Aromatic L-Amino Acid Decarboxylase (AADC) Is Crucial for Brain Development and Motor Functions

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare pediatric neuro-metabolic disease in children. Due to the lack of an animal model, its pathogenetic mechanism is poorly understood. To study the role of AADC in brain development, a zebrafish model of AADC deficiency was generated. We identified an aadc gene homolog, dopa decarboxylase (ddc), in the zebrafish genome. Whole-mount in situ hybridization analysis showed that the ddc gene is expressed in the epiphysis, locus caeruleus, diencephalic catecholaminergic clusters, and raphe nuclei of 36-h post-fertilization (hpf) zebrafish embryos. Inhibition of Ddc by AADC inhibitor NSD-1015 or anti-sense morpholino oligonucleotides (MO) reduced brain volume and body length. We observed increased brain cell apoptosis and loss of dipencephalic catecholaminergic cluster neurons in ddc morphants (ddc MO-injected embryos). Seizure-like activity was also detected in ddc morphants in a dose-dependent manner. ddc morphants had less sensitive touch response and impaired swimming activity that could be rescued by injection of ddc plasmids. In addition, eye movement was also significantly impaired in ddc morphants. Collectively, loss of Ddc appears to result in similar phenotypes as that of ADCC deficiency, thus zebrafish could be a good model for investigating pathogenetic mechanisms of AADC deficiency in children.芳香族L-氨基酸脱羧酶（Aromatic L-amino acid decarboxylase, AADC）缺乏症是一种罕见的儿童神经代谢疾病。由于缺乏合适的动物模型，其致病机制迄今尚未被充分阐明。为探究AADC在大脑发育中的作用，本研究成功构建了AADC缺乏症的斑马鱼（zebrafish）模型。我们在斑马鱼基因组中鉴定出aadc基因的同源物——多巴脱羧酶（dopa decarboxylase, ddc）基因。整体原位杂交（whole-mount in situ hybridization）分析显示，受精后36小时（hours post-fertilization, hpf）的斑马鱼胚胎中，ddc基因表达于松果体、蓝斑、间脑儿茶酚胺能神经元簇以及中缝核。使用AADC抑制剂NSD-1015或反义吗啉代寡核苷酸（anti-sense morpholino oligonucleotides, MO）抑制Ddc功能后，斑马鱼的脑容量减小、体长缩短。我们在ddc敲低胚胎（即注射ddc MO的胚胎，ddc morphants）中观察到脑细胞凋亡增加，且间脑儿茶酚胺能神经元簇的神经元丢失。此外，ddc敲低胚胎还呈现出剂量依赖性的癫痫样活动。ddc敲低胚胎的触觉反应敏感性降低，游泳行为受损，该表型可通过注射ddc质粒得以挽救。同时，ddc敲低胚胎的眼球运动也显著受损。综上，Ddc功能缺失所导致的表型与AADC缺乏症高度相似，因此斑马鱼可作为研究儿童AADC缺乏症致病机制的理想模型。