Institut für Ernährungswissenschaften

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Interaktion des bakteriellen Quorum Sensing Moleküls N-(3-oxododecanoyl)-L-Homoserin-Lacton (AHL-12) mit humanen neutrophilen Granulozyten
(2013) Kahle, Nadine; Hänsch, Gertrud Maria
To evade immune-defense mechanisms of the host, Pseudomonas aeruginosa form so called biofilms. To coordinate this complex process, the bacteria communicate via quorum sensing signals, such as N-(3-oxododecanoyl)-L-homoserine lactone (AHL-12). AHL-12 is also recognized by human polymorphonuclear neutrophils (PMN). It is chemotactic for PMN and thus might cause their directed migration to the site of infection in order to eliminate infiltrated microorganisms. Through different approaches, the aim of this work was to find out in which way AHL-12 interacts with PMN. As a first step, an AHL-12 induced signaling-pathway should be elucidated in in vitro experiments using primary, human PMN. In a further approach using radioactive- (3H-AHL-12) and fluorescence-labeled (AHL-12-FITC) AHL-molecules, the interaction of AHL-12 with PMN should be examined, especially with regard to the expression of a specific receptor for AHL-12 on PMN. In this work it was confirmed that AHL-12 induced chemotaxis of human PMN. After stimulation of PMN with AHL-12, MAPK-p38 was phosphorylated and hence activated. Furthermore, it was shown that MAPK-p38 phosphorylated MAPKAP-Kinase 2, which in turn phosphorylated and hence activated leukocyte specific protein 1 (LSP1). LSP1 finally affected chemotaxis via binding to F-Actin and by modulating the intensity of integrin-mediated adherence. The AHL-12 induced chemotaxis was inhibited by SB203580, an inhibitor of MAPK-p38. The question, whether there is a specific receptor for AHL-12 in PMN, could not be answered conclusively, because it was not possible to isolate a protein with receptor function using conventional methods such as immunoprecipitation and crosslinking. In uptake studies with 3H-AHL-12 and AHL-12-FITC, it was shown, that the major portion of AHL-12-FITC bound to the cell membrane. However, another portion got into the cells, which raises the possibility that an intracellular receptor or an intracellular binding protein for AHL-12, for example IQGAP1, exists. Taken together these data provide evidence that AHL-12 is chemotactic for PMN. Assuming that AHL-12 is released in the early phase of biofilm formation, before bacteria are embedded in the EPS, PMN have the chance to kill bacteria and thus could contribute to prevent biofilm formation.

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