Modulation of neural function in energy failure

描述(申请人提供)：人类葡萄糖转运蛋白I型缺乏(G1D)导致大脑葡萄糖流入减少和神经功能障碍，主要表现为癫痫。正常情况下，大多数葡萄糖被完全降解为二氧化碳和水，通过三羧酸(TCA)循环产生大脑能量，三羧酸循环也是合成和利用神经递质谷氨酸和GABA的核心。重要的是，一小部分葡萄糖并不直接产生能量，而是通过一种称为回旋反应的反应来补充自然的TCA循环前体损失。尽管这些生化原理由来已久，但目前尚不清楚大多数损害大脑新陈代谢并导致癫痫发作的疾病是如何扰乱脑组织(而不是体外)内的兴奋性的，包括导致棘波癫痫的G1D。这种对机制的认识差距严重限制了治疗，正如G1D的抗惊厥耐药性所表明的那样，这也是许多其他神经代谢疾病的规则。我们的实验室和临床的长期目标是机械地了解患者和小鼠模型中的这些大脑代谢-兴奋性关系，以开发药物和饮食疗法。本应用程序的目的是描述一种新的、健壮的G1D小鼠模型的过度兴奋性，并通过用饮食底物刺激失水和TCA循环来缓解这种过度兴奋。我们的人类数据和初步实验室结果，如在G1D小鼠中发现TCA周期前体耗竭以及新皮质和丘脑异常兴奋性，证明有理由更深入地研究这些机制，以了解癫痫超同步性是人类和小鼠G1D的中心特征。这导致了一个主要假设，即突触功能障碍对疾病病理生理学至关重要。该提案还包括治疗方面的考虑，即从普通饮食脂肪或生酮饮食中产生的偶数碳酮可以为TCA循环提供燃料，并缓解G1D的癫痫发作，但不会止痛。相比之下，我们的数据打开了一个新的治疗机会，因为在G1D中，注射奇碳脂肪有效地补充了大脑TCA周期的前体；导致了额外的假设，即它通过恢复神经功能比偶碳脂肪更有效。这些假说将在三个目标中得到验证：1)研究G1D中皮层过度兴奋的基础；2)将这一机械方法扩展到丘脑；3)通过恢复大脑代谢和功能。这项提议意义重大，因为它利用一个信息量非常大的小鼠模型，将重点放在脑组织中的新陈代谢-兴奋性关系和恢复上，这代表了神经代谢疾病方法的转变，在神经代谢疾病中，电生理学、13C核磁共振和质谱学提供了有助于潜在疗法的机制的补充理解。特别创新的是，结合了对电路或大脑关键区域突触功能的研究 对于癫痫、行为受损或智力低下，随着对清醒小鼠大脑代谢敏感的方法学的发展，对其他脑病具有广泛的适用性。综上所述，我们预计这项提议将有助于将G1D定义为突触障碍，并使其易于兴奋或代谢靶点的修饰。 公共卫生相关性：大多数癫痫是由参与能量代谢的基因突变引起的，是难治性的，只有通过终身姑息努力才能缓解。 构成了一个重要的健康问题。了解这些疾病是不断扩大的致残性疾病的一部分，如何与癫痫发作相关，通过发现大脑功能的新基本方面，并促进旨在恢复大脑能量和兴奋平衡的潜在疗法的开发，完成了NIH的使命。

DESCRIPTION (provided by applicant): Human glucose transporter type I-deficiency (G1D) leads to reduced brain glucose influx and neurological dysfunction principally manifested as epilepsy. Normally, most glucose is fully degraded into CO2 and water for brain energy generation via the tricarboxylic acid (TCA) cycle, which is also central to the synthesis and utilization of the neurotransmitters glutamate and GABA. Importantly, a fraction of glucose does not directly generate energy, but refills natural TCA cycle precursor loss through a reaction termed anaplerosis. Despite these long-established biochemical principles, it is unclear how most diseases that impair brain metabolism and cause seizures disrupt excitability within brain tissue (rather than in vitro), including G1D, which leads to spike-wave epilepsy. This knowledge gap about mechanisms critically limits treatment, as illustrated by anticonvulsant resistance in G1D, which is also the rule in many other neurometabolic disorders. Our laboratory and clinical long-term goal is to mechanistically understand these brain metabolism-excitability relationships in patients and mouse models to develop pharmacological and dietary therapies. The objectives of this application are to characterize hyperexcitability in a novel, robust G1D mouse model and to mitigate it by stimulating both anaplerosis and the TCA cycle with dietary substrates. Our human data and preliminary laboratory results, such as the finding of TCA cycle precursor depletion and of abnormal neocortical and thalamic excitability in G1D mice, justify investigating these mechanisms in more depth to understand epileptic hypersynchronization as a central feature of human and murine G1D. This leads to the main hypothesis that synaptic dysfunction is critical for disease pathophysiology. The proposal also includes the therapeutic consideration that even-carbon ketones, generated from common dietary fats or a ketogenic diet, can fuel the TCA cycle and ameliorate seizures in G1D, but are not anaplerotic. In contrast, our data open a new therapeutic opportunity because administered odd-carbon fat refills brain TCA cycle precursors efficiently in G1D; leading to the additional hypothesis that it restores neural functio more effectively than even-carbon fat via anaplerosis. The hypotheses will be tested in three aims: 1) Investigate the basis of cortical hyperexcitability in G1D; 2) Expand this mechanistic approach to the thalamus; 3) Restore brain metabolism and function via anaplerosis. The proposal is significant because its focus on metabolism-excitability relationships and anaplerosis in brain tissue using a very informative mouse model represents a shift in approach to neurometabolic diseases, where electrophysiology, 13C NMR and mass spectrometry offer a complementary understanding of mechanisms conducive to potential therapies. Particularly innovative is to combine an investigation of synaptic function in circuits or brain regions crucial for epilepsy, impaired behavior or mental retardation with the development of methodology sensitive to conscious mouse brain metabolism with broad applicability to other encephalopathies. In summary, we expect that this proposal will help define G1D as a synaptic disorder and render it amenable to excitable or metabolic target modification. PUBLIC HEALTH RELEVANCE: Most epilepsies caused by mutations in genes involved in energy metabolism are intractable and can only be alleviated by life-long palliative efforts, which constitutes an important health problem. Understanding how these disorders, which are part of an expanding group of disabling diseases, are associated with seizures fulfills the NIH mission by uncovering new fundamental aspects of brain function and by facilitating the development of potential therapies aimed to restore brain energy and excitation balance.