Freitas Leal Joames K, Adjobo-Hermans Merel J W, Brock Roland, Bosman Giel J C G M
Department of Biochemistry, Radboud Institute for Molecular Life Sciences, Radboud University Medical Centre, Nijmegen, The Netherlands.
Blood Transfus. 2017 May;15(3):232-238. doi: 10.2450/2017.0370-16.
During its 120 days sojourn in the circulation, the red blood cell (RBC) remodels its membrane. Acetylcholinesterase (AChE) is a glycosylphosphatidylinositol (GPI)-linked enzyme that may serve as a marker for membrane processes occurring this ageing-associated remodelling process.
Expression and enzymatic activity of AChE were determined on RBCs of various ages, as obtained by separation based on volume and density (ageing in vivo), and on RBCs of various times of storage in blood bank conditions (ageing in vitro), as well as on RBC-derived vesicles.
During ageing in vivo, the enzymatic activity of AChE decreases, but not the AChE protein concentration. In contrast, neither AChE activity nor concentration show a consistent, significant decrease during ageing in vitro. CD59, another GPI-linked protein that protects against complement-induced removal, also remains constant during storage. The cellular content of the integral membrane protein glycophorin A, however, decreases with storage time in the more dense RBC fractions. The latter are enriched in echinocytes and other misshapen cells during storage.
Our findings suggest that, during RBC ageing, GPI-linked proteins and integral membrane proteins are differentially sorted. Also, the vesicles that are generated in vitro show a fast and extensive loss of AChE activity, but not of AChE expression. Thus, AChE characteristics may constitute sensitive biomarkers of RBC ageing in vivo, and a source of information on the structural and functional changes that GPI-linked proteins undergo during ageing in vivo and in vitro. This information may help to understand RBC homeostasis and the effects of transfusion, especially in immunologically compromised patients.
红细胞（RBC）在循环系统中停留的120天里会重塑其细胞膜。乙酰胆碱酯酶（AChE）是一种糖基磷脂酰肌醇（GPI）连接的酶，可能作为这种与衰老相关的重塑过程中发生的膜过程的标志物。
通过基于体积和密度的分离（体内老化）获得不同年龄的红细胞，以及在血库条件下储存不同时间的红细胞（体外老化），还有红细胞衍生的囊泡，测定AChE的表达和酶活性。
在体内老化过程中，AChE的酶活性降低，但AChE蛋白浓度没有降低。相比之下，在体外老化过程中，AChE活性和浓度均未显示出一致的显著下降。CD59是另一种防止补体诱导清除的GPI连接蛋白，在储存过程中也保持不变。然而，在密度较大的红细胞组分中，整合膜蛋白血型糖蛋白A的细胞含量随储存时间而降低。在储存过程中，后者富含棘红细胞和其他畸形细胞。
我们的研究结果表明，在红细胞老化过程中，GPI连接蛋白和整合膜蛋白的分选方式不同。此外，体外产生的囊泡显示AChE活性快速且大量丧失，但AChE表达没有丧失。因此，AChE的特性可能构成体内红细胞老化的敏感生物标志物，以及关于GPI连接蛋白在体内和体外老化过程中所经历的结构和功能变化的信息来源。这些信息可能有助于理解红细胞的稳态以及输血的影响，尤其是在免疫功能低下的患者中。
