DNMT1 recruits RUNX1 and represses FOXO1 transcription to inhibit anti-inflammatory activity of regulatory T cells and augments sepsis-induced lung injury.

Sepsis-induced lung injury (ALI) is a critical condition characterized by excessive immune responses and tissue damage. Previous evidence has underscored an upregulation pattern of DNA methyltransferase 1 (DNMT1) in sepsis. This study reveals the key role of DNMT1 in modulating regulatory T cell (Treg) activity in septic ALI. A septic mouse model was generated through cecal ligation and puncture. Treatment with either DNMT1 antagonist Thioguanine (ThG) or AAV-sh-DNMT1 significantly reduced immune cell infiltration, reduced production of pro-inflammatory cytokines, and increasing production of anti-inflammatory cytokines in the bronchoalveolar lavage fluid (BALF) of mice, alongside improved lung pathology and integrity. Furthermore, the DNMT1 inhibition or silencing significantly enhanced population of FOXP3⁺ Tregs in the BALF and lung tissue. Similar trends were observed in mice with specific DNMT1 deletion in CD4⁺ T cells (DNMT1-CD4-ko). Regarding the mechanism, we observed that DNMT1 represses transcription of forkhead box O1 (FOXO1) by recruiting RUNX family transcription factor 1 (RUNX1) to the FOXO1 promoter. FOXO1-specific knockout in CD4⁺ T cells reduced anti-inflammatory activity of Tregs. Additionally, administration of the CD25 antibody exacerbated sepsis-induced ALI in DNMT1-CD4-ko mice. Collectively, these findings illustrate that targeting DNMT1 interacts with RUNX1 to repress transcription of FOXO1, which reduces immunomodulatory activity of Tregs and augments inflammatory cascades in septic lung injury.