The Regenerative Power of Stem Cells: Treating Bleomycin-Induced Lung Fibrosis

Figures & data

Table 1 Key Research Articles Contributing to the Field of Pulmonary Fibrosis

No.	Study	Contribution	Reference
1	Snider et al, 1978	Established bleomycin-induced lung injury animal model system to study human IPF	[17]
2	Adamson et al, 1988	Explored link between hyperoxia-induced alveolar epithelial injury, repair, and pulmonary fibrosis	[18]
3	Kuhn et al, 1989	Investigated architectural remodeling and connective tissue synthesis in pulmonary fibrosis	[19]
4	Zhang et al 1994	Explored myofibroblasts’ role in lung collagen gene expression during fibrosis	[20]
5	Sime et al, 1997	Studied adenovector-mediated gene transfer of active TGF-beta1 and induced fibrosis	[21]
6	Hagimoto et al, 2002	Investigated role of TGF-beta 1 in enhancing apoptosis of lung epithelial cells	[22]
7	Izbicki et al, 2002	Investigated the time course of bleomycin-induced lung fibrosis	[23]
8	Moodley et al, 2003	Demonstrated profibrotic role of Interleukin-6 in IPF	[24]
9	Kim et al, 2006	Explored alveolar epithelial cell mesenchymal transition, and role of extracellular matrix during fibrosis	[25]
10	Alder et al, 2008	Identified that telomere shortening may be an important contributor to the genetic susceptibility to IPF	[26]
11	Sisson et al, 2010	Investigated targeted injury to type II alveolar epithelial cells and fibrosis	[27]
12	Marmai et al, 2011	Observed alveolar epithelial cells expressing mesenchymal proteins in fibrosis	[28]
13	Raghu et al, 2011	Provided evidence-based guidelines for idiopathic pulmonary fibrosis diagnosis and management	[29]
14	Rock et al, 2011	Explored role of multiple stromal populations in pulmonary fibrosis	[30]
15	Barkauskas et al, 2013	Used lineage-tracing experiments to demonstrate long-term self-renewal and differentiation of AT2 cells	[5]
16	Huang et al, 2014	Established protocol for directed differentiation of hPSCs into lung and airway epithelial cells	[31]
17	Jain et al, 2015	Demonstrated plasticity of AT1 cells and a bidirectional lineage relationship between distinct differentiated alveolar epithelial cell types	[6]
18	Wang et al, 2018	Genetic marker (HopX/Igfbp2) based identification of AT1 subtypes and their fates during distinct cell fates during alveolar regeneration	[4]

Figure 1 An illustration of AT2-AT1 cell transition during fibrotic lung injury. The figure represents the process of AT2-AT1 cell transition during fibrotic lung injury. AT2 cells are shown to proliferate after the lung injury, where a fraction of these cells differentiating into mature AT1 cells. Also included are the representative cell types involved in the repair process (top right). Created with BioRender.com.

Figure 2 Lineage-tracing of cells during the repair phase of an injured lung by the Cre-ERT2 system. (a) Schematic representation of the Cre-ERT2 system. The presence of a stop codon flanked by loxP sites inhibits the expression of the reporter transgene (tdTomato). Upon tamoxifen treatment, the expressed Cre mediates site-specific recombination between loxP sites, which removes the intervening stop codon, and the reporter is expressed. (b) Lineage-tracing using Cre-ERT2 system enriches and identifies intermediate stages of transdifferentiated AT2 stem cells. Some of the identified intermediates are shown for representation. Similar enrichment can also be achieved using stem cell surface markers such as CD34, CD45, and Thy1. Created with BioRender.com.

Figure 3 Mechanotransduction-Mediated Signaling in AT2-AT1 Transition. The figure illustrates the signaling factors and progenitor stem cells involved in the AT2-AT1 transition in fibrotic lungs, as well as the role of the mesenchymal niche microenvironment in this process. The complex mechanical signaling pathways that control this transition are depicted, with a focus on the involvement of the small Rho GTPase family member Cdc42 in regulating the STAT-3 and STAT-1 signaling pathways. The effects of mechanotransduction on Wnt, Sox2, EGF, β-catenin, and Nkx2 proteins in the lung mesenchyme, which can alter lung development and repair, have also been demonstrated (bottom right). Created with BioRender.com.

Snider GL, Celli BR, Goldstein RH, O’Brien JJ, Lucey EC. Chronic interstitial pulmonary fibrosis produced in hamsters by endotracheal bleomycin. Lung volumes, volume-pressure relations, carbon monoxide uptake, and arterial blood gas studied. Am Rev Respir Dis. 1978;117(2):289–297. doi:10.1164/ARRD.1978.117.2.289

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Adamson IYR, Young L, Bowden DH. Relationship of alveolar epithelial injury and repair to the induction of pulmonary fibrosis. Am J Pathol. 1988;130(2):377.

