RiboTag translatomic profiling of Drosophila oenocytes under aging and induced oxidative stress

Regulation of insect cuticular hydrocarbon biosynthesis

Cuticular hydrocarbons (CHCs) play pleiotropic roles in insect survival and reproduction. They prevent desiccation and function as pheromones influencing different behaviors. While the genes in the CHC biosynthesis pathway have been extensively studied, the regulatory mechanisms that lead to different CHC compositions received far less attention. In this review, we present an overview of how different hormones and transcriptional factors regulate CHC synthesis genes, leading to different CHC compositions. Future research focusing on the regulatory mechanisms underlying CHC biosynthesis can lead to a better understanding of how insects could produce dynamic chemical profiles in response to different stimuli.

Whole organism and tissue-specific analysis of pexophagy in Drosophila

Peroxisomes are essential organelles involved in critical metabolic processes in animals such as fatty acid oxidation, ether phospholipid production and reactive oxygen species detoxification. We have generated transgenic Drosophila melanogaster models expressing fluorescent reporters for the selective autophagy of peroxisomes, a process known as pexophagy. We show that these reporters are colocalized with a peroxisomal marker and that they can reflect pexophagy induction by iron chelation and inhibition by depletion of the core autophagy protein Atg5. Using light sheet microscopy, we have been able to obtain a global overview of pexophagy levels across the entire organism at different stages of development. Tissue-specific control of pexophagy is exemplified by areas of peroxisome abundance but minimal pexophagy, observed in clusters of oenocytes surrounded by epithelial cells where pexophagy is much more evident. Enhancement of pexophagy was achieved by feeding flies with the iron chelator deferiprone, in line with past results using mammalian cells. Specific drivers were used to visualize pexophagy in neurons, and to demonstrate that specific depletion in the larval central nervous system of Hsc70-5, the Drosophila homologue of the chaperone HSPA9/mortalin, led to a substantial elevation in pexophagy.

Thermal variation influences the transcriptome of the major malaria vector Anopheles stephensi

The distribution and abundance of ectothermic mosquitoes are strongly affected by temperature, but mechanisms remain unexplored. We describe the effect of temperature on the transcriptome of Anopheles stephensi, an invasive vector of human malaria. Adult females were maintained across a range of mean temperatures (20 °C, 24 °C and 28 °C), with daily fluctuations of +5 °C and -4 °C at each mean temperature. Transcriptomes were described up to 19 days post-blood meal. Of the >3100 differentially expressed genes, we observed shared temporal expression profiles across all temperatures, suggesting their indispensability to mosquito life history. Tolerance to 20 and 28 ( + 5°C/-4°C) was associated with larger and more diverse transcriptomes compared to 24 ( + 5 °C/-4 °C). Finally, we identified two distinct trends in gene expression in response to blood meal ingestion, oxidative stress, and reproduction. Our work has implications for mosquitoes' response to thermal variation, mosquito immune-physiology, mosquito-malaria interactions and the development of vector control tools.

The Fourth Annual Symposium of the Midwest Aging Consortium

The Midwest Aging Consortium (MAC) has emerged as a critical collaborative initiative aimed at advancing our understanding of aging and developing strategies to combat the rising prevalence of age-related diseases. Founded in 2019, MAC brings together researchers from various disciplines and institutions across the Midwestern United States to foster interdisciplinary geroscience research. This report summarizes the highlights of the Fourth Annual Symposium of MAC, which was held at Iowa State University in May 2023. The symposium featured presentations on a wide array of topics, including studies on slow-aging animals, cellular senescence and senotherapeutics, the role of the immune system in aging, metabolic changes in aging, neuronal health in aging, and biomarkers for measuring the aging process. Speakers shared findings from studies involving a variety of animals, ranging from commonly used species such as mice, rats, worms, yeast, and fruit flies, to less-common ones like naked mole-rats, painted turtles, and rotifers. MAC continues to emphasize the importance of supporting emerging researchers and fostering a collaborative environment, positioning itself as a leader in aging research. This symposium not only showcased the current state of aging biology research but also highlighted the consortium's role in training the next generation of scientists dedicated to improving the healthspan and well-being of the aging population.

Peroxisomal import stress activates integrated stress response and inhibits ribosome biogenesis

Impaired organelle-specific protein import triggers a variety of cellular stress responses, including adaptive pathways to balance protein homeostasis. Most of the previous studies focus on the cellular stress response triggered by misfolded proteins or defective protein import in the endoplasmic reticulum or mitochondria. However, little is known about the cellular stress response to impaired protein import in the peroxisome, an understudied organelle that has recently emerged as a key signaling hub for cellular and metabolic homeostasis. To uncover evolutionarily conserved cellular responses upon defective peroxisomal import, we carried out a comparative transcriptomic analysis on fruit flies with tissue-specific peroxin knockdown and human HEK293 cells expressing dominant-negative PEX5C11A. Our RNA-seq results reveal that defective peroxisomal import upregulates integrated stress response (ISR) and downregulates ribosome biogenesis in both flies and human cells. Functional analyses confirm that impaired peroxisomal import induces eIF2α phosphorylation and ATF4 expression. Loss of ATF4 exaggerates cellular damage upon peroxisomal import defects, suggesting that ATF4 activation serves as a cellular cytoprotective mechanism upon peroxisomal import stress. Intriguingly, we show that peroxisomal import stress decreases the expression of rRNA processing genes and inhibits early pre-rRNA processing, which leads to the accumulation of 47S precursor rRNA and reduction of downstream rRNA intermediates. Taken together, we identify ISR activation and ribosome biogenesis inhibition as conserved adaptive stress responses to defective peroxisomal import and uncover a novel link between peroxisomal dysfunction and rRNA processing.

