Mona Ståhle

A genome-wide association study identifies new psoriasis susceptibility loci and an interaction between HLA-C and ERAP1

To identify new susceptibility loci for psoriasis, we undertook a genome-wide association study of 594,224 SNPs in 2,622 individuals with psoriasis and 5,667 controls. We identified associations at eight previously unreported genomic loci. Seven loci harbored genes with recognized immune functions (IL28RA, REL, IFIH1, ERAP1, TRAF3IP2, NFKBIA and TYK2). These associations were replicated in 9,079 European samples (six loci with a combined P < 5 × 10−8 and two loci with a combined P < 5 × 10−7). We also report compelling evidence for an interaction between the HLA-C and ERAP1 loci (combined P = 6.95 × 10−6). ERAP1 plays an important role in MHC class I peptide processing. ERAP1 variants only influenced psoriasis susceptibility in individuals carrying the HLA-C risk allele. Our findings implicate pathways that integrate epidermal barrier dysfunction with innate and adaptive immune dysregulation in psoriasis pathogenesis.

MicroRNAs and immunity: Novel players in the regulation of normal immune function and inflammation

The discovery of microRNAs (miRNAs) is one of the major scientific breakthroughs in recent years and has revolutionized the way we look at gene regulation. Although we are still at a very early stage in understanding their impact on immunity, miRNAs are changing the way we think about the development of the immune system and regulation of immune functions. MiRNAs are implicated in establishing and maintaining the cell fate of immune cells (e.g. miR-181a and miR-223), and they are involved in innate immunity by regulating Toll-like receptor signaling and ensuing cytokine response (e.g. miR-146). Moreover, miRNAs regulate central elements of the adaptive immune response such as antigen presentation (e.g. miR-155) and T cell receptor signaling (miR-181a). Recent evidence showing altered miRNA expression in chronic inflammatory diseases (e.g. miR-203 and miR-146) suggests their involvement in immune-mediated diseases. Furthermore, miRNAs have been implicated in viral immune escape and anti-viral defense (e.g. miR-196). In this review, we will summarize the latest findings about the role of miRNAs in the development of the immune system and regulation of immune functions and inflammation.

MicroRNAs: novel regulators in skin inflammation

Compelling evidence indicates that microRNAs (miRNAs), short, non‐protein coding RNAs, are critical for the development and survival of multicellular organisms. Recently, miRNAs were implicated in the pathogenesis of psoriasis and atopic eczema (AE), the two most common chronic inflammatory disorders in skin. In particular, miR‐203, the first skin‐specific miRNA, showing an intriguing expression profile being confined to skin epithelium, is specifically overexpressed in psoriasis. MiR‐146a, another miRNA showing specific upregulation in psoriasis, is involved in the regulation of innate immune responses and the tumour necrosis factor (TNF)‐α pathway. Interestingly, miR‐125b, another miRNA involved in the TNF‐α pathway, is also deregulated in psoriasis and AE. As skin inflammation may serve as a model for chronic inflammatory disorders, it is likely that miRNAs involved in skin inflammation will eventually emerge in other inflammatory or autoimmune disorders, and some of these may become disease markers and therapeutic targets. In this review we present an overview of what is currently known about the roles of miRNAs in chronic inflammatory skin disorders.

MiR-155 is overexpressed in patients with atopic dermatitis and modulates T-cell proliferative responses by targeting cytotoxic T lymphocyte–associated antigen 4

BACKGROUND MicroRNAs (miRNAs) are short noncoding RNAs that suppress gene expression at the posttranscriptional level. Atopic dermatitis is a common chronic inflammatory skin disease characterized by the presence of activated T cells within the skin. OBJECTIVE We sought to explore the role of miRNAs in the pathogenesis of atopic dermatitis. METHODS Global miRNA expression in healthy and lesional skin of patients with atopic dermatitis was compared by using TaqMan MicroRNA Low Density Arrays. miR-155 expression in tissues and cells was quantified by means of quantitative real-time PCR. The cellular localization of miR-155 was analyzed by means of in situ hybridization. The regulation of cytotoxic T lymphocyte-associated antigen (CTLA-4) by miR-155 was investigated by using luciferase reporter assays and flow cytometry. CTLA-4 expression and functional assays were performed on T(H) cells overexpressing miR-155. RESULTS miR-155 was one of the highest-ranked upregulated miRNAs in patients with atopic dermatitis. In the skin miR-155 was predominantly expressed in infiltrating immune cells. miR-155 was upregulated during T-cell differentiation/activation and was markedly induced by T-cell activators in PBMCs in vitro and by superantigens and allergens in the skin in vivo. CTLA-4, an important negative regulator of T-cell activation, was identified as a direct target of miR-155. Overexpression of miR-155 in T(H) cells resulted in decreased CTLA-4 levels accompanied by an increased proliferative response. CONCLUSION miR-155 is significantly overexpressed in patients with atopic dermatitis and might contribute to chronic skin inflammation by increasing the proliferative response of T(H) cells through the downregulation of CTLA-4.

