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Evidence for apoptosis of murine macrophages by Actinobacillus actinomycetemcomitans infection
Abstract:
The gram-negative bacterium Actinobacillus actinomycetemcomitans is considered an important etiological agent in periodontal diseases. In this study, we show that A. actinomycetemcomitans strains are cytotoxic for the murine macrophage cell line J774.1. On the other hand, Porphyromonas gingivalis strains, other gram-negative oral species implicated in adult periodontitis, showed weak cytotoxic effects. For this to occur, A. actinomycetemcomitans had to gain entry into the macrophages, since cytotoxicity was prevented by cytochalasin D. We demonstrate that cell death induced by A. actinomycetemcomitans Y4 occurs through apoptosis, as shown by changes in nuclear morphology, an increase in the proportion of fragmented DNA, and the typical ladder pattern of DNA fragmentation indicative of apoptosis. We further sought to determine whether the cytotoxicity induced by A. actinomycetemcomitans Y4 could be modulated by the protein kinase inhibitors H7 and HA1004. Apoptotic cell death induced by A. actinomycetemcomitans Y4 was suppressed by H7 but was relatively unaffected by HA1004. These findings suggest that the signals of protein kinases may regulate apoptosis induced by A. actinomycetemcomitans Y4. The ability of A. actinomycetemcomitans to promote the apoptosis of macrophages may be important for the initiation of infection and the development of periodontal diseases.
Insights
Actinobacillus actinomycetemcomitans induces apoptosis in macrophages, a key step in periodontal disease development. Protein kinase inhibitors like H7 can suppress this cell death, offering potential therapeutic insights.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Actinobacillus actinomycetemcomitans (Aa) is linked to periodontal diseases.
- Understanding Aa's interaction with host cells is crucial for disease pathogenesis.
Purpose of the Study:
- To investigate the cytotoxic effects of Aa on murine macrophages.
- To determine the mechanism of Aa-induced cell death and its modulation.
Main Methods:
- Exposure of J774.1 macrophages to Aa and Porphyromonas gingivalis strains.
- Assessment of cytotoxicity using cytochalasin D.
- Analysis of apoptosis markers (nuclear morphology, DNA fragmentation).
- Treatment with protein kinase inhibitors H7 and HA1004.
Main Results:
- Aa strains exhibited significant cytotoxicity towards macrophages, unlike P. gingivalis.
- Aa-induced cell death was confirmed as apoptosis, requiring bacterial entry.
- The protein kinase inhibitor H7 suppressed Aa-induced apoptosis, while HA1004 had minimal effect.
Conclusions:
- Aa actively induces apoptosis in macrophages, potentially facilitating infection and disease progression.
- Protein kinase signaling pathways appear to regulate Aa-induced apoptosis, suggesting therapeutic targets.