Genetically determined conidial longevity is positively correlated with superoxide dismutase, catalase, glutathione peroxidase, cytochrome c peroxidase, and ascorbate free radical reductase activities in Neurospora crassa

Oxygen tolerance and detoxification mechanisms of highly enriched planktonic anaerobic ammonium-oxidizing (anammox) bacteria

Oxygen is a key regulatory factor of anaerobic ammonium oxidation (anammox). Although the inhibitory effect of oxygen is evident, a wide range of oxygen sensitivities of anammox bacteria have been reported so far, which makes it difficult to model the marine nitrogen loss and design anammox-based technologies. Here, oxygen tolerance and detoxification mechanisms of four genera of anammox bacteria; one marine species ("Ca. Scalindua sp.") and four freshwater anammox species ("Ca. Brocadia sinica", "Ca. Brocadia sapporoensis", "Ca. Jettenia caeni", and "Ca. Kuenenia stuttgartiensis") were determined and then related to the activities of anti-oxidative enzymes. Highly enriched planktonic anammox cells were exposed to various levels of oxygen, and oxygen inhibition kinetics (50% inhibitory concentration (IC50) and upper O2 limits (DOmax) of anammox activity) were quantitatively determined. A marine anammox species, "Ca. Scalindua sp.", exhibited much higher oxygen tolerance capability (IC50 = 18.0 µM and DOmax = 51.6 µM) than freshwater species (IC50 = 2.7-4.2 µM and DOmax = 10.9-26.6 µM). The upper DO limit of "Ca. Scalindua sp." was much higher than the values reported so far (~20 µM). Furthermore, the oxygen inhibition was reversible even after exposed to ambient air for 12-24 h. The comparative genome analysis confirmed that all anammox species commonly possess the genes considered to function for reduction of O2, superoxide anion (O2•-), and H2O2. However, the superoxide reductase (Sor)-peroxidase dependent detoxification system alone may not be sufficient for cell survival under microaerobic conditions. Despite the fact that anaerobes normally possess no or little superoxide dismutase (Sod) or catalase (Cat), only Scalindua exhibited high Sod activity of 22.6 ± 1.9 U/mg-protein with moderate Cat activity of 1.6 ± 0.7 U/mg-protein, which was consistent with the genome sequence analysis. This Sod-Cat dependent detoxification system could be responsible for the higher O2 tolerance of Scalindua than other freshwater anammox species lacking the Sod activity.

The Entomopathogenic Fungus Beauveria bassiana Employs Autophagy as a Persistence and Recovery Mechanism during Conidial Dormancy

Many filamentous fungi develop a conidiation process as an essential mechanism for their dispersal and survival in natural ecosystems. However, the mechanisms underlying conidial persistence in environments are still not fully understood. Here, we report that autophagy is crucial for conidial lifespans (i.e., viability) and vitality (e.g., stress responses and virulence) in the filamentous mycopathogen Beauveria bassiana. Specifically, Atg11-mediated selective autophagy played an important, but not dominant, role in the total autophagic flux. Furthermore, the aspartyl aminopeptidase Ape4 was found to be involved in conidial vitality during dormancy. Notably, the vacuolar translocation of Ape4 was dependent on its physical interaction with autophagy-related protein 8 (Atg8) and associated with the autophagic role of Atg8, as determined through a truncation assay of a critical carboxyl-tripeptide. These observations revealed that autophagy acted as a subcellular mechanism for conidial recovery during dormancy in environments. In addition, a novel Atg8-dependent targeting route for vacuolar hydrolase was identified, which is essential for conidial exit from a long-term dormancy. These new insights improved our understanding of the roles of autophagy in the physiological ecology of filamentous fungi as well as the molecular mechanisms involved in selective autophagy. IMPORTANCE Conidial environmental persistence is essential for fungal dispersal in ecosystems while also serving as a determinant for the biocontrol efficacy of entomopathogenic fungi during integrated pest management. This study identified autophagy as a mechanism to safeguard conidial lifespans and vitality postmaturation. In this mechanism, the aspartyl aminopeptidase Ape4 translocates into vacuoles via its physical interaction with autophagy-related protein 8 (Atg8) and is involved in conidial vitality during survival. The study revealed that autophagy acted as a subcellular mechanism for maintaining conidial persistence during dormancy, while also documenting an Atg8-dependent targeting route for vacuolar hydrolase during conidial recovery from dormancy. Thus, these observations provided new insight into the roles of autophagy in the physiological ecology of filamentous fungi and documented novel molecular mechanisms involved in selective autophagy.

