Blocking Histone Methyltransferase MLL1 In Macrophages Inhibits Inflammatory Reaction And Promotes Bone Tissue Regeneration In A Mouse Periodontitis Model

Objective: Periodontitis is not only the main cause of tooth loss,but also an important risk factor for some systemic diseases.The increase of M1(classically activated)macrophages is a key factor leading to excessive inflammation of periodontal tissue and alveolar bone loss.Accumulating evidence indicates that a variety of epigenetic modifications can affect the polarization of macrophages,among which histone 3 lysine4-site trimethylation(H3K4me3)is the most active and long-lasting epigenetic mechanism of macrophage gene activation under inflammatory conditions.Mixed lineage leukemia protein 1(MLL1)is histone 3 lysine 4 site specific histone methyltransferase.So far,the role of MLL1 in periodontitis is not clear.The purpose of this study is to clarify the effects of MLL1 on M1 macrophage polarization and periodontitis,and then promote bone tissue regeneration in periodontitis by blocking histone methyltransferase MLL1 in macrophages,and provide a new idea for the treatment of alveolar bone loss caused by periodontitis.Methods: Firstly,the mice ligature-induced periodontitis model was established,and the phenotype and MLL1 expression of macrophages were detected by stimulating RAW264.7 using LPS in simulated inflammatory environment in vitro.Then macrophages were treated with MI-2(MLL1 inhibitor)to detect its effects on macrophage phenotype and inflammatory factors expression,and its effects on osteogenic differentiation were detected by indirect co-culture.Finally,local periodontal administration was used to verify the effect of MI-2 on alveolar bone regeneration in mice with periodontitis.Results: In vivo,infiltration of M1 macrophages in periodontitis tissue was increased and the expression of MLL1 was elevated.The increased expression of MLL1 and H3K4me3 in RAW264.7 cells induced by LPS was accompanied by the activation of NF-κ B signal pathway,and blocking MLL1 using MI-2 could inhibit the transition of macrophages to M1 and reduce the expression of TNF-α,IL-6 and IL-1 β by inhibiting the activation of NF-κ B signal pathway.The supernatant of macrophages treated with MI-2 could indirectly promote the expression of MC3T3-E1 osteogenesis-related proteins such as COL1A1,OCN and RUNX2,and increased ALP activity and calcium nodule formation.After local administration of MI-2 to tissue of a mouse periodontitis model,periodontal tissue destruction was decreased and alveolar bone regeneration was increased significantly.Conclusions: Blocking MLL1 in macrophage can inhibit inflammatory reaction and indirectly promote osteogenic differentiation,thus promotes bone tissue regeneration in a mouse periodontitis model.