Genetics of aging in Drosophila

Endurance exercise protects aging Drosophila from high-salt diet (HSD)-induced climbing capacity decline and lifespan decrease by enhancing antioxidant capacity

A high-salt diet (HSD) is a major cause of many chronic and age-related defects such as myocardial hypertrophy, locomotor impairment and mortality. Exercise training can efficiently prevent and treat many chronic and age-related diseases. However, it remains unclear whether endurance exercise can resist HSD-induced impairment of climbing capacity and longevity in aging individuals. In our study, flies were given exercise training and fed a HSD from 1-week old to 5-weeks old. Overexpression or knockdown of salt and dFOXO were built by UAS/Gal4 system. The results showed that a HSD, salt gene overexpression and dFOXO knockdown significantly reduced climbing endurance, climbing index, survival, dFOXO expression and SOD activity level, and increased malondialdehyde level in aging flies. Inversely, in a HSD aging flies, endurance exercise and dFOXO overexpression significantly increased their climbing ability, lifespan and antioxidant capacity, but they did not significantly change the salt gene expression. Overall, current results indicated that a HSD accelerated the age-related decline of climbing capacity and mortality via upregulating salt expression and inhibiting the dFOXO/SOD pathway. Increased dFOXO/SOD pathway activity played a key role in mediating endurance exercise resistance to the low salt tolerance-induced impairment of climbing capacity and longevity in aging DrosophilaThis article has an associated First Person interview with the first author of the paper.

Nutrigenomics as a tool to study the impact of diet on aging and age-related diseases: the Drosophila approach

Aging is a complex phenomenon caused by the time-dependent loss of cellular homeodynamics and consequently of physiological organismal functions. This process is affected by both genetic and environmental (e.g., diet) factors, as well as by their constant interaction. Consistently, deregulation of nutrient sensing and signaling pathways is considered a hallmark of aging. Nutrigenomics is an emerging scientific discipline that studies changes induced by diet on the genome and thus it considers the intersection of three topics, namely health, diet, and genomics. Model organisms, such as the fruit fly Drosophila melanogaster, have been successfully used for in vivo modeling of higher metazoans aging and for nutrigenomic studies. Drosophila is a well-studied organism with sophisticated genetics and a fully annotated sequenced genome, in which ~ 75% of human disease-related genes have functional orthologs. Also, flies have organs/tissues that perform the equivalent functions of most mammalian organs, while discrete clusters of cells maintain insect carbohydrate homeostasis in a way similar to pancreatic cells. Herein, we discuss the mechanistic connections between nutrition and aging in Drosophila, and how this model organism can be used to study the effect of different diets (including natural products and/or their derivatives) on higher metazoans longevity.

Healthy aging - insights from Drosophila

Human life expectancy has nearly doubled in the past century due, in part, to social and economic development, and a wide range of new medical technologies and treatments. As the number of elderly increase it becomes of vital importance to understand what factors contribute to healthy aging. Human longevity is a complex process that is affected by both environmental and genetic factors and interactions between them. Unfortunately, it is currently difficult to identify the role of genetic components in human longevity. In contrast, model organisms such as C. elegans, Drosophila, and rodents have facilitated the search for specific genes that affect lifespan. Experimental evidence obtained from studies in model organisms suggests that mutations in a single gene may increase longevity and delay the onset of age-related symptoms including motor impairments, sexual and reproductive and immune dysfunction, cardiovascular disease, and cognitive decline. Furthermore, the high degree of conservation between diverse species in the genes and pathways that regulate longevity suggests that work in model organisms can both expand our theoretical knowledge of aging and perhaps provide new therapeutic targets for the treatment of age-related disorders.

Altitudinal patterns for longevity, fecundity and senescence in Drosophila buzzatii

We tested for variation in longevity, senescence rate and early fecundity of Drosophila buzzatii along an elevational transect in Argentina, using laboratory-reared flies in laboratory tests performed to avoid extrinsic mortality. At 25 degrees C, females from lowland populations lived longer and had a lower demographic rate of senescence than females from highland populations. Minimal instead of maximal temperature at the sites of origin of population best predicted this cline. A very different pattern was found at higher test temperature. At 29.5 degrees C, longevity of males increased with altitude of origin of population. No clinal trend was apparent for longevity of females at 29.5 degrees C. There was evidence for a trade-off between early fecundity and longevity at non-stressful temperature (25 degrees C) along the altitudinal gradient. This trait association is consistent with evolutionary theories of aging. Population-by-temperature and sex-by-temperature interactions indicate that senescence patterns are expressed in environment specific ways.