Characterization of the autophagy-related gene BmATG8 in Bipolaris maydis

Autophagy is involved in cellular development and the maintenance of viability under nutrient deprivation in a wide range of eukaryotes. A filamentous ascomycete Bipolaris maydis, responsible for southern corn leaf blight, is also studied as a model fungus for sexual reproduction in filamentous ascomycetes that form filiform ascospores. In order to clarify the roles of autophagy in various stages of the life cycle of B. maydis, we constructed null mutants of BmATG8, an orthologue of the Saccharomyces cerevisiae autophagy gene ATG8 in B. maydis. Deletion of BmATG8 impaired localization of cytosolic components to the vacuole under nitrogen starvation, suggesting that autophagy was deficient in the null mutants. Additionally, fluorescent microscopic observations on a eGFP-fused BmATG8 expressing strain showed that BmATG8 is associated with autophagy-related structures. In vegetative growth, ΔBmATG8 strains showed a reduction in conidiation and aerial mycelial growth. Interestingly, the mutant conidia indicated loss of the germination rate under starvation conditions and affected longevity. However, germinated mutant conidia were still capable of infecting the host plant via appressoria. In sexual reproduction, ascospores with ΔBmATG8 genetic background were aborted. Our results revealed that autophagy plays a crucial role in the function of conidia, not in host infection via appressoria in B. maydis. In addition, conservation of the importance of autophagy in ascospore development is suggested among ascomycetes including species that form bitunicate ascus.

Tuning the inflammatory response to silver nanoparticles via quercetin in Caco-2 (co-)cultures as model of the human intestinal mucosa

Interaction of nanoparticles with food matrix components may cause unpredictable health complications. Using an improved Caco-2 cell-based in vitro (co-)culture model the potential of quercetin as one of the major food flavonoids to alter the effect of silver nanoparticles (Ag-NPs) <20 nm in the human intestinal mucosa at real life concentrations was investigated. Ag-NPs (15-90 μg/ml) decreased cell viability and reduced thiol groups, induced oxidative/nitrosative stress and lipid peroxidation and led to activity changes of various antioxidant enzymes after 3h exposure. The contribution of Ag(+) ions within the concentrations released from nanoparticles was shown to be less important, compared to Ag-NPs. While leading to inflammatory response in the intestines, Ag-NPs, paradoxically, also showed a potential anti-infammatory effect manifested in down-regulated IL-8 levels. Quercetin, co-administered with Ag-NPs, led to a reduction of cytotoxicity, oxidative stress, and recovered metabolic activity of Caco-2 cells, suggesting the protective effects of this flavonoid against the harmful effect of Ag-NPs. Quercetin not only alleviated the effect of Ag-NPs on the gastrointestinal cells, but also demonstrated a potential to serve as a tool for reversible modulation of intestinal permeability.

Comparative Proteomics Analyses of Two Races of Fusarium oxysporum f. sp. conglutinans that Differ in Pathogenicity

Fusarium oxysporum is a soil-inhabiting fungus that induces vascular wilt and root rot in a variety of plants. F. oxysporum f. sp. conglutinans (Foc), which comprises two races, can cause wilt disease in cabbage. Compared with race 1 (52557(-TM), R1), race 2 (58385(-TM), R2) exhibits much stronger pathogenicity. Here, we provide the first proteome reference maps for Foc mycelium and conidia and identify 145 proteins with different abundances among the two races. Of these proteins, most of the high-abundance proteins in the R2 mycelium and conidia are involved in carbohydrate, amino acid and ion metabolism, which indicates that these proteins may play important roles in isolate R2's stronger pathogenicity. The expression levels of 20 typical genes demonstrate similarly altered patterns compared to the proteomic analysis. The protein glucanosyltransferase, which is involved in carbohydrate metabolism, was selected for research. We knocked out the corresponding gene (gas1) and found that Foc-∆gas1 significantly reduced growth rate and virulence compared with wild type isolates. These results deepened our understanding of the proteins related to F. oxysporum pathogenicity in cabbage Fusarium wilt and provided new opportunities to control this disease.

Endogenous ergothioneine is required for wild type levels of conidiogenesis and conidial survival but does not protect against 254 nm UV-induced mutagenesis or kill

Ergothioneine, a histidine derivative, is concentrated in conidia of ascomycetous fungi. To investigate the function of ergothioneine, we crossed the wild type Neurospora crassa (Egt(+)) and an ergothioneine non-producer (Egt(-), Δegt-1, a knockout in NCU04343.5) and used the Egt(+) and Egt(-) progeny strains for phenotypic analyses. Compared to the Egt(+) strains, Egt(-) strains had a 59% reduction in the number of conidia produced on Vogel's agar. After storage of Egt(+) and Egt(-) conidia at 97% and 52% relative humidity (RH) for a time course to either 17 or 98 days, respectively, Egt(-) strains had a 23% and a 18% reduction in life expectancy at 97% and 52% RH, respectively, compared to the Egt(+) strains. Based on a Cu(II) reduction assay with the chelator bathocuproinedisulfonic acid disodium salt, ergothioneine accounts for 38% and 33% of water-soluble antioxidant capacity in N. crassa conidia from seven and 20 day-old cultures, respectively. In contrast, ergothioneine did not account for significant (α=0.05) anti-oxidant capacity in mycelia, which have lower concentrations of ergothioneine than conidia. The data are consistent with the hypothesis that ergothioneine has an antioxidant function in vivo. In contrast, experiments on the spontaneous mutation rate in Egt(+) and Egt(-) strains and on the effects of 254 nm UV light on mutation rate and conidial viability do not support the hypothesis that ergothioneine protects DNA in vivo.

