Age-related changes in Drosophila midgut are associated with PVF2, a PDGF/VEGF-like growth factor

The sex of organ geometry

Organs have a distinctive yet often overlooked spatial arrangement in the body1-5. We propose that there is a logic to the shape of an organ and its proximity to its neighbours. Here, by using volumetric scans of many Drosophila melanogaster flies, we develop methods to quantify three-dimensional features of organ shape, position and interindividual variability. We find that both the shapes of organs and their relative arrangement are consistent yet differ between the sexes, and identify unexpected interorgan adjacencies and left-right organ asymmetries. Focusing on the intestine, which traverses the entire body, we investigate how sex differences in three-dimensional organ geometry arise. The configuration of the adult intestine is only partially determined by physical constraints imposed by adjacent organs; its sex-specific shape is actively maintained by mechanochemical crosstalk between gut muscles and vascular-like trachea. Indeed, sex-biased expression of a muscle-derived fibroblast growth factor-like ligand renders trachea sexually dimorphic. In turn, tracheal branches hold gut loops together into a male or female shape, with physiological consequences. Interorgan geometry represents a previously unrecognized level of biological complexity which might enable or confine communication across organs and could help explain sex or species differences in organ function.

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.

Lactobacillus reuteri's multifaceted role in mitigating ionizing radiation-induced injury in Drosophila melanogaster

The numerous beneficial probiotic properties of Lactobacillus reuteri (L. reuteri) include decreasing metabolic syndrome, preventing disorders linked to oxidative stress, improving gut flora imbalances, controlling immunological function, and extending life span. Exposure to ionizing radiation is closely associated with several disorders. We examined the protective and salvaging effects of L. reuteri on ionizing radiation-induced injury to the intestinal tract, reproductive system, and nervous system of Drosophila melanogaster. We also examined its effects on lifespan, antioxidant capacity, progeny development, and behavioral aspects to assess the interaction between L. reuteri and ionizing radiation-induced injury. The findings demonstrated that L. reuteri improved the median survival time following irradiation and greatly extended its lifespan. In addition, it raised SOD activity, reduced ROS levels in intestinal epithelial cells, and increased the quantity of intestinal stem cells. Furthermore, L. reuteri enhanced the adult male flies' capacity to move. It also successfully safeguarded the generations' growth and development. L. reuteri dramatically enhanced expression of the AMPKα gene and regulated expression of its pathway-related gene, mTOR, as well as the autophagy-related genes Atg1 and Atg5 in female Drosophila exposed to irradiation. Notably, no prior reports have been made on the possible effects of L. reuteri on injuries caused by irradiation. As a result, our research offers important new information regarding L. reuteri's possible role as a shield against ionizing radiation-induced injury.

The zinc finger protein CG12744 regulates intestinal stem cells in aged Drosophila through the EGFR and BMP pathways

AIM

Aging is a process characterized by a time-dependent decline in the functionality of adult stem cells and is closely associated with age-related diseases. However, understanding how aging promotes disease and its underlying causes is critical for combating aging.

MAIN METHODS

The offspring of UAS-Gal4 and CG12744RNAiDrosophila were cultured for 33 days to evaluate the role of CG12744 in the aging intestine. Immunofluorescence was performed to detect specific cell type markers for assessing proliferation and differentiation. qRT-PCR was used to observe the changes in signaling regulating intestinal homeostasis in the aging intestine after CG12744 knockdown. 16S rRNA-seq analysis was also conducted to elucidate the role of gut microbes in CG12744-mediated intestinal dysfunction.

KEY FINDINGS

The mRNA levels of CG12744 were significantly increased in the aged midguts. Knockdown of CG12744 in progenitor cells further exacerbates the age-related intestinal hyperplasia and dysfunction. In particular, upon depletion of CG12744 in progenitors, enteroblasts (EBs) exhibited an increased propensity to differentiate along the enteroendocrine cell (EE) lineage. In contrast, the overexpression of CG12744 in progenitor cells restrained age-related gut hyperplasia in Drosophila. Moreover, CG12744 prevented age-related intestinal stem cell (ISC) overproliferation and differentiation by modulating the EGFR, JNK, and BMP pathways. In addition, the inhibition of CG12744 resulted in a significant increase in the gut microbial composition in aging flies.

SIGNIFICANCE

This study established a role for the CG12744 in regulating the proliferation and differentiation of adult stem cells, thereby identifying a potential therapeutic target for diseases caused by age-related dysfunction stem cell dysfunction.

Stem cell mTOR signaling directs region-specific cell fate decisions during intestinal nutrient adaptation

The adult intestine is a regionalized organ, whose size and cellular composition are adjusted in response to nutrient status. This involves dynamic regulation of intestinal stem cell (ISC) proliferation and differentiation. How nutrient signaling controls cell fate decisions to drive regional changes in cell-type composition remains unclear. Here, we show that intestinal nutrient adaptation involves region-specific control of cell size, cell number, and differentiation. We uncovered that activation of mTOR complex 1 (mTORC1) increases ISC size in a region-specific manner. mTORC1 activity promotes Delta expression to direct cell fate toward the absorptive enteroblast lineage while inhibiting secretory enteroendocrine cell differentiation. In aged flies, the ISC mTORC1 signaling is deregulated, being constitutively high and unresponsive to diet, which can be mitigated through lifelong intermittent fasting. In conclusion, mTORC1 signaling contributes to the ISC fate decision, enabling regional control of intestinal cell differentiation in response to nutrition.

