Keeping it tight: The relationship between bacterial dysbiosis, septate junctions, and the intestinal barrier in Drosophila

Comparison of distinct gut bacterial communities in different stage of prediapause and nondiapause larvae in Loxostege sticticalis

Introduction

Symbiotic microorganisms in insects regulate multiple physiological functions, widely participating in nutrient metabolism, immune regulation, and crucial regulatory roles in development. However, little is known about how microbial factors might respond to the preparation of insect diapause.

Methods

The gut bacterial communities of Loxostege sticticalis larvae induced at different photoperiod of long (LD16:8, nondiapause) and short (LD12:12, prediapause) daylength were compared, by 16S rRNA Illumina MiSeq.

Results

A total number of 42 phylum, 78 classes, 191 orders, 286 families, 495 genera, and 424 species were identified in the intestinal bacterial community of L. sticticalis larvae. Alpha diversity and beta diversity analyses revealed significant differences between nondiapause and prediapause larvae. In non-diapause larvae, the dominant intestinal bacteria were Firmicutes and Proteobacteria. In specific, in 3rd and 4th instar larvae, the main intestinal bacteria were Staphylococcus, while in 5th instar, it was JC017. For the prediapause larvae, the dominant phylum in 3rd instar larvae was Firmicutes, with the dominant genus of Staphylococcus, while in 4th and 5th instar larvae was Bacteroidota, with the dominant genus 4th instar was Staphylococcus, and in 5th instar was JC017. KEGG functional prediction analysis revealed that functional bacterial groups involved in metabolism had the highest abundance values. Specifically, the amino acid metabolism of metabolism-related functional genes in the 3rd instar prediapause larvae was significantly lower than that in the 4th and 5th instar prediapause larvae and the non-diapause treatment. However, the carbohydrate metabolism in 3rd instar prediapause larvae was significantly higher than that in 4th and 5th instar prediapause larvae and non-diapause treatments. The dominant bacterial phylum in the prediapause larvae at different stages of L. sticticalis was varied, and there were significant differences in community diversity and richness.

Discussion

These results suggest a complex interaction between the hosts' physiological state and its gut microbiota, indicating that bacterial communities may assist insects in adapting to diapause preparation by regulating their metabolic levels. This study lays the foundation for further understanding the physiological mechanisms by which intestinal microorganisms regulate overwintering dormancy in the L. sticticalis.

Total ginsenosides extend healthspan of aging Drosophila by suppressing imbalances in intestinal stem cells and microbiota

BACKGROUND

Disruption of stem cell and microbial homeostasis accelerates the aging process. Hence, maintaining these balances effectively delays aging and alleviates the symptoms of age-related diseases. Recent research indicates that targeting endoplasmic reticulum (ER) stress and immune deficiency (IMD) signalling may play a positive role in maintaining homeostasis in aging intestinal stem cells (ISC) and microbial equilibrium. Previous research has suggested that total ginsenosides (TG) derived from Panax ginseng C. A. Meyer may exhibit potential anti-aging properties by mitigating ER stress and mediating the IMD pathway. Nevertheless, it remains unclear whether TG improve ISC and microbial homeostasis by modulating ER stress and the IMD pathway to promote healthy aging.

PURPOSE

To elucidate whether TG promotes healthspan in Drosophila and its underlying molecular mechanisms, focusing on its role in regulating ER stress and the IMD pathway to maintain ISC and intestinal microbiota homeostasis.

METHODS

High performance liquid chromatography was performed to detect the main saponin monomer in TG. Survival rate, gut length, barrier function, and feeding/excretion behaviour assays were used to evaluate the effects of TG on the lifespan and gut health of Drosophila. At the stem cell level, "esg-luciferase" reporter system, esg-GFP/delta stem cell fluorescent labelling, and phospho-histone H3+ mitotic activity assays were employed to determine whether TG prevented natural aging or oxidative stress-associated ISC over-proliferation in Drosophila. Immunofluorescence staining was used to detect the effects of TG on ER stress during aging. Overexpression or interference of ER stress target genes and their related c-Jun N-terminal kinase (JNK) gene was manipulated using gene editing technology to verify the molecular mechanism by which TG maintains age-related ISC proliferation homeostasis. Molecular docking and isothermal titration calorimetry were used to verify the direct interactions between TG and ER stress target genes. In addition, at the intestinal flora level, 16S rDNA sequencing was used to analyse the effect of TG on the diversity and abundance of Drosophila intestinal flora and the possible functional pathways involved. RT-qPCR was performed to determine whether TG mediated the expression of target genes in the IMD pathway. A dominant bacterial species-specific mono-association analysis were performed to verify whether the effects of TG on IMD target genes and ISC proliferation depended on the direct control of the dominant bacterial species.

