Lifespan extension by preserving proliferative homeostasis in Drosophila

Dapagliflozin ameliorates intestinal stem cell aging by regulating the MAPK signaling pathway in Drosophila

Introduction

Intestinal stem cells (ISCs) possess the ability to self-renew and differentiate, which is essential for maintaining intestinal tissue homeostasis. However, their functionality significantly declines with age, leading to diminished tissue regeneration and an increased risk of age-associated diseases.

Methods

This study investigates the effects of Dapagliflozin (DAPA), a novel insulin sensitizer and SGLT2 inhibitor, on aging ISCs using the Drosophila melanogaster model. Our findings demonstrate that DAPA can inhibit the MAPK signaling pathway, as confirmed by network pharmacology analysis and molecular docking experiments.

Results

DAPA ameliorates ISC aging, improves intestinal function (including enhanced fecal excretion, restored intestinal barrier integrity and acid-base balance), and enhances healthspan. These results highlight the potential of DAPA as an anti-aging therapeutic agent.

Discussion

This study provides new evidence for the application of DAPA as an anti-aging treatment.

Werner syndrome exonuclease promotes gut regeneration and causes age-associated gut hyperplasia in Drosophila

Human Werner syndrome (adult progeria, a well-established model of human aging) is caused by mutations in the Werner syndrome (WRN) gene. However, the expression patterns and functions of WRN in natural aging remain poorly understood. Despite the link between WRN deficiencies and progeria, our analyses of human colon tissues, mouse crypts, and Drosophila midguts revealed that WRN expression does not decrease but rather increases in intestinal stem cells (ISCs) with aging. Mechanistically, we found that the Drosophila WRN homologue (WRNexo) binds to Heat shock 70-kDa protein cognate 3 (Hsc70-3/Bip) to regulate the unfolded protein response of the endoplasmic reticulum (UPRER). Activation of the WRNexo-mediated UPRER in ISCs is required for ISC proliferation during injury repair. However, persistent DNA damage during aging leads to chronic upregulation of WRNexo in ISCs, where excessive WRNexo-induced ER stress drives age-associated gut hyperplasia in Drosophila. This study reveals how elevated WRNexo contributes to stem cell aging, providing new insights into organ aging and the pathogenesis of age-related diseases, such as colon cancer.

Agar oligosaccharides improve the intestinal health of induced-aging mice by maintaining intestinal homeostasis via balancing the ISCs proliferation and differentiation

PURPOSE

Aging is a process that accompanies a decline in the function of various tissues and organs, especially affecting intestinal health. Agarose oligosaccharide (AOS) can prolong the lifespan of organisms and protect the intestine in the previous study. It was examined to evaluate the effects of AOS on intestinal health, and the potential associations between intestinal homeostasis and health status were further validated.

METHODS

D-galactose-induced aging mice were used to investigate the role of AOS in promoting intestinal health by determining intestinal physiology, microbiota and stem cells.

RESULTS

AOS supplementation decreased the clinical frailty index of aging mice with increasing intestinal length and crypt depth; moreover, it decreased the average flatulence index and PCNA protein content in the intestine. Besides, AOS contributed to the diversity of the gut microbiota by increasing the relative abundance of Bacteroidetes and other bacteria that could produce short-chain fatty acids. Furthermore, AOS affected the expression of proinflammatory factors in aging mice, promoting the proliferative equilibrium of intestinal stem cells.

CONCLUSION

These findings confirmed that AOS could improve intestinal health in aging mice by maintaining intestinal homeostasis, which provides new insights into the potential application of AOS as a prebiotic.

Nutrient-sensing alteration leads to age-associated distortion of intestinal stem cell differentiating direction

Nutrient-sensing pathways undergo deregulation in aged animals, exerting a pivotal role in regulating the cell cycle and subsequent stem cell division. Nevertheless, their precise functions in governing pluripotent stem cell differentiation remain largely elusive. Here, we uncovered a significant alteration in the cellular constituents of the intestinal epithelium in aged humans and mice. Employing Drosophila midgut and mouse organoid culture models, we made an observation regarding the altered trajectory of differentiation in intestinal stem cells (ISC) during overnutrition or aging, which stems from the erroneous activation of the insulin receptor signaling pathway. Through genetic analyses, we ascertained that the nutrient-sensing pathway regulated the direction of ISC differentiation by modulating the maturation of endosomes and SOX21A transcription factor. This study elucidates a nutrient-sensing pathway-mediated mechanism underlying stem cell differentiation, offering insights into the etiology of stem cell dysfunction in aged animals, including humans.

Kaempferol enhances intestinal repair and inhibits the hyperproliferation of aging intestinal stem cells in Drosophila

Introduction

Intestinal stem cells (ISCs) are crucial for tissue repair and homeostasis because of their ability to self-renew and differentiate. However, their functionality declines significantly with age, resulting in reduced tissue regeneration and a higher risk of age-related diseases. Addressing this decline in ISC performance during aging presents a substantial challenge. The specific impact of nutrients or dietary elements on ISC adaptive resizing is urgent to explore.

Methods

Drosophila ISCs are an ideal model for studying development and aging because of their genetic richness, ease of manipulation, and similarity to mammalian tissues. As the primary mitotically active cells in the Drosophila gut, ISCs are flexible in response to dietary and stress signals. Manipulating signaling pathways or dietary restrictions has shown promise in regulating ISC functions and extending lifespan in flies, these approaches face broader applications for aging research.

Results

Kaempferol is well-regarded for its antioxidant, anti-inflammatory, and potential anticancer effects. However, its impacts on ISCs and the associated mechanisms remain inadequately understood. Our findings indicate that Kaempferol accelerates gut recovery after damage and improves the organism's stress tolerance. Moreover, Kaempferol suppresses the hyperproliferation of aging ISCs in Drosophila. Further investigation revealed that the regulatory effects of Kaempferol on ISCs are mediated through the reduction of endoplasmic reticulum (ER) stress in aging flies and the modulation of excessive reactive oxygen species (ROS) levels via ER-stress pathways. Furthermore, Kaempferol exerts regulatory effects on the insulin signaling pathway, thereby contributing to the attenuation of ISC senescence.

Discussion

This study reveals that Kaempferol promotes intestinal homeostasis and longevity in aging flies by targeting ER stress and insulin signaling pathways, though the exact molecular mechanisms require further exploration. Future research will aim to dissect the downstream signaling events involved in these pathways to better understand how Kaempferol exerts its protective effects at the molecular level.

