Project 4 - Mechanisms of pyrophosphate dysregulation

项目4概要 焦磷酸失调的机制。羟基磷灰石在骨骼和牙齿中的沉积是一个非常重要的问题。 协调的生化过程，旨在平衡无机焦磷酸盐（PPi）的浓度， 有效的钙化抑制剂，以及局部浓度的磷酸盐（Pi），一种钙化促进剂， 建立适当的PPi/Pi比率，以使调节的组织矿化发生。当我们有一个好的 了解什么分子控制生理骨骼和牙齿矿化，有限的数据存在， 这些机制的改变是否会导致眼睛、大脑和大脑中的异位钙化， 血管在衰老疾病如年龄相关性黄斑变性（AMD）、阿尔茨海默病（AD）中的作用 和动脉粥样硬化。AMD的临床特征在于存在称为玻璃疣的细胞外沉积物， 位于视网膜色素上皮（RPE）和脉络膜微血管系统之间的区域称为 黄斑区的布鲁赫膜玻璃疣还在与视网膜病变相关的正常老化眼睛中观察到。 局部炎症和黄斑区大量大玻璃疣的存在是一个显著的风险 发展AMD的因素。虽然没有完全反映人类肿瘤病理生理学的鼠模型， AMD、Abcc 6-/-和Enpp 1-/-小鼠弹性假黄瘤（PXE）模型和全身性 婴儿动脉钙化（GACI），不仅表现为血管和脑钙化， 因此这些小鼠模型可以用作替代物来理解玻璃疣 阵在此PO 1部分中，我们将检验PPi/Pi比值失调的总体假设， 是衰老疾病中异位钙化的病理生理学基础，我们的研究主要集中在 眼部钙化鉴于组织非特异性碱性磷酸酶（TNAP）是主要的焦磷酸酶， 通过控制PPi/Pi比值，TNAP可能是预防/改善玻璃疣的有用药物靶点 阵因此，本项目4的目标旨在与其他PO 1相互支持， 成分，是通过遗传学方法探索PPi失调在眼钙化中的致病作用。 操纵PPi在体内的产生和降解。我们将研究PPi/Pi比率是否被 控制（无论是在脉络膜内皮细胞，RPE细胞或两个隔室）通过生产和功能 一种特殊类型的细胞外囊泡称为基质囊泡（MV），羟基磷灰石开始形成 在生理性骨骼/牙齿矿化过程中，或者如果该比例通过病理生理学 单独上调TNAP活性。我们还将进行药理学概念验证研究， 通过调节全身和局部PPi的产生和降解影响眼部钙化 浓度的在这一多学科团队努力的背景下完成这些研究，将导致 对AMD、AD和血管钙化的相关病理生理学的新见解，并将验证 用于治疗/预防异位钙化的未满足临床需求的药物途径， 这些高度流行的衰老疾病。

PROJECT 4 SUMMARY Mechanisms of pyrophosphate dysregulation. Hydroxyapatite deposition in bones and teeth is a carefully orchestrated biochemical process aimed at balancing the concentrations of inorganic pyrophosphate (PPi), a potent calcification inhibitor, and the local concentrations of phosphate (Pi), a calcification promoter, to establish a proper PPi/Pi ratio to enable regulated tissue mineralization to take place. While we have a good understanding of what molecules control physiological skeletal and dental mineralization, limited data exists as to whether alterations in those same mechanisms lead to ectopic calcification in the eyes, brain, and vasculature in diseases of aging such as age-related macular degeneration (AMD), Alzheimer's disease (AD) and atherosclerosis. AMD is clinically characterized by the presence of extracellular deposits known as drusen, located between the retinal pigment epithelium (RPE) and the choroidal microvasculature in the area known as the Bruch’s membrane in the macular region. Drusen is also observed in the normal aging eye associated with local inflammation, and the presence of a high number of large drusen in the macular region is a significant risk factor for developing AMD. While there are no murine models that fully reflect the pathophysiology of human AMD, the Abcc6-/- and the Enpp1-/- mouse models of pseudoxanthoma elasticum (PXE) and generalized arterial calcification of infancy (GACI) respectively, manifest not only vascular and brain calcification but also calcifications in the eyes and therefore these mouse models can be used as surrogates to understand drusen formation. In this PO1 component we will test the overarching hypothesis that dysregulation of the PPi/Pi ratio underlies the pathophysiology of ectopic calcification in diseases of aging, focusing our studies primarily on eye calcification. Given that tissue-nonspecific alkaline phosphatase (TNAP) is the major pyrophosphatase controlling the PPi/Pi ratio, TNAP may be a useful druggable target for the prevention/amelioration of drusen formation. Thus, the goals of this Project 4, designed to be mutually supportive with the other PO1 components, are to probe the causative role of PPi dysregulation in eye calcification by genetically manipulating the production and degradation of PPi in vivo. We will investigate if the PPi/Pi ratio is being controlled (either in the choroid endothelium, RPE cells or both compartments) via the production and function of a special type of extracellular vesicles known as matrix vesicles (MVs), where hydroxyapatite starts to form during physiological skeletal/dental mineralization, or if this ratio is controlled via the pathophysiological upregulation of TNAP activity alone. We will also conduct pharmacological proof-of-concept studies aimed at affecting calcification in the eye via modulating the production and degradation of systemic and local PPi concentrations. Completion of these studies, within the context of this multi-disciplinary team effort, will lead to novel insights into the interrelated pathophysiology of AMD, AD and vascular calcification and will validate a druggable pathway to address the unmet clinical need of treating/preventing ectopic calcification manifesting in these highly prevalent diseases of aging.