Glu-Leu-Arg-Negative CXC Chemokine Interferon γ Inducible Protein-9 As a Mediator of Epidermal–Dermal Communication During Wound Repair

Normal wound healing is a complex, highly regulated dynamic process that requires co-ordinate responses of both epidermal and dermal compartments. To accomplish the healing process several growth factors, chemokines, and matrix elements signal both cell proliferation and migration during the inflammatory and reparative phases and limit these responses during the remodeling phase. We have found that the Glu-Leu-Arg-negative CXC chemokines interferon γ inducible protein 10, monokine induced by interferon γ, and platelet factor 4, limit fibroblast responsiveness to growth factors, but the functioning of these factors in wound healing remains uncertain. We hypothesized that the keratinocyte-derived member of this Glu-Leu-Arg-negative CXC family, interferon γ inducible protein 9 (IP-9) CXCL11 (also known as I-TAC, β-R1, and H-174) signals to the dermal compartment to synchronize the re-epithelialization process. Interferon γ inducible protein 9 was produced after mechanical wounding of a keratinocyte monolayer, suggesting for the first time that this could be a wound response factor. Interferon γ inducible protein 9 limited epidermal growth factor (EGF)-induced fibroblast motility (57±7%) by the same protein kinase A (KA)-mediated inhibition of calpain activation and cell de-adhesion as described for interferon γ inducible protein 10. Surprisingly, interferon γ inducible protein 9 enhanced growth factor-induced motility in undifferentiated keratinocytes (137±19%) as determined in a two-dimensional in vitro wound healing assay, and interferon γ inducible protein 9 alone promoted motility in undifferentiated keratinocytes (49±10% of epidermal growth factor-induced motility). A stimulated keratinocyte/target cell coculture system revealed that interferon γ inducible protein 9 acts as a soluble keratinocyte-derived paracrine factor for both fibroblasts and keratinocytes. Further, we found that in both fibroblasts and undifferentiated keratinocytes, interferon γ inducible protein 9 exerted its action through modulation of a cytosolic protease, calpain. Interestingly, interferon γ inducible protein 9 increased calpain activity in undifferentiated keratinocytes, whereas the same chemokine inhibited the calpain activity in fibroblasts. This provides for a model whereby redifferentiated basal keratinocytes could limit fibroblast repopulation of the dermis underlying healed wounds while simultaneously promoting re-epithelialization of the remaining provisional wound.