Drosophila Fed ARA and EPA Yields Eicosanoids, 15S-Hydroxy-5Z,8Z, 11Z, 13E-Eicosatetraenoic Acid, and 15S-Hydroxy-5Z,8Z,11Z,13E,17Z-Eicosapentaenoic Acid

Functional characterization of eicosanoid signaling in Drosophila development

20-carbon fatty acid-derived eicosanoids are versatile signaling oxylipins in mammals. In particular, a group of eicosanoids termed prostanoids are involved in multiple physiological processes, such as reproduction and immune responses. Although some eicosanoids such as prostaglandin E2 (PGE2) have been detected in some insect species, molecular mechanisms of eicosanoid synthesis and signal transduction in insects have not been thoroughly investigated. Our phylogenetic analysis indicated that, in clear contrast to the presence of numerous receptors for oxylipins and other lipid mediators in humans, the Drosophila genome only possesses a single ortholog of such receptors, which is homologous to human prostanoid receptors. This G protein-coupled receptor, named Prostaglandin Receptor or PGR, is activated by PGE2 and its isomer PGD2 in Drosophila S2 cells. PGR mutant flies die as pharate adults with insufficient tracheal development, which can be rescued by supplying high oxygen. Consistent with this, through a comprehensive mutagenesis approach, we identified a Drosophila PGE synthase whose mutants show similar pharate adult lethality with hypoxia responses. Drosophila thus has a highly simplified eicosanoid signaling pathway as compared to humans, and it may provide an ideal model system for investigating evolutionarily conserved aspects of eicosanoid signaling.

Functional characterization of eicosanoid signaling in Drosophila development

20-carbon fatty acid-derived eicosanoids are versatile signaling oxylipins in mammals. In particular, a group of eicosanoids termed prostanoids are involved in multiple physiological processes, such as reproduction and immune responses. Although some eicosanoids such as prostaglandin E2 (PGE2) have been detected in some insect species, molecular mechanisms of eicosanoid synthesis and signal transduction in insects have not been thoroughly investigated. Our phylogenetic analysis indicated that, in clear contrast to the presence of numerous receptors for oxylipins and other lipid mediators in humans, the Drosophila genome only possesses a single ortholog of such receptors, which is homologous to human prostanoid receptors. This G protein-coupled receptor, named Prostaglandin Receptor or PGR, is activated by PGE2 and its isomer PGD2 in Drosophila S2 cells. PGR mutant flies die as pharate adults with insufficient tracheal development, which can be rescued by supplying high oxygen. Consistent with this, through a comprehensive mutagenesis approach, we identified a Drosophila PGE synthase whose mutants show similar pharate adult lethality with hypoxia responses. Drosophila thus has a highly simplified eicosanoid signaling pathway as compared to humans, and it may provide an ideal model system for investigating evolutionarily conserved aspects of eicosanoid signaling.

Omega-3 polyunsaturated fatty acids in the brain and visual system: Focus on invertebrates

A critical role of omega-3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid 22:6ω3 (DHA), in the development and function of the brain and visual system is well established. DHA, the most abundant omega-3 PUFA in the vertebrate brain, contributes to neuro- and synaptogenesis, neuronal differentiation, synaptic transmission and plasticity, neuronal network formation, memory and behaviour formation. Based on these data, the unique importance of DHA and its irreplaceability in neural and retinal tissues has been postulated. In this review, we consider omega-3 PUFA composition in the brain and retina of various invertebrates, and show that DHA has only been found in marine mollusks and crustaceans. A gradual decrease in the DHA content until its disappearance can be observed in the brain lipids of the series marine-freshwater-terrestrial crustaceans and marine-terrestrial mollusks, suggesting that the transition to the land lifestyle in the evolution of invertebrates, but not vertebrates, was accompanied by a loss of DHA. As with terrestrial crustaceans and mollusks, DHA was not found in insects, either terrestrial or aquatic, or in nematodes. We show that the nervous and visual systems of various DHA-free invertebrates can be highly enriched in alpha-linolenic acid 18:3ω3 or eicosapentaenoic acid 20:5ω3, which affect neurological and visual function, stimulating synaptogenesis, synaptic transmission, visual processing, learning and even cognition. The review data show that, in animals at different levels of organization, omega-3 PUFA are required for the functioning of the nervous and visual systems and that their specific needs can be met by various omega-3 PUFA.

