A1 Journal article – refereed
Interleukin-1 beta is internalised by viable Aggregatibacter actinomycetemcomitans biofilm and locates to the outer edges of nucleoids

List of Authors: Paino A, Lohermaa E, Sormunen R, Tuominen H, Korhonen J, Pöllänen MT, Ihalin R
Publication year: 2012
Journal: Cytokine
Journal name in source: CYTOKINE
Journal acronym: CYTOKINE
Number in series: 2
Volume number: 60
Issue number: 2
Number of pages: 10
ISSN: 1043-4666

The opportunistic pathogen Aggregatibacter actinomycetemcomitans causes periodontitis, which is a biofilm infection that destroys tooth-supportive tissues. Interleukin (IL)-1 beta, a central proinflammatory cytokine of periodontitis, is an essential first line cytokine for local inflammation that modulates the cell proliferation and anti-pathogen response of human gingival keratinocytes. Previously, we demonstrated that A. actinomycetemcomitans biofilms bind IL-1 beta; however, whether this binding is an active process is not known. In this study, we showed for the first time with immuno-electron microscopy that viable bacterial biofilm cells internalised IL-1 beta when co-cultured with an organotypic mucosa. Decreased biofilm viability hindered the ability of biofilm to sequester IL-1 beta and caused IL-1 beta leakage into the culture medium. In some A. actinomycetemcomitans cells, intracellular IL-1 beta localized to the outer edges of the nucleoids. We identified the DNA-binding protein HU as an IL-1 beta interacting protein with mass spectroscopy and showed the interaction of recombinant HU and IL-1 beta in vitro using enzyme-linked immunosorbent assay (ELISA). Close contact with a viable A. actinomycetemcomitans biofilm decreased the proliferation and apoptosis of human gingival keratinocytes as demonstrated using Ki-67 and the terminal deoxynncleotidyl transferase dUTP nick-end labelling (TUNEL) staining, respectively. Our results suggest that viable A. actinomycetemcomitans biofilms may disturb the critical first steps of local inflammation in periodontitis by binding and internalising IL-1 beta. The interaction of IL-1 beta with conserved HU provides a potential mechanism for shaping bacterial gene expression. (C) 2012 Elsevier Ltd. All rights reserved.

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