Dr. Tushar Desai specializes clinically in the treatment of general pulmonary and Interstitial Lung Diseases like Idiopathic Pulmonary Fibrosis (IPF). He has practiced pulmonary medicine since 2002.
Dr. Desai conducts basic and translational research on lung stem cells that repair and regenerate the lung after injury, and their role in diseases like IPF, Chronic Obstructive Pulmonary Disease (COPD), and lung adenocarcinoma. His lab also studies the molecular signals that regulate lung stem cell activity, and how the signals can be manipulated to restore their activity. He participates in research involving gene correction of CFTR in lung stem cells from patients with Cystic fibrosis followed by autologous stem cell transplantation to provide lifelong restoration of physiological activity.
- Pulmonary Disease
- Interstitial Lung Diseases
Associate Professor, Medicine - Pulmonary, Allergy & Critical Care Medicine
Member, Cardiovascular Institute
Member, Stanford Cancer Institute
Director of Graduate Studies, Stem Cell Biology PhD program (2021 - Present)
Director of Translational Lung Biology, Department of Medicine (2020 - Present)
Honors & Awards
Robert A. and Gertrude T. Hudson Endowed Professor, Stanford University School of Medicine (2020)
Elected Member, American Society for Clinical Investigation (2019)
Lung Force Gala Honoree, American Lung Association (2018)
Woods Family Endowed Faculty Scholar in Pediatric Translational Medicine, Stanford Child Health Research Institute (2016-2021)
Stanford Medical Student Teaching Recognition, Stanford University School of Medicine (2011-2014)
Robert Dawson Evans Fellow Excellence in Teaching Award, Boston University School of Medicine, Department of Internal Medicine (2000)
House Officer Research Award, University of Michigan Hospitals, Department of Internal Medicine (1998)
Worth F. Bloom M25 Prize, Tufts University School of Medicine (1995)
Boards, Advisory Committees, Professional Organizations
Member, American Society for Clinical Investigation (2019 - Present)
Member, Scientific Advisory Board, UK Regenerative Medicine Platform, Engineered Cell Environment Hub (2018 - Present)
Member, Scientific Advisory Committee, American Thoracic Society (ATS) (2015 - Present)
Fellowship: Boston University Pulmonary and Critical Care Fellowship (2002) MA
Residency: University of Michigan Health System Internal Medicine Residency (1998) MI
MD, MPH, Tufts University School of Medicine (1995)
BA, Amherst College, Psychology (1991)
Dawn T. Bravo, Sriram Vaidyanathan, Matthew H. Porteus, Calvin J. Kuo, Jayakar Nayak, Ameen Salahudeen and Tushar J. Desai. "United States Patent 17/353,049 Compositions and methods for airway tissue regeneration", Leland Stanford Junior University, Jun 21, 2021
Tushar Desai, Pehr Harbury, Daniel Riordan. "United States Patent 62/475,090 Molecular profiling using proximity ligation- in situ hybridization", Leland Stanford Junior University, Mar 22, 2017
Current Research and Scholarly Interests
My lab is focused on understanding the causes of and working towards specific molecular and cell-based treatments for lung diseases like cancer, pulmonary fibrosis, COPD. We focus our attention on lung stem cells and the molecular signals that regulate their activity to repair and regenerate lung tissue after injury. These same stem cells can become dysfunctional, generating cancer if they become overactive, and resulting in respiratory failure if they lose their potency. We are focused on Wnt signaling because this appears to be a key signal that confers stem cell potency in both mouse and human lung, and is overactive in diseases like lung adenocarcinoma and Idiopathic Pulmonary Fibrosis (IPF). My lab also studies the role of TERT in lung stem cell biology and repair of acute lung injury, which is a culprit gene mutation in IPF. Our experimental approaches involve mouse genetics, single cell genomics, organoid culture, lung slice culture, and we perform histological analysis of lung tissue using advanced fluorescence microscopy technologies. A portion of my lab is also involved in the invention of new technologies to facilitate highly multiplexed staining of protein (immunostaining) and RNA (in situ hybridization) of human tissues.
Lung stem cells can also be exploited to treat monogenic diseases, by using CRISPR to correct the genetic mutation then transplanting them back into the patient. This strategy of ex vivo gene correction in stem cells followed by autologous stem cell transplantation is already being trialed in blood disorders like Sickle cell anemia. We are part of a Stanford group that is using CRISPR to correct CFTR mutations in airway stem cells and working towards developing a protocol for safe and effective autologous transplantation into the sinuses of Cystic fibrosis patients. We hope to advance this cell-based therapeutic approach of transplanting stem cells into the airways and gas exchange region of the lungs to treat diseases resulting from loss of stem cell potency.
