Abstract：
Postnatal bone growth primarily relies on chondrocyte proliferation and osteogenic differentiation within the growth plate (GP) via endochondral ossification. Despite its importance, the GP is vulnerable to injuries, affecting 15-30 % of bone fractures. These injuries may lead to growth discrepancies, influence bone length and shape, and negatively affecting the patient\'s quality of life. This study aimed to investigate the molecular and cellular physiological and pathophysiological regeneration following sustained growth plate injury (GPI) in an ex vivo rat femur organotypic culture (OTC) model. Specifically, focusing on postnatal endochondral ossification process. 300 μm thick ex vivo bone cultures with a 2 mm long horizontal GPI was utilized. After 15 days of cultivation, gene expression analysis, histological and immunohistochemistry staining\'s were conducted to analyze key markers of endochondral ossification. In our OTCs we observed a significant increase in Sox9 expression due to GPI at day 15. The Ihh-PTHrP feedback loop was affected, favoring chondrocyte proliferation and maturation. Ihh levels increased significantly on day 7 and day 15, while PTHrP was downregulated on day 7. GPI had no impact on osteoclast number and activity, but gene expression analysis indicated OTCs\' efforts to inhibit osteoclast differentiation and activation, thereby reducing bone resorption. In conclusion, our study provides novel insights into the molecular and cellular mechanisms underlying postnatal bone growth and regeneration following growth plate injury (GPI). We demonstrate that chondrocyte proliferation and differentiation play pivotal roles in the regeneration process, with the Ihh-PTHrP feedback loop modulating these processes. Importantly, our ex vivo rat femur organotypic culture model allows for the detailed investigation of these processes, providing a valuable tool for future research in the field of skeletal biology and regenerative medicine.
摘要：
出生后骨生长主要依赖于软骨细胞增殖和通过软骨内骨化在生长板（GP）内的成骨分化。尽管它很重要,全科医生容易受伤，影响15-30%的骨折。这些伤害可能导致生长差异，影响骨骼长度和形状，并对患者的生活质量产生负面影响。本研究旨在研究离体大鼠股骨器官型培养（OTC）模型中持续生长板损伤（GPI）后的分子和细胞生理和病理生理再生。具体来说,关注产后软骨内骨化过程。使用具有2mm长的水平GPI的300μm厚的离体骨培养物。培养15天后，基因表达分析,进行组织学和免疫组织化学染色以分析软骨内骨化的关键标志物。在我们的OTC中,我们观察到在第15天由于GPI引起的Sox9表达的显著增加。Ihh-PTHrP反馈回路受到影响,有利于软骨细胞增殖和成熟。Ihh水平在第7天和第15天显著增加,而PTHrP在第7天下调。GPI对破骨细胞数量和活性没有影响，但基因表达分析表明OTC抑制破骨细胞分化和活化的努力，从而减少骨吸收。总之,我们的研究为生长板损伤(GPI)后出生后骨生长和再生的分子和细胞机制提供了新的见解.我们证明软骨细胞的增殖和分化在再生过程中起着关键作用。与Ihh-PTHrP反馈回路调制这些过程。重要的是,我们的离体大鼠股骨器官型培养模型允许对这些过程进行详细研究，为骨骼生物学和再生医学领域的未来研究提供了有价值的工具。
