Early events in the pathogenesis of interstitial pulmonary fibrosis (IPF) have been linked to faulty repair of injured alveolar epithelium where proliferating alveolar type II (AT2) cells do not effectively differentiate into type I (AT1) cells. This leads to irreversible damage, fibrosis, and loss of function. The mechanisms that normally control the process of differentiation of AT2 cells into AT1s are poorly understood, so regulatory molecules or pathways that are affected by these pathogenic events have not been elucidated. In this proposal, we will apply new concepts developed from recent in vitro modeling of normal human alveolar epithelial cell differentiation and in vivo modeling of pulmonary fibrosis is rats to study novel, interactive signaling pathways and nuclear factors that we predict are incorrectly regulated in fibrotic lung diseases, such as idiopathic pulmonary fibrosis. Our data indicates that excessive increases in sulfated extracellular matrix (ECM) as seen in pulmonary fibrosis, alters the effectiveness of key factors in the differentiation process, FoxA1 and Wnt7A, and stimulates a shift to regulatory factors which favor proliferation even in a high sulfated ECM environment. We will show that FoxA2, known to compensate for ineffective FoxA1 in development, is favored under these conditions and upregulates Wnt7B, which promotes proliferation over differentiation. Instead of stabilization of proliferation and phenotype, alveolar epithelial cells continue to attempt to achieve differentiation by producing more TGF2, which not only sustains the problem but promotes EMT and more fibrosis. The SPECIFIC HYPOTHESIS to be addressed is: The excessively high level of sulfated ECMs in interstitial pulmonary fibrosis favors sustained expression of FoxA2 and promotes TGF? signaling in alveolar epithelium, which together increase Wnt7B expression and signaling resulting in sustained proliferation, stalled differentiation, and prevention of the generation of fully mature AT1 cells. To address this hypothesis, we will examine the levels of expression of each of these and related molecules by histochemistry in patients with mild or severe stages of IPF. Results of these studies are expected to support the fundamental hypothesis that fixed whole and shed fragments of pericellular sulfated components of extracellular matrices alter the microenvironment of alveolar epithelial cells - which constitutes a critical determinant of how these cells interact, their proliferative potential, and differentiated fate by influencing defined responses to WNT and TGF2 signaling and specific gene regulation. They will provide essential information needed to better understand basic cell-cell and cell-ECM relationships in pulmonary fibrosis and the mechanisms that steer its pathogenesis.
Pulmonary fibrosis is a disease of unknown origin which causes stiffening of internal surfaces of the lung, which significantly reduces lung function. A potentially significant contributing factor to the development of fibrotic lung disease may the impaired ability of cells which line internal surfaces of the lung to renew themselves by dividing and differentiating. This grant will define specific changes in the expression of modulatory influences which prevent cells from effectively differentiating and promote tissue scaring.
