Autophagy Regulates Transglutaminase-1 Expression and Vitamin C Enhances Autophagic Activity in Keratinocytes

Vitamin C, known for its various effects on the skin, promotes epidermal differentiation and enhances skin barrier function. However, the underlying mechanism remains unclear. Autophagy is an intracellular degradation system that maintains cellular homeostasis. Although autophagy decrement has been associated with barrier defects in skin diseases, the mechanism by which autophagy regulates skin barrier function remains insufficiently understood. Therefore, this study aimed to investigate the relationship between autophagy and transglutaminase-1 (TGase-1), a molecule required to form the cornified envelope that contributes to skin barrier function. We also examined the effect of vitamin C on autophagy in epidermal keratinocytes. Autophagy modulation through the knockdown of autophagy-related molecules (ATG5, ATG7, and ATG13) significantly decreased TGase-1 expression in human epidermal keratinocytes. Furthermore, vitamin C treatment enhanced the autophagic activity of epidermal keratinocytes and suppressed TGase-1 expression decrease in ATG13 knockdown cells. In conclusion, TGase-1 expression can be regulated by autophagy, and vitamin C may be involved in skin barrier function through autophagy activation. Abbreviations: TGase-1: transglutaminase-1; CE: cornified envelope; ATG5: autophagy related 5; ATG7: autophagy related 7, ATG13: autophagy related 13, LOR: loricrin; FLG: filaggrin; TBP: TATA-box binding protein; LC3: microtubule-associated protein 1 light chain 3; CQ: chloroquine; VC: vitamin C; CTL: control.