Model Systems for PXE

描述（由申请人提供）：这是一项新的资助申请的第二次修订，涉及弹性假性黄瘤（PXE），这是一种常染色体隐性遗传病，其特征是多种器官结缔组织的异位矿化，包括皮肤、眼睛和心血管系统，具有相当高的发病率和死亡率。目前已知PXE是由编码多药耐药相关蛋白6 （MRP6）的ABCC6基因突变引起的，MRP6是一种假定的跨膜转运蛋白，主要在肝脏中表达，在肾脏近端小管中表达较少，在PXE患者的组织中表达水平非常低。增加这种疾病的复杂性的是，观察到有相当大的家族间和家族内异质性，诊断往往因发病晚而延迟，许多环境和生活方式变量似乎调节疾病的进展和最终结果。ABCC6表达改变导致外周组织异常矿化的病理机制细节目前尚不清楚。具体来说，MRP6及其生理配体的功能仍未公开。这一应用将利用在理解ABC转运蛋白方面取得的总体进展和我们最近开发的模型系统来研究这种疾病。该申请代表了三个主要研究小组之间的联盟，将解决以下具体目标：1)Abcc6-/-小鼠作为PXE的表型模型；2)人ABCC6/MRP6转运体的表征及生理底物的寻找。具体目标1提出发展异种共生和血浆/候选蛋白补充，广泛表征Abcc6-/-小鼠作为PXE模型。具体目标2提出了最先进的技术，以全局和候选分子方法识别MRP6的生理底物。这些生理底物将用于MRP6的结构-功能研究。这些特定的目标验证了PXE是基因组/环境界面上的一种遗传性疾病的统一假设，总体目标是确定导致PXE表型表达的分子事件。我们最近通过靶向消融Abcc6基因建立了PXE小鼠模型，并通过建立昆虫细胞转运系统来研究MRP6转运机制的细节以及PXE突变对其的影响，证明了这一应用的可行性。预计本研究结果将为PXE异常矿化和相关遗传性疾病的病理机制途径提供新的见解，并展望普通人群的共同特征，如年龄相关性黄斑变性和动脉硬化。对这些途径的理解有望为开发新的药理学方法提供机会，以改善甚至可能治愈这些目前难以治疗的疾病。

DESCRIPTION (provided by applicant): This second revision of a new grant application revolves around pseudoxanthoma elasticum (PXE), an autosomal recessive disorder characterized by ectopic mineralization of connective tissues in a variety of organs, including the skin, the eyes, and the cardiovascular system, with considerable morbidity and mortality. PXE is now known to result from mutations in the ABCC6 gene which encodes the multi-drug resistance-associated protein 6 (MRP6), a putative transmembrane transporter, expressed primarily in the liver, to a lesser extent in proximal tubules of kidneys, and at very low levels, if at all, in tissues afflicted by PXE. Adding to the complexity of this disorder are the observations that there is considerable both inter- and intra-familial heterogeneity, the diagnosis is often delayed due to late onset of manifestations, and a number of environmental and life-style variables appear to modulate the progression and eventual outcome of the disease. The pathomechanistic details leading from altered ABCC6 expression to aberrant mineralization in peripheral tissues are currently unknown. Specifically, the function of MRP6 and its physiologic ligand(s) remain undisclosed. This application will take advantage of the general progress made in understanding the ABC transporters and of our recent development of model systems to study this disorder. The application represents a consortium between three major research groups that will address the following Specific Aims: 1) The Abcc6-/- Mice as a Phenotypic Model of PXE; 2) Characterization of Human ABCC6/MRP6 Transporter and Search for the Physiological Substrates. The Specific Aim 1 proposes development of parabiosis and plasma/candidate protein supplementation, with extensive characterization of Abcc6-/- mice, as models for PXE. The Specific Aim 2 proposes state-of-the-art technologies to identify physiologic substrate(s) for MRP6 with global and candidate molecule approaches. Such physiologic substrates will then be used for structure-function studies of MRP6. These specific aims test the unifying hypothesis that PXE is a heritable disorder at the genome/environment interface, with an overall goal to define the molecular events that lead to phenotypic expression of PXE. The feasibility of this application is attested by our recent development of a mouse model for PXE through targeted ablation of the Abcc6 gene, and by establishment of the insect cell transport system to study the details of the MRP6 transport mechanisms as well as the effects of PXE mutations on it. It is expected that the results of this study will provide novel insights into the pathomechanistic pathways leading to aberrant mineralization in PXE and related heritable disorders, with perspective to common traits in general population, such as age-associated macular degeneration and arteriosclerosis. Understanding of such pathways is expected to provide opportunities for development of novel pharmacologic approaches to ameliorate, and perhaps cure, these currently intractable conditions. PUBLIC HEALTH REVELANCE. This research project revolves around pseudoxanthoma elasticum (PXE), a heritable disorder characterized by ectopic mineralization of connective tissues, with considerable morbidity and mortality. The overall goal of these studies is to identify the pathomechanistic pathways leading to abnormal mineralization, with translational implications. The results are expected to provide novel approaches to ameliorate, and perhaps cure, PXE and other related, currently intractable, mineralization disorders.