Aging is characterized by a growing risk of disease and death, yet the underlying pathophysiology is poorly understood. Indeed, little is known about how the functional decline of individual organ systems relates to the integrative physiology of aging and probability of death of the organism. Here we show that intestinal barrier dysfunction is correlated with lifespan across a range of Drosophila genotypes and environmental conditions, including mitochondrial dysfunction and dietary restriction. Regardless of chronological age, intestinal barrier dysfunction predicts impending death in individual flies. Activation of inflammatory pathways has been linked to aging and age-related diseases in humans, and an age-related increase in immunity-related gene expression has been reported in Drosophila. We show that the age-related increase in expression of antimicrobial peptides is tightly linked to intestinal barrier dysfunction. Indeed, increased antimicrobial peptide expression during aging can be used to identify individual flies exhibiting intestinal barrier dysfunction. Similarly, intestinal barrier dysfunction is more accurate than chronological age in identifying individual flies with systemic metabolic defects previously linked to aging, including impaired insulin/insulin-like growth factor signaling, as evidenced by a reduction in Akt activation and upregulation of dFOXO target genes. Thus, the age-dependent loss of intestinal integrity is associated with altered metabolic and immune signaling and, critically, is a harbinger of death. Our findings suggest that intestinal barrier dysfunction may be an important factor in the pathophysiology of aging in other species as well, including humans.ging involves the accumulation of damage to molecules, cells, and tissues, resulting in a decline in physiological functions and ultimately leading to an increased probability of death (1). Considerable progress has been made toward identifying genetic and environmental factors that modulate aging and lifespan, mainly as a result of pioneering work in invertebrate models, such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster (2). Our understanding of the integrative pathophysiology of aging and age-onset mortality remains very limited, however (3). A number of markers of human aging and age-onset disease have been identified, including a chronic state of inflammation (4) and the development of insulin resistance (5). In a similar fashion, Drosophila aging is also associated with the increased expression of immunity-related genes (6, 7) and characteristics of insulin/insulin-like growth factor signaling (IIS) impedance (8). The relationships between these different metabolic and inflammatory markers of aging and how they relate to age-related pathological changes remain unexplored, however. Moreover, although Drosophila is an important model for studying the genetics of aging, the ability to predict the age at which a fly will die based on a decline in organ function has proven elusive.The inte...

Summary Alterations in the composition of the intestinal microbiota have been correlated with aging and measures of frailty in the elderly. However, the relationships between microbial dynamics, age-related changes in intestinal physiology and organismal health remain poorly understood. Here, we show that dysbiosis of the intestinal microbiota, characterized by an expansion of the Gammaproteobacteria, is tightly linked to age-onset intestinal barrier dysfunction in Drosophila. Indeed, alterations in the microbiota precede and predict the onset of intestinal barrier dysfunction in aged flies. Changes in microbial composition occurring prior to intestinal barrier dysfunction contribute to changes in excretory function and immune gene activation in the aging intestine. In addition, we show that a distinct shift in microbiota composition follows intestinal barrier dysfunction leading to systemic immune activation and organismal death. Our results indicate that alterations in microbiota dynamics could contribute to and also predict varying rates of health decline during aging in mammals.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. 59apically and are in contact with the intestinal lumen (Fig. 1A, Supplementary Fig. 1A). 60Therefore, we hypothesized that age-related changes in SJ could directly contribute to 74and an enriched analysis of the dataset revealed that the "cell adhesion" gene ontology 75(GO) category was one of the most representative GO categories that change with age 76(Supplementary Table1). The expression level of the majority of these genes (16 of 18) 77was up-regulated in old flies, indicating that decreased transcription is not a primary 78 mechanism contributing to age-related changes in SJs in the midgut. 79In Drosophila, SJ are divided into two classes based on morphological 95One striking and consistent age-related change in SJs was observed at tricellular 96 junctions (TCJ) (arrowheads, Fig. 1D-I, L-M, P-T), the specialized junction at the 101In the adult posterior midgut, Gli co-localized with Dlg ( Fig. 2A-B'; Supplementary 102 Fig. 2A-A''), as described previously in wing discs 16, 17 . Gli protein was clearly detected 103at EC-EC and EC-EE cell TCJ (Fig. 2 A,C,F); however, no Gli protein was detected in 104ISCs/EBs (Fig. 2D). In midguts from aged flies, Gli localization was largely absent from 105 the TCJ, and protein levels were increased in the cytoplasm (Fig. 2F-H). In hindguts, no 106 changes in Gli localization or protein levels were observed, similar to our observation for 107 other SJ proteins ( Supplementary Fig. 1P-Q). Interestingly, Dlg appeared cytoplasmic, 108rather than membrane-localized, in ISC/EB 'nests', suggesting that definitive SJ may be 109 absent between ISC/EBs and that formation of SJ is coordinated with differentiation. 110Consistent with this hypothesis, SJ were not apparent between ISCs and EBs via EM 111( Fig. 2E). 112Given the significant changes in TCJ (Fig. 1 D-M, P-T) and the striking loss of Gli 113from TCJ in older animals ( Fig. 2G-H age was a significant factor contributing to changes in TCJ (Fig. 2I, J) 118To determine whether compromised TCJ function could contribute to age-related 119 changes in the intestine, Gli was depleted from TCJs using a drug-inducible version of 120 the GAL4-UAS system 19, 20 . Targeted gene expression using the 5966 GS GAL4 "driver" 125Depletion of Gli from ECs resulted in an accelerated loss of barrier integrity (Fig. 1263A ; Supplementary Fig. 2E). Integrity of the intestinal barrier can be assayed by feeding 127 flies a non-absorbable blue food dye. When the intestinal barrier is intact, the dye is 128 retaine...

SummaryInfections disturb metabolic homeostasis in many contexts, but the underlying connections are not completely understood. To address this, we use paired genetic and computational screens in Drosophila to identify transcriptional regulators of immunity and pathology and their associated target genes and physiologies. We show that Mef2 is required in the fat body for anabolic function and the immune response. Using genetic and biochemical approaches, we find that MEF2 is phosphorylated at a conserved site in healthy flies and promotes expression of lipogenic and glycogenic enzymes. Upon infection, this phosphorylation is lost, and the activity of MEF2 changes—MEF2 now associates with the TATA binding protein to bind a distinct TATA box sequence and promote antimicrobial peptide expression. The loss of phosphorylated MEF2 contributes to loss of anabolic enzyme expression in Gram-negative bacterial infection. MEF2 is thus a critical transcriptional switch in the adult fat body between metabolism and immunity.