)pLysS. After two steps of anion exchange chromatography, a great quantity of the purified enzyme (100mg/L fermented culture) with an enzymatic activity comparable to that of native duck and bovine SOD was finally obtained. Duck SOD is a homodimer with 153 residues for each subunit. The molecular mass of the recombinant enzyme is 15,540.0Da measured by mass spectrum, which well coincides with the estimated size of the sequence but significantly differs from that of the native counterpart. Five charge isomers were observed on isoelectricfocusing (IEF). The most interesting observation is that the thermal stability of duck SOD is much lower than that of the bovine enzyme as revealed by irreversible heat inactivation at 70 degrees C. These properties are discussed in relation to the distinctive free Cys residues in duck Cu,Zn SOD.

Solar UV irradiation and dermal photoaging

The skin is increasingly exposed to ambient UV-irradiation thus increasing risks for photooxidative damage with long-term detrimental effects like photoaging, characterized by wrinkles, loss of skin tone and resilience. Photoaged skin displays alterations in the cellular component and extracellular matrix with accumulation of disorganized elastin and its microfibrillar component fibrillin in the deep dermis and a severe loss of interstitial collagens, the major structural proteins of the dermal connective tissue. The unifying pathogenic agents for these changes are UV-generated reactive oxygen species (ROS) which deplete and damage non-enzymatic and enzymatic antioxidant defense systems of the skin. As well as causing permanent genetic changes, ROS activate cytoplasmic signal transduction pathways in resident fibroblasts that are related to growth, differentiation, senescence and connective tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in clinical and biochemical characteristics of photoaging. In addition, the relationship of photoaging to intrinsic aging of the skin will be briefly discussed. A decrease in the overall ROS load by efficient sunscreens or other protective agents may represent promising strategies to prevent or at least minimize ROS-induced photoaging.

Chronological ageing and photoageing of the fibroblasts and the dermal connective tissue

In recent years, the exposure of human skin to environmental and artificial UV irradiation has increased dramatically. This is due not only to increased solar UV irradiation as a consequence of stratospheric ozone depletion, but also to inappropriate social behaviour with the use of tanning salons still being very popular in the public view. Besides this, leisure activities and a lifestyle that often includes travel to equatorial regions add to the individual annual UV load. In addition to the common long-term detrimental effects such as immunosuppression and skin cancer, the photo-oxidative damage due to energy absorption of UV photons in an oxygenized environment leads to quantitative and qualitative alterations of cells and structural macromolecules of the dermal connective tissue responsible for tensile strength, resilience and stability of the skin. The clinical manifestations of UV/reactive oxygen species (ROS)-induced disturbances result in photoaged skin with wrinkle formation, laxity, leathery appearance as well as fragility, impaired wound healing capacities and higher vulnerability. Strategies to prevent or at least minimize ROS-induced photo-ageing and intrinsic ageing of the skin necessarily include protection against UV irradiation and antioxidant homeostasis.

Ultrastructural study of the FVB/N mouse thymus: presence of an immature epithelial cell in the medulla and premature involution

FVB/N inbred mice have been widely used to generate a variety of transgenic lines, but their physiology and especially their immunological characteristics are poorly documented. We therefore studied the ultrastructure of the thymus and the distribution of thymocyte subpopulations in FVB/N mice at several ages. In young FVB/N mice the stromal microenvironment exhibits the three types of epithelial cells and the two types of bone-marrow derived cells (macrophages and interdigitated cells) previously described in other strains of mice. Moreover, in the thymic medulla of young FVB/N mice, a fourth cell type with the morphological characteristics of an immature epithelial cell was present in relatively high number. Furthermore, thymocyte subpopulations distribution shows an earlier thymocyte maturation than in other strains. Finally, changes associated with thymic involution were observed about 5 months earlier than in many other mouse strains. Our results demonstrated that the FVB/N strain has a specific immunological status.

