Vitamin D: A Negative Regulator of Renin Expression

描述（由申请人提供）：本申请的主要目的是确定维生素D和甲状旁腺激素（PTH）在体内调节肾素-血管紧张素系统中的作用，肾素-血管紧张素系统在调节血压、电解质和体积稳态中起着至关重要的作用。最近，我们发现小鼠体内维生素D信号的破坏会导致肾素表达和血浆血管紧张素II产生的升高，从而导致高血压和水摄入量增加。我们证明肾素上调与VDR敲除（VDRKO）小鼠中与维生素D受体（VDR）消退相关的低钙血症无关，但与VDR失活相关的继发性甲状旁腺功能亢进是否也有助于肾素表达的增加尚不清楚。我们还证明1,25-二羟基维生素D3通过vdr依赖机制直接抑制细胞培养中的肾素表达，但仍需要体内证据来证明维生素D是肾素-血管紧张素系统的负内分泌调节剂。为了解决这些问题，我们提出了两个具体目标：(1)利用4.1 kb肾素基因启动子靶向转基因（Tg）小鼠肾素产生细胞中的人VDR （hVDR）表达，验证维生素D作为肾素表达的负调节因子的作用。与VDRKO小鼠相比，Tg小鼠将使我们能够直接评估VDR在体内正常钙和PTH条件下对肾素表达的调节作用。Tg小鼠肾素表达下调证实维生素D负性调节肾素表达。(2)通过生成和分析表达IIVDR转基因（VDRKO/hVDR）的VDRKO小鼠，明确维生素D和PTH在肾素表达调控中的作用。通过繁殖将hVDR引入VDRKO小鼠，VDRKO/hVDR小鼠将仅在肾素产生细胞中表达hVDR，并且仍然像VDRKO小鼠一样出现低钙血症、继发性甲状旁腺功能亢进和高浓度循环1,25 -二羟基维生素D3。因此，如果VDRKO/hVDR小鼠仍然表现出与VDRKO窝鼠相同的肾素上调，则可以得出PTH具有刺激作用而维生素D不具有抑制作用的结论；如果肾素在VDRKO/hVDR小鼠中的表达低于野生型小鼠，则说明甲状旁腺激素不具有刺激作用，维生素D确实是负调节因子；如果VDRKO/hVDR小鼠肾素表达低于VDRKO窝鼠，但高于野生型窝鼠，说明甲状旁腺激素刺激肾素表达，维生素D抑制肾素表达。

DESCRIPTION (provided by applicant): The main goal of this application is to define the role of vitamin D and parathyroid hormone (PTH) in the regulation of the renin-angiotensin system in vivo, which plays a crucial role in the regulation of blood pressure, electrolyte and volume homeostasis. Recently, we found that disruption of the vitamin D signaling in mice results in a deregulated elevation of renin expression and plasma angiotensin II production, leading to hypertension and increased water intake. We demonstrated that the renin up-regulation is independent of the hypocalcemia associated with vitamin D receptor (VDR) ablation in VDR knockout (VDRKO) mice, but whether the secondary hyperparathyroidism associated with VDR inactivation also contributes to the increase in renin expression remains unclear. We also demonstrated that 1,25-dihydroxyvitamin D3 directly suppresses renin expression in cell culture by a VDR-dependent mechanism, but in vivo evidence is still required to prove that vitamin D is a negative endocrine regulator of the renin-angiotensin system. To address these questions, we proposed two Specific Aims: (1) Verify the role of vitamin D as a negative regulator of renin expression by targeting human VDR (hVDR) expression in renin-producing cells in transgenic (Tg) mice using the 4.1 kb renin gene promoter. In contrast to VDRKO mice, the Tg mice will allow us to directly assess the role of VDR in vivo in the regulation of renin expression under a normal calcium and PTH condition. A down-regulation of renin expression in the Tg mice will confirm that vitamin D negatively regulates renin expression. (2) Clarify the role of vitamin D and PTH in the regulation of renin expression by generating and analyzing VDRKO mice that express the IIVDR transgene (VDRKO/hVDR). The hVDR will be introduced into VDRKO mice through breeding, and the VDRKO/hVDR mice will express hVDR only in renin-producing cells, and still develop hypocalcemia, secondary hyperparathyroidism and a high concentration of circulating 1 ,25-dihydroxyvitamin D3 like the VDRKO mice. Thus, if VDRKO/hVDR mice still show the same renin up-regulation as VDRKO littermates, it will be concluded that PTH has a stimulatory role and vitamin D does not play an inhibitory role; If renin expression in VDRKO/hVDR mice is lower than in wildtype littermates, it will indicate that PTH does not have a stimulatory effect and vitamin D is indeed a negative regulator; If renin expression in VDRKO/hVDR mice is lower than VDRKO littermates but higher than wildtype littermates, it will indicate that PTH stimulates and vitamin D suppresses renin expression.