Allicin Enhances Tight Junction Barrier Integrity While Modulating Milk Production via TRPA1 in Mouse Mammary Epithelial Cells

Garlic is utilized as a feed additive in livestock production. The pungent and spicy flavor of garlic is attributed to allicin, which functions as an agonist of the Ca²⁺ channel TRPA1. Although mammary epithelial cells (MECs) express TRPA1, the physiological role remains largely unexplored. During lactation, MECs produce milk components and maintain the blood-milk barrier by forming tight junctions (TJs). In this study, we investigated whether allicin regulates milk production and TJs in mouse MECs via TRPA1. Allicin inhibited casein production and strengthened the TJ barrier integrity by recruiting claudin-3 to the TJ region. Allicin induced TRPA1-mediated Ca²⁺ influx and inactivated STAT5 and Akt/mTOR signaling. Similarly, other TRPA1 agonists, allyl isothiocyanate (found in wasabi) and cinnamaldehyde (cinnamon), downregulated casein production and STAT5 inactivation. Notably, TRPA1 in MECs was expressed on the apical membrane in contact with milk, whereas its localization on the basolateral membrane could not be confirmed in this study. These findings suggest that the enhancement of TJ barrier integrity in MECs is a key physiological response to allicin that is mediated, at least in part, through TRPA1 localized to the apical membrane and accompanied by a concomitant reduction in milk production.