Regulation of Brain Glucose Metabolism by Alternate Fuels in Type 1 Diabetes

描述（由申请人提供）：通过强化胰岛素治疗使血糖水平正常化可降低糖尿病并发症的发生率。然而，此类治疗方案的益处仍然受到频繁且严重的低血糖发作的限制。这些事件会削弱大脑检测低血糖和激活反调节防御的能力，进一步增加随后发生低血糖的风险。因此，低血糖可能在没有任何警告症状的情况下或在睡眠期间发生，这凸显了采取预防策略并尽量减少其潜在不良后果（如癫痫发作、昏迷和永久性损伤）的必要性。这个问题在 1 型糖尿病 (T1DM) 中尤其值得关注，最近的研究表明，患者生命早期发生的严重且反复发生的低血糖可能会导致认知障碍和持久的脑损伤。此前，我们发现一元羧酸乙酸盐的转运和代谢在 T1DM 和复发性低血糖大鼠模型中上调，表明替代燃料消耗的增加在低血糖无意识中起着重要作用。然而，当我们研究更相关的替代燃料乳酸时，我们惊讶地发现，增强的乳酸运输并没有与增加的乳酸利用率同时出现，而是刺激了大脑葡萄糖代谢。我们在啮齿类动物中的观察结果已被最近一项针对 T1DM 受试者的研究所证实。这些发现支持乳酸在 T1DM 低血糖期间具有双重作用的概念，既作为葡萄糖代谢的底物又作为葡萄糖代谢的激活剂。最近，我们通过其对神经元丙酮酸脱氢酶（PDH）复合物活性的影响，对这种乳酸悖论有了更多的了解。我们的初步结果表明，PDH 在低血糖期间受到抑制，并且这种抑制可以通过血浆乳酸逆转。如果这个模型是正确的，T1DM 中保留的葡萄糖代谢可能在低血糖无意识中发挥重要作用，这是由于转运升高提高了脑乳酸水平并防止了 PDH 的抑制。因此，该提案的总体目标是确定反复低血糖背景下脑乳酸和葡萄糖代谢的相互作用，以建立 T1DM 患者维持脑代谢（和功能）并意识不到低血糖的分子机制。我们将使用 NMR 波谱来确定 13C 标记的葡萄糖和乳酸在复发性低血糖情况下对大脑代谢的贡献。此外，我们将使用药理学和 siRNA 敲低方法来确定 PDH 抑制激酶在低血糖情况下抑制 PDH 通量的作用。这些研究结果与人类的相关性将通过核磁共振波谱法在未意识到低血糖的 T1DM 患者和使用 13C-葡萄糖和乳酸的匹配对照中进行测试。

DESCRIPTION (provided by applicant): Normalization of blood glucose levels via intensive insulin therapy reduces the incidence of diabetic complications. However, the benefits of such treatment regimens remain limited by frequent and severe bouts of hypoglycemia. These episodes diminish the brain's capacity to detect hypoglycemia and to activate counterregulatory defenses, further increasing the risk of subsequent hypoglycemia. As a result, hypoglycemia can occur without warning symptoms or during sleep, underscoring the need for preventive strategies and of minimizing its potential adverse consequences like seizures, coma and permanent injury. This issue is of particular concern in type 1 diabetes (T1DM) where recent studies suggest that severe and recurrent hypoglycemia occurring early in a patient's life can result in cognitive impairment and lasting brain damage. Previously we found that transport and metabolism of the monocarboxylic acid acetate was upregulated in T1DM and in a recurrent hypoglycemia rat model indicating that enhanced alternate fuel consumption plays a major role in hypoglycemia unawareness. However, when we studied the more relevant alternate fuel lactate, we found to our surprise that enhanced lactate transport did not go hand in hand with increased lactate utilization, but stimulated brain glucose metabolism instead. Our observations in rodents have since been confirmed by a recent study in T1DM subjects. These findings support the concept of lactate having a dual role during hypoglycemia in T1DM, as both a substrate and as an activator of glucose metabolism. We have recently gained additional insight into this lactate paradox through its impact on neuronal pyruvate dehydrogenase (PDH) complex activity. Our preliminary results suggest that PDH is inhibited during hypoglycemia, and that this inhibition can be reversed by plasma lactate. If this model is correct the preserved glucose metabolism in T1DM, which may play an important role in hypoglycemia unawareness, is due to elevated transport raising brain lactate levels and preventing inhibition of PDH. Thus, the overall goal of this proposal is to define the interplay of brain lactate and glucose metabolism in the context of recurrent hypoglycemia to establish the molecular mechanism by which T1DM patients sustain brain metabolism (and function) and become unaware of hypoglycemia. We are going to use NMR spectroscopy to define the contributions of 13C-labeled glucose and lactate to brain metabolism in the setting of recurrent hypoglycemia. In addition we will use pharmacologic and siRNA knockdown approaches to determine the role of PDH inhibiting kinases in the suppression of PDH flux under hypoglycemia. The human relevance of these findings will be tested by NMR spectroscopy in T1DM patients with hypoglycemia unawareness and matched controls using 13C-glucose and lactate.