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

我们日本人和泰国人按照原计划，通过交换材料和信息，研究地中海贫血患者红细胞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，该病的表型表现不仅受基因型突变的影响，还受其他因素的影响；具有相似遗传缺陷的β -血凝症/Hb E患者的红细胞并不总是相似的，而是血红蛋白含量不同。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；-和-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。第一个因素是发现携带α -地中海贫血基因的β -地中海贫血患者的贫血严重程度。第二个因素是发现β -珠蛋白基因簇中XmuI限制性内切位点（^Ggamma基因上游158个核苷酸）的纯合子（+/+）的血红蛋白水平显著高于纯合子（+/-）的杂合子（+/-）。最后一个因素表明，在地中海红细胞中，钙蛋白酶（Ca^<2+>-依赖半胱氨酸蛋白酶）的活性较高，尽管伴有钙pastatin（一种内源性钙蛋白酶抑制剂）的活性高于正常细胞。在地中海贫血红细胞中也检测到膜蛋白的部分降解。这些结果提示α -和β -型珠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.