Changes in epidermal hyaluronan metabolism following UVB irradiation.

Background: Hyaluronan (HA) plays a role in keratinocyte proliferation and differentiation, and have shown different biological activities depending on its molecular mass. While many studies have shown changes in the amount of HA after UVB irradiation, molecular mass change remains to be elucidated.

Objective: To investigate the change in the molecular mass of HA after UVB irradiation in mouse epidermis.

Methods: The mice were irradiated with a single dose of UVB (0.15J/cm(2)). The amount of HA was examined using HABP sandwich assay. The molecular mass distribution was estimated by Sephacryl S-1000 chromatography. Has and Hyal mRNA expressions were detected by real-time PCR.

Results: On day 2 after UVB irradiation, both the amount of HA and the up-regulation of Has3 mRNA expression reached their maximum. The average HA molecular mass was about 1000 kDa, a level similar to that of the non-irradiated epidermis. On day 3, the average HA molecular mass drastically decreased to 100 kDa, while Hyal1, Hyal2, and Hyal3 mRNA expressions slightly increased. The amount of HA, however, remained high. On days 4 and 5, the amount of HA gradually decreased, but the molecular mass of HA remained low. A drastic reduction of the HA molecular mass after UVB irradiation was confirmed.

Conclusion: UVB irradiation elicits remarkable changes in the molecular mass of HA, as well as amount. These qualitative and quantitative changes of HA might play an important role in UVB-induced cell proliferation and differentiation. Further study will be required to resolve the mechanism of HA degradation in the epidermis.