Age-dependent changes in proteins of Drosophila melanogaster

Application of omics techniques in forensic entomology research

With the advent of the post-genome era, omics technologies have developed rapidly and are widely used, including in genomics, transcriptomics, proteomics, metabolomics, and microbiome research. These omics techniques are often based on comprehensive and systematic analysis of biological samples using high-throughput analysis methods and bioinformatics, to provide new insights into biological phenomena. Currently, omics techniques are gradually being applied to forensic entomology research and are useful in species identification, phylogenetics, screening for developmentally relevant differentially expressed genes, and the interpretation of behavioral characteristics of forensic-related species at the genetic level. These all provide valuable information for estimating the postmortem interval (PMI). This review mainly discusses the available omics techniques, summarizes the application of omics techniques in forensic entomology, and their future in the field.

Rapid cell type-specific nascent proteome labeling in Drosophila

Controlled protein synthesis is required to regulate gene expression and is often carried out in a cell type-specific manner. Protein synthesis is commonly measured by labeling the nascent proteome with amino acid analogs or isotope-containing amino acids. These methods have been difficult to implement in vivo as they require lengthy amino acid replacement procedures. O-propargyl-puromycin (OPP) is a puromycin analog that incorporates into nascent polypeptide chains. Through its terminal alkyne, OPP can be conjugated to a fluorophore-azide for directly visualizing nascent protein synthesis, or to a biotin-azide for capture and identification of newly-synthesized proteins. To achieve cell type-specific OPP incorporation, we developed phenylacetyl-OPP (PhAc-OPP), a puromycin analog harboring an enzyme-labile blocking group that can be removed by penicillin G acylase (PGA). Here, we show that cell type-specific PGA expression in Drosophila can be used to achieve OPP labeling of newly-synthesized proteins in targeted cell populations within the brain. Following a brief 2 hr incubation of intact brains with PhAc-OPP, we observe robust imaging and affinity purification of OPP-labeled nascent proteins in PGA-targeted cell populations. We apply this method to show a pronounced age-related decline in neuronal protein synthesis in the fly brain, demonstrating the capability of PhAc-OPP to quantitatively capture in vivo protein synthesis states. This method, which we call POPPi (PGA-dependent OPP incorporation), should be applicable for rapidly visualizing protein synthesis and identifying nascent proteins synthesized under diverse physiological and pathological conditions with cellular specificity in vivo.

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Phospholipid Changes in a Drosophila Model of Early Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a degenerative disease caused by motor neuron damage in the central nervous system, and it is difficult to diagnose early. Drosophila melanogaster is widely used to investigate disease mechanisms and discover biomarkers because it is easy to induce disease in Drosophila through genetic engineering. We performed matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to investigate changes in phospholipid distribution in the brain tissue of an ALS-induced Drosophila model. Fly brain tissues of several hundred micrometers or less were sampled using a fly collar to obtain reproducible tissue sections of similar sizes. MSI of brain tissues of Drosophila cultured for 1 or 10 days showed that the distribution of phospholipids, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA), phosphatidylserine (PS), and phosphatidylinositol (PI), was significantly different between the control group and the ALS group. In addition, the lipid profile according to phospholipids differed as the culture time increased from 1 to 10 days. These results suggest that disease indicators based on lipid metabolites can be discovered by performing MALDI-MSI on very small brain tissue samples from the Drosophila disease model to ultimately assess the phospholipid changes that occur in early-stage ALS.

Myosin dilated cardiomyopathy mutation S532P disrupts actomyosin interactions, leading to altered muscle kinetics, reduced locomotion, and cardiac dilation in Drosophila

Dilated cardiomyopathy (DCM), a life-threatening disease characterized by pathological heart enlargement, can be caused by myosin mutations that reduce contractile function. To better define the mechanistic basis of this disease, we employed the powerful genetic and integrative approaches available in Drosophila melanogaster. To this end, we generated and analyzed the first fly model of human myosin-induced DCM. The model reproduces the S532P human β-cardiac myosin heavy chain DCM mutation, which is located within an actin-binding region of the motor domain. In concordance with the mutation's location at the actomyosin interface, steady-state ATPase and muscle mechanics experiments revealed that the S532P mutation reduces the rates of actin-dependent ATPase activity and actin binding and increases the rate of actin detachment. The depressed function of this myosin form reduces the number of cross-bridges during active wing beating, the power output of indirect flight muscles, and flight ability. Further, S532P mutant hearts exhibit cardiac dilation that is mutant gene dose-dependent. Our study shows that Drosophila can faithfully model various aspects of human DCM phenotypes and suggests that impaired actomyosin interactions in S532P myosin induce contractile deficits that trigger the disease.

