Open Access

Christian Dominik Wetzler

• Die primäre Funktion der Haut ist die Abgrenzung des Körpers gegenüber der Umwelt, wodurch der Organismus vor destruktiven Einwirkungen (Xenobiotika, Mikroorganismen, UV-Licht) geschützt wird. Neben wichtigen sensorischen Funktionen ist die Haut außerdem beteiligt an der Regulation von Körpertemperatur sowie Wasserhaushalt und dient als wichtiges Sozialorgan. Da die Verletzung der Haut demnach schwerste Folgen für den Organismus hat, ist die Wundheilung ein essentieller Prozeß zur Aufrechterhaltung der Unversehrtheit der Haut. Der Prozeß der Wund heilung läßt sich in vier Phasen unterteilen (Koagulation, Entzündungsphase, Proliferationsphase, Remodellierungsphase), die zeitlich und räumlich überlappen (Moulin, 1995; Singer and Clark, 1999). ...
• The primary function of the skin is to serve as a protective barrier against the environment. After injury, wound healing represents an essential process for the body to maintain the integrity of the skin. This repair process can be subdivided in four major phases (coagulation phase, inflammatory phase, proliferative phase, and remodeling phase), which temporally and spatially overlap. Chronic wounds, which are a heterogeneous collection of dermal lesions, are characterized by a failure or delay of healing. Diabetes mellitus is a metabolic disease, which causes impaired repair conditions, thus leading to a prototypic chronic wound, the diabetic ulcer. For many years, genetically diabetic db/db and ob/ob mice have been used as a model system for impaired wound healing, and, accordingly, the observed wound healingdisorders have been explained by the diabetic phenotype of these animals. To assess whether the severely impaired process of cutaneous repair observed in db/db and ob/ ob mice is associated with dysregulated inflammatory processes, we determined the expressional kinetics for MIP-2 and MCP-1 in a model of excisional wounding. Wound repair in both db/db and ob/ob mice was characterized by a sustained inflammatory response and a prolonged expression of MIP-2 and MCP-1. Immunohistochemistry revealed that keratinocytes at the wound margins expressed MCP-1, whereas MIP-2 immunopositive signals were mainly observed in keratinocytes of hair follicles located adjacent to the wound site. Inactivation studies using neutralizing antibodies againstMCP-1 or MIP-2 indicated that sustained expression of these chemokines participated in the prolonged presence of neutrophils and macrophages at the wound site during diabeticrepair. Furthermore, our data provide evidence that late infiltration (day 13 after inju ry) of neutrophils and macrophages into wounds in db/db mice was associated with a simultaneous downregulation of mRNA for receptors specific for MIP-2 and MCP-1 in these animals. Inhibition of inducible nitric oxide synthase (iNOS) enzymatic activity during cutaneous wound repair leads to severely impaired tissue regeneration. To assess whether disturbed leukocyte infiltration might participate in impaired repair, we determined expressional kinetics of the neutrophil-attracting MIP-2 and the monocyte-attracting MCP-1 in excisional wounds of NO-deficient Balb/c mice. MCP-1 was induced in epithelial keratinocytes upon wounding, and our data indicate that NO serves a negative regulatory role for MCP-1 expression in vivo, as clearly reduced numbers of wound margin keratinocytes associated with NO-deficient repair compensate for high MCP-1 expression levels observed during normal healing. MIP-2 expression was restricted to hair follicles, which were not reduced in number during NO-deficient repair. In vitro studies confirmed a regulatory role of NO for keratinocyte-derived chemokine expression, as NO attenuated IL-1 ~- and TNF-a-induced MCP-1 mRNA expression, whereas NO augmented IL-1~induced IL-8 (functional human homologue to murine MIP-2) mRNA expression in the human keratinocyte cell line HaCaT. Recent studies revealed the endocrine cytokine leptin as a potent mitogen for epidermal keratinocytes during skin repair. As chronic wounds are characterized by a dysregulated and prolonged inflammatory phase, we investigated the role of leptin for the inflammatory response in cutaneous tissue repair. To this end, we supplemented leptin deficient ob/ob mice with recombinant murine leptin. An improved healing was restricted to leptin treatment, as only wounds of leptin treated animals were characterized by a multilayered neoepidermis and a multicellular granulation tissue after 13 days. We assessed wound inflammation by determination of wound chemokine expression (MIP-2, KC, MCP-1, RANTES) and influx of leukocyte subsets (neutrophils, macrophages). Wound inflammation was accelerated in leptin treated animals, as CXC- and CC-chemokine expression as well as subsequent neutrophil and macrophage numbers were decreased at late phases compared to the situation in diabetes-impaired repair of vehicle treated mice. Leptin differentially regulated leukocyte infiltration into the wound site, most likely by influencing epithelial derived chemokine expression. Interestingly, leptin action was clearly restricted to the CXC-chemokine/neutrophil axis of wound inflammation, as leptin blunted MIP-2 and KC expression in wound keratinocytes, and, subsequently, influx of neutrophils into the wound site. Remarkably, wounds of both leptin and vehicle treated mice were characterized by tremendous numbers of macro phages in the granulation tissue. There is evidence that leptin controls PMN immigration into peripheral wound sites in an indirect manner, as topical administration of leptin failed to alter neutrophil influx into the wound. Although regulatory mechanisms remain to be elucidated, one might speculate that neuroendocrine axes are involved in the regulation of immune cell influx.