The anti-aging effect of vitamin D and vitamin D receptor in Drosophila midgut

Adult stem cells are pivotal for maintaining tissue homeostasis, and their functional decline is linked to aging and its associated diseases, influenced by the niche cells' environment. Age- and cancer-related reduction of vitamin D and its receptor levels are well documented in human clinical studies. However, the mechanisms through which the vitamin D/vitamin D receptor pathway contributes to anti-aging and extends life expectancy are not well understood. In this study, we aimed to determine the protective role of the vitamin D/vitamin D receptor pathway in differentiated enterocytes (ECs) during intestinal stem cell (ISC) aging. By utilizing a well- established Drosophila midgut model for stem cell aging biology, we revealed that vitamin D receptor knockdown in ECs induced ISC proliferation, EC death, ISC aging, and enteroendocrine cell differentiation. Additionally, age- and oxidative stress-induced increases in ISC proliferation and centrosome amplification were reduced by vitamin D treatment. Our findings suggest a direct evidence of the anti-aging role of the vitamin D/vitamin D receptor pathway and provides insights into the molecular mechanisms underlying healthy aging in Drosophila.

The midgut epithelium of mosquitoes adjusts cell proliferation and endoreplication to respond to physiological challenges

BACKGROUND

Hematophagous mosquitoes transmit many pathogens that cause human diseases. Pathogen acquisition and transmission occur when female mosquitoes blood feed to acquire nutrients for reproduction. The midgut epithelium of mosquitoes serves as the point of entry for transmissible viruses and parasites.

RESULTS

We studied midgut epithelial dynamics in five major mosquito vector species by quantifying PH3-positive cells (indicative of mitotic proliferation), the incorporation of nucleotide analogs (indicative of DNA synthesis accompanying proliferation and/or endoreplication), and the ploidy (by flow cytometry) of cell populations in the posterior midgut epithelium of adult females. Our results show that the epithelial dynamics of post-emergence maturation and of mature sugar-fed guts were similar in members of the Aedes, Culex, and Anopheles genera. In the first three days post-emergence, ~ 20% of cells in the posterior midgut region of interest incorporated nucleotide analogs, concurrent with both proliferative activity and a broad shift toward higher ploidy. In mature mosquitoes maintained on sugar, an average of 3.5% of cells in the posterior midgut region of interest incorporated nucleotide analogs from five to eight days post-emergence, with a consistent presence of mitotic cells indicating constant cell turnover. Oral bacterial infection triggered a sharp increase in mitosis and nucleotide analog incorporation, suggesting that the mosquito midgut undergoes accelerated cellular turnover in response to damage. Finally, blood feeding resulted in an increase in cell proliferation, but the nature and intensity of the response varied by mosquito species and by blood source (human, bovine, avian or artificial). In An. gambiae, enterocytes appeared to reenter the cell cycle to increase ploidy after consuming blood from all sources except avian.

CONCLUSIONS

We saw that epithelial proliferation, differentiation, and endoreplication reshape the blood-fed gut to increase ploidy, possibly to facilitate increased metabolic activity. Our results highlight the plasticity of the midgut epithelium in mosquitoes' physiological responses to distinct challenges.

Ginseng promotes the function of intestinal stem cells through the Wnt/β-catenin signaling pathway in D-galactose-induced aging mice

BACKGROUND

Intestinal stem cells (ISCs) are the reservoir source of various types of intestinal cells, and the decline of stem cell function in the gut may be a potential factor for aging-related disease. The present study aimed to explore the regulatory mechanisms of Panax ginseng C.A.Meyer (Araliaceae, Panax genus) that could restore gut aging by enhancing intestinal function and regulating ISCs in aging mice based on the Wnt/β-catenin signaling pathway.

METHODS

A total of 60 ICR male mice were randomly divided into control, model, metformin, and ginseng water decoction (GWD) 3.6, 1.8, and 0.9 g/kg groups. The aging model was induced by 1 % D-galactose (s.c. 0.1 mL/10 g) for 28 days. Moreover, GWD was given to aging mice intragastrically (i.g.) once a day for 28 successive days. The learning memory ability, pathological status, and function in the ileum tissue, the activity of digestive enzymes, and short-chain fatty acid (SCFA) content in the colon were evaluated, and the related mechanism was investigated.

RESULTS

Ginseng can decrease the escape latency time and increase the swimming speed and the number of crossing platforms in aging mice. Moreover, the pathology of ileum tissue improved, the length of the intestinal villi increased, and the width of the villi and the depth of the crypts decreased. The activities of trypsin, α-amylase, and lipase increased in duodenal content and intestinal mucosa. In the colon, the content of SCFA, such as acetic acid, propionic acid and butyric acid, increased, indicating that ginseng significantly improves intestinal function impairment. The mRNA expressions and protein levels of β-catenin, C-myc, GSK-3β, Lgr5, and Olfm4 were upregulated in the ginseng group.

CONCLUSIONS

Ginseng improves intestinal function and regulates the function of ISCs in order to protect intestinal health by activating the Wnt/β-catenin signaling pathway in aging mice.

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.

Pvr regulates cyst stem cell division in the Drosophila testis niche, and has functions distinct from Egfr

Regulation of the rate of stem cell division is one of the key determinants of the abundance of differentiating progeny in stem cell-supported tissues, and mis-regulation can lead to tumorigenesis. The well-studied Drosophila testis niche is an excellent model system to study the regulation of stem cell division in vivo. This niche supports two stem cell populations-the germline stem cells (GSCs) and cyst stem cells (CySCs), which cluster around a group of cells called the hub. The differentiating cells of these two stem cell populations cooperate together to produce sperm. Signal transduction initiated by the epidermal growth factor receptor (Egfr) is a key regulatory pathway in the cyst lineage, and much of the study of this stem cell population has centered around understanding the complexities of the requirements for Egfr signaling. We examined another receptor tyrosine kinase, Pvr, the sole Drosophila PDGF/VEGF homolog, and found that it accumulates in the cyst lineage cells of the testis, while its ligand Pvf1 accumulates in the hub. Pvr inhibition caused a reduction in both CySC numbers and the proportion of CySCs in S phase, similar to Egfr inhibition. However, testes with Pvr inhibition exhibited a low-penetrance non-autonomous germ cell differentiation defect distinct from that observed with Egfr inhibition. Cyst cells with constitutively activated Pvr failed to support germ cell differentiation, as observed with constitutively activated Egfr. However, constitutively activated Pvr promoted tumorous accumulation of cyst cells outside of the niche, a phenotype not observed with constitutively activated Egfr. Thus, Egfr and Pvr have some receptor-specific functions and some shared functions in the cyst lineage cells of the testis.