The Roles of mitochondrial dysfunction and Reactive Oxygen Species in Aging and Senescence

The aging process deteriorates organs' function at different levels, causing its progressive decline to resist stress, damage, and disease. In addition to alterations in metabolic control and gene expression, the rate of aging has been connected with the generation of high amounts of Reactive Oxygen Species (ROS). The essential perspective in free radical biology is that reactive oxygen species (ROS) and free radicals are toxic, mostly cause direct biological damage to targets, and are thus a major cause of oxidative stress. Different enzymatic and non-enzymatic compounds in the cells have roles in neutralizing this toxicity. Oxidative damage in aging is mostly high in particular molecular targets, such as mitochondrial DNA and aconitase, and oxidative stress in mitochondria can cause tissue aging across intrinsic apoptosis. Mitochondria's function and morphology are impaired through aging, following a decrease in the membrane potential by an increase in peroxide generation and size of the organelles. Telomeres may be the significant trigger of replicative senescence. Oxidative stress accelerates telomere loss, whereas antioxidants slow it down. Oxidative stress is a crucial modulator of telomere shortening, and that telomere-driven replicative senescence is mainly a stress response. The age-linked mitochondrial DNA mutation and protein dysfunction aggregate in some organs like the brain and skeletal muscle, thus contributing considerably to these post-mitotic tissues' aging. The aging process is mostly due to accumulated damage done by harmful species in some macromolecules such proteins, DNA, and lipids. The degradation of non-functional, oxidized proteins is a crucial part of the antioxidant defenses of cells, in which the clearance of these proteins occurs through autophagy in the cells, which is known as mitophagy for mitochondria.

Time Flies-Age Grading of Adult Flies for the Estimation of the Post-Mortem Interval

The estimation of the minimum time since death is one of the main applications of forensic entomology. This can be done by calculating the age of the immature stage of necrophagous flies developing on the corpse, which is confined to approximately 2–4 weeks, depending on temperature and species of the first colonizing wave of flies. Adding the age of the adult flies developed on the dead body could extend this time frame up to several weeks when the body is in a building or closed premise. However, the techniques for accurately estimating the age of adult flies are still in their beginning stages or not sufficiently validated. Here we review the current state of the art of analysing the aging of flies by evaluating the ovarian development, the amount of pteridine in the eyes, the degree of wing damage, the modification of their cuticular hydrocarbon patterns, and the increasing number of growth layers in the cuticula. New approaches, including the use of age specific molecular profiles based on the levels of gene and protein expression and the application of near infrared spectroscopy, are introduced, and the forensic relevance of these methods is discussed.

Age-associated molecular changes are deleterious and may modulate life span through diet

Transition through life span is accompanied by numerous molecular changes, such as dysregulated gene expression, altered metabolite levels, and accumulated molecular damage. These changes are thought to be causal factors in aging; however, because they are numerous and are also influenced by genotype, environment, and other factors in addition to age, it is difficult to characterize the cumulative effect of these molecular changes on longevity. We reasoned that age-associated changes, such as molecular damage and tissue composition, may influence life span when used in the diet of organisms that are closely related to those that serve as a dietary source. To test this possibility, we used species-specific culture media and diets that incorporated molecular extracts of young and old organisms and compared the influence of these diets on the life span of yeast, fruitflies, and mice. In each case, the "old" diet or medium shortened the life span for one or both sexes. These findings suggest that age-associated molecular changes, such as cumulative damage and altered dietary composition, are deleterious and causally linked with aging and may affect life span through diet.

Candidate biomarkers for mosquito age-grading identified by label-free quantitative analysis of protein expression in Aedes albopictus females

We applied a "shotgun" approach based on nanoliquid chromatography-high resolution mass spectrometry associated to label free quantification (LFQ) to identify proteins varying with age, independently from the physiological state, in Aedes albopictus, a mosquito species which in the last decades invaded temperate regions in North America and Europe, creating concerns for associated high nuisance and risk of arbovirus transmission. The combined "shotgun" and LFQ approach was shown to be highly suitable to simultaneously compare several biological samples, as needed in a study aimed to analyze different age-groups and physiological states of adult mosquito females. The results obtained represent the first wide-scale analysis of protein expression in Ae. albopictus females: >1000 and 665 proteins were identified from few micrograms of crude protein extracts of mosquito heads and thoraxes, respectively. Six of these proteins were shown to significantly vary from 2- to 16-day-old females, independently from their physiological state (i.e. virgin, mated, host-seeking, blood-fed, and gravid).

BIOLOGICAL SIGNIFICANCE

Mosquito-borne diseases, such as malaria, dengue and other arboviroses, are a persistent cause of global mortality and morbidity, affecting hundreds of thousands of people. Billions of people living in tropical areas are at risk of being bitten every day by an infective mosquito female and the spread of tropical species such as Aedes albopictus to temperate areas is creating alarm in the northern hemisphere. Mosquito longevity is a critical factor affecting mosquito-borne pathogen transmission cycles and the mosquito capacity to transmit pathogens. However, large scale analyses of the age structure of mosquito field populations is hampered by the lack of optimal age-grading approaches. Our findings open new perspectives for the development of reliable, simple and cheap protein-based assays to age-grade Ae. albopictus females and, most likely, other mosquito species of higher medical relevance, such as the main dengue vector, Aedes aegypti, and the major Afrotropical malaria vectors. These assays would greatly contribute to epidemiological studies aimed at defining the actual vectorial capacity of a given mosquito species. Moreover, they would be very valuable in assessing the effectiveness of mosquito control interventions based on the relative ratio between young and old individuals before and after the intervention.

