Interleukin-1β is internalised by viable Aggregatibacter actinomycetemcomitans biofilm and locates to the outer edges of nucleoids.
The opportunistic pathogen Aggregatibacter actinomycetemcomitans causes periodontitis, which is a biofilm infection that destroys tooth-supportive tissues. Interleukin (IL)-1β, 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-1β; 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-1β when co-cultured with an organotypic mucosa. Decreased biofilm viability hindered the ability of biofilm to sequester IL-1β and caused IL-1β leakage into the culture medium. In some A. actinomycetemcomitans cells, intracellular IL-1β localized to the outer edges of the nucleoids. We identified the DNA-binding protein HU as an IL-1β interacting protein with mass spectroscopy and showed the interaction of recombinant HU and IL-1βin 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 deoxynucleotidyl 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-1β. The interaction of IL-1β with conserved HU provides a potential mechanism for shaping bacterial gene expression.
Department of Biochemistry and Food Chemistry, University of Turku, FI-20014 Turku, Finland.
Annamari
A
Paino
Elina
E
Lohermaa
Raija
R
Sormunen
Heidi
H
Tuominen
Jari
J
Korhonen
Marja T
MT
Pöllänen
Riikka
R
Ihalin
D000189:Actinobacillus Infections / Q000382:microbiology / Q000473:pathology; D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects; D001422:Bacterial Adhesion / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004269:DNA, Bacterial / Q000378:metabolism*; D051959:ELAV Proteins / Q000737:chemistry / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000382:microbiology / Q000473:pathology; D005881:Gingiva / Q000382:microbiology / Q000473:pathology; D006801:Humans; D053583:Interleukin-1beta / Q000378:metabolism*; D015603:Keratinocytes / Q000382:microbiology / Q000473:pathology; D050296:Microbial Viability / Q000187:drug effects; D008969:Molecular Sequence Data; D009092:Mucous Membrane / Q000187:drug effects / Q000382:microbiology / Q000473:pathology / Q000648:ultrastructure; D010406:Penicillins / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D013307:Streptomycin / Q000494:pharmacology
D004269:DNA, Bacterial; D051959:ELAV Proteins; D053583:Interleukin-1beta; D010406:Penicillins; D013307:Streptomycin