Building a Better Scar: Re-engineering Extracellular Matrix Structure in Dermal Scars
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Introduction Cutaneous scars represent a common surgical complication, yet no effective drug therapy for scar treatment currently exists despite huge patient and physician demand. A connexin 43 (Cx43) carboxyl terminus (CT) mimetic peptide, alpha Connexin Carboxy-Terminus 1 (αCT1), has demonstrated efficacy in improving long-term scar appearance in pre-clinical and clinical trials. However, current understanding of the mechanism-of-action by which αCT1 improves long-term scar appearance with early intervention treatment is not well understood. Methods In vivo: Scar biopsies from 1) human, 2) Sprague-Dawley rat, and 3) IAF Hairless guinea pig trials of αCT1 were examined for collagen matrix structure at 4 weeks (all models), and 2 and 6 weeks (rat and guinea pig models only). Collagen matrix variables examined included local disorganization of the fibers, a variable that is higher in unwounded skin compared to scar tissue, and density of the fibers, which is higher in scar tissue but can also be used as an early temporal marker of the rate of healing. In vitro: Primary murine dermal fibroblasts were isolated from the whole dermis of 3-4 week old transgenic mice expressing collagen 1(α2) GFP-tpz. Cells were sorted for expression via FACS and plated on prealigned collagen substrate for 7 days under conditions favorable to generating extracellular matrix. Results All in vivo scar biopsies demonstrated some level of altered collagen matrix structure with αCT1 treatment. Treated scars had higher local disorganization of the collagen fibers within the wound, and an increase in collagen matrix density compared to control at certain earlier timepoints that tended to decrease or disappear at later timepoints. The IAF Hairless guinea pig, a novel splinted wound healing model presented herein, was found to closely replicate the human dermal collagen profile and changes in collagen profile spurred by αCT1, significantly outperforming the traditional rat model. Primary dermal murine fibroblasts treated in vitro with αCT1 significantly increased synthesis of procollagen 1, the precursor of collagen 1 necessary for constructing the extracellular matrix, suggesting that at least part of the reason for higher collagen density at early in vivo timepoints is due to increased collagen synthesis by fibroblasts. Conclusion αCT1 treatment in the early stages of wound healing prompts individual fibroblasts to increase their output of collagen and create a more disorganized early collagen matrix. These early changes potentially spur the long-term scar appearance improvements seen in clinical trials, and provide a basis for future work to discover the cellular pathways to alter in order to improve wound healing and cutaneous scarring outcomes.
General Audience Abstract
Skin wounds frequently result in scars that can range from barely visible to enormous eyesores. Almost everyone will experience at least one skin wound in their lifetime leading to a scar that they wish were less visible, feeding the multi-billion dollar market for anti-scarring agents. However, many of the products on store shelves that claim to reduce scar appearance have not proven those claims. Most of the therapies that do have some degree of scientific evidence to support their claims are difficult to use properly, such as silicone sheeting, and often result in only minor improvements to scar appearance. Alpha Connexin Carboxy-Terminus 1 (αCT1), marketed in clinical trials as Granexin® gel, is a protein-based therapy that works on the cellular level to fundamentally alter the skin's initial reaction to wounding and improving long-term scar appearance. This dissertation explores the link between cellular processes altered by αCT1 and long-term clinical improvements in scar appearance by studying both the extracellular matrix present in the scar in human and animal models and the creation of that extracellular matrix by dermal fibroblasts. In both human and animal models, topical application of αCT1 had no effect on skin surface appearance at early timepoints of 2-6 weeks, correlating with previous research that found scar appearance only improved at 3+ months post-injury. However, deep within the newly constructed tissue of the scar, these studies show the collagen organizational structure of αCT1-treated scars is more similar to unwounded skin and slightly more dense at early timepoints, suggesting αCT1 marginally improved the speed of healing. These findings in humans and animals were also verified in part in cell culture experiments that found dermal fibroblasts increased collagen output in response to αCT1 treatment. A novel wound healing model in the hairless guinea pig, superior at replicating human skin than established models like the rat, is also presented and shown to have effects strongly similar to the human with αCT1 treatment. These results provide a fundamental insight into the mode-of-action by which αCT1 may improve long term scar appearance and identifies early collagen structure as a target for future therapeutics to modify, as well as a new animal model in which to test them.
- Doctoral Dissertations