Role of oxidative stress in Sclerotial differentiation and aflatoxin B1 biosynthesis in Aspergillus flavus

We show here that oxidative stress is involved in both sclerotial differentiation (SD) and aflatoxin B1 biosynthesis in Aspergillus flavus. Specifically, we observed that (i) oxidative stress regulates SD, as implied by its inhibition by antioxidant modulators of reactive oxygen species and thiol redox state, and that (ii) aflatoxin B1 biosynthesis and SD are comodulated by oxidative stress. However, aflatoxin B1 biosynthesis is inhibited by lower stress levels compared to SD, as shown by comparison to undifferentiated A. flavus. These same oxidative stress levels also characterize a mutant A. flavus strain, lacking the global regulatory gene veA. This mutant is unable to produce sclerotia and aflatoxin B1. (iii) Further, we show that hydrogen peroxide is the main modulator of A. flavus SD, as shown by its inhibition by both an irreversible inhibitor of catalase activity and a mimetic of superoxide dismutase activity. On the other hand, aflatoxin B1 biosynthesis is controlled by a wider array of oxidative stress factors, such as lipid hydroperoxide, superoxide, and hydroxyl and thiyl radicals.

Interconnections of reactive oxygen species homeostasis and circadian rhythm in Neurospora crassa

SIGNIFICANCE

Both circadian rhythm and the production of reactive oxygen species (ROS) are fundamental features of aerobic eukaryotic cells. The circadian clock enhances the fitness of organisms by enabling them to anticipate cycling changes in the surroundings. ROS generation in the cell is often altered in response to environmental changes, but oscillations in ROS levels may also reflect endogenous metabolic fluctuations governed by the circadian clock. On the other hand, an effective regulation and timing of antioxidant mechanisms may be crucial in the defense of cellular integrity. Thus, an interaction between the circadian timekeeping machinery and ROS homeostasis or signaling in both directions may be of advantage at all phylogenetic levels.

RECENT ADVANCES

The Frequency-White Collar-1 and White Collar-2 oscillator (FWO) of the filamentous fungus Neurospora crassa is well characterized at the molecular level. Several members of the ROS homeostasis were found to be controlled by the circadian clock, and ROS levels display circadian rhythm in Neurospora. On the other hand, multiple data indicate that ROS affect the molecular oscillator.

CRITICAL ISSUES

Increasing evidence suggests the interplay between ROS homeostasis and oscillators that may be partially or fully independent of the FWO. In addition, ROS may be part of a complex cellular network synchronizing non-transcriptional oscillators with timekeeping machineries based on the classical transcription-translation feedback mechanism.

FUTURE DIRECTIONS

Further investigations are needed to clarify how the different layers of the bidirectional interactions between ROS homeostasis and circadian regulation are interconnected.

Evidence suggesting a nitric oxide-scavenging activity for traditional crude drugs, and action mechanisms of Sanguisorbae Radix against oxidative stress and aging

In this series of experiments, we found that Sanguisorbae Radix extract possesses strong free radical-scavenging activity in vitro and in vivo. This crude drug protected against renal disease, which is closely associated with excessive generation of reactive oxygen species. We also showed that Sanguisorbae Radix extract can suppress lipid peroxidation and stimulate an antioxidant defense ability in SAM, suggesting that this crude drug may be an effective agent for ameliorating the pathological conditions related to excessive generation of free radicals and oxidant damage, particularly in the aging process.

'To repair or not to repair - no longer a question': repair of mitochondrial DNA shielding against age and cancer

The role of mitochondria in energy production and apoptosis is well known. The role of mitochondria and particularly the role of the mitochondria's own genome, mitochondrial (mt) DNA, in the process of ageing were postulated decades ago. However, this was discussed, debated and more or less disposed of. Recent data from elegant mouse models now confirm that mutations of mtDNA do indeed play a central and pivotal role in the ageing process. Newer reports also indicate a possible role of mtDNA mutations in the carcinogenesis of several organs. But is damaged mtDNA repaired, or is it simply degraded and discarded? This question appears to be answered now. According to recent data, mitochondria possess functional repair mechanisms such as base excision repair, double-strand break repair and mismatch repair, yet nucleotide excision repair has so far not been detected.

Repair of mitochondrial DNA in aging and carcinogenesis

Mitochondria are responsible for the generation of energy in the form of adenosine triphosphate. These organelles contain their own genetic material, mitochondrial (mt) DNA. This mtDNA has been hypothesized to play a role in the processes of aging and carcinogenesis. Initial reports have shown that there is no repair of cyclobutylpyrimidine dimers (CPD). More recent reports indicate however, that the mitochondrion contains several defence mechanisms against endogenous or exogenous damaging agents such as ultraviolet radiation or oxidative damage. The role of these defence mechanisms in the removal of mitochondrial DNA damage and the link to aging and carcinogenesis-associated processes are discussed in this review.

