Disrupting Mechanotransduction Decreases Fibrosis and Contracture in Split Thickness Skin Grafting

PURPOSE: Burns and other traumatic injuries represent a significant biomedical burden for humans. Despite our best care in specialized centers, a burn patient either dies from infection or the injury itself, or lives with the devastating consequences of pain and scarring. A cornerstone of burn therapy is to excise the dead tissue and close the wound with a split thickness skin graft (STSG). While this reestablishes the skin barrier function, it is associated with severe fibrosis and scar, a process that we have recently linked to mechanical signaling in murine models.1,2 Unfortunately, these small animal models do not truly replicate human scar formation because humans are over several orders of magnitude larger, and these fundamental differences have significantly limited the ability to translate discoveries from mice to humans. METHODS: We developed a clinically relevant porcine STSG model using standardized surgical techniques commonly applied for the clinical treatment of burn wounds and other soft-tissue defects. Full-thickness excisional wounds were created on the back of red Duroc pigs. STSG were harvested and secured on the wound bed with skin staples, bolster dressings and either treated with focal adhesion kinase inhibitor hydrogels or standard dressings as controls. We comprehensively characterized the tissue appearance and related porcine cell populations involved in healing at the single-cell level using scRNA-seq. RESULTS: We identify an upregulation of pro-inflammatory and mechanotransduction signaling pathways in standard split thickness skin grafts. Blocking mechanotransduction using a small molecule focal adhesion kinase inhibitor, we substantially promoted engraftment, reduced contracture, mitigated scar formation, restored collagen architecture, and ultimately improved graft biomechanical properties. We demonstrate that mechanotransduction blockade results in early upregulation of anti-inflammatory pathways in myeloid cells. At later time points, mechanical signaling shifts fibroblasts toward pro-fibrotic differentiation fates, whereas disruption of mechanotransduction blocked those responses and instead drove fibroblasts toward pro-regenerative states similar to unwounded skin. We then confirmed these two diverging fibroblast transcriptional trajectories in a 3D organotypic in vitro model of skin. CONCLUSIONS: Taken together, pharmacological blockade of mechanotransduction significantly improves large animal healing after STSG by promoting both acute, anti-inflammatory and chronic, regenerative transcriptional programs, resulting in healed tissue similar to unwounded skin. Our therapy could have significant translational implications and could be easily incorporated with the current standard of care to help those who experience traumatic and burn injuries. REFERENCES: 1. Wong VW, et al. Focal adhesion kinase links mechanical force to skin fibrosis via inflammatory signaling. Nature medicine 2011;18:148–152. 2. Mascharak S, et al. Preventing Engrailed-1 activation in fibroblasts yields wound regeneration without scarring. Science 2021;372.