Detection of Integrin avb6 in IPF, PSC, and COVID19 Using PET/CT
Detection of Integrin avb6 in Idiopathic Pulmonary Fibrosis, Primary Sclerosing Cholangitis, and Coronavirus Disease 2019 with [18F]FP-R01-MG-F2 with PET/CT
Independent Studies (6)
- Directed Reading in Medicine
MED 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Medicine
MED 280 (Aut, Win, Spr, Sum)
- Graduate Research
MED 399 (Aut, Win, Spr, Sum)
- Graduate Research
STEMREM 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
MED 370 (Aut, Win, Spr, Sum)
- Undergraduate Research
MED 199 (Aut, Win, Spr, Sum)
- Directed Reading in Medicine
Med Scholar Project Advisor
Joshua Guild, Marina Martinez
Postdoctoral Faculty Sponsor
Nicholas Juul, Matthew McCarra, Jung Ki Yoon
Doctoral Dissertation Advisor (AC)
Joshua Guild, Courtney Stockman
Laura Amaya, Alvaro Amorin, Jessica Arozqueta Basurto, Khristian Bauer-Rowe, Jeremy Bjelajac, Quenton Bubb, Carsten Charlesworth, Lori Dershowitz, Carolyn Dundes, William Feist, Franco Felix, Jonas Fowler, Hana Ghanim, Malachia Hoover, Nicole Horsley, Lauren Koepke, Ishan Kumar, Jennifer Parker, Suyash Raj, Julien Roth, Julie Sanchez, Archana Shankar, Aaron Tan, Sicong Wang, Maya Weigel
Postdoctoral Research Mentor
Nicholas Juul, Jung Ki Yoon
Graduate and Fellowship Programs
Pulmonary & Critical Care Medicine (Fellowship Program)
Dual inhibition of alphavbeta6 and alphavbeta1 reduces fibrogenesis in lung tissue explants from patients with IPF.
2021; 22 (1): 265
RATIONALE: alphav integrins, key regulators of transforming growth factor-beta activation and fibrogenesis in in vivo models of pulmonary fibrosis, are expressed on abnormal epithelial cells (alphavbeta6) and fibroblasts (alphavbeta1) in fibrotic lungs.OBJECTIVES: We evaluated multiple alphav integrin inhibition strategies to assess which most effectively reduced fibrogenesis in explanted lung tissue from patients with idiopathic pulmonary fibrosis.METHODS: Selective alphavbeta6 and alphavbeta1, dual alphavbeta6/alphavbeta1, and multi-alphav integrin inhibitors were characterized for potency, selectivity, and functional activity by ligand binding, cell adhesion, and transforming growth factor-beta cell activation assays. Precision-cut lung slices generated from lung explants from patients with idiopathic pulmonary fibrosis or bleomycin-challenged mouse lungs were treated with integrin inhibitors or standard-of-care drugs (nintedanib or pirfenidone) and analyzed for changes in fibrotic gene expression or TGF-beta signaling. Bleomycin-challenged mice treated with dual alphavbeta6/alphavbeta1 integrin inhibitor, PLN-74809, were assessed for changes in pulmonary collagen deposition and Smad3 phosphorylation.MEASUREMENTS AND MAIN RESULTS: Inhibition of integrins alphavbeta6 and alphavbeta1 was additive in reducing type I collagen gene expression in explanted lung tissue slices from patients with idiopathic pulmonary fibrosis. These data were replicated in fibrotic mouse lung tissue, with no added benefit observed from inhibition of additional alphav integrins. Antifibrotic efficacy of dual alphavbeta6/alphavbeta1 integrin inhibitor PLN-74809 was confirmed in vivo, where dose-dependent inhibition of pulmonary Smad3 phosphorylation and collagen deposition was observed. PLN-74809 also, more potently, reduced collagen gene expression in fibrotic human and mouse lung slices than clinically relevant concentrations of nintedanib or pirfenidone.CONCLUSIONS: In the fibrotic lung, dual inhibition of integrins alphavbeta6 and alphavbeta1 offers the optimal approach for blocking fibrogenesis resulting from integrin-mediated activation of transforming growth factor-beta.
View details for DOI 10.1186/s12931-021-01863-0
View details for PubMedID 34666752
- Developmental Insights into Lung Cancer ANNUAL REVIEW OF CANCER BIOLOGY, VOL 5, 2021 2021; 5: 351–69
First lung and kidney multi-organ transplant following COVID-19 Infection.
The Journal of heart and lung transplantation : the official publication of the International Society for Heart Transplantation
As the world responds to the global crisis of the COVID-19 pandemic an increasing number of patients are experiencing increased morbidity as a result of multi-organ involvement. Of these, a small proportion will progress to end-stage lung disease, become dialysis dependent, or both. Herein, we describe the first reported case of a successful combined lung and kidney transplantation in a patient with COVID-19. Lung transplantation, isolated or combined with other organs, is feasible and should be considered for select patients impacted by this deadly disease.
View details for DOI 10.1016/j.healun.2021.02.015
View details for PubMedID 34059432
- Lung stem cells and therapy for cystic fibrosis Lung Stem Cells in Development, Health and Disease (ERS Monograph) edited by Nikolic, M. Z., Hogan, B. L. 2021: 306-321
Targeted replacement of full-length CFTR in human airway stem cells by CRISPR/Cas9 for pan-mutation correction in the endogenous locus.
Molecular therapy : the journal of the American Society of Gene Therapy
Cystic fibrosis (CF) is a monogenic disease caused by impaired production and/or function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Although we have previously shown correction of the most common pathogenic mutation, there are many other pathogenic mutations throughout the CF gene. An autologous airway stem cell therapy in which the CFTR cDNA is precisely inserted into the CFTR locus may enable the development of a durable cure for almost all CF patients, irrespective of the causal mutation. Here, we use CRISPR/Cas9 and two adeno-associated viruses (AAV) carrying the two halves of the CFTR cDNA to sequentially insert the full CFTR cDNA along with a truncated CD19 (tCD19) enrichment tag in upper airway basal stem cells (UABCs) and human bronchial basal stem cells (HBECs). The modified cells were enriched to obtain 60-80% tCD19+ UABCs and HBECs from 11 different CF donors with a variety of mutations. Differentiated epithelial monolayers cultured at air-liquid interface showed restored CFTR function that was >70% of the CFTR function in non-CF controls. Thus, our study enables the development of a therapy for almost all CF patients, including patients who cannot be treated using recently approved modulator therapies.
