Role of glucocorticoids in hypoglycemia unawareness

描述(申请人提供)：I型糖尿病强化胰岛素治疗的危险并发症是低血糖、意识不清和反调节失败。低血糖诱导的糖皮质激素分泌与促进对低血糖的自主神经反应的丧失有关。然而，糖皮质激素本身既是反调节激素，也是维持肾上腺素分泌所必需的，肾上腺素是最快速和有效的反调节反应之一。这些相反的糖皮质激素作用对预防复发性低血糖的相对影响尚不清楚。此外，糖皮质激素和它们的主要神经调节因子促肾上腺皮质激素释放激素(CRH)不仅相互影响，而且可能对交感神经张力有相反的作用。阐明糖皮质激素对自主神经活动的作用机制和影响将有助于预防糖尿病患者的低血糖意识。为了解决这些问题，R21应用程序建议(目标1)改进低血糖诱导的逆调节失败的小鼠模型，与范德比尔特大学小鼠代谢生理学核心的研究人员密切合作，在小鼠反复低血糖的治疗方案中使用降糖钳技术。着眼于肾上腺髓质肾上腺素分泌是糖皮质激素依赖的逆调节的关键方面，我们将(目标2)在CRH基因敲除小鼠(CRH KO)中使用生理性糖皮质激素替代，以确定糖皮质激素与CRH对急性低血糖诱导的逆调节激素分泌和肾上腺髓质激活的相对影响。然后，我们将(目标3)将目标1中定义的复发性低血糖程序与目标2中的糖皮质激素操作相结合，以检验糖皮质激素独立于CRH抑制交感肾上腺对复发性低血糖反应的假设。最后，为了确定糖皮质激素对肾上腺素分泌相反作用的潜在神经机制，我们将(目标4)定位来自Aim 3的急性和反复低血糖WT和CRH KU小鼠大脑中神经元活动标记基因(c-fos)和特定神经递质表达的糖皮质激素依赖的变化。这些实验将建立低血糖无意识的小鼠模型，解决糖皮质激素对交感-肾上腺活性的相互冲突的影响，并揭示低血糖诱导的逆调节失败的潜在机制。

DESCRIPTION (provided by applicant): Hypoglycemia unawareness and counterregulatory failure are dangerous complications of intensive insulin therapy in type I diabetes. Hypoglycemia-induced glucocorticoid secretion has been implicated in promoting loss of autonomic responses to hypoglycemia. However, glucocorticoids are both counterregulatory hormones themselves and essential for maintaining secretion of epinephrine, one of the most rapid and effective counterregulatory responses. The relative influence of these opposing glucocorticoid actions on defenses against recurrent hypoglycemia are unknown. In addition, glucocorticoids and their primary neural regulator, corticotropin-releasing hormone (CRH), not only influence one another reciprocally but may also have opposing effects on sympathetic tone. Elucidating the mechanisms and impact of glucocorticoid effects on autonomic activity will aid in preventing hypoglycemia unawareness in diabetic patients. To address these issues, this R21 application proposes to (Aim 1) refine a mouse model of hypoglycemia-induced counterregulatory failure, working closely with investigators at the Mouse Metabolic Physiology Core of Vanderbilt University to use hypoglycemic clamp techniques in protocols for recurrent hypoglycemia in mice. Focusing on adrenomedullary epinephrine secretion as a key, glucocorticoid-dependent aspect of counterregulation, we will (Aim 2) use physiological glucocorticoid replacement in CRH knockout mice (CRH KO) to define the relative influence of glucocorticoids vs. CRH on counterregulatory hormone secretion and adrenomedullary activation induced by acute hypoglycemia. We will then (Aim 3) combine the recurrent hypoglycemia procedures defined in Aim 1 with the glucocorticoid manipulations of Aim 2 to test the hypothesis that glucocorticoids inhibit sympathoadrenal responses to recurrent hypoglycemia independently of CRH. Lastly, to identify potential neural mechanisms for the opposing effects of glucocorticoids on epinephrine secretion, we will (Aim 4) map glucocorticoid-dependent changes in expression of marker genes for neuronal activity (c-fos) and specific neurotransmitters in brains of acutely and recurrently hypoglycemic WT and CRH KU mice from Aim 3. These experiments will establish a mouse model for hypoglycemia unawareness, resolve the conflicting effects of glucocorticoids on sympathoadrenal activity, and reveal potential mechanisms for hypoglycemia-induced counterregulatory failure.