Molecular and Therapeutic Insights of Alpha-Lipoic Acid as a Potential Molecule for Disease Prevention

Alpha-lipoic acid is an organic, sulfate-based compound produced by plants, humans, and animals. As a potent antioxidant and a natural dithiol compound, it performs a crucial role in mitochondrial bioenergetic reactions. A healthy human body, on the other hand, can synthesize enough α-lipoic acid to scavenge reactive oxygen species and increase endogenous antioxidants; however, the amount of α-lipoic acid inside the body decreases significantly with age, resulting in endothelial dysfunction. Molecular orbital energy and spin density analysis indicate that the sulfhydryl (-SH) group of molecules has the greatest electron donating activity, which would be responsible for the antioxidant potential and free radical scavenging activity. α-Lipoic acid acts as a chelating agent for metal ions, a quenching agent for reactive oxygen species, and a reducing agent for the oxidized form of glutathione and vitamins C and E. α-Lipoic acid enantiomers and its reduced form have antioxidant, cognitive, cardiovascular, detoxifying, anti-aging, dietary supplement, anti-cancer, neuroprotective, antimicrobial, and anti-inflammatory properties. α-Lipoic acid has cytotoxic and antiproliferative effects on several cancers, including polycystic ovarian syndrome. It also has usefulness in the context of female and male infertility. Although α-lipoic acid has numerous clinical applications, the majority of them stem from its antioxidant properties; however, its bioavailability in its pure form is low (approximately 30%). However, nanoformulations have shown promise in this regard. The proton affinity and electron donating activity, as a redox-active agent, would be responsible for the antioxidant potential and free radical scavenging activity of the molecule. This review discusses the most recent clinical data on α-lipoic acid in the prevention, management, and treatment of a variety of diseases, including coronavirus disease 2019. Based on current evidence, the preclinical and clinical potential of this molecule is discussed.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43450-023-00370-1.

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.

The impact of aging on intestinal mucosal immune function and clinical applications

Immune cells and immune molecules in the intestinal mucosa participate in innate and adaptive immunity to maintain local and systematic homeostasis. With aging, intestinal mucosal immune dysfunction will promote the emergence of age-associated diseases. Although there have been a number of studies on the impact of aging on systemic immunity, relatively fewer studies have been conducted on the impact of aging on the intestinal mucosal immune system. In this review, we will briefly introduce the impact of aging on the intestinal mucosal barrier, the impact of aging on intestinal immune cells as well as immune molecules, and the process of interaction between intestinal mucosal immunity and gut microbiota during aging. After that we will discuss potential strategies to slow down intestinal aging in the elderly.

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.

INDY-From Flies to Worms, Mice, Rats, Non-Human Primates, and Humans

I’m Not Dead Yet (Indy) is a fly homologue of the mammalian SLC13A5 (mSLC13A5) plasma membrane citrate transporter, a key metabolic regulator and energy sensor involved in health, longevity, and disease. Reduction of Indy gene activity in flies, and its homologs in worms, modulates metabolism and extends longevity. The metabolic changes are similar to what is obtained with caloric restriction (dietary restriction). Similar effects on metabolism have been observed in mice and rats. As a citrate transporter, INDY regulates cytoplasmic citrate levels. Indy flies heterozygous for a P-element insertion have increased spontaneous physical activity, increased fecundity, reduced insulin signaling, increased mitochondrial biogenesis, preserved intestinal stem cell homeostasis, lower lipid levels, and increased stress resistance. Mammalian Indy knockout (mIndy-KO) mice have higher sensitivity to insulin signaling, lower blood pressure and heart rate, preserved memory and are protected from the negative effects of a high-fat diet and some of the negative effects of aging. Reducing mIndy expression in human hepatocarcinoma cells has recently been shown to inhibit cell proliferation. Reduced Indy expression in the fly intestine affects intestinal stem cell proliferation, and has recently been shown to also inhibit germ cell proliferation in males with delayed sperm maturation and decreased spermatocyte numbers. These results highlight a new connection between energy metabolism and cell proliferation. The overrall picture in a variety of species points to a conserved role of INDY for metabolism and health. This is illustrated by an association of high mIndy gene expression with non-alcoholic fatty liver disease in obese humans. mIndy (mSLC13A5) coding region mutations (e.g., loss-of-function) are also associated with adverse effects in humans, such as autosomal recessive early infantile epileptic encephalopathy and Kohlschütter−Tönz syndrome. The recent findings illustrate the importance of mIndy gene for human health and disease. Furthermore, recent work on small-molecule regulators of INDY highlights the promise of INDY-based treatments for ameliorating disease and promoting healthy aging.

Aging and “rejuvenation” of resident stem cells — a new way to active longevity?

This review presents the current data on the methodology for assessing the biological and epigenetic age, describes the concept of the epigenetic clock, and characterizes the main types of resident stem cells and the specifics of their aging. It has been shown that age-related changes in organs and tissues, as well as age-related diseases, are largely due to the aging of resident stem cells. The latter represent an attractive target for cell rejuvenation, as they can be isolated, cultured ex vivo, modified, and re-introduced into the resident niches. Two main methodologies for the cellular rejuvenation are presented: genetic reprogramming with zeroing the age of a cell using transient expression of transcription factors, and various approaches to epigenetic rejuvenation. The close relationship between aging, regeneration, and oncogenesis, and between these factors and the functioning of resident stem cell niches requires further precision studies, which, we are sure, can result in the creation of an effective anti-aging strategy and prolongation of human active life.

