Periodontal therapy alters gene expression of peripheral blood monocytes

Abstract

Aims: We investigated the effects of periodontal therapy on gene expression of peripheral blood monocytes.

Methods: Fifteen patients with periodontitis gave blood samples at four time points: 1 week before periodontal treatment (#1), at treatment initiation (baseline, #2), 6-week (#3) and 10-week post-baseline (#4). At baseline and 10 weeks, periodontal status was recorded and subgingival plaque samples were obtained. Periodontal therapy (periodontal surgery and extractions without adjunctive antibiotics) was completed within 6 weeks. At each time point, serum concentrations of 19 biomarkers were determined. Peripheral blood monocytes were purified, RNA was extracted, reverse-transcribed, labelled and hybridized with AffymetrixU133Plus2.0 chips. Expression profiles were analysed using linear random-effects models. Further analysis of gene ontology terms summarized the expression patterns into biologically relevant categories. Differential expression of selected genes was confirmed by real-time reverse transcriptase-polymerase chain reaction in a subset of patients.

Results: Treatment resulted in a substantial improvement in clinical periodontal status and reduction in the levels of several periodontal pathogens. Expression profiling over time revealed more than 11,000 probe sets differentially expressed at a false discovery rate of <0.05. Approximately 1/3 of the patients showed substantial changes in expression in genes relevant to innate immunity, apoptosis and cell signalling.

Conclusions: The data suggest that periodontal therapy may alter monocytic gene expression in a manner consistent with a systemic anti-inflammatory effect.

Fig. 1

Study flow chart.

Fig. 2

Subject based percentage of BOP (a), number of pockets ≥6 mm deep per subject (b), and mean bacterial levels in PL (c) at treatment initiation ("pre-treatment") and at the final examination (“post-treatment”). X-axis describes the patient number. Species abbreviations are as follows: Aa, Aggregatibacter actinomycetemcomitans; Pg, Porphyromonas gingivalis; Tf, Tannerella forsythia; Td, Treponema denticola; Pi, Prevotella intermedia; Fn, Fusobacterium nucleatum; Cr, Campylobacter rectus; Mm, Micromonas micros; Ec, Eikenella corrodens; Vp, Veillonella parvula; An, Actinomyces naeslundii.

Fig. 3

Variability in fold change for top genes across subjects. The median absolute value of the fold change for the top 390 probe sets (those meeting the Bonferroni criterion at a family-wise error rate of 0.05) is plotted for each patient. The light bars represent the fold change in expression between the two pre-treatment time points, representing background variability in expression. The dark bars indicate the fold change in expression between the last point (10-week) and the average baseline expression. Patient 11 had gene expression data for only one baseline time point so the control value could not be computed. The error bars indicate interquartile ranges.

Fig. 4

Visualization of the top 100 differentially expressed genes over time. Samples are grouped according to the time point obtained. “Fold change” describes the ratio of expression at time point #4 over the average expression at time points #1 and #2. “Fold change responders” describes the corresponding ratio exclusively based on the six patients with the most pronounced changes in gene expression (“top responders”, pats. # 8, 11, 35, 36, 40 and 45). Gene symbols in brackets (“[]”) are based on a separate sequence analysis for genes for which Affymetrix provided no annotation. Probe sets indicated by “—” in the gene symbol column did not have any associated gene symbol.

Fig. 5

Summary inflammatory score (SIS) change at completion of treatment (“Early SIS Change”; (a) and at the last examination (“Late SIS Change”; (b). X-axis describes the patient number. “Top responders” indicated by darker bars. For SIS computation, see “Materials and methods”.