View details for DOI 10.1016/j.ymthe.2021.03.023
View details for PubMedID 33794364
Progenitor identification and SARS-CoV-2 infection in human distal lung organoids.
The distal lung contains terminal bronchioles and alveoli that facilitate gas exchange. Three-dimensional in vitro human distal lung culture systems would strongly facilitate investigation of pathologies including interstitial lung disease, cancer, and SARS-CoV-2-associated COVID-19 pneumonia. We generated long-term feeder-free, chemically defined culture of distal lung progenitors as organoids derived from single adult human alveolar epithelial type II (AT2) or KRT5+ basal cells. AT2 organoids exhibited AT1 transdifferentiation potential while basal cell organoids developed lumens lined by differentiated club and ciliated cells. Single cell analysis of basal organoid KRT5+ cells revealed a distinct ITGA6+ITGB4+ mitotic population whose proliferation further segregated to a TNFRSF12Ahi subfraction comprising ~10% of KRT5+ basal cells, residing in clusters within terminal bronchioles and exhibiting enriched clonogenic organoid growth activity. Distal lung organoids were created with apical-out polarity to display ACE2 on the exposed external surface, facilitating SARS-CoV-2 infection of AT2 and basal cultures and identifying club cells as a novel target population. This long-term, feeder-free organoid culture of human distal lung, coupled with single cell analysis, identifies unsuspected basal cell functional heterogeneity and establishes a facile in vitro organoid model for human distal lung infections including COVID-19-associated pneumonia.
View details for DOI 10.1038/s41586-020-3014-1
View details for PubMedID 33238290
SARS-CoV-2 entry factors are highly expressed in nasal epithelial cells together with innate immune genes
We investigated SARS-CoV-2 potential tropism by surveying expression of viral entry-associated genes in single-cell RNA-sequencing data from multiple tissues from healthy human donors. We co-detected these transcripts in specific respiratory, corneal and intestinal epithelial cells, potentially explaining the high efficiency of SARS-CoV-2 transmission. These genes are co-expressed in nasal epithelial cells with genes involved in innate immunity, highlighting the cells' potential role in initial viral infection, spread and clearance. The study offers a useful resource for further lines of inquiry with valuable clinical samples from COVID-19 patients and we provide our data in a comprehensive, open and user-friendly fashion at www.covid19cellatlas.org.
View details for DOI 10.1038/s41591-020-0868-6
View details for Web of Science ID 000528517900001
View details for PubMedID 32327758
Advances in Proximity Ligation in situ Hybridization (PLISH).
2020; 10 (21): e3808
Understanding tissues in the context of development, maintenance and disease requires determining the molecular profiles of individual cells within their native in vivo spatial context. We developed a Proximity Ligation in situ Hybridization technology (PLISH) that enables quantitative measurement of single cell gene expression in intact tissues, which we have now updated. By recording spatial information for every profiled cell, PLISH enables retrospective mapping of distinct cell classes and inference of their in vivo interactions. PLISH has high sensitivity, specificity and signal to noise ratio. It is also rapid, scalable, and does not require expertise in molecular biology so it can be easily adopted by basic and clinical researchers.
View details for DOI 10.21769/BioProtoc.3808
View details for PubMedID 33659462
View details for PubMedCentralID PMC7842654
Niche Cells and Signals that Regulate Lung Alveolar Stem Cells In Vivo.
Cold Spring Harbor perspectives in biology
The distal lung is a honeycomb-like collection of delicate gas exchange sacs called alveoli lined by two interspersed epithelial cell types: the cuboidal, surfactant-producing alveolar type II (AT2) and the flat, gas-exchanging alveolar type I (AT1) cell. During aging, a subset of AT2 cells expressing the canonical Wnt target gene, Axin2, function as stem cells, renewing themselves while generating new AT1 and AT2 cells. Wnt activity endows AT2 cells with proliferative competency, enabling them to respond to activating cues, and simultaneously blocks AT2 to AT1 cell transdifferentiation. Acute alveolar injury rapidly expands the AT2 stem cell pool by transiently inducing Wnt signaling activity in "bulk" AT2 cells, facilitating rapid epithelial repair. AT2 cell "stemness" is thus tightly regulated by access to Wnts, supplied by a specialized single-cell fibroblast niche during maintenance and by AT2 cells themselves during injury repair. Two non-AT2 "reserve" cell populations residing in the distal airways also contribute to alveolar repair, but only after widespread epithelial injury, when they rapidly proliferate, migrate, and differentiate into airway and alveolar lineages. Here, we review alveolar renewal and repair with a focus on the niches, rather than the stem cells, highlighting what is known about the cellular and molecular mechanisms by which they control stem cell activity in vivo.
View details for DOI 10.1101/cshperspect.a035717
View details for PubMedID 32179507
Evaluation of integrin alphavbeta6 cystine knot PET tracers to detect cancer and idiopathic pulmonary fibrosis.
