Genomic-scale analysis of psoriatic skin reveals differentially expressed insulin-like growth factor-binding protein-7 after phototherapy

Background: Phototherapy is an effective therapy for psoriasis. The molecular mechanisms underlying its efficacy are not yet understood. Objectives: To compare the expression profiles of psoriatic epidermis in patients before and after undergoing phototherapy with the purpose of expounding the molecular mechanisms underlying the efficacy of this therapeutic modality. Methods: Patients with psoriasis were investigated before and after full courses of phototherapy: three patients completed 3 weeks of heliotherapy at the Dead Sea; three patients received narrowband ultraviolet B (NB-UVB) for a total of 20-27 treatments. Epidermal samples were analysed using oligonucleotide microarrays. Our microarray results led us to explore further and to quantify a specific gene, insulin-like growth factor-binding protein-7 (IGFBP7), using real-time quantitative reverse transcriptase-polymerase chain reaction assays and immunohistochemical protein expression. Results: We identified 315 genes modulated by phototherapy: the expressions of 248 genes (142 up; 106 down) were changed by Dead Sea treatment, 116 (71 up; 45 down) by NB-UVB and 49 (37 up; 12 down) were modulated regardless of treatment. The differentially changed genes include S100 calcium-binding proteins, dendritic cell markers, tumour necrosis factor-α target genes, matrix metalloproteinases and NFκB target genes. We also found that IGFBP7 mRNA and protein were significantly underexpressed in psoriatic compared with normal epidermis, and that phototherapy significantly increased their expression. Conclusions: IGFBP7 is underexpressed in psoriatic epidermis but is inducible by UVB.