ABSTRACT
As acidic glycocalyx on primary mouse microglial cells and a mouse microglial cell line Ra2, expression of polysialic acid (polySia/PSA), a polymer of the sialic acid Neu5Ac (N-acetylneuraminic acid), was demonstrated. PolySia is known to modulate cell adhesion, migration, and localization of neurotrophins mainly on neural cells. PolySia on Ra2 cells disappeared very rapidly after an inflammatory stimulus. Results of knockdown and inhibitor studies indicated that rapid surface clearance of polySia was achieved by secretion of endogenous sialidase Neu1 as an exovesicular component. Neu1-mediated polySia turnover was accompanied by the release of brain-derived neurotrophic factor normally retained by polySia molecules. Introduction of a single oxygen atom change into polySia by exogenous feeding of the non-neural sialic acid Neu5Gc (N-glycolylneuraminic acid) caused resistance to Neu1-induced polySia turnover and also inhibited the associated release of brain-derived neurotrophic factor. These results indicate the importance of rapid turnover of the polySia glycocalyx by exovesicular sialidases in neurotrophin regulation.
Subject(s)
Cell Membrane/metabolism , Extracellular Matrix/enzymology , Glycocalyx/metabolism , Microglia/metabolism , Nerve Growth Factors/metabolism , Neuraminidase/metabolism , Sialic Acids/metabolism , Animals , Animals, Newborn , Blotting, Western , Brain-Derived Neurotrophic Factor/metabolism , Cells, Cultured , Fluorescent Antibody Technique , Membrane Microdomains/metabolism , Mice , Mice, Inbred C57BL , Microglia/cytology , Nerve Growth Factors/genetics , Neuraminidase/genetics , Oxygen/metabolism , RNA, Messenger/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
BACKGROUND: The molecular pathogenesis underlying recurrent exacerbations of atopic dermatitis (AD) is unclear. Some peripheral CCR4(+) and CCR7(+) helper memory T cells express the specific homing receptor, sialyl 6-sulfo Lewis X (G152 glycan). This glycan loses receptor activity via cyclization of its sialic acid moiety, thus becoming cyclic sialyl 6-sulfo Lewis X (G159 glycan). These findings suggest that the disordered expression of G152 and G159 glycans may be associated with recurrent exacerbations of AD. OBJECTIVE: To assess the possible association of G152 and G159 glycans, which are expressed on peripheral helper T (Th) cells, with frequency of exacerbations. METHODS: The percentage of glycan-expressing cells among peripheral blood CD4(+)CD45RO(+) lymphocytes was determined by flow cytometry. The association of glycans with the frequency of exacerbations determined by recurrence scores as well as with current disease activity was statistically tested. RESULTS: Current disease activity was significantly associated with CCR4(+)CCR7(-) memory Th cells expressing CSLEX-1 glycan, the conventional skin-trafficking receptor without sialic-acid-cyclization activity. In contrast, the frequency of exacerbations was positively and negatively associated with CCR4(+)CCR7(+) memory Th cells expressing G152 and G159 glycans, respectively. Receiver operating characteristics analyses indicated that the ratio of the G152(+)/G159(+) cell percentages discriminated patients with highly recurrent AD with the best accuracy. CONCLUSION: Flow cytometric determination of G159 and G152 glycans on peripheral helper memory T cells may be clinically useful for identifying patients with highly recurrent AD. Disordered sialic acid cyclization of G152 glycan may underlie highly recurrent AD, which may provide a novel therapeutic approach.
Subject(s)
Dermatitis, Atopic/immunology , Dermatitis, Atopic/metabolism , Receptors, Lymphocyte Homing/metabolism , T-Lymphocytes, Helper-Inducer/immunology , T-Lymphocytes, Helper-Inducer/metabolism , Adult , Case-Control Studies , Cyclization , Dermatitis, Atopic/etiology , Female , Humans , Immunologic Memory , Lewis X Antigen/analogs & derivatives , Male , Middle Aged , N-Acetylneuraminic Acid/chemistry , Oligosaccharides/chemistry , Oligosaccharides/metabolism , Receptors, CCR4/metabolism , Receptors, CCR7/metabolism , Receptors, Lymphocyte Homing/chemistry , Recurrence , Sialyl Lewis X Antigen/analogs & derivatives , Young AdultABSTRACT
The neural cell adhesion molecule and the voltage-sensitive sodium channel alpha-subunit are the only two molecules in mammals known to be modified by alpha-2,8-linked polysialic acid (polySia). We found a new polySia-containing glycoprotein in human milk and identified it as CD36, a member of the B class of the scavenger receptor superfamily. The polySia-containing glycan chain(s) were removed by alkaline treatment but not by peptide:N-glycanase F digestion, indicating that milk CD36 contained polySia on O-linked glycan chain(s). Polysialylation of CD36 occurs not only in human milk but also in mouse milk. However, CD36 in human platelets is not polysialylated. PolySia CD36 is secreted in milk at any lactation stage and reaches peak level at 1 month after parturition. Thus, it is suggested that polySia of milk CD36 is significant for neonatal development in terms of protection and nutrition.
