SIGNIFICANCE OF THE 68-K SERINE PROTEASE IN SERUM AS A MARKER PROTEIN FOR BRAIN AGING

天然前体蛋白（APP）生成β -淀粉样蛋白（Abeta）及其在人脑中以老年斑和淀粉样血管病的形式积累，本质上与阿尔茨海默病的正常衰老和病理生理有关。比较分析了正常淋巴母细胞样细胞与家族性AD患者淋巴母细胞样细胞APP的加工和携带β肽的形成。从AD细胞培养基中纯化出68 kDa丝氨酸蛋白酶，该蛋白酶在β - n端切割寡肽。虽然该蛋白酶在β - n -末端附近切割天然LAPP，但天然脑APP不会被降解，这表明APP蛋白水解具有严格的组织特异性。我在人海马中搜索了能够切割天然脑APP的活性，分离并表征了HBP49的蛋白水解活性，并通过分子克隆明确了它是一种新型蛋白酶。生化和分子生物学分析表明，该蛋白酶在脑APP降解和生成β肽中具有生理功能，并可能在脑APP的蛋白质水解中发挥巯基糖缀合物的作用。免疫组化研究显示其在神经元核周表达，并在散发性AD患者的大脑中发现一些独特的免疫反应性病变。

Genetation of beta-amyloid (Abeta) from native precursor protein (APP) and its accumulation which appear as senile plaque and amyloid angiopathy in human brain are essentially associated with normal aging and pathophysiology of Alzheimer's disease. Processing of APP and formation of Abeta-bearing peptides were comparatively analyzed between normal lymphoblastoid cells and those derived from familial AD patients. 68 kDa serine protease was purified from culture medium of AD cells, which cleaves oligopeptides at the Abeta-N-terminus. Though this protease cleaves native LAPP in the vicinity of Abeta-N- terminus, native brain APP was not degraded, suggesting a strict tissue specificity in APP proteolysis. I searched for activities capable of cleaving native brain APP in human hippocampus, and HBP49 proteolytic activity was isolated and characterized, and the molecular cloning clarified as being a novel protease. Biochemical and molecular biological analyses suggested a physiological function of the protease in brain APP degradation and generation of Abeta peptides, and a possible role of sulfated glycocon-jugates attached to brain APP in the proteolysis. Immunohistochemical study showed its expression in neuronal perikarya, and some unique lesions with the immunoreactivity were found in brains of sporadic AD patients.