HORMONAL CONTROL OF RENAL 1,25(OH)2D3 BIOSYNTHESIS

描述(改编自申请人的摘要)：长期 拟议研究的目标是扩大目前对 荷尔蒙和离子调节哺乳动物的细胞机制 肾近端小管合成1，25-二羟基维生素D3 (1，25(OH)2D3)。1，25(OH)2D3是肠道钙和钙的主要调节因子 磷的吸收。1，25(OH)2D3的合成在生命周期中有所不同， 老年人生长期增减，以满足骨量 和磷的需求。骨矿物质需求与肾脏的整合 1，25(OH)2D3的合成尚不清楚，但甲状旁腺激素(PTH)， 主要是胰岛素样生长因子I(IGF-1)和低磷饮食(LPD 肾脏线粒体25-羟基维生素D3-1的识别刺激物 α羟基酶(1-OHase)。在近曲小管，甲状旁腺激素激活两者 CAMP/cAMP依赖的蛋白激酶(PKA)和磷脂酶C (PLC)/蛋白激酶C(PKC)信号系统。尽管这两个系统 可以介导PTH对1-OHase的作用，PTH激活PKC并刺激 1，25(OH)2D3在相同的生理浓度下，而 CAMP/PKA激活需要甲状旁腺素浓度。这个 IGF-1和LPD刺激1-OHase的机制尚不清楚，但 IGF-1可能促进PTH和LPD的1-OHase反应。 当前的应用程序建议测试总体假设，即 PLC/PKC系统介导PTH激活1-OHase 和/或肾旁分泌IGF-1在PTH和 洛城警察局。这些假设将通过以下具体目标进行检验：1) 鉴定与急慢性甲状旁腺激素相关的蛋白激酶C亚型 刺激大鼠近端小管1，25(OH)2D3的产生；2) 确定PTH、IGF-1和LPD是否净产生1，25(OH)2D3 相互刺激1-OHase和抑制24-OHase的结果 OHase活性；3)探索IGF-1的潜在机制 刺激近端小管1-OHase活性；以及4)利用来自 通过以上研究，探讨了1，25(OH)2D3还原的机理 老化过程中的生产。 建议的研究旨在提高对 1，25(OH)2D3的生理调控和缺陷1，25(OH)D3的产生 在衰老和骨丢失和骨折的疾病期间，例如 骨质疏松和原发性甲状旁腺功能亢进症。

DESCRIPTION (Adapted from the Applicant's Abstract): The long-term objectives of the proposed research are to expand present knowledge of the cellular mechanisms whereby hormones and ions regulate mammalian renal proximal tubule synthesis of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). 1,25(OH)2D3 is the major regulator of intestinal Ca and P absorption. 1,25(OH)2D3 synthesis varies during the life-cycle, increasing during growth and decreasing in the elderly, to meet bone Ca and P requirements. Integration of bone mineral requirements and renal 1,25(OH)2D3 synthesis remains unknown, but parathyroid hormone (PTH), insulin-like growth factor I (IGF-1) and low P diet (LPD) are major recognized stimuli of the renal mitochondrial 25-hydroxyvitamin D3-1 alpha hydroxylase (1-OHase). In proximal tubules, PTH activates both the cAMP/cAMP-dependent protein kinase (PKA) and the phospholipase C (PLC)/protein kinase C (PKC) signalling systems. Although either system could mediate PTH action on 1-OHase, PTH activates PKC and stimulates 1,25(OH)2D3 at the same physiologic concentration, whereas greater concentrations of PTH are required for cAMP/PKA activation. The mechanism whereby IGF-1 and LPD stimulate 1-OHase remains unknown, but IGF-1 may facilitate 1-OHase response to PTH and LPD. The current application proposes to test the overall hypotheses that the PLC/PKC system mediates PTH activation of 1-OHase and that systemic and/or renal paracrine IGF-1 amplifies 1-OHase activity during PTH and LPD. The hypotheses will be tested by the following Specific Aims: 1) to identify the PKC isoforms involved in acute and chronic PTH stimulation of rat proximal tubule 1,25(OH)2D3 production; 2) to determine whether net 1,25(OH)2D3 production by PTH, IGF-1 and LPD results from reciprocal stimulation of 1-OHase and suppression of 24- OHase activities; 3) to explore potential mechanisms whereby IGF-1 stimulates proximal tubule 1-OHase activity; and 4) using knowledge from the above studies, to investigate the mechanism for reduced 1,25(OH)2D3 production during aging. The proposed studies are intended to improve the understanding of physiologic control of 1,25(OH)2D3 and defective 1,25(OH)D3 production during aging and diseases of bone loss and fracture, such as osteoporosis and primary hyperparathyroidism.