Abstract 269 Poster Session I, Saturday, 5/1 (poster 147)

Background: Specific water channels, aquaporins (AQP), allow for a rapid and regulated transcellular water transport. In most tissues, such as brain, kidney and lung, there is a pronounced increase in water channel expression postnatally. In extremely preterm newborn infants, high transepidermal water loss is a clinical problem. This raises the question whether the developmental pattern of AQPs in skin differs from that in other tissues and whether AQPs contribute to this water loss.

Methods: After identifying two AQP isoforms in adult rat skin. AQP 1 and 3, we investigated the developmental pattern of AQP mRNA expression in embryonic (E) and postnatal (PN) rat skin, using semi-quantitative RT-PCR with beta-actin as a reference. The distribution of AQPs in the skin was studied with immunohistochemistry.

Results: AQP1 mRNA was highest in embryonic skin (E18 and 19), being 1.5-fold higher than in skin from rats born at term and 2-fold that found in PN12 and adult, a development pattern in the skin that differs dramatically from that in other tissues. AQP3 mRNA is 1.5-fold higher at E18 than at term. After birth, however, AQP3 are higher with adult values more than 2-fold higher than at term. Immunolocalisation revealed predominant labeling of AQP1 in capillaries with a tendency to stronger staining and more superficial pattern in embryonic skin. AQP3 was demonstrated at the apical-lateral membrane in the basal cells of the epidermis. Labeling was more intense in embryonic than in adult skin and was found in several cell layers. AQP3 was also demonstrated in hair follicles and sebaceous glands in adult skin.

Conclusion: We have demonstrated that the developmental pattern of AQPs in perinatal skin differs from that seen in other tissues with a decrease in AQP1mRNA expression with increasing gestational and postnatal age. AQP1 is located in skin capillaries and AQP3 in the basal cell layers of the epidermis; locations where an abundance of water channels could affect skin hydration and permeability. The results are compatible with the concept that a relatively high expression of water channels plays a role in the high transepidermal water loss in extremely preterm infants.