How does a fly die? Insights into ageing from the pathophysiology of Drosophila mortality

The fruit fly Drosophila melanogaster is a common animal model in ageing research. Large populations of flies are used to study the impact of genetic, nutritional and pharmacological interventions on survival. However, the processes through which flies die and their relative prevalence in Drosophila populations are still comparatively unknown. Understanding the causes of death in an animal model is essential to dissect the lifespan-extending interventions that are organism- or disease-specific from those broadly applicable to ageing. Here, we review the pathophysiological processes that can lead to fly death and discuss their relation to ageing.

Insidious chromatin change with a propensity to exhaust intestinal stem cells during aging

During aging, tissue stem cells can demonstrate two opposing phenotypes of tissue homeostasis disruption: proliferation and exhaustion. Stem cells can exhaust as a result of excessive cell proliferation or independently of cell proliferation. There are many silent changes in chromatin structures and gene expression that are not necessarily reflected in manifested phenotypes during aging. Here through analyses of chromatin accessibility and gene expression in intestinal progenitor cells during aging, we discovered changes of chromatin accessibility and gene expression that have a propensity to exhaust intestinal stem cells (ISCs). During aging, Trithorax-like (Trl) target genes, ced-6 and ci, close their chromatin structures and decrease their expression in intestinal progenitor cells. Inhibition of Trl, ced-6, or ci exhausts ISCs. This study provides new insight into changes of chromatin accessibility and gene expression that have a potential to exhaust ISCs during aging.

Viral infection disrupts intestinal homeostasis via Sting-dependent NF-κB signaling in Drosophila

Host-microbe interactions influence intestinal stem cell (ISC) activity to modulate epithelial turnover and composition. Here, we investigated the functional impacts of viral infection on intestinal homeostasis and the mechanisms by which viral infection alters ISC activity. We report that Drosophila A virus (DAV) infection disrupts intestinal homeostasis in Drosophila by inducing sustained ISC proliferation, resulting in intestinal dysplasia, loss of gut barrier function, and reduced lifespan. We found that additional viruses common in laboratory-reared Drosophila also promote ISC proliferation. The mechanism of DAV-induced ISC proliferation involves progenitor-autonomous epidermal growth factor receptor (EGFR) signaling, c-Jun N-terminal kinase (JNK) activity in enterocytes, and requires Sting-dependent nuclear factor κB (NF-κB) (Relish) activity. We further demonstrate that activating Sting-Relish signaling is sufficient to induce ISC proliferation, promote intestinal dysplasia, and reduce lifespan in the absence of infection. Our results reveal that viral infection can significantly disrupt intestinal physiology, highlight a novel role for Sting-Relish signaling, and support a role for viral infection in aging.

STING-NF-κB signaling: Viral infection drives gut aging effects

Viral infection causes an increase in age-related intestinal pathologies. New research finds that oral viral infection leads to intestinal stem-cell proliferation and a decrease in lifespan in Drosophila melanogaster that depends on Sting-NF-κB signaling.

Xbp1 targets canonical UPRER and non-canonical pathways in separate tissues to promote longevity

Transcription factors can reprogram gene expression to promote longevity. Here, we investigate the role of Drosophila Xbp1. Xbp1 is activated by splicing of its primary transcript, Xbp1u, to generate Xbp1s, a key activator of the endoplasmic reticulum unfolded protein response (UPRER). We show that Xbp1s induces the conical UPRER in the gut, promoting longevity from the resident stem cells. In contrast, in the fat body, Xbp1s does not appear to trigger UPRER but alters metabolic gene expression and is still able to extend lifespan. In the fat body, Xbp1s and dFOXO impinge on the same target genes, including the PGC-1α orthologue Srl, and dfoxo requires Xbp1 to extend lifespan. Interestingly, unspliceable version of the Xbp1 mRNA, Xbp1u can also extend lifespan, hinting at roles in longevity for the poorly characterized Xbp1u transcription factor. These findings reveal the diverse functions of Xbp1 in longevity in the fruit fly.

InR and Pi3K maintain intestinal homeostasis through STAT/EGFR and Notch signaling in enteroblasts

To maintain the integrity of the adult gut, the proliferation and differentiation of stem cells must be strictly controlled. Several signaling pathways control the proliferation and differentiation of Drosophila intestinal epithelial cells. Although the modulatory effects of insulin pathway components on cell proliferation have been characterized, their specific role in which cell type and how these components interact with other regulatory signaling pathways remain largely unclear. In this study, we found that InR/Pi3K has major functions in enteroblasts (EBs) that were not previously described. The absence of InR/Pi3K in progenitors leads to a decrease in the number of EBs, while it has no significant effect on intestinal stem cells (ISCs). In addition, we found that InR/Pi3K regulates Notch activity in ISCs and EBs in an opposite way. This is also the reason for the decrease in EB. On the one hand, aberrantly low levels of Notch signaling in ISCs inhibit their proper differentiation into EBs; on the other hand, the higher Notch levels in EBs promote their excessive differentiation into enterocytes (ECs), leading to marked increases in abnormal ECs and decreased proliferation. Moreover, we found that Upd/JAK/STAT signaling acts as an effector or modifier of InR/Pi3K function in the midgut and cooperates with EGFR signaling to regulate cell proliferation. Altogether, our results demonstrate that InR and Pi3K are essential for coordinating stem cell differentiation and proliferation to maintain intestinal homeostasis.

BNIP3 as a new tool to promote healthy brain aging

The article "Neuronal induction of BNIP3-mediated mitophagy slows systemic aging in Drosophila" reveals BCL2-interacting protein 3 as a therapeutic target to counteract brain aging and prolong overall organismal health with age. In this spotlight, we consider the roles of BNIP3, a mitochondrial outer membrane protein, in the adult nervous system, including its induction of mitophagy and prevention of dysfunctional mitochondria in the aged brain. Implications for other tissue types to reduce the burden of aging are further considered.

Endocrine Regulation of Aging in the Fruit Fly Drosophila melanogaster

The past few decades have witnessed increasing research clarifying the role of endocrine signaling in the regulation of aging in both vertebrates and invertebrates. Studies using the model organism fruit fly Drosophila melanogaster have largely advanced our understanding of evolutionarily conserved mechanisms in the endocrinology of aging and anti-aging. Mutations in single genes involved in endocrine signaling modify lifespan, as do alterations of endocrine signaling in a tissue- or cell-specific manner, highlighting a central role of endocrine signaling in coordinating the crosstalk between tissues and cells to determine the pace of aging. Here, we review the current landscape of research in D. melanogaster that offers valuable insights into the endocrine-governed mechanisms which influence lifespan and age-related physiology.

