Renal regulation of phosphate homeostasis and its effect on bone

肾脏对磷酸盐稳态的调节及其对骨的影响

• 批准号: 10656315
• 负责人: HARALD W. JUEPPNER
• 金额: $ 40.76万
• 依托单位: MASSACHUSETTS GENERAL HOSPITAL
• 依托单位国家: 美国
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10656315
• 关键词: Ablation; Adenylate Cyclase; Affect; Animal Model; Animals; Blood; Bone Density; Bone Resorption; Calcium; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Disease; Engineering; Excretory function; Fibroblasts; Homeostasis; Hormonal; Hormones; Human; Hypercalcemia; Hypophosphatemia; Impairment; Infusion procedures; Injections; Intervention; Investigation; Ions; Kidney; Knockout Mice; Knowledge; Minerals; Minor; Mus; Osteoblasts; Osteocytes; Osteogenesis; Osteoporosis; PTH gene; Parathyroid Hormone Receptor; Pathway interactions; Patients; Phenotype; Phospholipase C; Phospholipases A; Production; Proximal Kidney Tubules; Pseudohypoparathyroidism; Receptor Activation; Receptor Signaling; Recombinants; Regulation; Role; Second Messenger Systems; Signal Pathway; Signal Transduction; Thick; Transgenic Animals; Transgenic Mice; Vitamin D; Wild Type Mouse; bone; bone cell; bone loss; bone mass; bone metabolism; bone turnover; calcium metabolism; dentin matrix protein 1; hormone analog; hormone resistance; human disease; in vivo; inhibitor; inorganic phosphate; novel; parathyroid hormone (1-34); prevent; response; salt-inducible kinase; skeletal; tibia; transgene expression; urinary

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.

项目摘要/摘要 持续升高的甲状旁腺激素（PTH）引起高钙血症/低磷酸血症和 增强骨骼更新。这会导致骨质流失，因为骨骼分辨率更大地增加 而不是骨形成。相比之下，每日PTH注射只有瞬时小调增强骨形成 离子变化。令人惊讶的是，在骨骼中表达组成性活性PTH/PTHRP受体（PTHR1）的小鼠 （COL1-H223R或DMP1-H223R）显示出深刻的骨骼质量增加。同样，受影响的患者 假型甲状腺功能减退症（肾脏中的PTH抗性，但在骨骼中没有），用钙治疗1,25（OH）2 尽管PTH水平升高，但维生素D（1,25D）仍可以显示骨形成的主要增加。调查结果 转基因小鼠和人类疾病因此表明持续的PTHR1激活会增加骨骼 质量，如果超过泌尿磷酸盐排泄。大量证据表明尿液 PTH的磷酸排泄不仅取决于CAMP/PKA信号，还取决于IP3/PKC依赖性 机制。实际上，表达磷脂酶C（PLC）的D/D小鼠缺陷PTHR1不维持 当PTHR1连续激活时，磷酸盐排泄。此外，接收的野生型动物 [TRP1] PTH​​（1-34）的长期输注（一种有偏见的PTH模拟IP3信号传导）未能维持 磷酸盐排泄和1,25D产生。除了肾脏的重要性外，PTH刺激了 PLC/IP3/PKC信号是骨形成所必需的。例如，野生型小鼠的胫骨 长时间依赖PTH的PTHR1激活表明成纤维细胞样骨（FSB）的快速扩张 细胞；在连续PTH升高的D/D小鼠中未观察到这种成骨细胞前体 感染了[TRP1] PTH​​（1-34）的野生型小鼠，从而支持以下结论： 正常骨形成需要PTHR1。现在，我们将确定是否持续IP3/PKC信号 长期调节磷酸盐稳态和1,25D生产需要PTHR1，以及 如果超过尿磷酸盐排泄，连续PTHR1激活是否可以增强骨形成 可以防止。将追求两个目标：AIM 1将进一步探索是否依赖于PTH的IP3/PKC 持续的磷酸盐排泄需要信号传导，1,25D产生以及扩展 成骨细胞前体。 AIM 2将确定COL1-H223R小鼠和动物中的高骨量是否存在 通过骨细胞特异性SIK2/3消融可以通过促进肾磷酸盐排泄来逆转 独立于PTH的干预措施，即通过新的NPT2A抑制剂或重组FGF23。 我们还将确定“寻求骨”的PTH类似物是否可以诱导骨形成 连续的局部PTHR1激活，但肾作用有限，即无磷和不增加1,25D。 我们的研究将有助于进一步阐明PLC依赖性PTHR1信号在肾脏和骨骼中的作用， 以及磷酸盐在两种遗传改变的小鼠中维持高骨量的重要性。