Localization patterns of claudins in lactating goat mammary glands.

Claudin-3 is the primary tight junction regulator in goat mammary epithelium, with claudin-8 and -15 potentially involved in leukocyte migration.

This study investigated the localization patterns of claudin proteins—key components of tight junctions (TJs)—in mammary gland structures of lactating Tokara goats. TJs are critical for maintaining epithelial barriers, cell polarity, and regulating paracellular transport of water, ions, and molecules. Using immunofluorescence and western blotting, researchers examined claudin distribution across mammary alveoli, ducts, gland cisterns, and teat cisterns, alongside cultured goat mammary epithelial cells (GMECs), milk somatic cells, and blood leukocytes. Claudin-3 was consistently localized at TJ regions across all mammary structures and appears to be the primary regulator of passive ion and blood-derived component movement into milk. Claudin-4, -8, -10, and -16 were frequently found at TJ regions, while localization patterns of several claudins varied between the teat cistern and other mammary tissues—despite no significant differences in ion concentrations or blood-derived components in milk fractions. Somatic cell counts were highest in the last milk fraction collected. Notably, leukocytes in alveolar lumens expressed claudin-2, -12, and -15. Claudin-8 and -15 were detected across all sample types, suggesting roles in leukocyte migration across mammary epithelial TJs. These findings enhance understanding of mammary gland barrier function in small ruminants and may have implications for mastitis pathophysiology and milk quality research.

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