Mineralization and the Role of Matrixphosphoglycoprotein

描述(由申请人提供)：X连锁低磷血症(HYP)与肾脏磷酸盐处理、维生素D代谢和矿化的严重缺陷有关。了解骨矿物质/肾脏丢失的病理生理学机制是有效治疗高血压、牙周病、肿瘤引起的骨软化、肾结石、骨质疏松症、异位钙化和肾功能障碍的先决条件。我们有大量的初步数据支持这一假说，即牙齿和骨骼中的矿化是由MEPE(一种在HYP中显着升高的细胞外基质磷酸糖蛋白)和PHEX(一种在HYP中缺失的锌金属内肽酶)之间的蛋白质-蛋白质相互作用调节的。MEPE-PHEX蛋白质-蛋白质的相互作用保护MEPE不被HYP中显着升高的蛋白酶(尤其是组织蛋白酶B)所切割。成骨细胞和成牙本质细胞分泌的MEPE在没有PHEX的情况下被蛋白分解，释放出一段磷酸化的、富含天冬氨酸-丝氨酸、COOH末端的MEPE片段(ASARM-肽)。ASARM多肽(2 KDa)对大量的蛋白酶具有显著的抵抗力，导致Hyp水平升高。ASARM-肽抑制矿化，是正常矿化的负调控因子，ASARM-肽升高是HYP矿化缺陷的全部或部分原因。这项提案将特别关注MEPE和ASARM-肽在疾病和健康中矿化的作用。我们的具体目标是：1.在正常、超小鼠成骨细胞和HYP患者血清中，MEPE-ASARM-肽(S)的体内外结构表征和定量。2.MEPE ASARM多肽对体外和体内(大鼠)矿化作用的测定ASARM基序存在于许多牙齿-骨基质和唾液蛋白(MEPE、牙本质-基质-蛋白-1、骨桥蛋白、Statherin、牙本质涎磷蛋白等)中。这些基因都位于染色体4q21上。因此，阐明其在矿化中的作用对于了解牙齿和骨骼的发育是至关重要的。重要的是，该基序在MEPE的多种功能中所起的作用将与牙周病、致癌的低磷血症性骨软化(OHO)、HYP、骨质疏松以及牙齿、骨、肾结石和动脉的矿化障碍的治疗和理解有关。

DESCRIPTION (provided by applicant): X-linked hypophosphatemic rickets (HYP) is associated with severe defects in renal phosphate handling, vitamin D metabolism and mineralization. Understanding the pathophysiology of bone-mineral/renal loss disorders is prerequisite to effective treatment of HYP, periodontal disease, tumor induced osteomalacia, renal-stones, osteoporosis, ectopic-calcifications and renal dysfunction. We have substantive preliminary data that supports the hypothesis that mineralization in teeth and bone is regulated by a protein-protein interaction between MEPE (a matrix extracellular phosphoglycoprotein markedly elevated in HYP) and PHEX (a Zn-metalloendopeptidase defective in HYP). The MEPE-PHEX protein-protein interaction protects MEPE from proteolytic cleavage by proteases markedly elevated in HYP (notably cathepsin B). Osteoblast and odontoblast secreted-MEPE in the absence of PHEX is proteolytically cleaved, releasing a phosphorylated, acidic-aspartate-serine-rich, COOH-terminal MEPE-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 is a negative modulator of normal mineralization and elevated ASARM-peptide is wholly or in part responsible for the mineralization defects in HYP. This proposal will specifically focus on the role of MEPE and ASARM-peptides in mineralization in disease and health. Our specific aims will be: 1. Structural characterization and quantification of MEPE ASARM-peptide(s) in-vitro and in-vivo in normal and Hyp-mouse osteoblasts and HYP patient-serum. 2. Determination of MEPE ASARM-peptide effects on mineralization in-vitro and in-vivo (rats). The ASARM-motif is present in a number of tooth-bone matrix and salivary proteins (MEPE, dentin-matrix-protein-1, osteopontin, statherin, dentin-sialo-phosphoprotein, etc.) that all map to chromosome 4q21. Thus, the elucidation of its role in mineralization is of prime importance for understanding tooth and bone development. Importantly, the part the motif plays in the multiple functions of MEPE will have relevance to the treatment and understanding of periodontal disease, oncogenic hypophosphatemic osteomalacia (OHO), HYP, osteoporosis and disorders of mineralization in teeth, bone, renal-stones and arteries.