XPR1基因介导磷转运参与原发性家族性脑钙化症的机制研究

Primary familial brain calcification (PFBC) is a neurogenetic disease characterized by symmetrical cerebral calcification, often accompanied by a variety of neuropsychiatric symptoms. How the causing gene XPR1, identified in 2015, encoding the cell phosphorus transporter, participates in the pathogenesis of PFBC remains largely unknown. Preliminary results suggested the XPR1 mutations identified in PFBC patients affected the function of cell phosphorus transport and caused the high phosphorus state of the cells. And, we found the interaction between XPR1 protein and the known pathogenetic gene PDGFRB, suggesting that PDGFRB regulates the phosphorous transport of XPR1. In peripheral tissue, high phosphorus could activate MEK/ERK1/2 signaling pathway to induce vascular smooth muscle cells to differentiate into osteoblasts and resulted in vascular calcification. But in the central nervous systems, whether or not high phosphorus is involved in the formation of brain calcification has not been reported. The project will seek new interaction proteins of XPR1 by mass spectrometry, cell phosphorus transport and other experiments, and make clear the regulation mechanism of XPR1 phosphorous transport. On the other hand, we will combine with in vitro isolation of XPR1 specific expression of nerve cells and Xpr1 gene knockout mice model to explore the specific mechanism of high phosphorus in the formation of calcification through the MEK/ERK1/2 signaling pathway and osteoblast differentiation.

原发性家族性脑钙化症（PFBC）是以颅脑对称性的钙化为特征的神经系统遗传病，常伴有多种神经精神症状。2015年发现的新致病基因XPR1，编码磷转运蛋白，在PFBC发病中的作用尚不明确。我们前期针对PFBC患者中所发现的XPR1突变位点进行功能分析，发现突变影响磷排出功能，造成胞内高磷。同时，我们发现XPR1与已知致病基因PDGFRB存在互作，提示PDGFRB调控XPR1的磷转运功能。在外周组织，高磷可通过激活MEK/ERK1/2信号通路，诱导血管平滑肌细胞向成骨细胞分化，导致血管钙化。但在中枢，高磷是否参与脑钙化形成尚未见报道。本项目将通过质谱分析、细胞磷转运等实验，寻找XPR1新的互作蛋白，明确XPR1磷转运的调控机制。另一方面，结合体外分离XPR1特异表达的神经细胞和Xpr1基因敲除小鼠模型，从MEK/ERK1/2信号通路、成骨细胞转分化等角度共同探讨高磷在脑钙化形成中的具体机制。

原发性家族性脑钙化症（Primary familial brain calcification，PFBC）是以异常对称性的脑钙化为特征的神经系统遗传病，常伴运动障碍、认知障碍、精神障碍等。目前，已报道PFBC致病基因有SLC20A2、PDGFRB、PDGFB、XPR1及MYORG。本研究重点关注XPR1基因，其编码磷转运蛋白，在PFBC发病中的作用尚不明确。我们前期针对PFBC患者中所发现的XPR1突变位点进行功能分析，发现突变影响细胞的磷排出功能，XPR1可能与其他致病基因存在相互作用调控磷转运功能。本研究紧密围绕XPR1基因突变导致脑钙化的致病机制为关键科学问题，进行临床与基础结合的研究，完善PFBC临床评估-分子诊断体系，建立规范化的诊治流程，扩大临床样品数据库，发现多个致病基因的新发突变位点，结合细胞磷转运实验，扩展PFBC致病基因的突变谱，获得大数据量的基因型-临床表型分析数据。对XPR1特异性互作蛋白的筛选及鉴定，证实PDGFRB与XPR1存在互作关系，PDGFRB通过信号转导调控XPR1排磷功能，参与脑钙化发病机制。分别构建Xpr1基因敲除小鼠及斑马鱼模型，观察病理性脑钙化灶的形成过程，发现脑内小胶质细胞可能参与脑钙化形成的发病机制。以上结果为后续PFBC发病机制研究提供了理论和实践基础。