Mechanisms of Catecholaminergic Neurodegeneration

根据儿茶酚醛假说，产生儿茶酚胺多巴胺和去甲肾上腺素的神经元在路易体病（LBD）中是易感的，因为作为正常代谢的一部分在神经元内形成的3，4-二羟基苯乙醛（DOPAL）是对神经元完整性构成持续挑战的自毒素。促进DOPAL形成、增加DOPAL自发氧化、抑制DOPAL解毒或增强DOPAL诱导的蛋白质错误折叠的突变可能干扰将神经递质储存保持在健康范围内（稳态）的过程。DOPAL的有害作用，特别是通过与蛋白质α-突触核蛋白（AS）的相互作用，可能是累积的，并随着时间的推移而发展。将神经递质水平保持在一定范围内的补偿性自我平衡调节最终可能会消失，神经元迅速变性和死亡，以及因儿茶酚胺缺乏而导致的各种表现。 (A)帕金森病患者皮肤、下颌下腺（SMG）和心脏交感神经中的α-突触核蛋白（AS）沉积：一项尸检观察研究：尽管广泛怀疑，但对AS沉积在儿茶酚胺能神经元中的病理生理学意义了解甚少。在一项尸检研究中，我们定量了免疫反应性AS和酪氨酸羟化酶（TH，儿茶酚胺能神经元的标志物）的数量，并同时测定了三个交感去甲肾上腺素能神经支配的结构-皮肤，SMG和myocardum-从尸检证实PD患者的去甲肾上腺素含量。在所有三种组织中，PD患者与年龄匹配的对照组相比AS沉积增加。PD患者的皮肤和SMG样品中去甲肾上腺素和TH含量正常，而在心脏中，PD患者有严重的去甲肾上腺素缺乏和TH降低。这些发现表明，皮肤和SMG中的AS沉积可能是一种非致病性生物标志物，而心脏中交感神经中的AS可能是有毒的（PMID 35260194）。 (B)计算模型揭示了LBD的三阶段进展：当患者出现LBD症状时，已经有大量的儿茶酚胺能神经元损失。确定临床前LBD的生物标志物可能对于最大限度地提高疾病改善治疗的有效性至关重要。然而，临床前LBD中儿茶酚胺能神经变性的进展模式尚不清楚。我们扩展了以前发表的计算模型，该模型结合了多巴胺代谢产物3，4-二羟基苯乙醛（DOPAL）与AS的有害相互作用。建模表明，三阶段的损失，从稳态的第一阶段，以动态平衡和快速的儿茶酚胺消耗在第二阶段，以减缓进一步损失的症状第三阶段的儿茶酚胺含量。LBD患者心脏和壳核的经验性纵向神经影像学数据符合这种三相模式。将计算建模与临床实验室生物标志物相结合来检测临床前疾病，可以实现对LBD实验性治疗试验的疾病进展和靶向特异性神经元内功能障碍的个性化预测（PMID 35621196）。 (C)在PD的大鼠鱼藤酮模型中纹状体DOPAL增加：最近的一些报道表明，PD涉及与DOPAL积累相关的残留儿茶酚胺能神经元中的多种功能异常，这是PD发病机制的儿茶醛假说的焦点。需要一种动物模型，再现异常的儿茶酚胺神经化学模式和DOPAL积累。成年大鼠接受皮下载体或线粒体复合物1抑制剂鱼藤酮10天。与溶剂处理的对照动物相比，鱼藤酮处理的动物具有降低的运动活性，降低的组织多巴胺浓度，降低的囊泡隔离指数和醛脱氢酶活性，以及增加的DOPAL水平。因此，大鼠鱼藤酮模型涉及复制PD壳核中发现的模式的儿茶酚胺能神经元的功能异常，并为研究儿茶醛假说提供了合适的体内平台（PMID 34842277）。 (D)用于儿茶酚胺相关化合物的液相色谱-串联质谱法（LC-MS/MS）：通过液相色谱-电化学检测法对体液中的DOPAL进行生物化学测定在技术上受到限制。为了进一步开发通过测量DOPAL水平来阐明儿茶酚胺能神经变性机制的方法，液相色谱串联质谱法（LC-MS/MS）似乎是必要的。根据一项技术转让协议，我们正在评估市售LC-MS/MS系统是否能灵敏、特异地测量DOPAL和3，4-二羟基苯基乙醇醛（去甲肾上腺素的儿茶酚醛）。

According to the catecholaldehyde hypothesis, neurons that produce the catecholamines dopamine and norepinephrine are susceptible in Lewy body diseases (LBDs), because 3,4-dihydroxyphenylacetaldehyde (DOPAL) formed within the neurons as part of normal metabolism is an autotoxin that poses a continuous challenge to neuronal integrity. Mutations that promote DOPAL formation, increase spontaneous oxidation of DOPAL, inhibit detoxification of DOPAL, or enhance DOPAL-induced misfolding of proteins may interfere with processes that keep neurotransmitter stores within healthy bounds (homeostasis). Harmful effects of DOPAL, especially via interactions with the protein alpha-synuclein (AS), could be cumulative and progress over years. Compensatory, homeostatic adjustments that keep neurotransmitter levels within bounds eventually could give way, with rapid degeneration and death of the neurons and various manifestations resulting from catecholamine deficiency. (A) Alpha-synuclein (AS) deposition in sympathetic nerves in skin, submandibular gland (SMG), and heart in PD: A post-mortem observational study: The pathophysiological significance of AS deposition in catecholaminergic neurons, although widely suspected, has been poorly understood. In a post-mortem study we quantified the amounts of immunoreactive AS and tyrosine-hydroxylase (TH, a marker of catecholaminergic neurons) and concurrently assayed norepinephrine contents in three sympathetic noradrenergically innervated structures--skin, SMG, and myocardum--from patients with autopsy-proven PD. In all three tissues PD patients had increased AS deposition compared to age-matched controls. Norepinephrine