Collagen-producing lung cell atlas identifies multiple subsets with distinct localization and relevance to fibrosis

Abstract

Collagen-producing cells maintain the complex architecture of the lung and drive pathologic scarring in pulmonary fibrosis. Here we perform single-cell RNA-sequencing to identify all collagen-producing cells in normal and fibrotic lungs. We characterize multiple collagenproducing subpopulations with distinct anatomical localizations in different compartments of murine lungs. One subpopulation, characterized by expression of Cthrc1 (collagen triple helix repeat containing 1), emerges in fibrotic lungs and expresses the highest levels of collagens. Single-cell RNA-sequencing of human lungs, including those from idiopathic pulmonary fibrosis and scleroderma patients, demonstrate similar heterogeneity and CTHRC1-expressing fibroblasts present uniquely in fibrotic lungs. Immunostaining and in situ hybridization show that these cells are concentrated within fibroblastic foci. We purify collagen-producing subpopulations and find disease-relevant phenotypes of Cthrc1-expressing fibroblasts in in vitro and adoptive transfer experiments. Our atlas of collagen-producing cells provides a roadmap for studying the roles of these unique populations in homeostasis and pathologic fibrosis.

Emerging cellular and molecular determinants of idiopathic pulmonary fibrosis

“…Clusters 5 and 7 expressed smooth muscle cell markers, such as Acta2 and Myh11. Cluster 9 expressed pericyte markers [129].…”

TGF-β Pathway in Salivary Gland Fibrosis

“…In contrast, CTHRC1-null transgenic mice presented suppressed SMAD3 phosphorylation and alleviated hepatic fibrosis [80]. Interestingly, a recent single cell RNA sequencing study on human normal and fibrotic lung tissue presented that CTHRC1 was predominantly expressed in cells from pathologic fibrosis tissue and correlated with collagen gene expression [72]. This rather indicated a pro-fibrotic role of CTHRC1 in human pulmonary fibrosis.…”

“…The myofibroblast phenotype has been generally described as the 'classic' source of fibrotic proteins in the previous literature, whereas recent updates have suggested a more diverse phenotypic spectrum of fibroblastic cells in fibrosis. Stromal investigations of mouse and human fibrotic tissues revealed a prominent heterogeneous population of fibroblasts that had a 'non-αSMA' phenotype despite of collagen production [71][72][73]. The recent enablement of multiple marker expression at a single cell level by flow cytometry in human samples has given us a new level of insights on the heterogeneity and plasticity of fibrosis-associated molecules and cells [72,74,75].…”

“…Stromal investigations of mouse and human fibrotic tissues revealed a prominent heterogeneous population of fibroblasts that had a 'non-αSMA' phenotype despite of collagen production [71][72][73]. The recent enablement of multiple marker expression at a single cell level by flow cytometry in human samples has given us a new level of insights on the heterogeneity and plasticity of fibrosis-associated molecules and cells [72,74,75]. Collagen Triple Helix Repeat-Containing-1 (CTHRC1) is of particular interest in TGF-β1 regulated fibrosis with conflicting interpretations among preclinical studies.…”

Reproducible Single-Cell Genomic Research in Pulmonary and Critical Care Medicine

“…Hence, single-cell technologies have rapidly become a logical method of choice to study lung biology and disease (2). Specifically, single-cell RNA-seq has been applied to create reference atlases of normal human lung tissue (3-6), to study cellular cross-talk in multicellular lung cancer niches (7,8), to discover novel cell types in the normal lung (9) or in pulmonary fibrosis (10)(11)(12)(13)(14)(15)(16), to evaluate remodeling of the airway epithelium in asthma (17) or as a result of smoking (18), to study the immune response in cystic fibrosis (19), and in COVID-19 (20)(21)(22). By applying the power of single-cell techniques to causal experiments in model organisms or in vitro systems, investigators were able to provide mechanistic insights about the role of specific cell types to disease pathogenesis (23)(24)(25).…”