2019; 10 (1): 4673
Advances in precision molecular imaging promise to transform our ability to detect, diagnose and treat disease. Here, we describe the engineering and validation of a new cystine knot peptide (knottin) that selectively recognizes human integrin alphavbeta6 with single-digit nanomolar affinity. We solve its 3D structure by NMR and x-ray crystallography and validate leads with 3 different radiolabels in pre-clinical models of cancer. We evaluate the lead tracer's safety, biodistribution and pharmacokinetics in healthy human volunteers, and show its ability to detect multiple cancers (pancreatic, cervical and lung) in patients at two study locations. Additionally, we demonstrate that the knottin PET tracers can also detect fibrotic lung disease in idiopathic pulmonary fibrosis patients. Our results indicate that these cystine knot PET tracers may have potential utility in multiple disease states that are associated with upregulation of integrin alphavbeta6.
View details for DOI 10.1038/s41467-019-11863-w
View details for PubMedID 31611594
The human body at cellular resolution: the NIH Human Biomolecular Atlas Program
2019; 574 (7777): 187–92
Transformative technologies are enabling the construction of three-dimensional maps of tissues with unprecedented spatial and molecular resolution. Over the next seven years, the NIH Common Fund Human Biomolecular Atlas Program (HuBMAP) intends to develop a widely accessible framework for comprehensively mapping the human body at single-cell resolution by supporting technology development, data acquisition, and detailed spatial mapping. HuBMAP will integrate its efforts with other funding agencies, programs, consortia, and the biomedical research community at large towards the shared vision of a comprehensive, accessible three-dimensional molecular and cellular atlas of the human body, in health and under various disease conditions.
View details for DOI 10.1038/s41586-019-1629-x
View details for Web of Science ID 000489784200035
View details for PubMedID 31597973
View details for PubMedCentralID PMC6800388
An atlas of the aging lung mapped by single cell transcriptomics and deep tissue proteomics.
2019; 10 (1): 963
Aging promotes lung function decline and susceptibility to chronic lung diseases, which are the third leading cause of death worldwide. Here, we use single cell transcriptomics and mass spectrometry-based proteomics to quantify changes in cellular activity statesacross30 cell types and chart the lung proteome of young and old mice. We show that aging leads to increased transcriptional noise, indicating deregulated epigenetic control. We observe cell type-specific effects of aging, uncovering increased cholesterol biosynthesis in type-2 pneumocytes and lipofibroblasts and altered relative frequency of airway epithelial cells as hallmarks of lung aging. Proteomic profiling reveals extracellular matrix remodeling in old mice, including increased collagen IV and XVI and decreased Fraser syndrome complex proteins and collagen XIV. Computational integration of the aging proteome with the single cell transcriptomes predicts the cellular source of regulated proteins and creates an unbiased reference map of the aging lung.
View details for PubMedID 30814501
High-Efficiency, Selection-free Gene Repair in Airway Stem Cells from Cystic Fibrosis Patients Rescues CFTR Function in Differentiated Epithelia.
Cell stem cell
Cystic fibrosis (CF) is a monogenic disorder caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. Mortality in CF patients is mostly due to respiratory sequelae. Challenges with gene delivery have limited attempts to treat CF using in vivo gene therapy, and low correction levels have hindered ex vivo gene therapy efforts. We have used Cas9 and adeno-associated virus 6 to correct the ΔF508 mutation in readily accessible upper-airway basal stem cells (UABCs) obtained from CF patients. On average, we achieved 30%-50% allelic correction in UABCs and bronchial epithelial cells (HBECs) from 10 CF patients and observed 20%-50% CFTR function relative to non-CF controls in differentiated epithelia. Furthermore, we successfully embedded the corrected UABCs on an FDA-approved porcine small intestinal submucosal membrane (pSIS), and they retained differentiation capacity. This study supports further development of genetically corrected autologous airway stem cell transplant as a treatment for CF.
View details for DOI 10.1016/j.stem.2019.11.002
View details for PubMedID 31839569
Emergent high fatality lung disease in systemic juvenile arthritis.
Annals of the rheumatic diseases
To investigate the characteristics and risk factors of a novel parenchymal lung disease (LD), increasingly detected in systemic juvenile idiopathic arthritis (sJIA).In a multicentre retrospective study, 61 cases were investigated using physician-reported clinical information and centralised analyses of radiological, pathological and genetic data.LD was associated with distinctive features, including acute erythematous clubbing and a high frequency of anaphylactic reactions to the interleukin (IL)-6 inhibitor, tocilizumab. Serum ferritin elevation and/or significant lymphopaenia preceded LD detection. The most prevalent chest CT pattern was septal thickening, involving the periphery of multiple lobes ± ground-glass opacities. The predominant pathology (23 of 36) was pulmonary alveolar proteinosis and/or endogenous lipoid pneumonia (PAP/ELP), with atypical features including regional involvement and concomitant vascular changes. Apparent severe delayed drug hypersensitivity occurred in some cases. The 5-year survival was 42%. Whole exome sequencing (20 of 61) did not identify a novel monogenic defect or likely causal PAP-related or macrophage activation syndrome (MAS)-related mutations. Trisomy 21 and young sJIA onset increased LD risk. Exposure to IL-1 and IL-6 inhibitors (46 of 61) was associated with multiple LD features. By several indicators, severity of sJIA was comparable in drug-exposed subjects and published sJIA cohorts. MAS at sJIA onset was increased in the drug-exposed, but was not associated with LD features.A rare, life-threatening lung disease in sJIA is defined by a constellation of unusual clinical characteristics. The pathology, a PAP/ELP variant, suggests macrophage dysfunction. Inhibitor exposure may promote LD, independent of sJIA severity, in a small subset of treated patients. Treatment/prevention strategies are needed.
