Double-edged-sword effect of bisphosphonates on the osteogenic differentiation of human periodontal ligament stem cells

Bisphosphonates (BPs), widely used anti-resorptive agents for osteoporosis and cancer-related bone metastasis, can paradoxically contribute to medication-related osteonecrosis of the jaw (MRONJ). Our previous work showed that periodontal ligament stem cells (PDLSCs) from MRONJ patients display severely impaired osteogenesis; however, how BPs directly regulate PDLSC function remains unclear. In this study, human PDLSCs were exposed to graded concentrations of zoledronate (ZOL, 0.01-10 μM) to characterize dose-dependent effects on cell viability, apoptosis, and osteogenic differentiation. High-dose ZOL markedly reduced proliferation, induced apoptosis, and strongly inhibited osteogenesis. In contrast, low-dose ZOL promoted osteogenic differentiation <i>in vitro</i>, enhanced mineralization, and increased ectopic bone formation <i>in vivo</i>. Transcriptomic and molecular analyses revealed that ZOL activated Wnt/β-catenin and MAPK signaling, and blockade of either pathway attenuated the osteogenic enhancement. These findings demonstrate a double-edged-sword effect of BPs on PDLSCs: low-dose ZOL enhances osteogenesis through coordinated activation of Wnt/β-catenin and MAPK pathways, whereas high-dose exposure is cytotoxic and suppresses regenerative potential. The results underscore the necessity of precise BP dose control to maximize periodontal regeneration while minimizing MRONJ risk.