Lipid Metabolism in Relation to Carbohydrate Metabolism

Carbohydrates and lipids integrate into a complex metabolic network that is essential to maintain homeostasis. In insects, as in most metazoans, dietary carbohydrates are taken up as monosaccharides whose excess is toxic, even at relatively low concentrations. To cope with this toxicity, monosaccharides are stored either as glycogen or neutral lipids, the latter constituting a quasi-unlimited energy store. Breakdown of these stores in response to energy demand depends on insect species and on several physiological parameters. In this chapter, we review the multiple metabolic pathways and strategies linking carbohydrates and lipids that insects utilize to respond to nutrient availability, food scarcity or physiological activities.

Insect hormone PTTH regulates lifespan through temporal and spatial activation of NF-κB signaling during metamorphosis

The prothoracicotropic hormone (PTTH) is a well-known neuropeptide that regulates insect metamorphosis (the juvenile-to-adult transition) by inducing the biosynthesis of steroid hormones. However, the role of PTTH in adult physiology and longevity is largely unexplored. Here, we show that Ptth loss-of-function mutants are long-lived and exhibit increased resistance to oxidative stress in Drosophila. Intriguingly, we find that loss of Ptth blunt age-dependent upregulation of NF-κB signaling specifically in fly hepatocytes (oenocytes). We further show that oenocyte-specific overexpression of Relish/NF-κB blocks the lifespan extension of Ptth mutants, suggesting that PTTH regulates lifespan through oenocyte-specific NF-κB signaling. Surprisingly, adult-specific knockdown of Ptth did not prolong lifespan, indicating that PTTH controls longevity through developmental programs. Indeed, knockdown of PTTH receptor Torso in prothoracic gland (PG) during fly development prolongs lifespan. To uncover the developmental processes underlying PTTH-regulated lifespan, we perform a developmental transcriptomic analysis and identify an unexpected activation of NF-κB signaling in developing oenocytes during fly metamorphosis, which is blocked in Ptth mutants. Importantly, knockdown of Relish/NF-κB specifically in oenocytes during early pupal stages significantly prolongs the lifespan of adult flies. Thus, our findings uncover an unexpected role of PTTH in controlling adult lifespan through temporal and spatial activation of NF-κB signaling in developing hepatocytes and highlight the vital role of developmental NF-κB signaling in shaping adult physiology.

Ribosome Profiling and RNA Sequencing Reveal Translation and Transcription Regulation under Acute Heat Stress in Rainbow Trout (Oncorhynchus mykiss, Walbaum, 1792) Liver

Rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) is an important economic cold-water fish that is susceptible to heat stress. To date, the heat stress response in rainbow trout is more widely understood at the transcriptional level, while little research has been conducted at the translational level. To reveal the translational regulation of heat stress in rainbow trout, in this study, we performed a ribosome profiling assay of rainbow trout liver under normal and heat stress conditions. Comparative analysis of the RNA-seq data with the ribosome profiling data showed that the folding changes in gene expression at the transcriptional level are moderately correlated with those at the translational level. In total, 1213 genes were significantly altered at the translational level. However, only 32.8% of the genes were common between both levels, demonstrating that heat stress is coordinated across both transcriptional and translational levels. Moreover, 809 genes exhibited significant differences in translational efficiency (TE), with the TE of these genes being considerably affected by factors such as the GC content, coding sequence length, and upstream open reading frame (uORF) presence. In addition, 3468 potential uORFs in 2676 genes were identified, which can potentially affect the TE of the main open reading frames. In this study, Ribo-seq and RNA-seq were used for the first time to elucidate the coordinated regulation of transcription and translation in rainbow trout under heat stress. These findings are expected to contribute novel data and theoretical insights to the international literature on the thermal stress response in fish.

Translational regulation enhances distinction of cell types in the nervous system

Multicellular organisms are composed of specialized cell types with distinct proteomes. While recent advances in single-cell transcriptome analyses have revealed differential expression of mRNAs, cellular diversity in translational profiles remains underinvestigated. By performing RNA-seq and Ribo-seq in genetically defined cells in the Drosophila brain, we here revealed substantial post-transcriptional regulations that augment the cell-type distinctions at the level of protein expression. Specifically, we found that translational efficiency of proteins fundamental to neuronal functions, such as ion channels and neurotransmitter receptors, was maintained low in glia, leading to their preferential translation in neurons. Notably, distribution of ribosome footprints on these mRNAs exhibited a remarkable bias toward the 5' leaders in glia. Using transgenic reporter strains, we provide evidence that the small upstream open-reading frames in the 5' leader confer selective translational suppression in glia. Overall, these findings underscore the profound impact of translational regulation in shaping the proteomics for cell-type distinction and provide new insights into the molecular mechanisms driving cell-type diversity.

Emerging models for studying adipose tissue metabolism

Understanding adipose metabolism is essential for addressing obesity and related health concerns. However, the ethical and scientific pressure to animal testing, aligning with the 3Rs, has triggered the implementation of diverse alternative models for analysing anomalies in adipose metabolism. In this review, we will address this issue from various perspectives. Traditional adipocyte cell cultures, whether animal or human-derived, offer a fundamental starting point. These systems have their merits but may not fully replicate in vivo complexity. Established cell lines are valuable for high-throughput screening but may lack the authenticity of primary-derived adipocytes, which closely mimic native tissue. To enhance model sophistication, spheroids have been introduced. These three-dimensional cultures better mimicking the in vivo microenvironment, enabling the study of intricate cell-cell interactions, gene expression, and metabolic pathways. Organ-on-a-chip (OoC) platforms take this further by integrating multiple cell types into microfluidic devices, simulating tissue-level functions. Adipose-OoC (AOoC) provides dynamic environments with applications spanning drug testing to personalized medicine and nutrition. Beyond in vitro models, genetically amenable organisms (Caenorhabditis elegans, Drosophila melanogaster, and zebrafish larvae) have become powerful tools for investigating fundamental molecular mechanisms that govern adipose tissue functions. Their genetic tractability allows for efficient manipulation and high-throughput studies. In conclusion, a diverse array of research models is crucial for deciphering adipose metabolism. By leveraging traditional adipocyte cell cultures, primary-derived cells, spheroids, AOoCs, and lower organism models, we bridge the gap between animal testing and a more ethical, scientifically robust, and human-relevant approach, advancing our understanding of adipose tissue metabolism and its impact on health.

