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Background & Aims: Transgenic mice (HBUS) that express the epidermal growth factor (EGFR) ligand HBEGF and a constitutively active G protein-coupled receptor (US28) in intestinal epithelial cells develop serrated polyps in the cecum. Development of serrated polyps depends on the composition of the gut microbiota and is associated with bacterial invasion of the lamina propria, accompanied by induction of inflammation and upregulation of interleukin 1 beta (IL1B) and matrix metalloproteinase 3 (MMP3) in the cecum. We investigated the mechanisms by which these changes contribute to development of serrated polyps.
Methods: We performed studies with C57BL/6 (control) and HBUS mice. To accelerate polyp development, we increased the exposure of the bacteria to the lamina propria by injecting HBUS mice with diphtheria toxin, which binds transgenic HBEGF expressed by the epithelial cells and causes apoptosis. Mice were given injections of IL1B-neutralizing antibody and the MMP inhibitor NNGH. Intestinal tissues were collected from mice and analyzed by histology, reverse-transcription PCR, ELISAs, immunofluorescence, and flow cytometry. We examined fibroblast subsets in polyps using single-cell RNA sequencing.
Results: Administration of diphtheria toxin to HBUS mice accelerated development of serrated polyps (95% of treated mice developed polyps before 100 days of age, compared to 53% given vehicle). IL1B stimulated subsets of platelet derived growth factor receptor alpha (PDGFRA)-positive fibroblasts isolated from cecum, resulting in increased expression of MMP3. Neutralizing antibodies against IL1B or administration of the MMP inhibitor reduced the number of serrated polyps that formed in the HBUS mice. Single-cell RNA sequencing analysis revealed subsets of fibroblasts in serrated polyps that express genes that regulate matrix fibroblasts and inflammation.
Conclusions: In studies of mice, we found that barrier breakdown and expression of inflammatory factors contribute to development of serrated polyps. Subsets of cecal PDGFRA-positive fibroblasts are activated by release of IL1B from myeloid cells during early stages of serrated polyp development. MMP3 produced by PDGFRA-positive fibroblasts is important for serrated polyp development. Our findings confirm the functions of previously identified serrated polyp-associated molecules, and indicate roles for immune and stromal cells in serrated polyp development.
Zhengxiang He,Lili Chen
Sergio A Lira
Zhengxiang He,Lili Chen,Grace Chen,Paola Smaldini,Gerold Bongers,Jovani Catalan-Dibene,Glaucia C Furtado,Sergio A Lira