Vitamin D: A Negative Regulator of Renin Expression

描述(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)在调节体内肾素-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、电解质和容量平衡方面起着至关重要的作用。最近，我们发现小鼠体内维生素D信号的中断会导致肾素表达和血浆血管紧张素II水平的异常升高，从而导致高血压和水摄入量增加。我们证明，在VDR基因敲除(VDR)小鼠中，肾素上调与维生素D受体(VDR)去除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仍不清楚。我们还证明了1，25-二羟基维生素D3通过VDR依赖的机制直接抑制细胞培养中肾素的表达，但体内证据仍需证明维生素D是肾素-血管紧张素系统的负性内分泌调节因子。为了解决这些问题，我们提出了两个特定的目标：(1)通过使用4.1 kb肾素基因启动子在转基因(TG)小鼠的肾素产生细胞中靶向表达人VDR(HVDR)来验证维生素D作为肾素表达的负调节因子的作用。与VDRKO小鼠相比，TG小鼠将允许我们直接评估体内VDR在正常钙和甲状旁腺素条件下调节肾素表达的作用。TG小鼠肾素表达下调将证实维生素D对肾素表达有负面调节作用。(2)通过建立和分析表达IIVDR转基因(VDRKO/hVDR)的VDRKO小鼠，阐明维生素D和PTH在肾素表达调控中的作用。通过育种将hVDR导入VDRKO小鼠，VDRKO/hVDR小鼠将只在肾素产生细胞中表达hVDR，但仍会像VDRKO小鼠一样出现低钙血症、继发性甲状旁腺功能亢进症和循环中高浓度的1，25-二羟基维生素D3。因此，如果VDRKO/hVDR小鼠仍然表现出与VDRKO窝产仔相同的肾素上调，则可以得出结论：PTH具有刺激作用，而维生素D没有抑制作用；如果VDRKO/hVDR小鼠肾素表达低于野生型窝产仔，则表明PTH没有刺激作用，维生素D确实是负调节作用；如果VDRKO/hVDR小鼠肾素表达低于VDRKO窝产仔，但高于野生型窝产仔，则表明PTH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.