View details for DOI 10.1136/annrheumdis-2019-216040
View details for PubMedID 31562126
Single-cell Wnt signaling niches maintain stemness of alveolar type 2 cells.
Science (New York, N.Y.)
Alveoli, the lung's respiratory units, are tiny sacs where oxygen enters the bloodstream. They are lined by flat AT1 cells, which mediate gas exchange, and AT2 cells, which secret surfactant. Rare AT2s also function as alveolar stem cells. We show that AT2 lung stem cells display active Wnt signaling and many of them are near single, Wnt-expressing fibroblasts. Blocking Wnt secretion depletes these stem cells. Daughter cells leaving the Wnt niche transdifferentiate into AT1s: maintaining Wnt signaling prevents transdifferentiation whereas abrogating Wnt signaling promotes it. Injury induces AT2 autocrine Wnts, recruiting 'bulk' AT2s as progenitors. Thus, individual AT2 stem cells reside in single cell fibroblast niches providing juxtacrine Wnts that maintain them, whereas injury induces autocrine Wnts that transiently expand the progenitor pool. This simple niche maintains the gas exchange surface, and is coopted in cancer.
View details for PubMedID 29420258
Automated cell type classification in intact tissues by single-cell molecular profiling.
A major challenge in biology is identifying distinct cell classes and mapping their interactions in vivo. Tissue-dissociative technologies enable deep single cell molecular profiling but do not provide spatial information. We developed a proximity ligation- in situ hybridization technology (PLISH) with exceptional signal strength, specificity, and sensitivity in tissue. Multiplexed data sets can be acquired using barcoded probes and rapid label-image-erase cycles, with automated calculation of single cell profiles, enabling clustering and anatomical re-mapping of cells. We apply PLISH to expression profile ~2,900 cells in intact mouse lung, which identifies and localizes known cell types, including rare ones. Unsupervised classification of the cells indicates differential expression of 'housekeeping' genes between cell types, and re-mapping of two sub-classes of Club cells highlights their segregated spatial domains in terminal airways. By enabling single cell profiling of various RNA species in situ, PLISH can impact many areas of basic and medical research.
View details for PubMedID 29319504
Attenuated PDGF signaling drives alveolar and microvascular defects in neonatal chronic lung disease.
EMBO molecular medicine
Neonatal chronic lung disease (nCLD) affects a significant number of neonates receiving mechanical ventilation with oxygen-rich gas (MV-O2). Regardless, the primary molecular driver of the disease remains elusive. We discover significant enrichment for SNPs in the PDGF-Rα gene in preterms with nCLD and directly test the effect of PDGF-Rα haploinsufficiency on the development of nCLD using a preclinical mouse model of MV-O2 In the context of MV-O2, attenuated PDGF signaling independently contributes to defective septation and endothelial cell apoptosis stemming from a PDGF-Rα-dependent reduction in lung VEGF-A. TGF-β contributes to the PDGF-Rα-dependent decrease in myofibroblast function. Remarkably, endotracheal treatment with exogenous PDGF-A rescues both the lung defects in haploinsufficient mice undergoing MV-O2 Overall, our results establish attenuated PDGF signaling as an important driver of nCLD pathology with provision of PDGF-A as a protective strategy for newborns undergoing MV-O2.
View details for PubMedID 28923828
Early Identification of Bronchopulmonary Dysplasia Using Novel Biomarkers by Proteomic Screening.
American journal of respiratory and critical care medicine
View details for PubMedID 29053024
Trinucleotide repeat containing 6c (TNRC6c) is essential for microvascular maturation during distal airspace sacculation in the developing lung.
2017; 430 (1): 214–23
GW182 (also known asTNRC6) family members are critically involved in the final effector phase of miRNA-mediated mRNA repression. The three mammalian paralogs, TNRC6a, b and c, are thought to be redundant based on Argonaute (Ago) binding, tethering assays, and RNAi silencing of individual members in cell lines. To test this idea, we generated TNRC6a, b and c knockout mice. TNRC6a mutants die at mid-gestation, while b- and c- deleted mice are born at a Mendelian ratio. However, the majority of TNRC6b and all TNRC6c mutants die within 24h after birth, the latter with respiratory failure. Necropsy of TNRC6c mutants revealed normal-appearing airways that give rise to abnormally thick-walled distal gas exchange sacs. Immunohistological analysis of mutant lungs demonstrated a normal distribution of bronchiolar and alveolar cells, indicating that loss of TNRC6c did not abrogate epithelial cell differentiation. The cellular kinetics and relative proportions of endothelial, epithelial, and mesenchymal cells were also not altered. However, the underlying capillary network was simplified and endothelial cells had failed to become tightly apposed to the surface epithelium in TNRC6c mutants, presumably causing the observed respiratory failure. TGFβ family mutant mice exhibit a similar lung phenotype of thick-walled air sacs and neonatal lethality, and qRT-PCR confirmed dynamic downregulation of TGFβ1 and TGFβR2 in TNRC6c mutant lungs during sacculation. VEGFR, but not VEGF-A ligand, was also lower, likely reflecting the overall reduced capillary density in TNRC6c mutants. Together, these results demonstrate that GW182 paralogs are not functionally redundant in vivo. Surprisingly, despite regulating a general cellular process, TNRC6c is selectively required only in the distal lung and not until late in gestation for proper expression of the TGFβ family genes that drive sacculation. These results imply a complex and indirect mode of regulation of sacculation by TNRC6c, mediated in part by dynamic transcriptional repression of an inhibitor of TGFβ family gene expression.