Microbes affect gut epithelial cell composition through immune-dependent regulation of intestinal stem cell differentiation

Gut microbes play important roles in host physiology; however, the mechanisms underlying their impact remain poorly characterized. Here, we demonstrate that microbes not only influence gut physiology but also alter its epithelial composition. The microbiota and pathogens both influence intestinal stem cell (ISC) differentiation. Intriguingly, while the microbiota promotes ISC differentiation into enterocytes (EC), pathogens stimulate enteroendocrine cell (EE) fate and long-term accumulation of EEs in the midgut epithelium. Importantly, the evolutionarily conserved Drosophila NFKB (Relish) pushes stem cell lineage specification toward ECs by directly regulating differentiation factors. Conversely, the JAK-STAT pathway promotes EE fate in response to infectious damage. We propose a model in which the balance of microbial pattern recognition pathways, such as Imd-Relish, and damage response pathways, such as JAK-STAT, influence ISC differentiation, epithelial composition, and gut physiology.

Insect Gut Regeneration

In adult insects, as in vertebrates, the gut epithelium is a highly regenerative tissue that can renew itself rapidly in response to changing inputs from nutrition, the gut microbiota, ingested toxins, and signals from other organs. Because of its cellular and genetic similarities to the mammalian intestine, and its relevance as a target for the control of insect pests and disease vectors, many researchers have used insect intestines to address fundamental questions about stem cell functions during tissue maintenance and regeneration. In Drosophila, where most of the experimental work has been performed, not only are intestinal cell types and behaviors well characterized, but numerous cell signaling interactions have been detailed that mediate gut epithelial regeneration. A prevailing model for regenerative responses in the insect gut invokes stress sensing by damaged enterocytes (ECs) as a principal source for signaling that activates the division of intestinal stem cells (ISCs) and the growth and differentiation of their progeny. However, extant data also reveal alternative mechanisms for regeneration that involve ISC-intrinsic functions, active culling of healthy epithelial cells, enhanced EC growth, and even cytoplasmic shedding by infected ECs. This article reviews current knowledge of the molecular mechanisms involved in gut regeneration in several insect models (Drosophila and Aedes of the order Diptera, and several Lepidoptera).

Epithelial Stem Cells: Making, Shaping and Breaking the Niche

Epithelial stem cells maintain tissues throughout adult life and are tightly regulated by their microenvironmental niche to balance cell production and loss. These stem cells have been studied extensively as signal-receiving cells, responding to cues from other cell types and mechanical stimuli that comprise the niche. However, studies from a wide range of systems have identified epithelial stem cells as major contributors to their own microenvironment either through producing niche cells, acting directly as niche cells or regulating niche cells. The importance of stem cell contributions to the niche is particularly clear in cancer, where tumour cells extensively remodel their microenvironment to promote their survival and proliferation.

Epigenetic Clock and Circadian Rhythms in Stem Cell Aging and Rejuvenation

This review summarizes the current understanding of the interaction between circadian rhythms of gene expression and epigenetic clocks characterized by the specific profile of DNA methylation in CpG-islands which mirror the senescence of all somatic cells and stem cells in particular. Basic mechanisms of regulation for circadian genes CLOCK-BMAL1 as well as downstream clock-controlled genes (ССG) are also discussed here. It has been shown that circadian rhythms operate by the finely tuned regulation of transcription and rely on various epigenetic mechanisms including the activation of enhancers/suppressors, acetylation/deacetylation of histones and other proteins as well as DNA methylation. Overall, up to 20% of all genes expressed by the cell are subject to expression oscillations associated with circadian rhythms. Additionally included in the review is a brief list of genes involved in the regulation of circadian rhythms, along with genes important for cell aging, and oncogenesis. Eliminating some of them (for example, Sirt1) accelerates the aging process, while the overexpression of Sirt1, on the contrary, protects against age-related changes. Circadian regulators control a number of genes that activate the cell cycle (Wee1, c-Myc, p20, p21, and Cyclin D1) and regulate histone modification and DNA methylation. Approaches for determining the epigenetic age from methylation profiles across CpG islands in individual cells are described. DNA methylation, which characterizes the function of the epigenetic clock, appears to link together such key biological processes as regeneration and functioning of stem cells, aging and malignant transformation. Finally, the main features of adult stem cell aging in stem cell niches and current possibilities for modulating the epigenetic clock and stem cells rejuvenation as part of antiaging therapy are discussed.

The Role of Citrate Transporter INDY in Metabolism and Stem Cell Homeostasis

I'm Not Dead Yet (Indy) is a fly gene that encodes a homologue of mammalian SLC13A5 plasma membrane citrate transporter. Reducing expression of Indy gene in flies, and its homologues in worms, extends longevity. Indy reduction in flies, worms, mice and rats affects metabolism by regulating the levels of cytoplasmic citrate, inducing a state similar to calorie restriction. Changes include lower lipid levels, increased insulin sensitivity, increased mitochondrial biogenesis, and prevention of weight gain, among others. The INDY protein is predominantly expressed in fly metabolic tissues: the midgut, fat body and oenocytes. Changes in fly midgut metabolism associated with reduced Indy gene activity lead to preserved mitochondrial function and reduced production of reactive oxygen species. All these changes lead to preserved intestinal stem cell homeostasis, which has a key role in maintaining intestinal epithelium function and enhancing fly healthspan and lifespan. Indy gene expression levels change in response to caloric content of the diet, inflammation and aging, suggesting that INDY regulates metabolic adaptation to nutrition or energetic requirements by controlling citrate levels.

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.

Anchor maintains gut homeostasis by restricting the JNK and Notch pathways in Drosophila

The adult Drosophila intestinal epithelium must be tightly regulated to maintain regeneration and homeostasis. The dysregulation of the regenerative capacity is frequently associated with intestinal diseases such as inflammation and tumorigenesis. Here, we showed that the G protein-coupled receptor Anchor maintains Drosophila adult midgut homeostasis by restricting Jun-N-terminal kinase (JNK) and Notch pathway activity. anchor inactivation resulted in aberrant JNK pathway activation, which led to excessive enteroblast (EB) production and premature enterocyte (EC) differentiation. In addition, increased Notch levels promoted premature EC differentiation following the loss of anchor. This defect induced by the loss of anchor ultimately caused sensitivity to stress or environmental challenge in adult flies. Taken together, our results demonstrate that the activity of anchor is essential to coordinate stem cell differentiation and proliferation to maintain intestinal homeostasis.

