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.

When confronted with an infection, immune cells are rapidly activated to fight the threat. However, like all cells, they require energy to act. While most cells reduce their activity when nutrients are scarce, the immune system cannot afford to do so, as halting its response could put the entire body at risk from infection. It is not clear how immune cells manage this complex nutritional budgeting. Previous studies of fruit fly larvae infected with a parasitoid wasp revealed that immune cells secure extra energy by releasing a molecule called adenosine. This slows the metabolism of non-immune tissues, leaving more nutrients available for immune cells. However, the exact mechanism that immune cells use to produce adenosine remained uncertain. To further examine this process, Nedbalova et al. – who are part of the research group that carried out the previous work – extracted activated immune cells from a parasitoid-infected larva and fed them a labelled amino acid. Tracing this label revealed an increase in the number of chemical units known as methyl groups that had been added to molecules within the cell. This process, known as methylation, can regulate metabolic activity within cells and produces adenosine as a byproduct. Further genetic studies showed that if nutrient supplies were sufficient, the immune cells recycled this adenosine back into ATP, the body’s main energy currency. This suggests that if there were not enough nutrients to do this, the excess adenosine would slow the metabolism of non-immune cells, therefore securing more nutrients for the immune cells. Therefore, Nedbalova et al. hypothesise that these two processes could form the basis of a feedback mechanism that allows the immune cells to regulate their energy demands. Taken together, the findings suggest that adenosine may act as a sensor to reflect immune activity, with it being released when the cells are stimulated and recycled if they have enough energy. This hypothesis still requires further testing but, as adenosine pathways are present across all organisms, it could have implications for many physiological and disease-related processes.

• Keywords
• D. melanogaster, S-adenosylhomocysteinase, SAM transmethylation pathway, adenosine kinase, adenosine signaling, adenylate kinase, biochemistry, chemical biology, immunology, inflammation, privileged immunity,
• MeSH
• Adenosine * metabolism   MeSH
• Adenosine Kinase metabolism   MeSH
• Adenosine Triphosphate * metabolism   MeSH
• Drosophila melanogaster * immunology   parasitology   metabolism   growth & development   MeSH
• Larva immunology   metabolism   parasitology   growth & development   MeSH
• Methylation MeSH
• S-Adenosylmethionine * metabolism   MeSH
• Wasps MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Adenosine * MeSH
• Adenosine Kinase MeSH
• Adenosine Triphosphate * MeSH
• S-Adenosylmethionine * MeSH

Concentrative nucleoside transporters (Cnts) are unidirectional carriers that mediate the energy-costly influx of nucleosides driven by the transmembrane sodium gradient. Cnts are transmembrane proteins that share a common structural organization and are found in all phyla. Although there have been studies on Cnts from a biochemical perspective, no deep research has examined their role at the organismal level. Here, we investigated the role of the Drosophila melanogaster cnt1 gene, which is specifically expressed in the testes. We used the CRISPR/Cas9 system to generate a mutation in the cnt1 gene. The cnt1 mutants exhibited defects in the duration of copulation and spermatid maturation, which significantly impaired male fertility. The most striking effect of the cnt1 mutation in spermatid maturation was an abnormal structure of the sperm tail, in which the formation of major and minor mitochondrial derivatives was disrupted. Our results demonstrate the importance of cnt1 in male fertility and suggest that the observed defects in mating behavior and spermatogenesis are due to alterations in nucleoside transport and associated metabolic pathways.

• Keywords
• adenosine, cnt1, copulation, gamete, male fertility, mitochondria, spermatogenesis, testis,
• Publication type
• Journal Article MeSH

Adenosine (Ado) is an important signaling molecule involved in stress responses. Studies in mammalian models have shown that Ado regulates signaling mechanisms involved in "danger-sensing" and tissue-protection. Yet, little is known about the role of Ado signaling in Drosophila. In the present study, we observed lower extracellular Ado concentration and suppressed expression of Ado transporters in flies expressing mutant huntingtin protein (mHTT). We altered Ado signaling using genetic tools and found that the overexpression of Ado metabolic enzymes, as well as the suppression of Ado receptor (AdoR) and transporters (ENTs), were able to minimize mHTT-induced mortality. We also identified the downstream targets of the AdoR pathway, the modifier of mdg4 (Mod(mdg4)) and heat-shock protein 70 (Hsp70), which modulated the formation of mHTT aggregates. Finally, we showed that a decrease in Ado signaling affects other Drosophila stress reactions, including paraquat and heat-shock treatments. Our study provides important insights into how Ado regulates stress responses in Drosophila.

