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 （FGF23）是与异常骨矿化和肾磷酸盐消耗（Pi）相关的人类病理疾病的主要磷酸盐调节剂。然而，FGF23产生的调节因子、FGF23诱导Pi损耗和矿化缺陷的信号通路尚不完全清楚。我们的研究支持成纤维细胞生长因子2 （FGF2）的核异构体在FGF23的产生和生物学功能中的重要作用。通过在成骨细胞谱系细胞（HMWTg）小鼠和选择性缺失HMW亚型小鼠（HMWKO）小鼠中表达HMW亚型的新型小鼠模型，我们证明了HMWTg小鼠血清和骨骼中FGF23增加，侏儒症，骨密度降低，骨软化症，低磷血症，骨骼和肾脏中FGF23/ fgf受体/ klotho/MAPK和Wnt信号异常。初步数据显示，HMWFGF2亚型的消融增加了小鼠的骨密度，增加了血清磷酸盐，并显著降低了FGF23 mRNA。我们还观察到Hyp小鼠（X-linked hypophospemic佝偻病（XLH）小鼠模型）成骨细胞/骨细胞中核HMWFGF2的表达增加。我们也有令人兴奋的初步数据表明，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。我们的主要假设是HMWFGF2: i)通过增加骨中FGF23的产生在肾脏Pi稳态中起重要作用。ii)通过FGF23依赖和独立作用调节骨基质矿化。iii)导致Hyp小鼠Pi损耗和基质矿化缺陷。目的1将确定HMWFGF2异构体在HMW转基因小鼠肾脏中Pi稳态中的作用：我们的工作假设是HMWFGF2异构体增加骨中FGF23的产生，内分泌FGF23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HMWFGF2亚型/FGF23/FGFR和Wnt信号在成骨细胞分化和矿化中的作用。阻断FGF23、FGFR、MAPK/ERK和sclerostin对HMWTg小鼠骨形成的影响将被确定。目的3将检测敲除HMWFGF2对Pi和骨稳态的功能影响，以及HMWFGF2是否在Hyp小鼠Pi异常消耗和基质矿化缺陷中起重要作用。我们的工作假设是HMWFGF2同工型介导异常Pi稳态和骨矿化缺陷。通过检测磷酸盐稳态，HMW-/-小鼠和HMWFGF2缺失的Hyp小鼠与野生型幼崽的骨骼和肾脏表型将验证这一假设。我们还将评估这些小鼠的FGF/FGF受体和下游信号通路。这些建议的研究将极大地增强我们对HMWFGF2亚型在Pi稳态和基质矿化中的作用的理解，并可能为人类磷酸盐消耗障碍中调节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.