View details for PubMedID 28811219
Hedgehog-driven myogenic tumors recapitulate skeletal muscle cellular heterogeneity.
Experimental cell research
2016; 340 (1): 43–52
Hedgehog (Hh) pathway activation in R26-SmoM2;CAGGS-CreER mice, which carry a tamoxifen-inducible activated Smoothened allele (SmoM2), results in numerous microscopic tumor foci in mouse skeletal muscle. These tumors exhibit a highly differentiated myogenic phenotype and resemble human fetal rhabdomyomas. This study sought to apply previously established strategies to isolate lineally distinct populations of normal mouse myofiber-associated cells in order to examine cellular heterogeneity in SmoM2 tumors. We demonstrate that established SmoM2 tumors are composed of cells expressing myogenic, adipocytic and hematopoietic lineage markers and differentiation capacity. SmoM2 tumors thus recapitulate the phenotypic and functional hetereogeneity observed in normal mouse skeletal muscle. SmoM2 tumors also contain an expanded population of PAX7+ and MyoD+ satellite-like cells with extremely low clonogenic activity. Selective activation of Hh signaling in freshly isolated muscle satellite cells enhanced terminal myogenic differentiation without stimulating proliferation. Our findings support the conclusion that SmoM2 tumors represent an aberrant skeletal muscle state and demonstrate that, similar to normal muscle, myogenic tumors contain functionally distinct cell subsets, including cells lacking myogenic differentiation potential.
View details for PubMedID 26460176
Keeping it together: Pulmonary alveoli are maintained by a hierarchy of cellular programs.
2015; 37 (9): 1028-1037
The application of in vivo genetic lineage tracing has advanced our understanding of cellular mechanisms for tissue renewal in organs with slow turnover, like the lung. These studies have identified an adult stem cell with very different properties than classically understood ones that maintain continuously cycling tissues such as the intestine. A portrait has emerged of an ensemble of cellular programs that replenish the cells that line the gas exchange (alveolar) surface, enabling a response tailored to the extent of cell loss. A capacity for differentiated cells to undergo direct lineage transitions allows for local restoration of proper cell balance at sites of injury. We present these recent findings as a paradigm for how a relatively quiescent tissue compartment can maintain homeostasis throughout a lifetime punctuated by injuries ranging from mild to life-threatening, and discuss how dysfunction or insufficiency of alveolar repair programs produce serious health consequences like cancer and fibrosis.
View details for DOI 10.1002/bies.201500031
View details for PubMedID 26201286
Cellular mechanisms of alveolar pathology in childhood interstitial lung diseases: current insights from mouse genetics
CURRENT OPINION IN PEDIATRICS
2015; 27 (3): 341-347
Childhood interstitial lung diseases (ILDs) are a diverse class of disorders affecting the alveolar gas exchange region that lack specific treatments and are usually fatal. Here, we integrate recent insights into alveolar cell biology with histopathology from well characterized mutations of surfactant-associated genes. We take a reductionist approach by parsing discrete histological features and correlating each to perturbation of a particular function of the alveolar epithelial type II (AT2) cell, the central driver of disease, to generate a working model for the cellular mechanisms of disease pathogenesis.The application of genetically modified mice and single cell genomics has yielded new insights into lung biology, including the identification of a bipotent alveolar progenitor in development, mapping of adult AT2 stem cells in vivo, and demonstration that latent cooperative interactions with fibroblasts can be pathologically activated by targeted injury of the AT2 cell.As we learn more about individual and cooperative roles for alveolar cells in health, we can dissect how perturbations of specific cellular functions contribute to disease in childhood ILDs. We hope our updated model centered around the AT2 cell as the initiator of disease provides a cellular framework that researchers can build upon and revise as they identify the specific molecular signals within and between alveolar cells that mediate the diverse pathologic features, so that targeted pharmacologic and cell-based treatments for patients can ultimately be engineered.
View details for DOI 10.1097/MOP.0000000000000227
View details for Web of Science ID 000354214800013
View details for PubMedID 25888154
View details for PubMedCentralID PMC4466102
Reconstructing lineage hierarchies of the distal lung epithelium using single-cell RNA-seq.
