Studies on the Mechanism of Abnormal Proteolysis in Erythrocytes of Thalassemic Patients and its Application to Clinical Diagnosis

根据我们最初的计划，我们，日本人和泰国人，通过交换材料和信息，研究地中海贫血患者红细胞中异常蛋白水解的机制。我们在临床和分子水平上的分析表明，该疾病的表型表现不仅受到突变基因型的影响，而且还受到其他因素的影响;具有相似遗传缺陷的β-地中海贫血/Hb E患者的红细胞并不总是相似的，但血红蛋白含量可变。我们初步确定了以下三个可能改变地中海贫血临床表现的因素：α-和β-地中海贫血基因或其产物之间的相互作用、HbF基因和HbF基因的结构或功能以及蛋白酶活性。第一个因素是发现β-地中海贫血患者携带α-地中海贫血基因的严重程度无淀粉样变。β-珠蛋白基因簇中XmuI限制性位点（β-Ggamma基因上游158个核苷酸）的纯合子（+/+）比杂合子（+/-）的纯合子（-/-）具有显著更高的血红蛋白水平，这表明了第二个因素。最后一个因素是地中海贫血红细胞中钙蛋白酶（Ca^2+依赖性半胱氨酸蛋白酶）的活性高于正常细胞，尽管伴随着钙蛋白酶抑制剂（钙蛋白酶的内源性抑制剂）的活性也高于正常细胞。在地中海贫血红细胞中也检测到膜蛋白的部分降解。这些结果表明α-和β-型球蛋白的比例以及蛋白酶的活性在地中海贫血的临床研究中的重要性。

According to our original plan, we, Japanese and Thai, studies the mechanisms of abnormal proteolysis in the red blood cell of thalassemic patients, by exchanging material and information. Our analysis at clinical and molecular levels indicated that phenotypic manifestation of the disease is influenced not only by mutated genotypes but also by other factors ; the red cells of beta-thallasemia/Hb E patients with similar genetic defects were not always similar but variable in the hemoglobin content. We tentatively identified the following three factors that may modify clinical manifestation of thalassemia ; an interaction between alpha- and beta-thalassemia genes or their products, a structure or function of HbF gene, and Hb F gene, and protease activities. The first factor was suggested by the finding of amiliolated severity of beta-thalassemic patients with alpha-thalassemia gene. The second factor was indicated by the finding that homozygotes (+/+) with regard to XmuI restriction site (158 mucleotides upstream from the ^Ggamma gene) in the beta-globin gene cluster had significantly higher levels of hemoglobin than heterozygoted (+/-) of homozygotes (-/-). The last factor was suggested by a higher activity of calpain (Ca^<2+>-dependent cysteine protease), though accompanied by a higher activity of calpastatin (an endogenous inhibitor of calpain), in thalassemic red cells than in normal cells. Partial degradation of membrane proteins was also detected in thalassemic red cells. These results indicate the importance of the ratio of alpha- and beta-type globins as well as the activity of proteases in clinical investigation of thalassemia.