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.

Derlin-1 and TER94/VCP/p97 are required for intestinal homeostasis

Adult stem cells are critical for the maintenance of residential tissue homeostasis and functions. However, the roles of cellular protein homeostasis maintenance in stem cell proliferation and tissue homeostasis are not fully understood. Here, we find that Derlin-1 and TER94/VCP/p97, components of the ER-associated degradation (ERAD) pathway, restrain intestinal stem cell proliferation to maintain intestinal homeostasis in adult Drosophila. Depleting any of them results in increased stem cell proliferation and midgut homeostasis disruption. Derlin-1 is specifically expressed in the ER of progenitors and its C-terminus is required for its function. Interestingly, we find that increased stem cell proliferation is resulted from elevated ROS levels and activated JNK signaling in Derlin-1- or TER94-deficient progenitors. Further removal of ROS or inhibition of JNK signaling almost completely suppressed increased stem cell proliferation. Together, these data demonstrate that the ERAD pathway is critical for stem cell proliferation and tissue homeostasis. Thus we provide insights into our understanding of the mechanisms underlying cellular protein homeostasis maintenance (ER protein quality control) in tissue homeostasis and tumor development.

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.

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.

Zoledronate extends healthspan and survival via the mevalonate pathway in a FOXO-dependent manner

Over recent decades, increased longevity has not been paralleled by extended healthspan, resulting in more years spent with multiple diseases in older age. As such, interventions to improve healthspan are urgently required. Zoledronate is a nitrogen containing bisphosphonate, which inhibits the farnesyl pyrophosphate synthase (FPPS) enzyme, central to the mevalonate pathway. It is already used clinically to prevent fractures in osteoporotic patients, who have been reported to derive unexpected and unexplained survival benefits. Using Drosophila as a model we determined the effects of Zoledronate on lifespan, parameters of healthspan (climbing ability and intestinal dysplasia) and the ability to confer resistance to oxidative stress using a combination of genetically manipulated Drosophila strains and Western blotting. Our study shows that Zoledronate extended lifespan, improved climbing activity and reduced intestinal epithelial dysplasia and permeability with age. Mechanistic studies showed that Zoledronate conferred resistance to oxidative stress and reduced accumulation of X-ray-induced DNA damage via inhibition of FPPS. Moreover, Zoledronate was associated with inhibition of pAKT in the mTOR pathway downstream of the mevalonate pathway and required dFOXO for its action, both molecules associated with increased longevity. Taken together, our work indicates that Zoledronate, a drug already widely used to prevent osteoporosis and dosed only once a year, modulates important mechanisms of ageing. Its repurposing holds great promise as a treatment to improve healthspan.

Nutrient-Driven O-GlcNAcylation Controls DNA Damage Repair Signaling and Stem/Progenitor Cell Homeostasis

Stem/progenitor cells exhibit high proliferation rates, elevated nutrient uptake, altered metabolic flux, and stress-induced genome instability. O-GlcNAcylation is an essential post-translational modification mediated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which act in a nutrient- and stress-responsive manner. The precise role of O-GlcNAc in adult stem cells and the relationship between O-GlcNAc and the DNA damage response (DDR) is poorly understood. Here, we show that hyper-O-GlcNacylation leads to elevated insulin signaling, hyperproliferation, and DDR activation that mimic the glucose- and oxidative-stress-induced response. We discover a feedback mechanism involving key downstream effectors of DDR, ATM, ATR, and CHK1/2 that regulates OGT stability to promote O-GlcNAcylation and elevate DDR. This O-GlcNAc-dependent regulatory pathway is critical for maintaining gut homeostasis in Drosophila and the DDR in mouse embryonic stem cells (ESCs) and mouse embryonic fibroblasts (MEFs). Our findings reveal a conserved mechanistic link among O-GlcNAc cycling, stem cell self-renewal, and DDR with profound implications for stem-cell-derived diseases including cancer.

A TORC1-histone axis regulates chromatin organisation and non-canonical induction of autophagy to ameliorate ageing

Age-related changes to histone levels are seen in many species. However, it is unclear whether changes to histone expression could be exploited to ameliorate the effects of ageing in multicellular organisms. Here we show that inhibition of mTORC1 by the lifespan-extending drug rapamycin increases expression of histones H3 and H4 post-transcriptionally through eIF3-mediated translation. Elevated expression of H3/H4 in intestinal enterocytes in Drosophila alters chromatin organisation, induces intestinal autophagy through transcriptional regulation, and prevents age-related decline in the intestine. Importantly, it also mediates rapamycin-induced longevity and intestinal health. Histones H3/H4 regulate expression of an autophagy cargo adaptor Bchs (WDFY3 in mammals), increased expression of which in enterocytes mediates increased H3/H4-dependent healthy longevity. In mice, rapamycin treatment increases expression of histone proteins and Wdfy3 transcription, and alters chromatin organisation in the small intestine, suggesting that the mTORC1-histone axis is at least partially conserved in mammals and may offer new targets for anti-ageing interventions.

