Stimulation of epidermal calcium gradient loss increases the expression of hyaluronan and CD44 in mouse skin

Background. Hyaluronan (HA), a major extracellular matrix component in epidermis, has been found to accumulate in the epidermis after disruption of the epidermal barrier; however, the precise mechanisms underlying this process are not yet clear. Alterations in the epidermal calcium gradient are an important signal for permeability-barrier homeostasis. Thus, we hypothesized that epidermal calcium-ions might regulate HA expression. Aim. To investigate whether changes in the epidermal calcium gradient and subsequent induction of cytokines regulate HA, HA synthase (HAS) and HA receptor (CD44) expression in mouse epidermis, and to clarify the mechanisms of HA induction. Methods. Sonophoresis of 1.5 mmol/L Ca²⁺-containing gel or Ca²⁺-free gel was performed to manipulate the epidermal Ca²⁺ content without disrupting the permeability barrier. We also manipulated the Ca²⁺ gradient by tape-stripping with or without 2 h immersion in 1.2 mmol/L Ca ²⁺-containing solutions. Next we inhibited cytokine activity using tumour necrosis factor (TNF)-α or interleukin (IL)-1 inhibitors before sonophoresis. Six hours after each treatment, the expression of HA, HAS and CD44 were analysed using reverse transcription PCR and immunohistochemical stains. Results. Sonophoresis of Ca²⁺-free gel significantly increased HA, HAS3 and CD44 expression in epidermis and in tape-stripped skin. However, the inhibition of Ca²⁺ decrease in the upper epidermis by sonophoresis of Ca²⁺-containing gel or immersion of barrier-disrupted skin into a Ca²⁺-containing solution attenuated these inductions. Specific inhibitors of TNF-α and IL-1 specific inhibitors also abolished the sonophoresis-induced expression of HA, HAS3 and CD44. Conclusions. These results suggest that modulations in epidermal calcium regulate HA and CD44 expression directly or via induction of cytokines.