Cross-Talk Between Osteoclasts, Osteoblasts And Osteocytes Within Periapical Periodontitis

Incomplete bone healing remains a significant complication of periapical periodontitis, yet its underlying mechanisms remain unclear and warrant further investigation. To investigate the progression of incomplete bone healing, we employed both in vitro and in vivo models. For in vitro studies, CD14+ monocytes were stimulated with LPS, leading to the secretion of chemokines that recruited and mobilized osteoblasts. While osteoclast formation increased in the inflammatory environment, osteoblast proliferation remained unaffected; however, their mineralization capacity was impaired, accompanied by reduced expression of ALP and Runx2. Senescence pathway analysis revealed that conditioned medium from osteoclasts upregulated the senescence marker p16 in osteoblasts. To further examine bone healing in vivo, we established a hydrogel-LPS calvarial injection mouse model and monitored bone changes over 28 days. Compared to controls, LPS-treated mice exhibited significant bone loss at 7 days, which normalized by day 21. Surprisingly, immunohistochemical staining showed no changes in osteoblast markers (Runx2, Osterix), while the early osteocyte marker E11 increased without alterations in the mature osteocyte marker DMP1. These unexpected findings prompted a re-evaluation of prior single-cell RNA sequencing data from clinical periapical periodontitis samples, which similarly highlighted osteocyte pathway dysregulation. Our study demonstrates that prolonged LPS exposure promotes osteoclast formation, which induces osteoblast senescence and impairs mineralization in vitro. However, in vivo observations suggest a distinct mechanism, where residual LPS may primarily disrupt osteocyte function, further hindering bone healing.