Ruscus aculeatus extract promotes RNase 7 expression through ERK activation following inhibition of late-phase autophagy in primary human keratinocytes

Antimicrobial peptides (AMPs) are crucial for protecting human skin from infection. Therefore, the expression levels of beneficial AMPs such as ribonuclease 7 (RNase 7) must be appropriately regulated in healthy human skin. However, there is limited understanding regarding the regulating AMP expression, especially when using applications directly to healthy human skin. Here, we investigated the effects of the extract of Ruscus aculeatus (RAE), a medicinal plant native to Mediterranean Europe and Africa that is known to have a high safety level, on AMP expression in primary human keratinocytes. Treatment with RAE induced RNase 7 expression, which was suppressed by an extracellular signal-regulated kinase (ERK) inhibitor. The autophagic flux assay and the immunofluorescence analysis of microtubule-associated protein 1 light chain 3 (LC3)-Ⅱ and p62 showed that RAE inhibited late-phase autophagy. Moreover, both the inhibition of early-phase autophagy by EX-527, an inhibitor of silent information regulator of transcription 1 (SIRT1) and its enhancement by resveratrol, an activator of SIRT1 inhibited RNase 7 and ERK expression, indicating that autophagosome accumulation is necessary for RAE-induced RNase 7 expression. Additionally, spilacleoside was identified as the active component in RAE. These findings suggest that RAE promotes RNase 7 expression via ERK activation following inhibition of late-phase autophagy in primary human keratinocytes and that this mechanism is a novel method of regulation of AMP expression.