The Role of Exogenous Type VII Collagen on the Healing of Skin Wounds

Va Greater Los Angeles Healthcare System, Los Angeles CA

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Abstract

We have made the surprising finding that type VII (anchoring fibril) collagen (C7) exogenously administered to murine skin wounds, both topically and intravenously, induces dramatic acceleration of wound closure and the wounds heal with less scarring. This was an unexpected finding because, under normal conditions in unwounded skin, C7 is configured into large structures called anchoring fibrils which are confined to the junction between the dermis and epidermis, the dermal-epidermal junction (DEJ). For many years, we have studied the structure and function of C7 and were surprised to find that in the wound bed of healing skin wounds, C7 is not confined to the DEJ, but, rather, is widely distributed throughout the wound bed. We also developed procedures for making milligram quantities of recombinant human type VII collagen (rhC7). We added rhC7 to 1 x 1 cm standard full-thickness wounds on the backs of hairless mice and evaluated wound closure. We found that compared with vehicle control or no treatment, rhC7-treated wounds exhibited dramatic acceleration of wound closure. The same results also occurred when we treated skin wounds made in diabetic mice who exhibit delayed skin wound healing. We also transplanted human skin onto the backs of athymic mice, wounded the transplanted human skin and applied either vehicle or rhC7. Again, rhC7 induced accelerated wound closure in the human skin compared with the vehicle. rhC7 had specific activity since other large macromolecules (type I collagen, type IV collagen, fibronectin, and laminin 332) did not accelerate wound closure in these animals. It was also noted that the murine skin wounds treated with rhC7 healed with less clinical scarring. We then evaluated vehicle- and rhC7-treated murine wounds by histology and by immunohistochemistry for markers of scarring. Compared with vehicle-treated wounds, murine skin wounds treated with rhC7 exhibited a dramatic down-regulation of markers of scarring including collagen deposition, smooth muscle actin positive fibroblasts (myofibroblasts), connective tissue growth factor, periostin and pro- fibrotic isoforms of transforming growth factor beta (TGFb). Given these unexpected dramatic results, the subject of this grant is the role of C7 in the healing of skin wounds. Recently, we have also established the first and only diabetic pig with delayed healing of skin wounds. In this proposal, we wish to determine the influence of topically administered rhC7 on skin wounds made in domestic pigs, both normal and diabetic. Performing experiments with pigs is critical because pigskin is much more relevant to human skin. Pigs are tight-skinned animals and have skin the most similar to human skin. Pigs are the species of choice for wound healing studies. We will also determine if topical rhC7 inhibits scarring and generates elements of ?regenerative? healing rather than just ?reparative? healing. We will also establish the stability of rhC7 in pigskin wounds as a surrogate for healing human wounds. This will be important for determining the dose and dosing schedule of rhC7 as a new wound healing agent for humans with chronic skin wounds. Once the optimal dose and dosing schedule of topical rhC7 is established, we will determine if rhC7 accelerates wound closure and inhibits scarring in diabetic pigs. Wound healing is an enormous clinical problem, especially for military personnel and Veterans. Veterans often suffer predisposing conditions for chronic skin wounds such as diabetic ulcers, stasis dermatitis leg ulcers and decubitus ulcers from immobility due to spinal cord injuries. The problem is escalating due to rises in obesity and diabetes. We will evaluate for the first-time wound healing mechanisms in normal skin versus diabetic skin in the animal most relevant to humans. We have these exciting observations regarding skin wound responses to rhC7, but we do not know the pathophysiological mechanisms behind them. The planned experiments will inform us of the basic mechanisms underpinning these observations. They will also advance bringing rhC7 from the research laboratory to the clinic for patients, so-called ?bench-to-bedside? research. ! !