1. ^*Department of Dermatology, Jichi Medical University, Tochigi, Japan
2. ^†Kao Biological Science Laboratories, Tochigi, Japan

Correspondence: Genji Imokawa, Kao Biological Science Laboratories, 2606 Akabane, Ichikai-machi, Haga, Tochigi 321-34, Japan. Email: imokawag@dream.ocn.ne.jp

Received 24 March 2004; Revised 17 June 2004; Accepted 3 July 2004.

Abstract

Although ultraviolet B (UVB) irradiation perturbs the skin barrier, little is known about the mechanism(s) with respect to the metabolism of ceramide (Cer). We examined changes in intercellular lipids in murine stratum corneum following UVB irradiation. A single UVB (75 mJ per cm²) irradiation caused a significant increase in transepidermal water loss, which plateaued at day 4. In parallel, covalently bound Cer was significantly decreased with the greatest decrease at days 3–4. In contrast, the levels of other free, non-bound lipids (including Cer or acylceramides) were significantly increased for Cer, or remained unchanged at day 4 compared with non-irradiated controls. RT-PCR analysis demonstrated a significant decrease in mRNA encoding transglutaminase-1 (TGase1). The peak occurred 2–4 d after a single UVB irradiation, a time when covalently bound Cer was significantly downregulated in concert with the disruption of the skin barrier. Furthermore, UVB-induced epidermal hyperplasia occurred to the greatest extent between 2 and 4 d following UVB irradiation. These results suggest that decreases in covalently bound Cer in the stratum corneum are mediated via the downregulation of TGase-1 as well as by the rapid induction of epidermal hyperplasia, which is attributable to the perturbation of the skin barrier induced by UVB irradiation.