Mechanisms of altered extracellular matrix signaling in Osteogenesis Imperfecta

描述（由申请人提供）：成骨不全（OI）是一种使人衰弱的遗传性骨发育不良，可导致低骨量、骨畸形和骨折。尽管进行了广泛的研究，但OI背后的分子发病机制仍然知之甚少。大多数OI病例是由结构蛋白I型胶原（显性OI）或蛋白质I型胶原（显性OI）突变引起的。 复合物，后突变修改I型胶原蛋白（隐性OI）;这两种类型的突变往往导致生化过度修饰。I型胶原蛋白虽然对骨的结构完整性很重要，但对细胞外基质（ECM）细胞信号传导也是必不可少的。它与调节信号分子生物利用度的ECM组分广泛相互作用，从而影响组织特异性细胞行为。我们已经证明，转化生长因子β（TGFβ）信号通路的过度激活在显性（Col 1 α2tm1.1Mcbr）和隐性（Crtap-/-）OI小鼠模型中是致病的。然而，胶原结构改变或翻译后修饰导致OI信号改变的机制尚不清楚。富含亮氨酸的小蛋白聚糖（SLRP）是基质信号传导的重要调节剂，也结合I型胶原蛋白，并可以在结构蛋白和信号传导之间建立联系。目前，SLRP核心蛋白聚糖（Dcn）、双糖链蛋白聚糖（Bgn）和asporin（Aspn）是已知结合I型胶原和TGFβ的唯一基质组分。它们在骨中的重要性通过它们缺失时的表型来证明。Bgn敲除小鼠具有骨质疏松症表型，骨中TGFβ的螯合和信号传导改变。只有一篇论文研究了Dcn-/-小鼠的骨骼，但Dcn敲低的成骨细胞移植到小鼠体内会产生不成熟的、高度矿化的骨骼，让人想起OI患者的骨骼。来自人OI骨样品的核心蛋白聚糖和双糖蛋白聚糖以胎儿样形式产生和分泌，表明OI与SLRP变化之间存在联系。我们假设OI中I型胶原的变化干扰了与SLRP核心蛋白聚糖、双糖链蛋白聚糖和asporin的结合，从而改变了基质中TGFβ的可用性。我们的目的是通过比较SLRP与野生型、显性OI或隐性OI小鼠的I型胶原的生化相互作用，并确定SLRP对OI中TGFβ生物利用度和信号传导的影响，来验证这一假设。我们的初步数据表明，核心蛋白聚糖结合少的I型胶原蛋白从Crtap-/-突变小鼠比野生型小鼠。基于该数据和Dcn敲除成骨细胞的表型，本项目的第三个目的是表征Dcn-/-小鼠的骨表型，以评估与OI骨的表型重叠。这项研究对于建立疾病的共同机制具有重要意义，可能为显性或隐性OI患者提供潜在的治疗靶点。

DESCRIPTION (provided by applicant): Osteogenesis imperfecta (OI) is a debilitating genetic osteodysplasia that results in low bone mass, bone deformity, and bone fractures. Despite extensive research, the molecular pathogenesis behind OI is still poorly understood. Most cases of OI are caused by mutations in the structural protein type I collagen (dominant OI) or in protein complexes that post-translationally modify type I collagen (recessive OI); both types of mutations often lead to biochemical overmodification. Type I collagen, while important for structural integrity of bone is also essential for extracellular matrix (ECM) cell signaling. It extensively interacts with ECM components that regulate bioavailability of signaling molecules, thereby affecting tissue-specific cell behavior. We have demonstrated that excessive activation of the transforming growth factor-beta (TGFβ) signaling pathway is pathogenic in mouse models of dominant (Col1α2tm1.1Mcbr) and recessive (Crtap-/-) OI. However, the mechanism by which altered collagen structure or post-translational modification leads to altered signaling in OI is unclear. Small leucine-rich proteoglycans (SLRPs) are important regulators of matrix signaling that also bind type I collagen and could establish a link between structural proteins and signaling. Currently, the SLRPs decorin (Dcn), biglycan (Bgn), and asporin (Aspn) are the only matrix components known to bind both type I collagen and TGFβ. Their importance in bone is demonstrated by the phenotype in their absence. The Bgn- knockout mouse has an osteoporosis phenotype with altered sequestration and signaling of TGFβ in bone. Only one paper has studied the bone from Dcn-/- mice, but Dcn-knockdown osteoblast cells transplanted into mice generate immature, highly mineralized bone reminiscent of bone from OI patients. Decorin and biglycan from human OI bone samples are produced and secreted in a fetal-like form suggesting a connection between OI and changes in SLRPs. We hypothesize that changes in type I collagen in OI disturb binding to the SLRPs decorin, biglycan, and asporin, which in turn alters TGFβ availability in the matrix. We aim to test this hypothesis by comparing the biochemical interaction of SLRPs with type I collagen from wildtype, dominant OI, or recessive OI mice and determining the effects of SLRPs on TGFβ bioavailability and signaling in OI. Our preliminary data implies that decorin binds less to type I collagen from Crtap-/- mutant mice than wildtype mice. Based on this data and the phenotype of Dcn-knockout osteoblasts, the third aim of this project is to characterize the bone phenotype of the Dcn-/- mouse to assess the phenotypic overlap with OI bone. This research is important for establishing common mechanisms of disease, which may provide potential therapeutic targets for patients with dominant or recessive OI.