Tissue-specific O-GlcNAcylation profiling identifies substrates in translational machinery in Drosophila mushroom body contributing to olfactory learning

O-GlcNAcylation is a dynamic post-translational modification that diversifies the proteome. Its dysregulation is associated with neurological disorders that impair cognitive function, and yet identification of phenotype-relevant candidate substrates in a brain-region specific manner remains unfeasible. By combining an O-GlcNAc binding activity derived from Clostridium perfringens OGA (CpOGA) with TurboID proximity labeling in Drosophila, we developed an O-GlcNAcylation profiling tool that translates O-GlcNAc modification into biotin conjugation for tissue-specific candidate substrates enrichment. We mapped the O-GlcNAc interactome in major brain regions of Drosophila and found that components of the translational machinery, particularly ribosomal subunits, were abundantly O-GlcNAcylated in the mushroom body of Drosophila brain. Hypo-O-GlcNAcylation induced by ectopic expression of active CpOGA in the mushroom body decreased local translational activity, leading to olfactory learning deficits that could be rescued by dMyc overexpression-induced increase of protein synthesis. Our study provides a useful tool for future dissection of tissue-specific functions of O-GlcNAcylation in Drosophila, and suggests a possibility that O-GlcNAcylation impacts cognitive function via regulating regional translational activity in the brain.

Construction of single-cell cross-species chromatin accessibility landscapes with combinatorial-hybridization-based ATAC-seq

Despite recent advances in single-cell genomics, the lack of maps for single-cell candidate cis-regulatory elements (cCREs) in non-mammal species has limited our exploration of conserved regulatory programs across vertebrates and invertebrates. Here, we developed a combinatorial-hybridization-based method for single-cell assay for transposase-accessible chromatin using sequencing (scATAC-seq) named CH-ATAC-seq, enabling the construction of single-cell accessible chromatin landscapes for zebrafish, Drosophila, and earthworms (Eisenia andrei). By integrating scATAC censuses of humans, monkeys, and mice, we systematically identified 152 distinct main cell types and around 0.8 million cell-type-specific cCREs. Our analysis provided insights into the conservation of neural, muscle, and immune lineages across species, while epithelial cells exhibited a higher organ-origin heterogeneity. Additionally, a large-scale gene regulatory network (GRN) was constructed in four vertebrates by integrating scRNA-seq censuses. Overall, our study provides a valuable resource for comparative epigenomics, identifying the evolutionary conservation and divergence of gene regulation across different species.

Localization of nitric oxide-producing hemocytes in Aedes and Culex mosquitoes infected with bacteria

Mosquitoes are significant vectors of various pathogens. Unlike vertebrates, insects rely solely on innate immunity. Hemocytes play a crucial role in the cellular part of the innate immune system. The gaseous radical nitric oxide (NO) produced by hemocytes acts against pathogens and also functions as a versatile transmitter in both the immune and nervous systems, utilizing cyclic guanosine monophosphate (cGMP) as a second messenger. This study conducted a parallel comparison of NO synthase (NOS) expression and NO production in hemocytes during Escherichia coli K12 infection in four vector species: Aedes aegypti, Aedes albopictus, Culex pipiens molestus, and Culex pipiens quinquefasciatus. Increased NOS expression by NADPH diaphorase (NADPHd) staining and NO production by immunofluorescence against the by-product L-citrulline were observed in infected mosquito hemocytes distributed throughout the abdomens. NADPHd activity and citrulline labeling were particularly found in periostial hemocytes near the heart, but also on the ventral nerve chord (VNC). Pericardial cells of Ae. aegypti and Cx. p. molestus showed increased citrulline immunofluorescence, suggesting their involvement in the immune response. Oenocytes displayed strong NADPHd and citrulline labeling independent of infection status. This comparative study, consistent with findings in other species, suggests a widespread phenomenon of NO's role in hemocyte responses during E. coli infection. Found differences within and between genera highlight the importance of species-specific investigations.

DNA damage signaling in Drosophila macrophages modulates systemic cytokine levels in response to oxidative stress

Environmental factors, infection, or injury can cause oxidative stress in diverse tissues and loss of tissue homeostasis. Effective stress response cascades, conserved from invertebrates to mammals, ensure reestablishment of homeostasis and tissue repair. Hemocytes, the Drosophila blood-like cells, rapidly respond to oxidative stress by immune activation. However, the precise signals how they sense oxidative stress and integrate these signals to modulate and balance the response to oxidative stress in the adult fly are ill-defined. Furthermore, hemocyte diversification was not explored yet on oxidative stress. Here, we employed high-throughput single nuclei RNA-sequencing to explore hemocytes and other cell types, such as fat body, during oxidative stress in the adult fly. We identified distinct cellular responder states in plasmatocytes, the Drosophila macrophages, associated with immune response and metabolic activation upon oxidative stress. We further define oxidative stress-induced DNA damage signaling as a key sensor and a rate-limiting step in immune-activated plasmatocytes controlling JNK-mediated release of the pro-inflammatory cytokine unpaired-3. We subsequently tested the role of this specific immune activated cell stage during oxidative stress and found that inhibition of DNA damage signaling in plasmatocytes, as well as JNK or upd3 overactivation, result in a higher susceptibility to oxidative stress. Our findings uncover that a balanced composition and response of hemocyte subclusters is essential for the survival of adult Drosophila on oxidative stress by regulating systemic cytokine levels and cross-talk to other organs, such as the fat body, to control energy mobilization.

