Mineralization of the matrix in disease and health

描述（由申请人提供）： 遗传性和肿瘤获得性骨矿物质疾病提供了强大的模型，有助于理解负责维持健康，动态，矿化骨骼的一些分子机制。X连锁低磷血症性佝偻病（HYP）就是这样一种疾病，与矿化、肾磷酸盐处理和维生素D代谢的严重缺陷有关。MEPE（一种骨基质蛋白）和成骨细胞蛋白酶在HYP中显著升高。此外，PHEX，成骨细胞表达，质膜锚定锌金属肽酶是主要的缺陷负责的疾病。我们有实质性的初步数据支持的假设，MEPE和PHEX之间的蛋白质-蛋白质相互作用调节矿化。PHEX在体外保护MEPE免受蛋白酶（尤其是组织蛋白酶B）的蛋白水解切割，并且成骨细胞蛋白酶在Hyp中升高。在不存在PHEX的情况下，MEPE被切割，释放出磷酸化的、酸性的、富含丝氨酸-天冬氨酸的C-末端片段（ASARM-肽）。ASARM-肽（2kDa）对大量蛋白酶具有显著抗性，导致Hyp水平增加。ASARM-肽抑制矿化，并且提出升高的ASARM-肽是矿化缺陷的全部或部分原因。本申请将重点关注MEPE和ASARM-肽在矿化中的作用。我们的具体目标是：1. MEPE ASAM-肽在正常和Hyp成骨细胞和血清中的体外和体内结构表征和定量。2. MEPE ASARM-肽对体外和体内矿化作用的测定。3. MEPE-PHEX蛋白质-蛋白质相互作用的阐明。4. Hyp-osteoblast中蛋白酶升高与异常矿化和MEPE-PHEX相互作用的关系。ASARM基序存在于许多牙-骨基质和唾液蛋白中。这些包括MEPE、DMP 1、骨桥蛋白、statherin、DSPP，它们都定位于染色体4 q21。因此，阐明其在矿化中的作用对于理解骨矿化机制至关重要。重要的是，该基序所起的作用将与骨折风险、骨质疏松症、肿瘤诱导的骨软化（OHO）、HYP、牙周病、牙齿矿化障碍、骨、肾结石和动脉异位钙化以及肾骨营养不良的治疗和理解相关。

DESCRIPTION (provided by applicant): Inherited and tumor acquired bone-mineral disorders have provided powerful models that have helped understand some of the molecular-mechanisms responsible for maintaining a healthy, dynamic, mineralized-skeleton. X-linked hypophosphatemic rickets (HYP) is one such disease and is associated with severe defects in mineralization, renal phosphate handling, and vitamin D metabolism. MEPE, (a bone-matrix protein) and osteoblastic-proteases are elevated markedly in HYP. Also, PHEX, an osteoblast-expressed, plasma-membrane anchored Zn-metallopeptidase is the primary defect responsible for the disease. We have substantive preliminary data that supports the hypothesis that a protein-protein interaction between MEPE and PHEX regulates mineralization. PHEX protects MEPE from proteolytic cleavage by proteases (notably cathepsin B) in-vitro and osteoblastic-proteases are elevated in Hyp. In the absence of PHEX, MEPE is cleaved, releasing a phosphorylated, acidic, serine-aspartate rich, C-terminal fragment (ASARM-peptide). The ASARM-peptide (2 kDa), is remarkably resistant to a vast array of proteases resulting in increased levels in Hyp. The ASARM-peptide inhibits mineralization and elevated ASARM-peptide is proposed to be wholly or in part responsible for the mineralization defects. This application will focus on the role of MEPE and ASARM-peptides in mineralization. Our specific aims are: 1. Structural characterization and quantification of MEPE ASARM-peptide(s) in-vitro and in-vivo in normal and Hyp osteoblasts and serum. 2. Determination of MEPE ASARM-peptide effects on mineralization in-vitro and in-vivo. 3. Elucidation of MEPE-PHEX protein-protein interactions. 4. The role of elevated protease(s) in Hyp-osteoblasts in relation to abnormal mineralization and MEPE-PHEX interactions. The ASARM-motif is present in a number of tooth-bone matrix and salivary proteins. These include MEPE, DMP1, osteopontin, statherin, DSPP that all map to chromosome 4q21. Thus, the elucidation of its role in mineralization is of prime importance for understanding bone mineralization mechanisms. Importantly, the part the motif plays will have relevance to the treatment and understanding of bone-fracture risk, osteoporosis, tumor-induced osteomalacia (OHO), HYP, periodontal disease, disorders of mineralization in teeth, bone, renal-stones and ectopic calcifications in arteries and renal-osteodystrophy.