Peroxisomal monodehydroascorbate reductase. Genomic clone characterization and functional analysis under environmental stress conditions

In plant cells, ascorbate is a major antioxidant that is involved in the ascorbate-glutathione cycle. Monodehydroascorbate reductase (MDAR) is the enzymatic component of this cycle involved in the regeneration of reduced ascorbate. The identification of the intron-exon organization and the promoter region of the pea (Pisum sativum) MDAR 1 gene was achieved in pea leaves using the method of walking polymerase chain reaction on genomic DNA. The nuclear gene of MDAR 1 comprises nine exons and eight introns, giving a total length of 3,770 bp. The sequence of 544 bp upstream of the initiation codon, which contains the promoter and 5' untranslated region, and 190 bp downstream of the stop codon were also determined. The presence of different regulatory motifs in the promoter region of the gene might indicate distinct responses to various conditions. The expression analysis in different plant organs by northern blots showed that fruits had the highest level of MDAR. Confocal laser scanning microscopy analysis of pea leaves transformed with Agrobacterium tumefaciens having the binary vectors pGD, which contain the autofluorescent proteins enhanced green fluorescent protein and enhanced yellow fluorescent protein with the full-length cDNA for MDAR 1 and catalase, indicated that the MDAR 1 encoded the peroxisomal isoform. The functional analysis of MDAR by activity and protein expression was studied in pea plants grown under eight stress conditions, including continuous light, high light intensity, continuous dark, mechanical wounding, low and high temperature, cadmium, and the herbicide 2,4-dichlorophenoxyacetic acid. This functional analysis is representative of all the MDAR isoforms present in the different cell compartments. Results obtained showed a significant induction by high light intensity and cadmium. On the other hand, expression studies, performed by semiquantitative reverse transcription-polymerase chain reaction demonstrated differential expression patterns of peroxisomal MDAR 1 transcripts in pea plants grown under the mentioned stress conditions. These findings show that the peroxisomal MDAR 1 has a differential regulation that could be indicative of its specific function in peroxisomes. All these biochemical and molecular data represent a significant step to understand the specific physiological role of each MDAR isoenzyme and its participation in the antioxidant mechanisms of plant cells.

The free radical theory of aging

Aging is the accumulation of changes that increase the risk of death. Aging changes can be attributed to development, genetic defects, the environment, disease, and an inborn process: the aging process. The latter is the major risk factor for disease and death after age 28 in the developed countries. In these countries, average life expectancies at birth (ALE-B) now range from 76 to 79 years, 6-9 years less than the limit of approximately 85 years imposed by aging. Aging changes may be caused by free radical reactions. The extensive studies based on this possibility hold promise that the ALE-B can be extended to >85 years and the maximum life span increased.

Matrix-mediated cellular rejuvenation

Biomaterial surface morphology and chemistry influence cell responses mediated via signaling cascades that regulate a wide range of metabolic processes. These responses may range from changes in surface adhesion and remodeling of the extracellular matrix to activation of cytokine, cytoskeletal and other biochemical pathways regulating or modulating cellular morphology and function. The present study has focused on collagen Type I, a key extracellular matrix protein, and its potential impact on the process of cellular aging. This study was undertaken for several reasons. First, several investigators reported that growth of cells on a collagen matrix markedly enhanced the resistance of cells to stresses. Second, a large body of accumulated data strongly indicated a relationship between the potential to respond to stresses and cellular aging with the former strongly influencing the rate of the latter. Finally, it has been recently demonstrated that in aged cells one of the key aging-related processes previously considered irreversible, attenuation of the expression of a major stress response protein, Hsp70, can be reversed. This fact together with a probable regulatory role of the stress response potential in cellular aging suggested a possibility that the cellular aging process as a whole can be altered. Indeed, in the present study, growth on a denatured collagen matrices reversed in aged cells not only the attenuation of Hsp70 expression but also other aging-related processes, such as beta-galactosidase expression, increase in protein oxidation and changes in cell morphology. Moreover, it appeared to reduce the rate of aging in young cells. Understanding the nature of collagen matrix-mediated cellular rejuvenation might suggest approaches for interfering with organismic aging. Some immediate applications include cell rejuvenation for purposes of cloning and reduction of the rate of aging during expansion of stem cells for purposes of tissue engineering.

