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Zhang K, Yao E, Aung T, Chuang PT. The alveolus: Our current knowledge of how the gas exchange unit of the lung is constructed and repaired. Curr Top Dev Biol 2024; 159:59-129. [PMID: 38729684 DOI: 10.1016/bs.ctdb.2024.01.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2024]
Abstract
The mammalian lung completes its last step of development, alveologenesis, to generate sufficient surface area for gas exchange. In this process, multiple cell types that include alveolar epithelial cells, endothelial cells, and fibroblasts undergo coordinated cell proliferation, cell migration and/or contraction, cell shape changes, and cell-cell and cell-matrix interactions to produce the gas exchange unit: the alveolus. Full functioning of alveoli also involves immune cells and the lymphatic and autonomic nervous system. With the advent of lineage tracing, conditional gene inactivation, transcriptome analysis, live imaging, and lung organoids, our molecular understanding of alveologenesis has advanced significantly. In this review, we summarize the current knowledge of the constituents of the alveolus and the molecular pathways that control alveolar formation. We also discuss how insight into alveolar formation may inform us of alveolar repair/regeneration mechanisms following lung injury and the pathogenic processes that lead to loss of alveoli or tissue fibrosis.
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Affiliation(s)
- Kuan Zhang
- Cardiovascular Research Institute, University of California, San Francisco, CA, United States
| | - Erica Yao
- Cardiovascular Research Institute, University of California, San Francisco, CA, United States
| | - Thin Aung
- Cardiovascular Research Institute, University of California, San Francisco, CA, United States
| | - Pao-Tien Chuang
- Cardiovascular Research Institute, University of California, San Francisco, CA, United States.
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Riccetti MR, Green J, Taylor TJ, Perl AKT. Prenatal FGFR2 Signaling via PI3K/AKT Specifies the PDGFRA + Myofibroblast. Am J Respir Cell Mol Biol 2024; 70:63-77. [PMID: 37734036 PMCID: PMC10768833 DOI: 10.1165/rcmb.2023-0245oc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/21/2023] [Indexed: 09/23/2023] Open
Abstract
It is well known that FGFR2 (fibroblast growth factor receptor 2) signaling is critical for proper lung development. Recent studies demonstrate that epithelial FGFR2 signaling during the saccular phase of lung development (sacculation) regulates alveolar type 1 (AT1) and AT2 cell differentiation. During sacculation, PDGFRA (platelet-derived growth factor receptor-α)-positive lung fibroblasts exist as three functional subtypes: contractile myofibroblasts, extracellular matrix-producing matrix fibroblasts, and lipofibroblasts. All three subtypes are required during alveolarization to establish a niche that supports AT2 epithelial cell self-renewal and AT1 epithelial cell differentiation. FGFR2 signaling directs myofibroblast differentiation in PDGFRA+ fibroblasts during alveolar reseptation after pneumonectomy. However, it remains unknown if FGFR2 signaling regulates PDGFRA+ myo-, matrix, or lipofibroblast differentiation during sacculation. In this study, FGFR2 signaling was inhibited by temporal expression of a secreted dominant-negative FGFR2b (dnFGFR2) by AT2 cells from embryonic day (E) 16.5 to E18.5. Fibroblast and epithelial differentiation were analyzed at E18.5 and postnatal days 7 and 21. At all time points, the number of myofibroblasts was reduced and the number of lipo-/matrix fibroblasts was increased. AT2 cells are increased and AT1 cells are reduced postnatally, but not at E18.5. Similarly, in organoids made with PDGFRA+ fibroblasts from dnFGFR2 lungs, increased AT2 cells and reduced AT1 cells were observed. In vitro treatment of primary wild-type E16.5 adherent saccular lung fibroblasts with recombinant dnFGFR2b/c resulted in reduced myofibroblast contraction. Treatment with the PI3K/AKT activator 740 Y-P rescued the lack of myofibroblast differentiation caused by dnFGFR2b/2c. Moreover, treatment with the PI3K/AKT activator 740 Y-P rescued myofibroblast differentiation in E18.5 fibroblasts isolated from dnFGFR2 lungs.