Proteomic biomarkers for ageing the mosquito Aedes aegypti to determine risk of pathogen transmission

Biomarkers of the age of mosquitoes are required to determine the risk of transmission of various pathogens as each pathogen undergoes a period of extrinsic incubation in the mosquito host. Using the 2-D Difference Gel Electrophoresis (2-D DIGE) procedure, we investigated the abundance of up to 898 proteins from the Yellow Fever and dengue virus vector, Aedes aegypti, during ageing. By applying a mixed-effects model of protein expression, we identified five common patterns of abundance change during ageing and demonstrated an age-related decrease in variance for four of these. This supported a search for specific proteins with abundance changes that remain tightly associated with ageing for use as ageing biomarkers. Using MALDI-TOF/TOF mass spectrometry we identified ten candidate proteins that satisfied strict biomarker discovery criteria (identified in two out of three multivariate analysis procedures and in two cohorts of mosquitoes). We validated the abundances of the four most suitable candidates (Actin depolymerising factor; ADF, Eukaryotic initiation factor 5A; eIF5A, insect cuticle protein Q17LN8, and Anterior fat body protein; AFP) using semi-quantitative Western analysis of individual mosquitoes of six ages. The redox-response protein Manganese superoxide dismutase (SOD2) and electron shuttling protein Electron transfer oxidoreductase (ETO) were subject to post-translational modifications affecting their charge states with potential effects on function. For the four candidates we show remarkably consistent decreases in abundance during ageing, validating initial selections. In particular, the abundance of AFP is an ideal biomarker candidate for whether a female mosquito has lived long enough to be capable of dengue virus transmission. We have demonstrated proteins to be a suitable class of ageing biomarkers in mosquitoes and have identified candidates for epidemiological studies of dengue and the evaluation of new disease reduction projects targeting mosquito longevity.

Protein metabolism and lifespan in Caenorhabditis elegans

Lifespan of the versatile model system Caenorhabditis elegans can be extended by a decrease of insulin/IGF-1 signaling, TOR signaling, mitochondrial function, protein synthesis and dietary intake. The exact molecular mechanisms by which these modulations confer increased life expectancy are yet to be determined but increased stress resistance and improved protein homeostasis seem to be of major importance. In this chapter, we explore the interactions among several genetic pathways and cellular functions involved in lifespan extension and their relation to protein homeostasis in C. elegans. Several of these processes have been associated, however some relevant data are conflicting and further studies are needed to clarify these interactions. In mammals, protein homeostasis is also implicated in several neurodegenerative diseases, many of which can be modeled in C. elegans.

Aging enhances indirect flight muscle fiber performance yet decreases flight ability in Drosophila

We investigated the effects of aging on Drosophila melanogaster indirect flight muscle from the whole organism to the actomyosin cross-bridge. Median-aged (49-day-old) flies were flight impaired, had normal myofilament number and packing, barely longer sarcomeres, and slight mitochondrial deterioration compared with young (3-day-old) flies. Old (56-day-old) flies were unable to beat their wings, had deteriorated ultrastructure with severe mitochondrial damage, and their skinned fibers failed to activate with calcium. Small-amplitude sinusoidal length perturbation analysis showed median-aged indirect flight muscle fibers developed greater than twice the isometric force and power output of young fibers, yet cross-bridge kinetics were similar. Large increases in elastic and viscous moduli amplitude under active, passive, and rigor conditions suggest that median-aged fibers become stiffer longitudinally. Small-angle x-ray diffraction indicates that myosin heads move increasingly toward the thin filament with age, accounting for the increased transverse stiffness via cross-bridge formation. We propose that the observed protein composition changes in the connecting filaments, which anchor the thick filaments to the Z-disk, produce compensatory increases in longitudinal stiffness, isometric tension, power and actomyosin interaction in aging indirect flight muscle. We also speculate that a lack of MgATP due to damaged mitochondria accounts for the decreased flight performance.

A difference in the proteins found in young adults of inbred strains of Drosophila melanogaster which correlates with genetically-determined, long or short life span

One-dimensional electrophoresis was performed on extracts of flies collected from across all ages. Protein gel patterns were compared for two strains of Drosophila melanogaster with distinctly long and short adult life spans that result from different alleles of longevity genes. An inter-strain difference was observed in the changes in protein pattern in the 77 kDa region in period of day 0-5 after emerging. We propose that the protein involved is a product of autosomal longevity alleles A1 and A2 at the Jm A locus and is related to development of longevity potentials in the preimaginal stage.