Trametinib ameliorates aging-associated gut pathology in Drosophila females by reducing Pol III activity in intestinal stem cells

Pharmacological therapies are promising interventions to slow down aging and reduce multimorbidity in the elderly. Studies in animal models are the first step toward translation of candidate molecules into human therapies, as they aim to elucidate the molecular pathways, cellular mechanisms, and tissue pathologies involved in the anti-aging effects. Trametinib, an allosteric inhibitor of MEK within the Ras/MAPK (Ras/Mitogen-Activated Protein Kinase) pathway and currently used as an anti-cancer treatment, emerged as a geroprotector candidate because it extended lifespan in the fruit fly Drosophila melanogaster. Here, we confirm that trametinib consistently and robustly extends female lifespan, and reduces intestinal stem cell (ISC) proliferation, tumor formation, tissue dysplasia, and barrier disruption in guts in aged flies. In contrast, pro-longevity effects of trametinib are weak and inconsistent in males, and it does not influence gut homeostasis. Inhibition of the Ras/MAPK pathway specifically in ISCs is sufficient to partially recapitulate the effects of trametinib. Moreover, in ISCs, trametinib decreases the activity of the RNA polymerase III (Pol III), a conserved enzyme synthesizing transfer RNAs and other short, non-coding RNAs, and whose inhibition also extends lifespan and reduces gut pathology. Finally, we show that the pro-longevity effect of trametinib in ISCs is partially mediated by Maf1, a repressor of Pol III, suggesting a life-limiting Ras/MAPK-Maf1-Pol III axis in these cells. The mechanism of action described in this work paves the way for further studies on the anti-aging effects of trametinib in mammals and shows its potential for clinical application in humans.

The adhesion G-protein-coupled receptor mayo/CG11318 controls midgut development in Drosophila

Adhesion G-protein-coupled receptors (aGPCRs) form a large family of cell surface molecules with versatile tasks in organ development. Many aGPCRs still await their functional and pharmacological deorphanization. Here, we characterized the orphan aGPCR CG11318/mayo of Drosophila melanogaster and found it expressed in specific regions of the gastrointestinal canal and anal plates, epithelial specializations that control ion homeostasis. Genetic removal of mayo results in tachycardia, which is caused by hyperkalemia of the larval hemolymph. The hyperkalemic effect can be mimicked by a raise in ambient potassium concentration, while normal potassium levels in mayoKO mutants can be restored by pharmacological inhibition of potassium channels. Intriguingly, hyperkalemia and tachycardia are caused non-cell autonomously through mayo-dependent control of enterocyte proliferation in the larval midgut, which is the primary function of this aGPCR. These findings characterize the ancestral aGPCR Mayo as a homeostatic regulator of gut development.

The influence of the gut microbiome on ovarian aging

Ovarian aging occurs prior to the aging of other organ systems and acts as the pacemaker of the aging process of multiple organs. As life expectancy has increased, preventing ovarian aging has become an essential goal for promoting extended reproductive function and improving bone and genitourinary conditions related to ovarian aging in women. An improved understanding of ovarian aging may ultimately provide tools for the prediction and mitigation of this process. Recent studies have suggested a connection between ovarian aging and the gut microbiota, and alterations in the composition and functional profile of the gut microbiota have profound consequences on ovarian function. The interaction between the gut microbiota and the ovaries is bidirectional. In this review, we examine current knowledge on ovary-gut microbiota crosstalk and further discuss the potential role of gut microbiota in anti-aging interventions. Microbiota-based manipulation is an appealing approach that may offer new therapeutic strategies to delay or reverse ovarian aging.

Experimental validation and characterization of putative targets of Escargot and STAT, two master regulators of the intestinal stem cells in Drosophila melanogaster

Many organs contain adult stem cells (ASCs) to replace cells due to damage, disease, or normal tissue turnover. ASCs can divide asymmetrically, giving rise to a new copy of themselves (self-renewal) and a sister that commits to a specific cell type (differentiation). Decades of research have led to the identification of pleiotropic genes whose loss or gain of function affect diverse aspects of normal ASC biology. Genome-wide screens of these so-called genetic "master regulator" (MR) genes, have pointed to hundreds of putative targets that could serve as their downstream effectors. Here, we experimentally validate and characterize the regulation of several putative targets of Escargot (Esg) and the Signal Transducer and Activator of Transcription (Stat92E, a.k.a. STAT), two known MRs in Drosophila intestinal stem cells (ISCs). Our results indicate that regardless of bioinformatic predictions, most experimentally validated targets show a profile of gene expression that is consistent with co-regulation by both Esg and STAT, fitting a rather limited set of co-regulatory modalities. A bioinformatic analysis of proximal regulatory sequences in specific subsets of co-regulated targets identified additional transcription factors that might cooperate with Esg and STAT in modulating their transcription. Lastly, in vivo manipulations of validated targets rarely phenocopied the effects of manipulating Esg and STAT, suggesting the existence of complex genetic interactions among downstream targets of these two MR genes during ISC homeostasis.

Peroxiredoxins Play an Important Role in the Regulation of Immunity and Aging in Drosophila

Aberrant immune responses and chronic inflammation can impose significant health risks and promote premature aging. Pro-inflammatory responses are largely mediated via reactive oxygen species (ROS) and reduction-oxidation reactions. A pivotal role in maintaining cellular redox homeostasis and the proper control of redox-sensitive signaling belongs to a family of antioxidant and redox-regulating thiol-related peroxidases designated as peroxiredoxins (Prx). Our recent studies in Drosophila have shown that Prxs play a critical role in aging and immunity. We identified two important 'hubs', the endoplasmic reticulum (ER) and mitochondria, where extracellular and intracellular stress signals are transformed into pro-inflammatory responses that are modulated by the activity of the Prxs residing in these cellular organelles. Here, we found that mitochondrial Prx activity in the intestinal epithelium is required to prevent the development of intestinal barrier dysfunction, which can drive systemic inflammation and premature aging. Using a redox-negative mutant, we demonstrated that Prx acts in a redox-dependent manner in regulating the age-related immune response. The hyperactive immune response observed in flies under-expressing mitochondrial Prxs is due to a response to abiotic signals but not to changes in the bacterial content. This hyperactive response, but not reduced lifespan phenotype, can be rescued by the ER-localized Prx.

Devo-Aging: Intersections Between Development and Aging

There are two fundamental questions in developmental biology. How does a single fertilized cell give rise to a whole body? and how does this body later produce progeny? Synchronization of these embryonic and postembryonic developments ensures continuity of life from one generation to the next. An enormous amount of work has been done to unravel the molecular mechanisms behind these processes, but more recently, modern developmental biology has been expanded to study development in wider contexts, including regeneration, environment, disease, and even aging. However, we have just started to understand how the mechanisms that govern development also regulate aging. This review discusses examples of signaling pathways involved in development to elucidate how their regulation influences healthspan and lifespan. Therefore, a better knowledge of developmental signaling pathways stresses the possibility of using them as innovative biomarkers and targets for aging and age-related diseases.

