Amyloid beta (A4) precursor protein expression in human periodontitis-affected gingival tissues

Objective: Periodontitis involves periodontal tissue destruction and is associated with chronic inflammation and ageing. Periodontitis has recently been recognised as a risk factor for Alzheimer's disease (AD). We showed upregulation of molecules in the AD pathway including amyloid beta (A4) precursor protein (APP), a key gene in AD, interleukin-1 beta (IL-1β), and complement component 1 (q subcomponent, A chain) (C1QA) in periodontitis compared to healthy tissues. Here, we quantitatively analysed the expression levels of APP, IL-1β, and C1QA and determined the localisation of APP in gingival tissues.

Design: Fourteen chronic periodontitis patients and 14 healthy participants were enrolled. Six samples of total RNA from two distinct sites of healthy and periodontitis-affected gingival tissues from three randomly selected patients were used for microarray analyses, and significant biological pathways in periodontitis were identified. Differential gene expression of APP, IL-1β, and C1QA, which belong to the AD pathway, were analysed with quantitative reverse transcription real-time polymerase chain reaction (qRT-PCR) using samples from these 14 chronic periodontitis patients and 14 healthy controls. APP localisation was analysed with immunohistochemistry.

Results: APP, IL-1β, and C1QA mRNA levels were significantly upregulated in periodontitis-affected gingival tissues. APP was mainly localised in macrophages in gingival connective tissues underneath the epithelial layers.

Conclusions: An association between AD and periodontitis was detected with microarray and computer-aided data mining analyses. qRT-PCR identified differential gene expression in periodontitis-affected gingival tissue that may be related to AD pathogenesis. Elevated APP, IL-1β, and C1QA transcripts and APP-expressing macrophages in periodontitis-affected gingival tissues were observed, suggesting a relationship between periodontitis and AD pathogenesis.