ROLE OF GLUCOSE IN hAT1 GENE EXPRESSION

描述（由申请人提供）：高血压和糖尿病是糖尿病肾病发病机制中的两个主要危险因素。血管紧张素转换酶抑制剂治疗在糖尿病肾病患者中广泛有效，提示肾素血管紧张素系统在这种疾病的进展中起重要作用。血管紧张素II是肾素血管紧张素系统的活性成分，主要通过血管紧张素1型（AT 1）受体发挥作用。与大鼠中两个基因（AT 1A、AT 1B）编码AT 1受体相比，在人类中，单个基因编码血管紧张素1（hAT 1），这表明该受体的种属特异性表达和差异调节。在糖尿病中，从发病到终末期肾病，hAT 1受体表达在肾脏的不同区域中变化，但有一个例外，即近端小管，在近端小管中，该受体始终下调，表明受体的小管特异性调节。hAT 1受体的减少不能被ACE抑制剂逆转，表明受体下调不是由血管紧张素II的上调介导的。导致糖尿病中hAT 1受体下调的分子机制尚不清楚。近端小管中AT 1基因表达的任何改变（增加/减少）都具有显著的病理生理学后果。我们假设，在正常的生理，表达的hAT 1受体是通过正常的相互作用，葡萄糖和胰岛素之间的hAT 1基因转录。或者，在糖尿病中，当细胞外葡萄糖水平高而胰岛素水平低时，葡萄糖和胰岛素之间的平衡相互作用将发生变化，最终结果将是hAT 1基因表达降低。最近，我们已经确定了一个特定的序列在hAT 1基因启动子所需的基础转录和功能作为胰岛素反应（增强）元件。进一步的研究揭示了增强子上游的阻遏元件，其可以响应正常/高水平的细胞外葡萄糖。我们的观察结果是，在葡萄糖（正常/高）的存在下，胰岛素对hAT 1转录抑制没有增强作用，而在不存在葡萄糖或存在低葡萄糖的情况下，胰岛素增强hAT 1基因转录。此外，我们有证据表明，这些调控元件识别特定的核transacting因子诱导的葡萄糖和胰岛素。我们的观察是第一个证据表明，hAT 1基因转录的生理水平是由一个阻遏元件控制，可能通过葡萄糖和胰岛素之间的相互作用。虽然我们认识到葡萄糖和胰岛素都是hAT 1转录的重要调节因子，但在本提案中，我们将主要关注葡萄糖介导的hAT 1基因转录。因此，本申请的总体目标是确定葡萄糖在控制hAT 1基因转录中的功能意义，并鉴定与葡萄糖信号传导相关的特异性反式作用因子的作用，以了解在糖尿病和高血压等病理生理学中参与hAT 1基因调控的分子和生化机制。 非技术描述：激素血管紧张素II通过其受体蛋白在糖尿病介导的肾脏疾病的发展中起着非常重要的作用。在这项研究中，我们建议确定受体基因的调节和肾脏中高葡萄糖控制的因素。有了这些信息，我们希望能更好地了解受体的作用，并为糖尿病肾病的管理和治疗提供方向。

DESCRIPTION (provided by applicant): Hypertension and diabetes are two major risk factors in the pathogenesis of diabetic nephropathy. Angiotensin converting enzyme inhibitor therapy is broadly effective in patients with diabetic nephropathy suggesting an important role for renin angiotensin system in the progression of this disorder. Angiotensin II, the active component of the renin angiotensin system, acts primarily through angiotensin type 1 (AT1) receptors. Compared to rat in which two genes (AT1A, AT1B) code for AT1 receptor, in humans, a single gene code for angiotensin type 1 (hAT1), suggesting species specific expression and differential regulation of the receptor. In diabetes, from the onset to end-stage nephropathy, hAT1 receptor expression varies in different regions of the kidney with one exception, the proximal tubule in which, this receptor is down regulated at all times suggesting tubule specific regulation of the receptor. Reduction in hAT1 receptors could not be reversed by ACE inhibitors demonstrating that the receptor downregulation was not mediated by the up-regulation of angiotensin II. The molecular mechanisms leading to hAT1 receptor down-regulation in diabetes are not known. Any alterations (increase/decrease) in AT1 gene expression in proximal tubule have significant pathophysiological consequences. We hypothesize that in normal physiology, expression of the hAT1 receptor is achieved by normalized interactions between glucose and insulin on hAT1 gene transcription. Alternatively, in diabetes, when extracellular glucose levels are high and insulin levels are low, the equilibrium interaction between glucose and insulin will shift and the end-result will be decreased expression of hAT1 gene. Recently we have identified a specific sequence in the hAT1 gene promoter required for its basal transcription and functions as an insulin response (enhancer) element. Additional studies revealed a represser element upstream of the enhancer that can respond to normal/high levels of extracellular glucose. Our observation is that in the presence of glucose (normal/high), insulin has no enhancer effect on hAT1 transcriptional repression, where as in the absence of glucose or presence of low glucose insulin enhances the hAT1 gene transcription. In addition, we have evidence that these regulatory elements recognize specific nuclear transacting factors induced by glucose and insulin. Our observation is the first evidence that physiological levels of hAT1 gene transcription is controlled by a represser element perhaps through an interplay between glucose and insulin. Although we recognize that both glucose and insulin are important regulators of hAT1 transcription, in this proposal we will focus primarily on glucose mediated hAT1 gene transcription. Therefore, the overall goal of this application is to determine the functional significance of glucose in the control of hAT1 gene transcription and identify the role of specific transacting factors associated with glucose signaling in order to understand the molecular and biochemical mechanisms involved in the regulation of hAT1 gene in pathophysiology such as diabetes and hypertension. Non Technical description: Hormone angiotensin II through its receptor protein plays a very important role in the development of diabetes mediated kidney diseases. In this study we are proposing to identify the regulation of the receptor gene and factors that are controlled by high glucose in the kidney. With this information we are hoping to obtain a better understanding of the receptor action, and also a direction in the management and treatment of kidney diseases in diabetes.