Abstract：
Citrullinemia type 1 (CTLN1) is a rare autosomal recessive urea cycle disorder caused by deficiency of the cytosolic enzyme argininosuccinate synthetase 1 (ASS1) due to pathogenic variants in the ASS1 gene located on chromosome 9q34.11. Even though hyperammenomia is considered the major pathomechanistic factor for neurological impairment and cognitive dysfunction, a relevant subset of individuals presents with a neurodegenerative course in the absence of hyperammonemic decompensations. Here we show, that ASS1 deficiency induced by antisense-mediated knockdown of the zebrafish ASS1 homologue is associated with defective neuronal differentiation ultimately causing neuronal cell loss and consecutively decreased brain size in zebrafish larvae in vivo. Whereas ASS1-deficient zebrafish larvae are characterized by markedly elevated concentrations of citrulline - the biochemical hallmark of CTLN1, accumulation of L-citrulline, hyperammonemia or therewith associated secondary metabolic alterations did not account for the observed phenotype. Intriguingly, coinjection of the human ASS1 mRNA not only normalized citrulline concentration but also reversed the morphological cerebral phenotype and restored brain size, confirming conserved functional properties of ASS1 across species. The results of the present study imply a novel, potentially non-enzymatic (moonlighting) function of the ASS1 protein in neurodevelopment.
摘要：
1型瓜氨酸血症（CTLN1）是一种罕见的常染色体隐性遗传尿素循环障碍，由胞质酶精氨酸琥珀酸合成酶1（ASS1）的缺乏引起，这是由于位于9q34.11号染色体上的ASS1基因的致病性变异。尽管子宫肌瘤亢进被认为是神经功能缺损和认知功能障碍的主要病理机制因素，在没有高氨代偿的情况下，相关的个体子集表现为神经退行性过程。在这里我们展示，反义介导的斑马鱼ASS1同源基因敲低诱导的ASS1缺陷与神经元分化缺陷有关，最终导致斑马鱼幼虫体内神经元细胞丢失和大脑大小连续减小。而缺乏ASS1的斑马鱼幼虫的特征是瓜氨酸的浓度显著升高-CTLN1的生化标志，L-瓜氨酸的积累，高氨血症或与之相关的继发性代谢改变没有解释观察到的表型.有趣的是，人ASS1mRNA的共同注射不仅使瓜氨酸浓度正常化，而且逆转了脑形态表型和恢复了脑大小，确认跨物种ASS1的保守功能特性。本研究的结果暗示了一种新颖的，ASS1蛋白在神经发育中的潜在非酶（月光）功能。
