Tight Spatial and Temporal Control in Dynamic Basal to Distal Migration of Epithelial Inflammatory Responses and Infiltration of Cytoprotective Macrophages Determine Healing Skin Flap Transplants in Mice

In Brief Objective: We aimed to elucidate to date unknown molecular patterns of dynamic inflammatory tissue responses during uncomplicated healing of caudally pedicled skin flap transplants in mice. Summary Background Data: Distal skin flap ischemic necrosis is a well-known complication in surgery. To improve ischemic conditions in impaired skin flaps, recent work attempted to increase insufficient vascularity by application of angiogenic growth factors or pluripotent cells. Wound inflammation is in the center of tissue repair, but its temporal and spatial regulation remains nearly unstudied in conditions of transplanted skin flap tissue. Methods: RNase protection assay, quantitative real-time polymerase chain reaction, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and immunoblot techniques were used to determine expression and cellular localization of central inflammation-related chemokines, cytokines, enzymes and cell types upon skin flap transplantation. Results: We observed a marked keratinocyte-driven inflammation that moved from the caudal base to distal flap regions during healing. Keratinocytes of the skin flap epithelium expressed increasingly large amounts of chemokines (MIP-2, MCP-1) and cyclooxygenase (Cox)-2 particularly in distal portions of the transplant. The underlying wound bed did not appear to contribute essentially to the inflammatory response. Despite strong attracting chemokine signals, distal flap tissue was not infiltrated by excess numbers of neutrophils and macrophages. Moreover, infiltrating macrophages exhibited an anti-inflammatory phenotype characterized by the absence of NFκB activation and Cox-2 in the presence of a marked heme oxygenase (HO)-1 expression in surviving skin flap tissue. Conclusion: Survival of skin flap tissue might be determined by a cytoprotective type of wound macrophage in the presence of an intense epithelium-derived inflammation. We assessed molecular patterns of cutaneous inflammatory responses during uncomplicated healing of caudally pedicled skin flap transplants in mice. Using molecular biology, biochemical and histologic techniques, we showed that injury-induced keratinocyte-driven epithelial inflammation acts in concert with infiltrating cytoprotective macrophages to determine the survival of skin flap tissue.