Masaharu Uno

Signalling through RHEB-1 mediates intermittent fasting-induced longevity in C. elegans.

Dietary restriction is the most effective and reproducible intervention to extend lifespan in divergent species. In mammals, two regimens of dietary restriction, intermittent fasting (IF) and chronic caloric restriction, have proven to extend lifespan and reduce the incidence of age-related disorders. An important characteristic of IF is that it can increase lifespan even when there is little or no overall decrease in calorie intake. The molecular mechanisms underlying IF-induced longevity, however, remain largely unknown. Here we establish an IF regimen that effectively extends the lifespan of Caenorhabditis elegans, and show that the low molecular weight GTPase RHEB-1 has a dual role in lifespan regulation; RHEB-1 is required for the IF-induced longevity, whereas inhibition of RHEB-1 mimics the caloric-restriction effects. RHEB-1 exerts its effects in part by the insulin/insulin growth factor (IGF)-like signalling effector DAF-16 in IF. Our analyses demonstrate that most fasting-induced upregulated genes require RHEB-1 function for their induction, and that RHEB-1 and TOR signalling are required for the fasting-induced downregulation of an insulin-like peptide, INS-7. These findings identify the essential role of signalling by RHEB-1 in IF-induced longevity and gene expression changes, and suggest a molecular link between the IF-induced longevity and the insulin/IGF-like signalling pathway.

A Fasting-Responsive Signaling Pathway that Extends Life Span in C. elegans

Intermittent fasting is one of the most effective dietary restriction regimens that extend life span in C. elegans and mammals. Fasting-stimulus responses are key to the longevity response; however, the mechanisms that sense and transduce the fasting stimulus remain largely unknown. Through a comprehensive transcriptome analysis in C. elegans, we find that along with the FOXO transcription factor DAF-16, AP-1 (JUN-1/FOS-1) plays a central role in fasting-induced transcriptional changes. KGB-1, one of the C. elegans JNKs, acts as an activator of AP-1 and is activated in response to fasting. KGB-1 and AP-1 are involved in intermittent fasting-induced longevity. Fasting-induced upregulation of the components of the SCF E3 ubiquitin ligase complex via AP-1 and DAF-16 enhances protein ubiquitination and reduces protein carbonylation. Our results thus identify a fasting-responsive KGB-1/AP-1 signaling pathway, which, together with DAF-16, causes transcriptional changes that mediate longevity, partly through regulating proteostasis.

Environmental stresses induce transgenerationally inheritable survival advantages via germline-to-soma communication in Caenorhabditis elegans.

Hormesis is a biological phenomenon, whereby exposure to low levels of toxic agents or conditions increases organismal viability. It thus represents a beneficial aspect of adaptive responses to harmful environmental stimuli. Here we show that hormesis effects induced in the parental generation can be passed on to the descendants in Caenorhabditis elegans. Animals subjected to various stressors during developmental stages exhibit increased resistance to oxidative stress and proteotoxicity. The increased resistance is transmitted to the subsequent generations grown under unstressed conditions through epigenetic alterations. Our analysis reveal that the insulin/insulin-like growth factor (IGF) signalling effector DAF-16/FOXO and the heat-shock factor HSF-1 in the parental somatic cells mediate the formation of epigenetic memory, which is maintained through the histone H3 lysine 4 trimethylase complex in the germline across generations. The elicitation of memory requires the transcription factor SKN-1/Nrf in somatic tissues. We propose that germ-to-soma communication across generations is an essential framework for the transgenerational inheritance of acquired traits, which provides the offspring with survival advantages to deal with environmental perturbation.

Lifespan-regulating genes in C. elegans

The molecular mechanisms underlying the aging process have garnered much attention in recent decades because aging is the most significant risk factor for many chronic diseases such as type 2 diabetes and cancer. Until recently, the aging process was not considered to be an actively regulated process; therefore, discovering that the insulin/insulin-like growth factor-1 signaling pathway is a lifespan-regulating genetic pathway in Caenorhabditis elegans was a major breakthrough that changed our understanding of the aging process. Currently, it is thought that animal lifespans are influenced by genetic and environmental factors. The genes involved in lifespan regulation are often associated with major signaling pathways that link the rate of aging to environmental factors. Although many of the major mechanisms governing the aging process have been identified from studies in short-lived model organisms such as yeasts, worms and flies, the same mechanisms are frequently observed in mammals, indicating that the genes and signaling pathways that regulate lifespan are highly conserved among different species. This review summarizes the lifespan-regulating genes, with a specific focus on studies in C. elegans.

