Background: Inflammatory bowel diseases (IBD) are characterized by dysbiosis, defects in epithelial barrier function, and increased redox stress. The epithelial NADPH oxidase dual oxidase 2 (DUOX2) is altered in IBD patients before the onset of disease and in association with dysbiosis and dysplasia. We have shown that chronic activation of DUOX2 leads to microbiome-dependent colonic tumors. However, the role of DUOX2 activation in IBD is not fully understood. Herein, we interrogate the functional consequences of DUOX2 activity on the host and the microbiome.
Methods: Animal models were used to study distinct DUOX2 epithelial states (increased DUOX2 activation: villin-TLR4 (vTLR4) mice; no epithelial DUOX2 activity: vTLR4 DUOXA IEC-KO mice). Biochemical and permeability determinations were done under different conditions including steady state, germ-free (GF) and selectively colonized mice (altered Schaedler flora (ASF); engraftment with stool from active or inactive IBD patients or healthy subjects) or following supplemental butyrate. Characterization of the host-microbial interface was performed with deep RNA sequencing, metabolomics, and pathway analyses. Mechanistic studies were carried out in mouse derived colonoids and IBD patient biopsies and serum.
Results: ASF-colonized vTLR4 mice had increased levels of two ASF species from the genus Clostridium. Metabolome analysis revealed increased proportions of cholic and taurocholic acids and reduced amounts of inosine with DUOX2 activation. These molecules are implicated in the dampening of anti-tumor response and formation of genotoxic substances. Sustained activation of DUOX2 induced pro-inflammatory pathway activation without overt inflammation. vTLR4 mice had increased permeability and bacterial translocation, which was rescued by deletion of DUOX2. GF vTLR4 mice had increased DUOX2 activity and permeability but reduced inflammatory responses as compared to their SPF counterparts. IBD patients had increased transcript levels of DUOX2, decreased transcript levels of the tight junction protein ZO-1 in colon, and elevated plasma zonulin levels. Engraftment of GF mice with stool from the same IBD patients led to increased DUOX2 activity, low-grade inflammation, and permeability defects. DUOX2 activity and expression correlated with markers of permeability in both patients and mice. Butyrate treatment and histone deacetylase (HDAC) inhibition blocked DUOX2 signaling.
Conclusions: Our data establish a novel and clear connection between heightened DUOX2 activity and impairments in the integrity of the gut epithelial barrier and microbiome changes that in turn foster low-grade inflammation. This can be rescued by the microbial metabolite butyrate and HDAC inhibitors. We posit that therapies aimed at controlling DUOX2 activity through microbiome or metabolome-targeted approaches may be beneficial in IBD.

Gregory Conner

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