and TH contents were normal in skin and SMG samples from PD patients, whereas in the heart, PD patients had severe norepinephrine deficiency and decreased TH. These findings suggest that in skin and SMG AS deposition may be a non-pathogenic biomarker, whereas in the heart AS in sympathetic nerves may be toxic (PMID 35260194). (B) Computational modeling reveals tri-phasic progression of LBDs: By the time a patient develops symptoms of a LBD, there is already substantial loss of catecholaminergic neurons. Identifying biomarkers of preclinical LBDs may be crucial for maximizing the effectiveness of disease-modifying treatments. The pattern of progression of catecholaminergic neurodegeneration in preclinical LBDs, however, has been unknown. We extended on a previously published computational model that incorporates harmful interactions of the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) with AS. The modeling indicated tri-phasic loss of catecholamine contents, from homeostasis in the first phase to dyshomeostasis and rapid catecholamine depletion in the second phase to slow further loss in the symptomatic third phase. Empirical longitudinal neuroimaging data in both the heart and putamen of LBD patients fit with this tri-phasic pattern. Combining computational modeling with clinical laboratory biomarkers to detect preclinical disease may enable individualized predictions about disease progression and target specific intra-neuronal dysfunctions for experimental therapeutic trials in LBDs (PMID 35621196). (C) Increased striatal DOPAL in the rat rotenone model of PD: Several recent reports have indicated that PD involves multiple functional abnormalities in residual catecholaminergic neurons associated with buildup of DOPAL, the focus of the catecholaldehyde hypothesis for the pathogenetic mechanism of PD. An animal model is needed that reproduces the abnormal catecholamine neurochemical pattern and DOPAL accumulation. Adult rats received subcutaneous vehicle or the mitochondrial complex 1 inhibitor rotenone for 10 days. Compared to vehicle-treated control animals, rotenone-treated animals had reduced locomotor activity, decreased tissue dopamine concentrations, reduced indices of vesicular sequestration and of aldehyde dehydrogenase activity, and increased DOPAL levels. The rat rotenone model therefore involves functional abnormalities in catecholaminergic neurons that replicate the pattern found in PD putamen and provides a suitable in vivo platform for studying the catecholaldehyde hypothesis (PMID 34842277). (D) Liquid chromatography with tandem mass spectroscopy (LC-MS/MS) for catecholamine-related compounds: Biochemical assays of DOPAL in body fluids by liquid chromatography with electrocehmical detection are limited technologically. For further development of means to elucidate mechanisms of catecholaminergic neurodegneration by measuring levels of DOPAL, liquid chromatography with tandem mass spectroscopy (LC-MS/MS) seems necessary. Under a technology transfer agreement we are assessing whether a commercially available LC-MS/MS system measures DOPAL and 3,4-dihydroxyphenylglycolaldehyde (the catecholaldehyde of norepinephrine) sensitively and specifically.