Using stem cells derived from skin cells of patients with cystic fibrosis, the researchers demonstrated that the mini-lungs can be used to test potential new drugs for this debilitating lung disease.
This research is one of a number of studies that have used stem cells to grow organoids, 3D clusters of cells that mimic the behaviour and function of specific organs within the body. Other recent examples have been ‘mini-brains’ to study Alzheimer’s disease and ‘mini-livers’ to model liver disease. This technique is used to model disease and to screen for potential drugs as well as being an alternative to the use of animals in research. The findings were recently published in Stem Cells and Development.
Cystic fibrosis is a monogenic condition, though in some cases the causative mutation may differ between patients. One of the main characteristics of the disease is overwhelmed lungs due to thickened mucus causing difficulty in breathing and increasing the incidence of respiratory infection. Although patients have a shorter than average lifespan, advances in treatment mean the outlook has significantly in recent years.
The researchers used skin cells from patients with the most common form of cystic fibrosis which is caused by the delta-F508 mutation, a mutation in the CFTR gene which has a three in four occurrence is cystic fibrosis patients in UK. Specifically, the delta-F508 mutation causes the CFTR protein found in distal airway tissue to misfold and malfunction, as it is not appropriately expressed on the surface of the cell, where its purpose is to facilitate the movement of chloride transport through the cell membrane. This reduces the movement of water to the inside of the lung; as a consequence, the mucus becomes particular thick and prone to bacterial infection, which over time leads to scarring or fibrosis.
The team reprogrammed the skin cells to an induced pluripotent state. Using the induced pluripotent stem cells, they were able to recreate embryonic lung development in vitro by activating gastrulation, the process in which the lungs are formed, and followed by inducing these cells further to develop into distal airway tissue. The distal airway is the part of the lung responsible for gas exchange and is often implicated in disease, such as cystic fibrosis, some forms of lung cancer and emphysema.
“In a sense, what we’ve created are ‘mini-lungs’,” explains Nick Hannan from the University of Cambridge, who led the study. “While they only represent the distal part of lung tissue, they are grown from human cells and so can be more reliable than using traditional animal models, such as mice. We can use them to learn more about key aspects of serious diseases — in our case, cystic fibrosis.”
Using a fluorescent dye that is sensitive to the presence of chloride, the researchers were able to see whether the ‘mini-lungs’ were functional. Whilst the passage of chloride caused changes in fluorescence; these changes were not visible in malfunctioning cells from cystic fibrosis patients due to defective chloride transport across the cell membrane.
Furthermore, by reproducing the effects of a small molecule compound which is currently in phase II clinical trials and is known to restore CFTR function, this technique allowed the researchers to demonstrate that the ‘mini-lungs’ could be used in principle as a model to validate novel therapeutic compounds.
“We’re confident this process could be scaled up to enable us to screen tens of thousands of compounds and develop mini-lungs with other diseases such as lung cancer and idiopathic pulmonary fibrosis,” explained Nick Hannan. “This is far more practical, should provide more reliable data and is also more ethical than using large numbers of mice for such research.”
Hannan NRF, Sampaziotis F, Segeritz C, Hanley N, Vallier L. Generation of Distal Airway Epithelium from Multipotent Human Foregut Stem Cells. Stem Cells and Development, doi:10.1089/scd.2014.0512 [Epub ahead of print] (2015)
University of Cambridge press release: http://www.cam.ac.uk/research/news/scientists-grow-mini-lungs-to-aid-the-study-of-cystic-fibrosis