A PGC-1 tale: healthier intestinal stem cells, longer life

PGC-1 regulates energy homeostasis and mitochondrial activity. In this issue, Rera et?al. (2011) show that dPGC-1 overexpression in Drosophila intestinal stem cells and their immediate progeny extends organismal life span and protects against age-related loss of intestinal homeostasis and integrity, thereby establishing a link between mitochondria, tissue stem cells, and aging.     

Mitochondrial signaling, TOR, and life span

Growing evidence supports the concept that mitochondrial metabolism and reactive oxygen species (ROS) play a major role in aging and determination of an organism's life span. Cellular signaling pathways regulating mitochondrial activity, and hence the generation of ROS and retrograde signaling events originating in mitochondria, have recently moved into the spotlight in aging research. Involvement of the energy-sensing TOR pathway in both mitochondrial signaling and determination of life span has been shown in several studies. This brief review summarizes the recent progress on how mitochondrial signaling might contribute to the aging process with a particular emphasis on TOR signaling from invertebrates to humans.     

The cost of living longer. Fertility trades with immunity and life expectancy

There is an ancient balance struck between immunity and fertility. The ongoing trend in developed societies to have fewer children and later in life, might influence human life expectancy and disease susceptibility.Sexual reproduction and the mixing of alleles that it entails boosts diversity, but also poses a dilemma for individual organisms. Given that each organism has ultimately limited resources for reproduction, maintenance and immunity, the choice between fertility and long-term survival is one between two opposite poles of selection that operate across many animal and plant species. The balance between fertility and immunity has direct implications for human health; indeed a growing body of work is investigating the links between disease and reproductive biology. Moreover, epidemiological data shows that humans, especially in developed countries and particularly women, are becoming less fertile, but more immune to infectious and other diseases. This, in addition to factors such as improved healthcare, is further increasing human lifespan in wealthy societies.The hypothesis that investing more energy and resources into maintenance and immunity comes at the expense of fertility was first proposed by Thomas Kirkwood (1977), now Director of the Institute for Ageing and Health at Newcastle University in the UK. His theory was supported by epidemiological and historical data (Westendorp & Kirkwood, 1998), as well as animal experiments and molecular evidence. Yet, the exact nature of the link between reproduction and immunity has remained elusive.One problem, at least for plant and animal species that have internal fertilization, is the cost of this reproductive strategy whereby gametes from one partner, usually the male, enter the other. This is the heart of the sexual immunity problem, according to Michael Siva-Jothy, an entomologist at Sheffield University in the UK, whose interest in this relationship between reproduction and immunity has led him to study the phenomenon in vertebrates. “I would say, when you go from external to internal fertilisation, you create a huge problem,” he said. “It''s the same problem probably across all taxa, in that recipients of gametes are faced with how to defend their internal environment from non self, while allowing sperm to get through. Sperm are non self even to males, so must be in females.”The balance between fertility and immunity has direct implications for human health…Moreover, the link between reproduction and immunity extends beyond the female genital tract to include pregnancy in mammals and male fertility. A joint study between Princeton University in the USA and Edinburgh University in the UK found that among a population of isolated sheep in the Outer Hebrides—islands off the coast of Scotland—both males and females with high levels of antibodies were able to survive the occasional harsh winters that occur there, but reproduced less than did sheep with lower levels of antibodies during less harsh winters (Graham et al, 2010). During intervening periods, often lasting several years, the number of individuals with lower levels of antibodies within the population would increase, before being reduced again when the next harsh winter arrived.The fact that both male and female sheep were affected rules out anything to do with the female genital tract. “We do not know why the autoantibody responses were associated with reduced annual breeding success,” commented Andrea Graham, lead author of the study from Princeton University. “The same pattern occurred in both males and females, which suggests a resource allocation ‘trade-off''.”“I would say, when you go from external to internal fertilisation, you create a huge problem.”According to David Schneider, whose laboratory at Stanford University in the USA specializes in innate immunity and host–parasite interactions in Drosophila, the resource theory—that a living organism has limited resources available for growth, maintenance and reproduction—plays a major role in the relationship between fertility and immunity. “There seems to be some sort of limit on how much a body can do,” he said. “We can''t just keep doing more and there is a reason that we don''t have our immune response on all of the time.”By its nature, the resource theory is hard to establish beyond all doubt, but there is growing evidence that resource allocation plays an important role in a third instance in humans and probably all mammals: an internal conflict between mother and fetus. This too involves a trade-off, but for a different reason, because the interests of the fetus and the mother do not exactly coincide. The fetus, half of whose genes are paternal, wants to obtain as much of the mother''s resources as possible to optimize its growth during pregnancy. The mother''s best interest, however, lies in distributing her available resources equally among all the fetuses she will conceive during her lifetime. This conflict is played out through the immune systems of father, fetus and mother, and in particular through the major histocompatibility class (MHC) molecules. During pregnancy, the mother exhibits an inflammatory response to the paternal MHC proteins expressed by the fetus, which is often cited as evidence for the maternal–fetal conflict theory.A successful pregnancy therefore requires that the mother''s body tolerates the presence of MHCs and other antigens of paternal origin that are expressed by the fetus. There is some evidence that the father can manipulate this response: if the paternal MHC proteins are very different to the maternal ones, this tends to stimulate growth of the placenta, thereby increasing the resources available to the fetus (Madeja et al, 2011).A successful pregnancy therefore requires that the mother''s body tolerates the presence of MHCs and other antigens of paternal origin that are expressed by the fetus''The conflict theory