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Summary Autophagy provides a mechanism for the turnover of cellular organelles and proteins through a lysosome-dependent degradation pathway and is a possible mechanism in inflammatory disease. Periodontitis is an inflammatory disease caused by periodontal pathogens. Porphyromonas gingivalis, an important periodontal pathogen, activates cellular autophagy to provide a replicative niche while suppressing apoptosis in endothelial cells. However, the molecular basis for a causal relationship between P. gingivalis and autophagy is unclear. This research examines the involvement of P. gingivalis in autophagy through light chain 3 (LC3) and autophagic proteins, and the role of P. gingivalis-induced autophagy in the clearance of P. gingivalis and inflammation. To investigate the molecular mechanism of autophagy induced by P. gingivalis, PMA-differentiated THP-1-derived macrophages were infected with live P. gingivalis. The P. gingivalis increased the formation of autophagosomes in a multiplicity of infection-dependent manner, as well as autophagolysosomes. Porphyromonas gingivalis activated LC3-I/LC3-II conversion and increased the conjugation of autophagy-related 5 (ATG5) –ATG12 and the expression of Beclin1. The expressions of Beclin1, ATG5–ATG12 conjugate, and LC3-II were significantly inhibited by the presence of 3-methyladenine, an autophagy inhibitor. Interestingly, 3-methyladenine increased the survival of P. gingivalis and proinflammatory cytokine interleukin-1β production. The data indicate that P. gingivalis induces autophagy in PMA-differentiated THP-1-derived macrophages and in turn, macrophages eliminate P. gingivalis through an autophagic response, which can lead to the restriction of an excessive inflammatory response by downregulating interleukin-1β production. The induction of autophagy by P. gingivalis may play an important role in the periodontal inflammatory process and serve as a target for the development of new therapies.

Streptococcus mutans, a major etiological agent of dental caries, frequently causes systemic disease, such as subacute bacterial endocarditis, if it enters the bloodstream. In this study, the production pathways of the proinflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), induced by S. mutans in mouse macrophage were examined using a quantitative real-time polymerase chain reaction and an enzyme-linked immunosorbent assay. The S. mutans stimulated the expression of TNF-α and IL-1β mRNA at a multiplicity of infection of 1 : 100, which increased at 2 and 4 h, respectively, to 24 h. It also induced the production of high levels of the TNF-α and IL-1β proteins, which increased at 2 h and reached a peak at 4 and 24 h, respectively. Nuclear factor-κB (NF-κB) was activated and reached a maximum level 30 min after the S. mutans treatment. The expression of TNF-α and IL-1β mRNA and protein was suppressed by the treatment with pyrrolidine dithiocarbamate, an NF-κB inhibitor. The S. mutans-induced TNF-α expression was suppressed by the presence of SB203580, a p38 mitogen-activated protein (MAP) kinase inhibitor, or SP600125, a Jun N-terminal kinase (JNK) MAP kinase inhibitor. On the other hand, IL-1β expression was inhibited by extracellular signal-regulated kinase (ERK)/p38/JNK MAP kinase inhibitor pretreatment. In addition, TNF-α production was suppressed more in the Toll-like receptor 2(-/-) (TLR2(-/-)) macrophages than in the TLR4(-/-) macrophages, whereas IL-1β production was suppressed more in the TLR4(-/-) macrophages than in the TLR2(-/-) macrophages. These results show that S. mutans stimulates the production of TNF-α and IL-1β in the mouse macrophage cell line, RAW 264.7, by activating ERK/p38/JNK, and NF-κB through TLR2 and TLR4, respectively.