What do we mean by "aging"? Questions and perspectives revealed by studies in Drosophila

What is the nature of aging, and how best can we study it? Here, using a series of questions that highlight differing perspectives about the nature of aging, we ask how data from Drosophila melanogaster at the organismal, tissue, cellular, and molecular levels shed light on the complex interactions among the phenotypes associated with aging. Should aging be viewed as an individual's increasing probability of mortality over time or as a progression of physiological states? Are all age-correlated changes in physiology detrimental to vigor or are some compensatory changes that maintain vigor? Why do different age-correlated functions seem to change at different rates in a single individual as it ages? Should aging be considered as a single, integrated process across the scales of biological resolution, from organismal to molecular, or must we consider each level of biological scale as a separate, distinct entity? Viewing aging from these differing perspectives yields distinct but complementary interpretations about the properties and mechanisms of aging and may offer a path through the complexities related to understanding the nature of aging.

The septate junction component bark beetle is required for Drosophila intestinal barrier function and homeostasis

Age-related loss of intestinal barrier function has been documented across species, but the causes remain unknown. The intestinal barrier is maintained by tight junctions (TJs) in mammals and septate junctions (SJs) in insects. Specialized TJs/SJs, called tricellular junctions (TCJs), are located at the nexus of three adjacent cells, and we have shown that aging results in changes to TCJs in intestines of adult Drosophila melanogaster. We now demonstrate that localization of the TCJ protein bark beetle (Bark) decreases in aged flies. Depletion of bark from enterocytes in young flies led to hallmarks of intestinal aging and shortened lifespan, whereas depletion of bark in progenitor cells reduced Notch activity, biasing differentiation toward the secretory lineage. Our data implicate Bark in EC maturation and maintenance of intestinal barrier integrity. Understanding the assembly and maintenance of TCJs to ensure barrier integrity may lead to strategies to improve tissue integrity when function is compromised.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

Angelica sinensis polysaccharide extends lifespan and ameliorates aging-related diseases via insulin and TOR signaling pathways, and antioxidant ability in Drosophila

Angelica sinensis polysaccharide (ASP) is one of the principal active components of Angelica sinensis (AS) that is widely used in natural medicine and has various pharmacological activities, including antioxidant, anti-inflammatory, and enhancing immunity. However, its pharmacological role of anti-aging needs to be clarified. Here, we detected the beneficial effect and mechanism of ASP on healthy aging and aging-related diseases using the Drosophila melanogaster model. The results showed that oral administration of ASP remarkably extended lifespan, increased reproduction, improved climbing ability, and increased resistance to starvation and oxidative stress in aged flies, mainly via inhibiting insulin signaling (IIS) and TOR signaling and boosting antioxidant ability. Further, ASP supplementation protected against aging-induced intestinal homeostasis imbalance via inhibiting intestinal stem cells (ISCs) hyperproliferation and oxidative damage, improved sleep disorders via rescuing sleep rhythm in aged flies, and had a neuroprotective effect on Aβ42 transgenic flies. Taken together, our findings shed light on the possibility that ASP could increase lifespan, improve healthy aging, and ultimately reduce the incidence of age-related illnesses. It holds promise as a candidate for anti-aging intervention and treatment for aging-associated disorders.

The antioxidant effects of hedysarum polybotrys polysaccharide in extending lifespan and ameliorating aging-related diseases in Drosophila melanogaster

Hedysarum polybotrys polysaccharide (HPS) is one of the main active ingredients of Hedysarum with many health-beneficial properties, including antioxidant property, immunomodulatory, anti-inflammatory, and anti-tumor. However, the effect of HPS on anti-aging is still unclear. This study was to explore the protective function of HPS on aging and age-related diseases using Drosophila melanogaster. The results demonstrated that HPS supplementation promoted hatchability and prolonged lifespan by enhancing the antioxidative capacity. Administraction of HPS ameliorated age-related symptoms such as imbalanced intestinal homeostasis, sleep disturbances, and beta-amyloid (Aβ) induced Alzheimer's disease (AD) in flies, but did not modulate neurobehavioral deficits in the AD model of tauopathy and the Parkinson's disease (PD) model of Pink1 mutation. Overall, this study reveals that HPS has strong potential in the prevention of aging and age-related diseases, and provided a new candidate for the development of anti-aging drugs.

A state-of-the-art review on the MicroRNAs roles in hematopoietic stem cell aging and longevity

Aging is a biological process determined through time-related cellular and functional impairments, leading to a decreased standard of living for the organism. Recently, there has been an unprecedented advance in the aging investigation, especially the detection that the rate of senescence is at least somewhat regulated via evolutionarily preserved genetic pathways and biological processes. Hematopoietic stem cells (HSCs) maintain blood generation over the whole lifetime of an organism. The senescence process influences many of the natural features of HSC, leading to a decline in their capabilities, independently of their microenvironment. New studies show that HSCs are sensitive to age-dependent stress and gradually lose their self-renewal and regeneration potential with senescence. MicroRNAs (miRNAs) are short, non-coding RNAs that post-transcriptionally inhibit translation or stimulate target mRNA cleavage of target transcripts via the sequence-particular connection. MiRNAs control various biological pathways and processes, such as senescence. Several miRNAs are differentially expressed in senescence, producing concern about their use as moderators of the senescence process. MiRNAs play an important role in the control of HSCs and can also modulate processes associated with tissue senescence in specific cell types. In this review, we display the contribution of age-dependent alterations, including DNA damage, epigenetic landscape, metabolism, and extrinsic factors, which affect HSCs function during aging. In addition, we investigate the particular miRNAs regulating HSCs senescence and age-associated diseases. Video Abstract.

Intestinal barrier dysfunction: an evolutionarily conserved hallmark of aging

A major challenge in the biology of aging is to understand how specific age-onset pathologies relate to the overall health of the organism. The integrity of the intestinal epithelium is essential for the wellbeing of the organism throughout life. In recent years, intestinal barrier dysfunction has emerged as an evolutionarily conserved feature of aged organisms, as reported in worms, flies, fish, rodents and primates. Moreover, age-onset intestinal barrier dysfunction has been linked to microbial alterations, elevated immune responses, metabolic alterations, systemic health decline and mortality. Here, we provide an overview of these findings. We discuss early work in the Drosophila model that sets the stage for examining the relationship between intestinal barrier integrity and systemic aging, then delve into research in other organisms. An emerging concept, supported by studies in both Drosophila and mice, is that directly targeting intestinal barrier integrity is sufficient to promote longevity. A better understanding of the causes and consequences of age-onset intestinal barrier dysfunction has significant relevance to the development of interventions to promote healthy aging.

Targeting the "hallmarks of aging" to slow aging and treat age-related disease: fact or fiction?

