Defining the role of fibroblasts in skin expansion

Stretch-mediated tissue expansion is commonly used to grow extra skin for reconstructive surgeries. To ensure harmonious growth, the two main skin compartments, the epidermis and the dermis, must both expand in a coordinated manner. Although the epidermal response has been previously described, it remains unclear how fibroblasts, the main supporting cell type, respond to stretching in vivo. Here we map the transcriptional response of the entire skin during stretch-mediated tissue expansion, and we describe the fibroblast response to stretching in vivo. We show an increase in fibroblast volume accompanied by changes in organisation. We demonstrate that stretching forces fibroblasts to exit their quiescent state and restart proliferation. Concurrently, fibroblasts reduce collagen production and upregulate extracellular matrix remodelling factors, adopting a more embryonic-like program. Because embryonic fibroblasts are widely used as feeder layers to support the expansion of epidermal stem cells for clinical application, we leveraged this model to show that a low collagen state enhances epidermal stem cell self-renewal, thereby coordinating epidermal and dermal responses during skin expansion. These findings provide valuable insights to guide the design of in vivo stretch-mediated tissue expansion protocols and the production of in vitro skin grafts for clinical application.