Genomic instability in Down syndrome and Fanconi anemia assessed by micronucleus analysis and single-cell gel electrophoresis

Cytokinesis-block micronucleus (CB-MN) assay and single-cell gel electrophoresis (SCGE) were employed to analyze leukocytes from 14 Fanconi anemia (FA) patients, 30 Down syndrome (DS) patients, and 30 control individuals, to examine the sensitivity of these techniques to detect genomic instability in these 2 diseases. The DS patients presented increased DNA damage as measured by SCGE in relation to controls. The frequencies of micronuclei and dicentric bridges were similar to those of controls. Micronucleus frequency, dicentric bridge frequencies, and DNA damage were higher in FA patients than in controls. The high frequency of micronuclei observed in FA patients seems to be due to clastogenic events, because an increase in the frequency of dicentric bridges was also observed. Micronuclei are expressed mutations and need cell division to appear. The damage detected by SCGE is repairable, and does not require cell division. Under alkaline conditions, SCGE assesses double- and single-strand breaks and alkali-labile sites. The 2 methods are efficient for monitoring mutagenic events in exposed populations or in individuals with genetic instability. While the damage measured by micronucleus analysis is accumulated over a long period of time, DNA damage measured by SCGE reflects recent, unrepaired events.

Photoaging of the skin from phenotype to mechanisms

The skin is increasingly exposed to ambient UV-irradiation thus increasing its risk for photooxidative damage with longterm detrimental effects like photoaging, which is characterized by wrinkles, loss of skin tone, and resilience. Photoaged skin displays prominent alterations in the cellular component and the extracellular matrix of the connective tissue with an accumulation of disorganized elastin and its microfibrillar component fibrillin in the deep dermis and a severe loss of interstitial collagens, the major structural proteins of the dermal connective tissue. The unifying pathogenic agents for these changes are UV-generated reactive oxygen species (ROS) that deplete and damage non-enzymatic and enzymatic antioxidant defense systems of the skin. As well as causing permanent genetic changes, ROS activate cytoplasmic signal transduction pathways in resident fibroblasts that are related to growth, differentiation, senescence, and connective tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in biochemical and clinical characteristics of photoaging. In addition, the relationship of photoaging to intrinsic aging of the skin will be discussed. A decrease in the overall ROS load by efficient sunscreens or other protective agents may represent promising strategies to prevent or at least minimize ROS induced photoaging.

Correlations of glutathione peroxidase activity with memory impairment in adults with Down syndrome

BACKGROUND

Down syndrome (DS) is a genetic disorder (trisomy 21 in 96% of cases), associated with an excess of a key enzyme involved with free radical metabolism (FRM), superoxide dismutase-1 (SOD-1), that is encoded by a gene on chromosome 21. Consequently, SOD-1 activity is elevated in DS, which also occurs in conditions of oxidative stress, and is associated with a compensatory increase in glutathione peroxidase activity (GSHPx).

METHODS

This study examined the relationship of memory function with erythrocyte SOD-1, GSHPx and catalase (CAT) activity in 22-51 year old adults with DS.

RESULTS

Mean erythrocyte SOD-1 (p < .02) and GSHPx (p < .01), but not CAT (p = .76), activities were significantly greater in the DS group than the controls. In the DS group, erythrocyte GSHPx, but not SOD-1 or CAT activities, was significantly correlated with memory function (r = .625, p < .025, df = 13 for savings score, r = .631, p < .01, df = 14 for intrusion errors) but not with intelligence quotients.

CONCLUSIONS

These observations suggest a possible relationship between altered FRM with memory deficits among adults with DS within the age-range in that an age-related increase in the prevalence for Alzheimer's neuropathology is known to be robust before reaching a plateau of 100%.

Stable overexpression of manganese superoxide dismutase in mitochondria identifies hydrogen peroxide as a major oxidant in the AP-1-mediated induction of matrix-degrading metalloprotease-1

Reactive oxygen species (ROS) are important second messengers for the induction of several genes in a variety of physiological and pathological conditions. Here we addressed the question of whether isolated, unbalanced overexpression of the antioxidant enzyme manganese superoxide dismutase (Mn-SOD) may modulate signal transduction cascades, finally leading to connective tissue degradation, a hallmark in carcinogenesis and aging. Therefore, we generated stably Mn-SOD-overexpressing fibroblasts with an up to 4. 6-fold increase in Mn-SOD activity. The Mn-SOD-overexpressing cells revealed specific resistance to the superoxide anion (O-(2))-generating agent paraquat, whereas no resistance to UVA-generated oxidative stress was found. Treatment of the Mn-SOD-overexpressing cells with various ROS-generating systems resulted (due to the enhanced dismutation of superoxide anion to hydrogen peroxide) in an up to 9.5-fold increase in matrix-degrading metalloprotease-1 (MMP-1) mRNA levels. A similar increase in MMP-1 mRNA was also seen when the intracellular H(2)O(2) concentration was increased by the inhibition of different H(2)O(2)-detoxifying pathways. Furthermore, prooxidant conditions led to a strong induction of c-jun and c-fos mRNA levels resulting in a 4-fold higher transactivation of the transcription factor AP-1 in the Mn-SOD-overexpressing cells. Collectively, we have found that enhanced Mn-SOD activity, via an unbalanced H(2)O(2) overproduction and detoxification, induces MMP-1 mRNA levels, and this effect is at least partly mediated by the DNA recognition sequence AP-1.