Aging is a major risk factor for a number of chronic diseases, including neurodegenerative and cerebrovascular disorders. Aging processes have therefore been discussed as potential targets for the development of novel and broadly effective preventatives or therapeutics for age-related diseases, including those affecting the brain. Mechanisms thought to contribute to aging have been summarized under the term the "hallmarks of aging" and include a loss of proteostasis, mitochondrial dysfunction, altered nutrient sensing, telomere attrition, genomic instability, cellular senescence, stem cell exhaustion, epigenetic alterations and altered intercellular communication. We here examine key claims about the "hallmarks of aging". Our analysis reveals important weaknesses that preclude strong and definitive conclusions concerning a possible role of these processes in shaping organismal aging rate. Significant ambiguity arises from the overreliance on lifespan as a proxy marker for aging, the use of models with unclear relevance for organismal aging, and the use of study designs that do not allow to properly estimate intervention effects on aging rate. We also discuss future research directions that should be taken to clarify if and to what extent putative aging regulators do in fact interact with aging. These include multidimensional analytical frameworks as well as designs that facilitate the proper assessment of intervention effects on aging rate.

Quercetin Prevents Intestinal Stem Cell Aging via Scavenging ROS and Inhibiting Insulin Signaling in Drosophila

Adult stem cells, a class of cells that possess self-renewal and differentiation capabilities, modulate tissue regeneration, repair, and homeostasis maintenance. These cells undergo functional degeneration during aging, resulting in decreased tissue regeneration ability and increased disease incidence. Thus, it is essential to provide effective therapeutic solutions to preventing the aging-related functional decline of stem cells. Quercetin (Que) is a popular natural polyphenolic flavonoid found in various plant species. It exhibits many beneficial effects against aging and aging-related diseases; however, its efficacy against adult stem cell aging remains largely unclear. Drosophila possesses a mammalian-like intestinal system with a well-studied intestinal stem cell (ISC) lineage, making it an attractive model for adult stem cell research. Here, we show that Que supplementation could effectively prevent the hyperproliferation of ISCs, maintain intestinal homeostasis, and prolong the lifespan in aged Drosophila. In addition, we found that Que could accelerate recovery of the damaged gut and improve the tolerance of Drosophila to stressful stimuli. Furthermore, results demonstrated that Que prevents the age-associated functional decline of ISCs via scavenging reactive oxygen species (ROS) and inhibiting the insulin signaling pathway. Overall, our findings suggest that Que plays a significant role in delaying adult stem cell aging.

Shortened lifespan induced by a high-glucose diet is associated with intestinal immune dysfunction in Drosophila sechellia

Organisms can generally be divided into two nutritional groups: generalists that consume various types of food and specialists that consume specific types of food. However, it remains unclear how specialists adapt to only limited nutritional conditions in nature. In this study, we addressed this question by focusing on Drosophila fruit flies. The generalist Drosophila melanogaster can consume a wide variety of foods that contain high glucose levels. In contrast, the specialist Drosophila sechellia consumes only the Indian mulberry, known as noni (Morinda citrifolia), which contains relatively little glucose. We showed that the lifespan of D. sechellia was significantly shortened under a high-glucose diet, but this effect was not observed for D. melanogaster. In D. sechellia, a high-glucose diet induced disorganization of the gut epithelia and visceral muscles, which was associated with abnormal digestion and constipation. RNA-sequencing analysis revealed that many immune-responsive genes were suppressed in the gut of D. sechellia fed a high-glucose diet compared with those fed a control diet. Consistent with this difference in the expression of immune-responsive genes, high glucose-induced phenotypes were restored by the addition of tetracycline or scopoletin, a major nutritional component of noni, each of which suppresses gut bacterial growth. We propose that, in D. sechellia, a high-glucose diet impairs gut immune function, which leads to a change in gut microbiota, disorganization of the gut epithelial structure and a shortened lifespan.

Tiny Drosophila intestinal stem cells, big power

The signaling pathways are highly conserved between Drosophila and mammals concerning intestinal development, regeneration, and disease. The powerful genetic tools of Drosophila make it a valuable and convenient alternative to answer basic biological questions that can not be addressed using mammalian models. In this review, we discuss recent advances in how we use fly midgut to answer the following key questions: (1) How intestine stem cell niches are established; (2) which factors control asymmetric division of stem cells; (3) how intestinal cells interact with environmental factors, such as tissue damage, microbiota, and diet; (4) how to screen aging/cancer-related factors or drugs by fly intestine stem cells.

Drosophila as a Model Organism to Study Basic Mechanisms of Longevity

The spatio-temporal regulation of gene expression determines the fate and function of various cells and tissues and, as a consequence, the correct development and functioning of complex organisms. Certain mechanisms of gene activity regulation provide adequate cell responses to changes in environmental factors. Aside from gene expression disorders that lead to various pathologies, alterations of expression of particular genes were shown to significantly decrease or increase the lifespan in a wide range of organisms from yeast to human. Drosophila fruit fly is an ideal model system to explore mechanisms of longevity and aging due to low cost, easy handling and maintenance, large number of progeny per adult, short life cycle and lifespan, relatively low number of paralogous genes, high evolutionary conservation of epigenetic mechanisms and signalling pathways, and availability of a wide range of tools to modulate gene expression in vivo. Here, we focus on the organization of the evolutionarily conserved signaling pathways whose components significantly influence the aging process and on the interconnections of these pathways with gene expression regulation.

Long-lasting geroprotection from brief rapamycin treatment in early adulthood by persistently increased intestinal autophagy

The licensed drug rapamycin has potential to be repurposed for geroprotection. A key challenge is to avoid adverse side effects from continuous dosing. Here we show that geroprotective effects of chronic rapamycin treatment can be obtained with a brief pulse of the drug in early adulthood in female Drosophila and mice. In Drosophila, a brief, early rapamycin treatment of adults extended lifespan and attenuated age-related decline in the intestine to the same degree as lifelong dosing. Lasting memory of earlier treatment was mediated by elevated autophagy in intestinal enterocytes, accompanied by increased levels of intestinal LManV and lysozyme. Brief elevation of autophagy in early adulthood itself induced a long-term increase in autophagy. In mice, a 3-month, early treatment also induced a memory effect, with maintenance similar to chronic treatment, of lysozyme distribution, Man2B1 level in intestinal crypts, Paneth cell architecture and gut barrier function, even 6 months after rapamycin was withdrawn.