Polyunsaturated fatty acids stimulate immunity and eicosanoid production in Drosophila melanogaster

Eicosanoids are a class of molecules derived from C20 polyunsaturated fatty acids (PUFAs) that play a vital role in mammalian and insect biological systems, including development, reproduction, and immunity. Recent research has shown that insects have significant but lower levels of C20 PUFAs in circulation in comparison to C18 PUFAs. It has been previously hypothesized in insects that eicosanoids are synthesized from C18 precursors, such as linoleic acid (LA), to produce downstream eicosanoids. In this study, we show that introduction of arachidonic acid (AA) stimulates production of cyclooxygenase, lipoxygenase, and cytochrome P450-derived eicosanoids. Downstream immune readouts showed that LA stimulates phagocytosis by hemocytes, while both LA and AA stimulate increased antimicrobial peptide production when D. melanogaster is exposed to a heat-killed bacterial pathogen. In totality, this work identifies PUFAs that are involved in insect immunity and adds evidence to the notion that Drosophila utilizes immunostimulatory lipid signaling to mitigate bacterial infections. Our understanding of immune signaling in the fly and its analogies to mammalian systems will increase the power and value of Drosophila as a model organism in immune studies.

Discovery of aspirin-triggered eicosanoid-like mediators in a Drosophila metainflammation blood tumor model

Epidemiologic studies have linked the use of aspirin to a decline in chronic inflammation that underlies many human diseases, including some cancers. Aspirin reduces the levels of cyclooxygenase-mediated pro-inflammatory prostaglandins, promotes the production of pro-resolution molecules, and triggers the production of anti-inflammatory electrophilic mono-oxygenated (EFOX) lipid mediators. We investigated the effects of aspirin in fruit fly models of chronic inflammation. Ectopic Toll/NF-κB and JAK/STAT signaling in mutant D. melanogaster results in overproliferation of hematopoietic blood progenitors resulting in the formation of granuloma-like tumors. Ectopic JAK-STAT signaling also leads to metabolic inflammation. We report that aspirin-treated mutant flies experience reduction in metabolic inflammation, mitosis, ectopic immune signaling, and macrophage infiltration. Moreover, these flies synthesize 13-HODE, and aspirin triggers 13-oxoODE (13-EFOX-L₂) production. Providing the precursor of 13-HODE, linoleic acid, or performing targeted knockdown of the transcription factor STAT in inflammatory blood cells, boosts 13-EFOX-L₂ levels while decreasing metabolic inflammation. Thus, hematopoietic cells regulate metabolic inflammation in flies, and their effects can be reversed by pharmaceutical or dietary intervention, suggesting deep phylogenetic conservation in the ability of animals to resolve inflammation and repair tissue damage. These findings can help identify novel treatment targets in humans.

PI3K/Akt Cooperates with Oncogenic Notch by Inducing Nitric Oxide-Dependent Inflammation

The PI3K/Akt signaling pathway, Notch, and other oncogenes cooperate in the induction of aggressive cancers. Elucidating how the PI3K/Akt pathway facilitates tumorigenesis by other oncogenes may offer opportunities to develop drugs with fewer side effects than those currently available. Here, using an unbiased in vivo chemical genetic screen in Drosophila, we identified compounds that inhibit the activity of proinflammatory enzymes nitric oxide synthase (NOS) and lipoxygenase (LOX) as selective suppressors of Notch-PI3K/Akt cooperative oncogenesis. Tumor silencing of NOS and LOX signaling mirrored the antitumor effect of the hit compounds, demonstrating their participation in Notch-PI3K/Akt-induced tumorigenesis. Oncogenic PI3K/Akt signaling triggered inflammation and immunosuppression via aberrant NOS expression. Accordingly, activated Notch tumorigenesis was fueled by hampering the immune response or by NOS overexpression to mimic a protumorigenic environment. Our lead compound, the LOX inhibitor BW B70C, also selectively killed human leukemic cells by dampening the NOTCH1-PI3K/AKT-eNOS axis.

A combined computational strategy of sequence and structural analysis predicts the existence of a functional eicosanoid pathway in Drosophila melanogaster

This study reports on a putative eicosanoid biosynthesis pathway in Drosophila melanogaster and challenges the currently held view that mechanistic routes to synthesize eicosanoid or eicosanoid-like biolipids do not exist in insects, since to date, putative fly homologs of most mammalian enzymes have not been identified. Here we use systematic and comprehensive bioinformatics approaches to identify most of the mammalian eicosanoid synthesis enzymes. Sensitive sequence analysis techniques identified candidate Drosophila enzymes that share low global sequence identities with their human counterparts. Twenty Drosophila candidates were selected based upon (a) sequence identity with human enzymes of the cyclooxygenase and lipoxygenase branches, (b) similar domain architecture and structural conservation of the catalytic domain, and (c) presence of potentially equivalent functional residues. Evaluation of full-length structural models for these 20 top-scoring Drosophila candidates revealed a surprising degree of conservation in their overall folds and potential analogs for functional residues in all 20 enzymes. Although we were unable to identify any suitable candidate for lipoxygenase enzymes, we report structural homology models of three fly cyclooxygenases. Our findings predict that the D. melanogaster genome likely codes for one or more pathways for eicosanoid or eicosanoid-like biolipid synthesis. Our study suggests that classical and/or novel eicosanoids mediators must regulate biological functions in insects–predictions that can be tested with the power of Drosophila genetics. Such experimental analysis of eicosanoid biology in a simple model organism will have high relevance to human development and health.