Abstract
The human erythrocyte transmembrane sialoglycoprotein, glycophorin C (GYPC), plays a functional role in regulating red cell shape and mechanical stability. Antibodies to GYPC cause hemolytic disease of the fetus and newborn (HDFN) that is associated with classical Fcγ receptor-mediated phagocytosis. However, in vitro clonogenic studies with cord blood progenitor cells suggest that anti-GYPC also suppresses erythropoiesis, which is consistent with the observations of severe and early fetal anemia and late onset neonatal anemia [
Transfus Med 2005;15:125–32
]. The mechanism of the suppressive effect on erythropoiesis is unknown. The K562 erythroleukemic cell line treated with anti-GYPC is a potential model system to study the suppressive effect of anti-GYPC. The present in vitro studies were designed to confirm the effect of anti-GYPC on K562 cell growth and viability, and to evaluate changes in mitochondrial membrane potential, phosphatidylserine (PS) expression, propidium iodide (PI) binding, and caspase activation. K562 cells fail to grow in the presence of anti-GYPC confirming earlier CFU-E/BFU-E studies [Brit J Haematol 2006;133:443–4
], and increased the exofacial expression of PS/PI over time. This process was caspase-independent as demonstrated by the failure of Z-VAD, a caspase inhibitor, to reverse growth inhibition and PS/PI expression. A loss of mitochondrial membrane potential was demonstrated using JC-1, a cationic dye that is sensitive to potential-dependent accumulation or loss in mitochondria. There was a 50% increase in K562 cell mitochondrial membrane potential disruption after 2 days of culture with anti-GYPC (see figure). Morphological examination of May Grunwalde Giemsa-stained K562 cells treated with anti-GYPC for 2 days showed a decrease in mitotic activity compared to isotype treated cells. By day 4, the anti-GYPC treated cells were showing evidence of plasma membrane damage and cell death resulting from fragmentation and dissolution of the cytoplasm. The addition of hemin, an oxidative form of iron protoporphyrin IX known to induce erythroid differentiation of K562 cells, to anti-GYPC treated cells reversed growth inhibition by 45% but did not prevent the loss of mitochondrial membrane potential. Overall, although caspases appear to be unimportant in anti-GYPC induced cell death, the mitchondria play an important role as the early events leading to antibody-mediated suppression of erythropoiesis.
Mitochondrial Membrane Potential Disruption by Anti-GYPC