Deletions of the cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) genes, involved in the control of hydrogen sulfide biosynthesis, significantly affect lifespan and fitness components of Drosophila melanogaster

The gasotransmitter hydrogen sulfide (H2S) is an important biological mediator, playing an essential role in many physiological and pathological processes. It is produced by transsulfuration - an evolutionarily highly conserved pathway for the metabolism of sulfur-containing amino acids methionine and cysteine. Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) enzymes play a central role in cysteine metabolism and H2S production. Here we investigated the fitness components (longevity, stress resistance, viability of preimaginal stages, and reproductive function parameters) in D. melanogaster lines containing deletions of the CBS and CSE genes. Surprisingly, in most tests, CSE deletion improved, and CBS worsened the fitness. Lines with deletion of both CBS and CSE demonstrated better stress resistance and longevity than lines with single CBS deletion. At the same time, deletion of both CBS and CSE genes causes more serious disturbances of reproductive function parameters than single CBS deletion. Thus, a complex interaction of H2S-producing pathways and cellular stress response in determining the lifespan and fitness components of the whole organism was revealed.

The MicroRNA miR-277 Controls Physiology and Pathology of the Adult Drosophila Midgut by Regulating the Expression of Fatty Acid β-Oxidation-Related Genes in Intestinal Stem Cells

Cell division, growth, and differentiation are energetically costly and dependent processes. In adult stem cell-based epithelia, cellular identity seems to be coupled with a cell's metabolic profile and vice versa. It is thus tempting to speculate that resident stem cells have a distinct metabolism, different from more committed progenitors and differentiated cells. Although investigated for many stem cell types in vitro, in vivo data of niche-residing stem cell metabolism is scarce. In adult epithelial tissues, stem cells, progenitor cells, and their progeny have very distinct functions and characteristics. In our study, we hypothesized and tested whether stem and progenitor cell types might have a distinctive metabolic profile in the intestinal lineage. Here, taking advantage of the genetically accessible adult Drosophila melanogaster intestine and the availability of ex vivo single cell sequencing data, we tested that hypothesis and investigated the metabolism of the intestinal lineage from stem cell (ISC) to differentiated epithelial cell in their native context under homeostatic conditions. Our initial in silico analysis of single cell RNAseq data and functional experiments identify the microRNA miR-277 as a posttranscriptional regulator of fatty acid β-oxidation (FAO) in the intestinal lineage. Low levels of miR-277 are detected in ISC and progressively rising miR-277 levels are found in progenitors during their growth and differentiation. Supporting this, miR-277-regulated fatty acid β-oxidation enzymes progressively declined from ISC towards more differentiated cells in our pseudotime single-cell RNAseq analysis and in functional assays on RNA and protein level. In addition, in silico clustering of single-cell RNAseq data based on metabolic genes validates that stem cells and progenitors belong to two independent clusters with well-defined metabolic characteristics. Furthermore, studying FAO genes in silico indicates that two populations of ISC exist that can be categorized in mitotically active and quiescent ISC, of which the latter relies on FAO genes. In line with an FAO dependency of ISC, forced expression of miR-277 phenocopies RNAi knockdown of FAO genes by reducing ISC size and subsequently resulting in stem cell death. We also investigated miR-277 effects on ISC in a benign and our newly developed CRISPR-Cas9-based colorectal cancer model and found effects on ISC survival, which as a consequence affects tumor growth, further underlining the importance of FAO in a pathological context. Taken together, our study provides new insights into the basal metabolic requirements of intestinal stem cell on β-oxidation of fatty acids evolutionarily implemented by a sole microRNA. Gaining knowledge about the metabolic differences and dependencies affecting the survival of two central and cancer-relevant cell populations in the fly and human intestine might reveal starting points for targeted combinatorial therapy in the hope for better treatment of colorectal cancer in the future.

Nutrient Sensing via Gut in Drosophila melanogaster

Nutrient-sensing mechanisms in animals' sense available nutrients to generate a physiological regulatory response involving absorption, digestion, and regulation of food intake and to maintain glucose and energy homeostasis. During nutrient sensing via the gastrointestinal tract, nutrients interact with receptors on the enteroendocrine cells in the gut, which in return respond by secreting various hormones. Sensing of nutrients by the gut plays a critical role in transmitting food-related signals to the brain and other tissues informing the composition of ingested food to digestive processes. These signals modulate feeding behaviors, food intake, metabolism, insulin secretion, and energy balance. The increasing significance of fly genetics with the availability of a vast toolbox for studying physiological function, expression of chemosensory receptors, and monitoring the gene expression in specific cells of the intestine makes the fly gut the most useful tissue for studying the nutrient-sensing mechanisms. In this review, we emphasize on the role of Drosophila gut in nutrient-sensing to maintain metabolic homeostasis and gut-brain cross talk using endocrine and neuronal signaling pathways stimulated by internal state or the consumption of various dietary nutrients. Overall, this review will be useful in understanding the post-ingestive nutrient-sensing mechanisms having a physiological and pathological impact on health and diseases.

Selective autophagy controls innate immune response through a TAK1/TAB2/SH3PX1 axis

Selective autophagy is a catabolic route that turns over specific cellular material for degradation by lysosomes, and whose role in the regulation of innate immunity is largely unexplored. Here, we show that the apical kinase of the Drosophila immune deficiency (IMD) pathway Tak1, as well as its co-activator Tab2, are both selective autophagy substrates that interact with the autophagy protein Atg8a. We also present a role for the Atg8a-interacting protein Sh3px1 in the downregulation of the IMD pathway, by facilitating targeting of the Tak1/Tab2 complex to the autophagy platform through its interaction with Tab2. Our findings show the Tak1/Tab2/Sh3px1 interactions with Atg8a mediate the removal of the Tak1/Tab2 signaling complex by selective autophagy. This in turn prevents constitutive activation of the IMD pathway in Drosophila. This study provides mechanistic insight on the regulation of innate immune responses by selective autophagy.

The Mechanism of Stem Cell Aging

Stem cells have self-renewal ability and multi-directional differentiation potential. They have tissue repair capabilities and are essential for maintaining the tissue homeostasis. The depletion of stem cells is closely related to the occurrence of body aging and aging-related diseases. Therefore, revealing the molecular mechanisms of stem cell aging will set new directions for the therapeutic application of stem cells, the study of aging mechanisms, and the prevention and treatment of aging-related diseases. This review comprehensively describes the molecular mechanisms related to stem cell aging and provides the basis for further investigations aimed at developing new anti-stem cell aging strategies and promoting the clinical application of stem cells.

The Aged Intestine: Performance and Rejuvenation

Owing to the growing elderly population, age-related problems are gaining increasing attention from the scientific community. With senescence, the intestine undergoes a spectrum of changes and infirmities that are likely the causes of overall aging. Therefore, identification of the aged intestine and the search for novel strategies to rescue it, are required. Although progress has been made in research on some components of the aged intestine, such as intestinal stem cells, the comprehensive understanding of intestinal aging is still limited, and this restricts the in-depth search for efficient strategies. In this concise review, we discuss several aspects of intestinal aging. More emphasis is placed on the appraisal of current and potential strategies to alleviate intestinal aging, as well as future targets to rejuvenate the aged intestine.

