Differential regulation of hyaluronan metabolism in the epidermal and dermal compartments of human skin by UVB irradiation.

Hyaluronan (HA), a major component of the cutaneous extracellular-matrix, is involved in tissue repair. Human skin is exposed to and damaged by UVB-irradiation. Here, we investigate the regulation of HA metabolism in human skin during acute UVB-induced inflammation. Expression of HA synthesizing (HAS) and degrading enzymes hyaluronidase (HYAL) as evaluated by quantitative reverse transcribed PCR in response to UVB differed when fibroblasts and HaCaT-keratinocytes, representative cell types in dermis and epidermis, respectively, were compared. Both demonstrated temporally different expression patterns of these genes 3- and 24-hours post-irradiation. This resulted 24-hours post-irradiation in an increase in HAS gene expression in both fibroblasts and HaCaT-keratinocytes, and an increase in HYAL expression only in fibroblasts. HA-production as analyzed by the HA content of conditioned medium was reduced in HaCaT and fibroblast cultures 3-hours post-irradiation, whereas HA increased in HaCaT-cultures 24-hours post-irradiation but remained suppressed in fibroblasts-cultures. Consistently, immunohistochemical staining for HA in human skin 24-hours post-irradiation demonstrated an increased epidermal HA, but a decrease in the dermal compartment. Moreover, analysis of the HA content of dermal microdialysis-fluid revealed increased accumulation of HA degradation products 24-hours post-irradiation. These data demonstrate that there is a complex temporal and spatial regulation of HA-metabolism in skin in response to UVB irradiation.