Molecular mechanism of Sclerostin-mediated Wnt-inhibition

我们骨骼的骨骼并不构成死亡组织，而是经历了一个终生的重组过程。有三种细胞类型组织了这种重塑：形成骨的成骨细胞、分解骨组织的破骨细胞和作为主要调节者的骨细胞，它们维持着骨代谢和骨合成代谢之间的平衡。两个蛋白质家族，骨形态发生蛋白(BMPs)和Wnt家族，是这一调控网络的关键组成部分。放松对骨骼积累和移除的管制会导致严重的疾病，如骨化病(骨过度生长)或骨质疏松症(骨丢失)。后者影响了一大批患者，因为超过30%的绝经后女性患有骨质疏松症。硬化素在2003年被确定为一种因子，如果中和，它会导致骨量增加，使其成为骨生长相关疾病的主要靶点。与Dickkopf(DKK)蛋白类似，硬化素与LRP家族的Wnt辅受体结合，从而阻断Wnt的活性。硬化素阻断Wnt活性的分子机制在很大程度上仍不清楚。最近自己的研究首次深入了解了硬化素的结构/功能关系，表明它通过一种不同于DKK蛋白的机制来削弱Wnt的活性。在这项建议中，我们希望通过生化和生物物理手段来揭示硬化素介导的Wnt抑制的机制。由于硬化素是一种非常有希望的新的骨质疏松治疗靶点，我们想要确定硬化素中和抗体的结构，以及与硬化素结合的复合体的结构。为了了解抑制机制，我们还将确定硬化素-LRP6复合体的结构。结合对LRP6上硬化素结合表位的功能分析，这些数据将有助于开发治疗骨生长相关疾病的新药，如骨质疏松症和硬化性骨质疏松症/范布赫姆病。

The bones of our skeleton do not constitute dead tissue, but cycle through a life-long reorganization process. Three cell types organize this remodeling: bone-forming osteoblasts, osteoclasts dismantling bone tissue and osteocytes as the master regulators keeping the balance between osteocatabolic and osteoanabolic action. Two protein families, the bone morphogenetic proteins (BMPs) and the Wnt family, harbor key components of this regulatory network. Deregulation of bone buildup and removal lead to severe diseases such as osteopetrosis (bone overgrowth) or osteoporosis (bone loss). The latter is affecting a large group of patients as more than 30% of women after menopause suffer from osteoporosis. Sclerostin was identified in 2003 as a factor which, if neutralized, leads to an increase in bone mass making it to a prime target for bone growth related diseases. Similar to Dickkopf (Dkk) proteins Sclerostin binds to Wnt coreceptors of the LRP family thereby blocking Wnt activity. The molecular mechanism by which Sclerostin blocks Wnt activity is still largely unknown. Recent own studies have yielded first insights into the structure/function relationship of Sclerostin suggesting that it impairs Wnt activity by a mechanism different from that of the Dkk proteins. In this proposal we want to unravel the mechanism of Sclerostin-mediated Wnt inhibition by biochemical and biophysical means. As Sclerostin is a highly promising target for a new osteoporosis therapy we want to determine the structures of Sclerostin-neutralizing antibodies alone and in complex bound to Sclerostin. To understand the inhibition mechanism we will also determine the structure of the Sclerostin-LRP6 complex. Together with a functional analysis of the binding epitope of Sclerostin on LRP6 these data will facilitate the development of new drugs for the treatment of bone growth related diseases such as osteoporosis and Sclerosteosis/Van Buchem disease.