Laurent Seroude

Immunity and aging: the enemy within?

Functional analyses of changes in the immune response indicate that aging is associated with a decline of adaptive immunity whereas innate immunity is ramped up. Gene expression studies also support age‐dependent changes in immunity. Studies using a large panel of methodologies and multiple species show that some of the most dramatic transcriptional changes that occur during aging are associated with immunity. This observation leads to two fundamental questions: (1) Why is the immune response altered with age? (2) Is this a consequence of aging or does it contribute to it? The origin of these changes and the mechanistic relationship among them as well as with aging must be identified. In mammals, this task is complicated by the interdependence of the innate and adaptive immune systems. The value of invertebrates as model organisms to help answer these questions is presented. This includes a description of the immune response in invertebrate models and how it compares with vertebrates, focusing on conserved pathways. Finally, these questions are explored in light of recent reports and data from our laboratory. Experimental alterations of longevity indicate that the differential expression of immunity‐related genes during aging is linked to the rate of aging. Long‐lived nematodes are more resistant to pathogens and blocking the expression of immune‐related genes can prevent lifespan extension. These observations suggest that the immune response has a positive effect on longevity, possibly by increasing fitness. By contrast, it has been reported that activation of the immune system can reduce longevity upon starvation. We also observed that deregulation of the immune response has drastic effects on viability and longevity in Drosophila. These data suggest that the immune response results in a trade‐off between beneficial and detrimental effects that might profoundly affect the aging process. Given this, immunity may be an ally early in life, but turns out to be an enemy as we age.

Characterization of the Drosophila Gene‐Switch system in aging studies: a cautionary tale

Genetic studies have shown that in many model organisms, single gene mutations can dramatically influence aging. Systems that allow researchers to control a genes temporal and spatial expression pattern, known as inducible gene‐expression systems, are a valuable asset for the study of the influence of single genes on aging. One inducible gene‐expression system reported to allow temporal and tissue‐specific control of gene expression in Drosophila is the Gene‐Switch system. However, this system has not been extensively characterized in the context of aging research. This report uses six Gene‐Switch strains to examine the tissue localization and amount of expression achievable in the major tissue types of the fly. The quantitative analysis of adult flies fed with inducer through life reveals that the levels of expression are influenced by both the inducer concentration and the age of the animal in a strain‐specific manner. Furthermore, the relationship between inducer concentration and expression level is unique to each strain and, in some cases, to each gender. The analysis of the spatial expression patterns in several strains revealed expression in more tissue types than previously assumed. Finally, most Gene‐Switch strains display expression in the absence of inducer during development and/or during adulthood. These findings have important implications that may reconcile contradictions reported in studies investigating the effects of dFOXO on longevity. This study is an important guide to the design and interpretation of aging studies based on the Gene‐Switch system.

Functional analysis of the Drosophila immune response during aging

One of the most dramatic changes associated with aging involves immunity. In aging mammals, immune function declines and chronic inflammation develops. The biological significance of this phenomenon and its relationship with aging is a priority for aging research. Drosophila is an invaluable tool in understanding the effects of aging on the immune response. Similar to the state of chronic inflammation in mammals, Drosophila exhibits a drastic up‐regulation of immunity‐related genes with age. However, it remains unclear whether immune function declines with age as seen in mammals. We evaluated the impact of aging on Drosophila immune function by examining across age the ability to eliminate and survive different doses of bacterial invaders. Our findings show that aging reduces the capacity to survive a bacterial infection. In contrast, we found no evidence that aging affects the ability to eliminate bacteria indicating that the mechanisms underlying immune senescence are not involved in eliminating bacteria or preventing their proliferation.

Sod2 knockdown in the musculature has whole-organism consequences in Drosophila

Oxidative damage to cell macromolecules by reactive oxygen species is associated with numerous diseases and aging. In Drosophila, RNAi-mediated silencing of the mitochondrial antioxidant manganese superoxide dismutase (SOD2) throughout the body dramatically reduces life span, accelerates senescence of locomotor function, and enhances sensitivity to applied oxidative stress. Here, we show that Sod2 knockdown in the musculature alone is sufficient to cause the shortened life span and accelerated locomotor declines observed with knockdown of Sod2 throughout the body, indicating that Sod2 deficiency in muscle is central to these phenotypes. Knockdown of Sod2 in the muscle also increased caspase activity (a marker for apoptosis) and caused a mitochondrial pathology characterized by swollen mitochondria, decreased mitochondrial content, and reduced ATP levels. These findings indicate that Sod2 plays a crucial role in the musculature in Drosophila and that the consequences of SOD2 loss in this tissue extend to the viability of the organism as a whole.

Glial Hsp70 protects K+ homeostasis in the Drosophila brain during repetitive anoxic depolarization.

Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na+/K+-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K+ homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K+] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.

