BackgroundMicroRNAs (miRNAs) are small non-coding RNAs that play essential roles in cancer initiation and progression. Previously, we demonstrated that miR-126 acts as a tumor suppressor in colorectal cancer (CRC), and negatively associated with tumor progression, metastasis, and prognosis of patients with colon cancer. However, the role and mechanism of miR-126 in the progression of colitis-associated colorectal cancer (CAC) remain elusive.MethodsMice were modeling CAC with Azoxymethane(AOM) and Dextran sulfate sodium(DSS). The expression of miR-126 throughout the progression of CAC was analyzed by in situ hybridization (ISH). The effects of miR-126 on CAC were investigated on intestinal epithelium cells (IECs) specific miR-126 deletion (miR-126ΔIEC, cKO) mice and wild type (WT) mice by flow cytometry assay, immunohistochemistry, and enzyme-linked immunosorbent assay. The underlying mechanism was explored through mRNA Immunoprecipitation assay, establishing co-culture systems of IECs and macrophages, cell migration assays, IECs proliferation assays, and immunofluorescence staining.ResultsWe found that miR-126 expression decreased in the colon tissues during the development of CAC in the mouse model and patients’ tissue. Deletion of miR-126 exacerbated CAC in cKO mice. Then we identified CXCL12 as a direct and functional target of miR-126. By blocking the CXCL12/CXCR4 axis with AMD3100 in the CAC mouse model, the CAC tumorigenesis alleviated in mice from cKO+AMD3100 group compares to cKO mice. CXCL12, together with its receptor CXCR4 has been well studied in the effect on hematopoietic stem cells maintenance and homing, as well as being a potent chemokine attracting lymphocytes and macrophages. However, its function on CAC is still unclear. We found that miR-126 regulates the recruitment of macrophages via CXCL12, and down-regulated its IL-6 and IL-1β expression. Furthermore, we found that after co-cultured with miR-126 silenced cells, macrophages would promote colon cell migration, proliferation, and EMT activity, whereas anti-IL-6 antibodies dampened these phenotypes.ConclusionsCollectively, our studies indicate that miR-126 plays a protective role in the development and progression of CAC, and suggest that miR-126 may act as a novel molecular marker for early diagnosis of CAC in the future.