Preliminary investigation of the vitamin D pathway in periodontal connective tissue cells

The vitamin D pathway, from toll-like receptor activation to human cationic antimicrobial protein (hCAP-18/LL-37) generation, has been identified in monocytes and keratinocytes. This study aimed to investigate the vitamin D pathway in human gingival fibroblasts (hGFs) and human periodontal ligament cells (hPDLCs) and to provide preliminary evidence of its role in periodontal immune defense.

Primary cultures of hGFs and hPDLCs were stimulated with 1,25-dihydroxy vitamin D₃ and 25-hydroxy vitamin D₃ , with or without Porphyromonas gingivalis lipopolysaccharide. CYP27B1 RNA interference and vitamin D receptor (VDR) antagonism were also used for reverse proof. The mRNA expression of hCAP-18/LL-37, VDR, interleukin (IL)-6, IL-8, and monocyte chemotactic protein-1 were detected using real-time polymerase chain reaction. The LL-37 concentrations were measured using enzyme-linked immunosorbent assay.

In hGFs and hPDLCs, 25-hydroxy vitamin D₃ and 1,25-dihydroxy vitamin D₃ induced hCAP-18/LL-37 expression, which was further increased by Porphyromonas gingivalis lipopolysaccharide. If the function of CYP27B1 or VDR was blocked, the induction was significantly weakened. IL-8 and monocyte chemotactic protein-1 mRNA expression could be suppressed by the vitamin D pathway.

These findings suggest that the vitamin D pathway exists in hGFs and hPDLCs and plays an important role in immune defense in periodontal soft tissues.