Effects of Aggregatibacter actinomycetemcomitans leukotoxin on endothelial cells

Abstract

Aggregatibacter actinomycetemcomitans is a human pathogen that produces leukotoxin (LtxA) as a major virulence factor. In this study the effect of LtxA on microvascular endothelial cell viability and phenotype was studied. High doses of single LtxA treatment (500 ng/ml to 5 μg/ml) significantly and irreversibly decreased cell proliferation and induced apoptosis, as assessed by tetrazolium salt and annexin V assay, respectively. Apoptosis was partially inhibited by the pan-caspase inhibitor, z-VAD-fmk. LtxA caused a cell cycle arrest in the G2/M phase after 72 h. Between 500 ng/ml and 5 μg/ml, after long- or short-term stimulation LtxA increased the expression of ICAM-1 and VCAM-1, as well as the percentages of endothelial cells expressing these adhesion molecules. Thus, A. actinomycetemcomitans LtxA has substantial pro-inflammatory effects on human brain endothelial cells by upregulation of ICAM-1 and VCAM-1. Furthermore, LtxA in higher concentration was found to decrease proliferation and induces apoptosis in microvascular endothelial cells.

Structure and function of RTX toxins

“…LtxA triggers a potent release and activation of matrix metalloproteinase 8 from human neutrophils [229] and can also cause shrinkage lysis of human erythrocytes in a P2X receptor-dependent manner [230]. Finally, LtxA was found to induce proinflammatory effects on human brain endothelial cells and to trigger apoptosis in microvascular endothelial cells [231]. Altogether, the cytotoxicity of LtxA toward human leukocytes appears to be closely related to the pathogenic mechanisms of periodontitis inflammatory disease [232].…”

Aggregatibacter (Actinobacillus) actimycetemcomitans leukotoxin and human periodontitis – A historic review with emphasis on JP2

“…LtxA has been shown to induce a substantial pro‐inflammatory effect on human brain endothelial cells by up‐regulation of ICAM‐1 and VCAM‐1 [66]. A higher concentration of LtxA could decrease proliferation and induce apoptosis in microvascular endothelial cells.…”

Differential transcription of virulence genes in Aggregatibacter actinomycetemcomitans serotypes

“…Adhesins, such as Aae and Omp100, play a significant role in the interaction with gingival epithelial cells (10, 11), whereas the highly immunogenic outer membrane protein Omp29 (12) and the tetraphosphatase ApaH (13) are associated with invasion of non-phagocytic cells. Leukotoxin induces apoptosis not only in neutrophils and macrophages of humans and Old World primates (5) but also in endothelial cells (14). This organism's cytotoxic effects are also mediated by the cytolethal-distending toxin, which is involved in damage of the epithelial cells barrier (15) and in the interaction with the immune system (16, 17).…”