Effect of vitamin D3 on the increased expression of Bcl-xL in psoriasis

Psoriasis is a chronic skin disease characterized by epidermal hyperproliferation, which may be regulated by several mechanisms including apoptosis. In this study, we detected DNA fragmentation by the terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) method and immunohistochemically examined the expression of Bcl-x and Bax in psoriasis. We determined the expression of bcl-xL mRNA by RT-PCR, and also determined the effect of vitamin D(3) (VD3) on bcl-xL mRNA expression in cultured normal human keratinocytes by RT-PCR, and the expression of Bcl-xL in psoriatic lesions before and after topical application of VD3. A large number of TUNEL-positive cells as well as Bcl-xL - and Bax-positive cells were observed throughout the epidermis in psoriatic lesions. Whereas, in nonlesional and normal skin, only a few TUNEL-positive cells were observed and only the lower epidermis showed positive staining for Bcl-x and Bax. We also observed higher expression of bcl-xL mRNA in psoriatic lesions than in nonlesional and normal skin. The expression of bcl-xL mRNA in cultured normal human keratinocytes stimulated or not with IFN-gamma and PMA was suppressed by VD3 in a dose-dependent manner, and the expression of Bcl-xL, but not Bax, in psoriatic lesional skin decreased after topical application of VD3 for 4 weeks. In conclusion, it is suggested that the apoptotic process in psoriatic lesions is in part regulated by Bcl-xL, and decreasing the expression of Bcl-xL by treatment with VD3 might ameliorate psoriatic lesions by contributing to the completion of the apoptotic process.