Unraveling the Development of Cutaneous Neurofibromas in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a genetic disorder that leads to the formation of cutaneous neurofibromas (cNFs), benign nerve sheath tumors that develop in the skin and significantly impact patients' quality of life. cNF development begins with bi-allelic NF1 loss in Schwann cell (SC) lineage, followed by the recruitment of a complex tumor microenvironment consisting of fibroblasts, immune cells, blood vessels, axons and a dense extracellular matrix. Despite their high prevalence and clinical impact, the molecular mechanisms underlying cNF formation remain poorly understood. Here, we used an Nf1 knockout (Nf1-KO) mouse model, combined with immuno-histochemistry and single-cell transcriptomics, to explore the mechanisms driving cNF development. Our findings revealed that mutant SCs accumulate in the skin of young mice weeks before cNF onset. However, these cells remain quiescent until triggered by skin trauma, which induces their proliferation and the rapid formation of cNFs. Using a trauma-induced Nf1-KO model with scRNAseq, we conceived a transcriptomic atlas of growing and mature cNFs, as well as adjacent, seemingly healthy skin. This analysis identified a population of non-myelinating Aquaporin1highNestinlow SCs as the likely cells of origin for cNFs. These cells overexpress genes involved in axon growth and guidance, potentially driving the abnormal innervation observed in cNFs from both mice and patients. Additionally, we found that tumor SCs, along with dermal and/or epineurial fibroblasts and pericytes, overexpress collagen-encoding genes, contributing to the extensive fibrosis characteristic of cNFs. Notably, all of these cells exhibit high expression of Periostin and Tenascin C, key extracellular matrix components, highlighting them as novel therapeutic targets for cNF treatment. Overall design: To elucidate the cellular and molecular landscape driving cNF development in mice, we performed single-cell RNA sequencing (scRNAseq) on cNFs, adjacent healthy-looking skin (HLS), and control healthy skin (HS) at both the growth (P90) and stabilization (P365) periods of cNF development. To optimize cell dissociation while preserving transcriptomic integrity, we compared a 3-hour versus an 18-hour (overnight) dissociation protocol.