Effect of vitamin E on chromosomal aberrations in lymphocytes from patients with Down's syndrome

A possible protective effect of vitamin E (DL-alpha-tocopherol) on chromosomal damage was evaluated in lymphocytes from patients with Down's syndrome (DS) and from controls. This included the analysis of the basal and G2 chromosomal aberration frequencies in lymphocytes cultured with and without 100 microM vitamin E. The chromosomal damage in G2 was determined by scoring the number of chromosomal aberrations in lymphocyte cultures treated with 5 mM caffeine, 2 h before harvesting. Vitamin E treatment decreased the basal and G2 chromosomal aberrations both in control and DS lymphocytes. In DS cells, this protective effect, expressed as a decrease in the chromosomal damage, was greater (50%) than in controls (30%). These results suggest that the increment in basal and G2 aberrations yield in DS lymphocytes may be related to the increase in oxidative damage reported in these patients.

An evaluation of the role of mitochondria in neurodegenerative diseases: mitochondrial mutations and oxidative pathology, protective nuclear responses, and cell death in neurodegeneration

There is mounting evidence for mitochondrial involvement in neurodegenerative diseases including Alzheimer's and Parkinson's disease and amyotrophic lateral sclerosis. Mitochondrial DNA mutations, whether inherited or acquired, lead to impaired electron transport chain (ETC) functioning. Impaired electron transport, in turn, leads to decreased ATP production, formation of damaging free-radicals, and altered calcium handling. These toxic consequences of ETC dysfunction lead to further mitochondrial damage including oxidation of mitochondrial DNA, proteins, and lipids, and opening of the mitochondrial permeability transition pore, an event linked to cell death in numerous model systems. Although protective nuclear responses such as antioxidant enzymes and bcl-2 may be induced to combat these pathological changes, such a vicious cycle of increasing oxidative damage may insidiously damage neurons over a period of years, eventually leading to neuronal cell death. This hypothesis, a synthesis of the mitochondrial mutations and oxidative stress hypotheses of neurodegeneration, is readily tested experimentally, and clearly points out many potential therapeutic targets for preventing or ameliorating these diseases.

Psoralen photoactivation promotes morphological and functional changes in fibroblasts in vitro reminiscent of cellular senescence

Premature aging of the skin is a prominent side effect of psoralen photoactivation, a treatment used widely for various skin disorders. The molecular mechanisms underlying premature aging upon psoralen photoactivation are as yet unknown. Here we show that treatment of fibroblasts with 8-methoxypsoralen (8-MOP) and subsequent ultraviolet A (UVA) irradiation resulted in a permanent switch of mitotic to stably postmitotic fibroblasts which acquired a high level of de novo expression of SA-beta-galactosidase, a marker for fibroblast senescence in vitro and in vivo. A single exposure of fibroblasts to 8-MOP/UVA resulted in a 5.8-fold up-regulation of two matrix-degrading enzymes, interstitial collagenase (MMP-1) and stromelysin-1 (MMP-3), over a period of &gt;120 days, while TIMP-1, the major inhibitor of MMP-1 and MMP-3, was only slightly induced. This imbalance between matrix-degrading metalloproteases and their inhibitor may lead to connective tissue damage, a hallmark of premature aging. Superoxide anion and hydrogen peroxide, but not singlet oxygen, were identified as important intermediates in the downstream signaling pathway leading to these complex fibroblast responses upon psoralen photoactivation. Collectively, the end phenotype induced upon psoralen photoactivation shares several criteria of senescent cells. In the absence of detailed molecular data on what constitutes normal aging, it is difficult to decide whether the changes reported here reflect mechanisms underlying normal cellular aging/senescence or rather produce a mimic of cellular aging/senescence by quite different pathways.

