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Porphyromonas gingivalis lipopolysaccharide promotes platelet spreading and thrombosis via Cdc42 activation Senini, Vincent

Abstract

Background: Chronic periodontitis confers an increased risk for cardiovascular diseases, including thrombosis. However, the molecular mechanisms that potentially link periodontitis with thrombosis are undefined. Here I tested the hypothesis that gram-negative periodontal infection promotes pathological platelet activation and shape change. I focused specifically on lipopolysaccharide (LPS) signaling through Cdc42. Methods: Platelets were isolated from blood samples and allowed to spread on coverslips in the presence or absence of LPS purified from the periodontal pathogen Porphyromonas gingivalis. Platelets were fixed and stained with Alexa- 488-phalloidin to label the actin cytoskeleton. The degree of platelet spreading and shape change were quantified by confocal microscopy. In a translational pilot study, blood samples were obtained from human subjects exhibiting generalized severe chronic periodontitis (SP) or healthy periodontium (HP). Rotational thromboelastometry (ROTEM) was used to quantify the rate of clot formation via the intrinsic coagulation pathway. Results: LPS-treated platelets exhibited significantly (p<0.05) greater spreading and higher numbers of actin-rich filopodia (cell extensions) than controls. I also found that LPS stimulation directly activated Cdc42, the small GTPase responsible for filopodial formation. Exposure of whole blood samples to LPS significantly (p<0.05) reduced clotting times. Blood from SP patients clotted significantly (p<0.05) more rapidly and exhibited reduced partial thromboplastin times (aPTT) relative to HP controls. Conclusion: This is the first study to suggest a mechanism by which P. gingivalis LPS drives Cdc42 activation and platelet spreading. These data are consistent with the notion that periodontitis promotes accelerated clot formation and an increased risk of thrombosis.

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