Role of Vwc2-assisted activin signaling in bone formation

描述（由申请人提供）：最近，半胱氨酸结蛋白（CKP）家族由于其有效的生物学效应而受到了极大的关注，并且调节其功能似乎是一种有前景的治疗方法。我们通过生物信息学方法鉴定了CKP家族的一个新成员Vwc 2（vonWillebrand factor C domain containing 2），并对其功能进行了初步研究。我们的初步数据表明，Vwc 2基因表达与早期成骨细胞分化，Vwc 2蛋白存在于骨基质和优先定位在骨表面。当Vwc 2在MC 3 T3-E1（MC）成骨细胞系中稳定过表达时，体外矿化被显著抑制，这可能是通过其特异性结合转化生长因子（TGF）-β超家族成员，激活素A的2A亚基亚型。此外，当Vwc 2与激活素A蛋白一起添加时，与MC细胞中单独添加激活素A或Vwc 2相比，Smad 2磷酸化协同增强，表明Vwc 2促进激活素信号传导。最近，一些证据表明，激活素信号抑制成骨细胞的分化和矿化，而它的抑制这一信号通路导致增强骨形成和骨强度在体外和体内。作为获得这些目标的初步步骤，我们刚刚产生了小鼠，其中Vwc 2基因在感兴趣的组织中选择性过表达。因此，我们假设一个新的CKP成员，Vwc 2，调节骨矿化，通过协助激活素信号在成骨细胞。该探索性建议的目的是建立Vwc 2在体外激活素信号传导中的功能，并确定Vwc 2调节对体内生物矿化的影响。为了检验这一假设，提出了以下具体目标。1.探讨Vwc 2在体外调控成骨细胞功能的信号通路。2.研究Vwc 2在体内骨形成中的作用。从这项研究中获得的数据可能会提供深入了解这种新的CKP成员在骨形成中的生物学功能，并帮助新的分子设计用于骨形成和愈合的治疗。公共卫生相关性：虽然目前骨质疏松症药物市场主要由抗骨吸收药物主导，但它们未能促进骨丢失的替代。我们的研究不仅推进了我们对激活素信号传导中的新CKP成员Vwc 2的认识，而且有助于确定该信号传导途径导致骨形成抑制的分子机制。通过完成我们提出的研究，这项研究的逻辑延伸将进一步允许控制成骨细胞中的Vwc 2功能，从而允许对骨形成的潜在合成代谢作用，并提供对降低骨折风险的努力至关重要的骨形成的新知识。

DESCRIPTION (provided by applicant): Recently, significant attention has been paid to the cysteine knot protein (CKP) family due to their potent biological effects and modulation of their functions appears to be a promising therapeutic approach. By a bioinformatics approach, we have identified a novel member of CKP family, "Vwc2 (von Willebrand factor C domain containing 2)", and explored its potential functions. Our preliminary data indicated that Vwc2 gene expression is associated with early osteoblast differentiation, and that the Vwc2 protein is present in bone matrix and preferentially localized at the bone surface. When Vwc2 was stably overexpressed in MC3T3-E1 (MC) osteoblastic cell line, in vitro mineralization was markedly inhibited possibly via its specific binding to a transforming growth factor (TGF)-ss superfamily member, 2A subunit isoform of activin A. Moreover, when Vwc2 was added together with activin A protein, Smad2 phosphorylation was synergistically enhanced compared to either activin A or Vwc2 addition alone in MC cells indicating that Vwc2 facilitates activin signaling. Recently, several lines of evidence suggests that activin signaling inhibits osteoblastic differentiation and mineralization, whereas its inhibition of this signaling pathway leads to enhance bone formation and bone strength in vitro and in vivo. As a preliminary step of obtaining such objectives, we have just generated mice, in which the Vwc2 gene has been selectively overexpressed in tissues of interest. Thus, we hypothesize that a novel CKP member, Vwc2, modulates mineralization in bone by assisting activin signaling in osteoblasts. The objectives of this exploratory proposal are to establish the function of Vwc2 in activin signaling in vitro and to determine the effects of Vwc2 modulation on biomineralization in vivo. In order to test the hypothesis, the following specific aims are proposed. 1. To investigate the potential signaling pathway by which Vwc2 modulates osteoblast function in vitro. 2. To investigate roles of Vwc2 in bone formation in vivo. The data obtained from this study may provide insights into the biological functions of this novel CKP member in bone formation and help a new molecular design for therapies of bone formation and healing. PUBLIC HEALTH RELEVANCE: Although current osteoporosis drug market is heavily dominated by anti-resorptive agents, they fail to promote the replacement of bone loss. Our studies not only advance our knowledge of a new CKP member, Vwc2 in Activin signaling but also help define the molecular mechanisms of this signaling pathway leading to the inhibition of bone formation. By accomplishing our studies proposed, the logical extension of this research will further allow controlling the Vwc2 function in osteoblasts, thereby allowing the potential anabolic effects on bone formation, as well as provide new knowledge of bone formation critical for efforts directed at decreasing the risk of bone fracture.