An Important Role of the SDF-1/CXCR4 Axis in Chronic Skin Inflammation

Citation: Zgraggen S, Huggenberger R, Kerl K, Detmar M ( An Important Role of the SDF-1/CXCR4 Axis in Chronic Skin Inflammation Silvana Zgraggen 0 Reto Huggenberger 0 Katrin Kerl 0 Michael Detmar 0 Domenico Ribatti, University of Bari Medical School, Italy 0 1 Institute of Pharmaceutical Sciences, Swiss Federal Institute of Technology, ETH Zurich , Zurich , Switzerland , 2 Department of Dermatology, University Hospital Zurich , Zurich , Switzerland Inflammatory angiogenesis and vascular remodeling play key roles in the chronic inflammatory skin disease psoriasis, but little is known about the molecular mediators of vascular activation. Based on the reported elevated mRNA levels of the angiogenic chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 in psoriasis, we investigated the relevance of the SDF-1/CXCR4 axis in two experimental models of chronic psoriasis-like skin inflammation. The cutaneous expression of both SDF-1 and CXCR4 was upregulated in the inflamed skin of K14-VEGF-A transgenic mice and in imiquimod-induced skin inflammation, with expression of CXCR4 by blood vessels and macrophages. Treatment with the CXCR4 antagonist AMD3100 potently inhibited skin inflammation in both models, associated with reduced inflammatory angiogenesis and inflammatory cell accumulation, including dermal CD4+ cells and intraepidermal CD8+ T cells. Similar antiinflammatory effects were seen after treatment with a neutralizing anti-SDF-1 antibody. In vitro, inhibition of CXCR4 blocked SDF-1-induced chemotaxis of CD11b+ splenocytes, in agreement with the reduced number of macrophages after in vivo CXCR4 blockade. Our results reveal an important role of the SDF-1/CXCR4 axis in skin inflammation and inflammatory angiogenesis, and they indicate that inhibition of the SDF-1/CXCR4 axis might serve as a novel therapeutic strategy for chronic inflammatory skin diseases. - Funding: This work was supported by National Institutes of Health grant CA69184, Swiss National Science Foundation grants 3100A0-108207 and 31003A_130627, Commission of the European Communities grant LSHC-CT-2005-518178, Advanced European Research Council Grant LYVICAM, the Leducq Foundation Transatlantic Network of Excellence grant Lymph Vessels in Obesity and Cardiovascular Disease, Oncosuisse and Krebsliga Zurich (to M.D.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Psoriasis is a chronic inflammatory skin disease that affects 2% to 3% of the population worldwide [1]. The major features of psoriatic skin lesions are the thickening of the epidermis, associated with enhanced proliferation and aberrant terminal differentiation of epidermal keratinocytes, and the accumulation of inflammatory leukocytes, in particular dendritic cells and T cells [2]. There is a preferential accumulation of CD4+ cells in the dermis and of CD8+ cells in the epidermis of lesional psoriatic skin [2], and there are also increased numbers of macrophages whose function in the disease process is not fully understood [3]. A third and often overlooked - hallmark of psoriatic skin is represented by the pronounced inflammatory angiogenesis, leading to vascular remodeling [4]. This vascular activation is similar to the blood vessel changes observed in several other chronic inflammatory diseases, including rheumatoid arthritis, inflammatory bowel disease and chronic airway inflammation [5 7]. Vascular endothelial growth factor (VEGF)-A has been identified as the major angiogenesis factor in psoriatic skin since its expression is strongly upregulated in lesional epidermis [5], and the plasma levels of VEGF-A are elevated in psoriasis patients and correlate with disease severity [8]. Moreover, targeted chronic overexpression of VEGF-A in the epidermis of mice results in the spontaneous development of a chronic inflammatory skin disease that shares many features of human psoriasis [9,10], and inhibition of VEGF-A signaling inhibited inflammation in different murine models of psoriasis [912]. Together, these results indicate an important role of VEGF-A and angiogenesis in disease maintenance and progression, but additional factors that target the vascular system are likely involved. Several pro-inflammatory chemokines have been reported to also exhibit angiogenic properties [13,14]. In particular, stromal cell-derived factor-1 (SDF-1, also known as CXCL12) has been found to have angiogenic activity in different in vitro and in vivo systems [15,16], and its primary receptor CXCR4 is expressed by endothelial cells as well as monocytes and lymphocytes [17,18]. SDF-1 is expressed in several tissues including the skin and the bone marrow [19], and the SDF-1/CXCR4 axis is involved in a range of physiological processes such as embryonic development and stem cell motility [20]. Since VEGF-A upregulates CXCR4 in cultured human endothelial cells [16], and since elevated mRNA levels of both SDF-1 and CXCR4, as well as elevated SDF-1 protein levels, have been found in lesional psoriatic skin [2123], we hypothesized that the SDF-1/CXCR4 axis might play a potential role in the pathogenesis of chronic inflammatory skin diseases including psoriasis. Therefore, we first investigated the expression of CXCR4 in human psoriasis and of both SDF-1 and CXCR4 in two established experimental mouse models of chronic psoriasis-like skin inflammation - the keratin 14 (K14)VEGF-A transgenic mouse model of induced chronic cutaneous inflammation [9], and the imiquimod-induced psoriasis-like skin inflammation mouse model [24,25]. Next, we investigated the potential anti-inflammatory effects of blockade of CXCR4 signaling by systemic treatment with AMD3100, a specific CXCR4 antagonist [26], in both inflammation models, and we also studied the effects of a neutralizing anti-SDF-1 antibody. Our results reveal an important role of the SDF-1/CXCR4 axis in skin inflammation and inflammatory angiogenesis, and they indicate that inhibition of the SDF-1/CXCR4 axis might serve as a novel treatment strategy for chronic inflammatory skin diseases. Materials and Methods Ethics Statement The collection of specimens from clinically indicated excisions for this study was explicitly approved by the institutional review board (Kantonale Ethikkommission Z urich). Informed consent (both written and verbal) was obtained from patients for the use of their skin samples in this research project. Mice and treatments All mice used in this study were bred and housed in the animal facility of ETH Zurich. Experiments were performed in accordance with animal protocol 149/2008 and 117/2011 approved by the local veterinary authorities (Kantonales Veterinaramt Z urich). K14-VEGF-A transgenic mice have been described previously [10,27]. To induce a psoriasis-like skin inflammation in the ear skin [9] of these mice, a 2% oxa (...truncated)