**4.4 Nuclear hormone receptor activators**

Feingold and his co-workers demonstrated an important influence of nuclear hormone receptors on epidermal differentiation and stratum corneum barrier formation. Activation of PPAR by farnesol stimulated the differentiation of epidermal keratinocytes (Feingold 1999)(Hanley 2000). Cornified envelope formation and involucrin and transglutaminase protein and mRNA levels were also increased by the activation of PPAR(Feingold 2000). Interestingly, the inflammatory response was also inhibited (Sheu 2002). Topical application of PPAR activators accelerated barrier recovery after tape stripping or acetone treatment and prevented the epidermal hyperplasia induced by repeated barrier disruption (Feingold 1999). Regulation of nuclear hormone receptors might therefore be a possible approach for improvement of the cutaneous barrier.
