Mechanism for Reduced Adrenomedullary Epinephrine Release in Type 1 Diabetes

描述(申请人提供)：胰升糖素的释放，一种支持对急性低血糖的正常反调节反应(CRR)的主要荷尔蒙，在1型糖尿病(T1 DM)中基本上是不存在的。在缺乏它的情况下，其他循环中的CRR激素，如肾上腺素，在将血糖恢复到基础水平方面起着首要作用。然而，在T1 DM患者中，因低血糖而释放的肾上腺素也会减弱，这使得糖尿病患者特别容易出现无症状低血糖，如果不治疗，可能会导致昏迷和死亡。这一缺陷在肾上腺髓质(AM)的水平上进行了最低限度的研究，肾上腺髓质产生了体内所有循环中的肾上腺素。AM中的嗜铬细胞合成肾上腺素，并在中枢神经系统或其他循环激素的激活下释放。我们的初步数据显示，从链脲佐菌素(STZ)治疗的糖尿病大鼠分离的肾上腺髓质嗜铬细胞中，M胆碱乙酰胆碱受体(MAchR)信号转导受损，而3型mAchR是肾上腺髓质中的主要受体亚型，在糖尿病大鼠嗜铬细胞中内化的程度比对照组要大得多。这些数据使我假设，T1 DM患者肾上腺髓质mAchR的内在化减少了对低血糖的肾上腺素释放。为了验证这一假设，我计划：(1)确定糖尿病发病后这一缺陷发生的时间、减少的程度、缺陷的特异性以及糖尿病高血糖和低胰岛素血症在其发展中的参与程度。糖尿病的STZ模型将用于这些研究。体内实验将被用来研究在T1 DM期间对降糖和非降糖刺激的肾上腺髓质反应减弱的发展。分离的肾上腺和酶分离的嗜铬细胞将被用来评估烟碱和毒碱乙酰胆碱信号和肾上腺肾上腺素含量对这一缺陷的贡献。(2)通过检测糖尿病大鼠肾上腺髓质嗜铬细胞乙酰胆碱受体亚型烟碱能和毒碱能受体的mRNA、蛋白水平、细胞定位和功能特性，探讨肾上腺髓质嗜铬细胞乙酰胆碱受体在STZ诱导糖尿病时的功能特性。建议的实验结果将为肾上腺髓质肾上腺素释放缺陷奠定细胞基础，肾上腺素释放缺陷有助于T1 DM患者CRR的降低。健康相关性：该项目旨在调查糖尿病患者体内对低血糖反应的调节缺陷的细胞学基础。这一缺陷限制了基于胰岛素的治疗。 公共卫生相关性：该项目旨在调查糖尿病患者体内对低血糖反应的调节缺陷的细胞学基础。这一缺陷限制了基于胰岛素的治疗。

DESCRIPTION (provided by applicant): Release of glucagon, a principal hormone underlying the normal counter-regulatory response (CRR) to acute hypoglycemia is largely absent in type 1 diabetes mellitus (T1DM). In its absence, other circulating CRR hormones, such as epinephrine, take on primary importance in restoring plasma glucose to basal levels. However, epinephrine release in response to hypoglycemia is also attenuated in T1DM, making diabetic patients particularly prone to asymptomatic hypoglycemia that, if untreated, can lead to coma and death. This defect has been minimally studied at the level of the adrenal medulla (AM) which produces most of all circulating epinephrine in the body. Chromaffin cells in the AM synthesize epinephrine and release it when activated by the central nervous system or other circulating hormones. Our preliminary data show that muscarinic acetylcholine receptor (mAchR) signaling is impaired in adrenomedullary chromaffin cells isolated from streptozocin (STZ)-treated diabetic rats and that type 3 mAchR, a predominant receptor subtype in the adrenal medulla, is internalized to a much greater degree in diabetic chromaffin cells than in controls. These data led me to hypothesize that internalization of adrenomedullary mAchR in T1DM reduces epinephrine release in response to hypoglycemia. To test this hypothesis, I plan to: (1) Determine the time after the on-set of diabetes when this defect occurs, the extent of the reduction, the specificity of the deficit and the involvement of diabetic hyperglycemia and hypoinsulinemia in its development. The STZ model of diabetes will be used in these studies. In vivo experiments will be performed to study the development of reduced adrenomedullary response to hypoglycemic and non-hypoglycemic stimuli during T1DM. Isolated adrenal glands and enzymatically- isolated chromaffin cells will be used to evaluate the contributions of nicotinic and muscarinic acetylcholine signaling and adrenal epinephrine content to this deficit. (2) Investigate the functional properties of acetylcholine receptors in adrenomedullary chromaffin cells during STZ-induced diabetes by measuring mRNA, protein levels, cellular localization and functional properties of nicotinic and muscarinic acetylcholine receptor subtypes in chromaffin cells from diabetic animals. The results of the proposed experiments will establish the cellular basis for the adrenal medullary defect in epinephrine release that contributes to the reduced CRR in T1DM. Health relevance: This project seeks to investigate the cellular basis for defective regulation of the body's response to low blood glucose in diabetic patients. This defect limits insulin-based therapies. PUBLIC HEALTH RELEVANCE: This project seeks to investigate the cellular basis for defective regulation of the body's response to low blood glucose in diabetic patients. This defect limits insulin-based therapies.