FGF2 Isoforms in Bone and Phosphate Homeostasis

描述（由申请人提供）：成纤维细胞生长因子23（FGF 23）是与异常骨矿化和肾磷酸盐消耗（Pi）相关的人类病理性疾病中的主要磷酸盐调节剂。然而，FGF 23产生的调节剂、FGF 23诱导的Pi消耗和有缺陷的矿化的信号通路尚未完全了解。我们的研究支持成纤维细胞生长因子2（FGF 2）的核亚型在FGF 23的产生和生物学功能中的重要作用。使用在成骨细胞谱系细胞中表达HMW同种型的新型小鼠模型（HMWTg）小鼠和选择性缺失HMW同种型的小鼠（HMWKO）小鼠，我们证明HMWTg小鼠具有血清和骨中增加的FGF 23、侏儒症、骨矿物质密度（BMD）降低、骨软化症、低磷酸盐血症以及骨和肾中异常的FGF 23/FGF受体/ klotho/MAPK和Wnt信号传导。初步数据显示，HMWFGF 2亚型的消融增加了小鼠的BMD，增加了血清磷酸盐，并显著降低了FGF 23 mRNA。我们还观察到在Hyp小鼠（X连锁低磷血症性佝偻病（XLH）的小鼠模型）中成骨细胞/骨细胞中核HMWFGF 2的表达增加。我们也有令人兴奋的初步数据，HMW亚型在XLH患者的B淋巴细胞中过表达，支持这些研究的临床相关性。我们的中心假设是HMWFGF 2：i）通过增加骨中FGF 23的产生在肾中的Pi稳态中起重要作用。ii）通过FGF 23依赖性和非依赖性作用调节骨基质矿化。iii）在Hyp小鼠中导致Pi消耗和有缺陷的基质矿化。目的1将确定HMWFGF 2亚型在HMW转基因小鼠肾脏中Pi稳态中的作用：我们的工作假设是HMWFGF 2亚型增加骨中FGF 23的产生，并且内分泌FGF 23介导肾脏中异常的FGFR/klotho/MAPK信号传导，导致Pi消耗。目的2将评估HMWFGF 2亚型/FGF 23/FGFR和Wnt信号在成骨细胞分化和矿化中的作用。将确定FGF 23、FGFR、MAPK/ERK和硬化蛋白的阻断对HMWTg小鼠中骨形成的影响。目的3将检测HMWFGF 2基因敲除对Pi和骨稳态的功能影响，以及HMWFGF 2在Hyp小鼠中的异常Pi消耗和基质矿化缺陷中是否重要。我们的工作假设是，HMWFGF 2亚型介导异常Pi稳态和骨矿化缺陷。通过检查磷酸盐稳态、HMWFGF 2缺失的HMW-/-小鼠和Hyp小鼠与野生型同窝小鼠的骨骼和肾脏表型，将检验这一假设。我们还将评估这些小鼠中的FGF/FGF受体和下游信号通路。拟议的研究将大大提高我们对HMWFGF 2亚型在Pi稳态和基质矿化中的作用的理解，并可能为调节人类磷酸盐消耗性疾病中这些过程的机制提供新的和基本的见解。

DESCRIPTION (provided by applicant): Fibroblast Growth Factor 23 (FGF23) is the major phosphate regulator in human pathologic disorders associated with abnormal bone mineralization and renal phosphate wasting (Pi). However the regulators of FGF23 production, the signal pathway(s) for FGF23 induced Pi wasting and defective mineralization are not fully understood. Our studies support an important role for the nuclear isoforms of Fibroblast Growth Factor 2 (FGF2) in FGF23 production and biologic function. Using novel mouse models expressing HMW isoforms in osteoblast lineage cells (HMWTg) mice, and mice with selective deletion of the HMW isoforms (HMWKO) mice we demonstrate that HMWTg mice have increased FGF23 in serum and bone, dwarfism, decreased bone mineral density (BMD), osteomalacia, hypophosphatemia, and abnormal FGF23/FGFReceptor/ klotho/MAPK and Wnt signaling in bone and kidney. Preliminary data shows that ablation of the HMWFGF2 isoforms increased BMD, increased serum phosphate and significantly reduced FGF23 mRNA in mice. We also observed increased expression of nuclear HMWFGF2 in osteoblasts/osteocytes in Hyp mice, a murine model of X-linked hypophosphatemic rickets (XLH). We also have exciting preliminary data that HMW isoforms are overexpressed in B-lymphocytes from a patient with XLH supporting clinical relevance of these studies. Our Central Hypotheses are that HMWFGF2: i) plays an important role in Pi homeostasis in kidney by increasing FGF23 production in bone. ii) regulates bone matrix mineralization via FGF23 dependent and independent effects. iii) contributes to Pi wasting and defective matrix mineralization in Hyp mice. Aim 1 will determine the role of HMWFGF2 isoforms in Pi homeostasis in the kidney of HMW transgenic mice: Our working hypothesis is that HMWFGF2 isoforms increase FGF23 production in bone and that endocrine FGF23 mediates abnormal FGFR/klotho/MAPK signaling in kidney that leads to Pi wasting. Aim 2 will assess the role of HMWFGF2 isoforms/FGF23/FGFR and Wnt signaling in osteoblast differentiation and mineralization. Effects of blockade of FGF23, FGFR, MAPK/ERK and sclerostin on bone formation in HMWTg mice will be determined. Aim 3 will examine functional effects of knockout of HMWFGF2 on Pi and bone homeostasis and whether HMWFGF2 is important in the abnormal Pi wasting and matrix mineralization defect in Hyp mice. Our working hypothesis is that HMWFGF2 isoforms mediate abnormal Pi homeostasis and defective bone mineralization. Examining phosphate homeostasis, the skeletal and kidney phenotypes of HMW-/- mice and Hyp mice with deletion of HMWFGF2 versus wild type littermates will test this hypothesis. We will also assess FGF/FGF Receptor and downstream signaling pathways in these mice. The proposed studies will greatly enhance our understanding of the role of HMWFGF2 isoforms in Pi homeostasis and matrix mineralization and may provide novel and fundamental insights into the mechanisms that regulate these processes in human phosphate wasting disorders.