1823 Research Article Introduction Inefficient wound healing represents an important health problem for individuals suffering accidental, surgical or chronic skin lesions and has special relevance for the elderly and for immunosuppressed, diabetic or cancer patients (Reed and Clark, 1985; Schafer and Werner, 2008). Tissue repair is a complex process that involves new blood vessel formation and the recruitment to the wound of inflammatory cells, such as macrophages and neutrophils, to eliminate contaminants and bacteria and fibroblasts that produce extracellular matrix (ECM) components (e.g. collagen and fibronectin). In parallel to the formation of granulation tissue, increased proliferation and migration of keratinocytes takes place to repair the damaged epidermis (Eckes et al., 1999; Martin, 1997; Schafer and Werner, 2008; Singer and Clark, 1999). The intermediate molecules involved in adult skin repair are only partially known. Nevertheless, analysis of overexpression and knockout animal models has revealed the important contribution of adhesion molecules such as β1 integrins (Grose et al., 2002; White et al., 2004), growth factors such as FGF and HGF (Werner and Grose, 2003), ECM constituents such as osteopontin (Mori et al., 2008) and cytokines such as TGFβ (Ashcroft et al., 1997; Singer and Clark, 1999). TGFβ is one of the best characterized profibrogenic molecules (Bauer and Schuppan, 2001; Kanzler et al., 1999) and alterations in its synthesis, secretion and intracellular signaling are associated with many pathological states including cancer and tissue fibrosis (Blobe et al., 2000; Corchero et al., 2004; Massague, 2000; Massague and Chen, 2000). Despite the fact that exogenous TGFβ3 administration is currently under clinical trial as a novel anti-scarring agent (Shah et al., 1995), the effect of this cytokine on tissue repair remains controversial. Some studies suggest that TGFβ regulates wound healing because its expression is increased by platelets, inflammatory cells and fibroblasts located at the site of injury (Amendt et al., 2002; Leibovich and Ross, 1975; Schafer and Werner, 2007). Genetic manipulation of TGFβ or its receptors, however, can both promote and inhibit tissue regeneration (Amendt et al., 2002; Brown et al., 1995; Crowe et al., 2000; Shah et al., 1999). Furthermore, additional work has revealed that depending on the level of TGFβ activity and/or the experimental model used, this cytokine has been shown not to affect (Leask et al., 2008), to inhibit (Hosokawa et al., 2005; Yang et al., 2001) or to promote skin re-epithelialization (Gailit et al., 1994; Reynolds et al., 2005; Reynolds et al., 2008). TGFβ-dependent signaling is mediated by its binding and activation of plasma membrane serine-threonine kinase receptors that will phosphorylate and activate intracellular intermediates of the Smad family of proteins (Smad2, Smad3 and Smad4). Activated Smads will heterodimerize and enter the cell nucleus where they activate target gene expression (Massague, 2000; Siegel and Massague, 2003). The aryl hydrocarbon (dioxin) receptor (AhR) is a member of the class VII of basic-helix-loop-helix-PAS (bHLH-PAS) family of transcription factors. AhRs regulate gene expression through heterodimerization with the nuclear protein aryl hydrocarbon receptor nuclear translocator ARNT (Furness et al., 2007). In Delayed wound healing caused by inefficient re-epithelialization underlines chronic skin lesions such as those found in diabetes. The dioxin receptor (AhR) modulates cell plasticity and migration and its activation by occupational polycyclic aromatic hydrocarbons (PAHs) results in severe skin lesions such as contact hypersensitivity, dermatitis and chloracne. Using wild- type (Ahr +/+ ) and AhR-null (Ahr –/– ) mouse primary keratinocyte cultures and tissue explants, we show that lack of AhR increases keratinocyte migration and accelerates skin re-epithelialization without affecting cell proliferation or recruitment of inflammatory cells. Wounds in Ahr –/– animals had elevated numbers of fibroblasts and increased collagen content in their granulation tissue. Importantly, Ahr –/– dermal fibroblasts secreted higher levels of active TGFβ that increased keratinocyte migration in culture and that could account for over-activation of the TGFβ pathway and for faster wound healing in the AhR- null neo-epithelium. Consistently, a TGFβ neutralizing antibody decreased keratinocyte migration in culture and halted re- epithelialization in Ahr –/– mice. Moreover, in vivo treatment with an antisense oligonucleotide for AhR increased TGFβ signaling and improved re-epithelialization in wounds of wild-type mice. These data indicate that AhR is relevant for wound repair and suggest that AhR downmodulation might be a potential new tool for the treatment of chronic, surgical or accidental wounds. Supplementary material available online at http://jcs.biologists.org/cgi/content/full/122/11/1823/DC1 Key words: Dioxin receptor, TGFβ, Wound healing Summary Loss of dioxin-receptor expression accelerates wound healing in vivo by a mechanism involving TGFβ Jose M. Carvajal-Gonzalez 1 , Angel Carlos Roman 1 , M. Isabel Cerezo-Guisado 1, *, Eva M. Rico-Leo 1 , Gervasio Martin-Partido 2 and Pedro M. Fernandez-Salguero 1,‡ 1 Departamento de Bioquímica y Biología Molecular and 2 Departamento de Biologia Celular, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s/n, 06080-Badajoz, Spain *Present address: Departamento de Inmunologia y Oncologia, Centro Nacional de Biotecnologia-CNB, C/ Darwin 3, 28049-Madrid, Spain ‡ Author for correspondence (e-mail: pmfersal@unex.es) Accepted 25 February 2009 Journal of Cell Science 122, 1823-1833 Published by The Company of Biologists 2009 doi:10.1242/jcs.047274 Journal of Cell Science JCS ePress online publication date 12 May 2009