Increased expression of glucagon-like peptide-1 receptors in psoriasis plaques

Recent case reports suggest that treatment with glucagon-like peptide-1 (GLP-1) agonists results in clinical improvement of psoriasis. The purpose of this study was to determine whether GLP-1 receptors (GLP-1Rs) are found in the skin of healthy volunteers and psoriasis patients and if so, whether GLP-1Rs are located on keratinocytes or immune cells. Three mm-punch skin biopsies were taken for gene expression analysis from six healthy volunteers and from affected and unaffected skin of six psoriasis patients. In addition, a blood sample was obtained from all participants. Cultured human keratinocytes were either untreated or incubated with tumor necrosis factor- (TNF-), interferon- (IFN-) or a combination of TNF- and IFN- for 48h. Total RNA was extracted from all the samples, reversely transcribed and analysed for the expression of GLP-1R using real-time PCR. Gene expression analysis showed expression of GLP-1Rs in five of six skin biopsies from psoriasis plaques, in one of six biopsies from unaffected psoriatic skin and in one of six biopsies from healthy skin. GLP-1R expression was found in the blood of both healthy volunteers and psoriasis patients. No GLP-1R expression was found in either stimulated or unstimulated cultured human keratinocytes. Our results show increased presence of GLP-1Rs in psoriasis plaques and that this most likely is due to infiltration with immune cells. This offers a possible explanation for the positive effect of treatment with GLP-1R agonists in patients with psoriasis.