RESULTS

Our results suggest that administration of TG delays the decline in gut morphology and function in aging Drosophila. TG prevents age-associated ISC hyperproliferation by inhibiting ER stress IRE1-mediated JNK signaling. Furthermore, oral TG prevented aging-associated ISC and gut microbiota dysbiosis by remodelling the gut microbiota and inhibiting Acetobacter-mediated activation of IMD target genes.

CONCLUSION

TG promotes healthy aging by inhibiting the excessive proliferation of ISC and alleviating intestinal microbial imbalance, thereby providing new insights for the research and development of anti-aging TG products.

Compromised junctional integrity phenocopies age-dependent renal dysfunction in Drosophila Snakeskin mutants

Transporting epithelia provide a protective barrier against pathogenic insults while allowing the controlled exchange of ions, solutes and water with the external environment. In invertebrates, these functions depend on formation and maintenance of 'tight' septate junctions (SJs). However, the mechanism by which SJs affect transport competence and tissue homeostasis, and how these are modulated by ageing, remain incompletely understood. Here, we demonstrate that the Drosophila renal (Malpighian) tubules undergo an age-dependent decline in secretory capacity, which correlates with mislocalisation of SJ proteins and progressive degeneration in cellular morphology and tissue homeostasis. Acute loss of the SJ protein Snakeskin in adult tubules induced progressive changes in cellular and tissue architecture, including altered expression and localisation of junctional proteins with concomitant loss of cell polarity and barrier integrity, demonstrating that compromised junctional integrity is sufficient to replicate these ageing-related phenotypes. Taken together, our work demonstrates a crucial link between epithelial barrier integrity, tubule transport competence, renal homeostasis and organismal viability, as well as providing novel insights into the mechanisms underpinning ageing and renal disease.

Intestinal stem cells and their niches in homeostasis and disease

Tissues such as the intestine harbor stem cells that have remarkable functional plasticity in response to a dynamic environment. To adapt to the environment, stem cells constantly receive information from their surrounding microenvironment (also called the 'niche') that instructs them how to adapt to changes. The Drosophila midgut shows morphological and functional similarities to the mammalian small intestine and has been a useful model system to study signaling events in stem cells and tissue homeostasis. In this review, we summarize the current understanding of the Drosophila midgut regarding how stem cells communicate with microenvironmental niches including enteroblasts, enterocytes, enteroendocrine cells and visceral muscles to coordinate tissue regeneration and homeostasis. In addition, distant cells such as hemocytes or tracheal cells have been shown to interact with stem cells and influence the development of intestinal diseases. We discuss the contribution of stem cell niches in driving or counteracting disease progression, and review conceptual advances derived from the Drosophila intestine as a model for stem cell biology.

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

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

Gut microbiome-mediated mechanisms in aging-related diseases: are probiotics ready for prime time?

Chronic low-grade inflammation affects health and is associated with aging and age-related diseases. Dysregulation of the gut flora is an important trigger for chronic low-grade inflammation. Changes in the composition of the gut flora and exposure to related metabolites have an effect on the inflammatory system of the host. This results in the development of crosstalk between the gut barrier and immune system, contributing to chronic low-grade inflammation and impairment of health. Probiotics can increase the diversity of gut microbiota, protect the gut barrier, and regulate gut immunity, thereby reducing inflammation. Therefore, the use of probiotics is a promising strategy for the beneficial immunomodulation and protection of the gut barrier through gut microbiota. These processes might positively influence inflammatory diseases, which are common in the elderly.

Intestinal barrier dysfunction: an evolutionarily conserved hallmark of aging

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

How commensal microbes shape the physiology of Drosophila melanogaster

The interactions between animals and their commensal microbes profoundly influence the host's physiology. In the last decade, Drosophila melanogaster has been extensively used as a model to study host-commensal microbes interactions. Here, we review the most recent advances in this field. We focus on studies that extend our understanding of the molecular mechanisms underlying the effects of commensal microbes on Drosophila's development and lifespan. We emphasize how commensal microbes influence nutrition and the intestinal epithelium homeostasis; how they elicit immune tolerance mechanisms and how these physiological processes are interconnected. Finally, we discuss the importance of diets and microbial strains and show how they can be confounding factors of microbe mediated host phenotypes.