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Kuhn C, Boldt J, King TE, Crouch E, Vartio T, McDonald JA. An Immunohistochemical study of architectural remodeling and connective tissue synthesis in pulmonary fibrosis. Am Rev Respir Dis. 2012;140(6):1693–1703. doi:10.1164/AJRCCM/140.6.1693

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Zhang K, Rekhter MD, Gordon D, Phan SH. Myofibroblasts and their role in lung collagen gene expression during pulmonary fibrosis. A combined immunohistochemical and in situ hybridization study. Am J Pathol. 1994;145(1):114.

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Sime PJ, Xing Z, Graham FL, Csaky KG, Gauldie J. Adenovector-mediated gene transfer of active transforming growth factor-beta1 induces prolonged severe fibrosis in rat lung. J Clin Invest. 1997;100(4):768–776. doi:10.1172/JCI119590

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Hagimoto N, Kuwano K, Inoshima I, et al. TGF-β1 as an Enhancer of Fas-Mediated Apoptosis of Lung Epithelial Cells. J Immunol. 2002;168(12):6470–6478. doi:10.4049/JIMMUNOL.168.12.6470

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Izbicki G, Segel MJ, Christensen TG, Conner MW, Breuer R. Time course of bleomycin-induced lung fibrosis. Int J Exp Pathol. 2002;83(3):111–119. doi:10.1046/J.1365-2613.2002.00220.X

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Moodley YP, Misso NLA, Scaffidi AK, et al. Inverse Effects of Interleukin-6 on Apoptosis of Fibroblasts from Pulmonary Fibrosis and Normal Lungs. Am Rev Respir Dis. 2003;29(4):490–498. doi:10.1165/RCMB.2002-0262OC

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Kim KK, Kugler MC, Wolters PJ, et al. Alveolar epithelial cell mesenchymal transition develops in vivo during pulmonary fibrosis and is regulated by the extracellular matrix. Proc Natl Acad Sci U S A. 2006;103(35):13180–13185. doi:10.1073/PNAS.0605669103/SUPPL_FILE/05669FIG_9.JPG

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Alder JK, Chen JJL, Lancaster L, et al. Short telomeres are a risk factor for idiopathic pulmonary fibrosis. Proc Natl Acad Sci U S A. 2008;105(35):13051–13056. doi:10.1073/PNAS.0804280105/SUPPL_FILE/0804280105SI.PDF

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Sisson TH, Mendez M, Choi K, et al. Targeted injury of type ii alveolar epithelial cells induces pulmonary fibrosis. Am J Respir Crit Care Med. 2010;181(3):254–263. doi:10.1164/rccm.200810-1615OC

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Marmai C, Sutherland RE, Kim KK, et al. Alveolar epithelial cells express mesenchymal proteins in patients with idiopathic pulmonary fibrosis. Am J Physiol - Lung Cell Mol Physiol. 2011;301(1):71–78. doi:10.1152/AJPLUNG.00212.2010/SUPPL_FILE/SUPPDATA.PDF

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Raghu G, Collard HR, Egan JJ, et al. An Official ATS/ERS/JRS/ALAT Statement: idiopathic Pulmonary Fibrosis: evidence-based Guidelines for Diagnosis and Management. Am J Respir Crit Care Med. 2011;183(6):788. doi:10.1164/RCCM.2009-040GL

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Rock JR, Barkauskas CE, Cronce MJ, et al. Multiple stromal populations contribute to pulmonary fibrosis without evidence for epithelial to mesenchymal transition. Proc Natl Acad Sci U S A. 2011;108(52):E1475–E1483. doi:10.1073/PNAS.1117988108/SUPPL_FILE/PNAS.201117988SI.PDF

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Barkauskas CE, Cronce MJ, Rackley CR, et al. Type 2 alveolar cells are stem cells in adult lung. J Clin Invest. 2013;123(7):3025–3036. doi:10.1172/JCI68782

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Huang SXL, Islam MN, O’Neill J, et al. Efficient generation of lung and airway epithelial cells from human pluripotent stem cells. Nat Biotechnol. 2013;32(1):84–91. doi:10.1038/nbt.2754

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Jain R, Barkauskas CE, Takeda N, et al. Plasticity of Hopx(+) type I alveolar cells to regenerate type II cells in the lung. Nat Commun. 2015;6:6727. doi:10.1038/ncomms7727

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Wang Y, Tang Z, Huang H, et al. Pulmonary alveolar type I cell population consists of two distinct subtypes that differ in cell fate. Proc Natl Acad Sci. 2018;115(10):2407–2412. doi:10.1073/pnas.1719474115

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