Macrophage-derived insulin antagonist ImpL2 induces lipoprotein mobilization upon bacterial infection

Intratumor HIF-1α modulates production of a cachectic ligand to cause host wasting

Tumor-host interactions play critical roles in cancer-associated cachexia. Previous studies have identified several cachectic proteins secreted by tumors that impair metabolic homeostasis in multiple organs, leading to host wasting. The molecular mechanisms by which malignant tumors regulate the production or secretion of these cachectic proteins, however, still remain largely unknown. In this study, we used different Drosophila cachexia models to investigate how malignant tumors regulate biosynthesis of ImpL2, a conserved cachectic protein that inhibits systemic insulin/IGF signaling and suppresses anabolism of host organs. Through bioinformatic and biochemical analysis, we found that hypoxia-inducible factor HIF-1α/Sima directly binds to the promoter region of ImpL2 gene for the first time, promoting its transcription in both tumors and non-tumor cells. Interestingly, expressing HphA to moderately suppress HIF-1α/Sima activity in adult yki 3SA gut tumors or larval scrib 1 Ras V12 disc tumors sufficiently decreased ImpL2 expression and improved organ wasting, without affecting tumor growth. We further revealed conserved regulatory mechanisms conserved across species, as intratumor HIF-1α enhances the production of IGFBP-5, a mammalian homolog of fly ImpL2, contributing to organ wasting in both tumor-bearing mice and patients. Therefore, our study provides novel insights into the mechanisms by which tumors regulate production of cachectic ligands and the pathogenesis of cancer-induced cachexia.

Adipocyte metabolic state regulates glial phagocytic function

Excess dietary sugar profoundly impacts organismal metabolism and health, yet it remains unclear how metabolic adaptations in adipose tissue influence other organs, including the brain. Here, we show that a high-sugar diet (HSD) in Drosophila reduces adipocyte glycolysis and mitochondrial pyruvate uptake, shifting metabolism toward fatty acid oxidation and ketogenesis. These metabolic changes trigger mitochondrial oxidation and elevate antioxidant responses. Adipocyte-specific manipulations of glycolysis, lipid metabolism, or mitochondrial dynamics non-autonomously modulate Draper expression in brain ensheathing glia, key cells responsible for neuronal debris clearance. Adipocyte-derived ApoB-containing lipoproteins maintain basal Draper levels in glia via LpR1, critical for effective glial phagocytic activity. Accordingly, reducing ApoB or LpR1 impairs glial clearance of degenerating neuronal debris after injury. Collectively, our findings demonstrate that dietary sugar-induced shifts in adipocyte metabolism substantially influence brain health by modulating glial phagocytosis, identifying adipocyte-derived ApoB lipoproteins as essential systemic mediators linking metabolic state with neuroprotective functions.

SAM transmethylation pathway and adenosine recycling to ATP are essential for systemic regulation and immune response

During parasitoid wasp infection, activated immune cells of Drosophila melanogaster larvae release adenosine to conserve nutrients for immune response. S-adenosylmethionine (SAM) is a methyl group donor for most methylations in the cell and is synthesized from methionine and ATP. After methylation, SAM is converted to S-adenosylhomocysteine, which is further metabolized to adenosine and homocysteine. Here, we show that the SAM transmethylation pathway is up-regulated during immune cell activation and that the adenosine produced by this pathway in immune cells acts as a systemic signal to delay Drosophila larval development and ensure sufficient nutrient supply to the immune system. We further show that the up-regulation of the SAM transmethylation pathway and the efficiency of the immune response also depend on the recycling of adenosine back to ATP by adenosine kinase and adenylate kinase. We therefore hypothesize that adenosine may act as a sensitive sensor of the balance between cell activity, represented by the sum of methylation events in the cell, and nutrient supply. If the supply of nutrients is insufficient for a given activity, adenosine may not be effectively recycled back into ATP and may be pushed out of the cell to serve as a signal to demand more nutrients.

Inter-organ communication in Drosophila: Lipoproteins, adipokines, and immune-metabolic coordination

Inter-organ communication networks are essential for maintaining systemic homeostasis in multicellular organisms. In Drosophila melanogaster, studies of adipokines and lipoproteins reveal evolutionarily conserved mechanisms coordinating metabolism, immunity, and behavior. This mini-review focuses on two key pathways: the adipokine Unpaired 2 (Upd2) and lipoprotein-mediated signaling. Upd2, a leptin analog, mediates fat-brain communication to regulate insulin secretion, sleep, and feeding behavior. Recent work has uncovered an LC3/Atg8-dependent secretion mechanism for Upd2, linking nutrient sensing to systemic adaptation. Lipoproteins, particularly ApoLpp and LTP, function beyond lipid transport, orchestrating neural maintenance and immune responses. During infection, macrophage-derived signals trigger lipoprotein-mediated lipid redistribution to support host defense. Additionally, muscle tissue emerges as an unexpected mediator of immune-metabolic coordination through inter-organ signaling. These findings highlight the intricate cross-talk between organs required for organismal survival and suggest therapeutic strategies for metabolic disorders.

Ketogenesis nutritionally supports brain during bacterial infection in Drosophila

Mounting an immune response is a nutritionally demanding process that requires the systemic redistribution of energy stores towards the immune system. This is facilitated by cytokine-induced insulin resistance, which simultaneously promotes the mobilization of lipids and carbohydrates while limiting their consumption in immune-unrelated processes, such as development, growth, and reproduction. However, this adaptation also restricts the availability of nutrients to vital organs, which must then be sustained by alternative fuels. Here, we employed an experimental model of severe bacterial infection in Drosophila melanogaster to investigate whether ketogenesis may represent a metabolic adaptation for overcoming periods of nutritional scarcity during the immune response. We found that the immune response to severe bacterial infection is accompained by increased ketogenesis in the fat body and macrophages, leading to elevated levels of β-hydroxybutyrate in circulation. Although this metabolic adaptation is essential for survival during infection, it is not required for the elimination of the pathogen itself. Instead, ketone bodies predominately serve as an energy source for the brain neurons during this period of nutrient scarcity.