Mitochondrial Control of Stem Cell State and Fate: Lessons From Drosophila

Over the years, Drosophila has served as a wonderful genetically tractable model system to unravel various facets of tissue-resident stem cells in their microenvironment. Studies in different stem and progenitor cell types of Drosophila have led to the discovery of cell-intrinsic and extrinsic factors crucial for stem cell state and fate. Though initially touted as the ATP generating machines for carrying various cellular processes, it is now increasingly becoming clear that mitochondrial processes alone can override the cellular program of stem cells. The last few years have witnessed a surge in our understanding of mitochondria's contribution to governing different stem cell properties in their subtissular niches in Drosophila. Through this review, we intend to sum up and highlight the outcome of these in vivo studies that implicate mitochondria as a central regulator of stem cell fate decisions; to find the commonalities and uniqueness associated with these regulatory mechanisms.

white regulates proliferative homeostasis of intestinal stem cells during ageing in Drosophila

Tissue integrity is contingent on maintaining stem cells. Intestinal stem cells (ISCs) over-proliferate during ageing, leading to tissue dysplasia in Drosophila melanogaster. Here we describe a role for white, encoding the evolutionarily conserved ATP-binding cassette transporter subfamily G, with a particularly well-characterized role in eye colour pigmentation, in ageing-induced ISC proliferation in the midgut. ISCs increase expression of white during ageing. ISC-specific inhibition of white suppresses ageing-induced ISC dysregulation and prolongs lifespan. Of the proteins that form heterodimers with White, Brown mediates ISC dysregulation during ageing. Metabolomics analyses reveal previously unappreciated, profound metabolic impacts of white inhibition on organismal metabolism. Among the metabolites affected by White, tetrahydrofolate is transported by White, is accumulated in ISCs during ageing and is indispensable for ageing-induced ISC over-proliferation. Since Thomas Morgan's isolation of a white mutant as the first Drosophila mutant, white mutants have been used extensively as genetic systems and often as controls. Our findings provide insights into metabolic regulation of stem cells mediated by the classic gene white.

A glucose-supplemented diet enhances gut barrier integrity in Drosophila

Dietary intervention has received considerable attention as an approach to extend lifespan and improve aging. However, questions remain regarding optimal dietary regimes and underlying mechanisms of lifespan extension. Here, we asked how an increase of glucose in a chemically defined diet extends the lifespan of adult Drosophila melanogaster We showed that glucose-dependent lifespan extension is not a result of diminished caloric intake, or changes to systemic insulin activity, two commonly studied mechanisms of lifespan extension. Instead, we found that flies raised on glucose-supplemented food increased the expression of cell-adhesion genes, delaying age-dependent loss of intestinal barrier integrity. Furthermore, we showed that chemical disruption of the gut barrier negated the lifespan extension associated with glucose treatment, suggesting that glucose-supplemented food prolongs adult viability by enhancing the intestinal barrier. We believe our data contribute to understanding intestinal homeostasis, and may assist efforts to develop preventative measures that limit effects of aging on health.

Taurine represses age-associated gut hyperplasia in Drosophila via counteracting endoplasmic reticulum stress

As they age, adult stem cells become more prone to functional decline, which is responsible for aging‐associated tissue degeneration and diseases. One goal of aging research is to identify drugs that can repair age‐associated tissue degeneration. Multiple organ development‐related signaling pathways have recently been demonstrated to have functions in tissue homeostasis and aging process. Therefore, in this study, we tested several chemicals that are essential for organ development to assess their ability to delay intestinal stem cell (ISC) aging and promote gut function in adult Drosophila. We found that taurine, a free amino acid that supports neurological development and tissue metabolism in humans, represses ISC hyperproliferation and restrains the intestinal functional decline seen in aged animals. We found that taurine represses age‐associated ISC hyperproliferation through a mechanism that eliminated endoplasmic reticulum (ER) stress by upregulation of the target genes of unfolded protein response in the ER (UPR^ER) and inhibiting the c‐Jun N‐terminal kinase (JNK) signaling. Our findings show that taurine plays a critical role in delaying the aging process in stem cells and suggest that it may be used as a natural compound for the treatment of age‐associated, or damage‐induced intestinal dysfunction in humans.

Loss of Slug Compromises DNA Damage Repair and Accelerates Stem Cell Aging in Mammary Epithelium

DNA damage activates checkpoints that limit the replicative potential of stem cells, including differentiation. These checkpoints protect against cancer development but also promote tissue aging. Because mice lacking Slug/Snai2 exhibit limited stem cell activity, including luminobasal differentiation, and are protected from mammary cancer, we reasoned that Slug might regulate DNA damage checkpoints in mammary epithelial cells. Here, we show that Slug facilitates efficient execution of RPA32-mediated DNA damage response (DDR) signaling. Slug deficiency leads to delayed phosphorylation of ataxia telangiectasia mutated and Rad3-related protein (ATR) and its effectors RPA32 and CHK1. This leads to impaired RAD51 recruitment to DNA damage sites and persistence of unresolved DNA damage. In vivo, Slug/Snai2 loss leads to increased DNA damage and premature aging of mammary epithelium. Collectively, our work demonstrates that the mammary stem cell regulator Slug controls DDR checkpoints by dually inhibiting differentiation and facilitating DDR repair, and its loss causes unresolved DNA damage and accelerated aging.

Tissue Adaptation to Environmental Cues by Symmetric and Asymmetric Division Modes of Intestinal Stem Cells

Tissues must adapt to the different external stimuli so that organisms can survive in their environments. The intestine is a vital organ involved in food processing and absorption, as well as in innate immune response. Its adaptation to environmental cues such as diet and biotic/abiotic stress involves regulation of the proliferative rate and a switch of division mode (asymmetric versus symmetric) of intestinal stem cells (ISC). In this review, we outline the current comprehension of the physiological and molecular mechanisms implicated in stem cell division modes in the adult Drosophila midgut. We present the signaling pathways and polarity cues that control the mitotic spindle orientation, which is the terminal determinant ensuring execution of the division mode. We review these events during gut homeostasis, as well as during its response to nutrient availability, bacterial infection, chemical damage, and aging. JNK signaling acts as a central player, being involved in each of these conditions as a direct regulator of spindle orientation. The studies of the mechanisms regulating ISC divisions allow a better understanding of how adult stem cells integrate different signals to control tissue plasticity, and of how various diseases, notably cancers, arise from their alterations.

The eroding chromatin landscape of aging stem cells

Adult stem cells undergo both replicative and chronological aging in their niches, with catastrophic declines in regenerative potential with age. Due to repeated environmental insults during aging, the chromatin landscape of stem cells erodes, with changes in both DNA and histone modifications, accumulation of damage, and altered transcriptional response. A body of work has shown that altered chromatin is a driver of cell fate changes and a regulator of self-renewal in stem cells and therefore a prime target for juvenescence therapeutics. This review focuses on chromatin changes in stem cell aging and provides a composite view of both common and unique epigenetic themes apparent from the studies of multiple stem cell types.