Aging is a deprivation syndrome driven by a germ-soma conflict

Evolution through natural selection can be described as driven by a perpetual conflict of individuals competing for limited resources. Recently, I postulated that the shortage of resources godfathered the evolutionary achievements of the differentiation-apoptosis programming [Rev. Neurosci. 12 (2001) 217]. Unicellular deprivation-induced differentiation into germ cell-like spores can be regarded as the archaic reproduction events which were fueled by the remains of the fratricided cells of the apoptotic fruiting body. Evidence has been accumulated suggesting that conserved through the ages as the evolutionary legacy of the germ-soma conflict, the somatic loss of immortality during the ontogenetic segregation of primordial germ cells recapitulates the archaic fate of the fruiting body. In this heritage, somatic death is a germ cell-triggered event and has been established as evolutionary-fixed default state following asymmetric reproduction in a world of finite resources. Aging, on the other hand, is the stress resistance-dependent phenotype of the somatic resilience that counteracts the germ cell-inflicted death pathway. Thus, aging is a survival response and, in contrast to current beliefs, is antagonistically linked to death that is not imposed by group selection but enforced upon the soma by the selfish genes of the "enemy within". Environmental conditions shape the trade-off solutions as compromise between the conflicting germ-soma interests. Mechanistically, the neuroendocrine system, particularly those components that control energy balance, reproduction and stress responses, orchestrate these events. The reproductive phase is a self-limited process that moulds onset and progress of senescence with germ cell-dependent factors, e.g. gonadal hormones. These degenerate the regulatory pacemakers of the pineal-hypothalamic-pituitary network and its peripheral, e.g. thymic, gonadal and adrenal targets thereby eroding the trophic milieu. The ensuing cellular metabolic stress engenders adaptive adjustments of the glucose-fatty acid cycle, responses that are adequate and thus fitness-boosting under fuel shortage (e.g. during caloric restriction) but become detrimental under fuel abundance. In a Janus-faced capacity, the cellular stress response apparatus expresses both tolerogenic and mutagenic features of the social and asocial deprivation responses [Rev. Neurosci. 12 (2001) 217]. Mediated by the derangement of the energy-Ca(2+)-redox homeostatic triangle, a mosaic of dedifferentiation/apoptosis and mutagenic responses actuates the gradual exhaustion of functional reserves and eventually results in a multitude of aging-related diseases. This scenario reconciles programmed and stochastic features of aging and resolves the major inconsistencies of current theories by linking ultimate and proximate causes of aging. Reproduction, differentiation, apoptosis, stress response and metabolism are merged into a coherent regulatory network that stages aging as a naturally selected, germ cell-triggered and reproductive phase-modulated deprivation response.

Aging: overview

Aging is a universal process that began with the origination of life about 3.5 billion years ago. Accumulation of the diverse deleterious changes produced by aging throughout the cells and tissues progressively impairs function and can eventually cause death. Aging changes can be attributed to development, genetic defects, the environment, disease, and an inborn process--the aging process. The chance of death at a given age serves as a measure of the average number of aging changes accumulated by persons of that age, that is, of physiologic age, and the rate of change of this measure as the rate of aging. Chances for death are decreased by improvements in general living conditions. As a result, during the past two millennia average life expectancy at birth (ALE-B), determined by the chances for death, of humans has risen from 30 years, in ancient Rome, to almost 80 years today in the developed countries. Chances for death in the developed countries are now near limiting values and ALE-Bs are approaching plateau values that are 6-9 years less than the potential maximum of about 85 years. Chances for death are now largely determined by the inherent aging process after age 28. Only 1.1% of female cohorts in Sweden die before this age; the remainder die off at an exponentially increasing rate with advancing age. The inherent aging process limits ALE-B to around 85 years, and the maximum life span (MLS) to about 122 years. Past efforts to increase ALE-B did not require an understanding of aging. Such knowledge will be necessary in the future to significantly increase ALE-B and MLS, and to satisfactorily ameliorate the medical, economic, and social problems associated with advancing age. The many theories advanced to account for aging should be used, to the extent it is feasible, to help with these important practical problems, including applications of the free radical theory of aging. Past measures evolved by societies to ensure adequate care for older individuals are rapidly becoming inadequate because of changes in life style, the growing percentage of older people, declining fertility rates, and the diminishing size of the work forces to provide for the elderly. Measures are being advanced to help with this problem. Prospects are bright for further increases in the span of functional life and improvements in the lives of the elderly.

A natural extracellular factor that induces Hsp72, inhibits apoptosis, and restores stress resistance in aged human cells

Experiments with cultured cells showed that most cellular stress resistance components are specialized for certain types of damage. For example, superoxide dismutase protects from oxidative damage; DNA repair enzymes guard against mutagens and other DNA-damaging agents. On the other hand, the major inducible heat shock protein Hsp72 protects cells from a large variety of stresses and thus represents a generalized repair/stress resistance component. Hsp72 not only refolds damaged proteins but also interferes with programmed cell death signaling pathways, thus providing cells with time to repair the damage, hence its universality as a stress protector. In the present study we demonstrate the occurrence in murine and human ascites fluids (AF) of a natural nontoxic extracellular factor (ascites Hsp72-inducing factor, AHIF) capable of activating Hsp72 expression in different types of cells via a pathway distinct from the heat shock response pathway. AHIF is unique in that it is the first physiological factor capable of inducing synthesis of Hsp72 not only in young cells but, remarkably, also in aged human cells that largely have lost the ability to express Hsp72 in response to stresses, a manifestation at the cellular level of a progressive impairment in the ability to adapt to environmental changes which characterizes aging. Pretreatment of aged human cells with AF triggers Hsp72 expression at levels seen in young stressed cells and protects cells from a variety of otherwise lethal stressful treatments such as heat shock, TNF, UV irradiation, etoposide, and menadione. Activation of Hsp72 expression is essential for antiapoptotic action of AHIF because specific inhibition of Hsp72 expression by antisense RNA abolishes the cytoprotective effect of AF. In view of an important link between stress resistance and longevity in different organisms, the abilities of AHIF make it a unique candidate for the role of a systemic regulator of the aging process. While a cell-autonomous stress response diminishes with aging, aged cells retain the ability to respond to an extracellular factor which induces the expression of Hsp72. This finding opens up exciting possibilities for using AF factor to restore stress resistance to old cells and organisms and the possibility of interfering with the aging process. The ability to induce stress resistance in young cells and to restore it in aged cells could serve as a basis for developing effective antiapoptotic therapies.

