Molecular basis of aceruloplasminemia : Expression of the ceruloplasmin gene in aceruloplasminemia

尖锐纤溶酶血症是一种常染色体隐性神经退行性疾病，其特征是铁积聚在大脑和内脏器官。这是一种由铜蓝蛋白基因突变引起的功能丧失疾病。临床上，这种疾病包括成人发病的神经系统疾病、视网膜变性和糖尿病。在基底神经节中观察到大量的铁积累和广泛的神经元损失。铁浓度升高与乙酰纤溶酶血症患者脑内脂质过氧化增加有关。星形胶质细胞增大或变形，球状结构是尖状纤溶酶血症的特征性神经病理表现。此外，变形的星形胶质细胞和球状结构对抗4-羟基壬烯醛抗体反应积极，表明氧化应激增加参与了急性纤溶酶血症脑神经元细胞死亡。目前已鉴定出大约38种铜蓝蛋白基因突变引起的青铜质纤溶酶血症。利用中国仓鼠卵巢细胞表达系统，研究了日本基因P177R突变和荷兰基因G631R突变导致的两种错义铜蓝蛋白的生物合成。P177R突变蛋白保留在内质网中。据预测，G631R突变蛋白改变了单个I型铜结合位点的相互作用，阻止了铜与apoceruloplasmin的结合，导致apoceruloplasmin的合成和分泌。错义突变的分子分析显示了铜蓝蛋白不同的结构-功能关系。突变型铜蓝蛋白的研究揭示了铜蓝蛋白血症的分子发病机制以及铜蓝蛋白的生物合成、转运和功能。

Aceruloplasminemia is an autosomal recessive neurodegenerative disease characterized by iron accumulation in the brain as well as visceral organs. It is a loss-of-function disorder caused by mutations in the ceruloplasmin gene. Clinically, this disease consists of the triad of adult-onset neurological disease, retinal degeneration and diabetes mellitus. Massive iron accumulation and extensive loss of neurons are observed in the basal ganglia. The elevated iron concentration is associated with increased lipid peroxidation in the brains of aceruloplasminemia patients. Enlarged or deformed astrocytes and spheroid-like globular structures are characteristic neuropathological findings in aceruloplasminemia. Moreover, deformed astrocytes and globular structures react positively to anti-4-hydroxynonenal antibody, suggesting that increased oxidative stress is involved in neuronal cell death in aceruloplasminemia brain. About 38 aceruloplasminemia-causing mutations in the ceruloplasmin gene have been identified. We examined the biosynthesis of two missense ceruloplasmin proteins that result from a Japanese P177R mutation and a Dutch G631R mutation, using Chinese hamster ovary cell expression system. The P177R mutant protein is retained in the endoplasmic reticulum. The G631R mutant protein, predicted to alter the interactions at a single type I copper-binding site, prevented incorporation of copper into apoceruloplasmin and resulted in the synthesis and secretion only of apoceruloplasmin. Molecular analysis of missense mutations showed different structure-function relationships in ceruloplasmin protein. The investigation of mutant ceruloplasmin reveals new insights into molecular pathogenesis of aceruloplasminemia as well as biosynthesis, trafficking, and function of ceruloplasmin.