Inhibitory effect of strawberry geranium (Saxifraga stolonifera) on Toll-like receptor 2-mediated inflammatory response in human skin keratinocytes

Strawberry geranium (Saxifraga stolonifera [L.] Meeb) has traditionally been used as a drug to treat skin disorders in Japan. However, little is known about its physiological effects on skin keratinocytes. Aim of the study: We investigated the anti-inflammatory effects of a strawberry geranium extract (SGE) on human skin keratinocytes. The human keratinocyte cell line, HaCaT, was treated with SGE, and then stimulated with tumor necrosis factor (TNF)-α. The expression of 207 genes related to the innate immune system was analyzed using DNA microarrays. The effect of SGE on the target proteins in primary human epidermal keratinocytes was confirmed by quantitative reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay. The mechanisms of action and active components involved in the suppressive effect of SGE were evaluated by fractionation and a transcription assay. The microarray analysis revealed that SGE primarily suppressed Toll-like receptor (TLR)2 expression through procyanidin B2 3,3′-di-O-gallate, without TLR2 downregulation, in TNF-α-stimulated HaCaT cells. SGE suppressed TLR2 expression and interleukin (IL)-8 production induced by TLR2 ligands in primary human epidermal keratinocytes and HaCaT cells. Multiple components downregulating TLR2 expression suppressed the Sp1 activity. We identified a novel physiological function of SGE, which suppresses TLR2 expression and TLR2-mediated inflammation in human skin keratinocytes. This study provides significant insights into the anti-inflammatory effect of SGE in human skin. [Display omitted] •SGE suppressed TLR 2 expression in TNF-α-stimulated HaCaT cells.•Components downregulating TLR2 expression were accompanied by Sp1 suppression.•SGE suppresses TLR2-mediated inflammation in human skin keratinocytes.