CHARACTERIZATION OF MISSENSE MUTATIONS AND BIOCHEMICAL ANALYSIS OF INCREASED LIPID PEROXIDATION AND MITOCHONDRIAL DYSFUNCTION IN ACERULOPLASMINEMIA

无铜蓝蛋白血症是一种影响铁代谢的常染色体隐性遗传病，由铜蓝蛋白基因突变引起。它的特点是铁积累在大脑以及内脏器官。临床上，该疾病由视网膜变性、糖尿病和神经系统疾病三联征组成。以往报道的铜蓝蛋白基因突变几乎都是截短突变。为了阐明血浆铜蓝蛋白血症的分子发病机制，研究了两个错义突变体的血浆铜蓝蛋白生物合成。P177R突变导致血浆铜蓝蛋白在内质网内作为载脂蛋白定位。H978Q突变导致血清铜蓝蛋白缺乏铁氧化酶活性，与铜结合减少相关。独特的中枢神经系统参与将铜蓝蛋白血症与其他遗传性和获得性铁储存疾病区分开来。过量的铁是生物氧化的有效催化剂。我们发现，铁浓度的增加与三个aceroplasminemia患者的脑脂质过氧化反应增加。正电子发射断层扫描显示皮质葡萄糖和氧代谢低下。复合物I和IV的基底神经节的线粒体呼吸链中的酶活性分别降低至约50%和43%。大脑皮质和小脑皮质也分别降低约62%和65%。这些结果表明，铁介导的自由基可能有助于增加脂质过氧化和损伤的线粒体能量代谢的aceroplasminemia脑。

Aceruloplasminemia, an autosomal recessive disorder that affects iron metabolism, is caused by mutations of the ceruloplasmin gene. It is characterized by iron accumulation in the brain as well as visceral organs. Clinically, the disease consists of the triad of retinal degeneration, diabetes mellitus, and neurologic disease. Almost all the mutations in the ceruloplasmin gene reported previously were truncation mutations. To elucidate the molecular pathogenesis of aceruloplasminemia, the ceruloplasmin biosynthesis of two missense mutants was examined. A P177R mutation results in the location of ceruloplasmin within the endoplasmic reticulum as apoprotein. An H978Q mutation results in detectable serum ceruloplasmin devoid of ferroxidase activity associated with decreased copper incorporation.The unique involvement of the central nervous system distinguishes aceruloplasminemia from other inherited and acquired iron storage disorders. Excess iron functions as a potent catalyst of biologic oxidation. We showed that an increased iron concentration is associated with increased lipid peroxidation in the brains of three aceruloplasminemia patients. Positron emission tomography showed cortical glucose and oxygen hypometabolism. Enzyme activities in the mitochondrial respiratory chain of the basal ganglia were reduced to about 50% and 43% respectively for complexes I and IV. Those of the cerebral and cerebellar cortices also were decreased approximately 62% and 65%. These findings suggest that iron-mediated free radicals may contribute to increased lipid peroxidation and the impairment of mitochondrial energy metabolism in aceruloplasminemia brains.