Epidemiologic studies reveal that asthmatic children have lower lung function during childhood that persists into adulthood compared to healthy children. Bronchial biopsies from asthmatic children demonstrate that features of airway remodeling, including excessive sub-epithelial extracellular matrix deposition, are already present in early childhood. Together, these data suggest that early structural changes in the asthmatic airway may contribute to lung function declines that manifest early in the natural history of asthma. Although inhaled corticosteroids reduce morbidity, treatment does not alter the natural history of asthma nor prevent lung function decline. Improved understanding of mechanisms that drive airway remodeling is fundamental to the development of future interventions to prevent airway remodeling. Evidence from animal models and human bronchial biopsies suggest that the bronchial epithelium secretes proteins that may regulate lung fibroblasts and airway remodeling. We have demonstrated that primary bronchial epithelial cells (BECs) from asthmatic children exhibit greater expression of pro-remodeling factors including TGF?2 than cells from healthy children. We have reported that in co-culture BECs from healthy children markedly down-regulate fibroblast-to-myofibroblast transition (FMT) and lung fibroblast expression of extracellular matrix (ECM) components involved in airway remodeling. This down-regulation is significantly less when fibroblasts are co-cultured with asthmatic BECs. Data from our human BEC model systems suggest prostaglandin E2 (PGE2) and the activing inhibitor follistatin-like-3 (FSTL3) as epithelial-secreted proteins that tonically inhibit fibroblast functin. There is a paucity of data regarding the molecular regulation of the expression and secretion of TGF?2, PGE2 and/or FSTL3 in airway epithelia. In preliminary studies, we found that molecules that inhibit the ERK, WNT/?-catenin, and protein kinase C (PKC) signaling alter expression of TGF?2, PGE2 and FSTL3 by BECs, suggesting that dysregulation of these pathways in BECs could lead to a pro-fibrotic phenotype, and that interventions that enhance ERK and PKC, or inhibit WNT/?-catenin signaling in BECs may decrease FMT and inhibit HLF proliferation and ECM expression. We will use innovative BEC/fibroblast co-culture model systems with primary BEC from well-characterized asthmatic and healthy children and adults to test our hypotheses that in normal airways a balance of epithelial-secreted stimulatory and inhibitory factors regulate fibroblasts and inhibit FMT, limiting ECM deposition. We hypothesize that dysregulated WNT/?-catenin, PKC and ERK signaling in asthmatic epithelium results in increased TGF?2, and decreased PGE2 and FSTL3 secretion by epithelial cells, leading to increased fibroblast proliferation, FMT, and ECM deposition. Finally, we will test our hypotheses that FMT, fibroblast proliferation and ECM expression, and BEC secretion of TGF?2, activing A, PGE2 and FSTL3, in co-cultures are associated with asthma severity, exacerbations, and/or lung function among the asthmatic children and adults who donated BECs.
Using airway epithelial cell/fibroblast co-culture model systems with primary airway epithelial cells from well-characterized asthmatic and healthy children we will investigate mechanisms that drive airway remodeling. Improved understanding of these mechanisms is fundamental to the development of future clinical interventions to alter the natural course of asthma and prevent lung function decline.
