Propionibacterium acnes is one of the most significant pathogenic factors of acne vulgaris. This bacteria relates to acne by various pathways. It has also been reported that P. acnes influences pro-inflammatory cytokine production in keratinocytes in vitro. However, the influence on the differentiation of keratinocytes by P. acnes has not been studied extensively. We analyzed the expression of keratinocyte differentiation-specific markers, keratins, and pro-inflammatory cytokines in normal human epidermal keratinocytes (NHEK) exposed to P. acnes in vitro. All P. acnes strains used in this study increased transglutaminase (TGase), keratin 17 (K17) and interleukin (IL) mRNA expression levels in NHEK, and decreased K1 and K10 expression levels. Some P. acnes strains increased involucrin and K6 mRNA expression levels in NHEK and decreased filaggrin, K6 and K16 expression levels in vitro. This experiment clarified that P. acnes influences the differentiation of NHEK in vitro. As a result, P. acnes influenced the expression of not only pro-inflammatory cytokines but also some keratinocyte differentiation-specific markers and keratins in NHEK. Our results suggest that P. acnes relates to acne pathogenesis by not only the induction of inflammation but also in the differentiation of keratinocytes. Moreover, it was considered that the reaction of NHEK to P. acnes may be different depending on the type of bacteria.
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