has implications for the health of both fetus and mother, since the inflammatory response can cause significant harm or even death to both. It can, for example, cause an excessive immunological response to low virulence bacteria such as Fusobacteria that are commonly present in the upper genital tract and normally cause few problems. This excessive immune response is associated with premature delivery (Gomez et al, 1997). There is also evidence that pre-eclampsia—a systemic maternal disease that is characterized by hypertension and proteinuria, and which is potentially fatal to both mother and fetus—is caused in some cases by maternal–fetal conflict (Ness, 2004).According to David van Bodegom from the Department of Gerontology and Geriatrics at Leiden University in the Netherlands, the strength of the mother''s immunity can determine whether conception will occur in the first place. He referred to a study finding that women attending IVF clinics because of problems conceiving children were much more likely to suffer spontaneous abortions and at the same time had elevated immune function.Van Bodegom suggested that such findings have significant societal implications, given the negative selection pressure against fertility in women caused by the trend to have smaller families. “In the past, the next generation would be produced by a limited number of very fertile women who had large families, while now all women have 1.8 to 2.4 children depending on the country,” he said. Less fertile mothers receive assistance through IVF and other measures to conceive, while more fertile ones use contraceptive drugs and other methods to limit their reproduction. “So now only a few children are descendants of very fertile women,” said van Bodegom.There is a parallel trend in wealthier nations towards having children later in life. “The Netherlands has the European record for the highest average age of [mothers giving birth to their] first child, I think now 30 years,” said van Bodegom. The first trend suggests that fertility problems among women will increase, as will the need for assistance. The second trend towards having children later would select for women who retain their fertility for longer.… women with late menopauses tend to live longer, which may suggest they have stronger immune systems and in turn perhaps lower overall fertilityThe two trends—lower fertility overall but retaining it for longer—seem to pull in opposite directions but might actually favour the same women. According to van Bodegom, women with late menopauses tend to live longer, which might suggest they have stronger immune systems and in turn perhaps lower overall fertility. This is still speculation at present, but there is a clear correlation between the late onset of menopause and longevity (Ossewaarde et al, 2005). Selection pressure for delayed menopause onset should therefore lead to increased life expectancy among women, van Bodegom suggested.But there is a downside to late motherhood: the high physiological demands of pregnancy itself. A recent study in the UK found that although overall levels of death during pregnancy or childbirth had decreased dramatically since surveys began in 1952, the maternal death rate from indirect causes had actually increased over the last 20 years (Cantwell et al, 2011). These indirect causes include cardiac disease, hypertension, diabetes and neurological disorders brought on or accentuated by pregnancy.… exposure to heavy metals can also trigger the production of antibodies acting against sperm and cause male infertility…The report prompted David Williams, a Consultant Obstetric Physician at University College Hospital in London, and others to argue in the British Medical Journal that this rise in death rate was the result of an increase in average age of pregnant mothers (Nelson-Piercy et al, 2011). Older women tend to weigh more, which increases the risk of diabetes and hypertension in particular during pregnancy, Williams argued. Older women were are also less well equipped to deal with the physical and physiological rigours of pregnancy, and this in turn translated into increased risk of disease and complications. Given that this trend towards later pregnancies is unlikely to be reversed, Williams and his colleagues have called for more specialist physicians and greater awareness among all doctors.Although the greatest focus on the links between fertility, immunity and longevity has been on women, there is mounting evidence that the story includes men. Some studies demonstrate a link between immunity and spermatogenesis in humans, mostly showing that sperm itself is recognized as non-self in men and can trigger the production of anti-sperm antibodies (ASAs). This would explain why there is a barrier between the testes, where sperm are produced and stored, and the blood: to prevent sperm antigens from leaking out and triggering ASA production.Yet, the barrier is not impenetrable: chronic infection of the genitals can cause the production of ASAs, perhaps by maintaining a high level of immunity. Moreover, exposure to heavy metals can also trigger the production of antibodies acting against sperm and cause male infertility, which would partly explain an overall decline in male fertility observed during the past half century or more in some countries, possibly triggered by exposure to mercury in dental tooth fillings (Podzimek et al, 2005).However, despite the presence of ASAs from the man, sperm are still able to reach the oocyte. Even so, some researchers have suggested that by binding to the sperm, ASAs make it unable to complete the so-called acrosome reaction needed to penetrate the oocyte (Bohring et al, 2004). This reaction occurs in some form in almost all sexually reproducing species after the fusion between sperm and oocyte, and enables the acrosome—a cap-like structure on the head of the sperm—to release its contents. These contents include surface antigens and enzymes that break down the coat of the oocyte and allow fertilization to occur. Antibodies attached to the sperm head can prevent the all-important acrosome reaction from taking place.… humans in developed societies have been subject to an extraordinary selective shift during the past half century, which increased life expectancy and immunity at the cost of fertilityImmunity therefore seems linked to fertility in both men and women, although it remains to be seen whether the inverse relationship applies in men: that is, individuals who are more fertile also have lower levels of immunity. However, the fate of sheep in the Outer Hebrides suggests this might well be the case. In fact, another epidemiological study of human longevity and reproductive success indicates that there is such a trade-off in both men and women (Thomas et al, 2000).These diverse data from various fields show that humans in developed societies have been subject to an extraordinary selective shift during the past half century, which increased life expectancy and immunity at the cost of fertility. It is also clear that this development is not over yet and that it will have profound health and social implications for both sexes in future generations.     