MiR-125b, a MicroRNA Downregulated in Psoriasis, Modulates Keratinocyte Proliferation by Targeting FGFR2

MicroRNAs (miRNAs) are short, single-stranded, noncoding RNAs that play important roles in the regulation of gene expression. We previously identified a characteristic miRNA expression profile in psoriasis, distinct from that of healthy skin. One of the most downregulated miRNAs in psoriasis skin was microRNA-125b (miR-125b). In this study, we aimed to identify the potential role(s) of miR-125b in psoriasis pathogenesis. In situ hybridization results showed that the major cell type responsible for decreased miR-125b levels in psoriasis lesions was the keratinocyte. Overexpression of miR-125b in primary human keratinocytes suppressed proliferation and induced the expression of several known differentiation markers. Conversely, inhibition of endogenous miR-125b promoted cell proliferation and delayed differentiation. Fibroblast growth factor receptor 2 (FGFR2) was identified as one of the direct targets for suppression by miR-125b by luciferase reporter assay. The expression of miR-125b and FGFR2 was inversely correlated in both transfected keratinocytes and in psoriatic skin. Knocking down FGFR2 expression by siRNA suppressed keratinocyte proliferation, but did not enhance differentiation. Altogether, our results demonstrate a role for miR-125b in the regulation of keratinocyte proliferation and differentiation, partially through the regulation of FGFR2. Loss of miR-125b in psoriasis skin may contribute to hyperproliferation and aberrant differentiation of keratinocytes.

Excessive body weight and smoking associates with a high risk of onset of plaque psoriasis.

Accumulating evidence indicates that body weight, alcohol and smoking are associated with psoriasis. However, these factors have scarcely been investigated in relation to onset and disease activity at onset of psoriasis. A population-based case-control study was performed including 373 cases with onset of first-time plaque psoriasis within 12 months and matched healthy controls. Psoriasis activity was measured using the Psoriasis Area and Severity Index (PASI). Analyses were performed using conditional logistic regression. In multivariable analyses for each unit increment in body mass index, there was statistically significant 9% increased risk for psoriasis onset and 7% higher risk for increased PASI. Obesity (body mass index > or =30) compared with normal body weight was associated with a two-fold increased risk for psoriasis onset. Smoking was associated with a 70% increased risk for onset, but was not related to PASI. A positive association with alcohol drinking was observed among men, but not among women. No associations were observed for weight gain and use of smokeless tobacco. Our results indicate that excessive body weight and smoking are risk factors for onset of psoriasis and that higher body mass index increases the PASI of plaque psoriasis at onset.

MicroRNA-125b Down-regulates Matrix Metallopeptidase 13 and Inhibits Cutaneous Squamous Cell Carcinoma Cell Proliferation, Migration, and Invasion

Background: The role of microRNAs in cutaneous squamous cell carcinoma (cSCC) is not well understood. Results: cSCC has a unique miRNAome. MicroRNA-125b is down-regulated in human cSCC and suppresses growth and motility of cSCC cells through targeting Matrix Metallopeptidase 13. Conclusion: MicroRNA-125b may play a tumor suppressive role in cSCC. Significance: This study suggests a role for microRNAs in cSCC pathogenesis. Cutaneous squamous cell carcinoma (cSCC) is the second most common human cancer. Although dysregulation of microRNAs (miRNAs) is known to be involved in a variety of cancers, the role of miRNAs in cSCC is unclear. In this study, we aimed to identify tumor suppressive and oncogenic miRNAs involved in the pathogenesis of cSCC. MiRNA expression profiles in healthy skins (n = 4) and cSCCs (n = 4) were analyzed using MicroRNA Low Density Array. MiR-125b expression was analyzed by quantitative real-time PCR and in situ hybridization in skin biopsies from 40 healthy donors, 13 actinic keratosis, and 74 cSCC patients. The effect of miR-125b was analyzed in wound closure, colony formation, migration, and invasion assays in two cSCC cell lines, UT-SCC-7 and A431. The genes regulated by miR-125b in cSCC were identified by microarray analysis and its direct target was validated by luciferase reporter assay. Comparing cSCC with healthy skin, we identified four up-regulated miRNAs (miR-31, miR-135b, miR-21, and miR-223) and 54 down-regulated miRNAs, including miR-125b, whose function was further examined. We found that miR-125b suppressed proliferation, colony formation, migratory, and invasive capacity of cSCC cells. Matrix metallopeptidase 13 (MMP13) was identified as a direct target suppressed by miR-125b, and there was an inverse relationship between the expression of miR-125b and MMP13 in cSCC. Knockdown of MMP13 expression phenocopied the effects of miR-125b overexpression. These findings provide a novel molecular mechanism by which MMP13 is up-regulated in cSCCs and indicate that miR-125b plays a tumor suppressive role in cSCC.

