Using Gene Editing, Drug Discovery for Abnormal Lung Stem Cells

Two nationally recognized experts in cloning and stem cell science from the University of Houston are taking the first step toward limiting the consequences of chronic inflammation in cystic fibrosis (CF) by identifying the source of this persistent and enigmatic inflammation in CF lungs.

Frank McKeon and Wa Xian in the Department of Biology and Biochemistry and the Stem Cell Center at UH have received a $2.7 million grant from the National Heart, Lung, and Blood Institute to examine pro-inflammatory stem cell variants in cystic fibrosis.

Cystic fibrosis is an inherited and progressive disease that causes long-lasting lung infections and limits the ability to breathe. It is caused by a defect in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) and affects more than 30,000 people in the United States. That defect instructs the body to produce abnormally sticky and thick mucus that clogs organs, particularly lungs, causing chronic lung disease marked by infections and inflammation.

While inflammation in the CF lung was always assumed to be a normal response to bacterial infections, recent studies have cast doubt on that link and rendered the source of this inflammation a mystery.

“That raised the possibility that inflammation, and perhaps other pathogenic features of CF, are maintained by elements that emerge in the disease that are entirely independent of CFTR activity,” said McKeon.

Interestingly, the same situation may be operating in chronic obstructive pulmonary disease (COPD), where inflammation and disease progression continues despite smoking cessation. In COPD, recent studies reported from the Xian-McKeon lab have shown a strong correlation between the emergence of pro-inflammatory stem cell variants and the disease itself. Xian and McKeon are on the faculty of the UH College of Natural Sciences and Mathematics

Using technology that clones stem cells from normal lungs, the Xian-McKeon lab found that the COPD lung was dominated by three stem cell variants that drive all the pathology of COPD including inflammation, fibrosis and mucin hypersecretion.

“Given the known pathological similarities between COPD and cystic fibrosis, we asked whether the cystic fibrosis lung is also dominated by pathogenic stem cells,” said Xian. “We generated stem cell libraries from four CF lungs that showed not only the three variants seen in COPD but two additional, proinflammatory variants.”

The team hypothesizes that these CF stem cell variants play key roles in the progression of CF and represent pathogenic elements of this disease triggered by, and yet independent of, the CFTR gene.

To identify key inflammatory drivers in the three variants, McKeon and Xian will use CRISPR-Cas9 gene editing, which allows them to quickly create cell models.

“CRISPR-Cas9 genome editing, coupled with our xenograft models, offers a powerful and feasible means of assessing the hierarchy of factors secreted by these three pro-inflammatory stem cell variants found in the CF lung,” said Xian.

The Xian-McKeon studies come on the cusp of a new class of cystic fibrosis drugs that restore CFTR activity in these patients.

"The clinical studies suggest the early application of the CFTR modulators will be game-changers for CF, though their impact on advanced lung disease may be more modest,” noted McKeon.

Foreseeing the need for companion drugs for advanced CF, the Xian-McKeon laboratory is developing small molecule combinations that selectively target the pathogenic stem cell variants in the CF lung, while sparing the normal cells needed for regenerative repair.

"This is a race against time for patients with CF and other chronic lung diseases, and the targets are now clear," said Xian.

- Laurie Fickman, University Media Relations