Mineralization of the matrix in disease and health

描述（由申请人提供）：从海洋向陆地过渡的生命的古老遗产是骨骼和肾脏在调节矿化和Ca/PO 4稳态中的作用。骨肾轴中的关键参与者是一组相关的细胞外基质蛋白（SIBLING）。这些蛋白质都映射到染色体4 q上的紧密聚集区域。一种独特的蛋白质PHEX，间接或直接调节至少两种姐妹蛋白（MEPE和DMP 1）。PHEX是一种寻找底物的锌金属内肽酶，也可以作为孤儿配体或受体发挥作用。PHEX功能的丧失导致X连锁低磷酸盐血症性佝偻病，并且新的细胞因子FGF 23（一种磷酸激素）在磷酸盐表型中起主要作用。我们的数据证实了PHEX与MEPE的直接结合，MEPE是一种在骨骼、牙齿和肾脏近曲小管中表达的SIBLING蛋白。这些蛋白质之间的结合发生在PHEX Zn结合基序和称为ASAM基序的MEPE的短COOH末端区域之间。这个短的区域对蛋白水解有很好的抵抗力，并且在物种间是保守的。在生物学上，释放的ASARM-肽是一种有效的矿化抑制剂，抑制肾磷酸盐处理并与羟基磷灰石结合。PHEX与MEPE的结合可用于调节ASARM肽的释放，从而局部控制矿化。PHEX还以高亲和力结合游离ASARM-肽，并且还通过水解使肽失活。在HYP中，以及PHEX功能的丧失，存在MEPE和成骨细胞蛋白酶活性的显著上调。这导致MEPE和DMP 1的降解以及ASARM-肽从这两种蛋白质和可能的其它SIBLING蛋白质（DSPP、骨桥蛋白BSP、釉蛋白）的释放。这些抗蛋白酶的ASARM-肽在肾脏、骨骼、尿液和循环中积累。为了研究SIBLING、PHEX和ASARM肽的作用，我们制备了在骨中过表达MEPE蛋白50倍和在肾中过表达MEPE蛋白7倍的转基因小鼠（MEPE-TRG）。我们的具体目标是：1.表征MEPE-TRG小鼠的骨和肾PO 4表型，2.确定MEPE和ASARM-肽的加工形式在MEPE-TRG、HYP和NPT 2a-/-小鼠中的骨和肾钙化作用，3.设计PHEX合成肽作为探测ASARM肽和PHEX在健康和疾病中的作用的工具。公共卫生相关性：最近发现的一类新的骨牙和肾蛋白（SIBLING）在维持骨骼健康和调节磷酸盐方面发挥着重要作用。来自这些蛋白质的生物活性加工肽影响疾病和健康中的矿化、骨形成、骨生长和软组织钙化。对这些新蛋白质的研究将有助于开发针对矿物质损失疾病（遗传性和肿瘤获得性）、肾性骨营养不良、肾移植、异位动脉钙化、肾钙化和骨质疏松症的疗法。

DESCRIPTION (provided by applicant): An ancient legacy of life transitioning from oceans to land is the role of the skeleton and kidney in regulating mineralization and Ca/PO4 homeostasis. Key players in this bone kidney axis are a group of related extracellular matrix proteins (SIBLINGs). These proteins all map to a tightly clustered region on chromosome 4q. A unique protein PHEX, regulates at least two SIBLING proteins (MEPE and DMP1), indirectly or directly. PHEX is a zn-metalloendopeptidase in search of a substrate and may also play a role as an orphan ligand or receptor. Loss of PHEX function results in X-linked hypophosphatemic rickets and a novel cytokine FGF23 (a phosphatonin), plays a major role in the phosphate phenotype. Our data confirms direct binding of PHEX to MEPE, a SIBLING protein expressed in bone, teeth and in the proximal convoluted tubules of the kidney. The binding between these proteins occurs between the PHEX Zn-binding motif and a short COOH-terminal region of MEPE called the ASARM-motif. This short region is exquisitely resistant to proteolysis and conserved across species. Biologically, the released ASARM-peptide is a potent inhibitor of mineralization, inhibits renal phosphate handling and binds to hydroxyapatite. Binding of PHEX to MEPE may serve to regulate release of the ASARM peptide and thus locally control mineralization. PHEX also binds with high affinity to free ASARM- peptide and also inactivates the peptide by hydrolysis. In HYP, as well as a loss of PHEX function, there is a marked up regulation of MEPE and osteoblastic protease activity. This results in degradation of MEPE and DMP1 and release of ASARM-peptides from both these proteins and perhaps other SIBLING proteins (DSPP, osteopontin BSP, enamelin). These protease resistant ASARM-peptides accumulate in kidney, bone, urine and in the circulation. To study the role of SIBLINGs, PHEX and ASARM- peptides we have made transgenic mice (MEPE-TRG) that overexpress MEPE protein 50X in bone and 7X in kidney. Our specific aims are: 1. Characterize bone and renal PO4 phenotypes of MEPE-TRG mice, 2. Determine the bone and renal- calcification roles of processed forms of MEPE and ASARM-peptides in MEPE-TRG, HYP and NPT2a-/- mice, 3. Design PHEX synthetic peptides as tools to probe the role of ASARM peptides and PHEX in health and disease. PUBLIC HEALTH RELEVANCE: A new class of recently discovered bone-teeth and renal proteins (SIBLINGs) play a major role in upholding the health of the skeleton and regulating phosphate. Bioactive processed peptides from these proteins impact on mineralization, bone formation, bone growth and soft tissue calcification in disease and health. The study of these new proteins will help develop therapies for mineral loss disorders (inherited and tumor-acquired), renal osteodystrophy, renal transplantation, ectopic arterial-calcification, renal calcification and osteoporosis.