Protein Kinase C-Dependent Upregulation of miR-203 Induces the Differentiation of Human Keratinocytes

Terminal differentiation of keratinocytes is a multistep process that requires a coordinated program of gene expression. We aimed to explore the possible involvement of a previously unreported class of non-coding RNA genes, microRNAs (miRNAs) in keratinocyte differentiation by using miRNA expression profiling. Out of 365 miRNAs tested, 7 showed significant change between keratinocytes cultured in low or high calcium concentration. The highest-ranked upregulated gene was miR-203, whose expression was significantly upregulated in response to calcium and other inducers of keratinocyte differentiation such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and vitamin D(3). Differentiation-induced upregulation of miR-203 expression was blocked by treatment with specific inhibitors of protein kinase C (PKC), GF109203X, and Ro31-8220. Moreover, our results showed that the activator protein-1 (AP-1) proteins c-Jun and JunB regulate miR-203 expression in keratinocytes. In contrast to inducers of keratinocyte differentiation, epidermal growth factor and keratinocyte growth factor suppressed miR-203 expression in keratinocytes below the basal level. Overexpression of miR-203 in keratinocytes resulted in enhanced differentiation, whereas inhibition of miR-203 suppressed calcium-induced terminal differentiation as judged by involucrin expression. These results suggest that upregulation of miR-203 in human keratinocytes is required for their differentiation and is dependent on the activation of the PKC/AP-1 pathway.

Antimicrobial protein hCAP18/LL-37 is highly expressed in breast cancer and is a putative growth factor for epithelial cells

Human cathelicidin antimicrobial protein hCAP18/LL‐37 is an effector molecule of the nonspecific innate immune system. hCAP18/LL‐37 is present in leukocytes and is expressed in skin and other epithelia, where it is upregulated in association with inflammation and injury. In addition, antimicrobial proteins including cathelicidins have been proposed to play a role in the nonspecific defense against tumors. To assess its potential role in tumor host defense, we investigated the expression of hCAP18/LL‐37 in a series of breast carcinomas. Unexpectedly, we found that hCAP18/LL‐37 was strongly expressed in the tumor cells and not in the adjacent stroma. To test the hypothesis that hCAP18/LL‐37 may provide a growth advantage for the tumor cells, we treated human epithelial cell lines with synthetic biologically active LL‐37 peptide and found a significant increase in cell proliferation. In addition, transgenic expression of hCAP18 in 2 different human epithelial cell lines resulted in increased proliferation of both cell types. These findings do not support the hypothesis that LL‐37 has an antitumor effect, but rather suggest that hCAP18/LL‐37 may promote tumor cell growth in breast cancer.

MicroRNA-31 Is Overexpressed in Psoriasis and Modulates Inflammatory Cytokine and Chemokine Production in Keratinocytes via Targeting Serine/Threonine Kinase 40

Psoriasis is characterized by a specific microRNA expression profile, distinct from that of healthy skin. MiR-31 is one of the most highly overexpressed microRNAs in psoriasis skin; however, its biological role in the disease has not been studied. In this study, we show that miR-31 is markedly overexpressed in psoriasis keratinocytes. Specific inhibition of miR-31 suppressed NF-κB–driven promoter luciferase activity and the basal and TNF-α–induced production of IL-1β, CXCL1/growth-related oncogene-α, CXCL5/epithelial-derived neutrophil-activating peptide 78, and CXCL8/IL-8 in human primary keratinocytes. Moreover, interference with endogenous miR-31 decreased the ability of keratinocytes to activate endothelial cells and attract leukocytes. By microarray expression profiling, we identified genes regulated by miR-31 in keratinocytes. Among these genes, we identified serine/threonine kinase 40 (STK40), a negative regulator of NF-κB signaling, as a direct target for miR-31. Silencing of STK40 rescued the suppressive effect of miR-31 inhibition on cytokine/chemokine expression, indicating that miR-31 regulates cytokine/chemokine expression via targeting STK40 in keratinocytes. Finally, we demonstrated that TGF-β1, a cytokine highly expressed in psoriasis epidermis, upregulated miR-31 expression in keratinocytes in vitro and in vivo. Collectively, our findings suggest that overexpression of miR-31 contributes to skin inflammation in psoriasis lesions by regulating the production of inflammatory mediators and leukocyte chemotaxis to the skin. Our data indicate that inhibition of miR-31 may be a potential therapeutic option in psoriasis.