2014; 509 (7500): 371-375
The mammalian lung is a highly branched network in which the distal regions of the bronchial tree transform during development into a densely packed honeycomb of alveolar air sacs that mediate gas exchange. Although this transformation has been studied by marker expression analysis and fate-mapping, the mechanisms that control the progression of lung progenitors along distinct lineages into mature alveolar cell types are still incompletely known, in part because of the limited number of lineage markers and the effects of ensemble averaging in conventional transcriptome analysis experiments on cell populations. Here we show that single-cell transcriptome analysis circumvents these problems and enables direct measurement of the various cell types and hierarchies in the developing lung. We used microfluidic single-cell RNA sequencing (RNA-seq) on 198 individual cells at four different stages encompassing alveolar differentiation to measure the transcriptional states which define the developmental and cellular hierarchy of the distal mouse lung epithelium. We empirically classified cells into distinct groups by using an unbiased genome-wide approach that did not require a priori knowledge of the underlying cell types or the previous purification of cell populations. The results confirmed the basic outlines of the classical model of epithelial cell-type diversity in the distal lung and led to the discovery of many previously unknown cell-type markers, including transcriptional regulators that discriminate between the different populations. We reconstructed the molecular steps during maturation of bipotential progenitors along both alveolar lineages and elucidated the full life cycle of the alveolar type 2 cell lineage. This single-cell genomics approach is applicable to any developing or mature tissue to robustly delineate molecularly distinct cell types, define progenitors and lineage hierarchies, and identify lineage-specific regulatory factors.
View details for DOI 10.1038/nature13173
View details for PubMedID 24739965
- Alveolar progenitor and stem cells in lung development, renewal and cancer. Nature 2014; 507 (7491): 190-194
- Stem cells: Differentiated cells in a back-up role. Nature 2013; 503 (7475): 204-205
Smooth muscle protein 22 alpha-mediated patchy deletion of Bmpr1a impairs cardiac contractility but protects against pulmonary vascular remodeling
2008; 102 (3): 380-388
Vascular expression of bone morphogenetic type IA receptor (Bmpr1a) is reduced in lungs of patients with pulmonary arterial hypertension, but the significance of this observation is poorly understood. To elucidate the role of Bmpr1a in the vascular pathology of pulmonary arterial hypertension and associated right ventricular (RV) dysfunction, we deleted Bmpr1a in vascular smooth muscle cells and in cardiac myocytes in mice using the SM22alpha;TRE-Cre/LoxP;R26R system. The LacZ distribution reflected patchy deletion of Bmpr1a in the lung vessels, aorta, and heart of SM22alpha;TRE-Cre;R26R;Bmpr1a(flox/+) and flox/flox mutants. This reduction in BMPR-IA expression was confirmed by Western immunoblot and immunohistochemistry in the flox/flox group. This did not affect pulmonary vasoreactivity to acute hypoxia (10% O2) or the increase in RV systolic pressure and RV hypertrophy following 3 weeks in chronic hypoxia. However, both SM22alpha;TRE-Cre;R26R;Bmpr1a(flox/+) and flox/flox mutant mice had fewer muscularized distal pulmonary arteries and attenuated loss of peripheral pulmonary arteries compared with age-matched control littermates in hypoxia. When Bmpr1a expression was reduced by short interference RNA in cultured pulmonary arterial smooth muscle cells, serum-induced proliferation was attenuated explaining decreased hypoxia-mediated muscularization of distal vessels. When Bmpr1a was reduced in cultured microvascular pericytes by short interference RNA, resistance to apoptosis was observed and this could account for protection against hypoxia-mediated vessel loss. The similar elevation in RV systolic pressure and RV hypertrophy, despite the attenuated remodeling with chronic hypoxia in the flox/flox mutants versus controls, was not a function of elevated left ventricular end diastolic pressure but was associated with increased periadventitial deposition of elastin and collagen, potentially influencing vascular stiffness.
View details for DOI 10.1161/CIRCRESAHA.107.161059
View details for Web of Science ID 000253194600018
View details for PubMedID 18079409
View details for PubMedCentralID PMC2652676
- In vitro and in vivo gene therapy vector evolution via multispecies interbreeding and retargeting of adeno-associated viruses J Virol 2008; 82 (12): 5887-5911
Inhibition of Tgf beta signaling by endogenous retinoic acid is essential for primary lung bud induction
2007; 134 (16): 2969-2979
Disruption of retinoic acid (RA) signaling during early development results in severe respiratory tract abnormalities, including lung agenesis. Previous studies suggest that this might result from failure to selectively induce fibroblast growth factor 10 (Fgf10) in the prospective lung region of the foregut. Little is known about the RA-dependent pathways present in the foregut that may be crucial for lung formation. By performing global gene expression analysis of RA-deficient foreguts from a genetic [retinaldehyde dehydrogenase 2 (Raldh2)-null] and a pharmacological (BMS493-treated) mouse model, we found upregulation of a large number of Tgfbeta targets. Increased Smad2 phosphorylation further suggested that Tgfbeta signaling was hyperactive in these foreguts when lung agenesis was observed. RA rescue of the lung phenotype was associated with low levels of Smad2 phosphorylation and downregulation of Tgfbeta targets in Raldh2-null foreguts. Interestingly, the lung defect that resulted from RA-deficiency could be reproduced in RA-sufficient foreguts by hyperactivating Tgfbeta signaling with exogenous TGF beta 1. Preventing activation of endogenous Tgfbeta signaling with a pan-specific TGFbeta-blocking antibody allowed bud formation and gene expression in the lung field of both Raldh2-null and BMS493-treated foreguts. Our data support a novel mechanism of RA-Tgfbeta-Fgf10 interactions in the developing foregut, in which endogenous RA controls Tgfbeta activity in the prospective lung field to allow local expression of Fgf10 and induction of lung buds.
