Extracellular vesicle-like nanoparticles from Lactobacillus delbrueckii protect keratinocyte barrier function with involvement of TRPV4 signaling.

Dry skin (xerosis) induced by low temperature and detergents may be alleviated by improving epidermal barrier function and reducing transepidermal water loss. Fermentation products from lactic acid bacteria can improve moisture retention, and extracellular vesicle-like nanoparticles (EV-LNPs) may contribute to this effect, although the mechanisms remain unclear. We investigated whether Lactobacillus delbrueckii-derived EV-LNPs protect keratinocyte barrier function and assessed the possible contributions of hydroxy fatty acids and transient receptor potential vanilloid 4 (TRPV4), a warmth-responsive Ca²⁺ channel. In PSVK1 human keratinocytes, low-temperature exposure reduced transepithelial electrical resistance (TEER) without affecting proliferation. EV-LNPs prepared from L. delbrueckii cultured in medium containing 10% low-fat milk restored TEER and increased zonula occludens-1 (ZO-1) and occludin expression. A lipophilic fraction concentrated 10-fold reproduced the TEER-enhancing effect of intact EV-LNPs. Mass spectrometry detected candidate 12-hydroxystearic acid and ricinoleic acid, which increased nuclear factor of activated T cells (NFAT) reporter activity and preserved junctional ZO-1 and occludin. Although hydroxy fatty acid levels in the active EV-LNP fraction were lower than the concentrations required for NFAT activation by the individual compounds, preincubation with EV-LNPs enhanced NFAT activation at lower 12-hydroxystearic acid concentrations. These findings suggest that EV-LNPs facilitate the activity of hydroxy fatty acids present at low abundance. Crotamiton attenuated NFAT reporter activation and barrier protection. Collectively, reporter, pharmacological, ectopic-expression, and lipid analyses support lipid-mediated TRPV4-associated signaling. L. delbrueckii-derived EV-LNPs and their lipophilic components may represent postbiotic factors for supporting keratinocyte barrier function under low-temperature and detergent stress.