Cholesterol regulates DAF-16 nuclear localization and fasting-induced longevity in C. elegans.

Abstract Cholesterol has attracted significant attention as a possible lifespan regulator. It has been reported that serum cholesterol levels have an impact on mortality due to age‐related disorders such as cardiovascular disease. Diet is also known to be an important lifespan regulator. Dietary restriction retards the onset of age‐related diseases and extends lifespan in various organisms. Although cholesterol and dietary restriction are known to be lifespan regulators, it remains to be established whether cholesterol is involved in dietary restriction‐induced longevity. Here, we show that cholesterol deprivation suppresses longevity induced by intermittent fasting, which is one of the dietary restriction regimens that effectively extend lifespan. We also found that cholesterol is required for the fasting‐induced upregulation of transcriptional target genes such as the insulin/IGF‐1 pathway effector DAF‐16 and that cholesterol deprivation suppresses the long lifespan of the insulin/IGF‐1 receptor daf‐2 mutant. Remarkably, we found that cholesterol plays an important role in the fasting‐induced nuclear accumulation of DAF‐16. Moreover, knockdown of the cholesterol‐binding protein NSBP‐1, which has been shown to bind to DAF‐16 in a cholesterol‐dependent manner and to regulate DAF‐16 activity, suppresses both fasting‐induced longevity and DAF‐16 nuclear accumulation. Furthermore, this suppression was not additive to the cholesterol deprivation‐induced suppression, which suggests that NSBP‐1 mediates, at least in part, the action of cholesterol to promote fasting‐induced longevity and DAF‐16 nuclear accumulation. These findings identify a novel role for cholesterol in the regulation of lifespan. HighlightsCholesterol plays a crucial role in intermittent fasting‐induced longevity.Cholesterol regulates fasting‐induced upregulation of DAF‐16 target genes.Cholesterol regulates DAF‐16 nuclear localization.These effects of cholesterol may be mediated, at least in part, through NSBP‐1.

The MicroRNA Machinery Regulates Fasting-Induced Changes in Gene Expression and Longevity in Caenorhabditis elegans

Intermittent fasting (IF) is a dietary restriction regimen that extends the lifespans of Caenorhabditis elegans and mammals by inducing changes in gene expression. However, how IF induces these changes and promotes longevity remains unclear. One proposed mechanism involves gene regulation by microRNAs (miRNAs), small non-coding RNAs (∼22 nucleotides) that repress gene expression and whose expression can be altered by fasting. To test this proposition, we examined the role of the miRNA machinery in fasting-induced transcriptional changes and longevity in C. elegans. We revealed that fasting up-regulated the expression of the miRNA-induced silencing complex (miRISC) components, including Argonaute and GW182, and the miRNA-processing enzyme DRSH-1 (the ortholog of the Drosophila Drosha enzyme). Our lifespan measurements demonstrated that IF-induced longevity was suppressed by knock-out or knockdown of miRISC components and was completely inhibited by drsh-1 ablation. Remarkably, drsh-1 ablation inhibited the fasting-induced changes in the expression of the target genes of DAF-16, the insulin/IGF-1 signaling effector in C. elegans. Fasting-induced transcriptome alterations were substantially and modestly suppressed in the drsh-1 null mutant and the null mutant of ain-1, a gene encoding GW182, respectively. Moreover, miRNA array analyses revealed that the expression levels of numerous miRNAs changed after 2 days of fasting. These results indicate that components of the miRNA machinery, especially the miRNA-processing enzyme DRSH-1, play an important role in mediating IF-induced longevity via the regulation of fasting-induced changes in gene expression.

The MYST family histone acetyltransferase complex regulates stress resistance and longevity through transcriptional control of DAF‐16/FOXO transcription factors

The well‐known link between longevity and the Sir2 histone deacetylase family suggests that histone deacetylation, a modification associated with repressed chromatin, is beneficial to longevity. However, the molecular links between histone acetylation and longevity remain unclear. Here, we report an unexpected finding that the MYST family histone acetyltransferase complex (MYS‐1/TRR‐1 complex) promotes rather than inhibits stress resistance and longevity in Caenorhabditis elegans. Our results show that these beneficial effects are largely mediated through transcriptional up‐regulation of the FOXO transcription factor DAF‐16. MYS‐1 and TRR‐1 are recruited to the promoter regions of the daf‐16 gene, where they play a role in histone acetylation, including H4K16 acetylation. Remarkably, we also find that the human MYST family Tip60/TRRAP complex promotes oxidative stress resistance by up‐regulating the expression of FOXO transcription factors in human cells. Tip60 is recruited to the promoter regions of the foxo1 gene, where it increases H4K16 acetylation levels. Our results thus identify the evolutionarily conserved role of the MYST family acetyltransferase as a key epigenetic regulator of DAF‐16/FOXO transcription factors.