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Affiliation(s)
- Matthew R. Riccetti
- Division of Neonatology and Pulmonary Biology and
- Molecular and Developmental Biology Graduate Program, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio
| | - Jenna Green
- Division of Neonatology and Pulmonary Biology and
| | - Thomas J. Taylor
- Division of Neonatology and Pulmonary Biology and
- College of Arts and Sciences, University of Cincinnati, Cincinnati, Ohio; and
| | - Anne-Karina T. Perl
- Division of Neonatology and Pulmonary Biology and
- Molecular and Developmental Biology Graduate Program, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio
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He H, Bell SM, Davis AK, Zhao S, Sridharan A, Na CL, Guo M, Xu Y, Snowball J, Swarr DT, Zacharias WJ, Whitsett JA. PRDM3/16 Regulate Chromatin Accessibility Required for NKX2-1 Mediated Alveolar Epithelial Differentiation and Function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.20.570481. [PMID: 38187557 PMCID: PMC10769259 DOI: 10.1101/2023.12.20.570481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Differential chromatin accessibility accompanies and mediates transcriptional control of diverse cell fates and their differentiation during embryogenesis. While the critical role of NKX2-1 and its transcriptional targets in lung morphogenesis and pulmonary epithelial cell differentiation is increasingly known, mechanisms by which chromatin accessibility alters the epigenetic landscape and how NKX2-1 interacts with other co-activators required for alveolar epithelial cell differentiation and function are not well understood. Here, we demonstrate that the paired domain zinc finger transcriptional regulators PRDM3 and PRDM16 regulate chromatin accessibility to mediate cell differentiation decisions during lung morphogenesis. Combined deletion of Prdm3 and Prdm16 in early lung endoderm caused perinatal lethality due to respiratory failure from loss of AT2 cell function. Prdm3/16 deletion led to the accumulation of partially differentiated AT1 cells and loss of AT2 cells. Combination of single cell RNA-seq, bulk ATAC-seq, and CUT&RUN demonstrated that PRDM3 and PRDM16 enhanced chromatin accessibility at NKX2-1 transcriptional targets in peripheral epithelial cells, all three factors binding together at a multitude of cell-type specific cis-active DNA elements. Network analysis demonstrated that PRDM3/16 regulated genes critical for perinatal AT2 cell differentiation, surfactant homeostasis, and innate host defense. Lineage specific deletion of PRDM3/16 in AT2 cells led to lineage infidelity, with PRDM3/16 null cells acquiring partial AT1 fate. Together, these data demonstrate that NKX2-1-dependent regulation of alveolar epithelial cell differentiation is mediated by epigenomic modulation via PRDM3/16.
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Affiliation(s)
- Hua He
- Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, West China Second University Hospital Sichuan University, Chengdu, Sichuan, 610041, China
- NHC Key Laboratory of Chronobiology, Sichuan University, Sichuan 610041, China
| | - Sheila M. Bell
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Ashley Kuenzi Davis
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Shuyang Zhao
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Anusha Sridharan
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Cheng-Lun Na
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Minzhe Guo
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
- Department of Pediatrics, University of Cincinnati College of Medicine
| | - Yan Xu
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
- Department of Pediatrics, University of Cincinnati College of Medicine
| | - John Snowball
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
| | - Daniel T. Swarr
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
- Department of Pediatrics, University of Cincinnati College of Medicine
| | - William J. Zacharias
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
- Department of Pediatrics, University of Cincinnati College of Medicine
| | - Jeffrey A. Whitsett
- Perinatal Institute, Division of Neonatology and Pulmonary Biology, Cincinnati Children’s Hospital Medical Center
- Department of Pediatrics, University of Cincinnati College of Medicine