Premature thymic involution, observed at the ultrastructural level, in two lineages of human-SOD-1 transgenic mice

The human Cu/Zn superoxide dismutase (hSOD-1) gene, catalyses the dismutation of O2 to H2O2 and O2. It is located on chromosome 21 in q22.1 and is overexpressed in Down's syndrome (DS) patients. These patients present various abnormalities including mental retardation, congenital heart disease, immunological deficits and premature aging. In order to explore the potential role of SOD-1 overexpression in DS, we have generated two lineages of transgenic mice for the hSOD-1 gene and studied, at the ultrastructural level, the effect of hSOD-1 overexpression on the thymic microenvironment. Modification of the cellular architecture and morphology associated with a lipidic invasion, signs of a premature involution of the thymus, were observed in both lineages. A rupture of the filamentous network in the extracellular and probably also in the intracellular matrix was first observed. These results correlate the thymic alterations visualized in light microscopy, on the thymus from DS patients, and raise the question of the relationship between the SOD-1 overexpression and the different morphological alterations associated with the premature thymic involution observed in SOD-1 transgenic mice. They suggest that thymic and immunological impairments present in DS patients may be related to the SOD-1 gene dosage effect.

Superoxide dismutase, aging, and degenerative disease

Over 15 years of research on correlations between superoxide dismutase (SOD) activity and aging or life span have failed to provide a consistent picture of the role of SOD in aging. While genetic manipulations that increase CuZn-SOD activity have only a slight, if any, effect on maximum life span in several species, they do increase resistance to oxidative stress. However, increasing both CuZn-SOD and catalase does significantly increase maximum life span. Decreased SOD expression in a variety of species increases their vulnerability to oxidative stress, and in the case of genetically altered CuZn-SOD, leads to premature death of motor neurons in humans. Little is known about the regulation of expression of SOD and other antioxidant defense enzymes in eukaryotes. The research summarized below collectively suggest that SOD plays an important role in longevity and degenerative disease, but much remains to be learned before manipulation of SOD expression can be considered for effective intervention in either process.

Correlation between senescence and DNA repair in cells from young and old individuals and in premature aging syndromes

Cellular aging appears to be related to and perhaps caused by diminished DNA repair. To elucidate direct correlations between DNA repair capacity and senescence various parameters of cellular aging and DNA repair were studied simultaneously. Of special interest are features of DNA repair and senescence in cultured diploid fibroblasts derived either from healthy young or elderly probands as well as from patients suffering from premature senescence syndromes (Werner syndrome, Cockayne syndrome, ataxia telangiectasia and Down syndrome). Here we demonstrate the striking parallelism between reduced maximal lifespan, elevated levels of spontaneous chromosomal breaks, higher incidence of formation of micronuclei, a significant prolongation of cell cycle duration and a diminished reactivation of in vitro injured plasmid after transfection in cells from old individuals and from patients with premature senescence syndromes, suggesting a causal relationship between senescence and DNA damage.

Transgenic and knock-out mice: models of neurological disease

Besides providing useful model systems for basic science, studies based on modification of the mammalian germ line are changing our understanding of pathogenetic principles. In this article, we review the most popular techniques for generating specific germ line mutations in vivo and discuss the impact of various transgenic models on the study of neurodegenerative diseases. The "gain of function" approach, i.e., ectopic expression of exogenous genes in neural structures, has deepened our understanding of neurodegeneration resulting from infection with papova viruses, picorna viruses, and human retroviruses. Further, inappropriate expression of mutated cellular molecules in the nervous system of transgenic mice is proving very useful for studying conditions whose pathogenesis is controversial, such as Alzheimer's disease and motor neuron diseases. As a complementary approach, ablation of entire cell lineages by tissue-specific expression of toxins has been useful in defining the role of specific cellular compartments. Modeling of recessive genetic diseases, such as Lesch-Nyhan syndrome, was helped by the development of techniques for targeted gene deletion (colloquially termed "gene knock-out"). Introduction of subtle homozygous mutations in the mouse genome was made possible by the latter approach. Such "loss of function" mutants have been used for clarifying the role of molecules thought to be involved in development and structural maintenance of the nervous system, such as the receptors for nerve growth factor and the P0 protein of peripheral myelin. In addition, these models are showing their assets also in the study of enigmatic diseases such as spongiform encephalopathies.

