miR-146a Inhibits Biofilm-Derived Cutibacterium acnes-Induced Inflammatory Reactions in Human Keratinocytes

Acne is a chronic inflammatory skin disorder that often involves the formation of Cutibacterium acnes (C. acnes) biofilms. Several MicroRNAs (miRNAs) are known to be involved in inflammatory responses. However, it is unknown whether miRNAs play a role in the inflammatory reaction triggered by C. acnes biofilm. In this study, we investigated the role of miR-146a in biofilm-derived C. acnes-induced inflammatory responses. Increased expressions of miR-146a and Toll-like Receptor (TLR) 2 were detected in acne lesions. In the presence of biofilm-derived C. acnes, TLR2 and its downstream NF-kB and MAPK pathways were activated in keratinocytes. Subsequently, miR-146a was upregulated in these cells along with the induction of IL-6, IL-8, and tumor necrosis factor (TNF)-α. Furthermore, our data indicates that miR-146a could directly bind the 3'-untranslated region of IRAK1 and TNF receptor-associated factor 6 (TRAF6) and suppress their expression, leading to an inhibition of biofilm-derived C. acnes-induced activation of NF-kB, p38, and ERK1/2 pathways. Overall, our results indicate that biofilm-derived C. acnes induces miR-146a, which can downregulate the production of IL-6, -8, and TNF-α in acne inflammation by inhibiting the TLR2/IRAK1/TRAF6/NF-κB and MAPK pathways.