Background: The skin is constantly exposed to various external stimuli including humidity variations. Low humidity affects skin properties such as decreased water content of the stratum corneum, reduced skin elasticity, and itching. However, the effects of humidity on the skin cells are not completely understood. This study aimed to investigate how low humidity affects keratinocytes of the skin. Methods and results: In the present study, the effects of dry environment on the gene expression profile of epidermal keratinocytes were demonstrated using a three-dimensional skin model (3D-skin), composed of keratinocytes. Exposure of 3D-skin to low humidity (relative humidity ~ 10%) increased the expression levels of various genes, including those related to signal transduction and immune system. Accordingly, p38 mitogen-activated protein kinase (MAPK) signaling in keratinocytes of the 3D-skin was activated in response to low humidity for 30 min. Additionally, several chemokines, such as chemokine (C-X-C motif) ligand 1 (CXCL1) and Chemokine (C-C motif) ligand 20 (CCL20), were up regulated after 3 h of exposure to low humidity. Conclusions: We hypothesize that increased chemokine production may affect the immune system of the whole skin through chemoattractants. Our findings imply that keratinocytes sense low humidity and resultant activation of some cell-signaling pathways leads to variations in gene expression profiles including various chemokines. We provide evidence that keratinocytes adapt to external humidity variations.
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