Metformin is a drug commonly prescribed to treat patients with type 2 diabetes. Here we show that long-term treatment with metformin (0.1% w/w in diet) starting at middle age extends healthspan and lifespan in male mice, while a higher dose (1% w/w) was toxic. Treatment with metformin mimics some of the benefits of calorie restriction, such as improved physical performance, increased insulin sensitivity, and reduced LDL and cholesterol levels without a decrease in caloric intake. At a molecular level, metformin increases AMP-activated protein kinase activity and increases antioxidant protection, resulting in reductions in both oxidative damage accumulation and chronic inflammation. Our results indicate that these actions may contribute to the beneficial effects of metformin on healthspan and lifespan. These findings are in agreement with current epidemiological data and raise the possibility of metformin-based interventions to promote healthy aging.

The workshop entitled ‘Interventions to Slow Aging in Humans: Are We Ready?’ was held in Erice, Italy, on October 8–13, 2013, to bring together leading experts in the biology and genetics of aging and obtain a consensus related to the discovery and development of safe interventions to slow aging and increase healthy lifespan in humans. There was consensus that there is sufficient evidence that aging interventions will delay and prevent disease onset for many chronic conditions of adult and old age. Essential pathways have been identified, and behavioral, dietary, and pharmacologic approaches have emerged. Although many gene targets and drugs were discussed and there was not complete consensus about all interventions, the participants selected a subset of the most promising strategies that could be tested in humans for their effects on healthspan. These were: (i) dietary interventions mimicking chronic dietary restriction (periodic fasting mimicking diets, protein restriction, etc.); (ii) drugs that inhibit the growth hormone/IGF-I axis; (iii) drugs that inhibit the mTOR–S6K pathway; or (iv) drugs that activate AMPK or specific sirtuins. These choices were based in part on consistent evidence for the pro-longevity effects and ability of these interventions to prevent or delay multiple age-related diseases and improve healthspan in simple model organisms and rodents and their potential to be safe and effective in extending human healthspan. The authors of this manuscript were speakers and discussants invited to the workshop. The following summary highlights the major points addressed and the conclusions of the meeting.

We present genome-wide microarray expression analysis of 11,000 genes in an aging potentially mitotic tissue, the liver. This organ has a major impact on health and homeostasis during aging. The effects of life-and health-span-extending caloric restriction (CR) on gene expression among young and old mice and between long-term CR (LT-CR) and short-term CR (ST-CR) were examined. This experimental design allowed us to accurately distinguish the effects of aging from those of CR on gene expression. Aging was accompanied by changes in gene expression associated with increased inflammation, cellular stress, and fibrosis, and reduced capacity for apoptosis, xenobiotic metabolism, normal cell-cycling, and DNA replication. LT-CR and just 4 weeks of ST-CR reversed the majority of these changes. LT-CR produced in young mice a pattern of gene expression that is a subset of the changes found in old LT-CR mice. It is possible that the early changes in gene expression, which extend into old age, are key to the life-and health-span-extending effects of CR. Further, ST-CR substantially shifted the ''normo-aging'' genomic profile of old control mice toward the ''slow-aging'' profile associated with LT-CR. Therefore, many of the genomic effects of CR are established rapidly. Thus, expression profiling should prove useful in quickly identifying CRmimetic drugs and treatments.P ublished microarray studies of mammalian aging have focused on the postmitotic tissues, muscle and brain (1-3). These studies found that aging was associated with changes in gene expression linked to the development of the characteristic age-related pathologies of these tissues. In contrast to muscle and brain, the liver is a potentially mitotic tissue that is thought to age well from a clinical perspective (4). The liver is the central organ for the regulation of glucose homeostasis, xenobiotic metabolism and detoxification, and steroid hormone biosynthesis and degradation. This organ also has a major impact on health and homeostasis through its control of serum protein composition. While differentiated hepatic functions are generally well maintained with age, changes do occur. Serum and biliary cholesterol rise, liver regeneration declines, hepatic drug clearance decreases, and liver volume and blood flow decrease (4). The resilience of the liver to aging, and its central role in the maintenance of whole body health and homeostasis make it an intriguing target for genome-wide expression analysis of aging.Caloric restriction (CR) is the only intervention shown to extend lifespan in mammals (5). It is also the most effective means known of reducing cancer incidence and increasing the mean age of onset of age-related diseases and tumors (6). Our studies made use of an experimental design that allowed us to clearly distinguish the effects of diet from those of age on genome-wide expression patterns. Another distinctive aspect of the study allowed us to resolve changes in gene expression induced directly by CR from those that arise over time as a consequence of ...

