Renal regulation of phosphate homeostasis and its effect on bone

项目摘要/摘要 持续升高的甲状旁腺激素(PTH)会导致高钙血症/低磷血症和 提高骨骼的周转率。这会导致骨丢失，因为骨吸收增加得更明显 而不是骨形成。相比之下，每天注射甲状旁腺素只会增加短暂矿物质的骨形成。 离子发生了变化。令人惊讶的是，在骨骼中表达固有活性的PTH/PTHrP受体(PTHR1)的小鼠 (COL1-H_223R或DMP1-H_223R)显示骨量显著增加。同样，受 假性甲状旁腺功能减退症(肾脏甲状旁腺激素抵抗，但骨不抵抗)，用钙和1，25(OH)2治疗 维生素D(1，25D)，尽管甲状旁腺素水平升高，但仍能显著促进骨形成。中的发现 因此，转基因小鼠和人类疾病表明，PTHR1的持续激活可以增加骨骼 如果防止了过量的尿磷排泄，就会产生大量的磷酸盐。相当多的证据表明，尿液 甲状旁腺激素的磷酸排泄不仅依赖于cAMP/PKA信号，还依赖于IP3/PKC 机械装置。事实上，表达磷脂酶C(PLC)缺陷的PTHR1的D/D小鼠不能持续 当PTHR1被持续激活时，磷酸盐排泄。此外，野生动物受到了 长期输注[Trp1]PTH(1-34)，一种带有受损的IP3信号的偏向PTH类似物，未能维持 磷酸盐排泄和1，25D生产。除了对肾脏的重要性外，甲状旁腺素刺激 PLC/IP3/PKC信号通路是骨形成所必需的。例如，野生型小鼠的胫骨正在经历 甲状旁腺激素依赖的PTHR1活性延长显示成纤维样间质骨(FSB)迅速扩张 在甲状旁腺激素持续升高的D/D小鼠中未观察到这种成骨前体细胞。 野生型小鼠注射了[Trp1]PTH(1-34)，从而支持了PLC信号在 PTHR1是正常骨形成所必需的。我们现在将确定持久的IP3/PKC信令 在PTHR1是长期调节磷酸盐稳态和1，25D生产所必需的，以及 如果尿磷排泄过量，持续的PTHR1激活是否可以促进骨形成 是可以预防的。将追求两个目标：目标1将进一步探讨PTH依赖的IP3/PKC 信号是持续的磷酸盐排泄、1，25D生产和扩展所必需的 成骨细胞前体细胞。目的2将测定COL1-H223R小鼠和动物的高骨量 在骨细胞特异性SIK2/3消融中，通过促进肾脏磷酸盐排泄可以逆转消融 PTH非依赖性干预，即通过一种新的NPT2a抑制剂或通过重组FGF23。 我们还将确定“寻骨”甲状旁腺素类似物是否可以诱导骨形成，因为 持续的局部PTHR1激活，但肾脏作用有限，即无磷尿和NO 1，25D增加。 我们的研究将有助于进一步阐明PLC依赖的PTHR1信号在肾脏和骨骼中的作用。 以及磷酸盐在两只基因改变的小鼠保持高骨量中的重要性。

PROJECT SUMMARY/ABSTRACT Continuously elevated parathyroid hormone (PTH) causes hypercalcemia/hypophosphatemia and enhances bone turnover. This results in bone loss because bone resorption increases more prominently than bone formation. In contrast, daily PTH injection enhances bone formation with only transient mineral ion changes. Surprisingly, mice expressing a constitutively active PTH/PTHrP receptor (PTHR1) in bone (Col1-H223R or Dmp1-H223R) show profound bone mass increases. Likewise, patients affected by pseudohypoparathyroidism (PTH-resistance in kidney, but not in bone), treated with calcium and 1,25(OH)2 vitamin D (1,25D), can show a major increase in bone formation, despite elevated PTH levels. Findings in transgenic mice and a human disease thus suggested that persistent PTHR1 activation can increase bone mass, if excess urinary phosphate excretion is prevented. Considerable evidence indicates that urinary phosphate excretion by PTH depends not only on cAMP/PKA signaling, but also on IP3/PKC-dependent mechanisms. In fact, D/D mice expressing a phospholipase C (PLC)-deficient PTHR1 do not sustain phosphate excretion when the PTHR1 is continuously activated. Furthermore, wild-type animals receiving long-term infusions of [Trp1]PTH(1-34), a biased PTH analog with impaired IP3 signaling, failed to sustain phosphate excretion and 1,25D production. In addition to its renal importance, PTH-stimulated PLC/IP3/PKC signaling is required for bone formation. For example, tibiae of wild-type mice undergoing prolonged PTH-dependent PTHR1 activation showed rapid expansion of fibroblast-like stromal bone (FSB) cells; such osteoblast precursors were not observed in D/D mice with continuous PTH elevations and in wild-type mice infused with [Trp1]PTH(1-34), thus supporting the conclusion that PLC-signaling at the PTHR1 is required for normal bone formation. We will now determine whether persistent IP3/PKC-signaling at the PTHR1 is required for long-term regulation of phosphate homeostasis and 1,25D production, and whether continuous PTHR1 activation can enhance bone formation, if excess urinary phosphate excretion can be prevented. Two aims will be pursued: Aim 1 will explore further whether PTH-dependent IP3/PKC signaling is required for sustained phosphate excretion, for 1,25D production, and for expansion of osteoblast precursors. Aim 2 will determine whether the high bone mass in Col1-H223R mice and animals with osteocyte-specific SIK2/3 ablation can be reversed by promoting renal phosphate excretion through PTH-independent interventions, namely through a novel NPT2a inhibitor or through recombinant FGF23. We will also determine whether “bone-seeking” PTH analogs can induce bone formation because of continuous local PTHR1 activation, yet limited renal actions, i.e. no phosphaturia and no 1,25D increase. Our investigations will help clarify further the role of PLC-dependent PTHR1 signaling in kidney and bone, and the importance of phosphate in maintaining high bone mass in two genetically altered mice.