Background:Although polySia is known to retain neurotrophins, their releasing mechanism remains unknown. Results: PolySia present on the cell surface of microglia is rapidly cleared by Neu1 sialidase on exovesicles secreted upon inflammatory stimulus, leading to neurotrophin release. Conclusion: Exovesicular Neu1 regulates rapid turnover of polySia and concomitant neurotrophin function. Significance: First demonstration of on-site turnover of polySia and its physiological significance.

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.

No abstract