Human Lung Regeneration Research Articles

An interview with Purushothama Rao Tata.

Purushothama Rao Tata is an Assistant Professor in the Department of Cell Biology at Duke University Medical Center. His lab is focussed on understanding the cellular basis of cell plasticity and self-organization in regeneration and tumorigenesis, using the lung as a model system. In 2022, Tata was awarded a Rising Star award from the International Society for Regenerative Biology. We caught up with Tata over Zoom to learn how an early plant tissue culture experiment led to a career working on human lung regeneration, the role serendipity has played in his research and the importance of switching off.

KRT5+/p63+ Stem Cells Undergo Senescence in the Human Lung with Pathological Aging.

Adult lungs present high cellular plasticity against stress and injury, mobilizing stem/progenitor populations from conducting airways to maintain tissue homeostasis and gas exchange in alveolar spaces. With aging, pulmonary functional and structural deterioration occurs, mainly in pathological conditions, which is associated with impaired stem cell activity and increased senescence in mice. However, the impact of these processes underlying lung physiopathology in relation to aging has not been explored in humans. In this work, we analyzed stem cell (SOX2, p63, KRT5), senescence (p16INK4A, p21CIP, Lamin B1) and proliferative (Ki67) markers in lung samples from young and aged individuals, with and without pulmonary pathology. We identified a reduction in SOX2+ cells but not p63+ and KRT5+ basal cells in small airways with aging. In alveoli, we revealed the presence of triple SOX2+, p63+ and KRT5+ cells specifically in aged individuals diagnosed with pulmonary pathologies. Notably, p63+ and KRT5+ basal stem cells displayed colocalization with p16INK4A and p21CIP, as well as with low Lamin B1 staining in alveoli. Further studies revealed that senescence and proliferation markers were mutually exclusive in stem cells with a higher percentage colocalizing with senescence markers. These results provide new evidence of the activity of p63+/KRT5+ stem cells on human lung regeneration and point out that regeneration machinery in human lung is activated under stress due to aging, but fails to repair in pathological cases, as stem cells would likely become senescent.

Promises and Challenges of Cell-Based Therapies to Promote Lung Regeneration in Idiopathic Pulmonary Fibrosis.

The lung epithelium is constantly exposed to harmful agents present in the air that we breathe making it highly susceptible to damage. However, in instances of injury to the lung, it exhibits a remarkable capacity to regenerate injured tissue thanks to the presence of distinct stem and progenitor cell populations along the airway and alveolar epithelium. Mechanisms of repair are affected in chronic lung diseases such as idiopathic pulmonary fibrosis (IPF), a progressive life-threatening disorder characterized by the loss of alveolar structures, wherein excessive deposition of extracellular matrix components cause the distortion of tissue architecture that limits lung function and impairs tissue repair. Here, we review the most recent findings of a study of epithelial cells with progenitor behavior that contribute to tissue repair as well as the mechanisms involved in mouse and human lung regeneration. In addition, we describe therapeutic strategies to promote or induce lung regeneration and the cell-based strategies tested in clinical trials for the treatment of IPF. Finally, we discuss the challenges, concerns and limitations of applying these therapies of cell transplantation in IPF patients. Further research is still required to develop successful strategies focused on cell-based therapies to promote lung regeneration to restore lung architecture and function.

Regeneration of the lung alveolus by an evolutionarily conserved epithelial progenitor.

Functional tissue regeneration is required for restoration of normal organ homeostasis after severe injury. While some organs, such as the intestine, harbor active stem cells throughout homeostasis and regeneration1, more quiescent organs like the lung often contain facultative progenitor cells which are recruited after injury to participate in regeneration2,3. Here we show that a Wnt-responsive alveolar epithelial progenitor (AEP) lineage within the alveolar type 2 (AT2) cell population acts as a major facultative progenitor cell in the distal lung. AEPs are a stable lineage during alveolar homeostasis but expand rapidly to regenerate a large proportion of the alveolar epithelium after acute lung injury. AEPs exhibit a distinct transcriptome, epigenome, and functional phenotype with specific responsiveness to Wnt and Fgf signaling. In distinction to other proposed lung progenitor cells, human AEPs (hAEPs) can be directly isolated via expression of the conserved cell surface marker TM4SF1, and hAEPs act as functional human alveolar epithelial progenitor cells in 3D organoids. Together, our results identify the AEP lineage as an evolutionarily conserved alveolar progenitor and a new target for human lung regeneration strategies.

