Prolonged recovery of ultraviolet B-irradiated skin in neuropsin (KLK8)-deficient mice

Background Neuropsin (KLK8), a serine protease of the kallikrein family, is thought to be involved in the function of keratinocytes, i.e. migration, differentiation and desquamation. However, how neuropsin participates is still unknown. Objective To observe the epidermal function of serine protease in neuropsin-deficient mice. Methods We irradiated the skin of neuropsin-deficient mice with ultraviolet light to induce acute inflammation and compared the morphology with that of wild-type mice. Results We observed a phenotypic change in the epidermis. An acute inflammatory dose of ultraviolet light induced a marked increase in neuropsin mRNA expression in the skin. The signal intensity of the mRNA expression was highest on day 2-3 after irradiation, when keratinocytes were aligned irregularly in the recovery period. Morphological comparison between neuropsin -/- and +/+ mice revealed that an irregular alignment of cells in the thickened epidermis was obvious on day 2 after irradiation in the wild-type mice, whereas it was prolonged for at least 2 days in the neuropsin-deficient mice. The stratum corneum of neuropsin-deficient mice was remarkably thicker than that of the wild-type mice at 5, 14 and 21 days after irradiation. The increase, as a response to this stimulus, in involucrin immunoreactivity, a marker for cell envelope assembly, was delayed in the mutant mice. Conclusions Thus, neuropsin might be involved early in the process of differentiation, such as in the assembly of the cell envelope, but not in migration and desquamation.