Altered metabolism of membrane glycosphingolipids in erythrocytes of paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is currently accepted to be a stem-cell disorder of a clonal nature with increased susceptibility to autologous complement attack. Consequent hemolytic feature has been partly explained by lack of complement regulatory membrane proteins such as decay-accelerating factor (DAF) or C8-binding protein that anchored to membrane via glycosyl-phosphatidyl inositol (GPI) lipids. Recent reports suggest essential PNH lesion is the synthetic defect of sugar moiety of the PI-anchor. In PNH, the abnormal expression of C3b/C4b receptor (CRI) glycoproteins, or glycophorin-alpha have been also pointed out. These altered expression of glycoproteins and glyceroglycolipids, especially in the carbohydrate structures, prompted us to analyze biochemically the membrane glycosphingolipids as one of major glycoconjugates in PNH. As results, PNH erythrocytes showed altered metabolism of gangliosides in comparison to control erythrocytes from healthy donors. IV6 NeuAc-nLc4 Cer and highly polar gangliosides variably disappeared in PNH erythrocytes, partly due to impaired sialylation of glycolipids. These results suggest metabolic disorder of carbohydrates of membrane glycoconjugates as a new aspect of PNH.