View details for DOI 10.1242/dev.006221
View details for Web of Science ID 000248385000009
View details for PubMedID 17634193
Distinct roles for retinoic acid receptors alpha and beta in early lung morphogenesis
2006; 291 (1): 12-24
Retinoic acid (RA) signaling is required for normal development of multiple organs. However, little is known about how RA influences the initial stages of lung development. Here, we used a combination of genetic, pharmacological and explant culture approaches to address this issue, and to investigate how signaling by different RA receptors (RAR) mediates the RA effects. We analyzed initiation of lung development in retinaldehyde dehydrogenase-2 (Raldh2) null mice, a model in which RA signaling is absent from the foregut from its earliest developmental stages. We provide evidence that RA is dispensable for specification of lung cell fate in the endoderm. By using synthetic retinoids to selectively activate RAR alpha or beta signaling in this model, we demonstrate novel and unique functions of these receptors in the early lung. We show that activation of RAR beta, but not alpha, induces expression of the fibroblast growth factor Fgf10 and bud morphogenesis in the lung field. Similar analysis of wild type foregut shows that endogenous RAR alpha activity is required to maintain overall RA signaling, and to refine the RAR beta effects in the lung field. Our data support the idea that balanced activation of RAR alpha and beta is critical for proper lung bud initiation and endodermal differentiation.
View details for DOI 10.1016/j.ydbio.2005.10.045
View details for Web of Science ID 000236128300002
View details for PubMedID 16427040
Retinoic acid selectively regulates Fgf10 expression and maintains cell identity in the prospective lung field of the developing foregut
2004; 273 (2): 402-415
Although respiratory tract defects that result from disruption of retinoic acid (RA) signaling have been widely reported, the mechanism by which endogenous RA regulates early lung morphogenesis is unknown. Here, we provide novel evidence that a major role for RA is to selectively maintain mesodermal proliferation and induce fibroblast growth factor 10 (Fgf10) expression in the foregut region where the lung forms. By using a pan-RAR antagonist (BMS493) in foregut explant cultures, we show that bud initiation is selectively blocked in the prospective respiratory region by failure to induce Fgf10 in the corresponding mesoderm. The RA regulation of Fgf10 expression occurs only in this region, within a defined developmental window, and is not seen in other foregut derivatives such as thyroid and pancreas where Fgf10 is also required for normal development. Furthermore, we show that RA activity is essential in the lung field to maintain lung cell identity in the endoderm; RAR antagonism disrupts expression of thyroid transcription factor 1 (Ttf1), an early marker of the respiratory region in the endoderm, and surfactant protein C (Sp-C) mRNAs. Our observations in mouse foregut cultures are corroborated by data from an in vivo model of vitamin A deficiency in rats. Our study supports RA as an essential regulator of gene expression and cellular activities during primary bud formation.
View details for DOI 10.1016/j.ydbio.2004.04.039
View details for Web of Science ID 000223681000018
View details for PubMedID 15328022
- COPD: Clinical Manifestations, Diagnosis, and Treatment Baum's Textbook of Pulmonary Diseases (Eds: James D. Crapo, Jeffrey Glassroth, Joel Karlinsky, and Talmadge E. King Jr.) 2004; 7th ed
Growth factors in lung development and disease: friends or foe?
2002; 3: 2-?
Growth factors mediate tissue interactions and regulate a variety of cellular functions that are critical for normal lung development and homeostasis. Besides their involvement in lung pattern formation, growth and cell differentiation during organogenesis, these factors have been also implicated in modulating injury-repair responses of the adult lung. Altered expression of growth factors, such as transforming growth factor beta1, vascular endothelial growth factor and epidermal growth factor, and/or their receptors, has been found in a number of pathological lung conditions. In this paper, we discuss the dual role of these molecules in mediating beneficial feedback responses or responses that can further damage lung integrity; we shall also discuss the basis for their prospective use as therapeutic agents.
View details for PubMedID 11806837
View details for PubMedCentralID PMC64813
Participation of urokinase-type plasminogen activator receptor in the clearance of fibrin from the lung
AMERICAN JOURNAL OF PHYSIOLOGY-LUNG CELLULAR AND MOLECULAR PHYSIOLOGY
1999; 277 (3): L573-L579
In vitro studies have demonstrated that the binding of urokinase-type plasminogen activator (uPA) to its cell surface receptor (uPAR) greatly accelerates plasminogen activation. However, the role of uPAR in clearing abnormal fibrin deposits from the lung is uncertain. Knowing that uPA binding to uPAR is species specific, we used adenoviral vectors to transfer human or murine uPA genes into human or mouse epithelial cells in vitro and to mouse lungs in vivo. By measuring degradation of fluorescein-labeled fibrin, we found that uPA lysed fibrin matrices more efficiently when expressed in cells of the same species. A monoclonal antibody that blocks the binding of human uPA to human uPAR suppressed fibrin degradation by human cells expressing human uPA but not murine uPA. Importantly, 3 days after intratracheal delivery of the vectors, mice receiving murine uPA transgenes degraded fibrin matrices formed within their air spaces more efficiently than animals transduced with human uPA genes. These results show that uPA bound to uPAR increases the efficiency of fibrinolysis on epithelial cell surfaces in a biologically relevant fashion.
View details for Web of Science ID 000082425100017
View details for PubMedID 10484465