PJ34 Prevents Trauma-Induced Heterotopic Ossification without Adverse Bone Healing: An in vivo and in vitro Investigation

Introduction: Trauma-induced heterotopic ossification (THO) is a complication characterized by ectopic lamellar bone formation in soft tissues after trauma. Current treatments are limited by low efficiency, recurrence, and potential impairment of bone healing, highlighting the need for new strategies. Mesenchymal stem cell (MSC) recruitment and osteogenic differentiation are critical in THO pathogenesis. Poly ADP-ribose polymerase 1 (PARP1) is involved in regulating osteogenic differentiation, and PJ34, a PARP1 inhibitor, may have potential in THO prevention. Methods: This study investigated PJ34’s effects on THO and bone healing through in vitro and in vivo experiments. In vitro experiments, the effects of different concentrations of PJ34 on the proliferation, recruitment, migration, alkaline phosphatase (ALP) activity, mineralization and the expression of osteogenesis-related genes of bone marrow stromal cells (BMSCs) were assessed. In vivo experiments involved constructing mouse THO models and tibial fracture models to evaluate the impact of PJ34 on ectopic bone formation and fracture healing. Results: In vitro, PJ34 dose-dependently inhibited BMSC proliferation, recruitment, migration, alkaline phosphatase (ALP) activity, and mineralization. In vivo, PJ34 significantly reduced heterotopic bone formation in a mouse THO model without impairing fracture healing. PJ34 also downregulated the expression of osteogenic genes (Runx2, BMP-2, ALP, OPN, BGLAP) in BMSCs. Conclusion: These findings preliminarily indicate that PJ34 prevents THO by inhibiting proliferation, migration, and osteogenic differentiation of BMSC, without adverse effects on normal bone healing. This supports PJ34’s potential as a novel therapeutic agent for THO prevention, offering a safer alternative to current treatments, though further mechanistic validation is needed. Keywords: trauma-induced heterotopic ossification, PARP1, PJ34, bone healing, BMSC