Mechanisms of initiation of skeletal mineralization

描述（由申请人提供）：软骨内成骨是一个由矿化启动子和抑制剂介导的精心安排的过程。实验证据表明，在细胞外基质以及软骨细胞和成骨细胞来源的基质囊泡（MVs）的管腔内，沿胶原原纤维存在羟基磷灰石晶体。磷酸酶与此有关，但其身份和功能尚不清楚。我们的工作重点是阐明三种磷酸酶，PHOSPHO1，组织非特异性碱性磷酸酶（TNAP）和核苷磷酸焦磷酸水解酶（NPP1）在建立有利于控制生理骨骼矿化的Pi/PPi比率中的协同作用。我们目前的骨骼矿化启动机制模型涉及矿化启动的囊内PHOSPHO1功能和Pi内流到MVs的功能，以及矿化在囊外进展中的TNAP， NPP1功能。这个假设驱动的竞争性更新应用程序旨在测试骨骼矿化启动的综合模型的关键方面，该模型结合了许多不同的生化观察，例如，由PHOSPHO1在囊内生成Pi， Pi生成与TNAP降解Pi， Pi转运体在pv中的作用，局部生成Pi与系统性Pi的需求，以及pv介导的与胶原介导的ECM矿化。该提案还将推进重要的转化研究，包括Phospho1基因突变在早发性脊柱侧凸和成骨不完全样综合征发展中的可能参与，Phospho1基因突变对低磷代谢严重程度的可能复合作用，以及Phospho1在内侧血管钙化（终末期肾病、肥胖、糖尿病和衰老中发病率高的疾病）中的可能作用。

DESCRIPTION (provided by applicant): Endochondral ossification is a carefully orchestrated process mediated by promoters and inhibitors of mineralization. Experimental evidence has pointed to the presence of hydroxyapatite crystals along collagen fibrils in the extracellular matrix and also within the lumen of chondrocyte- and osteoblast-derived matrix vesicles (MVs). Phosphatases are implicated, but their identities and functions remain unclear. Our work centers on elucidating the concerted action of three phosphatases, PHOSPHO1, tissue-nonspecific alkaline phosphatase (TNAP) and nucleosidetriphosphate pyrophosphohydrolase (NPP1) in establishing a Pi/PPi ratio conducive to controlled physiological skeletal mineralization. Our current model of the mechanisms of initiation of skeletal mineralization implicate intra-vesicular PHOSPHO1 function and Pi influx into MVs in the initiation of mineralization and the functions of TNAP, NPP1 in the extra-vesicular progression of mineralization. This hypothesis-driven competitive renewal application seeks to test crucial aspects of this comprehensive model of initiation of skeletal mineralization that unifies a number of disparate biochemical observations, e.g., intravesicular Pi-generation by PHOSPHO1, Pi-generation versus PPi-degradation by TNAP, the role of Pi- transporters in MVs, the need for locally produced Pi versus systemic Pi, and MV-mediated versus collagen- mediated ECM mineralization. This proposal will also advance significant translational studies into the possible involvement of Phospho1 gene mutations in the development of early-onset scoliosis and osteogenesis imperfecta-like syndrome, the possible compounding effect of Phospho1 gene mutations on the severity of hypophosphatasia, and the putative role of PHOSPHO1 in medial vascular calcification, a condition with high morbidity in end-stage renal disease, obesity, diabetes and aging. PUBLIC HEALTH RELEVANCE: Our work focuses on elucidating the functional interplay of three phosphatases (PHOSPHO1, TNAP and NPP1) during the initiation of skeletal mineralization, a process of fundamental importance to all vertebrate animal species, including mice and humans. Alterations in the function of these phosphatases lead to soft bone conditions, including rickets, osteomalacia, spontaneous fractures, loss of teeth as well as inappropriate calcification of soft tissues in the form of osteoarthritis and arterial calcification. Our work has clear translational applications to rare diseases, such as hypophosphatasia and osteogenesis imperfecta, and also prevalent diseases, including scoliosis, osteoarthritis and medial vascular calcification.