The Endocrine and Skeletal Actions of the PTG-derived Cyp27b1

 描述（由申请人提供）：维生素D代谢失调可导致多种疾病，包括高钙血症、继发性甲状旁腺功能亢进、低钙血症、低磷血症、佝偻病、骨软化和生长迟缓。维生素D的生物活性形式，1，25-二羟基维生素D3（1，25 D），是由酶Cyp 27 b1（25-二羟基维生素D 1-α羟化酶）。肾脏Cyp 27 b1一直被认为是循环1，25 D的主要来源。这一40年的原则主要是根据以下观察建立的：肾功能下降与无肾动物模型和慢性肾脏疾病患者血清1，25 D水平下降密切相关。众所周知，甲状旁腺激素（PTH）激活其肾受体以增加Cyp 27 b1表达，并随后升高血清1，25 D水平。然而，这些范例符合基本的观察结果，没有考虑到许多组织表达1-α羟化酶并产生1，25 D的事实。我们的初步研究在小鼠维生素D受体（VDR）或Cyp 27 b1基因敲除专门针对甲状旁腺细胞表明，Cyp 27 b1表达的甲状旁腺（PTG）可能是一个主要的来源，循环1，25 D和发挥内分泌作用的矿物质和骨骼的稳态。我们进一步发现，新鲜分离的小鼠PTG与PTH（1-34）孵育显著增加了这些PTG中的Cyp 27 b1蛋白和RNA，表明PTH直接调节这种酶。上述研究共同导致我们假设甲状旁腺Cyp 27 b1是循环1，25 D的主要来源，其受PTH和其他激素和矿物质因子的直接调节。为了验证这一假设，我们将（1）确定PT衍生Cyp 27 b1在小鼠模型中的激素、矿物质和骨骼作用，以及（2）确定调节Cyp 27 b1在PTG中表达和功能的机制和全身因素。成功完成该奖学金项目将为维生素D和矿物质代谢的新监管模式提供支持，并将为我提供甲状旁腺生理学，细胞生物学，维生素D代谢和小鼠遗传学方面的基本培训，并将扩大我作为独立研究科学家的发展技能。

 DESCRIPTION (provided by applicant): Dysregulation of vitamin D metabolism can lead to several diseases including hypercalcemia, secondary hyperparathyroidism, hypocalcemia, hypophosphatemia, rickets, osteomalacia and growth retardation. The bioactive form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25D), is made by the enzyme Cyp27b1 (25- dihydroxyvitamin D 1-alpha hydroxylase). Renal Cyp27b1 has long been considered the primary source of circulating 1,25D. This 40-year principle was established mainly from the observation that decreased renal function is strongly associated with decreased serum 1,25D levels in anephric animal models and patients with chronic kidney disease. It is well known that parathyroid hormone (PTH) activates its renal receptors to increase Cyp27b1 expression, and subsequently, to elevate serum 1,25D levels. However, these paradigms fit basic observations that do not take into account the fact that many tissues express the 1-alpha hydroxylase and generate 1,25D. Our preliminary studies in mice with vitamin D receptor (VDR) or Cyp27b1 gene knockout targeted specifically to parathyroid cells suggest that the Cyp27b1 expressed in parathyroid gland (PTG) could be a major source of circulating 1,25D and exert endocrine actions on mineral and skeletal homeostasis. We further found that the incubation of freshly isolated mouse PTGs with PTH(1-34) profoundly increased Cyp27b1 protein and RNA in these PTGs, indicating direct regulation of this enzyme by PTH. The above studies together led us to hypothesize that the parathyroid Cyp27b1 is a prominent source of circulating 1,25D that is subject to direct regulation by PTH and other hormonal and mineral factors. To test this hypothesis we will (1) determine the hormonal, mineral, and skeletal actions of PT-derived Cyp27b1 in the mouse model, and (2) determine the mechanisms and systemic factors that regulate Cyp27b1 expression and function in the PTG. Successful completion of this fellowship project will lend support to new regulatory paradigms for vitamin D and mineral metabolism and will provide me with essential training in parathyroid physiology, cell biology, vitamin D metabolism and mouse genetics, and will expand my technical skills in my development as an independent research scientist.