Milk Polysialic Acid Levels Rapidly Decrease in Line with the N-Acetylneuraminic Acid Concentrations during Early...

Area of Science:

• * Mammary gland biology and immunology.
• * Glycobiology and molecular mechanisms of sialylation.

Background:

• * Sialylated milk oligosaccharides and glycoconjugates are crucial for mucosal barrier, gut microbiome, and immune system health.
• * N-acetylneuraminic acid (Neu5Ac) is the major sialic acid in milk, existing as monosialyl-residues or polymers (polysialic acid, polySia).
• * These biomolecules are essential for mammary gland health and offspring development.

Purpose of the Study:

• * To investigate sialylation processes, including Neu5Ac and polySia levels, during lactation in German Holstein cows.
• * To identify the source of milk polySia and the expression of relevant enzymes in the mammary gland.

Main Methods:

• * Analysis of milk and udder tissue samples at different lactation time points.
• * Quantification of Neu5Ac and polySia levels in milk.
• * Immunohistochemistry of udder tissue to detect polySia.
• * Analysis of polysialyltransferase gene expression (ST8SiaII and ST8SiaIV).

Main Results:

• * Neu5Ac and polySia levels in milk rapidly decreased within the first three days of lactation, with significant interindividual variation.
• * Sialylation status remained relatively constant in mature milk.
• * Mammary gland epithelial cells showed strong polySia staining, indicating they are a source of milk polySia.
• * Expression of polysialyltransferases ST8SiaII and ST8SiaIV was confirmed.

Conclusions:

• * Mammary gland epithelial cells contribute to milk polySia production.
• * The heterogeneous sialylation status of milk may have implications for udder and offspring health.
• * Understanding sialylation dynamics is important for optimizing mammary gland function and neonatal development.