Src family kinases suppress differentiation of brown adipocytes and browning of white adipocytes.

Brown adipocytes and beige adipocytes can expend energy, generate heat, and increase whole‐body energy expenditure. The detailed mechanisms of adipogenesis and thermogenesis of these cells are still obscure. Here, we show that Src family kinases (SFKs) regulate both brown adipogenesis and browning of white adipocytes. To identify factors involved in brown adipogenesis, we first examined the effect of several chemical inhibitors on the differentiation of brown preadipocytes isolated from mouse brown adipose tissue (BAT) and found that treatment with PP2, the specific inhibitor of SFKs, promoted the differentiation. Another inhibitor of SFKs, PP1, also promoted the brown adipogenesis, whereas an inactive analogue of PP2, PP3, did not. Moreover, over‐expression of C‐terminal Src kinase (CSK), the negative regulator of SFKs, also promoted brown adipogenesis. Next, we examined the effect of inhibition of SFKs on the differentiation of white preadipocytes isolated from white adipose tissue (WAT). Our results showed that either PP2 treatment or CSK‐over‐expression generated Ucp1‐positive beige adipocytes, thus inducing browning of white adipocytes. Finally, our analysis showed that the expression levels and activity of SFKs in WAT were much higher than in BAT. These results taken together suggest that SFKs regulate differentiation and browning of fat cells in vivo.

Identification of Signaling Pathways That Mediate Dietary Restriction-Induced Longevity in Caenorhabditis elegans

Aging is a complex process of accumulation of molecular, cellular, and organ damage leading to loss of function and increased vulnerability to disease and death. Despite the complexity of aging, progress has been made in not only understanding molecular mechanisms that regulate aging but also devising interventions which extend lifespan. Recent work has shown that a reduction in food intake without causing malnutrition, dietary restriction (DR), can increase the healthy lifespan of laboratory model organisms, including yeasts, flies, worms, fish, rodents, and rhesus monkeys. DR has also been shown to protect rodents and rhesus monkeys from age-related disorders, and it reduces risk factors for diabetes, cardiovascular disease, and cancers in humans [1, 2]. In mammals, two types of DR regimens, chronic calorie restriction (CR) and intermittent fasting (IF), have proven effective in increasing lifespan and disease resistance [3, 4]. In CR, there is actually a net decrease in calorie intake. In contrast, IF, in which animals are subjected to fasting intermittently, can extend lifespan without a net decrease in total calorie intake. However, an IF regimen has not been established in invertebrate model organisms. Moreover, because it seemed that both CR and IF regimens extend lifespan through a common mechanism, the two regimens have not been strictly distinguished.

Molecular mechanisms regulating lifespan and environmental stress responses

Throughout life, organisms are subjected to a variety of environmental perturbations, including temperature, nutrient conditions, and chemical agents. Exposure to external signals induces diverse changes in the physiological conditions of organisms. Genetically identical individuals exhibit highly phenotypic variations, which suggest that environmental variations among individuals can affect their phenotypes in a cumulative and inhomogeneous manner. The organismal phenotypes mediated by environmental conditions involve development, metabolic pathways, fertility, pathological processes, and even lifespan. It is clear that genetic factors influence the lifespan of organisms. Likewise, it is now increasingly recognized that environmental factors also have a large impact on the regulation of aging. Multiple studies have reported on the contribution of epigenetic signatures to the long-lasting phenotypic effects induced by environmental signals. Nevertheless, the mechanism of how environmental stimuli induce epigenetic changes at specific loci, which ultimately elicit phenotypic variations, is still largely unknown. Intriguingly, in some cases, the altered phenotypes associated with epigenetic changes could be stably passed on to the next generations. In this review, we discuss the environmental regulation of organismal viability, that is, longevity and stress resistance, and the relationship between this regulation and epigenetic factors, focusing on studies in the nematode C. elegans.