D3, D1, AT1 Receptor Interaction--Genetic Hypertension

Jose项目的总体目标是确定肾脏中D3、D1和AT1受体的相互作用。D3多巴胺受体可以调节肾脏的钠转运和血压，而不依赖于D1受体，因为D3受体在小鼠体内的破坏会增加血压，并削弱它们排泄急性盐水负荷的能力。然而，D3受体也可以与D1受体协同作用，增加钠的排泄。在遗传性高血压的啮齿动物模型(Dahl盐敏感和自发性高血压大鼠，SHR)中，D3受体的利钠作用受损，D1和D3受体之间的相互作用丢失。遗传性高血压患者肾脏D1R功能受损是由于G蛋白偶联受体4型(GRK4)活性增强所致。GRK4基因座与人类原发性高血压相关，GRK4变异与人类高血压相关。这些变异体在中国仓鼠卵巢和HEK细胞中的异源表达会损害D1受体的功能，过度表达GRK4变异体A142V的小鼠会患高血压，并对D1受体激动剂刺激的利钠反应受损。此外，抑制人类高血压患者肾脏近端小管细胞(或细胞系)上的GRK4活性可恢复D1受体功能，选择性地抑制肾脏GRK4的表达可减轻SHR血压的升高。遗传性高血压患者肾脏D3受体功能受损是否继发于GRK4活性升高，从而同时损害了D3和D3受体，目前尚不清楚。然而，D3-/-小鼠的D1受体功能受损，肾脏增加 肾素含量与AT1受体的关系。因此，D3-/-小鼠的D1受体减少和AT1受体功能增加可能是导致它们排泄生理盐水负荷的能力受损和高血压的原因之一。Jose项目的总体假设是，肾脏近端小管钠转运部分地受到D1、D3和AT1受体之间的相互作用的调节，尤其是通过受体/受体的相互作用，以及长期的通过受体表达的调节。此外，在遗传性高血压中，由于GRK4活性增加而导致的D3(和D1)受体功能受损，使得AT1受体的作用不受阻碍。具体目的I将检验这样的假设，即小鼠的D3受体缺陷既损害了D1受体的功能，又使AT1受体的功能畅通无阻。《特定目标2》将检验GRK4活性增加的假设，这是由于 在遗传性高血压中，结构性活性变异会损害D3受体的功能。使用分子生物学和药理学工具的这些研究结果可能会揭示GRK4调节几个基因的能力可能会使GRK4功能障碍成为遗传性高血压的主要原因。

The overall goal of Project by Jose is to determine D3, D1, and AT1 receptor interaction in the kidney. The D3 dopamine receptor can regulate renal sodium transport and blood pressure independent of the D1 receptor because disruption of the D3 receptor in mice increases blood pressure and impairs their ability to excrete an acute saline load. However, the D3 receptor can also synergistically interact with the D1 receptor to increase sodium excretion. In rodent models of genetic hypertension (Dahl salt sensitive and spontaneously hypertensive rat, SHR), the natriuretic effect of D3 receptors is impaired and the interaction between the D1 and D3 receptor is lost. The impairment of the renal D1 receptor function in genetic hypertension is caused by increased activity of G protein-coupled receptor kinase, type 4 (GRK4). GRK4 gene locus is linked to and GRK4 variants are associated with human essential hypertension. Heterologous expression of these variants in Chinese hamster ovary and HEK cells impairs D1 receptor function and mice overexpressing the GRK4 variant A142V develop hypertension and have an impaired natriuretic response to D1 receptor agonist stimulation. Moreover, inhibition of GRK4 activity in renal proximal tubule cells (or cell lines) from human hypertensives restores D1 receptor function and selective renal inhibition of GRK4 expression attenuates the increase in blood pressure in SHRs. Whether the impaired renal D3 receptor function in genetic hypertension is secondary to increased GRK4 activity, which impairs both the D1 and D3 receptor, is not known. However, D3-/- mice have impaired D1 receptor function, and increased renal renin content and AT1 receptor. Thus, a decreased D1 receptor and an increased AT1 receptor function in D3-/- mice may contribute to their impaired ability to excrete a saline load and hypertension. The overall hypothesis of Project by Jose is that renal proximal tubule sodium transport is regulated, in part, by an interaction among D1, D3 and AT1 receptors, acutely, by receptor/receptor interaction, and chronically, by regulation of receptor expression. Moreover, in genetic hypertension, impaired D3 (and D1) receptor function due to increased GRK4 activity, allows unimpeded AT1 receptor action. Specific aim I will test the hypothesis that D3 receptor deficiency in mice both impairs D1 receptor function and allows unimpeded AT1 receptor function. Specific aim 2 will test the hypothesis that increased GRK4 activity, due to constitutively active variants, impairs D3 receptor function in genetic hypertension. The results of these studies, using molecular biological and pharmacological tools, may shed light into the possibility that ability of GRK4 to regulate several genes may make GRK4 dysfunction a major cause of genetic hypertension.