Antioxidant Effects of Caffeic Acid Lead to Protection of Drosophila Intestinal Stem Cell Aging

The dysfunction or exhaustion of adult stem cells during aging is closely linked to tissue aging and age-related diseases. Circumventing this aging-related exhaustion of adult stem cells could significantly alleviate the functional decline of organs. Therefore, identifying small molecular compounds that could prevent the age-related decline of stem cell function is a primary goal in anti-aging research. Caffeic acid (CA), a phenolic compound synthesized in plants, offers substantial health benefits for multiple age-related diseases and aging. However, the effects of CA on adult stem cells remain largely unknown. Using the Drosophila midgut as a model, this study showed that oral administration with CA significantly delayed age-associated Drosophila gut dysplasia caused by the dysregulation of intestinal stem cells (ISCs) upon aging. Moreover, administering CA retarded the decline of intestinal functions in aged Drosophila and prevented hyperproliferation of age-associated ISC by suppressing oxidative stress-associated JNK signaling. On the other hand, CA supplementation significantly ameliorated the gut hyperplasia defect and reduced environmentally induced mortality, revealing the positive effects of CA on tolerance to stress responses. Taken together, our findings report a crucial role of CA in delaying age-related changes in ISCs of Drosophila.

Multiscale analysis reveals that diet-dependent midgut plasticity emerges from alterations in both stem cell niche coupling and enterocyte size

The gut is the primary interface between an animal and food, but how it adapts to qualitative dietary variation is poorly defined. We find that the Drosophila midgut plastically resizes following changes in dietary composition. A panel of nutrients collectively promote gut growth, which sugar opposes. Diet influences absolute and relative levels of enterocyte loss and stem cell proliferation, which together determine cell numbers. Diet also influences enterocyte size. A high sugar diet inhibits translation and uncouples intestinal stem cell proliferation from expression of niche-derived signals, but, surprisingly, rescuing these effects genetically was not sufficient to modify diet’s impact on midgut size. However, when stem cell proliferation was deficient, diet’s impact on enterocyte size was enhanced, and reducing enterocyte-autonomous TOR signaling was sufficient to attenuate diet-dependent midgut resizing. These data clarify the complex relationships between nutrition, epithelial dynamics, and cell size, and reveal a new mode of plastic, diet-dependent organ resizing.

JNK Signaling in Drosophila Aging and Longevity

The evolutionarily conserved c-Jun N-terminal kinase (JNK) signaling pathway is a critical genetic determinant in the control of longevity. In response to extrinsic and intrinsic stresses, JNK signaling is activated to protect cells from stress damage and promote survival. In Drosophila, global JNK upregulation can delay aging and extend lifespan, whereas tissue/organ-specific manipulation of JNK signaling impacts lifespan in a context-dependent manner. In this review, focusing on several tissues/organs that are highly associated with age-related diseases-including metabolic organs (intestine and fat body), neurons, and muscles-we summarize the distinct effects of tissue/organ-specific JNK signaling on aging and lifespan. We also highlight recent progress in elucidating the molecular mechanisms underlying the tissue-specific effects of JNK activity. Together, these studies highlight an important and comprehensive role for JNK signaling in the regulation of longevity in Drosophila.

Regeneration, Rejuvenation, and Replacement: Turning Back the Clock on Tissue Aging

While some animals, such as planaria and hydra, appear to be capable of seemingly endless cycles of regeneration, most animals experience a gradual decline in fitness and ultimately die. The progressive loss of cell and tissue function, leading to senescence and death, is generally referred to as aging. Adult ("tissue") stem cells maintain tissue homeostasis and facilitate repair; however, age-related changes in stem cell function over time are major contributors to loss of organ function or disease in older individuals. Therefore, considerable effort is being invested in restoring stem cell function to counter degenerative diseases and age-related tissue dysfunction. Here, we will review strategies that could be used to restore stem cell function, including the use of environmental interventions, such as diet and exercise, heterochronic approaches, and cellular reprogramming. Maintaining optimal stem cell function and tissue homeostasis into late life will likely extend the amount of time older adults are able to be independent and lead healthy lives.

Balancing DNA repair to prevent ageing and cancer

DNA damage is a constant stressor to the cell. Persistent damage to the DNA over time results in an increased risk of mutation and an accumulation of mutations with age. Loss of efficient DNA damage repair can lead to accelerated ageing phenotypes or an increased cancer risk, and the trade-off between cancer susceptibility and longevity is often driven by the cell's response to DNA damage. High levels of mutations in DNA repair mutants often leads to excessive cell death and stem cell exhaustion which may promote premature ageing. Stem cells themselves have distinct characteristics that enable them to retain low mutation rates. However, when mutations do arise, stem cell clonal expansion can also contribute to age-related tissue dysfunction as well as heightened cancer risk. In this review, we will highlight increasing DNA damage and mutation accumulation as hallmarks common to both ageing and cancer. We will propose that anti-ageing interventions might be cancer preventative and discuss the mechanisms through which they may act.

Roles of mitochondrial unfolded protein response in mammalian stem cells

The mitochondrial unfolded protein response (UPRmt) is an evolutionarily conserved adaptive mechanism for improving cell survival under mitochondrial stress. Under physiological and pathological conditions, the UPRmt is the key to maintaining intracellular homeostasis and proteostasis. Important roles of the UPRmt have been demonstrated in a variety of cell types and in cell development, metabolism, and immune processes. UPRmt dysfunction leads to a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease, and immune disease. Stem cells have a special ability to self-renew and differentiate into a variety of somatic cells and have been shown to exist in a variety of tissues. These cells are involved in development, tissue renewal, and some disease processes. Although the roles and regulatory mechanisms of the UPRmt in somatic cells have been widely reported, the roles of the UPRmt in stem cells are not fully understood. The roles and functions of the UPRmt depend on stem cell type. Therefore, this paper summarizes the potential significance of the UPRmt in embryonic stem cells, tissue stem cells, tumor stem cells, and induced pluripotent stem cells. The purpose of this review is to provide new insights into stem cell differentiation and tumor pathogenesis.

