Purinergic regulation of the renal microvasculature

自动调节控制是肾小球前微血管系统的一种固有特性，它涉及肌源性控制管腔直径，并结合肾小管球球反馈(TGF)机制增强能力。远端肾小管的致密黄斑细胞充当监测远端肾小管液体流动和/或成分的“传感器”。确切地说，致密黄斑如何传达调节传入小动脉阻力的需要以及“信使分子”的身份仍然知之甚少。我们实验室以前的研究得出了我们的中心假设，即ATP通过激活P2X1和P2Y2受体介导依赖于转化生长因子的肾血管收缩，从而在预防高血压肾小球损伤中发挥重要作用。贝尔和他的同事最近报告说，致密斑细胞确实会对刺激转化生长因子信号的刺激做出反应，从而释放三磷酸腺苷。我们已经证明了P2X1的失活 受体信号，同时中断自动调节的血管收缩。高血压动物肾脏的自我调节能力和P2X1受体激活均受损。因此，P2X1受体的激活可能是研究高血压引起的自我调节能力下降的机制的一个可能的靶点。腺苷也被认为是介导转化生长因子反应的信号分子，最近使用A1受体基因敲除小鼠进行的工作重新引起了人们对这一想法的兴趣。这一假设规定 转化生长因子介导的传入小动脉血管收缩涉及A1受体的激活。目前的提案将全面审视这两个相互竞争的假说，并将解决在确定导致转化生长因子的信号机制方面存在的几个重要问题。实验将使用独特的P2X1和A1受体基因敲除小鼠进行，并将直接检查微血管自动调节控制的机制。研究分为三个具体目标。具体目标1将检验以下假设 在缺乏P2X1受体的小鼠中，转化生长因子介导的血管收缩功能受损。具体目标2将验证这一假说，即钙内流和Rho-Kinase通路的激活有助于由P2X1和P2Y2受体激活所引起的持续的自调性血管收缩。具体目标3将验证这样的假设，即去除P2X1受体将加剧高血压相关的肾脏损伤，以回应血管紧张素II依赖、盐敏感的高血压。这些研究结果将为P2X1受体介导的肾微血管功能调节机制，以及与肾小球前自我调节功能受损相关的肾损害与P2X1受体激活之间的关系提供新的信息。

Autoregulatory control is an intrinsic property of the preglomerular microvasculature that involves myogenic control of lumenal diameter combined with the tubuloglomerular feedback(TGF) mechanism for enhanced capability. Macula densa cells of the distal tubule serve as "sensors" monitoring distal tubular fluid flow and/or composition. Exactly, how the macula densa communicates the need to adjust afferent arteriolar resistance and the identity of the "messenger molecule" remains poorly understood. Previous studies from our laboratory have led to our central hypothesis that ATP mediates TGF-dependent renal vasoconstriction via P2X1 and P2Y2 receptor activation, and thereby plays an important role in preventing hypertensive glomerular injury. Bell and coworkers recently reported that macula densa cells indeed release ATP in response to stimuli that evoke TGF signals. We have shown that inactivation of P2X1 receptor signaling, simultaneously interrupts autoregulatory vasoconstriction. Both autoregulatory capability and P2X1 receptor activation are impaired in kidneys from hypertensive animals. Therefore, P2X1 receptor activation is a likely target for investigating the mechanisms responsible for the hypertension-induced decline in autoregulatory capability. Adenosine is also postulated as the signaling molecule mediating TGF responses, and recent work, performed using A 1 receptor knockout mice, has renewed interest in this idea. The hypothesis dictates that TGF-mediated, afferent arteriolar vasoconstriction involves activation of A1 receptors. The current proposal will take a comprehensive look at these two competing hypotheses and will resolve several important questions that exist regarding identification of the signaling mechanism responsible for TGF. Experiments will be performed using unique P2X1 and A1 receptor knockout mice and will directly examine the mechanisms of microvascular autoregulatory control. Studies are divided into three specific aims. Specific aim 1 will test the hypothesis that TGF-mediated vasoconstriction is impaired in mice lacking the P2X1 receptor. Specific aim 2 will test the hypothesis that calcium influx and activation of the Rho-kinase pathway contribute to the sustained autoregulatory vasoconstriction evoked by P2X1 and P2Y2 receptor activation. Specific aim 3 will test the hypothesis that P2X1 receptor ablation will exacerbate hypertension related renal injury in response to angiotensin II-dependent, salt-sensitive hypertension. The results of these studies will provide new information on the mechanisms of P2X1 receptor mediated regulation of renal microvascular function, and the relationship between P2X 1 receptor activation and renal damage associated with impairment of preglomerular autoregulatory performance.