Examining the Proteome of Drosophila Across Organism Lifespan

A survey of the proteome of Drosophila melanogaster at nine time points across the adult lifespan based on several mass-spectrometry-based techniques is presented. In total, there is evidence for 5902 unique peptides corresponding to 1699 different proteins. Of hundreds of relatively abundant components, many appear to be highly dynamic as the adult fly ages. Of those proteins that we observe changing with age, a majority, associated with metabolism, reproduction, and development, are down-regulated. Other biological pathways such as defense response also show variable changes, where some proteins are down-regulated and others are up-regulated. The observed variations are compared with a report of genome-wide changes at the transcriptome level at different ages and the similarities and differences are presented.

Gene transcript profiling in aging research

Advances in biotechnology have led to methods for quantifying the relative concentrations of thousands of mRNAs in parallel. While these are powerful methods that can be used for both hypothesis testing and hypothesis generation, gene transcript profiling has some limitations as a tool to study aging. These include the difficulty in separating effects of aging from analytical and biological variability, statistical problems associated with simultaneous determination of so many different gene transcripts, and uncertainty about the functional significance of changes in mRNA concentrations. In this review, these issues are discussed with a focus on two methods for profiling mRNAs--serial analysis of gene expression (SAGE) and DNA arrays.

Attenuated expression of 70-kDa heat shock protein in WI-38 human fibroblasts during aging in vitro

We examined the effects of cellular aging on the expression of the heat shock-inducible HSP70 gene in WI-38 diploid human fibroblasts serially passaged in vitro. The senescence of the cells was established by evaluating population doubling level, cell density at confluency, and cell morphology along with the detection of senescence-associated beta-galactosidase activity (histochemically detectable at pH 6), a reliable marker of aging in low-density cultures. A marked decrease in the synthesis and accumulation of the inducible HSP70 protein was observed in serum-fed late passage cells exposed to a severe heat shock (30 min at 45 degrees C) in comparison to early passage cells. However, the degree of HSF-DNA binding, monitored by gel retardation assay was similar in both early and late passage cells. Similarly, Northern blotting analysis indicated that comparable amounts of inducible HSP70 mRNA were present in the total RNA fraction, in the total polyadenylated RNA fraction, or in the nuclear polyadenylated RNA fraction extracted from both early and late passage cells. In contrast, much less inducible HSP70 mRNA was detected in the total cytoplasmic RNA fraction or in the polyadenylated cytoplasmic RNA fraction of late passage cells. Thus age-related differences in heat-induced HSP70 synthesis and accumulation observed in serum-fed WI-38 cells appeared to result from an impairment in the posttranscriptional processing of the HSP70 mRNA at a level following the polyadenylation step and preceding translocation from the nucleus to the cytoplasm. When HF were serum deprived for 20 h before heat shock, the induction of HSP70 mRNA was less than 30% reduced in early passage cells in comparison to serum-fed cells; however, the level of HSP70 mRNA was markedly (over 80%) decreased in serum-deprived late passage cells. This result indicated that the presence of serum has a strong influence on heat shock-induced HSP70 gene expression in human fibroblasts aging in vitro.

Age-dependent accumulation of advanced glycation end-products in adult Drosophila melanogaster

Advanced glycation end-product(s) (AGE) are formed in biological systems when reducing sugars react with amino groups on proteins. Long-lived proteins such as collagen and lens crystallins are known to be susceptible to AGE modification and may play a major role in the development of diabetes and other age-related pathologies. It has been previously suggested that AGE formation might affect the lifespan of experimental animals. Our study is the first to examine the effect of AGE accumulation on the life span of an organism, Drosophila melanogaster. We found that Drosophila melanogaster maintained at 24 degrees C accumulate significant AGE over their lifespan. Young flies (10 days old) had 44% less AGE than senescent flies (75 days old). We were able to reduce AGE accumulation in Drosophila melanogaster by raising the flies on a medium containing a known AGE inhibitor, aminoguanidine HCl. Reduction of AGE in flies failed to increase their mean lifespan, and high concentrations (40 mM) reduced the mean life span, which suggests that aminoguanidine is toxic at levels near those required for inhibition of AGE formation. However, the common fruit fly, Drosophila melanogaster, provides a simple model system to study the age-dependent accumulation of glycated proteins and their inhibition by novel compounds.