Better Together: Interorganellar Communication in the Regulation of Proteostasis

An extensive network of chaperones and folding factors is responsible for maintaining a functional proteome, which is the basis for cellular life. The underlying proteostatic mechanisms are not isolated within organelles, rather they are connected over organellar borders via signalling processes or direct association via contact sites. This review aims to provide a conceptual understanding of proteostatic mechanisms across organelle borders, not focussing on individual organelles. This discussion highlights the precision of these finely tuned systems, emphasising the complicated balance between cellular protection and adaptation to stress. In this review, we discuss widely accepted aspects while shedding light on newly discovered perspectives.

tRNA-derived small RNAs are embedded in the gene regulatory network instructing Drosophila metamorphosis

A class of noncoding RNAs, referred to as tsRNAs, is emerging with a potential to exert a new layer in gene regulation. These RNAs are breakdown products of tRNAs, either through active processing or passive cleavage or both. Since tRNAs are part of the general machinery for translation, their expression levels and activities are tightly controlled, raising the possibility that their breakdown products, tsRNAs, may provide a link between the overall translational status of a cell to specific changes in gene regulatory network. We hypothesize that Drosophila pupation, being a special developmental stage during which there is a global limitation of nutrients, represents a system in which such a link may readily reveal itself. We show that specific tsRNAs indeed show a dynamic accumulation upon entering the pupal stage. We describe experiments to characterize the mode of tsRNA action and, through the use of such gained knowledge, conduct a genome-wide analysis to assess the functions of dynamically expressed tsRNAs. Our results show that the predicted target genes are highly enriched in biological processes specific to this stage of development including metamorphosis. We further show that tsRNA action is required for successful pupation, providing direct support to the hypothesis that tsRNAs accumulated during this stage are critical to the gene expression program at this stage of development.

Markers and mechanisms of death in Drosophila

Parameters correlated with age and mortality in Drosophila melanogaster include decreased negative geotaxis and centrophobism behaviors, decreased climbing and walking speed, and darkened pigments in oenocytes and eye. Cessation of egg laying predicts death within approximately 5 days. Endogenous green fluorescence in eye and body increases hours prior to death. Many flies exhibit erratic movement hours before death, often leading to falls. Loss of intestinal barrier integrity (IBI) is assayed by feeding blue dye ("Smurf" phenotype), and Smurf flies typically die within 0-48 h. Some studies report most flies exhibit Smurf, whereas multiple groups report most flies die without exhibiting Smurf. Transgenic reporters containing heat shock gene promoters and innate immune response gene promoters progressively increase expression with age, and partly predict remaining life span. Innate immune reporters increase with age in every fly, prior to any Smurf phenotype, in presence or absence of antibiotics. Many flies die on their side or supine (on their back) position. The data suggest three mechanisms for death of Drosophila. One is loss of IBI, as revealed by Smurf assay. The second is nervous system malfunction, leading to erratic behavior, locomotor malfunction, and falls. The aged fly is often unable to right itself after a fall to a side-ways or supine position, leading to inability to access the food and subsequent dehydration/starvation. Finally, some flies die upright without Smurf phenotype, suggesting a possible third mechanism. The frequency of these mechanisms varies between strains and culture conditions, which may affect efficacy of life span interventions.

Social isolation shortens lifespan through oxidative stress in ants

Social isolation negatively affects health, induces detrimental behaviors, and shortens lifespan in social species. Little is known about the mechanisms underpinning these effects because model species are typically short-lived and non-social. Using colonies of the carpenter ant Camponotus fellah, we show that social isolation induces hyperactivity, alters space-use, and reduces lifespan via changes in the expression of genes with key roles in oxidation-reduction and an associated accumulation of reactive oxygen species. These physiological effects are localized to the fat body and oenocytes, which perform liver-like functions in insects. We use pharmacological manipulations to demonstrate that the oxidation-reduction pathway causally underpins the detrimental effects of social isolation on behavior and lifespan. These findings have important implications for our understanding of how social isolation affects behavior and lifespan in general.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte Nuclear Factor 4

Sexual attraction and perception are crucial for mating and reproductive success. In Drosophila melanogaster, the male-specific isoform of Fruitless (Fru), FruM, is a known master neuro-regulator of innate courtship behavior to control the perception of sex pheromones in sensory neurons. Here, we show that the non-sex-specific Fru isoform (FruCOM) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of FruCOM in oenocytes resulted in adults with reduced levels of cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 (Hnf4) as a key target of FruCOM in directing fatty acid conversion to hydrocarbons. Fru or Hnf4 depletion in oenocytes disrupts lipid homeostasis, resulting in a sex-dimorphic CHC profile that differs from doublesex- and transformer-dependent CHC dimorphism. Thus, Fru couples pheromone perception and production in separate organs to regulate chemosensory communications and ensure efficient mating behavior.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte nuclear factor 4

Sexual attraction and perception, governed by separate genetic circuits in different organs, are crucial for mating and reproductive success, yet the mechanisms of how these two aspects are integrated remain unclear. In Drosophila , the male-specific isoform of Fruitless (Fru), Fru M , is known as a master neuro-regulator of innate courtship behavior to control perception of sex pheromones in sensory neurons. Here we show that the non-sex specific Fru isoform (Fru COM ) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of Fru COM in oenocytes resulted in adults with reduced levels of the cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 ( Hnf4 ) as a key target of Fru COM in directing fatty acid conversion to hydrocarbons in adult oenocytes. fru - and Hnf4 -depletion disrupts lipid homeostasis, resulting in a novel sex-dimorphic CHC profile, which differs from doublesex - and transformer -dependent sexual dimorphism of the CHC profile. Thus, Fru couples pheromone perception and production in separate organs for precise coordination of chemosensory communication that ensures efficient mating behavior.

Teaser

Fruitless and lipid metabolism regulator HNF4 integrate pheromone biosynthesis and perception to ensure robust courtship behavior.

