title: Analysis of aquaporin 9 expression in human epidermis and cultured keratinocytes.
abstract: Aquaporin 9 (AQP9) is a member of the aquaglyceroporin family that transports glycerol, urea and other small solutes as well as water. Compared to the expression and function in epidermal keratinocytes of AQP3, another aquaglyceroporin, our knowledge of epidermal AQP9 remains elusive. In this study, we investigated the expression of AQP9 in the human epidermis and cultured keratinocytes. Immunofluorescence studies revealed that AQP9 expression is highly restricted to the stratum granulosum of the human epidermis, where occludin is also expressed at the tight junctions. Interestingly, the AQP3 staining decreased sharply below the cell layers in which AQP9 is expressed. In cultured normal human epidermal keratinocytes (NHEK), knock-down of AQP9 expression in the differentiated cells induced by RNA interference reduced glycerol uptake, which was not as pronounced as was the case with AQP3 knock-down cells. In contrast, similar reduction of urea uptake was detected in AQP9 and AQP3 knock-down cells. These findings suggested that AQP9 expression in NHEK facilitates at least the transport of glycerol and urea. Finally, we analyzed the effect of retinoic acid (RA), a potent stimulator of keratinocyte proliferation, on AQP3 and AQP9 mRNA expression in differentiated NHEK. Stimulation with RA at 1 μM for 24 h augmented AQP3 expression and down-regulated AQP9 expression. Collectively, these results indicate that AQP9 expression in epidermal keratinocytes is regulated in a different manner from that of AQP3.
authors.affiliation: Innovative Beauty Science Laboratory, Kanebo Cosmetics Inc., Odawara, Japan ; Department of Biomedical Engineering, Toin University of Yokohama, Yokohama, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Sugiyama
authors.affiliation: Innovative Beauty Science Laboratory, Kanebo Cosmetics Inc., Odawara, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Yamazaki
authors.affiliation: Innovative Beauty Science Laboratory, Kanebo Cosmetics Inc., Odawara, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kusaka-Kikushima
authors.affiliation: Department of Dermatology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Nakahigashi
authors.affiliation: Department of Biomedical Engineering, Toin University of Yokohama, Yokohama, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Hagiwara
authors.affiliation: Department of Dermatology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Miyachi
keywords: AQP3; AQP9; AQPs, aquaporins; DUOX1, dual oxidase I; Differentiated keratinocytes; Epidermis; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; LXR, liver X receptor; NHEK, normal human epidermal keratinocytes; PPARγ, peroxisome proliferators-activated receptor gamma; RA, retinoic acid; SG, stratum granulosum; TJs, tight junctions; VD3, 1,25-dihydroxyvitamin D3