Interleukin-22 drives nitric oxide-dependent DNA damage and dysplasia in a murine model of colitis-associated cancer

Abstract

The risk of colon cancer is increased in patients with Crohn's disease and ulcerative colitis. Inflammation-induced DNA damage could be an important link between inflammation and cancer, although the pathways that link inflammation and DNA damage are incompletely defined. RAG2-deficient mice infected with Helicobacter hepaticus (Hh) develop colitis that progresses to lower bowel cancer. This process depends on nitric oxide (NO), a molecule with known mutagenic potential. We have previously hypothesized that production of NO by macrophages could be essential for Hh-driven carcinogenesis, however, whether Hh-infection induces DNA damage in this model and whether this depends on NO has not been determined. Here, we demonstrate that Hh infection of RAG2-deficient mice rapidly induces expression of iNOS and the development of DNA double-stranded breaks (DSBs) specifically in proliferating crypt epithelial cells. Generation of DSBs depended on iNOS activity, and further, induction of iNOS, the generation of DSBs, and the subsequent development of dysplasia were inhibited by depletion of the Hh-induced cytokine IL-22. These results demonstrate a strong association between Hh-induced DNA damage and the development of dysplasia, and further suggest that IL-22 dependent induction of iNOS within crypt epithelial cells rather than macrophages is a driving force in this process.

Mutagenicity of Helicobacter hepaticus infection in the lower bowel mucosa of 129/SvEv Rag2−/‐Il10−/−gpt delta mice is influenced by sex

“…RONS can induce DNA damage via elevation of DNA adducts such as ethno‐adducts, 7,8‐dihydro‐8‐oxoguanine (8‐oxoG) and other mutagenic precursors in vitro and in vivo . Our previous studies indicated that H. hepaticus infection in Rag2 −/− mice induced progression of intestinal pathology from inflammation, dysplasia to carcinoma during the duration of infection, and this process is mediated in part by elevated production of NO . The increased production of NO as evidenced by elevation of urinary nitrate excretion was correlated with H. hepaticus ‐induced overexpression of Tnfα and iNos primarily in macrophages and lower bowel epithelial cells in concert with neutrophils .…”

“…It has been documented that H. hepaticus infection in Rag2 ‐deficient mice stimulates iNos expression, which is considered an important mechanism for promoting DNA double‐strand breaks (DSBs) and intestinal carcinogenesis . We sought to assess patterns of γ‐H2AX foci positivity, the most sensitive marker for detecting DSBs, and the subsequent DNA damage repair response (DDR) in the lower bowel epithelial cells of RagIl10gpt mice.…”

“…females. Elevated iNos expression can enhance DSBs, as indicated by higher levels of γH2AX foci+ epithelial cells, and also directly induce point genomic mutations in the lower bowel of H. hepaticus ‐infected RagIl10gpt males compared to H. hepaticus ‐infected RagIl10gpt females . More DSBs in the H. hepaticus ‐infected males may also in part be due to stronger suppression of Atm transcription.…”

“…It has been proposed that dysbiosis in intestinal microbial compositions and pathogenic bacterial infections are key factors to trigger inflammation in IBD and may contribute to the development of colon cancer . Persistent chronic inflammation can lead to excessive production of RONS by inflammatory cells, which also is in part due to iNos‐mediated generation of NO being increased in epithelial cells . RONS can induce DNA damage via elevation of DNA adducts such as ethno‐adducts, 7,8‐dihydro‐8‐oxoguanine (8‐oxoG) and other mutagenic precursors in vitro and in vivo .…”

Nitric Oxide Engages an Anti-inflammatory Feedback Loop Mediated by Peroxiredoxin 5 in Phagocytes

“…In chronic inflammation, the antioxidant response can mitigate tissue damage but may be insufficient to resolve inflammation on its own. In fact, chronic inflammation and RNI exposure have been shown to drive tumorigenesis in mouse models of colon cancer (Meira et al, 2008; Wang et al, 2017). Thus, the antioxidant response induced by RNIs plays an important protective role against chronic inflammation.…”