Dietary Restriction Impacts Peripheral Circadian Clock Output Important for Longevity in Drosophila

Circadian clocks may mediate lifespan extension by caloric or dietary restriction (DR). We find that the core clock transcription factor Clock is crucial for a robust longevity and fecundity response to DR in Drosophila. To identify clock-controlled mediators, we performed RNA-sequencing from abdominal fat bodies across the 24 h day after just 5 days under control or DR diets. In contrast to more chronic DR regimens, we did not detect significant changes in the rhythmic expression of core clock genes. Yet we discovered that DR induced de novo rhythmicity or increased expression of rhythmic clock output genes. Network analysis revealed that DR increased network connectivity in one module comprised of genes encoding proteasome subunits. Adult, fat body specific RNAi knockdown demonstrated that proteasome subunits contribute to DR-mediated lifespan extension. Thus, clock control of output links DR-mediated changes in rhythmic transcription to lifespan extension.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Microgravity-induced stress mechanisms in human stem cell-derived cardiomyocytes

Exposure to outer space microgravity poses a risk for the development of various pathologies including cardiovascular disease. To study this, we derived cardiomyocytes (CMs) from human-induced pluripotent stem cells and exposed them to simulated microgravity (SMG). We combined different “omics” and chromosome conformation capture technologies with live-cell imaging of various transgenic lines to discover that SMG impacts on the contractile velocity and function of CMs via the induction of senescence processes. This is linked to SMG-induced changes of reactive oxygen species (ROS) generation and energy metabolism by mitochondria. Taken together, we uncover a microgravity-controlled axis causing contractile dysfunctions to CMs. Our findings can contribute to the design of preventive and therapeutic strategies against senescence-associated disease.

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Simulated microgravity (SMG) causes ROS production in human cardiomyocytes (CMs)

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SMG inhibits mitochondria function and energy metabolism and induces senescence of CMs

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SMG attenuates contractile velocity, beating frequency and Ca²⁺ influx in CMs

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SMG induces chromosomal changes and modifies the chromosomal architecture in CMs

Insights into the Structure and Function of the Pex1/Pex6 AAA-ATPase in Peroxisome Homeostasis

The AAA-ATPases Pex1 and Pex6 are required for the formation and maintenance of peroxisomes, membrane-bound organelles that harbor enzymes for specialized metabolism. Together, Pex1 and Pex6 form a heterohexameric AAA-ATPase capable of unfolding substrate proteins via processive threading through a central pore. Here, we review the proposed roles for Pex1/Pex6 in peroxisome biogenesis and degradation, discussing how the unfolding of potential substrates contributes to peroxisome homeostasis. We also consider how advances in cryo-EM, computational structure prediction, and mechanisms of related ATPases are improving our understanding of how Pex1/Pex6 converts ATP hydrolysis into mechanical force. Since mutations in PEX1 and PEX6 cause the majority of known cases of peroxisome biogenesis disorders such as Zellweger syndrome, insights into Pex1/Pex6 structure and function are important for understanding peroxisomes in human health and disease.

Is Turkish coffee protects Drosophila melanogaster on cadmium acetate toxicity by promoting antioxidant enzymes?

With their increasing use in today's industry, heavy metals cause biochemical and biophysical changes by affecting the control and regulatory systems of living things. Cadmium (Cd), a heavy metal, spreads to the environment through both natural sources and industrial activities. It is taken into the organism through water, food, skin contact or smoke. Systems and organs of living things are directly or indirectly affected by Cd toxicity. Besides their recreational usage, herbal products such as coffee are preferred in alternative medicine because of their antioxidant, anti-inflammatory, anticancer and antidiabetic effects. Turkish coffee (TK) is a drink rich in flavorings, phenolic compounds and antioxidant compounds. The study evaluated the possible antioxidant role of TK against oxidative stress induced by Cadmium acetate (CdA) in the fat tissues of old-young female individuals of Drosophila melanogaster. The female flies were fed with either a standard diet, or CdA (10-30 mg), or TK (2%), or both (CdA + TK) for 3 and 10 days. Following the completion of the feeding period, the amounts of fatbody and oxidative stress markers (oxidative stress index, malondialdehyde), activities of antioxidant enzymes (Glutathione-S-transferase, Catalase, and Superoxide dismutase) and their levels were measured. Fat body lipid droplets were high in the individuals exposed to high concentrations of CdA. It was determined that lipid droplets decreased but did not significantly alter oxidative stress in the individuals treated with TK (p = 0.05). This article may be of help in terms of the use of TK compounds as antioxidants to evaluate their effects in preventing heavy metal accumulation and stress in the aging process.

Roles of Insect Oenocytes in Physiology and Their Relevance to Human Metabolic Diseases

Oenocytes are large secretory cells present in the abdomen of insects known to synthesize very-long-chain fatty acids to produce hydrocarbons and pheromones that mediate courtship behavior in adult flies. In recent years, oenocytes have been implicated in the regulation of energy metabolism. These hepatocyte-like cells accumulate lipid droplets under starvation and can non-autonomously regulate tracheal waterproofing and adipocyte lipid composition. Here, we summarize evidence, mostly from Drosophila, establishing that oenocytes perform liver-like functions. We also compare the functional differences in oenocytes and the fat body, another lipid storage tissue which also performs liver-like functions. Lastly, we examine signaling pathways that regulate oenocyte metabolism derived from other metabolic tissues, as well as oenocyte-derived signals that regulate energy homeostasis.

Peroxisomal Stress Response and Inter-Organelle Communication in Cellular Homeostasis and Aging

Peroxisomes are key regulators of cellular and metabolic homeostasis. These organelles play important roles in redox metabolism, the oxidation of very-long-chain fatty acids (VLCFAs), and the biosynthesis of ether phospholipids. Given the essential role of peroxisomes in cellular homeostasis, peroxisomal dysfunction has been linked to various pathological conditions, tissue functional decline, and aging. In the past few decades, a variety of cellular signaling and metabolic changes have been reported to be associated with defective peroxisomes, suggesting that many cellular processes and functions depend on peroxisomes. Peroxisomes communicate with other subcellular organelles, such as the nucleus, mitochondria, endoplasmic reticulum (ER), and lysosomes. These inter-organelle communications are highly linked to the key mechanisms by which cells surveil defective peroxisomes and mount adaptive responses to protect them from damages. In this review, we highlight the major cellular changes that accompany peroxisomal dysfunction and peroxisomal inter-organelle communication through membrane contact sites, metabolic signaling, and retrograde signaling. We also discuss the age-related decline of peroxisomal protein import and its role in animal aging and age-related diseases. Unlike other organelle stress response pathways, such as the unfolded protein response (UPR) in the ER and mitochondria, the cellular signaling pathways that mediate stress responses to malfunctioning peroxisomes have not been systematically studied and investigated. Here, we coin these signaling pathways as "peroxisomal stress response pathways". Understanding peroxisomal stress response pathways and how peroxisomes communicate with other organelles are important and emerging areas of peroxisome research.