Ageing, metabolism and the intestine

The intestinal epithelium serves as a dynamic barrier to the environment and integrates a variety of signals, including those from metabolites, commensal microbiota, immune responses and stressors upon ageing. The intestine is constantly challenged and requires a high renewal rate to replace damaged cells in order to maintain its barrier function. Essential for its renewal capacity are intestinal stem cells, which constantly give rise to progenitor cells that differentiate into the multiple cell types present in the epithelium. Here, we review the current state of research of how metabolism and ageing control intestinal stem cell function and epithelial homeostasis. We focus on recent insights gained from model organisms that indicate how changes in metabolic signalling during ageing are a major driver for the loss of stem cell plasticity and epithelial homeostasis, ultimately affecting the resilience of an organism and limiting its lifespan. We compare findings made in mouse and Drosophila and discuss differences and commonalities in the underlying signalling pathways and mechanisms in the context of ageing.

The Snakeskin-Mesh Complex of Smooth Septate Junction Restricts Yorkie to Regulate Intestinal Homeostasis in Drosophila

Tight junctions in mammals and septate junctions in insects are essential for epithelial integrity. We show here that, in the Drosophila intestine, smooth septate junction proteins provide barrier and signaling functions. During an RNAi screen for genes that regulate adult midgut tissue growth, we found that loss of two smooth septate junction components, Snakeskin and Mesh, caused a hyperproliferation phenotype. By examining epitope-tagged endogenous Snakeskin and Mesh, we demonstrate that the two proteins are present in the cytoplasm of differentiating enteroblasts and in cytoplasm and septate junctions of mature enterocytes. In both enteroblasts and enterocytes, loss of Snakeskin and Mesh causes Yorkie-dependent expression of the JAK-STAT pathway ligand Upd3, which in turn promotes proliferation of intestinal stem cells. Snakeskin and Mesh form a complex with each other, with other septate junction proteins and with Yorkie. Therefore, the Snakeskin-Mesh complex has both barrier and signaling function to maintain stem cell-mediated tissue homeostasis.

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Snakeskin and Mesh are septate junction proteins essential for intestinal homeostasis

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Snakeskin and Mesh act in enteroblasts and enterocytes to regulate stem cell division

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Snakeskin and Mesh form a complex with and restrict the activity of Yorkie

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Loss of Snakeskin and Mesh allows Yorkie to promote Upd3 expression and growth

Intestinal Stem Cell Aging: Origins and Interventions

Regenerative processes that maintain the function of the gastrointestinal (GI) epithelium are critical for health and survival of multicellular organisms. In insects and vertebrates, intestinal stem cells (ISCs) regenerate the GI epithelium. ISC function is regulated by intrinsic, local, and systemic stimuli to adjust regeneration to tissue demands. These control mechanisms decline with age, resulting in significant perturbation of intestinal homeostasis. Processes that lead to this decline have been explored intensively in Drosophila melanogaster in recent years and are now starting to be characterized in mammalian models. This review presents a model for age-related regenerative decline in the fly intestine and discusses recent findings that start to establish molecular mechanisms of age-related decline of mammalian ISC function.

Intestinal Snakeskin Limits Microbial Dysbiosis during Aging and Promotes Longevity

Intestinal barrier dysfunction is an evolutionarily conserved hallmark of aging, which has been linked to microbial dysbiosis, altered expression of occluding junction proteins, and impending mortality. However, the interplay between intestinal junction proteins, age-onset dysbiosis, and lifespan determination remains unclear. Here, we show that altered expression of Snakeskin (Ssk), a septate junction-specific protein, can modulate intestinal homeostasis, microbial dynamics, immune activity, and lifespan in Drosophila. Loss of Ssk leads to rapid and reversible intestinal barrier dysfunction, altered gut morphology, dysbiosis, and dramatically reduced lifespan. Remarkably, restoration of Ssk expression in flies showing intestinal barrier dysfunction rescues each of these phenotypes previously linked to aging. Intestinal up-regulation of Ssk protects against microbial translocation following oral infection with pathogenic bacteria. Furthermore, intestinal up-regulation of Ssk improves intestinal barrier function during aging, limits dysbiosis, and extends lifespan. Our findings indicate that intestinal occluding junctions may represent prolongevity targets in mammals.