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

无铜蓝蛋白血症是一种常染色体隐性遗传性神经退行性疾病，其特征是铁在大脑和内脏器官中积聚。这是一种由铜蓝蛋白基因突变引起的功能丧失障碍。临床上，本病由成人起病的神经系统疾病、视网膜变性和糖尿病三部分组成。基底节内可见大量铁蓄积和神经元广泛丢失。铁浓度升高与无纤维蛋白溶酶血症患者大脑中的脂质过氧化反应增加有关。肿大或变形的星形细胞和类球形结构是无浆蛋白血症特有的神经病理学表现。此外，变形的星形胶质细胞和球状结构对抗4-羟基壬烯酸抗体呈阳性反应，表明氧化应激增加参与了无浆菌血症脑内神经细胞的死亡。目前已鉴定出约38个铜蓝蛋白基因突变导致无蓝蛋白血症。我们使用中国仓鼠卵巢细胞表达系统检测了日本的P177R突变和荷兰的G631R突变导致的两个错义铜蓝蛋白的生物合成。P177R突变蛋白保留在内质网中。G631R突变蛋白预计会改变单一I型铜结合位点的相互作用，阻止铜进入载脂蛋白，并导致仅合成和分泌载脂蛋白。错义突变的分子分析表明铜蓝蛋白具有不同的结构-功能关系。对铜蓝蛋白突变体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.