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

血浆无铜蓝蛋白血症是一种常染色体隐性遗传的神经退行性疾病，其特征是铁在大脑以及内脏器官中蓄积。它是一种由铜蓝蛋白基因突变引起的功能丧失性疾病。在临床上，这种疾病由成人发病的神经系统疾病、视网膜变性和糖尿病三联体组成。在基底神经节中观察到大量的铁积累和神经元的广泛损失。铁浓度升高与血浆纤溶酶血症患者脑内脂质过氧化反应增加有关。增大或变形的星形胶质细胞和球状样球状结构是浆细胞蛋白血症的特征性神经病理学表现。此外，变形的星形胶质细胞和球状结构对抗4-羟基壬烯醛抗体呈阳性反应，这表明增加的氧化应激参与了浆胞浆蛋白血症脑中的神经元细胞死亡。约38 aceruloplasmin基因突变引起的血浆铜蓝蛋白血症已被确定。我们研究了两个错义铜蓝蛋白蛋白的生物合成，导致日本P177 R突变和荷兰G631 R突变，使用中国仓鼠卵巢细胞表达系统。P177 R突变蛋白保留在内质网中。G631 R突变蛋白，预测改变在一个单一的I型铜结合位点的相互作用，防止掺入铜到apoceruloplasmin，并导致在apoceruloplasmin的合成和分泌。错义突变的分子分析显示铜蓝蛋白的不同结构-功能关系。对突变型铜蓝蛋白的研究为铜蓝蛋白血症的分子发病机制以及铜蓝蛋白的生物合成、运输和功能提供了新的认识。

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.