Network-level and population genetics analysis of the insulin/TOR signal transduction pathway across human populations

Genes and proteins rarely act in isolation, but they rather operate as components of complex networks of interacting molecules. Therefore, for understanding their evolution, it may be helpful to take into account the interaction networks in which they participate. It has been shown that selective constraints acting on genes depend on the position that they occupy in the network. Less understood is how the impact of local adaptation at the intraspecific level is affected by the network structure. Here, we analyzed the patterns of molecular evolution of 67 genes involved in the insulin/target of rapamycin (TOR) signal transduction pathway. This well-characterized pathway plays a key role in fundamental processes such as energetic metabolism, growth, reproduction, and aging and is involved in metabolic disorders such as obesity, insulin resistance, and diabetes. For that purpose, we combined genotype data from worldwide human populations with current knowledge of the structure and function of the pathway. We identified the footprint of recent positive selection in nine of the studied genomic regions. Most of the adaptation signals were observed among Middle East and North African, European, and Central South Asian populations. We found that positive selection preferentially targets the most central elements in the pathway, in contrast to previous observations in the whole human interactome. This observation indicates that the impact of positive selection on genes involved in the insulin/TOR pathway is affected by the pathway structure.     

Molecular population genetics of the insulin/TOR signal transduction pathway: a network-level analysis in Drosophila melanogaster

The IT-insulin/target of rapamycin (TOR)-signal transduction pathway is a relatively well-characterized pathway that plays a central role in fundamental biological processes. Network-level analyses of DNA divergence in Drosophila and vertebrates have revealed a clear gradient in the levels of purifying selection along this pathway, with the downstream genes being the most constrained. Remarkably, this feature does not result from factors known to affect selective constraint such as gene expression, codon bias, protein length, and connectivity. The present work aims to establish whether the selective constraint gradient detected along the IT pathway at the between-species level can also be observed at a shorter time scale. With this purpose, we have surveyed DNA polymorphism in Drosophila melanogaster and divergence from D. simulans along the IT pathway. Our network-level analysis shows that DNA polymorphism exhibits the same polarity in the strength of purifying selection as previously detected at the divergence level. This equivalent feature detected both within species and between closely and distantly related species points to the action of a general mechanism, whose action is neither organism specific nor evolutionary time dependent. The detected polarity would be, therefore, intrinsic to the IT pathway architecture and function.     

