ROLE OF GLUCOSE IN hAT1 GENE EXPRESSION

点击翻译按钮获取中文摘要

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 codes 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 AT1gene 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 repressor 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 h AT1 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 repressor 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 path physiology such as diabetes and hypertension.