Junk DNA and sectorial gene repression

Transcriptional repression in eukaryotes often involves tens or hundreds of kilobase pairs, two to three orders of magnitude more than the bacterial operator/repressor model does. Classical repression, represented by this model, was maintained over the whole span of evolution under different guises, and consists of repressor factors interacting primarily with promoters and, in later evolution, also with enhancers. The use of much larger amounts of DNA in the other mode of repression, here called the sectorial mode ('superrepression'), results in the conceptual transfer of so-called junk DNA to the domain of functional DNA. This contribution to the solution of the c-value paradox involves perhaps 15% of genomic 'junk,' and encompasses the bulk of the introns, thought to fill a stabilizing role in sectorially repressed chromatin structures. In the case of developmental genes, such structures appear to be heterochromatoid in character. However, solid clues regarding general structural features of superrepressed terminal differentiation genes remain elusive. The competition among superrepressible DNA sectors for sectorially binding factors offers, in principle, a molecular mechanism for developmental switches. Position effect variegation may be considered an abnormal manifestation of normal processes that underly development and involve heterochromatoid sectorial repression, which is apparently required for local elimination or modulation of morphological features (morpholysis). Sectorial repression of genes participating either in development or in terminal differentiation is considered instrumental in establishing stable cell types, and provides a basis for the distinction between determination and cell type specification. The gamut of possible stable cell types may have been broadened by the appearance in evolution of heavy isochores. Additional types of relatively frequent GC-rich cis-acting DNA motifs may offer reiterated binding sites to factors endowed with a selective (though not individually strong) affinity for these motifs. The majority of sequence motifs thought to be used in superrepression need not be individually maintained by natural selection. It is re-emphasized that the dispensability of sequences is not an indicator of their nonfunctionality and that in many cases, along noncoding sequences, nucleotides tend to fill functions collectively, rather than individually.

Total RNA, rRNA and poly(A)+RNA abundances during aging in Caenorhabditis elegans

This is the second in a series of studies in which we characterize gene expression at the level of RNA during aging in the nematode Caenorhabditis elegans. Here, we quantitatively analyzed total RNA, poly(A)+ RNA, and ribosomal RNA as a function of chronological age in two different strains (TJ1060 and TJ1061) having wild-type life spans and in a long-lived age-1 mutant strain (TJ1062). In addition, we compared the age-dependent abundance patterns of these RNAs in two different culture environments. Total RNA yield did not show a consistent pattern of age-related changes. However, total RNA yield was significantly higher in all three strains when grown on agar than when grown in liquid. In addition, total RNA yield was significantly lower from strain TJ1061 than from strain TJ1060 and TJ1062. Relative to total RNA, rRNA did not exhibit any consistent differences with age, strain or environment. Poly(A)+ RNA decreased by 23-43% in old animals from the long-lived strain and one of the wild-type strains, but was not changed in the second wild-type strain. In addition, control experiments to determine the amount of RNA contributed by E. coli bacteria (present in the nematode culture medium as a food source) suggest that the age-1 mutant strain has a lower bacterial infection rate, which may contribute to the increased life span of this strain.

The expression of the EF1 alpha genes of Drosophila is not associated with the extended longevity phenotype in a selected long-lived strain

A quantitative dot blot analysis was performed to determine whether the expression of the EF-1 alpha genes of Drosophila melanogaster are associated with the extended longevity phenotype characteristic of our genetically selected long-lived strain. These data were compared to that obtained from two normal-lived strains and from two iso-chromosomal strains with an intermediate life span. The relative mRNA levels of both EF-1 alpha genes (EF-1 alpha F1 and EF-1 alpha F2) for all five strains were measured through the larval, pupal, and early adult stages, and statistically analyzed. Our findings from these studies indicate that the F2 mRNA tracks with the extended longevity; however, the F1 mRNA is the major component and, thus, the relative total expression of these genes at the mRNA level is approximately equivalent for all five strains. These conclusions suggest that the expression of the EF-1 alpha genes is not associated with the extended longevity phenotype.

Germ-line expression of the I factor, a functional LINE from the fruit fly Drosophila melanogaster, is positively regulated by reactivity, a peculiar cellular state

I factor is a functional LINE (long interspersed nucleotidic element) which is mobilized in the germ-line of dysgenic SF females during I-R hybrid dysgenesis. Such females are obtained when an oocyte from a reactive stock, devoid of I factors but characterized by a level of reactivity, i.e. its potential for hybrid dysgenesis, is fertilized by a spermatozoon from an I factor-containing inducer stock. In a previous paper we described the expression of an I factor-lacZ fusion. Expression was detected in the ovaries of reactive and dysgenic flies only. In this paper we show that this transgenic activity can be quantified and depends upon the maternally inherited reactivity. Reactivity is not just a permissive state and modifiers of the reactivity level such as heat treatment and ageing change the level of expression of our transgenic fusion accordingly. Moreover, ageing through generations has the same cumulative and reversible effect on both reactivity and I factor expression. Using our fusion as a test for reactivity we show that the silencing of I factor after its introduction into a reactive genome may not be established in a single generation.

Two-dimensional protein electrophoretic analysis of postponed aging in Drosophila

Five populations of Drosophila melanogaster that had been selected for postponed aging were compared with five control populations using two-dimensional protein gel electrophoresis. The goals of the study were to identify specific proteins associated with postponed aging and to survey the population genetics of the response to selection. A total of 321 proteins were resolvable per population; these proteins were scored according to their intensity. The resulting data were analyzed using resampling, combinatoric, and maximum parsimony methods. The analysis indicated that the populations with postponed aging were different from their controls with respect to specific proteins and with respect to the variation between populations. The populations selected for postponed aging were more heterogeneous between populations than were the control populations. Maximum parsimony trees separate the selected populations, as a group, from their controls, thereby exhibiting a homoplastic pattern.

