Porphyromonas gingivalis inhibits M2 activation of macrophages by suppressing α‐ketoglutarate production in mice

Reprograming of metabolic pathways is critical in governing the polarization of macrophages into classical proinflammatory M1 or alternative anti-inflammatory M2 phenotypes in metabolic diseases, such as diabetes. Porphyromonas gingivalis, a keystone pathogen of periodontitis, causes an imbalance in M1/M2 activation, resulting in a hyperinflammatory environment that promotes the pathogenesis of periodontitis. However, whether P. gingivalis infection modulates metabolic pathways to alter macrophage polarization remains unclear. Bone-marrow-derived macrophages (BMDMs) were collected from 6-week-old female C57BL/6 mice and stimulated with P. gingivalis, P. gingivalis-derived LPS or IL-4. Relative gene expression and protein production were measured by quantitative real-time PCR, RNA sequencing and western blotting. Colorimetric assays were also performed to assess the amounts of α-ketoglutarate (α-KG) and succinate. P. gingivalis or P. gingivalis-derived LPS-induced inflammatory responses enhanced M1 macrophages and suppressed M2 macrophages, even in the presence of IL-4. P. gingivalis inhibited Idh1/2 and Gpt1/2 mRNA expression, and increased Akgdh mRNA expression, thus decreasing the ratio of α-KG/succinate. Supplementation of cell-permeable dimethyl-α-KG dramatically restored M2 activation during P. gingivalis infection. Our study suggests that P. gingivalis maintains a hyperinflammatory state by suppressing the production of α-KG by M2 macrophages.