Abstract Rationale: Application of single cell RNAseq (scRNAseq) in idiopathic pulmonary fibrosis (IPF) and multiple murine models has revealed two unique disease associated fibroblast subsets, the Cthrc1+ fibrotic population, and a population expressing inflammatory markers whose function is unclear. We, and others, have demonstrated that inflammatory fibroblasts are derived from homeostatic fibroblasts and can differentiate to Cthrc1+ fibroblasts. There is also data in mice suggesting that TGFβ inhibition prevents the emergence of Cthrc1+ fibrotic fibroblasts without impacting the inflammatory fibroblast population. Using our inducible genetic murine model of PF, reductionist organoid systems, and scRNAseq from IPF we present evidence and mechanism for inflammatory fibroblasts as a potential regenerative population in the alveolar niche. Methods: Tamoxifen administration to SftpcI73T conditional allelic knock-in mice, induces expression of mutant protein and promotes an inflammatory cascade followed by fibrogenesis. ScRNA-seq and population RNA-seq of bleomycin and SftpcI73T murine models were compared with publicly available data sets from IPF to identify population specific surface marker expression and potential epithelial ligand-receptor pairs. Flow cytometry approaches developed to isolate fibroblast populations were applied for in-vitro organoid modeling and validation of signaling pathways. In-vivo murine intervention in TGFβ signaling was further applied to confirm functional biology of inflammatory fibroblasts. Results: Informatic analysis of human and mouse inflammatory fibroblasts identifies expression of multiple BMP antagonists that have previously been associated with epithelial proliferation. Furthermore, human inflammatory fibroblasts also express key epithelial growth factors including FGF2 and FGF7. Murine organoid modeling confirms that inflammatory fibroblasts support alveolar organoid formation through the inhibition of BMP signaling. As was previously demonstrated in bleomycin, the inhibition of TGFβ signaling in SftpcI73T does not alter the inflammatory fibroblast population, rather this population is sustained, and alveolar epithelial proliferation increases. Additionally, we did not find any evidence for increase inflammation in the mouse lung due to inflammatory fibroblasts preservation. Finally, human data suggests that two populations of inflammatory fibroblasts are present in the lung with only one subset found to express the BMP antagonists and growth factors required to promote alveolar epithelial proliferation. Conclusions: Our data identifies that inflammatory fibroblasts in the alveolar niche inhibit BMP signaling and allow for epithelial expansion. We also determine differences between murine and human inflammatory fibroblasts suggesting that human inflammatory fibroblasts have a greater potential to drive epithelial expansion. These data shed light on the functional role of inflammatory fibroblasts, further refining our understanding of fibroblast heterogeneity in IPF.
Stem cells, cell therapies, and bioengineering in lung biology and diseases 2023
Repair and regeneration of a diseased lung using stem cells or bioengineered tissues is an exciting therapeutic approach for a variety of lung diseases and critical illnesses. Over the past decade, increasing evidence from preclinical models suggests that mesenchymal stromal cells, which are not normally resident in the lung, can be used to modulate immune responses after injury, but there have been challenges in translating these promising findings to the clinic. In parallel, there has been a surge in bioengineering studies investigating the use of artificial and acellular lung matrices as scaffolds for three-dimensional lung or airway regeneration, with some recent attempts of transplantation in large animal models. The combination of these studies with those involving stem cells, induced pluripotent stem cell derivatives, and/or cell therapies is a promising and rapidly developing research area. These studies have been further paralleled by significant increases in our understanding of the molecular and cellular events by which endogenous lung stem and/or progenitor cells arise during lung development and participate in normal and pathological remodeling after lung injury. For the 2023 Stem Cells, Cell Therapies, and Bioengineering in Lung Biology and Diseases Conference, scientific symposia were chosen to reflect the most cutting-edge advances in these fields. Sessions focused on the integration of “omics” technologies with function, the influence of immune cells on regeneration, and the role of the extracellular matrix in regeneration. The necessity for basic science studies to enhance fundamental understanding of lung regeneration and to design innovative translational studies was reinforced throughout the conference.
Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)
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