Periodontal ligament (PDL) cells are critical for the bone remodeling process in periapical lesions since they can differentiate into osteoblasts and secrete osteoclastogenesis-promoting cytokines. Post-translational histone modifications including alterations of the methylation status of H3K27 are involved in cell differentiation and inflammatory reaction. The histone demethylase Jumonji domain-containing 3 (Jmjd3) specifically removes methylation of H3K27. We investigated whether Jmjd3 is involved in the osteogenic differentiation and secretion of PDL cells' inflammatory factors. Jmjd3 expression in periapical lesions was examined by immunostaining. Using siRNA specific for Jmjd3 or the specific Jmjd3 inhibitor GSK-J4, we determined Jmjd3's roles in osteogenic differentiation and cytokine production by real-time RT-PCR. The locations of Jmjd3 and NF-κB were analyzed by immunocytochemistry. Compared to healthy PDLs, the periapical lesion samples showed higher Jmjd3 expression. Treatment with GSK-J4 or Jmjd3 siRNA suppressed PDL cells' osteogenic differentiation by suppressing the expressions of bone-related genes (Runx2, Osterix, and osteocalcin) and mineralization. Jmjd3 knockdown decreased the expressions of cytokines (TNF-α, IL-1β, and IL-6) induced by lipopolysaccharide extracted from Porphyromonas endodontalis (Pe-LPS). Pe-LPS induced the nuclear translocations of Jmjd3 and NF-κB; the latter was inhibited by GSK-J4 treatment. Jmjd3 appears to regulate PDL cells' osteogenic differentiation and proinflammatory cytokine expressions.
Keywords: histone demethylase Jmjd3; osteogenic differentiation; periapical lesions; periodontal ligament cell; proinflammatory cytokines.