Transcriptome Profiling of Aggregatibacter actinomycetemcomitans Stimulated Peri-implantitis Model
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Hypothesis: Aggregatibacter actinomycetemcomitans (A.a) infection of dental implant abutments can induce peri-implant inflammation associated with peri-implant bone loss. Mutation of A.a virulence alters A.a - mediated host inflammation and peri-implant bone loss. Objective: To define by RNA sequencing the tissue transcriptomes present in healthy and A.a-infected peri-implant tissues in the rat oral implant model. Methods: Aa was grown on trypticase soy agar. Thirty-six female 5-month year old rats were used. Two-piece titanium implants (1.2x3.0 mm) were fabricated. The abutments were attached to the external hex of all implants. The abutments were then surface treated using grit blasting aluminum oxide (50) and hydrofluoric acid. The abutments were then inoculated with either Aa wild type (n=7), or Aa double deletion mutant of leukotoxin and cytolelthal distending (DS7S-1) (n=7) and sterile sham (n=8) in vitro for 3 days. Implants were installed in maxillary bone of rats. Micro-CT scans were taken at baseline (0), weeks 3 and 8. CT scans were then overlaid to assess for bone loss. Peri-implant tissue was harvested at 8 weeks for RNA sequencing. The transcriptomes were analyzed and compared using bioinformatic tools. Results: Our study demonstrated the role of Aa in inducing the innate immune response at the epithelium, which ultimately resulted in peri-implantitis. Wild type Aa and mutant Aa induced responses that were associated with TLR4 receptors suggesting that they are signaling through conserved innate immunity mechanism. Mutant Aa appeared to strongly induce mucosal expression of Wig-1, a modulator of P53 function. Finally, the mutant Aa also induced upregulation of tight junction protein Claudin-2 and a component of Dynein, which controls microtubule function. The mutant Aa induced gene expression associated with rapid epithelial turnover and diminished epithelial structural integrity, was also seen with GO terms. This implied an impact on the structural function of the epithelium. Aa was able to induce innate immune response at the peri-implant tissues, and changes that are associated with pro-inflammatory pathophysiology. Perhaps, the epithelium can be a target area for therapy. Conclusions: Results of this study implicate Aa – related changes in the epithelial barrier function of oral mucosa in the pathophysiology of peri-implantitis.