Heat shock induces changes in the expression and binding of ubiquitin in senescent Drosophila melanogaster

We examined the effect of aging on the expression of ubiquitin RNA and the binding of the ubiquitin polypeptide to proteins following heat shock in Drosophila melanogaster. Heat-shocked adult flies transcribe two major RNA species--one of 4.4 kb and one of about 6 kb that hybridize to the polyubiquitin-encoding probe. Several less abundant RNAs were also observed but the 4.4-kb band was present as the major RNA species in both stressed and nonstressed flies of both ages. The 6-kb fragment was more abundant in heat shocked aged flies than in younger flies. The quantitative expression of the polyubiquitin gene increased in proportion to the duration of the heat stress. Moreover, the induction of the polyubiquitin RNA was markedly elevated during aging following heat shock. Hybridization of Northern blots with the monoubiquitin gene probe revealed a band of 0.9 kb that was not significantly affected by heat stress. We also investigated the relationship between the changes in polyubiquitin gene expression and the formation of ubiquitin-protein complexes in aging heat-shocked flies. Heat shock to old flies results in a significant increase in the level of proteins immunoprecipitated by anti-ubiquitin antibodies. In the case of proteins synthesized 2 h before heat shock, most of the ubiquitinated proteins were of high molecular weight. For those proteins synthesized during a 30-min heat shock and the 2 h following heat shock, two major immunoprecipitated bands were observed: an 80-kD and a 70-kD polypeptide. The ubiquitination of a 60 kD protein was also observed in nonstressed flies, but its formation was drastically reduced following heat shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes with aging and physical exercise in ascorbic acid content and proliferative response of murine lymphocytes

Ascorbic acid content and lymphoproliferative response to phytohemagglutinin were measured in lymphocytes from axillary nodes, spleen and thymus of young (15 +/- 2 weeks) and old (60 +/- 5 weeks) BALB/c mice. Ascorbic acid content in lymphocytes from spleen and thymus was found to be significantly higher and the lymphoproliferative response in the three immunocompetent organs significantly lower in old mice as compared to young mice. Moreover, young and old BALB/c mice were required to maintain a swimming activity until exhaustion (exhaustive exercise) or 90 min of swimming each day for a total of 20 days (continuous exercise). In both young and old mice the stress produced by exhaustive exercise and confirmed by the existence in serum of significantly increased levels of corticosterone compared to controls, caused a significant decrease in ascorbic acid content as well as in lymphoproliferative response. Continuous exercise, characterized by the presence in serum of significantly decreased levels of corticosterone compared to controls, produced the most significant decrease in ascorbic acid content from young and old murine lymphocytes. Moreover, this exercise resulted in a significant increase in lymphoproliferative response. Our results suggest that aging results in an increase in the ascorbic acid content of lymphocytes accompanied by a decline in the lymphoproliferative response in old BALB/c mice.

An update on the mitochondrial-DNA mutation hypothesis of cell aging

Our electron microscopic study of aging insects and mammals suggests that metazoan senescence is linked to a gradual process of mitochondrial breakdown (and lipofuscin accumulation) in fixed postmitotic cells. This led us to propose in the early 1980s an oxyradical-mitochondrial DNA damage hypothesis, according to which metazoan aging may be caused by mutation, inactivation or loss of the mitochondrial genome (mtDNA) in irreversibly differentiated cells. This extranuclear somatic gene mutation concept of aging is in agreement with the fact that mtDNA synthesis takes place at the inner mitochondrial membrane near the sites of formation of highly reactive oxygen species and their products. Mitochondrial DNA may be unable to counteract the damage inflicted by those by-products of respiration because, in contrast to the nuclear genome, it lacks excision and recombination repair. Since mtDNA contains the structural genes for 13 hydrophobic proteins of the respiratory chain and ATP synthase as well as mitochondrial rRNAs and tRNAs, damage to this organellar genome will decrease or prevent the 'rejuvenation' of the mitochondria through the process of macromolecular turnover and organelle fission. Thus deprived of the ability to regenerate their mitochondria, the fixed postmitotic cells will sustain a decrease in the number of functional organelles, with resulting decline in ATP production. At higher levels of biological organization, this will lead to a loss in the bioenergetic capacity of cells, with concomitant decreases in ATP dependent protein synthesis and specialized physiological function, thus paving the way for age related degenerative diseases. The above concept is supported by a wealth of recent observations confirming the genomic instability of mitochondria and suggesting that animal and human aging is accompanied by mtDNA deletions and other types of injury to the mitochondrial genome. Our hypothesis of mtDNA damage is integrated with the classic concepts of Weissman and Minot in order to provide a preliminary explanation of the evolutionary roots of aging and reconcile the programed and stochastic views of metazoan senescence.

