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Activating transcription factor 3 regulates immune and metabolic homeostasis

ABSTRACT: Integration of metabolic, stress and immune responses plays a fundamental role during animal development to maintain energy homeostasis while ensuring growth and proper developmental timing. Perturbation of metabolic and immune signaling circuits has detrimental consequences to animal development including growth retardation, organ malfunction and emergence of the metabolic syndrome. Here, we demonstrate that the Drosophila basic region-leucine zipper (bZIP) protein, Activating transcription factor 3 (Atf3), safeguards a balance of metabolic and immune system responses during fly development. Loss of Atf3 function results in lethality during late-larval and pupal stages. Atf3-deficient larvae exhibit phenotypes resembling the metabolic syndrome in mammals. Excessive accumulation of lipids in the larval fat body and gut is accompanied by altered expression of genes involved in lipid metabolism. Moreover, the fat body of atf3 mutants becomes infiltrated by hemocytes. The major pro-inflammatory pathways signaling through JNK and Imd are hyperactivated in atf3 mutants, causing ectopic expression of antimicrobial peptide genes. Suppression of the immune response, achieved by reducing the gene dose of the transcription factors FOXO or NF-kappaB/Relish, significantly improves lipid metabolism and normalizes gene expression profile of atf3 mutants. In addition, heterozygosity of relish partially rescues lethality of the atf3 mutants. Our data thus identify Atf3 as an essential player that links metabolic and immune system homeostasis during animal development.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE36377 | GEO | 2012/11/05

SECONDARY ACCESSION(S): PRJNA153257

REPOSITORIES: GEO

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Project description:The intricate regulation of gut homeostasis is dependent on a fine-tuned regulation of the host defense to avoid detrimental immune activation. We have previously applied Drosophila to show that mutants of the short isoform of the POU transcription factor Pdm1/nubbin (nub) have a constitutively active immune response, altered gut microbiota and shortened lifespan. Here, we studied the role of Nub-PB, the larger isoform derived from the nub gene. Both Nub protein isoforms contain the C-terminal POU and Homeo domains whereas Nub-PB encompasses a longer N-terminal end. Microarray analysis revealed that targeted misexpression of Nub-PB in immunocompetent organs triggers a strong and broad expression of immune genes in a comparable manner to Nub-PD mutants. The seemingly antagonistic functions of the two isoforms were confirmed by co-overexpression of both forms, which resulted in normal expression levels of antimicrobial peptide (AMP) genes. Cell line experiments demonstrated a synergistic activation of AMPs by the combined transfection with Nub-PB and NF-kB/Relish. In agreement with this finding, Relish was indispensable for Nub-PB-driven diptericin expression, suggesting that Nub-PB acts as a Relish co-activator. Moreover, Nub-PB triggered strong expression of gut-specific drosomycin-like genes in a JAK/STAT pathway-dependent manner. Using RNA interference, we found that Nub-PB influences antimicrobial peptide expression in gut but not fat body tissues. Moreover, Nub-PB expression levels in gut enterocytes correlated with the gut bacterial load as well as host lifespan, suggesting a profound role in host immunity. Surprisingly, Nub-PB-overexpression caused a hypersensitive infection phenotype as flies succumbed within 24 h to orally administered Erwinia carotovora carotovora 15. Nub-PB thus appears to be a central activator of gut immunity that requires tight control, executed at least in part, by isoform antagonism to maintain immune homeostasis.

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Activating transcription factor 3 regulates immune and metabolic homeostasis

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