Diminished osteoprotegerin production by gingival fibroblasts from periodontitis patients is associated with their reduced ability to suppress osteoclastogenesis.

Osteoclast-mediated alveolar bone resorption is a key hallmark of periodontitis. Gingival fibroblasts (GFs) play multifaceted roles in the progression of chronic inflammation; however, their involvement in osteoclastogenesis remains controversial. Here, we analyzed the effects of mediators secreted by GFs from healthy donors and periodontitis patients on osteoclast formation. We observed strong suppression of receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis by conditioned media from healthy donor GFs, which was independent of any prior in vitro stimulation or infection. These media contained high levels of osteoprotegerin (OPG), and GFs were identified as the main OPG source in gingival tissue using a 3D organotypic reconstructed human gingiva model and a single-cell RNA-seq dataset. Notably, GFs from periodontitis patients produced significantly less OPG compared to GFs from healthy individuals and were less effective at suppressing osteoclastogenesis. Finally, siRNA-mediated silencing of OPG expression in GFs from periodontitis patients further decreased their inhibitory effect on osteoclast formation, confirming the central role of OPG in osteoclastogenesis regulation by GFs. Collectively, these results demonstrate that in healthy gingival tissue, GFs exert bone-protective effects by inhibiting osteoclast formation. However, prolonged exposure to the microenvironment of the inflamed gingival tissue could impair this protective function through sustained reduction of OPG production, which may contribute to alveolar bone resorption in periodontitis.