Gene expression patterns in the black blowfly (Phormia regina) as revealed by two-dimensional electrophoresis of proteins. I. Developmental stage-specific and sex-specific differences

The black blowfly, Phormia regina, has been implicated in human myiasis and as a contact vector of viral and bacterial diseases present in carrion to which female flies are attracted for egg deposition. Inbred strains of P. regina are an excellent model system for studying gene expression in the developmental stages of such holometabolous dipteran parasites. However, information regarding gene and protein expression patterns in P. regina is limited. We used ISO-DALT high-resolution, two-dimensional electrophoresis with silver staining to establish fundamental protein maps for examination of the stage-specific gene expression patterns in the 615 most abundant proteins of the eggs, first- and third-instar larvae, pupae, and male and female adults. We also used a differential extraction technique to identify the major cuticular proteins of the adults. The results show 48 clearly identifiable stage-specific and sex-specific proteins. Thus, approximately 8% of the most abundant proteins exhibit developmental changes. These analyses serve as an initial data base for further studies of ontogenetic regulation, organellar origin, and physiologic function of the stage-specific proteins in the life cycle of these opportunistically parasitic dipterans.

An integrated theory of aging as the result of mitochondrial-DNA mutation in differentiated cells

We maintain that aging of humans and animals derives from a mutation or inactivation (probably followed by endonuclease digestion) of the mitochondrial genome of differentiated cells. This extranuclear somatic mutation hypothesis of aging is based on the finding that mitochondrial DNA (mtDNA) synthesis takes place at the inner mitochondrial membrane near the sites of formation of highly reactive oxygen species and their products, such as lipoperoxides and malonaldehyde. The mtDNA may be unable to counteract the damage inflicted by those by-products of respiration because, in contrast to the nuclear genome, it lacks histone protection and scission repair. Since the mitochondrial genome controls the synthesis of several hydrophobic proteins of the inner mitochondrial membrane, the postulated mutation, inactivation or loss of mtDNA will prevent the replication of the organelles. Thus deprived of the ability to regenerate their mitochondrial populations, the cells will sustain an irreversible decline in their bioenergetic ability, with concomitant senescent loss of physiological performance and eventual death. The above hypothesis is integrated with the concepts of Minot, Pearl and others in order to offer a more comprehensive view of aging.

Heat stress induced enhancement of heat shock protein gene activity in the honey bee (Apis mellifera)

We employed in vitro translation of mRNA and product separation using SDS-PAGE to examine the heat-shock response of the worker honey bee. Increases in the levels of 6 translatable RNA populations were observed following heat stress. The greatest response was observed among bees aged 9 days. Slight levels of induction of 70 and 82 kDa heat shock proteins were evident among bees taken directly from the colony.

Isolation and identification of aging-related cDNAs in the mouse

To identify genes whose expression changes as a function of aging, we screened mouse cDNA libraries with cDNAs from mice of different ages. Specifically, whole-mouse cDNA libraries were constructed in lambda gt10 using poly(A) RNA from young (3 month) and old (27 month) C57BL/6J inbred mice and these lambda plaques were hybridized with radioactive cDNAs made from pooled poly(A) RNA from animals 3 or 33 months of age. Five clones were isolated that showed an aging-related pattern of expression and four of these were identified by computerized sequence matching to the GenBank database: MUP2 (a major urinary protein); Q10 of the MHC locus; a cytoskeletal actin gene; and creatine kinase. One gene whose expression increases with aging and is most abundant in spleen remains unidentified. All five cDNAs showed 4-fold to 17-fold changes with aging in their steady-state mRNA levels in at least one tissue.

Analysis of effect of age on synthesis of specific proteins by hepatocytes

The effect of age on the synthesis of specific proteins by hepatocytes was studied in Fischer F344 rats using two-dimensional polyacrylamide gel electrophoresis. Almost all proteins synthesized by hepatocytes from young rats were synthesized by hepatocytes isolated from old rats. Of over 500 proteins visually compared by two-dimensional polyacrylamide gel electrophoresis, only 11 proteins were observed to disappear and/or appear consistently with increasing age. The rates of synthesis of 36 randomly chosen proteins were quantified. Interestingly, the synthesis of 35 of the 36 proteins decreased between 5 and 30 months of age. The decrease in protein synthesis varied (15% to 70%) from one protein to another; i.e., a heterogeneity was observed in the age-related decrease in the synthesis of proteins. The age-related decrease in protein synthesis was statistically significant for 53% of the proteins studied. The total decrease in the rate of synthesis of all 36 proteins studied was 40% between 5 and 30 months of age, which is essentially the same as the decrease in total protein synthesis by suspension of hepatocytes isolated from 5- and 30-month-old rats. The results of this study demonstrate that the mechanism underlaying aging is different from development, which is characterized by a major change in the species of proteins synthesized by a cell.

