Impact of Wnt1 mutation on skeletal remodeling, bone matrix quality, fracture healing and response to mechanical stimulation

了解骨形成成骨细胞的分子调控具有巨大的临床意义，因为它可能为开发新的骨合成代谢治疗方案铺平道路。Wnt信号通路对控制成骨细胞活性的关键影响已经通过几种方法得到证实，包括不仅在小鼠中获得的遗传数据，而且在患有遗传性骨病的人类中获得的遗传数据。我们和其他人最近在早发性骨质疏松症患者中发现了杂合WNT 1突变，而纯合WNT 1突变被发现会导致更严重的儿童骨骼疾病，被归类为成骨不全XV型（OI-XV）。我们还发现，成骨细胞系细胞中Wnt 1的失活导致骨量降低并伴有骨折，而在转基因小鼠模型中，成骨细胞中可诱导的Wnt 1表达导致快速的骨合成代谢反应。在本项目中，我们将重点放在另一种小鼠模型上，在该模型中，我们将先前在OI-XV患者中鉴定的G177 C突变引入小鼠Wnt 1基因。与Wnt 1-/-小鼠不同，所得到的Wnt 1G 177 C/G177 C小鼠没有显示出可检测到的脑异常，但它们的骨量在4周龄时已经显著减少。在6个月的年龄，我们观察到自发性骨折的发病率高Wnt 1G 177 C/G177 C小鼠，骨折骨痂的组织学分析表明脂肪细胞的不寻常的积累。同样值得注意的是，尽管只有中度骨质减少，但Wnt 1G 177 C/G177 C小鼠的骨折发生率很高，从而表明Wnt 1突变深刻地影响骨基质组成和质量。我们两个小组之间的合作旨在i）了解Wnt 1在成骨细胞中的分子功能，ii）定义介导Wnt 1的骨合成代谢影响的负责受体（复合物），iii）评估Wnt 1突变对已建立的截骨模型中骨折愈合的影响，以及iv）分析Wnt 1作为骨合成代谢对机械负荷反应的介导剂的假定作用。我们的共同努力将产生关于Wnt 1在骨骼中的关键作用的额外分子知识。这可能为在生理骨重建或骨再生的背景下开发专门增加成骨细胞活性和骨质量的新药铺平道路。

Understanding the molecular regulation of bone-forming osteoblasts is of tremendous clinical importance, as it might pave the way to develop novel osteoanabolic treatment options. The key impact of the Wnt signaling pathway for controlling osteoblast activity has been demonstrated by several means, including genetic data, obtained not only in mice, but also in humans with inherited bone disorders. We, and others have recently identified heterozygous WNT1 mutations in individuals with early-onset osteoporosis, whereas homozygous WNT1 mutations were found to cause a more severe childhood bone disorder, classified as osteogenesis imperfecta type XV (OI-XV). We could also show that inactivation of Wnt1 in osteoblast lineage cells causes low bone mass with accompanying fractures, whereas inducible Wnt1 expression in osteoblasts causes a rapid osteoanabolic response in a transgenic mouse model.For the present project we will focus on another mouse model, where we have introduced the G177C mutation, previously identified in a patient with OI-XV, into the murine Wnt1 gene. The resulting Wnt1G177C/G177C mice, unlike Wnt1-/- mice, did not display a detectable brain abnormality, but their bone mass was significantly reduced already at 4 weeks of age. At the age of 6 months we observed a high incidence of spontaneous fractures in Wnt1G177C/G177C mice, and histological analysis of the fracture callus indicated an unusual accumulation of adipocytes. It is also noteworthy that the high fracture incidence of the Wnt1G177C/G177C mice occurred despite only moderate osteopenia, thereby suggesting that Wnt1 mutation profoundly affects bone matrix composition and quality. The collaboration between our two groups aims at i) understanding the molecular function of Wnt1 in osteoblasts, ii) defining the responsible receptor (complex) mediating the osteoanabolic influence of Wnt1, iii) assessing the impact of Wnt1 mutation on fracture healing in an established osteotomy model, and iv) analyzing the putative role of Wnt1 as a mediator of the osteoanabolic response towards mechanical loading. Our combined efforts will generate additional molecular knowledge on the critical role of Wnt1 in the skeleton. This might pave the way for the development of novel drugs specifically increasing osteoblast activity and bone quality in the context of physiological bone remodeling or bone regeneration.