Drosophila melanogaster experimental model to test new antimicrobials: a methodological approach

Given the increasing concern about antimicrobial resistance among the microorganisms that cause infections in our society, there is an urgent need for new drug discovery. Currently, this process involves testing many low-quality compounds, resulting from the in vivo testing, on mammal models, which not only wastes time, resources, and money, but also raises ethical questions. In this review, we have discussed the potential of D. melanogaster as an intermediary experimental model in this drug discovery timeline. We have tackled the topic from a methodological perspective, providing recommendations regarding the range of drug concentrations to test based on the mechanism of action of each compound; how to treat D. melanogaster, how to monitor that treatment, and what parameters we should consider when designing a drug screening protocol to maximize the study's benefits. We also discuss the necessary improvements needed to establish the D. melanogaster model of infection as a standard technique in the drug screening process. Overall, D. melanogaster has been demonstrated to be a manageable model for studying broad-spectrum infection treatment. It allows us to obtain valuable information in a cost-effective manner, which can improve the drug screening process and provide insights into our current major concern. This approach is also in line with the 3R policy in biomedical research, in particular on the replacement and reduce the use of vertebrates in preclinical development.

IGFBP7 promotes endothelial cell repair in the recovery phase of acute lung injury

IGFBP7 has been found to play an important role in inflammatory diseases, such as acute lung injury (ALI). However, the role of IGFBP7 in different stages of inflammation remains unclear. Transcriptome sequencing was used to identify the regulatory genes of IGFBP7, and endothelial IGFBP7 expression was knocked down using Aplnr-Dre mice to evaluate the endothelial proliferation capacity. The expression of proliferation-related genes was detected by Western blotting and RT-PCR assays. In the present study, we found that knockdown of IGFBP7 in endothelial cells significantly decreases the expression of endothelial cell proliferation-related genes and cell number in the recovery phase but not in the acute phase of ALI. Mechanistically, using bulk-RNA sequencing and CO-IP, we found that IGFBP7 promotes phosphorylation of FOS and subsequently up-regulates YAP1 molecules, thereby promoting endothelial cell proliferation. This study indicated that IGFBP7 has diverse roles in different stages of ALI, which extends the understanding of IGFBP7 in different stages of ALI and suggests that IGFBP7 as a potential therapeutic target in ALI needs to take into account the period specificity of ALI.

JAK/STAT mediated insulin resistance in muscles is essential for effective immune response

BACKGROUND

The metabolically demanding nature of immune response requires nutrients to be preferentially directed towards the immune system at the expense of peripheral tissues. We study the mechanisms by which this metabolic reprograming occurs using the parasitoid infection of Drosophila larvae. To overcome such an immune challenge hemocytes differentiate into lamellocytes, which encapsulate and melanize the parasitoid egg. Hemocytes acquire the energy for this process by expressing JAK/STAT ligands upd2 and upd3, which activates JAK/STAT signaling in muscles and redirects carbohydrates away from muscles in favor of immune cells.

METHODS

Immune response of Drosophila larvae was induced by parasitoid wasp infestation. Carbohydrate levels, larval locomotion and gene expression of key proteins were compared between control and infected animals. Efficacy of lamellocyte production and resistance to wasp infection was observed for RNAi and mutant animals.

RESULTS

Absence of upd/JAK/STAT signaling leads to an impaired immune response and increased mortality. We demonstrate how JAK/STAT signaling in muscles leads to suppression of insulin signaling through activation of ImpL2, the inhibitor of Drosophila insulin like peptides.

CONCLUSIONS

Our findings reveal cross-talk between immune cells and muscles mediates a metabolic shift, redirecting carbohydrates towards immune cells. We emphasize the crucial function of muscles during immune response and show the benefits of insulin resistance as an adaptive mechanism that is necessary for survival.

How to eliminate pathogen without killing oneself? Immunometabolism of encapsulation and melanization in Drosophila

Cellular encapsulation associated with melanization is a crucial component of the immune response in insects, particularly against larger pathogens. The infection of a Drosophila larva by parasitoid wasps, like Leptopilina boulardi, is the most extensively studied example. In this case, the encapsulation and melanization of the parasitoid embryo is linked to the activation of plasmatocytes that attach to the surface of the parasitoid. Additionally, the differentiation of lamellocytes that encapsulate the parasitoid, along with crystal cells, is accountable for the melanization process. Encapsulation and melanization lead to the production of toxic molecules that are concentrated in the capsule around the parasitoid and, at the same time, protect the host from this toxic immune response. Thus, cellular encapsulation and melanization represent primarily a metabolic process involving the metabolism of immune cell activation and differentiation, the production of toxic radicals, but also the production of melanin and antioxidants. As such, it has significant implications for host physiology and systemic metabolism. Proper regulation of metabolism within immune cells, as well as at the level of the entire organism, is therefore essential for an efficient immune response and also impacts the health and overall fitness of the organism that survives. The purpose of this "perspective" article is to map what we know about the metabolism of this type of immune response, place it in the context of possible implications for host physiology, and highlight open questions related to the metabolism of this important insect immune response.