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The Role of Gap Junction Intracellular Communication during Collagen-Fibroblast Interactions in Wound Repair
Cell to cell signaling through Gap Junction Intracellular Communication (GJIC) channels plays an important role in numerous cellular activities associated with wound repair. One key aspect of wound repair is the reorganization of the granulation tissue collagen matrix by fibroblasts, which results in wound contraction. It is believed that the fibroblast organizes the collagen matrix through the translocation of collagen fibril segments (CFS), 10µm long intermediate structures, which are then incorporated into collagen fibers. This mechanism of repair has been demonstrated in an organ culture through a wounded chick embryo tendon explant repair model.
An in-vitro model of collagen organization and wound contraction by fibroblasts is the fibroblast populated collagen lattice (FPCL). FPCL containing 100,000 human dermal fibroblasts and 1.25 mg of native collagen per milliliter of DMEM with 10% serum were treated with 10 µM of the free fatty acid, oleamide, a potent naturally produced GJIC inhibitor. GJIC between fibroblasts in the FPCL was demonstrated by passage of Lucifer Yellow dye between microinjected fibroblasts and their coupled neighbors. Additionally, an organ culture model for CFS translocation by fibroblasts is the healing of an injured 14 day old chick embryo tendon explant. Injured tendons were treated with oleamide in order to evaluate the role of GJIC in tendon repair by the translocation of CFS. Fluorescently labeled CFS were added to the organ cultured tendon explants to demonstrate the localization of fluorescence during the course of tendon repair.
FPCLs treated with oleamide demonstrated reduced FPCL contraction compared to controls. Four hrs after placing wounded chick embryo tendon explants in organ culture with tagged CFS, fluorescence was evenly distributed along the entire surface of the explants. At 24 hrs, in control tendon explants, fluorescent microscopy revealed intense fluorescence localized at the injury site. In comparison, at 24 hrs after injury, the oleamide treated tendon explants demonstrated a uniform distribution of the fluorescently labeled CFS, demonstrating an inhibition of tendon explant repair. Inhibition of GJIC with oleamide blocked the translocation and incorporation of fluorescently labeled CFS at the repair site.
In conclusion, both FPCL contraction and the translocation of CFS for wound repair involves direct cell-cell communication through GJIC channels. Interfering with GJIC between fibroblasts disrupts the interaction of fibroblasts with CFS, which is critical for lattice contraction and incorporation at the tendon wound edges. Therefore, direct rapid communication between fibroblasts through GJIC channels coordinates the interactions of fibroblasts with the CFS within collagen lattices as well as with the translocation along the surface of fibroblasts to the site of repair in wounded tendon explants.