Affiliation:
1. Department of Oral Microbiology, Division of Oral Infection Health Sciences, Asahi University School of Dentistry, Mizuho, Gifu, Japan
2. Department of Sports Dentistry, Meikai University School of Dentistry, Sakado, Saitama, Japan
3. Asahi University School of Dental Hygienists, Mizuho, Gifu, Japan
Abstract
Dental plaque, a highly structured polymicrobial biofilm, persistently forms in the oral cavity and is a common problem affecting oral health. The role of oral defense factors in either collaborating or disrupting host–microbiome interactions remains insufficiently elucidated. This study aims to explore the role of LL-37, a critical antimicrobial peptide in the oral cavity, in dental plaque formation. Through immunostaining dental plaque specimens, we observed that LL-37 and DNA colocalized in the samples, appearing as condensed clusters. In vitro experiments revealed that LL-37 binds rapidly to oral bacterial DNA, forming high molecular weight, DNase-resistant complexes. This interaction results in LL-37 losing its inherent antibacterial activity. Further, upon the addition of LL-37, we observed a visible increase in the precipitation of bacterial DNA. We also discovered a significant correlation between the levels of the DNA–LL-37 complex and LL-37 within dental plaque specimens, demonstrating the ubiquity of the complex within the biofilm. By using immunostaining on dental plaque specimens, we could determine that the DNA–LL-37 complex was present as condensed clusters and small bacterial cell-like structures. This suggests that LL-37 immediately associates with the released bacterial DNA to form complexes that subsequently diffuse. We also demonstrated that the complexes exhibited similar Toll-like receptor 9–stimulating activities across different bacterial species, including Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, and Streptococcus salivarius. However, these complexes prompted dissimilar activities, such as the production of IL-1β in monocytic cells via both NLRP3 pathway-dependent and pathway-independent mechanisms. This study, therefore, reveals the adverse role of LL-37 in dental plaque, where it binds bacterial DNA to form complexes that may precipitate to behave like an extracellular matrix. Furthermore, the unveiled stimulating properties and species-dependent activities of the oral bacterial DNA–LL-37 complexes enrich our understanding of dental plaque pathogenicity and periodontal innate immune responses.
Funder
ogawa science and technology foundation
Japan Society for the Promotion of Science