Zoledronate promotes bone formation by blocking osteocyte-osteoblast communication during bone defect healing

Area of Science:

• Bone Biology
• Pharmacology
• Cellular Mechanisms

Background:

• Nitrogen-containing bisphosphonates (N-BPs) are established antiresorptive agents targeting osteoclasts.
• Emerging evidence suggests N-BPs also influence bone-forming cells, but mechanisms remain unclear.
• The role of osteocytes in N-BP effects on bone healing requires further investigation.

Purpose of the Study:

• To elucidate the cellular mechanisms by which N-BPs, specifically zoledronate (ZA), regulate bone defect healing.
• To investigate the paradoxical effects of ZA on osteoblasts and osteocytes.
• To explore the impact of ZA on the osteocytic-osteoblastic communication network.

Main Methods:

• Bone histomorphometry to assess new bone formation.
• Analysis of osteoblast and osteoclast markers (alkaline phosphatase, TRAP).
• Assessment of SOST expression, osteocyte morphology, osteocytic-canalicular system (OLCS) integrity, dentin matrix protein 1, and connexin 43 expression.

Main Results:

• Systemic ZA administration significantly increased new bone formation.
• ZA elevated osteoblast and osteoclast numbers on bone surfaces.
• ZA upregulated SOST in osteocytes, disrupted OLCS, reduced connexin 43, and impaired cell communication, yet promoted bone formation via Wnt signaling.

Conclusions:

• Zoledronate treatment enhances bone defect healing through complex cellular interactions.
• ZA disrupts osteocyte-osteoblast communication by reducing gap junctions and altering the osteocytic network.
• Sustained SOST expression in osteocytes, induced by ZA, appears to activate Wnt signaling, driving increased bone formation.