Ageing, Drosophila melanogaster and Epigenetics

Ageing is a phenomenon where the accumulation of all the stresses that alter the functions of living organisms, halter them from maintaining their physiological balance and eventually lead to death. The emergence of epigenetic tremendously contributed to the knowledge of ageing. Epigenetic changes in cells or tissues like deoxyribonucleic acid (DNA) methylation, modification of histone proteins, transcriptional modification and also the involvement of non-coding DNA has been documented to be associated with ageing. In order to study ageing, scientists have taken advantage of several potential organisms to aid them in their study. Drosophila melanogaster has been an essential model in establishing current understanding of the mechanism of ageing as they possess several advantages over other competitors like having homologues to more than 75% of human disease genes, having 50% of Drosophila genes are homologues to human genes and most importantly they are genetically amenable. Here, we would like to summarise the extant knowledge about ageing and epigenetic process and the role of Drosophila as an ideal model to study epigenetics in association with ageing process.

Lipoic acid rejuvenates aged intestinal stem cells by preventing age-associated endosome reduction

The age‐associated decline of adult stem cell function is closely related to the decline in tissue function and age‐related diseases. However, the underlying mechanisms that ultimately lead to the observed functional decline of stem cells still remain largely unexplored. This study investigated Drosophila midguts and found a continuous downregulation of lipoic acid synthase, which encodes the key enzyme for the endogenous synthesis of alpha‐lipoic acid (ALA), upon aging. Importantly, orally administration of ALA significantly reversed the age‐associated hyperproliferation of intestinal stem cells (ISCs) and the observed decline of intestinal function, thus extending the lifespan of Drosophila. This study reports that ALA reverses age‐associated ISC dysfunction by promoting the activation of the endocytosis–autophagy network, which decreases in aged ISCs. Moreover, this study suggests that ALA may be used as a safe and effective anti‐aging compound for the treatment of ISC‐dysfunction‐related diseases and for the promotion of healthy aging in humans.

Capsaicin Functions as Drosophila Ovipositional Repellent and Causes Intestinal Dysplasia

Plants generate a plethora of secondary compounds (toxins) that potently influence the breadth of the breeding niches of animals, including Drosophila. Capsaicin is an alkaloid irritant from hot chili peppers, and can act as a deterrent to affect animal behaviors, such as egg laying choice. However, the mechanism underlying this ovipositional avoidance remains unknown. Here, we report that Drosophila females exhibit a robust ovipositional aversion to capsaicin. First, we found that females were robustly repelled from laying eggs on capsaicin-containing sites. Second, genetic manipulations show that the ovipositional aversion to capsaicin is mediated by activation of nociceptive neurons expressing the painless gene. Finally, we found that capsaicin compromised the health and lifespan of flies through intestinal dysplasia and oxidative innate immunity. Overall, our study suggests that egg-laying sensation converts capsaicin into an aversive behavior for female Drosophila, mirroring an adaptation to facilitate the survival and fitness of both parents and offspring.

Fatty acid β-oxidation is required for the differentiation of larval hematopoietic progenitors in Drosophila

Cell-intrinsic and extrinsic signals regulate the state and fate of stem and progenitor cells. Recent advances in metabolomics illustrate that various metabolic pathways are also important in regulating stem cell fate. However, our understanding of the metabolic control of the state and fate of progenitor cells is in its infancy. Using Drosophila hematopoietic organ: lymph gland, we demonstrate that Fatty Acid Oxidation (FAO) is essential for the differentiation of blood cell progenitors. In the absence of FAO, the progenitors are unable to differentiate and exhibit altered histone acetylation. Interestingly, acetate supplementation rescues both histone acetylation and the differentiation defects. We further show that the CPT1/whd (withered), the rate-limiting enzyme of FAO, is transcriptionally regulated by Jun-Kinase (JNK), which has been previously implicated in progenitor differentiation. Our study thus reveals how the cellular signaling machinery integrates with the metabolic cue to facilitate the differentiation program.

Stem cells are special precursor cells, found in all animals from flies to humans, that can give rise to all the mature cell types in the body. Their job is to generate supplies of new cells wherever these are needed. This is important because it allows damaged or worn-out tissues to be repaired and replaced by fresh, healthy cells.

As part of this renewal process, stem cells generate pools of more specialized cells, called progenitor cells. These can be thought of as half-way to maturation and can only develop in a more restricted number of ways. For example, so-called myeloid progenitor cells from humans can only develop into a specific group of blood cell types, collectively termed the myeloid lineage.

Fruit flies, like many other animals, also have several different types of blood cells. The fly’s repertoire of blood cells is very similar to the human myeloid lineage, and these cells also develop from the fly equivalent of myeloid progenitor cells. These progenitors are found in a specialized organ in fruit fly larvae called the lymph gland, where the blood forms. These similarities between fruit flies and humans mean that flies are a good model to study how myeloid progenitor cells mature.

A lot is already known about the molecules that signal to progenitor cells how and when to mature. However, the role of metabolism – the chemical reactions that process nutrients and provide energy inside cells – is still poorly understood. Tiwari et al. set out to identify which metabolic reactions myeloid progenitor cells require and how these reactions might shape the progenitors’ development into mature blood cells.

The experiments in this study used fruit fly larvae that had been genetically altered so that they could no longer perform key chemical reactions needed for the breakdown of fats. In these mutant larvae, the progenitors within the lymph gland could not give rise to mature blood cells. This showed that myeloid progenitor cells need to be able to break down fats in order to develop properly.

These results highlight a previously unappreciated role for metabolism in controlling the development of progenitor cells. If this effect also occurs in humans, this knowledge could one day help medical researchers engineer replacement tissues in the lab, or even increase our own bodies’ ability to regenerate blood, and potentially other organs.

