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.

Reconstituting Mouse Lungs with Conditionally Reprogrammed Human Bronchial Epithelial Cells

We developed methods for conditionally reprogramming (CR) primary human bronchial epithelial cells (HBECs) to extend their functional lifespan and permit their differentiation into both upper and lower airway lung epithelium. We also developed a bioreactor to support vascular perfusion and rhythmic breathing of decellularized mouse lungs reconstituted with CR HBECs isolated from patients with and without cystic fibrosis (CF). While conditionally reprogrammed cells only differentiate into an upper airway epithelium after 35 days at the air-liquid interface, in reconstituted lungs these cells differentiate into upper airway bronchial epithelium and lower airway alveolar structures after 12 days. Rapid scale-up and the ability to obtain clonal derivatives of primary patient-derived HBECs without the need for genetic manipulation may permit rapid reconstitution of the lung epithelium; facilitating the study of lung disease in tissue-engineered models.

Development and characterization of a naturally derived lung extracellular matrix hydrogel

The complexity and rapid clearance mechanisms of lung tissue make it difficult to develop effective treatments for many chronic pathologies. We are investigating lung derived extracellular matrix (ECM) hydrogels as a novel approach for delivery of cellular therapies to the pulmonary system. The main objectives of this study include effective decellularization of porcine lung tissue, development of a hydrogel from the porcine ECM, and characterization of the material's composition, mechanical properties, and ability to support cellular growth. Our evaluation of the decellularized tissue indicated successful removal of cellular material and immunogenic remnants in the ECM. The self-assembly of the lung ECM hydrogel was rapid, reaching maximum modulus values within 3 min at 37°C. Rheological characterization showed the lung ECM hydrogel to have a concentration dependent storage modulus between 15 and 60 Pa. The purpose of this study was to evaluate our novel ECM derived hydrogel and measure its ability to support 3D culture of MSCs in vitro and in vivo delivery of MSCs. Our in vitro experiments using human mesenchymal stem cells demonstrated our novel ECM hydrogel's ability to enhance cellular attachment and viability. Our in vivo experiments demonstrated that rat MSC delivery in pre-gel solution significantly increased cell retention in the lung over 24 h in an emphysema rat model. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1922-1935, 2016.

Strategies for whole lung tissue engineering

Recent work has demonstrated the feasibility of using decellularized lung extracellular matrix scaffolds to support the engineering of functional lung tissue in vitro. Rendered acellular through the use of detergents and other reagents, the scaffolds are mounted in organ-specific bioreactors where cells in the scaffold are provided with nutrients and appropriate mechanical stimuli such as ventilation and perfusion. Though initial studies are encouraging, a great deal remains to be done to advance the field and transition from rodent lungs to whole human tissue engineered lungs. To do so, a variety of hurdles must be overcome. In particular, a reliable source of human-sized scaffolds, as well as a method of terminal sterilization of scaffolds, must be identified. Continued research in lung cell and developmental biology will hopefully help identify the number and types of cells that will be required to regenerate functional lung tissue. Finally, bioreactor designs must be improved in order to provide more precise ventilation stimuli and vascular perfusion in order to avoid injury to or death of the cells cultivated within the scaffold. Ultimately, the success of efforts to engineer a functional lung in vitro will critically depend on the ability to create a fully endothelialized vascular network that provides sufficient barrier function and alveolar-capillary surface area to exchange gas at rates compatible with healthy lung function.

Fibroblast engraftment in the decellularized mouse lung occurs via a β1-integrin-dependent, FAK-dependent pathway that is mediated by ERK and opposed by AKT

Creation of bioartificial organs has been enhanced by the development of strategies involving decellularized mammalian lung. Because fibroblasts critically support lung function through a number of mechanisms, study of these cells in the context of the decellularized lung has the potential to improve the structure and function of tissue-engineered lungs. We characterized the engraftment and survival of a mouse fibroblast cell line in decellularized rat lung slices and found a time-dependent increase in cell numbers assessed by hematoxylin and eosin staining, cell proliferation assessed by Ki67 staining, and minimal cell death assessed by TUNEL staining. We developed a repopulation index to allow quantification of cell survival that accounts for variation in cell density throughout the seeded scaffold. We then applied this method to the study of mouse lung scaffolds and found that decellularization of presliced mouse lungs produced matrices with preserved alveolar architecture and proteinaceous components including fibronectin, collagens I and IV, laminin, and elastin. Treatment with a β1-integrin-neutralizing antibody significantly reduced the repopulation index after 24 h of culture. Treatment with focal adhesion kinase (FAK) inhibitor and extracellular signal-regulated kinase (ERK) inhibitor further reduced initial repopulation scores while treatment with AKT inhibitor increased initial scores. Rho-associated kinase inhibitor had no discernible effect. These data indicate that initial adhesion and survival of mouse fibroblasts in the decellularized mouse lung occur in a β1-integrin-dependent, FAK/ERK-dependent manner that is opposed by AKT.