Translation complex stabilization on messenger RNA and footprint profiling to study the RNA responses and dynamics of protein biosynthesis in the cells

During protein biosynthesis, ribosomes bind to messenger (m)RNA, locate its protein-coding information, and translate the nucleotide triplets sequentially as codons into the corresponding sequence of amino acids, forming proteins. Non-coding mRNA features, such as 5' and 3' untranslated regions (UTRs), start sites or stop codons of different efficiency, stretches of slower or faster code and nascent polypeptide interactions can alter the translation rates transcript-wise. Most of the homeostatic and signal response pathways of the cells converge on individual mRNA control, as well as alter the global translation output. Among the multitude of approaches to study translational control, one of the most powerful is to infer the locations of translational complexes on mRNA based on the mRNA fragments protected by these complexes from endonucleolytic hydrolysis, or footprints. Translation complex profiling by high-throughput sequencing of the footprints allows to quantify the transcript-wise, as well as global, alterations of translation, and uncover the underlying control mechanisms by attributing footprint locations and sizes to different configurations of the translational complexes. The accuracy of all footprint profiling approaches critically depends on the fidelity of footprint generation and many methods have emerged to preserve certain or multiple configurations of the translational complexes, often in challenging biological material. In this review, a systematic summary of approaches to stabilize translational complexes on mRNA for footprinting is presented and major findings are discussed. Future directions of translation footprint profiling are outlined, focusing on the fidelity and accuracy of inference of the native in vivo translation complex distribution on mRNA.

Drosophila melanogaster: A Powerful Tiny Animal Model for the Study of Metabolic Hepatic Diseases

Animal experimentation is limited by unethical procedures, time-consuming protocols, and high cost. Thus, the development of innovative approaches for disease treatment based on alternative models in a fast, safe, and economic manner is an important, yet challenging goal. In this paradigm, the fruit-fly Drosophila melanogaster has become a powerful model for biomedical research, considering its short life cycle and low-cost maintenance. In addition, biological processes are conserved and homologs of ∼75% of human disease-related genes are found in the fruit-fly. Therefore, this model has been used in innovative approaches to evaluate and validate the functional activities of candidate molecules identified via in vitro large-scale analyses, as putative agents to treat or reverse pathological conditions. In this context, Drosophila offers a powerful alternative to investigate the molecular aspects of liver diseases, since no effective therapies are available for those pathologies. Non-alcoholic fatty liver disease is the most common form of chronic hepatic dysfunctions, which may progress to the development of chronic hepatitis and ultimately to cirrhosis, thereby increasing the risk for hepatocellular carcinoma (HCC). This deleterious situation reinforces the use of the Drosophila model to accelerate functional research aimed at deciphering the mechanisms that sustain the disease. In this short review, we illustrate the relevance of using the fruit-fly to address aspects of liver pathologies to contribute to the biomedical area.

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.

What fuels the fly: Energy metabolism in Drosophila and its application to the study of obesity and diabetes

The organs and metabolic pathways involved in energy metabolism, and the process of ATP production from nutrients, are comparable between humans and Drosophila melanogaster This level of conservation, together with the power of Drosophila genetics, makes the fly a very useful model system to study energy homeostasis. Here, we discuss the major organs involved in energy metabolism in Drosophila and how they metabolize different dietary nutrients to generate adenosine triphosphate. Energy metabolism in these organs is controlled by cell-intrinsic, paracrine, and endocrine signals that are similar between Drosophila and mammals. We describe how these signaling pathways are regulated by several physiological and environmental cues to accommodate tissue-, age-, and environment-specific differences in energy demand. Last, we discuss several genetic and diet-induced fly models of obesity and diabetes that can be leveraged to better understand the molecular basis of these metabolic diseases and thereby promote the development of novel therapies.

Advances in deciphering the genetic basis of insect cuticular hydrocarbon biosynthesis and variation

Cuticular hydrocarbons (CHCs) have two fundamental functions in insects. They protect terrestrial insects against desiccation and serve as signaling molecules in a wide variety of chemical communication systems. It has been hypothesized that these pivotal dual traits for adaptation to both desiccation and signaling have contributed to the considerable evolutionary success of insects. CHCs have been extensively studied concerning their variation, behavioral impact, physiological properties, and chemical compositions. However, our understanding of the genetic underpinnings of CHC biosynthesis has remained limited and mostly biased towards one particular model organism (Drosophila). This rather narrow focus has hampered the establishment of a comprehensive view of CHC genetics across wider phylogenetic boundaries. This review attempts to integrate new insights and recent knowledge gained in the genetics of CHC biosynthesis, which is just beginning to incorporate work on more insect taxa beyond Drosophila. It is intended to provide a stepping stone towards a wider and more general understanding of the genetic mechanisms that gave rise to the astonishing diversity of CHC compounds across different insect taxa. Further research in this field is encouraged to aim at better discriminating conserved versus taxon-specific genetic elements underlying CHC variation. This will be instrumental in greatly expanding our knowledge of the origins and variation of genes governing the biosynthesis of these crucial phenotypic traits that have greatly impacted insect behavior, physiology, and evolution.

