Department of Orthopedic Surgery, the Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China.
Department of Rehabilitation Medicine, Center of Bone Metabolism and Repair, State Key Laboratory of Trauma, Burns and Combined Injury, Trauma Center, Research Institute of Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, China.
Int J Biol Sci. 2017 Sep 21;13(10):1254-1265. doi: 10.7150/ijbs.21258. eCollection 2017.
Bone fracture healing is processed through multiple stages including the cartilaginous callus formation and its transition to bony callus. FGFR3 negatively regulates chondrogenesis and enhances osteogenesis during skeleton development. We previously found in mice carrying gain-of-function mutation of FGFR3 that FGFR3 delays the healing of un-stabilized fracture that heals mainly through endochondral ossification. Since fracture is regularly treated in clinics with rigid fixation, and stabilized fracture is healed largely through intramembranous ossification, we asked whether FGFR3, a key regulator of osteogenesis, also affect the regeneration of stabilized fracture. We found that gain-of-function mutation of FGFR3 inhibits the initiation of chondrogenesis and the subsequent bone formation. We further studied whether PTH1-34 can improve the osteopenia and delayed healing of the stabilized tibia fracture in mice with achondroplasia. Fracture healing was evaluated by radiography, micro-CT, biomechanical tests, histology, and real-time polymerase chain reaction (RT-PCR) analysis. We found that PTH 1-34 can alleviate the decreased bone mass and compromised architecture in ACH mice. Histological analysis revealed that administration of PTH1-34 increased the size of both the total callus and cartilaginous callus at 14 days after the surgery in ACH mice. RT-PCR data suggested that systemic PTH1-34 accelerated the initiation of chondrogenesis and chondrocyte maturation (earlier and higher levels of expression of chondrogenesis related markers) and enhanced the osteogenic differentiation in the fracture callus in ACH mice. These results indicate that the PTH1-34 administration resulted in an enhanced callus formation during bone fracture healing in ACH mice, which is at least in part mediated by an increase of cartilaginous callus at early stage and the promotion of bone formation in bony callus. In summary, in this study we revealed that FGFR3 delays the regeneration of stabilized fracture by inhibiting both the chondrogenesis and osteogenesis, and PTH1-34 treatment can improve the dysregulated bone metabolism and delayed bone injury healing resulting from gain-of-function mutation of FGFR3.
骨愈合是通过多个阶段进行的，包括软骨痂形成及其向骨性痂的转化。FGFR3 负调控软骨生成，并在骨骼发育过程中增强成骨作用。我们之前在携带 FGFR3 功能获得性突变的小鼠中发现，FGFR3 延迟了未稳定骨折的愈合，这种骨折主要通过软骨内骨化愈合。由于骨折在临床上通常用刚性固定治疗，而稳定的骨折主要通过膜内骨化愈合，我们想知道作为成骨关键调节因子的 FGFR3 是否也会影响稳定骨折的再生。我们发现，FGFR3 的功能获得性突变抑制了软骨生成的起始和随后的骨形成。我们进一步研究了甲状旁腺素 1-34（PTH1-34）能否改善成骨不全症小鼠稳定胫骨骨折的骨质疏松症和延迟愈合。通过放射学、微 CT、生物力学测试、组织学和实时聚合酶链反应（RT-PCR）分析评估骨折愈合。我们发现，PTH1-34 可以减轻 ACH 小鼠的骨量减少和骨结构受损。组织学分析显示，在 ACH 小鼠手术后 14 天，PTH1-34 给药增加了总骨痂和软骨痂的大小。RT-PCR 数据表明，全身 PTH1-34 加速了软骨生成和软骨细胞成熟（更早和更高水平的软骨生成相关标志物的表达），并增强了 ACH 小鼠骨折痂中的成骨分化。这些结果表明，PTH1-34 给药导致 ACH 小鼠骨折愈合过程中骨痂形成增强，这至少部分是通过早期软骨痂增加和促进骨性痂中的骨形成介导的。总之，在这项研究中，我们揭示了 FGFR3 通过抑制软骨生成和成骨作用来延迟稳定骨折的再生，而 PTH1-34 治疗可以改善由 FGFR3 功能获得性突变引起的失调的骨代谢和延迟的骨损伤愈合。
