Pyruvate dehydrogenase encephalopathy: mechanisms and therapy

摘要 这一建议是丙酮酸脱氢酶(PDH)缺乏症的首批机制研究之一 脑病(PDHD)，一种先天的发育性大脑疾病。PDHD导致大脑新陈代谢受损 和神经功能障碍，表现为婴儿和婴儿的智力残疾和顽固性癫痫发作 孩子们。基本的生化框架已初步阐明在体外使用细胞培养和 匀浆。正常情况下，PDH接收大脑约80%的葡萄糖代谢流量，将其转化为 三羧酸(TCA)循环的底物。三氯乙酸循环负责大脑能量的产生和 也用于合成调节兴奋性的神经递质谷氨酸和GABA。剩下的 20%的大脑葡萄糖补充自然的TCA循环前体损失，这是通过一个单独的过程完成的 这就是所谓的自闭症。然而，在PDHD中，失调症也可以继发下调。然而，尽管 这些由来已久的生化原理，目前尚不清楚PDHD是如何导致脑病的。特别是， 对PDHD脑组织内的新陈代谢或兴奋性知之甚少，而对脑部疾病的了解更少。 VIVO上下文。这一知识鸿沟极大地限制了治疗，pdhd的药物耐受性就是例证。 癫痫发作。这项应用的目的是在体内表征异常的神经兴奋性和 在一个新的，强大的PDHD小鼠模型中的代谢，并通过刺激TCA循环和 用不同的饮食底物恢复。我们的初步结果包括异常的新皮质兴奋性 在活体PDHD和改善大脑TCA周期前体耗竭方面，因此有理由研究这些 更深入的机制。这导致了第一个普遍的假设，即代谢依赖于燃料(而不是 固定的)皮质功能障碍是疾病病理生理学的中心特征。该提案还包括 治疗方面的考虑：含有偶数个碳的酮体，由普通的 饮食脂肪或生酮饮食可以促进TCA循环并改善PDHD患者的癫痫发作，但不能 纠正性欲不足。相比之下，我们的数据显示，外源性无性脂肪代谢产物中含有一种奇数 碳的数量可以补充大脑TCA循环的前体，这导致了第二个普遍的假设： 奇碳脂肪比偶碳脂肪能更有效地恢复PDHD患者的神经功能。这些 两个普遍的假设将在三个目的中被检验：1)研究大脑皮层的电生理基础 2)检测与突触功能相关的关键代谢机制；3)恢复大脑 新陈代谢和兴奋性通过无性欲的奇碳脂肪衍生物。总而言之，我们希望帮助定义 PDHD是一种兴奋性障碍，并确立了逆性调节的治疗价值，从而启动了 医学实践转型的第一步，利用代谢或兴奋的靶点。

ABSTRACT This proposal constitutes one of the first mechanistic investigations of pyruvate dehydrogenase (PDH) deficiency encephalopathy (PDHD), an inborn developmental brain disorder. PDHD leads to impaired brain metabolism and neurological dysfunction that manifests as intellectual disability and intractable seizures in infants and children. The elementary biochemical framework has been elucidated primarily in vitro using cell cultures and homogenates. Normally PDH receives about 80% of the brain’s glucose metabolic flux, converting it into substrate for the tricarboxylic acid (TCA) cycle. The TCA cycle is responsible for brain energy generation and also for the synthesis of the neurotransmitters glutamate and GABA, which regulate excitability. The remainder 20% of brain glucose refills natural TCA cycle precursor loss, which is accomplished through a separate process known as anaplerosis. Yet, anaplerosis can also be secondarily downregulated in PDHD. Nevertheless, despite these long-established biochemical principles, it is unknown how PDHD causes encephalopathy. In particular, very little is known about metabolism or excitability within PDHD brain tissue and even less is known in an in vivo context. This knowledge gap drastically limits therapy, as illustrated by the drug-refractoriness of PDHD seizures. The objectives of this application are to characterize in vivo abnormal neural excitability and metabolism in a novel, robust PDHD mouse model and to mitigate them by stimulating both the TCA cycle and anaplerosis with alternative dietary substrates. Our preliminary results include abnormal neocortical excitability in PDHD in vivo and amelioration of brain TCA cycle precursor depletion, and thus justify investigating these mechanisms in greater depth. This leads to a first general hypothesis that metabolic fuel-dependent (rather than fixed) cortical dysfunction is a central feature of disease pathophysiology. The proposal also includes the therapeutic consideration that ketone bodies containing an even number of carbons, generated from common dietary fats or a ketogenic diet, can fuel the TCA cycle and ameliorate seizures in PDHD patients, but cannot correct anaplerotic deficits. In contrast, our data that exogenous anaplerotic fat metabolites containing an odd number of carbons can additionally refill brain TCA cycle precursors, lead to a second general hypothesis: That odd-carbon fat restores neural function in PDHD more effectively via anaplerosis than even-carbon fat. These two general hypotheses will be tested in three aims: 1) Investigate the electrophysiological bases of cortical hyperexcitability in PDHD; 2) Test key metabolic mechanisms relevant to synaptic function; 3) Restore brain metabolism and excitability via anaplerotic odd-carbon fat derivatives. In summary, we expect to help define PDHD as an excitability disorder and establish the therapeutic value of anaplerotic modulation, thus initiating the first step of a medical practice transformation by capitalizing on metabolic or excitable targets.