Thinking globally and acting locally with TOR

The target of rapamycin (TOR) pathway regulates ribosome biogenesis, protein synthesis, nutrient import, autophagy and cell cycle progression. After 30 years of concentrated attention, how TOR controls these processes is only now beginning to be understood. Recent advances have identified a wide array of TOR inputs, including amino acids, oxygen, ATP and growth factors, as well the regulatory proteins that facilitate their effects on TOR. Such proteins include AMPK, Rheb and the tumor suppressors LKB1, p53, and Tsc1/2. It has only recently been appreciated that TOR resides in two distinct signaling complexes with differing regulatory roles, only one of which is rapamycin-sensitive, thus opening a new avenue of inquiry into TOR function. Finally, TOR appears to regulate feeding behavior by facilitating communication between organ systems, and is thus implicated in the regulation of glucose and fat homeostasis, and possibly diabetes and obesity. TOR thus functions to coordinate growth-permitting inputs with growth-promoting outputs on both a cellular and an organismal level.     

TOR and aging: less is more

Metabolism and mitochondrial activity are thought to be important determinants of life span. A new study in this issue of Cell Metabolism (Bonawitz et al., 2007) suggests that the TOR pathway controls mitochondrial respiration in yeast and that the harder mitochondria work, the longer yeast live.     

'Genetics is not the issue': insurers on genetics and life insurance

This article offers an analysis of the way private insurers deal with the issue of genetics and insurance. Drawing on specific written insurance sources, a reconstruction is made of internal debates on genetics and insurance within the private insurance world in Europe and the United States. The article starts by analyzing the way insurers initially framed the issue of genetics. It proceeds by showing how ideas with respect to this issue developed beyond public policy debates in the nineties. Although not a strictly linear development, a trend towards a change in perspective can be demonstrated: at the beginning most insurance companies took another stance than they do nowadays. The article concludes by questioning the effect of these changes within the insurance world for the definition of the problem with respect to genetics and insurance. Does taking into account the public concerns around genetics also include taking genetics as a public problem?     

Generation of a cell culture-adapted hepatitis C virus with longer half life at physiological temperature

Background

We previously reported infectious HCV clones that contain the convenient reporters, green fluorescent protein (GFP) and Renilla luciferase (Rluc), in the NS5a-coding sequence. Although these viruses were useful in monitoring viral proliferation and screening of anti-HCV drugs, the infectivity and yield of the viruses were low.

Methodology/Principal Findings

In order to obtain a highly efficient HCV cultivation system, we transfected Huh7.5.1 cells [1] with JFH 5a-GFP RNA and then cultivated cells for 20 days. We found a highly infectious HCV clone containing two cell culture-adapted mutations. Two cell culture-adapted mutations which were responsible for the increased viral infectivity were located in E2 and p7 protein coding regions. The viral titer of the variant was ∼100-fold higher than that of the parental virus. The mutation in the E2 protein increased the viability of virus at 37°C by acquiring prolonged interaction capability with a HCV receptor CD81. The wild-type and p7-mutated virus had a half-life of ∼2.5 to 3 hours at 37°C. In contrast, the half-life of viruses, which contained E2 mutation singly and combination with the p7 mutation, was 5 to 6 hours at 37°C. The mutation in the p7 protein, either singly or in combination with the E2 mutation, enhanced infectious virus production about 10–50-fold by facilitating an early step of virion production.

Conclusion/Significance

The mutation in the E2 protein generated by the culture system increases virion viability at 37°C. The adaptive mutation in the p7 protein facilitates an earlier stage of virus production, such as virus assembly and/or morphogenesis. These reporter-containing HCV viruses harboring adaptive mutations are useful in investigations of the viral life cycle and for developing anti-viral agents against HCV.     

To subjugate NPY is to improve the quality of life and live longer

The interactive network of neuropeptide Y (NPY) and cohorts is necessary for integrating the hypothalamic regulation of appetite and energy expenditure with the endocrine and neuroendocrine systems on a daily basis. Genetic and environmental factors that produce an insufficiency of leptin restraint on NPY and cognate receptors deregulate the homeostasis to engender various life-threatening risk factors. Recent studies from our laboratory show that neurotherapy consisting of a single central administration of recombinant adeno-associated virus vector encoding the leptin gene can repress the hypothalamic NPY system for the lifetime of rodents. A major benefit of this stable tonic restraint is deceleration of pathophysiologic sequalae that shorten life span. These include suppression of weight gain, fat accumulation, circulating adipokines, amelioration of major symptoms of metabolic syndrome, improved reproduction and bone health. Thus, sustained repression of NPY signaling in the hypothalamus by leptin transgene expression can improve the quality of life and extend longevity.     