Age-related changes in antioxidant enzymes and lipid peroxidation in brains of control and transgenic mice overexpressing copper-zinc superoxide dismutase

The aim of our study was first to obtain a comprehensive profile of the brain antioxidant defense potential and peroxidative damage during aging. We investigated copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), seleno-dependent glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R) activities, endogenous and in vitro stimulated lipid peroxidation in 40 brains of control mice divided into 3 age groups: 2 months (young), 12 months (middle-aged) and 28 months (old). We found a positive correlation between age and activities of CuZnSOD (r = 0.47; P < 0.01) and GSH-PX (r = 0.72; P < 0.0001). CuZnSOD and GSH-PX activities are independently regulated during brain aging since temporal changes of these two enzymes do not correlate. No modification in MnSOD activity and basal lipid peroxidation was observed as a function of age. Nevertheless, stimulated lipid peroxidation was significantly higher at 12 months (6.53 +/- 0.71 mumole MDA/g tissue) than at 2 months (5.69 +/- 0.90) and significantly lower at 28 months (5.13 +/- 0.33) than at 12 months. Second, we used genetic manipulations to construct transgenic mice that specifically overexpress CuZnSOD to understand the role of CuZnSOD in neuronal aging. The human CuZnSOD transgene expression was stable during aging. The increased CuZnSOD activity in the brain (1.9-fold) of transgenic mice resulted in an enhanced rate of basal lipid peroxidation and in increased MnSOD activity in the 3 age groups. Other antioxidant enzymes did not exhibit modifications indicating the independence of the regulation between CuZnSOD and glutathione-related enzymes probably due to their different cellular localization in the brain.

The role of alterations in free radical metabolism in mediating cognitive impairments in Down's syndrome

Down's syndrome (DS) is a genetic disorder involving an excess of chromosome 21 (trisomy 21) in approximately 96% of the cases and comprises approximately 15% of the population with mental retardation (Heller, 1969). In addition to the constitutional mental deficiencies associated with the syndrome many DS patients develop dementia associated with Alzheimer's disease (AD) in their later years of life (Thase et al., 1984). The genetic locus for Cu,Zn-superoxide dismutase (SOD1), a key enzyme in free radical metabolism, is located on chromosome 21, and the activity level of this enzyme is elevated by approximately 50% in a variety of cells of DS patients (see Kedziora and Bartosz, 1988; Sinet, 1982). Because alterations in free radical metabolism may be involved in neuronal death and may be associated with a number of pathological manifestations of DS, it is important to understand the role of free radical metabolism in cognitive impairments of DS, the topic discussed in this chapter.

Cellular clones and transgenic mice overexpressing copper-zinc superoxide dismutase: models for the study of free radical metabolism and aging

Down's Syndrome (DS), the most frequent of congenital birth defects, results from the trisomy of the chromosome numbered 21 in all cells of affected patients. This disease is characterized by developmental anomalies, mental retardation and features of rapid aging, particularly in the brain where the occurrence of Alzheimer's disease (AD) is observed in all trisomy 21 patients over the age of 35. Elucidation of the biological mechanisms leading to brain aging in DS might provide new insight into the understanding of brain aging and AD in normal people. Copper-zinc superoxide dismutase (CuZnSOD) is one of the genes encoded by chromosome 21. As a consequence of gene dosage excess, CuZnSOD activity and protein are increased by 50% in all DS tissues. The level of CuZnSOD protein and mRNA is particularly high in hippocampal pyramidal neurons susceptible to degenerative processes in AD and in dopaminergic melanized-neurons vulnerable in Parkinson's disease. Increased CuZnSOD activity in these age-related neurodegenerative disorders might result in H2O2 overproduction and subsequently promote peroxidative damages within cells. Increase of seleno-dependent glutathione peroxidase (Se-GPx) in DS cells supports this concept. In order to test this hypothesis, cell and animal models of CuZnSOD overexpression have been designed. In cells transfected with the human CuZnSOD gene, and increased Se-GPx activity is observed, a situation which mimics DS. In mice transgenic for the human CuZnSOD, the expression pattern of the transgene in the brain is similar to that in humans, and we can observe an increased peroxidation in this tissue. These data, like others in the literature, support the hypothesis that excess CuZnSOD induces an imbalance in the regulation of oxygen-derived free radical production which might result in peroxidative brain damage and possibly contribute to accelerated aging and age-related neuropathology.