Purple sweet potato extract maintains intestinal homeostasis and extend lifespan through increasing autophagy in female Drosophila melanogaster

Purple sweet potatoes extract (PSPE) have been used as a natural food antioxidant with high anthocyanin concentrations. Research investigated the lifespan and the mechanisms of PSPE on female Drosophila melanogaster. Supplementation of PSPE extended the lifespan by 16.3% and had a protective effect on injury by oxidative stress. PSPE treatment enhanced the endogenous antioxidant enzyme activity and reduced malondialdehyde (MDA) content. Furthermore, PSPE significantly up-regulated foxo-related genes, inhibited mTOR mRNA expression, and activated autophagy to maintain intestinal homeostasis. Meanwhile, PSPE improved intestinal barrier dysfunction by 22.86%, decelerated the abnormal proliferation rate of intestinal stem cell (ISCs) by 23.77%, and improved intestinal integrity in geriatric D. melanogaster. In conclusion, PSPE may maintain intestinal homeostasis, and improve the antioxidant and stress resistance capacity through the insulin and rapamycin pathway, thereby extending the lifespan. Therefore, it provides active support to the development and application of PSPE in functional food. PRACTICAL APPLICATIONS: In recent years, with the increase of age, age-related complications have generally increased and seriously affected people's healthy life. Purple sweet potato is a nutrient-rich substance, which not only has a unique color but also contains rich anthocyanins, so it has many potential biological and pharmacological functions. Our results showed that the PSPE had a good effect of maintaining the intestinal homeostasis of the older adult, and provided a favorable theoretical basis for the development of PSPE functional products and scientific academic research.

Aging-related upregulation of the homeobox gene caudal represses intestinal stem cell differentiation in Drosophila

The differentiation efficiency of adult stem cells undergoes a significant decline in aged animals, which is closely related to the decline in organ function and age-associated diseases. However, the underlying mechanisms that ultimately lead to this observed decline of the differentiation efficiency of stem cells remain largely unclear. This study investigated Drosophila midguts and identified an obvious upregulation of caudal (cad), which encodes a homeobox transcription factor. This factor is traditionally known as a central regulator of embryonic anterior-posterior body axis patterning. This study reports that depletion of cad in intestinal stem/progenitor cells promotes quiescent intestinal stem cells (ISCs) to become activate and produce enterocytes in the midgut under normal gut homeostasis conditions. However, overexpression of cad results in the failure of ISC differentiation and intestinal epithelial regeneration after injury. Moreover, this study suggests that cad prevents intestinal stem/progenitor cell differentiation by modulating the Janus kinase/signal transducers and activators of the transcription pathway and Sox21a-GATAe signaling cascade. Importantly, the reduction of cad expression in intestinal stem/progenitor cells restrained age-associated gut hyperplasia in Drosophila. This study identified a function of the homeobox gene cad in the modulation of adult stem cell differentiation and suggested a potential gene target for the treatment of age-related diseases induced by age-related stem cell dysfunction.

Adult stem cells undergo an aging-related decline of differentiation efficiency in aged animals. However, the underlying mechanisms that ultimately lead to this observed decline of differentiation efficiency in stem cells still remain largely unclear. By using the Drosophila midgut as a model system, this study identified the homeobox family transcription factor gene caudal (cad), the expression of which is significantly upregulated in intestinal stem cells (ISCs) and progenitor cells of aged Drosophila. Depletion of cad promoted quiescent ISCs to become activate and produce enterocytes (ECs) in midguts under normal gut homeostasis conditions; However, overexpression of cad resulted in the failure of ISC differentiation and intestinal epithelial regeneration after injury. Moreover, cad prevents ISC-to-EC differentiation by inhibiting JAK/STAT signaling, and the expressions of Sox21a and GATAe. Reduction of cad expression in intestinal stem/progenitor cells restrained age-associated gut hyperplasia in Drosophila. These findings enable a detailed understanding of the roles of homeobox genes in the modulation of adult stem cell aging in humans. This will be beneficial for the treatment of age-associated diseases that are caused by a functional decline of stem cells.

The Drosophila model to interrogate triacylglycerol biology

The deposition of storage fat in the form of triacylglycerol (TAG) is an evolutionarily conserved strategy to cope with fluctuations in energy availability and metabolic stress. Organismal TAG storage in specialized adipose tissues provides animals a metabolic reserve that sustains survival during development and starvation. On the other hand, excessive accumulation of adipose TAG, defined as obesity, is associated with an increasing prevalence of human metabolic diseases. During the past decade, the fruit fly Drosophila melanogaster, traditionally used in genetics and developmental biology, has been established as a versatile model system to study TAG metabolism and the etiology of lipid-associated metabolic diseases. Similar to humans, Drosophila TAG homeostasis relies on the interplay of organ systems specialized in lipid uptake, synthesis, and processing, which are integrated by an endocrine network of hormones and messenger molecules. Enzymatic formation of TAG from sugar or dietary lipid, its storage in lipid droplets, and its mobilization by lipolysis occur via mechanisms largely conserved between Drosophila and humans. Notably, dysfunctional Drosophila TAG homeostasis occurs in the context of aging, overnutrition, or defective gene function, and entails tissue-specific and organismal pathologies that resemble human disease. In this review, we summarize the physiology and biochemistry of TAG in Drosophila and outline the potential of this organism as a model system to understand the genetic and dietary basis of TAG storage and TAG-related metabolic disorders.

The Emerging Roles of JNK Signaling in Drosophila Stem Cell Homeostasis

The Jun N-terminal kinase (JNK) pathway is an evolutionary conserved kinase cascade best known for its roles during stress-induced apoptosis and tumor progression. Recent findings, however, have identified new roles for this pleiotropic pathway in stem cells during regenerative responses and in cellular plasticity. Here, we provide an overview of recent findings about the new roles of JNK signaling in stem cell biology using two well-established Drosophila models: the testis and the intestine. We highlight the pathway’s roles in processes such as proliferation, death, self-renewal and reprogramming, and discuss the known parallels between flies and mammals.

Functional conservation in genes and pathways linking ageing and immunity

At first glance, longevity and immunity appear to be different traits that have not much in common except the fact that the immune system promotes survival upon pathogenic infection. Substantial evidence however points to a molecularly intertwined relationship between the immune system and ageing. Although this link is well-known throughout the animal kingdom, its genetic basis is complex and still poorly understood. To address this question, we here provide a compilation of all genes concomitantly known to be involved in immunity and ageing in humans and three well-studied model organisms, the nematode worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the house mouse Mus musculus. By analysing human orthologs among these species, we identified 7 evolutionarily conserved signalling cascades, the insulin/TOR network, three MAPK (ERK, p38, JNK), JAK/STAT, TGF-β, and Nf-κB pathways that act pleiotropically on ageing and immunity. We review current evidence for these pathways linking immunity and lifespan, and their role in the detrimental dysregulation of the immune system with age, known as immunosenescence. We argue that the phenotypic effects of these pathways are often context-dependent and vary, for example, between tissues, sexes, and types of pathogenic infection. Future research therefore needs to explore a higher temporal, spatial and environmental resolution to fully comprehend the connection between ageing and immunity.