By sequencing genetic material at a cell-by-cell level, researchers have described how type 2-high asthma affects the airways and results in mucus production with more detail than ever before. These findings, which help move forward scientific understanding of the biology behind asthma and could inform the development of targeted treatments for asthma and other airway diseases, were presented at the American Society of Human Genetics (ASHG) 2018 Annual Meeting in San Diego, California.
Type 2-high asthma, a subtype of asthma caused by elevated levels of proteins known as type 2 cytokines, affects about half of asthma patients and often results in more severe disease than other subtypes. Type 2 cytokines affect the function of airway epithelial cells – cells at the surface of the airways – causing them to produce a viscous mucus that leads to symptoms of asthma.
In a two-part study, led by Nathan Jackson, PhD in the laboratory of Max A. Seibold at National Jewish Health and with collaborating institutions, they first studied these epithelial cells in a laboratory culture model designed to mimic the surface of human airways, and then confirmed their findings in asthma patients.
They used a relatively new approach called single-cell transcriptomics, in which they sequenced the RNA in each cell individually after stimulating airway epithelium cultures with the type 2 cytokine IL-13 and allowing the IL-13 to affect which genes were transcribed into RNA and to what extent.
“In the past, this type of research was based on bulk sequencing from thousands of cells, which provided some gene expression data but did not represent any cell in the epithelium,” explained Dr. Jackson, who presented the work. “To understand the biology behind type 2-high asthma, we need to understand the mechanisms that operate in individual cells and learn how different types of cells function. Then, once we understand the biology, we can intervene.”
The researchers learned which genes and proteins drove the production of mucus, identified the cell types affected, and compared these patterns in time frames mimicking acute (48 hours) and chronic (11 days) disease. They combined these results to define 11 distinct airway epithelial cell states and to describe the patterns of protein function that triggered cells to transition from one state to another, causing symptoms of asthma. To measure the real-world applicability of their findings, they followed up by examining transcriptome changes in nasal swabs from 698 children with type 2-high asthma.
“The results lined up between the laboratory and patients – stunningly so,” said Dr. Seibold. “In patients, we were able to obtain a snapshot of the changes that occur in the disease, and the cell culture allowed us to understand the details.”
By describing how airway cells change in the disease state, researchers can develop drugs to inhibit that process and reverse mucus obstruction, potentially returning the airway to an unobstructed state, Dr. Seibold added. Beyond asthma, this approach may have relevance to other airway diseases such as cystic fibrosis and the common cold.
Building on their findings, the researchers are continuing to analyze patient samples, as well as launching more detailed studies of the genes identified and their contributions to protein activity. They are also exploring the use of CRISPR/Cas9-based gene editing to knock out or modify the genes involved in mucus production.