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Porphyromonas gingivalis seems to perturb the cytokine network to maintain periodontal disease. Although endothelial cells are a leading source of interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1), the effect of P. gingivalis on the cells remains unclear. We used reverse transcription-PCR (RT-PCR) to assess levels of IL-8 and MCP-1 mRNA and enzyme-linked immunosorbent assays (ELISA) to evaluate their protein production by human umbilical vein endothelial cells (HUVEC) challenged with P. gingivalis. IL-8 and MCP-1 protein levels decreased in response to challenge with P. gingivalis, and N-a- p-tosyl- L-lysine chloromethylketone (TLCK) prevented the degradation of these chemokines. Furthermore, the bacteria upregulated expression of the mRNAs of these chemokines. Our results indicate that P. gingivalis proteases degraded IL-8 and MCP-1. Degradation of chemokines secreted from endothelial cells may decrease the recruitment of leukocytes and their migration through the endothelium, thus contributing to a delay in the host immune defense mechanism.

Osteoprotegerin (OPG) is a key regulator of osteoclastogenesis during the progression of periodontitis. Recent reports suggest that osteoprotegerin may also prevent arterial calcification and contribute to endothelial cell survival. To determine whether the vascular functions of osteoprotegerin are involved in periodontitis, we examined whether osteoprotegerin contributed to the survival of endothelial cells damaged by Porphyromonas gingivalis cysteine proteinases (gingipains). Gingipain proteinases cleave a broad range of host proteins, and are important virulence factors of P. gingivalis, a major causative bacterium of adult periodontitis. Human microvascular endothelial cells (HMVEC) were exposed to activated gingipain extracts from P. gingivalis 381, with and without pretreatment with osteoprotegerin. Cell viability was quantified by the tetrazolium (WST-8) reduction assay, and apoptosis was examined using Hoechst 33342 nuclear staining. After 16 h of treatment with activated gingipain extracts, HMVEC showed near-complete detachment from the tissue culture dish, and apoptosis was evident by 24 h. Pretreatment of HMVEC with osteoprotegerin reduced the extent of both cellular detachment and apoptotic cell death. Our results indicated that osteoprotegerin pretreatment protected HMVEC against detachment and apoptotic cell death induced by gingipain-active bacterial cell extracts. These results also suggest that osteoprotegerin may function as a survival factor for endothelial cells during periodontitis.

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