Acknowledgements The work was supported by grants from

Acknowledgements The work was supported by grants from Swedish Research Council (J.Z.H.) (A.R.M.). We thank Protein Science Facility (PSF), Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden. We thank Prof. Ralf Morgenstern (Department for Environmental Medicine, Karolinska Institutet, Sweden) for valuable discussions.
Introduction The 5-Lipoxygenase (5-LO) is an essential enzyme expressed in various leukocytes and involved in the oxygenation of arachidonic Calphostin C to the biosynthesis of leukotrienes (LT) and lipoxins (LX), which are lipid mediators related to inflammatory reactions [1,2]. These eicosanoids exert opposite roles in the immune response; LTs are potent agents associated to leukocyte activation, chemotaxis and phagocytosis [3–5] while LXs are essentially anti-inflammatory mediators [6]. Besides leukocytes, skin resident cells are also competent to produce LTs [7], which are present in exudates from human skin diseases like psoriasis [8], systemic sclerosis [9] and atopic dermatitis [10]. Then, the mediators induced by 5-LO in almost all cells of the body in response to cell membrane injury are supposed to modulate the inflammatory response in wound healing [11]. The cutaneous repair is a complex process that involves inflammation, tissue formation and remodeling. In the initial inflammatory and cellular reactions that follow injury, neutrophils are the first cells recruited to the damaged site, followed by monocytes and lymphocytes [12,13]. The phagocytic cells that participate in the cleaning of cellular debris produce a wide variety of proteinases, reactive oxygen species and inflammatory mediators that dictate the outcome of tissue repair [13]. Moreover, in addition to defense functions, these leukocytes are also important source of growth factors and cytokines, which initiate the proliferative phase of wound healing by contributing to the proliferation or migration of keratinocytes and dermal fibroblasts to the lesion [14,15]. The fibroblasts deposit extracellular matrix accompanied by angiogenesis that leads to the formation of blood vessels. Finally, this newly formed granulation tissue is replaced by a mature scar, with synthesis, remodeling of collagen and resolution of the local inflammation [16]. Then, since the participation of inflammatory mediators such as LT induced by 5-LO in tissue repair is still not completely clear, this study aimed to understand the role of this enzyme and its products in cutaneous wound healing.
Materials and methods
Results
Discussion The 5-LO pathway has been subjected to intense investigation as a therapeutic target for inflammatory diseases and although the presence of LT has been described in various pathologies [20–22] the exact role of 5-LO and its products in the cutaneous wound healing was not completely clear yet. Therefore, in the present study we pointed to 5-LO as an essential player in the inflammatory response that precedes complete skin repair. Indeed, the faster closure in the absence of 5-LO could be explained by a more controlled inflammatory response, since these mice showed differential accumulation of eosinophils, neutrophils, mast cells and lymphocytes in the wounds or draining lymph nodes. We also demonstrated that without 5-LO the lesions had less edema and a thinner layer of fibrin. It is known that LT, one of the main products from 5-LO pathway, are important lipid mediators that activate leukocytes and stimulate the migration of these cells to the site of inflammation [23]. Similarly, this enzyme was demonstrated to be an important negative regulator of bone fracture healing, once this repair was accelerated in the absence of 5-LO [24]. Cysteinyl leukotrienes (cysLT), mainly represented by LTC4, D4 and E4 are generated primarily by cells of the innate immune system during inflammatory process. These mediators, produced by the 5-LO pathway after cleavage of arachidonic acid, interact with their receptors, cysLTR1 or cysLTR2, which are expressed (especially cysLTR1) on the outer membrane of a range of cells including basophils, mast cells, dendritic cells, eosinophils, monocytes, macrophages, B cells and CD4+ T cells [25]. Because the activation of this pathway is related to the immunopathogenesis of several inflammatory and chronic disorders such as bronchial asthma, selective antagonists of cysLTs receptors, such as pranlukast [26], zafirlukast [27] and montelukast [28] have been developed since 1995. However, anti-inflammatory activities of cysLTR1 antagonists are not only related to the inhibition per se of these receptors, but also to the inhibition of the activity of the transcription factor NFκB [29]; prostaglandin E synthase [30], eosinophil adhesion and migration [31]. In accordance, the inhibition of cysLTR1 in our study accelerated wound repair, pointing to these LT as important mediators of skin inflammation during tissue injury.