Sleep Loss Can Cause Death through Accumulation of Reactive Oxygen Species in the Gut

The view that sleep is essential for survival is supported by the ubiquity of this behavior, the apparent existence of sleep-like states in the earliest animals, and the fact that severe sleep loss can be lethal. The cause of this lethality is unknown. Here we show, using flies and mice, that sleep deprivation leads to accumulation of reactive oxygen species (ROS) and consequent oxidative stress, specifically in the gut. ROS are not just correlates of sleep deprivation but drivers of death: their neutralization prevents oxidative stress and allows flies to have a normal lifespan with little to no sleep. The rescue can be achieved with oral antioxidant compounds or with gut-targeted transgenic expression of antioxidant enzymes. We conclude that death upon severe sleep restriction can be caused by oxidative stress, that the gut is central in this process, and that survival without sleep is possible when ROS accumulation is prevented. VIDEO ABSTRACT.

Genomic instability and cancer: lessons from Drosophila

Cancer is a genetic disease that involves the gradual accumulation of mutations. Human tumours are genetically unstable. However, the current knowledge about the origins and implications of genomic instability in this disease is limited. Understanding the biology of cancer requires the use of animal models. Here, we review relevant studies addressing the implications of genomic instability in cancer by using the fruit fly, Drosophila melanogaster, as a model system. We discuss how this invertebrate has helped us to expand the current knowledge about the mechanisms involved in genomic instability and how this hallmark of cancer influences disease progression.

Anti-Aging Effect of the Ketone Metabolite β-Hydroxybutyrate in Drosophila Intestinal Stem Cells

Age-related changes in tissue-resident adult stem cells may be closely linked to tissue aging and age-related diseases, such as cancer. β-Hydroxybutyrate is emerging as an important molecule for exhibiting the anti-aging effects of caloric restriction and fasting, which are generally considered to be beneficial for stem cell maintenance and tissue regeneration. The effects of β-hydroxybutyrate on adult stem cells remain largely unknown. Therefore, this study was undertaken to investigate whether β-hydroxybutyrate supplementation exerts beneficial effects on age-related changes in intestinal stem cells that were derived from the Drosophila midgut. Our results indicate that β-hydroxybutyrate inhibits age- and oxidative stress-induced changes in midgut intestinal stem cells, including centrosome amplification (a hallmark of cancers), hyperproliferation, and DNA damage accumulation. Additionally, β-hydroxybutyrate inhibits age- and oxidative stress-induced heterochromatin instability in enterocytes, an intestinal stem cells niche cells. Our results suggest that β-hydroxybutyrate exerts both intrinsic as well as extrinsic influence in order to maintain stem cell homeostasis.

An abundant quiescent stem cell population in Drosophila Malpighian tubules protects principal cells from kidney stones

Adult Drosophila Malpighian tubules have low rates of cell turnover but are vulnerable to damage caused by stones, like their mammalian counterparts, kidneys. We show that Drosophilarenal stem cells (RSCs) in the ureter and lower tubules comprise a unique, unipotent regenerative compartment. RSCs respond only to loss of nearby principal cells (PCs), cells critical for maintaining ionic balance. Large polyploid PCs are outnumbered by RSCs, which replace each lost cell with multiple PCs of lower ploidy. Notably, RSCs do not replenish principal cells or stellate cells in the upper tubules. RSCs generate daughters by asymmetric Notch signaling, yet RSCs remain quiescent (cell cycle-arrested) without damage. Nevertheless, the capacity for RSC-mediated repair extends the lifespan of flies carrying kidney stones. We propose that abundant, RSC-like stem cells exist in other tissues with low rates of turnover where they may have been mistaken for differentiated tissue cells.

Receptor Tyrosine Kinases in Development: Insights from Drosophila

Cell-to-cell communication mediates a plethora of cellular decisions and behaviors that are crucial for the correct and robust development of multicellular organisms. Many of these signals are encoded in secreted hormones or growth factors that bind to and activate cell surface receptors, to transmit the cue intracellularly. One of the major superfamilies of cell surface receptors are the receptor tyrosine kinases (RTKs). For nearly half a century RTKs have been the focus of intensive study due to their ability to alter fundamental aspects of cell biology, such as cell proliferation, growth, and shape, and because of their central importance in diseases such as cancer. Studies in model organisms such a Drosophila melanogaster have proved invaluable for identifying new conserved RTK pathway components, delineating their contributions, and for the discovery of conserved mechanisms that control RTK-signaling events. Here we provide a brief overview of the RTK superfamily and the general mechanisms used in their regulation. We further highlight the functions of several RTKs that govern distinct cell-fate decisions in Drosophila and explore how their activities are developmentally controlled.

The TORC1 inhibitor Nprl2 protects age-related digestive function in Drosophila

Aging and age-related diseases occur in almost all organisms. Recently, it was discovered that the inhibition of target of rapamycin complex 1 (TORC1), a conserved complex that mediates nutrient status and cell metabolism, can extend an individual’s lifespan and inhibit age-related diseases in many model organisms. However, the mechanism whereby TORC1 affects aging remains elusive. Here, we use a loss-of-function mutation in nprl2, a component of GATOR1 that mediates amino acid levels and inhibits TORC1 activity, to investigate the effect of increased TORC1 activity on the occurrence of age-related digestive dysfunction in Drosophila. We found that the nprl2 mutation decreased Drosophila lifespan. Furthermore, the nprl2 mutant had a distended crop, with food accumulation at an early age. Interestingly, the inappropriate food distribution and digestion along with decreased crop contraction in nprl2 mutant can be rescued by decreasing TORC1 activity. In addition, nprl2-mutant flies exhibited age-related phenotypes in the midgut, including short gut length, a high rate of intestinal stem cell proliferation, and metabolic dysfunction, which could be rescued by inhibiting TORC1 activity. Our findings showed that the gastrointestinal tract aging process is accelerated in nprl2-mutant flies, owing to high TORC1 activity, which suggested that TORC1 promotes digestive tract senescence.