Bone marrow mesenchymal stem cell-derived circHECTD1 targets claudin1 through the CTCF/METTL3 axis to alleviate ulcerative colitis : Short title: BMSC-derived circHECTD1 alleviates UC.

OBJECTIVE

Ulcerative colitis (UC) is an inflammatory bowel disease that lacks satisfactory treatment. This study aimed to investigate the role of bone marrow mesenchymal stem cell-derived exosomal circHECTD1 (Exo-circHECTD1) in UC and its mechanism of action.

METHODS

An inflammatory model was created using LPS-stimulated MODE-K cells and an UC mouse model was established using dextran sodium sulfate (DSS). Cell proliferation was assessed using CCK-8. Apoptosis and Th17/Treg cell differentiation were analyzed by flow cytometry. Inflammatory factors were detected using ELISA. FITC fluorescence intensity was measured to evaluate permeability. m6A modification and molecular binding were detected using immunoprecipitation methods. Luciferase reporters were used to evaluate METTL3 promoter activity. RT-qPCR was used to detect RNA expression and western blotting was used to detect METTL3, CTCF, claudin1, and tight junction proteins (ZO-1, occludin).

RESULTS

Exo-circHECTD1 enhanced viability and permeability and reduced apoptosis and inflammation factor levels in LPS-treated MODE-K cells. Moreover, it reduced the Th17/Treg ratio, regulated gut microbiota, and promoted the recovery of mice with DSS-induced UC. Claudin1 knockdown reversed the protective effect of Exo-circHECTD1 on UC models. CircHECTD1 binds to CTCF, which binds to the METTL3 promoter and promotes METTL3 promoter activity. METTL3 upregulates the level of claudin1 m6A modification and inhibits claudin1 expression. CTCF or METTL3 knockdown alleviated LPS-induced MODE-K cell damage.

CONCLUSION

Exo-circHECTD1 inhibits METTL3 transcription by binding to CTCF to reduce claudin1 m6A modification and promote claudin1 expression, thereby regulating the balance of gut microbiota and Th17/Treg cells and alleviating UC.