A Direct Role for Dual Oxidase in Drosophila Gut Immunity

Abstract

Because the mucosal epithelia are in constant contact with large numbers of microorganisms, these surfaces must be armed with efficient microbial control systems. Here, we show that the Drosophila nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme, dual oxidase (dDuox), is indispensable for gut antimicrobial activities. Adult flies in which dDuox expression is silenced showed a marked increase in mortality rate even after a minor infection through ingestion of microbe-contaminated food. This could be restored by the specific reintroduction of dDuox, demonstrating that this oxidase generates a unique epithelial oxidative burst that limits microbial proliferation in the gut. Thus, oxidant-mediated antimicrobial responses are not restricted to the phagocytes, but rather are used more broadly, including in mucosal barrier epithelia.

NADPH oxidases in lung biology and pathology: Host defense enzymes, and more

“…Expression of DUOX1 and DUOX2 in thyrocytes was found to be inducible in response to cAMP stimulation by forskolin (12,92), but this was not observed in human epithelial cells ( (90) and unpublished results), and the human DUOX promoters does not appear to contain a cAMP-responsive element (94). The differences in DUOX1/2 promoter regions are consistent with the highly variable transcriptional regulation of airway epithelial DUOX1 and DUOX2 in response to pro-inflammatory cytokines or to bacterial or viral stimuli (36,83,96). For example, DUOX1 mRNA expression in primary airway epithelial cultures is induced 3-5 fold by the Th2 cytokines interleukin (IL)-4 and IL-13 (83), which induce ciliatedto-mucus cell transdifferentiation and mucus hyperplasia during allergic airway inflammation (97,98).…”

“…Natural missense mutations within the extracellular peroxidase-like domain of DUOX2 result in impaired oxidative protein folding in the endoplasmic reticulum (ER) and trafficking to the plasma membrane, suggesting an alternative functional role for this domain (33,34). Nevertheless, some studies have claimed intrinsic peroxidase activity associated with DUOX proteins in C. elegans or Drosophila (35,36), and of airway epithelial DUOX2 (37), although the presence of a separate, as yet unidentified, peroxidase cannot be ruled out. Other possible functions of the peroxidase homology domain of DUOX include a superoxide dismutase-like activity, to promote exclusive H 2 O 2 production (32,34), or a docking site for secreted peroxidases that utilize DUOXgenerated H 2 O 2 .…”

“…DUOX1 expression is also dramatically enhanced after hormonal differentiation of fetal lung epithelial cells to alveolar type II cells (90). In contrast, airway epithelial expression of DUOX2, but not DUOX1, is dramatically upregulated by the Th1 cytokine IFN-γ, and after rhinovirus or bacterial infection (36,83,96). DUOX1/2 expression in human thyrocytes was recently found to be downregulated in the presence of IL-1α/IFN-γ (99).…”

Nox enzymes, ROS, and chronic disease: An example of antagonistic pleiotropy

“…Examination of 45 polymorphisms in ten Nox/ROS-related genes including p47 phox , p67 phox , p40 phox , p22 phox , gp91 phox , Duox1, and Duox2 in a cohort of 95 lung disease individuals and 95 control individuals did not show an association of these polymorphisms with increased susceptibility to infectious or inflammatory lung diseases including tuberculosis, asthma, and sarcoidosis [25]. A role for Duox in insect innate immunity has been proposed based upon the finding that when Duox expression is reduced in Drosophila intestine using RNAi, there is increased lethality upon exposure to food-borne bacteria [26]. On the other hand, suppression of Duox expression is also associated with a molting defect that results in the maturation of a small number of adults that are particularly susceptible to death by stresses, for example ether anaesthesia (Ritsick, D. and Lambeth, D., unpublished), making it unclear in my opinion whether increased lethality upon exposure to bacteria represents a specific role for Duox or an example of increased lethality in response to a stress in a generally compromised animal.…”

Bacterial strategies to overcome insect defences

“…Indeed, RoS-dependent protection against ingested microorganisms might constitute the first line of inducible defence in D. melanogaster. The ingestion of bacteria results in an increase in RoS that is synthesized by the NADPH oxidase enzyme dDuox 21 . Adult flies in which dDuox expression was silenced by RNA interference showed a marked increase in their mortality rate after ingestion of food that was contaminated with microorganisms; ingested bacteria were shown to persist and proliferate throughout the intestinal tract of flies when dDuox expression was silenced.…”