Evaluation of salivary sirtuin 2 as a novel biomarker for periodontitis

Abstract

SIRT2 is an NAD-dependent histone deacetylase (HDAC) that is involved in the regulation of gene expression and protein function. This study aimed to evaluate SIRT2 as a salivary biomarker for periodontitis and investigate any association between SIRT2 and the inflammatory processes relevant to periodontitis. Immune responses were investigated in vitro using THP1 monocytes differentiated into macrophages using phorbol 12-myristate 13-acetate (PMA) and stimulated with TLR2 or TLR4 agonists. Analysis using qPCR and western blotting showed there were no significant changes to SIRT2 mRNA or intracellular protein expression respectively after stimulation with TLR agonists. Secreted SIRT2 levels measured by ELISA were significantly elevated after stimulation with TLR2 agonists but not after stimulation with TLR4 agonists. TLR agonists had no effect on SIRT2 deacetylation activity in macrophages. Inhibition experiments in macrophages showed that SIRT2 regulates secretion of TNFα, IL-6, IL-8, and IL-1β as measured by ELISA. Multiple regression analysis (ANCOVA) showed that SIRT2 was significantly elevated in periodontitis when accounting for the influence of age but SIRT2 levels did not correlate with clinical measurements of periodontitis such as bleeding on probing and pocket depth. Receiver operating characteristic (ROC) curve analysis showed that salivary SIRT2 could detect periodontitis with a high degree of sensitivity and specificity (AUC 89%). In summary, SIRT2 levels accurately represent the presence of periodontitis, but do not correlate with clinical measures of periodontitis, which may limit its utility as a diagnostic biomarker. We have demonstrated a novel TLR2-mediated pathway of SIRT2 secretion from THP1-derived macrophages which may explain the elevated levels of SIRT2 present in the saliva of patients with periodontitis but will require further investigation. We have also shown that SIRT2 mediates the secretion of pro-inflammatory cytokines after stimulation with TLR agonists which may be of relevance to the pathogenesis of periodontitis.