Germ-line versus somatic cells. I. Stereological study of differentiating embryonic tissues of Tetrodontophora bielanensis (Hexapoda, Collembola)

We examined five different somatic tissues and compared them with germ-line cells to verify the "disposable soma" theory. Two embryonic stages and second-stage juveniles of Tetrodontophora bielanensis Waga, 1842 (Hexapoda, Collembola) were studied. Our results show that changes in relative volume of mitochondria during differentiation of cells correlate well with transformations of cell morphology. During morphological transformation of differentiating somatic cells, the relative volume of mitochondria in their cytoplasm is high, whereas in the differentiated tissues, this parameter is much lower. Surprisingly, the highest value of relative volume density of mitochondria is found in the cytoplasm of germ-line cells. If we accept that this parameter indicates the cell metabolism rate, then our results should be taken as supporting the "disposable soma" theory. It is also conceivable that the higher volume of mitochondria in the germ-line cells have nothing to do with energy production but, for instance, with the production or function of nuage material (germ-cell determinant) in the germ-line cells. These two possibilities are discussed.

A unifying view of ageing and disease: the double-agent theory

The quest for therapies based on molecular genetics (pharmacogenomics, DNA microarrays, etc.) drives pharmaceutical research into individual diseases of old age, but has failed to deliver an unequivocal clinical breakthrough. Attempts to treat most age-related diseases using antioxidant supplements have been equally disappointing, despite the clear benefits of a healthy diet. The double-agent theory is a new, unifying synthesis that draws on flaws in three leading theories of ageing. It argues that there is a tradeoff between oxidative stress as a critical redox signal that marshals genetic defences against physiological stress (such as infection) and oxidative stress as a cause of ageing and age-related disease. The stress response and ageing are linked by redox-sensitive transcription factors, such as NFkappaB. Ageing is a function of rising intracellular oxidative stress, rather than chronological time, but this relationship is obscured because free-radical leakage from mitochondria also tends to rise with age. Mitochondrial leakage produces a genetic response which mirrors that following infection, but because mitochondrial leakage is continuous the shift in gene expression is persistent, leading to the chronic inflammation characteristic of old age. Age-related diseases are thus the price we pay for redox control of stress-gene expression. Because the selective pressure favouring the stress response in youth is stronger than that penalising degenerative diseases after reproductive decline, we may be homeostatically refractory to antioxidant supplements that 'swamp' the redox switch. Furthermore, because genetic selection takes place predominantly in the reductive homeostatic environment of youth, alleles associated with age-related diseases are not inherently damaging (they do not inevitably express a negative effect over time), but are simply less effective in the oxidising conditions of old age. Gene therapies for age-related diseases are unlikely to succeed unless oxidative stress can be controlled physiologically, thereby altering the activity and function of potentially hundreds of genes.

A systematic RNAi screen identifies a critical role for mitochondria in C. elegans longevity

We report a systematic RNA interference (RNAi) screen of 5,690 Caenorhabditis elegans genes for gene inactivations that increase lifespan. We found that genes important for mitochondrial function stand out as a principal group of genes affecting C. elegans lifespan. A classical genetic screen identified a mutation in the mitochondrial leucyl-tRNA synthetase gene (lrs-2) that impaired mitochondrial function and was associated with longer-lifespan. The long-lived worms with impaired mitochondria had lower ATP content and oxygen consumption, but differential responses to free-radical and other stresses. These data suggest that the longer lifespan of C. elegans with compromised mitochrondria cannot simply be assigned to lower free radical production and suggest a more complex coupling of metabolism and longevity.

Metabolic alterations in genetically selected Drosophila strains with different longevities

Sometime ago we obtained biomarker data suggesting that the earliest determining event in the expression of the extended longevity phenotype in our selected strains of Drosophila took place early in adult life at about 5-7 days of age. In a later series of experiments we documented that our La and Lb long lived strains underwent a specific up-regulation of the antioxidant defense system (ADS) genes and enzymes. This led to a reduction in oxidative damage and an extended longevity. In the current work, we assayed the activity of 17 metabolically important enzymes in 5-7 day old flies of 13 strains variously selected for different longevities. We conclude that the two sets of replicated long-lived strains have an altered metabolic pattern (relative to normal-lived animals) which is consistent with an increased flux through the pentose shunt and an enhanced NADP+ reducing system to support the increased activity of the ADS enzymes. This result can be interpreted as a shift of energy expenditure from reproduction to somatic maintenance. We conclude that theories based on differential energy allocations appear to empirically explain, at least in part, the mechanisms underlying the transformation of a normal longevity phenotype to an extended longevity phenotype.

Comments to paper by S. Rattan: applying hormesis in aging research and therapy--a perspective from evolutionary biology

The phenomenon of hormesis is discussed from an evolutionary biology perspective, i.e. in a context of fitness. Some of the evolutionary theories of aging are outlined. The influence of associations between traits and their environmental specificity is highlighted. Questions about consistency of the impact of hormetic agents across life stages are raised and finally the uniformity of definitions across disciplines is shortly discussed.

Molecular signals versus the Loi de Balancement

Life history tradeoffs are often thought to be caused by the allocation of limited resources among competing traits such as reproduction, somatic growth and maintenance. One line of evidence supporting this comes from eliminating reproduction, for example, by surgically removing gonads. However, recent evidence from the nematode Caenorhabditis elegans suggests that the apparent tradeoffs it shows might not be due to resource allocation at all but rather to the effects of a molecular signal originating in the germ line that represses longevity. These results should cause us to rethink the interpretation of many classic experiments in life history evolution.