Extending functional life span

Average life expectancy at birth is a rough measure of the span of healthy, productive life--the functional life span. In the developed countries average life expectancies at birth now range from 76-79 years, six to nine years less than the limit of about 85 years imposed by aging. Aging is the accumulation of changes that increase the risk of death. Aging changes can be attributed to development, genetic defects, the environment, disease, and the inborn aging process. The latter is the major risk factor for disease and death after age 28 in the developed countries. The free radical theory of aging arose in 1954; it postulated that aging changes were caused by free radical reactions. There is now a growing consensus, largely based on the results of measures to minimize more-or-less random endogenous free radical reactions, that such reactions are a major cause of aging, possibly the only one. Some of these studies are presented following a brief discussion of free radical reactions.

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.

Antioxidant systems and erythrocyte life-span in mammals

1. Erythrocyte antioxidant systems--superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) and glutathione reductase (GR)--were discussed in relation to life-spans in some mammalian species. 2. The erythrocyte life-span of different mammals was found to be correlated with the levels of SOD, GSH-Px and GSH. 3. Data reviewed indicates that the erythrocyte life-span of each species is governed by both the oxygen radical formation and the efficiency of intrinsic antioxidant systems.

Selection and analysis of superoxide dismutase mutants of Neurospora

A survey of 12 genetically distinct, heat-sensitive mutants of Neurospora revealed three (un-1, un-3, and un-17) that are specifically deficient in the superoxide dismutase (SOD) isozymes SOD-2 (mitochondrial), SOD-3 (mitochondrial), SOD-4 (exocellular), respectively. Genetic analysis of the three mutants indicates that the enzyme deficiencies are probably the cause of the heat-sensitive phenotype. The phenotypes of the mutants are (1) no growth at the normally optimal temperature 35 degrees C and comparatively inferior growth at 15-30 degrees C; (2) inferior resistance to the oxidants paraquat or oxygen; (3) female sterility; and (4) inferior conidial viability and longevity. Paraquat or O2 inhibition is alleviated respectively by desferrioxamine-Mn (a SOD mimic) and tocopherol. Diverse antioxidants, including tocopherol, are therapeutic for the heat-sensitive and female-sterile phenotypes, and for inferior growth of wild type at stressfully high temperatures. The results support previous theories that heat stress is a form of oxyradical/oxidant stress and that antioxidant enzymes such as SOD are essential for normal growth, development, and longevity. Since the three genes may encode the three enzymes and are not closely linked to either one another or the family of antioxidant-enzyme regulatory genes Age-1, the latter apparently trans-regulate their expression.

Genetical, developmental, and thermal regulation of antioxidant enzymes in Neurospora

Three characteristics of the biochemical genetics of antioxidant enzyme regulation in Neurospora and enteric bacteria are analogous. This paper reports two additional analogies:responsiveness to change in respiratory rate or thermal stress. A negative regulatory Neurospora mutant is defective in those responses. Although several differences are noted, the common denominator of the two organisms is probably an oxy-regulon, a global unit of genetic function. The degree of homology of bacterial and fungal antioxidant enzyme regulatory mechanisms at the molecular-genetic and signal transduction levels of organization remains to be examined. The hypothesis that the genetic control of antioxidant enzymes is a prerequisite for cellular differentiation of Neurospora is discussed.

Pharmacogenetics of cyclic guanylate, antioxidants, and antioxidant enzymes in Saccharomyces

Supplements of antioxidants, superoxide dismutase (SOD), catalase, cyclic guanylate (cGMP), and theophylline, or omission of iron and copper from the medium are therapeutic for the inferior growth and viability of yeast mutants doubly deficient in mitochondrial and exocellular SOD isozymes under oxidative stresses. Cyclic adenylate tends to be ineffective or counterproductive. Oxy-stress resistant revertants are cross-resistant to other oxy-stresses and acquire one, the other, or both isozymes. The principal conclusions are: i) a genetic defect in cGMP metabolism probably compromises regulation of the enzymes' synthesis; ii) the enzymes are only essential for growth and viability under oxidative stresses; iii) oxidative toxicity is mediated by both exo- and endocellular oxy-radicals, particularly hydroxyl radicals; and iv) the pharmacogenetic features and the mutants' phenotypes are quite similar to those of negative antioxidant enzyme regulatory mutants of the related ascomycete Neurospora.

