Basement membrane proteins in NF1-associated neurofibroma extracellular matrix characterize tumor development and treatment response to MEK inhibitor

Neurofibromatosis Type 1 (NF1) is one of the neurocutaneous, tumor-predisposing genetic disorders. Neurofibroma is the most common NF1-associated tumors. A hallmark feature of neurofibroma is an abundant collagen-rich extracellular matrix (ECM) that constitutes more than 50 percent of the tumor dry weight. However, little is known about the mechanism underlying ECM deposition and its cellular origin during neurofibroma development and treatment response. We performed a systematic investigation of ECM enrichment during plexiform neurofibroma (pNF) development, which identified basement membrane proteins as the most upregulated ECM component. Moreover, following MEK inhibitor treatment, the basement membrane protein profile in ECM displayed an overall down-regulation signature, suggesting ECM reduction as one of the therapeutic benefits of MEK inhibition. Through these proteomic studies, TGF-β1 signaling was identified as playing a role in ECM dynamics. Indeed, TGF-β1 overexpression promoted pNF progressionin vivo. Furthermore, by integrating single-cell RNA sequencing, we found that immune cells in the tumor microenvironment produce TGF-β1 to induce Schwann cells to produce and deposit basement membrane proteins for ECM remodeling. Following NF1 loss, neoplastic Schwann cells further increased basement membrane protein deposition in response to TGF-β1. Our data delineate the regulation governing ECM dynamics in pNF and suggest that basement membrane proteins have the potential to serve as markers for disease diagnosis and treatment response.