Regulation of Renal Hemodynamics by Adenosine Mediated Coincident Signaling

说明(申请人提供)：利尿剂用于高血压、心力衰竭、肝功能障碍和慢性肾脏疾病等疾病的药物治疗。这些疾病状态与肾脏交感神经张力增加有关，进而最终导致肾血流量(RBF)和肾小球滤过率(GFR)下降。不幸的是，利尿剂治疗也被证明增加了肾交感神经张力，从而增加了在这些患者中已经存在的对肾脏血流动力学的有害影响。这一效应可能是利尿剂抵抗和不耐受条件下的一个促成机制，这些条件限制了当前利尿剂的治疗潜力。为了解决这一重大的公共卫生问题，正在努力开发适用于保护肾脏血流动力学的慢性治疗的新利尿剂药物。我们实验室的观察表明，选择性A1腺苷受体(A1AR)拮抗剂BG9928可以减轻肾交感神经刺激(RSNs)引起的肾血管收缩。这些发现表明，肾神经效应器连接处A1AR的激活增强了肾交感神经传递。RSNs可以增加神经效应连接中去甲肾上腺素(NE)和三磷酸腺苷(ATP)的浓度(也是将三磷酸腺苷代谢成腺苷的酶)。由于腺苷在调节肾交感神经传递中的确切作用尚不明确，我们的总体目标是研究腺苷增强RSNs的血管收缩反应的机制。同时，我们将展示选择性A1AR拮抗剂在保持良好的肾脏血流动力学的同时发挥利尿作用的方法。由于连接前的A1AR是抑制性的，我们认为连接后的A1AR是腺苷对RSNs反应的主要作用部位。也提出腺苷通过重合信号(通路的汇聚)增强NE的血管收缩作用。为了验证我们的假设，我们将使用多种方法/技术，为这一奖学金申请提供相当大的培训潜力。1)我们将证明，在释放NE的情况下，只有A1AR亚型的拮抗作用可以减少RSNs引起的血管收缩。2)我们将使用A1AR基因敲除动物证明，只有连接后受体的重建才能恢复对RSNs的野生型反应。3)利用离体肾脏和体外实验，我们将论证腺苷和去甲肾上腺素之间一致信号增强RSNs收缩反应的确切机制。该项目的完成，除了巨大的培训潜力外，还将确定腺苷调节肾脏血流动力学的以前未被认识的机制，并支持在肾交感神经张力升高的情况下使用A1AR拮抗剂。从这些实验中获得的信息将引起广大受众的兴趣，从研究肾脏生理学的基础科学家到评估利尿剂治疗的潜在治疗益处和/或并发症的临床医生。 公共卫生相关性：长期使用利尿剂作为心脏、肝脏和肾脏疾病的治疗干预措施，是公共卫生的重大关切。目前的利尿剂虽然在短期疾病治疗中相对有效，但具有不受欢迎的副作用，从而限制了它们的治疗潜力。这项奖学金申请研究了内源性分子腺苷在调节肾交感神经传递中的作用，并将阐明一类新兴利尿剂的作用机制，这些利尿剂针对的是肾脏中的腺苷介导的信号传递。

DESCRIPTION (provided by applicant): Diuretics are used as a pharmacological therapeutic intervention in diseases including hypertension, heart failure, liver dysfunction and chronic kidney disease. These disease states are associated with increased renal sympathetic tone, which in turn, ultimately leads to decreases in both renal blood flows (RBF) and glomerular filtration rate (GFR). Unfortunately, diuretic treatment has been shown to also increase renal sympathetic tone thus adding to the observed deleterious effects on kidney hemodynamics already present in these patients. This effect could be a contributing mechanism underlying the conditions of diuretic resistance and intolerance which limit the therapeutic potential of the current diuretics. To address this significant public health issue, effort is being put forth to develop new diuretic drugs suitable for chronic treatment that preserve renal hemodynamics. Observations from our laboratory demonstrate that BG9928, a selective A1 adenosine receptor (A1AR) antagonist, reduces renal sympathetic nerve stimulation (RSNS)-induced renal vasoconstriction. These findings suggest that A1AR activation in the renal neuroeffector junction potentiates renal sympathetic neurotransmission. RSNS has been shown to increase the concentration of norepinephrine (NE) and ATP (also the enzymes that metabolize ATP to adenosine) in the neuroeffector junction. Since the precise role that adenosine plays in modulating renal sympathetic neurotransmission remains undefined, our overall objective is to examine the mechanism by which adenosine enhances the vasoconstrictive response to RSNS. In conjunction, we will demonstrate the means by which selective A1AR antagonists exert their diuretic effects while preserving favorable renal hemodynamics. Since pre-junctional A1ARs are inhibitory, we suggest here that it is the post-junctional A1ARs that are the predominant site of action of adenosine in response to RSNS. Also propose that adenosine potentiates NE's vasoconstrictive actions via coincident signaling (convergence of pathways). To test our hypothesis, we will use multiple approaches/techniques providing considerable training potential for this fellowship application. 1) We will demonstrate that antagonism of only the A1AR subtype will reduce RSNS-induced vasoconstriction in the presence of released NE. 2) We will show using A1AR knock-out animals that reconstitution of only the post-junction receptors restores the wild-type response to RSNS. 3) Using isolated kidneys and in vitro experiments, we will demonstrate the precise mechanism of coincident signaling between adenosine and NE that increases the vasoconstrictive response to RSNS. The completion of this project, in addition to the significant training potential, will identify a previously unappreciated mechanism for adenosine in regulating renal hemodynamics and support for the use of A1AR antagonists in conditions with elevated renal sympathetic tone. The information obtained from these experiments will be of interest to a broad audience, ranging from basic scientists studying renal physiology to clinical physicians evaluating potential therapeutic benefit and/or complications of diuretic treatment. PUBLIC HEALTH RELEVANCE: The long-term use of diuretics as a therapeutic intervention for diseases of the heart, liver and kidney represents a significant concern for public health. The current classes of diuretics, although relatively effective in short-term disease management, possess undesired side effects thus limiting their therapeutic potential. This fellowship grant application examines the role of the endogenous molecule adenosine in modulating renal sympathetic neurotransmission and will elucidate the mechanism of action of an emerging class of diuretics that target adenosine-mediated signaling in the kidney.