8S-lipoxygenase products activate peroxisome proliferator-activated receptor alpha and induce differentiation in murine keratinocytes.

To determine the function and mechanism of action of the 8S-lipoxygenase (8-LOX) product of arachidonic acid, 8S-hydroxyeicosatetraenoic acid (8S-HETE), which is normally synthesized only after irritation of the epidermis, transgenic mice with 8-LOX targeted to keratinocytes through the use of a loricrin promoter were generated. Histological analyses showed that the skin, tongue, and stomach of transgenic mice are highly differentiated, and immunoblotting and immunohistochemistries of skin showed higher levels of keratin-1 expression compared with wild-type mice. The labeling index, however, of the transgenic epidermis was twice that of the wild-type epidermis. Furthermore, 8S-HETE treatment of wild-type primary keratinocytes induced keratin-1 expression. Peroxisome proliferator activated receptor alpha (PPARalpha) was identified as a crucial component of keratin-1 induction through transient transfection with expression vectors for PPARalpha, PPARgamma, and a dominant-negative PPAR, as well as through the use of known PPAR agonists. From these studies, it is concluded that 8S-HETE plays an important role in keratinocyte differentiation and that at least some of its effects are mediated by PPARalpha.