MicroRNAs: novel regulators involved in the pathogenesis of psoriasis?

Abstract

MicroRNAs are a recently discovered class of posttranscriptional regulators of gene expression with critical functions in health and disease. Psoriasis is the most prevalent chronic inflammatory skin disease in adults, with a substantial negative impact on the patients' quality of life. Here we show for the first time that psoriasis-affected skin has a specific microRNA expression profile when compared with healthy human skin or with another chronic inflammatory skin disease, atopic eczema. Among the psoriasis-specific microRNAs, we identified leukocyte-derived microRNAs and one keratinocyte-derived microRNA, miR-203. In a panel of 21 different human organs and tissues, miR-203 showed a highly skin-specific expression profile. Among the cellular constituents of the skin, it was exclusively expressed by keratinocytes. The up-regulation of miR-203 in psoriatic plaques was concurrent with the down-regulation of an evolutionary conserved target of miR-203, suppressor of cytokine signaling 3 (SOCS-3), which is involved in inflammatory responses and keratinocyte functions. Our results suggest that microRNA deregulation is involved in the pathogenesis of psoriasis and contributes to the dysfunction of the cross talk between resident and infiltrating cells. Taken together, a new layer of regulatory mechanisms is involved in the pathogenesis of chronic inflammatory skin diseases.

Figure 1. MicroRNA expression profiling in psoriasis, atopic eczema and healthy skin.

(A) microRNA (miRNA) array comparison of skin from healthy individuals (H, n = 4) and lesional skin from patients with psoriasis (PSO, n = 3) and atopic eczema (AE, n = 3). Total RNA from skin biopsies was labeled and hybridized to microarrays containing probes corresponding to known miRNA sequences. The heat map summarizes the biological replicates for the skin specimens, and four technical replicates for each set. Color intensity is scaled within each row so that the highest expression value corresponds to bright red and the lowest to bright green. Gene names are listed to the right. (B) miRNAs showing more than 1.7-fold change between psoriasis and healthy skin (left) and atopic eczema and healthy skin (right) according to the SAM algorithm. miRNAs that are over-expressed in both psoriasis and in atopic eczema are highlighted in yellow, miRNAs that are down-regulated in both diseases are highlighted in blue. (C) The expressions of the functionally active, mature forms of four miRNAs were analyzed using quantitative real-time PCR in the skin of 26 healthy individuals, and lesional skin samples of 20 patients with atopic eczema and 25 patients with psoriasis. The results for individual patients and mean are shown. Data are expressed in relative units compared to U48 RNA. ***p<0.001, **p<0.01.

Figure 2. Expression of miR-203, miR-146a, miR-21 and miR-125b in human organs.

The expressions of the functionally active, mature forms of miR-203, miR-21, miR-146a and miR-125b were analyzed using quantitative real-time PCR in 20 healthy organs and tissues (each a pool of three donors) as well as in healthy skin (n = 26), lesional atopic eczema (n = 20) and psoriasis (n = 25) skin samples. Error bars represent the standard error of the mean. Data are expressed in relative units compared to U48 RNA. ***p<0.001, **p<0.01.

Figure 3. Expression of miR-203, miR-146a, miR-21 and miR-125b in the cellular constituents of the skin.

The expressions of the functionally active, mature forms of miR-203, miR-146a, miR-21 and miR-125b were analyzed in the cellular constituents of the skin including primary adult keratinocytes, dermal fibroblasts, melanocytes, monocyte-derived dendritic cells (MDDCs), polymorphonuclear leukocytes (PMN), granulocytes, eosinophils, CD69⁺ cells, CD19⁺ cells, CD56⁺ cells, CD4⁺CD25^high cells, CD8⁺ cells, CD4⁺ cells and mast cells using quantitative real-time PCR. Data are expressed in relative units compared to U48 RNA.

Figure 4. SOCS-3 may be a molecular target of miR-203 posttranscriptional repression.

(A) SOCS-3 is an evolutionarily conserved target of miR-203. The putative targets site of miR-203 is highly conserved among species. The 8mer seed sequence in the 3′UTR of SOCS-3 gene corresponding to miR-203 binding site is underlined. (B) In situ hybridization with LNA-oligonucleotide probes specific to miR-203 in skin sections from healthy skin and psoriatic lesional skin. Data are representative of 6 healthy and 6 psoriatic individuals. Note strong staining in the suprabasal layers of the epidermis in psoriatic skin. The expression of SOCS-3 in healthy and psoriasis skin samples was detected using immunohistochemistry. Original magnification 200x. (C) The expression of SOCS-3 in skin from healthy individuals or lesional skin of psoriatic patients was analyzed using Western blot analysis. SOCS-3 protein levels are expressed as relative units. Bars represent means of SOCS-3 protein levels in healthy skin (n = 6) and psoriatic lesional skin (n = 11) ± SEM. ** p<0.01.