Critical role for the TGF-β1/mTORC1 signaling axis in defining the transcriptional identity of CTHRC1+ pathologic fibroblasts.

Fibrosis, marked by excess extracellular matrix (ECM) deposition, is the end stage of many diseases. Single-cell studies have highlighted the emergence of disease-specific fibroblast populations, including a high collagen-synthesizing CTHRC1+ subpopulation. The profibrotic cytokine TGF-β1 promotes fibrogenesis via cooperation between Smad and mTORC1/4E-BP1 signaling axes. Using CRISPR-Cas9 gene editing, we report that more than one-third of TGF-β1-regulated matrisome genes are under mTORC1 control. Mapping the transcriptome of TGF-β1-stimulated fibroblasts revealed similarity to CTHRC1+ fibroblasts identified in idiopathic pulmonary fibrosis (IPF). This overlap is lost when mTORC1 is disabled. Using the selective mTORC1 inhibitor RMC-5552, we confirm a causal role for mTORC1 in promoting the acquisition of the collagen-high, CTHRC1+ phenotype in response to TGF-β1 stimulation in fibroblasts derived from patients with either IPF or lung adenocarcinoma. We conclude that mTORC1 plays a key role in shaping the transcriptional identity of these fibroblasts, with implications for therapeutic inhibition of mTORC1 in fibrosis and cancer.