[P3-2-36] Antimicrobial peptide LL-37 facilitates accumulation of oral bacterial DNA in dental plaque
Keywords:LL-37、DNA-LL-37 complex、Dental plaque
Dental plaque, a unique polybacterial biofilm, produces an extracellular matrix constructed into highly organized bacterial communities. Despite the uncertainty surrounding its properties, DNA is recognized as an essential component of this matrix based on recent studies. LL-37, a crucial antimicrobial peptide, is sourced from periodontal cells and migrated neutrophils, or secreted into saliva and gingival crevicular fluids, serving a protective function for the oral environment. Its cationic properties might be instrumental in modulating DNA binding, thereby generating inflammatory compounds. The precise contribution of LL-37 to dental plaque formation remains elusive. In this study, we investigated the function of LL-37 by immunostaining dental plaque samples, which exhibited the colocalization of LL-37 and DNA as clusters with a nebulous appearance. LL-37 was found to rapidly associate with bacterial DNA, resulting in the formation of high-molecular-weight complexes that are resistant to DNase. Applying an antibody specifically recognizing the DNA-LL-37 complex during immunostaining unveiled nebulous clusters and diminutive formations, likely corresponding to bacterial cells, within the dental plaque. These observations suggest that LL-37 promptly interacts with DNA liberated from ruptured bacteria to form complexes that spread and aggregate as nebulous clusters.In addition , we noted that the DNA complexes derived from Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, and Streptococcus salivarius had comparable Toll-like receptor 9-dependent stimulatory effects, but exhibited considerable variability in monocytic cell activities. These activities included NLRP3-dependent and -independent synthesis of IL-1β. Interestingly, the S. salivarius DNA complex appeared to counteract the inflammatory complex in the cells. Therefore, LL-37 seems to promote DNA accumulation in dental plaque through the complex formation, while oral bacterial DNA complexes have stimulatory properties that have not been previously identified. Our study adds to the current understanding of the LL-37-DNA interaction in dental plaque and provides novel insights into the biology of dental plaque and the immunology of periodontal diseases.