The differential expression of protease activated receptors contributes to functional differences between dark and...

Dark skin has different properties in comparison to fair skin. Melanocytes have been shown to partly contribute to these differences, however, the involvement of keratinocytes from dark or fair skin is not well demonstrated.

This study investigated the proliferation and barrier function of dark keratinocytes (DK) and fair keratinocytes (FK), and the role of protease activated receptor (PAR)1 and PAR2.

DK and FK were isolated from human neonatal foreskins. Cells were treated with PAR1/PAR2 agonists or antagonists, proliferation was measured by BrdU assay; permeability by the flux of FITC-dextran; protein expression by immunostaining or western blot.

When compared to FK, DK proliferated significantly slower; had higher cell permeability; expressed less phosphorylated (P)-ERK/ERK, caspase-14, E-cadherin, tissue growth factor (TGF)-β3 and PAR1; and expressed more PAR2, and matrix metalloproteinase (MMP)-9. Activation of PAR1 or inhibition of PAR2 stimulated cell proliferation and ERK activation, and in concordance inhibition of PAR1 or activation of PAR2 suppressed cell proliferation and ERK activation in both DK and FK. Inhibition of PAR2 decreased and inhibition of PAR1 increased cell permeability. In foreskin sections, the epidermis of dark foreskin expressed less caspase-14 and the same level but different distribution of E-cadherin, when compared to fair foreskin.

These data highlight functional differences in proliferation and barrier integrity between HK and FK that are partly associated with their differential expression of PAR1 and PAR2.