Genetic coregulation of longevity and antioxienzymes in Neurospora crassa

Further analysis of a model of the biochemical genetics of cellular longevity in Neurospora crassa confirms and amplifies the hypothesis that antioxienzymes and lifespans are genetically co-regulated. The model consists of seven classes of closely related strains with genetically determined median lifespans ranging from 7 to 90 days and differing by about 15-day intervals. The nuclear gene mutations Age- and age+ respectively decrease and increase both lifespans and the constitutive enzyme activities relative to the wild-type parent. Here the number of such enzymes correlated with lifespans is extended from 6 to 12. Four of these enzymes have not been previously noted in Neurospora. Statistical analysis indicates that the genes may coordinate the 12 enzymes' activities with respect to one another to facilitate their "collaborative" function. The genes probably perform a regulatory role in the synthesis of the antioxienzymes. Neurospora may have a global unit of genetic function, an oxy-regulon, analogous to that of enteric bacteria.

Pharmacogenetics of cyclic guanylate, antioxidants, and antioxidant enzymes in Neurospora

Previous studies indicate that antioxidant enzyme regulatory gene mutants (Age-) of Neurospora are defective in cellular longevity and development, numerous antioxienzymes, and cAMP, and that dietary cGMP confers normal longevity. Here it is shown that cGMP also phenotypically cures the developmental and enzymatic defects. At least 5 of the 12 known antioxidant enzyme deficiencies are normalized by cGMP.cGMP-mediated enzyme induction apparently requires gene transcription: actinomycin D is inhibitory. The mutants' inferior growth and development are stimulated by feeding cGMP, the cyclic nucleotide phosphodiesterase inhibitor theophylline, antioxidant enzymes, and antioxidants or by omission of both ferrous and cupric ions normally added to the culture medium. The analysis indicates that the inferior growth and development probably is a consequence of the formation of toxic hydroxyl radicals. The mutants are rather specific, conditional cGMP auxotrophs and respond to physiological concentrations of that nucleotide: cAMP tends to be ineffective. The observations indicate that: i) genetic regulation of antioxidant enzymes is a determinant of not only cellular longevity, but also normal growth and development; and ii) the enzymes do indeed provide defense against free radical/oxidant toxicity. The hypothesis that cGMP is a second messenger in regulation of the expression of antioxidant enzyme genes is consistent with experimental data, but remains to be verified.

Review of genetic investigations into the aging processes of Drosophila

The field has progressed to the point where a genetic investigation of the aging processes in Drosophila can be viewed as constituting both a serious and a feasible research program. There now exists at least one single gene mutant which yields an accelerated aging phenotype, at least two single gene null mutants affecting enzymes implicated in regulating the aging process and resulting in premature death, and at least two strains created by artificial selection which produce extended-longevity phenotypes. In addition, genes such as adh have an indirect and interactive effect upon the animal's longevity and might also play an important role in the genetic regulation of this process. Although far from complete, some essential tools are now in place and are being used to answer some of the questions posed by Martin. Of the several theories put forth to explain aging in Drosophila, it appears as if the data best uphold the free radical and the protein synthesis/gene expression theories. It is entirely possible that these two theories are complementary aspects of a broader underlying process. The genetic mechanisms controlling these physiological processes clearly do so in concert with certain environmental factors. The net effect of their interactions may be the decreased synthetic and repair ability of the cell as suggested by Lamb and by Webster. It is probably true that aging and longevity are multicausal phenotypes. Our only hope of understanding such a complex phenotype is to dissect it genetically, one (or a few) genes at a time under rigidly controlled conditions. Thorough genetic description of each system will be the prerequisite to their molecular analysis. This will likely result in multiple explanations, ideally one for each system. Yet these multiple molecular genetic explanations may well enable us to see some commonality underlying the aging process in this organism. The fact that several different lines of evidence appear to be converging on a small number of theoretical explanations is an encouraging sign. We should also be heartened by the extraordinary increase in our knowledge of embryonic development in Drosophila as a result of just such a strategy. And we should not forget that the homeotic mutants which now play such a large role in the deciphering of embryogenesis were once classified as "complex loci" and that the then-accepted explanations gave no hint of the underlying molecular relationships. For now it is fair to conclude that aging in Drosophila may be viewed as a genetically-determined, environmentally-modulated, event-dependent process.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for three differentially regulated catalase genes in Neurospora crassa: effects of oxidative stress, heat shock, and development

Genetic and biochemical studies demonstrated that Neurospora crassa possesses three catalases encoded by three separate structural genes. The specific activities of the three enzymes varied in response to superoxide-mediated stress, heat shock, and development. The three loci, which we designated cat-1, cat-2, and cat-3, map to the right arms of chromosomes III, VII, and III, respectively. The cat-1-encoded enzyme (designated Cat-1; estimated molecular weight, 315,000; pI 5.2) was the predominant catalase in rapid-growth mycelium, and its activity was substantially increased in paraquat-treated and heat-shocked mycelium. Cat-2 (Mw, 165,000; pI 5.4) was absent from rapid-growth mycelium but present at low levels in conidia and stationary-phase mycelium. It was the predominant catalase in extracts derived from mycelium that had been heat shocked for 2 h. Cat-3 (Mw, 340,000; pI 5.5) was the predominant catalase in extracts from mature conidia.