Rosy Beginnings: Studying Peroxisomes in Drosophila

Research using the fruit fly Drosophila melanogaster has traditionally focused on understanding how mutations affecting gene regulation or function affect processes linked to animal development. Accordingly, flies have become an essential foundation of modern medical research through repeated contributions to our fundamental understanding of how their homologs of human genes function. Peroxisomes are organelles that metabolize lipids and reactive oxygen species like peroxides. However, despite clear linkage of mutations in human genes affecting peroxisomes to developmental defects, for many years fly models were conspicuously absent from the study of peroxisomes. Now, the few early studies linking the Rosy eye color phenotype to peroxisomes in flies have been joined by a growing body of research establishing novel roles for peroxisomes during the development or function of specific tissues or cell types. Similarly, unique properties of cultured fly Schneider 2 cells have advanced our understanding of how peroxisomes move on the cytoskeleton. Here, we profile how those past and more recent Drosophila studies started to link specific effects of peroxisome dysfunction to organ development and highlight the utility of flies as a model for human peroxisomal diseases. We also identify key differences in the function and proliferation of fly peroxisomes compared to yeast or mammals. Finally, we discuss the future of the fly model system for peroxisome research including new techniques that should support identification of additional tissue specific regulation of and roles for peroxisomes.

Isolation and transcriptomic analysis of Anopheles gambiae oenocytes enables the delineation of hydrocarbon biosynthesis

The surface of insects is coated in cuticular hydrocarbons (CHCs); variations in the composition of this layer affect a range of traits including adaptation to arid environments and defence against pathogens and toxins. In the African malaria vector, Anopheles gambiae quantitative and qualitative variance in CHC composition have been associated with speciation, ecological habitat and insecticide resistance. Understanding how these modifications arise will inform us of how mosquitoes are responding to climate change and vector control interventions. CHCs are synthesised in sub-epidermal cells called oenocytes that are very difficult to isolate from surrounding tissues. Here we utilise a transgenic line with fluorescent oenocytes to purify these cells for the first time. Comparative transcriptomics revealed the enrichment of biological processes related to long chain fatty acyl-CoA biosynthesis and elongation of mono-, poly-unsaturated and saturated fatty acids and enabled us to delineate, and partially validate, the hydrocarbon biosynthetic pathway in An. gambiae.

Impaired peroxisomal import in Drosophila oenocytes causes cardiac dysfunction by inducing upd3 as a peroxikine

Aging is characterized by a chronic, low-grade inflammation, which is a major risk factor for cardiovascular diseases. It remains poorly understood whether pro-inflammatory factors released from non-cardiac tissues contribute to the non-autonomous regulation of age-related cardiac dysfunction. Here, we report that age-dependent induction of cytokine unpaired 3 (upd3) in Drosophila oenocytes (hepatocyte-like cells) is the primary non-autonomous mechanism for cardiac aging. We show that upd3 is significantly up-regulated in aged oenocytes. Oenocyte-specific knockdown of upd3 is sufficient to block aging-induced cardiac arrhythmia. We further show that the age-dependent induction of upd3 is triggered by impaired peroxisomal import and elevated JNK signaling in aged oenocytes. We term hormonal factors induced by peroxisome dysfunction as peroxikines. Intriguingly, oenocyte-specific overexpression of Pex5, the key peroxisomal import receptor, blocks age-related upd3 induction and alleviates cardiac arrhythmicity. Thus, our studies identify an important role of hepatocyte-specific peroxisomal import in mediating non-autonomous regulation of cardiac aging.

Peroxisomal Dysfunction in Neurological Diseases and Brain Aging

Peroxisomes exist in most cells, where they participate in lipid metabolism, as well as scavenging the reactive oxygen species (ROS) that are produced as by-products of their metabolic functions. In certain tissues such as the liver and kidneys, peroxisomes have more specific roles, such as bile acid synthesis in the liver and steroidogenesis in the adrenal glands. In the brain, peroxisomes are critically involved in creating and maintaining the lipid content of cell membranes and the myelin sheath, highlighting their importance in the central nervous system (CNS). This review summarizes the peroxisomal lifecycle, then examines the literature that establishes a link between peroxisomal dysfunction, cellular aging, and age-related disorders that affect the CNS. This review also discusses the gap of knowledge in research on peroxisomes in the CNS.

Causal roles of mitochondrial dynamics in longevity and healthy aging

Mitochondria are organized in the cell in the form of a dynamic, interconnected network. Mitochondrial dynamics, regulated by mitochondrial fission, fusion, and trafficking, ensure restructuring of this complex reticulum in response to nutrient availability, molecular signals, and cellular stress. Aberrant mitochondrial structures have long been observed in aging and age-related diseases indicating that mitochondrial dynamics are compromised as cells age. However, the specific mechanisms by which aging affects mitochondrial dynamics and whether these changes are causally or casually associated with cellular and organismal aging is not clear. Here, we review recent studies that show specifically how mitochondrial fission, fusion, and trafficking are altered with age. We discuss factors that change with age to directly or indirectly influence mitochondrial dynamics while examining causal roles for altered mitochondrial dynamics in healthy aging and underlying functional outputs that might affect longevity. Lastly, we propose that altered mitochondrial dynamics might not just be a passive consequence of aging but might constitute an adaptive mechanism to mitigate age-dependent cellular impairments and might be targeted to increase longevity and promote healthy aging.

Extension of Drosophila lifespan by Korean red ginseng through a mechanism dependent on dSir2 and insulin/IGF-1 signaling

Many studies have indicated that Korean red ginseng (KRG) has anti-inflammatory and anti-oxidative effects, thereby inducing many health benefits in humans. Studies into the longevity effects of KRG are limited and have provided contradictory results, and the molecular mechanism of lifespan extension by KRG is not elucidated yet. Herein, the longevity effect of KRG was investigated in Drosophila melanogaster by feeding KRG extracts, and the molecular mechanism of lifespan extension was elucidated by using longevity-related mutant flies. KRG extended the lifespan of Drosophila when administrated at 10 and 25 μg/mL, and the longevity benefit of KRG was not due to reduced feeding, reproduction, and/or climbing ability in fruit flies, indicating that the longevity benefit of KRG is a direct effect of KRG, not of a secondary artifact. Diet supplementation with KRG increased the lifespan of flies on a full-fed diet but not of those on a restricted diet, and the longevity effect of KRG was diminished by the mutation of dSir2, a deacetylase known to mediate the benefits of dietary restriction. Similarly, the longevity effect of KRG was mediated by the reduction of insulin/IGF-1 signaling. In conclusion, KRG extends the lifespan of Drosophila through Sir2 and insulin/IGF-1 signaling and has potential as an anti-aging dietary-restriction mimetic and prolongevity supplement.

