Clinical Severity of β-thalassaemia/Hb E Disease Is Associated with Differential Activities of the Calpain-Calpastatin Proteolytic System

Earlier observations in the literature suggest that proteolytic degradation of excess unmatched α-globin chains reduces their accumulation and precipitation in β-thalassaemia erythroid precursor cells and have linked this proteolytic degradation to the activity of calpain protease. The aim of this study was to correlate the activity of calpain and its inhibitor, calpastatin, with different degrees of disease severity in β-thalassaemia. CD34+ cells were enriched from peripheral blood of healthy individuals (control group) and patients with mild and severe clinical presentations of β0-thalassaemia/Hb E disease. By ex vivo cultivation promoting erythroid cell differentiation for 7 days, proerythroblasts, were employed for the functional characterization of the calpain-calpastatin proteolytic system. In comparison to the control group, enzymatic activity and protein amounts of μ-calpain were found to be more than 3-fold increased in proerythroblasts from patients with mild clinical symptoms, whereas no significant difference was observed in patients with severe clinical symptoms. Furthermore, a 1.6-fold decrease of calpastatin activity and 3.2-fold accumulation of a 34 kDa calpain-mediated degradation product of calpastatin were observed in patients with mild clinical symptoms. The increased activity of calpain may be involved in the removal of excess α-globin chains contributing to a lower degree of disease severity in patients with mild clinical symptoms.既往文献中的早期研究表明，过量未配对α-珠蛋白链（α-globin chains）的蛋白水解降解，可减少其在β地中海贫血（β-thalassaemia）红系前体细胞中的蓄积与沉积，并将该蛋白水解过程与钙蛋白酶（calpain protease）的活性相关联。本研究旨在探讨钙蛋白酶及其抑制剂钙蛋白酶抑制蛋白（calpastatin）的活性与β地中海贫血不同疾病严重程度之间的相关性。研究人员从健康个体（对照组）以及表现为轻度、重度临床症状的β0地中海贫血/血红蛋白E（β0-thalassaemia/Hb E）病患者的外周血中富集CD34+细胞。通过体外培养促进红系细胞分化7天，获取早幼红细胞（proerythroblasts），用于钙蛋白酶-钙蛋白酶抑制蛋白蛋白水解系统的功能表征。与对照组相比，轻度临床症状患者的早幼红细胞中，μ-钙蛋白酶（μ-calpain）的酶活性与蛋白表达量均升高3倍以上；而重度临床症状患者则未观察到显著差异。此外，轻度临床症状患者的钙蛋白酶抑制蛋白活性降低1.6倍，且钙蛋白酶介导产生的34千道尔顿（34 kDa）钙蛋白酶抑制蛋白降解产物的积累量升高3.2倍。钙蛋白酶活性的增强可能参与清除过量α-珠蛋白链，进而降低轻度临床症状患者的疾病严重程度。