A stretch-responsive fibroblast program promotes epidermal stem cell self-renewal during 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. How fibroblasts respond to stretch-mediated tissue expansion in supporting keratinocyte proliferation remains unclear. Here we map the fibroblast transcriptional response to stretching in vivo and 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.