Increased Expression of DUOX2 Is an Epithelial Response to Mucosal Dysbiosis Required for Immune Homeostasis in Mouse Intestine

Abstract

BACKGROUND & AIMS Dual oxidase 2 (DUOX2), a hydrogen-peroxide generator at the apical membrane of gastrointestinal epithelia, is upregulated in patients with inflammatory bowel disease (IBD) before the onset of inflammation, but little is known about its effects. We investigated the role of DUOX2 in maintaining mucosal immune homeostasis in mice. METHODS We analyzed the regulation of DUOX2 in intestinal tissues of germ-free vs conventional mice, mice given antibiotics or colonized with only segmented filamentous bacteria, mice associated with human microbiota, and mice with deficiencies in interleukin (IL)23 and 22 signaling. We performed 16S rRNA gene quantitative PCR of intestinal mucosa and mesenteric lymph nodes of Duoxa−/− mice that lack functional DUOX enzymes. Genes differentially expressed in Duoxa−/− mice compared to co-housed wild type littermates were correlated with gene expression changes in early-stage IBD using gene set enrichment analysis. RESULTS Colonization of mice with segmented filamentous bacteria upregulated intestinal expression of DUOX2. DUOX2 regulated redox-signaling within mucosa-associated microbes and restricted bacterial access to lymphatic tissues of the mice, thereby reducing microbiota-induced immune responses. Induction of Duox2 transcription by microbial colonization did not require the mucosal cytokines IL17 or IL22, although IL22 increased expression of Duox2. Dysbiotic, but not healthy human microbiota, activated a DUOX2 response in recipient germ-free mice that corresponded to abnormal colonization of the mucosa with distinct populations of microbes. In Duoxa−/− mice, abnormalities in ileal mucosal gene expression at homeostasis recapitulated those in patients with mucosal dysbiosis. CONCLUSIONS DUOX2 regulates interactions between the intestinal microbiota and the mucosa to maintain immune homeostasis in mice. Mucosal dysbiosis leads to increased expression of DUOX2, which might be a marker of perturbed mucosal homeostasis in patients with early-stage IBD.

Deficiency in Duox2 activity alleviates ileitis in GPx1- and GPx2-knockout mice without affecting apoptosis incidence in the crypt epithelium

“…Because Nox1- TKO ileum does not have elevated TNF-α levels [9], we suspect that the high crypt apoptosis in the Duoxa- TKO mice causes slight leakiness, which exposes mucosa to luminal microbial products and increases cytokine production. Mice without Duox2 activity have higher mucosal bacterial intake [5]. This is consistent with the idea that Duox2 plays an essential role in antibacterial defense.…”

“…1A, B). The primary impact of the Duoxa -KO construct in the gut is from losing DUOX2 activity since Duox1 is not expressed there [5], [41]. Duoxa -TKO mice also have normal lengths of ileum and colon (Fig.…”

“…The NOX1 complex produces superoxide whereas the DUOX2 complex produces H 2 O 2 . Their ileum and colon expression is induced from low-basal levels in response to bacterial colonization of germ-free (B6 and 129 strain) mice [4], [5]. NOX1 and DUOX2 genes are moderately and highly induced, respectively, in the ileum and colon of IBD patients compared to healthy controls [6], [7], [8].…”

“…Duoxa -KO disabled Duoxa1 and Duoxa2 gene expression; the Duoxa1 and Duoxa2 are accessory proteins required for Duox1 and Duox2 enzymatic activity [10]. In the intestine, DUOX1 is barely expressed [5]. Therefore, the major impact of the Duoxa-KO is suppressing Duox2 activity in the intestine.…”

NADPH oxidase-1 deficiency offers little protection in Salmonella typhimurium-induced typhlitis in mice

“…Both Nox1 and Duox2 gene are barely expressed in the intestine of germ-free mice and are highly elevated when colonized with commensal bacteria[6,7]. Duox2 and Duoxa2 (DUOX maturation factor-2) expression is highly elevated in Helicobacter felis- infected mouse gastric epithelium compared to uninfected mice[8].…”