Lay eggs, live longer: division of labor and life span in a clonal ant species

Abstract Due to a trade-off between reproduction and life span, highly fertile individuals often live shorter lives than nonreproductive conspecifics. Perennial eusocial insects are exceptional in that reproductive queens live considerably longer than the nonreproductive workers. The two female castes may differ strongly in morphology, ontogeny, physiology, diet, behavior, and mating, and all these differences could be responsible for life span differences. In the ponerine ant Platythyrea punctata , morphological and ontogenetic caste differences do not exist. Instead, all workers are capable of producing diploid offspring through thelytokous parthenogenesis, and colonies are essentially clones. Here, we show that reproductives live significantly longer than nonreproductive workers. Reproductives stay in the nest during their whole life, whereas nonreproductives switch from intranidal tasks to foraging when they get older. Different work load and different hormone titers might proximately underlie the different life span of reproductives and nonreproductives in this ant.     

Sex, drugs and recombination: the wild life of Aspergillus

Throughout the eukaryotes, sexual reproduction is an almost universal phenomenon. However, within the Kingdom Fungi, this relationship is not so clear‐cut. Fungi exhibit a spectrum of reproductive modes and life‐cycles; amongst the better known species, sexual reproduction is often facultative, can be rare, and in over half of the known Ascomycota (the moulds) is unknown ( Taylor et al. 1999 ). However, over the last decade, it has become apparent that many of these asexual mitosporic taxa undergo cryptic recombination via unobserved mechanisms and that wholly asexual fungi are, in fact, a rarity ( Taylor et al. 1999, 2001 ; Heitman 2010 ). This revolution in our understanding of fungal sexuality has come about in two ways: Firstly, sexual reproduction leaves an imprint on fungal genomes by maintaining genes required for mating and by generating patterns of mutation and recombination restricted to meiotic processes. Secondly, scientists have become better at catching fungi in flagrante delicto. The genus Aspergillus is one such fungus where a combination of population genetics, genomics and taxonomy has been able to intuit the existence of sex, then to catch the fungus in the act and formally describe their sexual stages. So, why are sexy moulds exciting? One species in particular, Aspergillus flavus, is notorious for its ability to produce a diverse array of secondary metabolites, of which the polyketide aflatoxins (AF) are carcinogenic and others (such as cyclopiazonic acid) are toxigenic. Because of the predilection of A. flavus to grow on crops, such as peanuts, corn and cotton, biocontrol is widely used to mitigate infection by pre‐applying nonaflatoxigenic (AF?) strains to competitively exclude the wild‐type AF+ strains. However, the eventual fate in nature of these biocontrol strains is not known. In this issue of Molecular Ecology, Olarte et al. (2012) make an important contribution by using laboratory crosses of A. flavus to show that not only is AF highly heritable, but AF? strains can become AF+ via crossing over during meiosis. This observation has raised the spectre of cross‐breeding and non‐mendelian inheritance of AF between native and biocontrol strains of the fungus, leading to an increase in the natural diversity of the fungus with perhaps unanticipated consequences.     

Structure of TOR and its complex with KOG1

The target of rapamycin (TOR) is a large (281 kDa) conserved Ser/Thr protein kinase that functions as a central controller of cell growth. TOR assembles into two distinct multiprotein complexes: TORC1 and TORC2. A defining feature of TORC1 is the interaction of TOR with KOG1 (Raptor in mammals) and its sensitivity to a rapamycin-FKBP12 complex. Here, we have reconstructed in three dimensions the 25 A resolution structures of endogenous budding yeast TOR1 and a TOR-KOG1 complex, using electron microscopy. TOR features distinctive N-terminal HEAT repeats that form a curved tubular-shaped domain that associates with the C-terminal WD40 repeat domain of KOG1. The N terminus of KOG1 is in proximity to the TOR kinase domain, likely functioning to bring substrates into the vicinity of the catalytic region. A model is proposed for the molecular architecture of the TOR-KOG1 complex explaining its sensitivity to rapamycin.