• Keywords
• cytotoxicity, equilibrative nucleoside transporter, heat-shock protein 70, modifier of mdg4, mutant huntingtin, neurodegeneration,
• Publication type
• Journal Article MeSH

Drosophila imaginal disc growth factor 2 (IDGF2) is a member of chitinase-like protein family (CLPs) able to induce the proliferation of imaginal disc cells in vitro. In this study we characterized physiological concentrations and expression of IDGF2 in vivo as well as its impact on the viability and transcriptional profile of Drosophila cells in vitro. We show that IDGF2 is independent of insulin and protects cells from death caused by serum deprivation, toxicity of xenobiotics or high concentrations of extracellular adenosine (Ado) and deoxyadenosine (dAdo). Transcriptional profiling suggested that such cytoprotection is connected with the induction of genes involved in energy metabolism, detoxification and innate immunity. We also show that IDGF2 is an abundant haemolymph component, which is further induced by injury in larval stages. The highest IDGF2 accumulation was found at garland and pericardial nephrocytes supporting its role in organismal defence and detoxification. Our findings provide evidence that IDGF2 is an important trophic factor promoting cellular and organismal survival.

• MeSH
• Drosophila immunology   metabolism   MeSH
• Energy Metabolism * MeSH
• Glycoproteins metabolism   MeSH
• Hemolymph chemistry   MeSH
• Cells, Cultured MeSH
• Inactivation, Metabolic * MeSH
• Immunity, Innate * MeSH
• Drosophila Proteins metabolism   MeSH
• Gene Expression Profiling MeSH
• Cell Survival drug effects   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Glycoproteins MeSH
• Idgf2 protein, Drosophila MeSH Browser
• Drosophila Proteins MeSH

Adenosine (Ado) is a ubiquitous metabolite that plays a prominent role as a paracrine homeostatic signal of metabolic imbalance within tissues. It quickly responds to various stress stimuli by adjusting energy metabolism and influencing cell growth and survival. Ado is also released by dead or dying cells and is present at significant concentrations in solid tumors. Ado signaling is mediated by Ado receptors (AdoR) and proteins modulating its concentration, including nucleoside transporters and Ado deaminases. We examined the impact of genetic manipulations of three Drosophila genes involved in Ado signaling on the incidence of somatic mosaic clones formed by the loss of heterozygosity (LOH) of tumor suppressor and marker genes. We show here that genetic manipulations with the AdoR, equilibrative nucleoside transporter 2 (Ent2), and Ado deaminase growth factor-A (Adgf-A) cause dramatic changes in the frequency of hyperplastic outgrowth clones formed by LOH of the warts (wts) tumor suppressor, while they have almost no effect on control yellow (y) clones. In addition, the effect of AdoR is dose-sensitive and its overexpression leads to the increase in wts hyperplastic epithelial outgrowth rates. Consistently, the frequency of mosaic hyperplastic outgrowth clones generated by the LOH of another tumor suppressor, discs overgrown (dco), belonging to the wts signaling pathway is also dependent on AdoR. Our results provide interesting insight into the maintenance of tissue homeostasis at a cellular level.

• MeSH
• Drosophila melanogaster MeSH
• Membrane Transport Proteins genetics   MeSH
• Mutation * MeSH
• Drosophila Proteins genetics   MeSH
• Receptors, Purinergic P1 genetics   MeSH
• Signal Transduction genetics   MeSH
• Loss of Heterozygosity MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• adenosine deaminase-related growth factor, Drosophila MeSH Browser
• ENT2 protein, Drosophila MeSH Browser
• Membrane Transport Proteins MeSH
• Drosophila Proteins MeSH
• Receptors, Purinergic P1 MeSH