Lung Stem Cell Heterogeneity in Advanced Cystic Fibrosis

Despite congenital CFTR mutations and the severity of advanced cystic fibrosis (CF), the onset and progression of lung disease in these patients is not uniform. This phenomenon raises the possibility that symptomatic CF involves contributions to the disease process of an epigenetic nature beyond those conferred by CFTR mutations themselves. As the first test of this hypothesis, I asked in my studies how lung stem cells from patients with end-stage CF differ from those of normal patients without CFTR mutations. Using technology that enables single stem cell cloning, we found that in addition to the normal lung stem cell (NM) of control patients that can differentiate to cells of terminal bronchiolar and alveolar lineages, end-stage CF patients are dominated by five additional stem cell variants including ones committed to goblet cell metaplasia (GCM), GCM marked by constitutive inflammation (iGCM), squamous cell metaplasia (SCM), SCM marked by inflammatory gene expression (iSCM), and finally, one that is apparently normal but with constitutive inflammation (iNM). Importantly, stem cell libraries generated from all four of the CF patients express each of these stem cell types, and xenografts of these libraries yield epithelial structures marked by massive intra-luminal leukocyte infiltration and extensive submucosal fibrosis. Xenografting of individual NM, iNM, GCM, iGCM, SCM, and iSCM clones has revealed that fibrosis is primarily mediated by SCM and iSCM while the leukocyte attraction is triggered by iNM, iGCM, and iSCM. Long-term passaging of these clonal types revealed that these phenotypes were absolute and likely epigenetically committed. Remarkably, similar variants pre-exist as minor constituents in control lung and fetal lung that conceivably act as sentinels for pathogen incursions. And while these individual clones and the collective library of such clones recapitulate some of the major pathological features of the CF lung including inflammation, correction of CFTR deficiency via lentiviral transduction has no impact on the proinflammatory phenotype of these variant epithelial clones. Our conclusions from these studies are that end-stage CF patients display a heterogeneity of lung stem cells that is epigenetic in origin and includes variants that conceivably contribute to the progression of CF disease presentation.Biology and Biochemistry, Department o