Int J Oral Biol.  2017 Mar;42(1):17-23. 10.11620/IJOB.2017.42.1.17.

Chracterization of THP-1 Cell Death Induced by Porphyromonas gingivalis Infection

Affiliations
  • 1Department of Oral Microbiology, School of Dentistry, Pusan National University, Yangsan 50612, Korea. jchung@pusan.ac.kr

Abstract

BACKGROUND
Periodontitis is generally a chronic disorder characterized by the breakdown of tooth-supporting tissues. P. gingivalis, a Gram-negative anaerobic rod, is one of the major pathogens associated with periodontitis. Frequently, P. gingivalis infection leads to cell death. However, the correlation between P. gingivalis-induced cell death and periodontal inflammation remains to be elucidated. Among cell deaths, the death of immune cells appears to play a significant role in inflammatory response. Thus, the aim of this study was to examine P. gingivalis-induced cell death, focusing on autophagy and apoptosis in THP-1 cells.
METHODS
Human acute monocytic leukemia cell line (THP-1) was used for all experiments. Autophagy induced by P. gingivalis in THP-1 cells was examined by Cyto ID staining. Intracellular autophagic vacuoles were observed by fluorescence microscopy using staining Acridine orange (AO); and 3-methyladenine (3-MA) was used to inhibit autophagy. Total cell death was measured by LDH assay. Cytokine production was measured by an ELISA method.
RESULTS
P. gingivalis induced autophagy in an MOI-dependent manner in THP-1 cells, but 3-MA treatment decreased autophagy and increased the apoptotic blebs. P. gingivalis infection did not increase apoptosis compared to the control cells, whereas inhibition of autophagy by 3-MA significantly increased apoptosis in P. gingivalis-infected THP-1 cells. Inhibition of autophagy by 3-MA also increased total cell deaths and inflammatory cytokine production, including IL-1β and TNF-α.
CONCLUSION
P. gingivalis induced autophagy in THP-1 cells, but the inhibition of autophagy by 3-MA stimulated apoptosis, leading to increased cell deaths and pro-inflammatory cytokines production. Hence, the modulation of cell deaths may provide a mechanism to fight against invading microorganisms in host cells and could be a promising way to control inflammation.

Keyword

P. gingivalis; macrophage; cell death; autophagy; apoptosis; periodontitis

MeSH Terms

Acridine Orange
Apoptosis
Autophagy
Blister
Cell Death*
Cell Line
Cytokines
Enzyme-Linked Immunosorbent Assay
Humans
Inflammation
Leukemia, Monocytic, Acute
Macrophages
Methods
Microscopy, Fluorescence
Periodontitis
Porphyromonas gingivalis*
Porphyromonas*
Vacuoles
Acridine Orange
Cytokines
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