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Regulation of basal cell plasticity : implications for airway epithelial remodeling in asthma

University of British Columbia

Asthma is characterized by reversible airflow limitation, airway inflammation and remodeling, which includes increased smooth muscle mass, sub-epithelial fibrosis, goblet cell metaplasia and loss of columnar epithelial cells. Basal cells are progenitor cells of the pseudostratified airway epithelium that undergo distinct phenotypic transitions to maintain epithelial homeostasis following damage. We hypothesized that differentiation of epithelial basal cells is defective in asthma, leading to impaired repair. We used three distinct in vitro models of human airway epithelial basal cell plasticity – epithelial-mesenchymal transition (EMT), repair of mechanical scratch wounds, and differentiation at air-liquid interface – which together provide a complete overview of basal cell function in epithelial repair. In Chapter 3 we assessed the ability of transforming growth factor (TGF)-β₁ to induce molecular reprogramming indicative of EMT and found that basal cells from asthmatic and non-asthmatic patients undergo TGFβ₁-induced EMT. However, an expanded population of basal cells in differentiated epithelial cultures from asthmatic donors led to an increased EMT response. In Chapter 4 we found that inhibition of ΔNp63α impaired restitution of scratch wounds in monolayer culture, due to decreased proliferation. Additionally, ΔNp63α regulated several genes known to be involved in epithelial repair, including β-catenin, epidermal growth factor receptor, and jagged1. In Chapter 5 we found that basal epithelial cells from asthmatic donors with (+) and without (-) exercise-induced bronchoconstriction (EIB) were impaired in the transition to a ciliated but not goblet cell phenotype in an air-liquid interface (ALI) model of mucociliary differentiation. EIB(-) asthmatics also had an expansion of the basal cell population and shorter cilia. In Chapter 6, we used an unbiased RNA sequencing approach to identify aberrant expression of pathways involved in actin cytoskeleton dynamics and cellular metabolism that were distinctly different in EIB(-) and EIB(+) asthma during mucociliary differentiation. We also identified a miRNA-mRNA network that regulates the epithelial transition from proliferation to differentiation. This thesis provides compelling evidence that lineage commitment and molecular reprogramming in basal cells are skewed in asthma to favour epithelial plasticity in response to TGFβ₁, rather than mucociliary differentiation, and that epithelial remodeling is more pronounced in the EIB(-) phenotype of asthma.

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2014-07-25

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/48495

Experimental Medicine

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/