Evaluation of average life span of epithelial and stromal cells of human prostate by superoxide dismutase activity

Little is known about the cell kinetics on which development of benign prostatic hyperplasia is based. This prompted us to study the superoxide dismutase (SOD) activity, which is known 1) to correlate with the life span of cells and 2) to decrease with advancing age of cells. Therefore, SOD was measured in epithelium and stroma of the human prostate from patients of various ages (20-86 years) and compared with the activity in the postmitotic skeletal muscle. It was found that the highest mean specific SOD activity is present in skeletal muscle (4.0 mU.mg protein-1), followed by the stroma (2.1 mU.mg protein-1) and epithelium (1.4 mU.mg protein-1). Similar results were obtained when SOD activity was expressed per DNA (5.03, 1.73, and 0.16 mU.micrograms DNA-1, respectively). Comparing the slope of the age-dependent regression lines, it was demonstrated that the slope of the stroma is much closer to the slope of the postmitotic skeletal muscle than the slope of the epithelium. From the data, it was calculated that the average life span of stromal cells is probably longer than 30 years and of epithelial cells longer than 2 years. Hence in human prostatic tissue the average cell death rate might be rather low.

Genetic analyses of aging processes in Drosophila

Genetic investigations into the aging processes of Drosophila have a long history. Much of the earlier work attempted the analysis of longevity in already existing and (usually) short-lived strains and mutants, but was unsuccessful because there was no way of assuring that the genes involved actually affected the normal aging processes. Success was achieved only when procedures were devised to specifically select for mutants and/or strains affecting the normal aging processes. Recent work has shown that the life span may be genetically altered either via an acceleration of the normal aging rate or via the stage-specific lengthening of certain portions of the adult life span. A variety of evidence suggests that aging is best viewed as a genetically determined, environmentally modulated, event dependent process. The evidence underlying these observations is discussed, a possible genetic model is presented and future directions are suggested.

Correlates of longevity in two strains of the housefly, Musca domestica

The general objective of this study was to identify biochemical correlates of longevity in the housefly by comparing two strains of flies that have different longevities. The average and the maximum life spans of the longer-lived "Cambridge" strain flies were 46% and 23%, respectively, greater than the shorter-lived "Thuron" strain flies. The hypothesis that longer-lived organisms have relatively more efficient mechanisms to minimize oxidative stress and maintain a relatively more reduced redox potential was tested. All measurements were made on 8-day-old male flies maintained under identical conditions. Flies of the longer-lived strain had a lower metabolic rate and contained lesser amounts of H2O2 and thiobarbituric acid-reactants than the flies of the shorter-lived strain. Reduced glutathione concentration and activities of catalase, glutathione reductase and thioltransferase were higher in the longer-lived strain indicating that longer-lived flies manifest lower levels of oxidative stress and greater ability to maintain a relatively more reducing environment than the shorter-lived flies. Superoxide dismutase (SOD) activity was similar in the two strains, but the SOD/metabolic rate ratio was higher in the longer-lived strain. Total activity of glutathione S-transferases was comparable in the two strains suggesting that differences in detoxification ability are not correlated with longevity. Only S-glutamylcysteine synthetase activity was greater in the shorter-lived strain suggesting that variation in longevity is not due to reduction in the ability to synthesize GSH. Overall, the results support the view that parameters associated with oxidative stress play a role in the aging process of the houseflies.

Oxidation of Neurospora crassa glutamine synthetase

The glutamine synthetase of Neurospora crassa, either purified or in cell extracts, was inactivated by ascorbate plus FeCl3 and by H2O2 plus FeSO4. The inactivation reaction was oxygen dependent, inhibited by MnCl2 and EDTA, and stimulated in cell extracts by sodium azide. This inactivation could also be brought about by adding NADPH to the cell extract. The alpha and beta polypeptides of the active glutamine synthetase were modified by these inactivating reactions, giving rise to two novel acidic polypeptides. These modifications were observed with the purified enzyme, with cell extracts, and under in vivo conditions in which glutamine synthetase is degraded. The modified glutamine synthetase was more susceptible to endogenous phenylmethylsulfonyl fluoride-insensitive proteolytic activity, which was inhibited by MnCl2 and stimulated by EDTA. The possible physiological relevance of enzyme oxidation is discussed.

Initial observations on the role of glutathione peroxidases in Euglena

The algae Euglena gracilis possesses two glutathione (GSH) peroxidase: a GSH peroxidase that reduces organic hydroperoxides as well as hydrogen peroxide (GSH peroxidase 1); and a GSH peroxidase associated with GSH transferase that is active only with organic hydroperoxide substrates (GSH peroxidase 2). Preliminary experiments with Euglena were conducted to explore the in vivo role of the GSH peroxidases. The enzymes were not induced in response to the stimulation of cellular processes that generate oxidant species, such as beta-oxidation or photosynthesis. The levels of GSH peroxidase 1 were approximately twofold higher in autotrophic cultures containing the herbicide DCMU. GSH peroxidase 1 was most active in stationary phase cells; while the levels of GSH peroxidase 2 were fairly constant throughout growth. Under conditions where lipid peroxidation was induced in Euglena, the addition of either GSH peroxidase plus GSH reduced the lipid peroxide levels more than tenfold.