Skeletal FGF23 production mediated by GPCR/Gq/PKC signaling

摘要 成纤维细胞生长因子-23(FGF23)是一种骨源性磷酸激素，在这种调节中起着关键作用 血磷水平和维生素D代谢的变化。FGF23功能失调是其发病机制的基础 在几种矿物质离子代谢异常的骨骼疾病中。肾脏患者血清FGF23水平也升高 衰竭和FGF23水平升高极大地促进了与慢性疾病相关的矿物质和骨骼障碍 肾脏疾病。需要有效的策略来控制骨骼FGF23的产生，以改善 这些疾病的临床治疗。然而，管理FGF23生产的机制仍然很差 明确的、阻碍实现这一目标的进展。已经描述了几种FGF23刺激物，但 它们作用的分子决定因素还不完全清楚。细胞内的信号通路是 目前还不清楚它们之间是如何相互作用的。我们现在已经确定了 溶血磷脂酸(LPA)作为一种新的FGF23合成刺激物，发现它通过G 蛋白偶联受体LPAR1。我们还发现，消融LPAR1可以阻断小鼠体内FGF23的表达 急性肾损伤模型。我们的初步实验也强烈表明，LPA的作用 涉及GQ/11/PKC信号通路，其作用机制依赖于MAPK-ERK1/2信号通路。 此外，我们的结果有力地表明，LPA-Gq/11/PKC通路在FGF23的产生中起关键作用 1，25-二羟基维生素D(1，25D)诱导。在本提案中，我们将研究FGF23的这一新范式 在骨细胞中合成。目的1将确定骨细胞特异性GQ/11/PKC信号在LPA诱导中的作用 FGF23的产生，检测该通路与MAPK-ERK1/2信号的相互作用，并确定 它是否在膳食磷酸盐诱导的FGF23水平升高中起作用。对于这些研究，我们将 采用GQ/11α在骨细胞中有条件地消融的小鼠(GQ/11αDmp1KO小鼠，在我们实验室可获得)，作为 以及适合研究FGF23合成的骨细胞/成骨样细胞系。目标2将阐明 1，25D和LPA-GQ/11/PKC信号在FGF23产生中的作用之间的串扰，使用两个细胞- 基于检测和小鼠模型(GQ/11αDmp1KO和维生素D受体基因敲除小鼠，也可在我们的 实验室)。目的3将研究GQ/11/PKC信号在FGF23过度产生的病理条件下的作用。 包括X连锁低磷血症(XLH)和肾功能衰竭。我们将使用Hyp MICE(一个成熟的 模型)，与GQ/11αDmp1KO小鼠杂交。用于研究肾功能衰竭引起的FGF23 在生产过剩的情况下，我们将采用高腺嘌呤饮食诱导的慢性肾脏疾病模型。我们的研究将 阐明LPA-GQ/11/PKC通路作为骨细胞产生FGF23的刺激因子的作用并鉴定 它与FGF23合成的其他重要系统调节因子的细胞作用的关系。我们的 因此，预测结果将显著增加对FGF23合成的控制机制的知识 并有可能为由不受调控的FGF23作用引起或影响的疾病产生新的药物靶点。

Abstract Fibroblast growth factor-23 (FGF23), a bone-derived phosphaturic hormone, plays a key role in the regulation of serum phosphate levels and vitamin D metabolism. Dysregulated FGF23 actions underlie the pathogenesis of several skeletal diseases with abnormal mineral ion metabolism. Serum FGF23 levels also rise in kidney failure, and elevated FGF23 levels contribute greatly to the mineral and bone disorder associated with chronic kidney disease. Effective strategies for controlling skeletal FGF23 production are needed in order to improve the clinical management of these disorders. However, mechanisms governing FGF23 production remain poorly defined, impeding progress toward this goal. Several FGF23 stimulators have been described, but the molecular determinants of their actions are incompletely understood. The intracellular signaling pathways are not elucidated, and it remains unknown how those interact with one another. We have now identified lysophosphatidic acid (LPA) as a novel stimulator of FGF23 synthesis and found that it acts through its G protein-coupled receptor LPAR1. We also showed that ablation of LPAR1 blocks the rise of FGF23 in a mouse model of acute kidney injury. Our preliminary experiments also strongly suggested that the action of LPA involves Gq/11/PKC signaling pathway operating via a mechanism that depends on MAPK-ERK1/2 signaling. Moreover, our results strongly suggested that the LPA-Gq/11/PKC pathway is critical for FGF23 production induced by 1,25-dihydroxyvitamin D (1,25D). In this proposal, we will investigate this novel paradigm of FGF23 synthesis in osteocytes. Aim 1 will determine the role of osteocyte-specific Gq/11/PKC signaling in LPA-induced FGF23 production, examine the interaction of this pathway with MAPK-ERK1/2 signaling, and determine whether it plays a role in the dietary phosphate-induced elevation of FGF23 levels. For those studies, we will employ mice in which Gq/11α are ablated conditionally in osteocytes (Gq/11αDmp1KO mice, available in our lab), as well as osteocyte/osteoblast-like cell lines suitable for studying FGF23 synthesis. Aim 2 will elucidate the cross-talk between the action of 1,25D and LPA-Gq/11/PKC signaling in FGF23 production, using both cell- based assays and mouse models (Gq/11αDmp1KO and vitamin D receptor knockout mice, also available in our lab). Aim 3 will examine the role of Gq/11/PKC signaling in pathological conditions of excess FGF23 production, including X-linked hypophosphatemic rickets (XLH) and renal failure. We will employ Hyp mice (an established model of XLH), which will be crossed with Gq/11αDmp1KO mice. For studying renal failure-induced FGF23 overproduction, we will use a model of chronic kidney disease induced by adenine-rich diet. Our studies will elucidate the role of the LPA-Gq/11/PKC pathway as a stimulator of FGF23 production in osteocytes and identify its relationship with the cellular actions of other important systemic regulators of FGF23 synthesis. Our predicted results will thus markedly increase the knowledge of the mechanisms controlling FGF23 synthesis and are likely to yield new drug targets for diseases caused or affected by dysregulated FGF23 actions.