Bioengineered lungs generated from human iPSCs-derived epithelial cells on native extracellular matrix.

The development of an alternative source for donor lungs would change the paradigm of lung transplantation. Recent studies have demonstrated the potential feasibility of using decellularized lungs as scaffolds for lung tissue regeneration and subsequent implantation. However, finding a reliable cell source and the ability to scale up for recellularization of the lung scaffold still remain significant challenges. To explore the possibility of regeneration of human lung tissue from stem cells in vitro, populations of lung progenitor cells were generated from human iPSCs. To explore the feasibility of producing engineered lungs from stem cells, we repopulated decellularized human lung and rat lungs with iPSC-derived epithelial progenitor cells. The iPSCs-derived epithelial progenitor cells lined the decellularized human lung and expressed most of the epithelial markers when were cultured in a lung bioreactor system. In decellularized rat lungs, these human-derived cells attach and proliferate in a manner similar to what was observed in the decellularized human lung. Our results suggest that repopulation of lung matrix with iPSC-derived lung epithelial cells may be a viable strategy for human lung regeneration and represents an important early step toward translation of this technology.

Development of a genetically modifiable epithelial in-vitro culture system from human embryonic lung epithelial stem cells: towards human lung regeneration in end-stage respiratory failure

BackgroundRegeneration of healthy lung tissue in patients with end-stage respiratory disease would cure disease. Therefore, a detailed understanding of lung development is needed. The most important epithelial stem-cell population in developing lungs is found in distal branching tips, and these Sox9+ lung epithelial stem cells (LESCs) generate all epithelial lineages. Our objective was to develop a self-renewing, genetically modifiable epithelial in-vitro culture system from human embryonic LESCs. MethodsHuman embryonic LESCs were characterised using genome-wide transcriptional analysis (RNA-seq, Illumina, San Diego, CA, USA) and immunohistochemistry at 5–20 weeks postconception. LESCs were microdissected, and self-renewing expansion in three-dimensional (3D) organoid culture was established empirically. We assessed similarity between cultured and fresh LESCs via RNA-seq and immunohistochemistry. Organoids were differentiated in vitro, or in vivo by xenotransplantation into bleomycin-injured mouse lungs or kidney capsule. SOX9 was deleted with CRISPR–Cas9. FindingsRNA-seq of LESCs identified broad-scale transcriptional differences between mouse and human embryonic lung stem cells. Human LESCs were successfully expanded for more than 10 months as karyotypically stable 3D organoids using a combination of seven signalling molecules. The LESC stem-cell markers, transcriptome, and organoid morphology were maintained throughout the culture period. Bronchiolar and alveolar differentiation was achieved in vitro and in vivo. Moreover, xenotransplantation of organoids into bleomycin-injured adult mouse lungs was extremely efficient. Knocking out SOX9 led to a loss-of-self-renewing phenotype. InterpretationOur novel genetically modifiable human embryonic lung culture system enables for the first time, to our knowledge, the in-vitro study of human lung development and disease. We anticipate that this system will transform lung regenerative medicine by guiding development of improved protocols for induced pluripotent stem-cell differentiation and adult stem-cell manipulation in vivo, benefiting patients with end-stage respiratory disease. Furthermore, our lung injury–xenotransplantation protocol provides the first method for efficient future cell therapy. FundingWellcome Trust (PhD programme for clinicians), Medical Research Council, Addenbrooke's Charitable Trust.

Deficient retinoid-driven angiogenesis may contribute to failure of adult human lung regeneration in emphysema

BackgroundMolecular pathways that regulate alveolar development and adult repair represent potential therapeutic targets for emphysema. Signalling via retinoic acid (RA), derived from vitamin A, is required for mammalian alveologenesis, and...

P118 The role of the retinoic acid pathway in human lung regeneration

Recent studies into retinoic acid (RA)-induced alveolar regeneration in rodent models of emphysema and bronchopulmonary dyplasia strongly suggest a latent regenerative potential of the adult mammalian lung. RA signalling is...