Differential expression of peroxisome proliferator-activated receptor subtypes during the differentiation of human keratinocytes

The expression of mRNA encoding peroxisome proliferator-activated receptor (PPAR) subtypes in human keratinocytes was determined by semiquantitative r everse transcriptase-polymerase chain reaction. When normal human keratinoc ytes were induced to differentiate by shifting the culture medium to high C a2+ concentration, the expression of PPAR-alpha and -gamma mRNA was increas ed, whereas that of PPAR-delta remained unchanged. At the protein level, th e expression of PPAR in cultured human keratinocytes was demonstrated by a DNA mobility shift assay and the functionality of the receptor subtypes was assessed by transactivation experiments. In epidermis reconstructed in vit ro, the level of PPAR-alpha and -gamma mRNA was also associated with kerati nocyte differentiation. In lesional compared with nonlesional psoriatic epi dermis, the expression of PPAR-a and -gamma mRNA was reduced, indicating th at these two subtypes are tightly linked to the epidermal differentiation p rocess.