Mechanical force application and inflammation induce osteoclastogenesis by independent pathways

Area of Science:

• Periodontal biology
• Cellular and molecular mechanisms
• Biomaterials and tissue engineering

Background:

• Periodontal ligament fibroblasts (PDLF) play a crucial role in maintaining periodontal health.
• Understanding how mechanical forces and inflammation affect PDLF function is vital for treating periodontal diseases and optimizing orthodontic treatments.
• Existing research has not fully elucidated the combined effects of mechanical stress and inflammatory mediators on PDL fibroblast behavior.

Purpose of the Study:

• To investigate the functional responses of PDL fibroblasts under mechanical force, inflammatory conditions, or a combination of both.
• To analyze changes in cell proliferation, viability, cell cycle, collagen production, and key signaling molecules like OPG and RANKL.
• To compare the effects on PDL fibroblasts with those on gingival fibroblasts (GFs) and osteoblasts (Saos2 cells).

Main Methods:

• Preparation of inflammatory supernatants by stimulating human neutrophils with Porphyromonas gingivalis.
• Exposure of primary human PDL fibroblasts, GFs, and Saos2 cells to inflammatory supernatants.
• Simulation of orthodontic mechanical force on PDLFs using centrifugation.
• Assessment of cell proliferation, viability, cell cycle distribution, collagen expression, OPG, and RANKL levels.

Main Results:

• Mechanical force increased PDLF metabolic rate and shifted the cell cycle to G0/G1, arresting proliferation and elevating collagen and RANKL levels, with a mild increase in OPG.
• Combined mechanical force and inflammatory supernatant did not alter PDLF viability, proliferation, or cytokine expression.
• Inflammatory supernatant alone increased RANKL expression in GFs but had no significant effect on PDLFs or Saos2 cells.

Conclusions:

• Mechanical force significantly modulates PDLF function, impacting proliferation, collagen synthesis, and RANKL expression.
• While inflammation alone did not affect PDLFs or osteoblasts, it upregulated RANKL in gingival fibroblasts.
• The study suggests that the interplay between mechanical forces and periodontal inflammation may contribute to bone catabolism and resorption via distinct cellular mechanisms.