RIS-1/psoriasin expression in epithelial skin cells indicates their selective role in innate immunity and in inflammatory skin diseases including acne

Objective: RIS-1/psoriasin/S100A7 is an epithelial antimicrobial peptide, whose expression is upregulated in inflammatory skin diseases and is induced by retinoids. Its molecular expression was investigated in skin cell cultures and in skin specimens to better understand its role in inflammatory procedures of the pilosebaceous unit. Methods: rtPCR and northern blotting of RIS-1/psoriasin and the retinoid-metabolizing genes CYP26AI and CRABP-II were performed in cells cultures (keratinocytes, sebocytes, fibroblasts, endothelial cells, melanocytes, lymphocytes and prostate cells; native and treated with retinoids) and in situ hybridization in normal and inflamed skin (acne, psoriasis). Results: a) RIS-1/psoriasin is expressed in keratinocytes and fibroblasts in vitro and in keratinocytes of the stratum granulosum in vivo. Retinoids in vitro and inflammatory conditions in vivo increase the levels of RIS-1/psoriasin in keratinocytes (both), sebocytes (inflammation only) and fibroblasts (retinoids). Sebocytes and fibroblasts are the metabolically most active skin cells, since they can upregulate the expression of CRABP-II and CYP26AI, genes responsible for retinoid metabolism. Inflammation modifies the compartmentation of RIS-1/psoriasin in sebaceous glands and the follicular root sheaths. Conclusion: The present data indicate that anti-inflammatory treatment targeting the epithelial compartments of the skin, including such with antibacterial peptides, may be promising for inflammatory skin diseases.