Background
Macrophages are the major source of WNT ligands. However, the regulation of WNT expression in macrophages has not been studied. In the present study, we have discovered that activation of canonical β-Catenin signaling suppresses WNT expression in macrophages. EVs from these pre-conditioned macrophages promoted intestinal stem cell regeneration and mitigated intestinal injury. Method: ChIP-seq analysis and validation studies using recombinant DNA construct expressing Luciferase reporter under WNT promoter (e.g. WNT5a and WNT9b) were conducted to demonstrate the involvement of β-Catenin in the transcriptional regulation of WNT expression. The regulatory role of β-Catenin in WNT expression in macrophages was examined by treating these cells with a Tankyrase inhibitor. In addition, the gene expressing β-Catenin was deleted in macrophages using Csf1r.iCre; Ctnnb1fl/fl mice model. Both pharmacological and genetically modulated macrophages were examined for WNT expression and activity by qPCR and TCF/LEF luciferase assay respectively. Additionally, Csf1r.iCre; Ctnnb1fl/fl mice were exposed to irradiation to compare the radiosensitivity with their wildtype littermate. Extracellular vesicles (EVs) were isolated from pre-conditioned WNT-enriched macrophages and infused in irradiated C57BL/6 and Lgr5/eGFP-IRES-Cre-ERT2; R26-ACTB-tdTomato-EGFP mice to determine the regenerative response of intestinal stem cell (ISC) and epithelial repair. Regenerative effects of EVs were also examined in mice model DSS induced colitis. Result: ChIP-seq analysis and subsequent validation study suggested physical association of β-Catenin with WNT promoters to suppress WNT expression. Macrophage specific deletion of gene expressing β-Catenin or pharmacological inhibition of Tankyrase improves the WNT expression in macrophages several folds compared to control. Transfusion of these preconditioned macrophages or EVs from these cells delivers optimum level of morphogenic WNT to injured epithelium, activates ISC regeneration and mitigated radiation induced intestinal injury. Intestinal epithelium in Csf1r.iCre; Ctnnb1fl/fl mice also showed radioresistance compared to wild type littermate. Moreover, EVs derived from WNT enriched macrophages can mitigate intestinal injury in mice model of DSS induced acute colitis.
Conclusion
The study provides substantial evidence that macrophage-targeted modulation of canonical WNT signaling induces WNT expression in macrophages. Treatment with preconditioned macrophage derived WNT-enriched EVs can be a promising therapeutic approach against intestinal injury.