Functional Expression of AQP3 in Human Skin Epidermis and Reconstructed Epidermis

Abstract

The purpose of this study was to examine the presence of aquaporin water channels in human skin and to assess their functional role. On western blots of human epidermis obtained from plastic surgery, a strong signal was obtained with polyclonal anti-aquaporin-3 antibodies. By indirect immunofluorescence on 5 microm cryosections, anti-aquaporin-3 antibodies strongly stained keratinocyte plasma membranes in human epidermis, whereas no staining was observed in the dermis or the stratum corneum or when anti-aquaporin-3 antibodies were preabsorbed with the peptide used for immunization. Similarly, a strong signal with anti-aquaporin-3 antibodies was observed in keratinocyte plasma membranes of reconstructed human epidermis in culture at the air-liquid interface for up to 3 wk. The keratinocyte plasma membrane localization of aquaporin-3 was confirmed at the electron microscope level in prickle cells. In addition an intracellular localization of aquaporin-3 was also detected in epidermis basal cells. Osmotically induced transepidermal water permeability was measured on stripped human skin and on reconstructed epidermis. Water transport across both stripped human skin and 2-3 wk reconstructed epidermis was comparable, inhibited by > 50% by 1 mM HgCl2 and fully inhibited by acid pH. By stopped-flow light scattering, keratinocyte plasma membranes, where aquaporin-3 is localized, exhibited a high, pH-sensitive, water permeability. Although human skin is highly impermeable to water, this is primarily accounted for by the stratum corneum, where a steep water content gradient was demonstrated. In contrast, the water content of viable strata of the epidermis is remarkably constant. Our results suggest that the human epidermis, below the stratum corneum, exhibits a high, aquaporin-3-mediated, water permeability. We propose that the role of aquaporin-3 is to water-clamp viable layers of the epidermis in order to improve the hydration of the epidermis below the stratum corneum.

An emerging consensus on aquaporin translocation as a regulatory mechanism

“…Chimeric proteins involving substitution of the AQP2 N-terminus for that of the AQP3 was able to re-direct localisation of AQP2 from its original site at the apical membrane to its new site at the basolateral membrane. Interestingly, despite this clear amino acid-sorting motif, membrane expression of AQP3 is not polarised in red blood cells (Roudier et al, 1998) or in epidermal keratinocytes and in the epidermis "basal cells"; AQP3 may be predominantly intracellular (Sougrat et al, 2002).…”

Prevention of Skin Tumorigenesis and Impairment of Epidermal Cell Proliferation by Targeted Aquaporin-3 Gene Disruption

“…The mechanisms underlying these phenomena were attributed to the glyceroltransporting function of aquaglyceroporins. In mammalian skin, AQP3 is expressed in plasma membranes of the basal epidermal cell layer (4,16,25). A human keratocarcinoma cell line has also been found to express AQP3 (20).…”

Expression and Localization of Aqua-glyceroporins AQP3 and AQP9 in Rat Oral Epithelia

“…In renal collecting ducts, AQP3 is localized at the basolateral membrane, where epithelial cells would encounter possible osmotic water loss due to the difference in tonicity between luminal urine and intracellular fluid 7,8) . AQP3 is also present in the squamous epithelium of skin, where it serves as a barrier against water loss and improves hydration below the cornified layer 12,26,32) . AQP9 expression has been reported in several tissues, including those of the digestive tract, liver, and skin.…”