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

β-淀粉样蛋白（beta-amyloid，A β）由天然前体蛋白（native precursor protein，APP）产生，在人脑中以老年斑和淀粉样血管病的形式蓄积，与正常衰老和阿尔茨海默病（Alzheimer's disease，AD）的病理生理过程密切相关。比较分析了正常淋巴母细胞和家族性AD患者的APP加工和A β肽的形成。从AD细胞的培养基中纯化68 kDa丝氨酸蛋白酶，其在A β-N-末端切割寡肽。虽然该蛋白酶在A β-N-末端附近切割天然LAPP，但天然脑APP不被降解，表明APP蛋白水解具有严格的组织特异性。我搜索了能够切割人海马中的天然脑APP的活性，并分离和表征了HBP 49蛋白水解活性，并且分子克隆澄清为一种新的蛋白酶。生物化学和分子生物学分析表明，该蛋白酶在脑APP降解和产生Abeta肽中具有生理功能，并且与脑APP连接的硫酸化糖缀合物在蛋白水解中可能起作用。免疫组化结果显示其主要表达于神经元胞体周围，散发性AD患者脑内也有其特有的免疫反应性病变。

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.