Dissociation of learning and performance deficits in aged mice

The present study was undertaken to determine whether an age-related learning deficit would occur in a complex visual discrimination task and whether the learning impairment could be separated from performance deficits. The study also sought to determine whether treatment with an inhibitor of protein synthesis, anisomycin, would impair learning in this task. Two age groups (7-10 mo; 27-30 mo) of C56BL/6j mice were given training in a five-choice, simultaneous, visual discrimination task. Errors, freezing, avoidances, and response latencies were recorded. Results revealed that the difference in errors between the two groups disappeared during the middle part of training whereas the difference in the performance measures persisted until the end of training. Anisomycin caused increased errors in the adult but not the old mice. These results indicate that old mice can learn a discrimination task as well as adults but the rate of learning is slower, whereas their physical performance on the task is persistently inferior to adult mice.

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)

Patterns of amino acid incorporation in long-lived genetic strains of Drosophila melanogaster

This study examined the age-dependent alterations in the in vivo incorporation of labeled amino acids into protein during the adult life spans of males and females obtained from genetically based long-lived and control strains of Drosophila melanogaster. All four groups tested showed significant decreases (ca. 50%) in the uptake of labeled amino acids as a function of age. Each of the four groups had their own characteristic temporal pattern of functional decrement. Both the long-lived and the control females have similar patterns of amino acid incorporation, but the onset of these changes is delayed by 10 to 20 days in long-lived animals. These alterations in protein synthesis appear to be related to corresponding changes in the female fecundity patterns of each strain. The male patterns differ from one another and from the female patterns, but they both show periods of high fluctuation early in life followed by a terminal period of relatively low and constant synthesis. These data are consistent with the view that the overall alterations in the longevity of these two strains are likely due to changes in the timing of particular events in the adult life cycle.

Aging results in an unusual expression of Drosophila heat shock proteins

We used high-resolution two-dimensional polyacrylamide gel electrophoresis to evaluate the effect of aging on the heat shock response in Drosophila melanogaster. Although the aging process is not well understood at the molecular level, recent observations suggest that quantitative changes in gene expression occur as these fruit flies approach senescence. Such genetic alterations are in accord with our present data, which clearly show marked differences in the synthesis of heat shock proteins between young and old fruit flies. In 10-day-old flies, a heat shock of 20 min results in the expression of 14 new proteins as detectable by two-dimensional electrophoresis of [35S]methionine-labeled polypeptides, whereas identical treatment of 45-day-old flies leads to the expression of at least 50 new or highly up-regulated proteins. In addition, there is also a concomitant increase in the rate of synthesis of a number of the normal proteins in the older animals. Microdensitometric determinations of the low molecular weight heat shock polypeptides on autoradiographs of five age groups revealed that their maximum expression occurs at 47 days for a population of flies with a mean life span of 33.7 days. Moreover, a heat shock effect similar to that observed in senescent flies occurs in young flies fed canavanine, an arginine analogue, before heat shock.

Metabolic rates in genetically based long lived strains of Drosophila

The goal of these experiments was to determine if the increased longevity characteristics of our genetically selected long lived line of Drosophila could be attributed to metabolic differences. The data shows an inverse relationship between life span and temperature for both the long lived (L) and normal (R) strains; however, the higher longevity of the L strain relative to the R strain is not affected by these treatments. Therefore, the genetic factors unique to the L strain do not affect the same processes affected by the temperature treatments. A second set of experiments detected a linear relationship between the MDMR (mean daily metabolic rate) and the ambient adult temperature. However, at each temperature, the MDMR of either strain was statistically equivalent; a finding which demonstrates that an increased life span depends on something other than conservation of calories. A third set of experiments looked at the metabolic efficiency of the two strains and were not able to detect any statistically significant differences. The two strains appear to expend approximately equivalent numbers of calories per day in an approximately equivalent manner. These data are interpreted in the context both of a previously postulated genetic switch mechanism believed responsible for initiating the onset of senescence, and of contemporary reinterpretations of the "rate of living" theory which implicates the essential role of various anti-oxidant defense systems.

Aging hypotheses, aging markers and the concept of biological age

The following two points are made in this article: (1) the likely existence of more than one underlying cause of senescence strengthens the case for the development of a number of reliable markers of aging and (2) the concept of a single biological or functional age for an organism should be used with great caution, if at all.

Age dependent changes in the expression of Drosophila mitochondrial proteins

A subset of 43 [35S]methionine labeled mitochondrial proteins, identified on two dimensional electrophoresis gels of whole body extracts of adult Drosophila, were compared between two age groups. These flies, which except for their spermatocytes consist entirely of postmitotic cells, were 6 days old and 38 days old, with the mean life span of this inbred strain being 32.5 days. Qualitative changes in any of these mitochondrial polypeptides were not found, but significant quantitative differences were observed. Quantitation of the 43 mitochondrial proteins was carried out by computer assisted microdensitometry of autoradiograms of the gel patterns. The total amount of isotope incorporated into the mitochondrial proteins of the senescent flies decreased to 71% of that of the young insects. This decrease was heterogeneously distributed among the 43 proteins; however, six remained unchanged and one protein (mol. wt = 75; pI = 7.4) was increased 2.4 times in the senescent flies. These data clearly provide evidence that the age-dependent changes in the expression of mitochondrial proteins are quantitative and not qualitative.