On the Fly: Recent Progress on Autophagy and Aging in Drosophila

Autophagy ensures the lysosome-mediated breakdown and recycling of self-material, as it not only degrades obsolete or damaged intracellular constituents but also provides building blocks for biosynthetic and energy producing reactions. Studies in animal models including Drosophila revealed that autophagy defects lead to the rapid decline of neuromuscular function, neurodegeneration, sensitivity to stress (such as starvation or oxidative damage), and stem cell loss. Of note, recently identified human Atg gene mutations cause similar symptoms including ataxia and mental retardation. Physiologically, autophagic degradation (flux) is known to decrease during aging, and this defect likely contributes to the development of such age-associated diseases. Many manipulations that extend lifespan (including dietary restriction, reduced TOR kinase signaling, exercise or treatment with various anti-aging substances) require autophagy for their beneficial effect on longevity, pointing to the key role of this housekeeping process. Importantly, genetic (e.g., Atg8a overexpression in either neurons or muscle) or pharmacological (e.g., feeding rapamycin or spermidine to animals) promotion of autophagy has been successfully used to extend lifespan in Drosophila, suggesting that this intracellular degradation pathway can rejuvenate cells and organisms. In this review, we highlight key discoveries and recent progress in understanding the relationship of autophagy and aging in Drosophila.

Ocular Albinism Type 1 Regulates Deltamethrin Tolerance in Lymantria dispar and Drosophila melanogaster

The ocular albinism type 1 (OA1), a pigment cell-specific integral membrane glycoprotein, is a member of the G-protein-coupled receptor (GPCR) superfamily that binds to heterotrimeric G proteins in mammalian cells. We aimed to characterize the physiological functions an insect OA1 from Lymantria dispar (LdOA1) employs in the regulation of insecticide tolerance. In the present study, we investigated the roles of LdOA1 in response to deltamethrin exposure in both L. dispar and Drosophila melanogaster. LdOA1 was expressed at the lowest level during the 4^th instar stage, while LdOA1 was significantly upregulated in the 5^th instar and male stages. Knockdown of LdOA1 by injecting dsRNA of LdOA1 into gypsy moth larvae caused a 4.80-fold higher mortality than in control larvae microinjected with dsRNA of GFP under deltamethrin stress. Nine out of 11 L. dispar CYP genes were significantly downregulated under deltamethrin stress in LdOA1 silenced larvae as compared to control larvae. Moreover, the LdOA1 gene was successfully overexpressed in D. melanogaster using transgenic technique. The deltamethrin contact assay showed that the LdOA1 overexpression in flies significantly enhanced the tolerance to deltamethrin compared to the control flies. Furthermore, the downstream Drosophila CYP genes were upregulated in the LdOA1 overexpression flies, suggesting LdOA1 may play a master switch role in P450-mediated metabolic detoxification. This study is the first report of an insect OA1 gene regulating insecticide tolerance and potentially playing a role in the regulation of downstream cytochrome P450 expression. These results contribute to the future development of novel insecticides targeting insect GPCRs.

Age-Dependent Changes in Transcription Factor FOXO Targeting in Female Drosophila

FOXO transcription factors have long been associated with longevity control and tissue homeostasis. Although the transcriptional regulation of FOXO have been previously characterized (especially in long-lived insulin mutants and under stress conditions), how normal aging impacts the transcriptional activity of FOXO is poorly understood. Here, we conducted a chromatin immunoprecipitation sequencing (ChIP-Seq) analysis in both young (2-week-old) and aged (5-week-old) wild-type female fruit flies, Drosophila melanogaster, to evaluate the dynamics of FOXO gene targeting during aging. Intriguingly, the number of FOXO-bound genes dramatically decreases with age (from 2617 to 224). Consistent to the reduction of FOXO binding activity, many genes targeted by FOXO in young flies are transcriptionally altered with age, either up-regulated (FOXO-repressing genes) or down-regulated (FOXO-activating genes) in adult head tissue. In addition, we show that many FOXO-bound genes in wild-type flies are unique from those in insulin receptor substrate chico mutants. Distinct from chico mutants, FOXO targets specific cellular processes (e.g., actin cytoskeleton) and signaling pathways (e.g., Hippo, MAPK) in young wild-type female flies. FOXO targeting on these pathways decreases with age. Interestingly, FOXO targets in aged flies are enriched in cellular processes like chromatin organization and nucleosome assembly. Furthermore, FOXO binding to core histone genes is well maintained at aged flies. Together, our findings provide new insights into dynamic FOXO targeting under normal aging and highlight the diverse and understudied regulatory mechanisms for FOXO transcriptional activity.

Organelle aging: Lessons from model organisms

Most cellular processes descend into failure during aging. While a large collection of longevity pathways has been identified in the past decades, the mechanism for age-related decline of cellular homeostasis and organelle function remains largely unsolved. It is known that many organelles undergo structural and functional changes during normal aging, which significantly contributes to the decline of tissue function at old ages. Since recent studies have revealed an emerging role of organelles as regulatory hubs in maintaining cellular homeostasis, understanding of organelle aging will provide important insights into the cellular basis of organismal aging. Here we review current progress on the characterization of age-dependent structural and functional alterations in the more well-studied organelles, as well as the known mechanisms governing organelle aging in model organisms, with a special focus on the fruit fly Drosophila melanogaster.