In Gastrointestinal epithelium the balance between apoptosis and renewal of intestinal epithelial cells (IECs) maintains the structure, and is typically renewed over three to five days. Intestinal inflammation and epithelial injury, which occurs in diseases such as inflammatory bowel disease (IBD), ulcerative colitis (UC) and Crohn's disease (CD), has been demonstrated to increase apoptosis of IECs. Research has focussed on maintaining the apoptosis/renewal balance mainly through suppression of inflammation, such as neutralisation of cytokines including TNF and IFN. Strategies to promote self-renewal are relatively less common as the repair and proliferation of IECs in IBD, as the process is not completely elucidated.
CD47 and its counter receptor SIRPα regulate phagocytosis by macrophages and other phagocytes. CD47 has also been implicated in regulation of stem cell self-renewal by modulation of c‑Myc expression. CD47 knockdown increased proliferation of endothelial progenitor cell, mouse lung endothelial cells and renal tubular epithelial cells and CD47 KO mice are resistant to induction of IBD with dextran sulfate sodium (DSS) or TNBS, however the mechanisms of action remain unclear.
In this study the authors aimed to determine the role of CD47 in IEC self-renewal after DSS mediated inflammation and IBD. They used an experimental mouse model of colitis and generated organoids from CD47 KO mice intestinal crypts. They also used wound healing assays, flow cytometry and immunofluorescence analysis.
Colon biopsies (six each) from Crohn's disease (CD), ulcerative colitis (UC) patients and subjects without intestinal inflammation were stained with anti-CD47 and epithelial marker E‑cadherin. CD47 was significantly upregulated in the UC and CD patients compared to control subjects.
Infiltration of CD11b+ inflammatory immune cells were detected in the UC and CD patients.
In a mouse model of DSS-induced colitis, CD47 upregulation was detected in the IECs by western blotting and immunofluorescence, suggesting a correlation between colitis and CD47 expression.
In human intestinal epithelial cell lines, HT‑29 and HCoEpiC cells treated with IFNγ, TNFα or IL‑17 for 6 hours CD47 expression, measured by flow cytometry, was significantly increased. This was confirmed by qPCR.
WT and CD47 KO mice were treated with DSS for 7 days. CD47 KO mice had significantly less intestinal epithelial tissue damage compared to WT, which showed lesser effects on body weight and shortening of the intestine.
Intestinal epithelial organoids were isolated from WT and CD47 KO mice. Organoids were cultured in matrigel and treated with IL‑17 or TNFα. Organoids from CD47 KO mice demonstrated more proliferation with or without cytokine treatment.
In a wound healing scratch assay, using CT26 cell, a CD47 expression vector inhibited wound closure whilst CD47 siRNA enhanced wound closure. This was also confirmed in HT‑29 cells.
Expression levels of Oct4, Klf4, Sox2 and c‑Myc (OKSM) were higher in isolated epithelium from CD47 KO mice compared to WT.
In CT26 cells transfected with an expression vector for CD47, levels of Oct4, Klf4, Sox2 and c‑Myc were reduced whilst CD47 siRNA had the opposite effect.
In this study, the authors demonstrated that epithelial cell CD47 expression in the colon is strongly induced in patients with UC and CD and in mouse with DSS-induced experimental colitis. They also demonstrated increased expression of CD47 in response to inflammatory cytokines. In a mouse model of experimental colitis CD47 KO promotes proliferation and self-renewal resulting in less intestinal tissue damage, maintaining the integrity of the epithelial barrier.
He et al. CD47 is a negative regulator of intestinal epithelial cell self-renewal following DSS-induced experimental colitis. Nature Scientific Reports 10:10180 (2020)