Differential gene expression and aging.

It has been established that an intricate program of gene expression controls progression through the different stages in development. The equally complex biological phenomenon known as aging is genetically determined and environmentally modulated. This review focuses on the genetic component of aging, with a special emphasis on differential gene expression. At least two genetic pathways regulating organism longevity act by modifying gene expression. Many genes are also subjected to age-dependent transcriptional regulation. Some age-related gene expression changes are prevented by caloric restriction, the most robust intervention that slows down the aging process. Manipulating the expression of some age-regulated genes can extend an organisms life span. Remarkably, the activity of many transcription regulatory elements is linked to physiological age as opposed to chronological age, indicating that orderly and tightly controlled regulatory pathways are active during aging.

Genetic approaches to study aging in Drosophila melanogaster.

The process of aging can be described as a progressive decline in an organisms function that invariably results in death. This decline results from the activities of intrinsic genetic factors within an organism. The relative contributions of the biological and environmental components to senescence are hard to measure, however different strategies have been devised in Drosophila melanogaster to isolate and identify genetic influences on aging. These strategies include selective breeding, quantitative trait loci (QTL) mapping and single gene mutant analysis. Selective breeding effectively demonstrated a genetic, heritable component to aging while QTL mapping located regions within the Drosophila genome carrying loci that influence the aging process. Within the past decade, single gene mutant analysis has facilitated the identification of specific genes whose activities play a determinative role in Drosophila aging. This review will focus on the application of selective breeding, QTL mapping and single gene mutant analysis used in Drosophila to study aging as well as the results obtained through these strategies to date.

Tissue-specific targeting of Hsp26 has no effect on heat resistance of neural function in larval Drosophila.

Hsp26 belongs to the small heat-shock protein family and is normally expressed in all cells during heat stress. We aimed to determine if overexpression of this protein protects behavior and neural function in Drosophila melanogaster during heat stress, as has previously been shown for Hsp70. We used the UAS-GAL4 expression system to drive expression of Hsp26 in the whole animal (ubiquitously), in the motoneurons, and in the muscles of wandering third-instar larvae. There were slight increases in time to crawling failure and normalized excitatory junction potential (EJP) area for some of the transgenic lines, but these were not consistent. In addition, Hsp26 had no effect on the temperature at failure of EJPs, normalized EJP peak amplitude, and normalized EJP half-width. Overexpression larvae had a similar number of motoneuronal boutons and length of nerve terminals as controls, indicating that the occasional protective effects on locomotion were not due to changes at the synapse. We conclude that overexpression had a small thermoprotective effect on locomotion and no effect on neural function. As it has been shown that Hsp26 requires action of other Hsps to reactivate the denatured proteins to which it binds, we propose that at least in larvae, the function of Hsp26 was masked in the relative absence of other Hsps.

Tissue-specific downregulation of EDTP removes polyglutamine protein aggregates and extends lifespan in Drosophila

Drosophila egg-derived tyrosine phosphatase (EDTP, also called JUMPY) is a lipid phosphatase essential in the oogenesis and muscle function in the adult stage. Although mammalian JUMPY negatively regulates autophagy, loss-of-JUMPY causes muscle dysfunction and is associated with a rare genetic disorder centronuclear myopathy. Here we show that tissue-specific downregulation of EDTP in Drosophila non-muscle tissues, particularly glial cells, completely removes polyglutamine (polyQ) protein aggregates and improves survivor. Additionally, tissue-specific downregulation of EDTP in glial cells or motoneurons extends lifespan. We demonstrate an approach to fine-tune the expression of a disease-associated gene EDTP for the removal of polyQ protein aggregate and lifespan extension in Drosophila.

Regulating the UAS/GAL4 system in adult Drosophila with Tet-off GAL80 transgenes

The UAS/GAL4 system is the most used method in Drosophila melanogaster for directing the expression of a gene of interest to a specific tissue. However, the ability to control the temporal activity of GAL4 with this system is very limited. This study constructed and characterized Tet-off GAL80 transgenes designed to allow temporal control of GAL4 activity in aging adult muscles. By placing GAL80 under the control of a Tet-off promoter, GAL4 activity is regulated by the presence or absence of tetracycline in the diet. Almost complete inhibition of the expression of UAS transgenes during the pre-adult stages of the life cycle is obtained by using four copies and two types of Tet-off GAL80 transgenes. Upon treatment of newly emerged adults with tetracycline, induction of GAL4 activity is observed but the level of induction is influenced by the concentration of the inducer, the age, the sex and the anatomical location of the expression. The inhibition of GAL4 activity and the maintenance of induced expression are altered in old animals. This study reveals that the repressive ability of GAL80 is affected by the age and sex of the animal which is a major limitation to regulate gene expression with GAL80 in aged Drosophila.