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Chong L, Ahmadvand N, Noori A, Lv Y, Chen C, Bellusci S, Zhang JS. Injury activated alveolar progenitors (IAAPs): the underdog of lung repair. Cell Mol Life Sci 2023; 80:145. [PMID: 37166489 PMCID: PMC10173924 DOI: 10.1007/s00018-023-04789-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2023] [Revised: 04/11/2023] [Accepted: 04/24/2023] [Indexed: 05/12/2023]
Abstract
Alveolar epithelial type II cells (AT2s) together with AT1s constitute the epithelial lining of lung alveoli. In contrast to the large flat AT1s, AT2s are cuboidal and smaller. In addition to surfactant production, AT2s also serve as prime alveolar progenitors in homeostasis and play an important role during regeneration/repair. Based on different lineage tracing strategies in mice and single-cell transcriptomic analysis, recent reports highlight the heterogeneous nature of AT2s. These studies present compelling evidence for the presence of stable or transitory AT2 subpopulations with distinct marker expression, signaling pathway activation and functional properties. Despite demonstrated progenitor potentials of AT2s in maintaining homeostasis, through self-renewal and differentiation to AT1s, the exact identity, full progenitor potential and regulation of these progenitor cells, especially in the context of human diseases remain unclear. We recently identified a novel subset of AT2 progenitors named "Injury-Activated Alveolar Progenitors" (IAAPs), which express low levels of Sftpc, Sftpb, Sftpa1, Fgfr2b and Etv5, but are highly enriched for the expression of the surface receptor programmed cell death-ligand 1 (Pd-l1). IAAPs are quiescent during lung homeostasis but activated upon injury with the potential to proliferate and differentiate into AT2s. Significantly, a similar population of PD-L1 positive cells expressing intermediate levels of SFTPC are found to be expanded in human IPF lungs. We summarize here the current understanding of this newly discovered AT2 progenitor subpopulation and also try to reconcile the relationship between different AT2 stem cell subpopulations regarding their progenitor potential, regulation, and relevance to disease pathogenesis and therapeutic interventions.
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Affiliation(s)
- Lei Chong
- Department of Pediatric Respiratory Medicine, National Key Clinical Specialty of Pediatric Respiratory Medicine, Institute of Pediatrics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, 325027, Zhejiang, China
| | - Negah Ahmadvand
- Department of Cell Biology, Duke University School of Medicine, Durham, NC27710, USA
| | - Afshin Noori
- Cardio Pulmonary Institute, Department of Pulmonary and Critical Care Medicine and Infectious Diseases, Universities of Giessen and Marburg Lung Center, Justus-Liebig University Giessen, 35392, Giessen, Germany
| | - Yuqing Lv
- Medical Research Center, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, 325000, Zhejiang, China
- The Quzhou Affiliated Hospital of Wenzhou Medical University, Quzhou People's Hospital, Quzhou, 324000, Zhejiang, China
| | - Chengshui Chen
- The Quzhou Affiliated Hospital of Wenzhou Medical University, Quzhou People's Hospital, Quzhou, 324000, Zhejiang, China
- Zhejiang Provincial Key Laboratory of Interventional Pulmonology and Department of Pulmonary and Critical Care Medicine, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, 325000, Zhejiang, China
| | - Saverio Bellusci
- The Quzhou Affiliated Hospital of Wenzhou Medical University, Quzhou People's Hospital, Quzhou, 324000, Zhejiang, China.
- Laboratory of Extracellular Matrix Remodelling, Cardio Pulmonary Institute, Department of Pulmonary and Critical Care Medicine and Infectious Diseases, Universities of Giessen and Marburg Lung Center, Member of the German Lung Center, Justus-Liebig University Giessen, 35392, Giessen, Germany.
| | - Jin-San Zhang
- Medical Research Center, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, 325000, Zhejiang, China.
- The Quzhou Affiliated Hospital of Wenzhou Medical University, Quzhou People's Hospital, Quzhou, 324000, Zhejiang, China.
- Zhejiang Provincial Key Laboratory of Interventional Pulmonology and Department of Pulmonary and Critical Care Medicine, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, 325000, Zhejiang, China.
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