Evidence for a lipofibroblast-to- Cthrc1 + myofibroblast reversible switch during the development and resolution of lung fibrosis in young mice.

BACKGROUND: Fibrosis is often associated with aberrant repair mechanisms that ultimately lead to organ failure. In the lung, idiopathic pulmonary fibrosis (IPF) is a fatal form of interstitial lung disease (ILD) to which there is currently no curative therapy. From the cell biology point of view, the cell of origin and eventual fate of activated myofibroblasts (aMYFs) have taken center stage as these cells are believed to drive structural remodeling and lung function impairment. While aMYFs are now widely believed to originate from resident fibroblasts, the heterogeneity of aMYFs and ultimate fate during fibrosis resolution remain elusive. We have previously shown that aMYFs dedifferentiation and acquisition of a lipofibroblast (LIF)-like phenotype represent a route of fibrosis resolution. METHODS: In this study, we combined genetic lineage tracing and single-cell transcriptomics in mice, and data mining of human IPF datasets to decipher the heterogeneity of aMYFs and investigate differentiation trajectories during fibrosis resolution. Furthermore, organoid cultures were utilized as a functional readout for the alveolar mesenchymal niche activity during various phases of injury and repair in mice. RESULTS: Our data demonstrate that aMYFs consist of four subclusters displaying unique pro-alveologenic versus profibrotic profiles. Alveolar fibroblasts displaying a high LIF-like signature largely constitute both the origin and fate of aMYFs during fibrogenesis and resolution respectively. The heterogeneity of aMYFs is conserved in humans and a significant proportion of human aMYFs displays a high LIF signature. CONCLUSION: Our work identifies a subcluster of aMYFs that is potentially relevant for future management of IPF.

Stem/Progenitor Cells and Related Therapy in Bronchopulmonary Dysplasia.

Bronchopulmonary dysplasia (BPD) is a chronic lung disease commonly seen in preterm infants, and is triggered by infection, mechanical ventilation, and oxygen toxicity. Among other problems, lifelong limitations in lung function and impaired psychomotor development may result. Despite major advances in understanding the disease pathologies, successful interventions are still limited to only a few drug therapies with a restricted therapeutic benefit, and which sometimes have significant side effects. As a more promising therapeutic option, mesenchymal stem cells (MSCs) have been in focus for several years due to their anti-inflammatory effects and their secretion of growth and development promoting factors. Preclinical studies provide evidence in that MSCs have the potential to contribute to the repair of lung injuries. This review provides an overview of MSCs, and other stem/progenitor cells present in the lung, their identifying characteristics, and their differentiation potential, including cytokine/growth factor involvement. Furthermore, animal studies and clinical trials using stem cells or their secretome are reviewed. To bring MSC-based therapeutic options further to clinical use, standardized protocols are needed, and upcoming side effects must be critically evaluated. To fill these gaps of knowledge, the MSCs' behavior and the effects of their secretome have to be examined in more (pre-) clinical studies, from which only few have been designed to date.

Highlighting fibroblast plasticity in lung fibrosis: the WI-38 cell line as a model for investigating the myofibroblast and lipofibroblast switch.

Background: Myofibroblasts (MYFs) are generally considered the principal culprits in excessive extracellular matrix deposition and scar formation in the pathogenesis of lung fibrosis. Lipofibroblasts (LIFs), on the other hand, are defined by their lipid-storing capacity and are predominantly found in the alveolar regions of the lung. They have been proposed to play a protective role in lung fibrosis. We previously reported that a LIF to MYF reversible differentiation switch occurred during fibrosis formation and resolution. In this study, we tested whether WI-38 cells, a human embryonic lung fibroblast cell line, could be used to study fibroblast differentiation towards the LIF or MYF phenotype and whether this could be relevant for idiopathic pulmonary fibrosis (IPF). Methods: Using WI-38 cells, Fibroblast (FIB) to MYF differentiation was triggered using TGF-ß1 treatment and FIB to LIF differentiation using Metformin treatment. We also analyzed the MYF to LIF and LIF to MYF differentiation by pre-treating the WI-38 cells with TGF-ß1 or Metformin respectively. We used IF, qPCR and bulk RNA-Seq to analyze the phenotypic and transcriptomic changes in the cells. We correlated our in vitro transcriptome data from WI-38 cells (obtained via bulk RNA sequencing) with the transcriptomic signature of LIFs and MYFs derived from the IPF cell atlas as well as with our own single-cell transcriptomic data from IPF patients-derived lung fibroblasts (LF-IPF) cultured in vitro. We also carried out alveolosphere assays to evaluate the ability of the proposed LIF and MYF cells to support the growth of alveolar epithelial type 2 cells. Results: WI-38 cells and LF-IPF display similar phenotypical and gene expression responses to TGF-ß1 and Metformin treatment. Bulk RNA-Seq analysis of WI-38 cells and LF-IPF treated with TGF-ß1, or Metformin indicate similar transcriptomic changes. We also show the partial conservation of the LIF and MYF signature extracted from the Habermann et al. scRNA-seq dataset in WI-38 cells treated with Metformin or TGF-ß1, respectively. Alveolosphere assays indicate that LIFs enhance organoid growth, while MYFs inhibit organoid growth. Finally, we provide evidence supporting the MYF to LIF and LIF to MYF reversible switch using WI-38 cells. Conclusions: WI-38 cells represent a versatile and reliable model to study the intricate dynamics of fibroblast differentiation towards the MYF or LIF phenotype associated with lung fibrosis formation and resolution, providing valuable insights to drive future research.

Cross-Talk Between Inflammation and Fibroblast Growth Factor 10 During Organogenesis and Pathogenesis: Lessons Learnt From the Lung and Other Organs.

The adult human lung is constantly exposed to irritants like particulate matter, toxic chemical compounds, and biological agents (bacteria and viruses) present in the external environment. During breathing, these irritants travel through the bronchi and bronchioles to reach the deeper lung containing the alveoli, which constitute the minimal functional respiratory units. The local biological responses in the alveoli that follow introduction of irritants need to be tightly controlled in order to prevent a massive inflammatory response leading to loss of respiratory function. Cells, cytokines, chemokines and growth factors intervene collectively to re-establish tissue homeostasis, fight the aggression and replace the apoptotic/necrotic cells with healthy cells through proliferation and/or differentiation. Among the important growth factors at play during inflammation, members of the fibroblast growth factor (Fgf) family regulate the repair process. Fgf10 is known to be a key factor for organ morphogenesis and disease. Inflammation is influenced by Fgf10 but can also impact Fgf10 expression per se. Unfortunately, the connection between Fgf10 and inflammation in organogenesis and disease remains unclear. The aim of this review is to highlight the reported players between Fgf10 and inflammation with a focus on the lung and to propose new avenues of research.