Development of enthesopathy in the mouse model of X-linked hypophosphatemia

X连锁低磷血症是最常见的遗传性软骨病，其特征是 PHEX基因突变。这些突变导致血清FGF23水平升高，从而导致 低磷血症、软骨病和软骨病。FGF23还抑制维生素D 1-a-羟基酶(Cyp27b1)，从而 阻止1，25二羟基维生素D(1，25D)的生产。末端(腱-骨)的病理性矿化 附着点)，称为末端病，是XLH的一种使人衰弱的并发症，会引起极大的疼痛 以及受影响个人的行动能力受损。受影响的常见部位包括膝盖骨和跟腱。 XLH型终末病的发病机制尚不清楚。我们之前证明了阿喀琉斯 XLH型(Hyp)小鼠肾小管有肥大细胞(HECs)的扩张，表现为 P14增强的BMP/IHH信号异常的软骨形成表型。复方丹参对Hyp小鼠的治疗作用 1，25D或FGF23封闭抗体(FGF23Ab)在发育早期(P2)类似地预防终末期疾病 尽管FGF23在骨骼中的表达急剧增加，但这表明1，25D作用受损是 在Hyp Enthesis中观察到BMP/IHH信号增强。在患有XLH的小鼠和人类中，1，25D 治疗不能逆转终端病，支持需要早期恢复1，25D的假说 预防末梢病。FGF23抗体诱导小鼠和小鼠血清1，25D水平的升高 提示FGF23Ab可能不能有效预防XLH患者的终末病。 目前还没有关于优化的1，25D单一治疗或FGF23单抗对XLH患者终端病的影响的数据。 因此，考虑到小鼠和人类对1，25D和FGF23抗体的相似反应，对激素的研究 XLH型终末病的调控对于指导今后预防终末病的临床研究具有重要意义。 初步数据显示，XLH型终末症是由1，25D活动受损引起的，而不是特定的行为 FGF23或Hyp突变的后果。在AIM I上的研究将检查具有全局缺失的 Cyp27b1、FGF23或两者都带有或不带有Hyp突变，以解决损害1，25D的假设 ACTION导致BMP/IHH信号增强和终末性病变。研究还将阐明，如果当地人口减少 1，25D作用导致终末病。由于我们的数据显示BMP信号的增加伴随着 增强GDF5在Hyp包膜中的表达，AIM II的研究将确定GDF5/BMP的致病作用 高血压终末病发生发展中的信号转导。研究将确定WT中GDF5表达的时间进程 和Hyp enals。消融包膜中的GDF5将确定GDF5在BMP/IHH激活中的作用 XLH型终末病中的信号转导。抑制Hyp小鼠的BMP信号将表明IHH信号被激活 BMP信号通过末端传递，BMP/IHH信号的增强直接导致末端病变。已被占用 总之，这些研究将确定XLH型终末症和正常的新的激素和分子调节剂。 雌蕊发育。他们还将确定新疗法的设计目标，以预防终末期疾病。

X-linked hypophosphatemia (XLH) is the most common form of inheritable rickets characterized by mutations in PHEX. These mutations result in elevated serum levels of FGF23, which leads to hypophosphatemia, rickets, and osteomalacia. FGF23 also inhibits vitamin D 1-a-hydroxylase (Cyp27b1), thus blocking 1,25 dihydroxyvitamin D (1,25D) production. Pathologic mineralization of the enthesis (tendon-bone attachment site), referred to as enthesopathy, is a debilitating complication of XLH that causes significant pain and impaired mobility in affected individuals. Common sites affected include the patellar and Achilles entheses. The pathogenesis of XLH enthesopathy is poorly understood. We previously demonstrated that Achilles entheses from mice with XLH (Hyp) have an expansion of hypertrophic appearing cells (HECs) that exhibit an aberrant chondrogenic phenotype with enhanced BMP/IHH signaling by P14. Treatment of Hyp mice with 1,25D or a FGF23 blocking antibody (FGF23Ab) early in development (P2) similarly prevented enthesopathy despite the dramatic increase in FGF23 expression in bone, suggesting impaired 1,25D action underlies the enhanced BMP/IHH signaling observed in Hyp enthesopathy. In both mice and humans with XLH, 1,25D therapy cannot reverse enthesopathy, supporting the hypothesis that early restoration of 1,25D is needed to prevent enthesopathy. The increase in serum 1,25D levels wane post-initiation of FGF23Ab in both mice and humans with XLH, suggesting FGF23Ab may not be effective in preventing enthesopathy in XLH patients. There is no data on the effects of optimized 1,25D monotherapy or FGF23Ab on enthesopathy in XLH patients. Therefore, given the similar responses of mice and humans to 1,25D and FGF23Ab, studies on the hormonal regulation of XLH enthesopathy are essential to guiding future clinical studies on enthesopathy prevention. Preliminary data show that XLH enthesopathy results from impaired 1,25D action, not actions specific to FGF23 or consequences of the Hyp mutation. Studies in Aim I will examine mice with global deletions of Cyp27b1, FGF23, or both with or without the Hyp mutation to address the hypothesis that impaired 1,25D action leads to enhanced BMP/IHH signaling and enthesopathy. Studies will also elucidate if decreased local 1,25D action leads to enthesopathy. Since our data demonstrates increased BMP signaling is accompanied by enhanced GDF5 expression in Hyp entheses, studies in Aim II will identify a pathogenic role for GDF5/BMP signaling in Hyp enthesopathy development. Studies will determine the time course of GDF5 expression in WT and Hyp entheses. Ablation of GDF5 in Hyp entheses will define the role of GDF5 in the activation of BMP/IHH signaling in XLH enthesopathy. Inhibition of BMP signaling in Hyp mice will show that IHH signaling is activated by BMP signaling in entheses and enhanced BMP/IHH signaling directly leads to enthesopathy. Taken together, these studies will identify novel hormonal and molecular regulators of XLH enthesopathy and normal enthesis development. They will also identify targets for the design of new therapies to prevent enthesopathy.