BackgroundSmall RNAs complex with proteins to mediate a variety of functions in animals and plants. Some small RNAs, particularly miRNAs, circulate in mammalian blood and may carry out a signaling function by entering target cells and modulating gene expression. The subject of this study is a set of circulating 30–33 nt RNAs that are processed derivatives of the 5′ ends of a small subset of tRNA genes, and closely resemble cellular tRNA derivatives (tRFs, tiRNAs, half-tRNAs, 5′ tRNA halves) previously shown to inhibit translation initiation in response to stress in cultured cells.ResultsIn sequencing small RNAs extracted from mouse serum, we identified abundant 5′ tRNA halves derived from a small subset of tRNAs, implying that they are produced by tRNA type-specific biogenesis and/or release. The 5′ tRNA halves are not in exosomes or microvesicles, but circulate as particles of 100–300 kDa. The size of these particles suggest that the 5′ tRNA halves are a component of a macromolecular complex; this is supported by the loss of 5′ tRNA halves from serum or plasma treated with EDTA, a chelating agent, but their retention in plasma anticoagulated with heparin or citrate. A survey of somatic tissues reveals that 5′ tRNA halves are concentrated within blood cells and hematopoietic tissues, but scant in other tissues, suggesting that they may be produced by blood cells. Serum levels of specific subtypes of 5′ tRNA halves change markedly with age, either up or down, and these changes can be prevented by calorie restriction.ConclusionsWe demonstrate that 5′ tRNA halves circulate in the blood in a stable form, most likely as part of a nucleoprotein complex, and their serum levels are subject to regulation by age and calorie restriction. They may be produced by blood cells, but their cellular targets are not yet known. The characteristics of these circulating molecules, and their known function in suppression of translation initiation, suggest that they are a novel form of signaling molecule.

Caloric restriction (CR), the consumption of fewer calories while avoiding malnutrition, decelerates the rate of aging and the development of age-related diseases. CR has been viewed as less effective in older animals and as acting incrementally to slow or prevent age-related changes in gene expression. Here we demonstrate that CR initiated in 19-month-old mice begins within 2 months to increase the mean time to death by 42% and increase mean and maximum lifespans by 4.7 (P ‫؍‬ 0.000017) and 6.0 months (P ‫؍‬ 0.000056), respectively. The rate of age-associated mortality was decreased 3.1-fold. Between the first and second breakpoints in the CR survival curve (between 21 and 31 months of age), tumors as a cause of death decreased from 80% to 67% (P ‫؍‬ 0.012). Genome-wide microarray analysis of hepatic RNA from old control mice switched to CR for 2, 4, and 8 weeks showed a rapid and progressive shift toward the gene expression profile produced by long-term CR. This shift took place in the time frame required to induce the health and longevity effects of CR. Shifting from long-term CR to a control diet, which returns animals to the control rate of aging, reversed 90% of the gene expression effects of long-term CR within 8 weeks. These results suggest a cause-and-effect relationship between the rate of aging and the CR-associated gene expression biomarkers. Therefore, therapeutics mimicking the gene-expression biomarkers of CR may reproduce its physiological effects.C aloric restriction (CR), the consumption of fewer calories while avoiding malnutrition, is a robust method of decelerating aging and the development of age-related diseases (1). The effects of CR are conserved in nearly every species tested, perhaps including humans (2). CR delays the onset and reduces the incidence and severity of age-related diseases, including cancer (2, 3).Quantitative changes in the activity of genes can control the rate of aging and the development of age-related diseases in invertebrates and mammals (4, 5). Numerous cross-sectional studies of the relationship between CR and gene expression have been published (6). Almost without exception, they have been interpreted as though they were performed longitudinally. This has led to the widespread view that the major effect of CR is to prevent agerelated changes in gene expression. Funding and publication bias has reinforced this notion (6).We previously found that in old mice, a 4-week shift from long-term control (LT-CON) to short-term CR (ST-CR) reproduced 55% of the gene-expression changes induced by long-term CR (LT-CR; ref. 7). ST-CR reversed Ϸ70% of the age-related changes in gene expression seemingly prevented by LT-CR (7). These results suggested for the first time that many of the gene expression changes produced by LT-CR respond rapidly to diet.The studies described above left several important questions unanswered. First, which of the changes in gene expression are related to the health and longevity effects of CR? Further, what are the kinetics of the changes in gene exp...