The role of histone methylation of H3K4 in polarization of macrophages stimulated by immune complex and lipopolysaccharide and its therapeutic potential in sepsis

Abstract

Macrophage plasticity is a process that allows macrophages to switch between two opposing phenotypes based on differential stimuli. Functional plasticity of macrophages contributes to disease pathogenesis such as cancer, metabolic diseases, autoimmune diseases and systemic infections. Epigenetics plays an important role in regulating this process. Macrophages stimulated with lipopolysaccharide (LPS) (M(LPS)) produce high level of pro-inflammatory cytokines such as IL-12, TNFα and IL-6 and low level of anti-inflammatory cytokine IL-10, while macrophages stimulated with LPS in the presence of immune complex (IC) (M(IC)) produce high level of IL-10 and low level of IL-12. In this study, we investigated the plasticity of M(LPS) to become M(IC) in vitro and compared the active histone mark (trimethylation on lysine 4 of histone 3 (H3K4me3)) between M(LPS) and M(IC) using murine bone marrow-derived macrophages. We found that macrophages exhibited functional plasticity from M(LPS) to M(IC) upon re-polarization after two days of resting in vitro. Phosphorylation of p38, p44/42, p65 and Akt in M(IC) re-polarized from M(LPS) was similar to M(IC) stimulated from resting macrophages. To obtain the epigenetic profiles of M(LPS) and M(IC), global H3K4me3 enrichments in both activated macrophages were compared. M(LPS) and M(IC) displayed marked differences in genome-wide enrichment of H3K4me3. M(IC) showed increased global enrichment of H3K4me3 whereas M(LPS) decreased enrichment when compared to unstimulated macrophages. Furthermore, M(IC) exhibited high H3K4me3 enrichment in all cis-regulatory elements. At individual gene, increased H3K4me3 enrichments were observed in the promoters of known genes associated with M(IC) including Il10, Cxcl1, Csf3 and Il33 when compared with M(LPS). Finally, to evaluate the therapeutic application of M(IC), we investigated the impact of M(IC) on systemic immune response by adoptive transfer of M(IC) in LPS-induced endotoxemia model. Cytokine profiles revealed that mice receiving an adoptive transfer of M(IC) acutely reduced the serum inflammatory cytokines IL-1β and IL-p12p70. This study highlighted the importance of epigenetics in regulating macrophages activation and functions of M(IC) that may influence macrophage plasticity and the potential therapeutic use of macrophage in vivo.