Abstract
BACKGROUND: 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. MATERIALS AND METHODS: 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. RESULTS: 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. DISCUSSION: 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.
