Wnt1新剪接突变c.104+1G>A致成骨不全的致病作用及分子机制研究

Wnt1突变可致成骨不全（OI），然而其致病机制仍不清楚。我们在1例OI患儿中发现新的Wnt1突变c.104+1G>A。据此突变构建的大鼠模型表现出自发性骨折等表型，与患儿临床症状类似。我们前期研究发现，突变成骨细胞分化异常，且经典WNT信号通路活性降低。同时一种重要的BMP结合抑制因子——BMPER表达显著升高。WNT和BMP通路是促进成骨细胞分化的关键信号，且已有报道二者可协同作用。因此，我们推测：WNT1通路失活可通过BMPER协同抑制BMP通路，二者共同作用引发OI。为验证此推测，我们将：1. 在突变成骨细胞中，检测BMP信号通路的活性；2. 分析敲低BMPER是否可逆转突变成骨细胞分化异常；3. 在突变大鼠骨组织中检测BMPER表达量及BMP通路活性并分析敲低BMPER是否可挽救突变大鼠OI表型。本项目可进一步揭示Wnt1突变致OI的分子机制，还可为临床治疗该类疾病提供实验依据。

Mutations of Wnt1 has been associated with osteogenesis imperfecta (OI), however, the underlying pathogenic mechanism remain elusive. In one case of OI, we found a novel splicing mutation c.104+1G>A in Wnt1. The rat model with same mutation (Wnt1sp) showed skeletal abnormalities such as spontaneous fracture, similar to the clinical symptoms of the OI patient. Our preliminary data showed that Wnt1sp osteoblasts differentiated abnormally and the activity of canonical WNT signaling pathway decreased. More interesting, the expression of BMPER (BMP binding endothelial regulator), an important inhibitor of BMP, was found to be significantly increased. Both WNT and BMP pathway are key regulators of osteoblast differentiation, and they have been reported to have synergistic effects. According our findings and other’s reports, we speculate that in Wnt1sp osteoblasts, the reduction of WNT1/WNT signaling activity results in high level of BMPER, by which the activity of BMP signaling pathway is inhibited. Finally, the low activity of WNT and BMP signaling together cause the abnormal differentiation of osteoblasts. We intend to verify this hypothesis by: (1) detecting the activity of BMP signaling pathway in Wnt1sp osteoblasts; (2) knocking down BMPER or activating BMP pathway to rescue the abnormal differentiation of Wnt1sp osteoblasts; (3) detecting BMPER expression and BMP signaling activity in bone tissue of Wnt1sp rats; (4) knocking down BMPER or activating BMP pathway to rescue the OI phenotype of Wnt1sp rat. Our project will not only shed light on the pathogenic mechanisms of OI caused by Wnt1 mutation, but also provide novel therapeutic treatment target for such kind of disease.