Role of Muc5b in Honeycomb Cyst Formation
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Project summary The overall scientific goal of this proposal is to build upon our findings in MUC5B-associated idiopathic pulmonary fibrosis (IPF) to understand the basic mechanisms of pulmonary fibrosis. IPF is a devastating disease that claims 5 million lives worldwide annually. It is characterized by progressive lung fibrosis and formation of microscopic honeycomb (HC) cysts. Although some therapies have recently become available, treatment of IPF is limited by our understanding of its pathobiology. We have found that a gain-of-function polymorphism 3kb upstream of the MUC5B gene is the strongest risk factor for development of IPF. In preliminary experiments in mice, we demonstrate that overexpression of Muc5b leads to an enhancement of fibrosis provoked by bleomycin and influenza. However, overexpression of Muc5b without lung injury is not sufficient to provoke fibrosis. Gene expression analysis in IPF has demonstrated an association of MUC5B expression with HC. Likewise, we and others, have discovered that HCs contain significant MUC5B protein. A recent publication noted that mice develop HC-like cysts in the setting of influenza injury, and that cyst formation depends on the Notch developmental pathway. Notch signals have also been demonstrated to be important for HC formation in IPF. We have found that influenza-associated HC-like cysts in mice contain copious Muc5b, and in human lung epithelial cell lines Notch inhibition significantly reduces MUC5B expression. However, the interplay of NOTCH and MUC5B in IPF are completely unknown. Given the apparent role of Notch in the expression of Muc5b and HC-like cysts, and the characterized role of Muc5b in human and murine fibrosis models, we hypothesized that Notch modulates lung injury repair and promotes pulmonary fibrosis through downstream Muc5b expression. In Aim 1 of this proposal, I will establish a role for Notch in pulmonary fibrosis and Muc5b expression by testing whether Notch is necessary or sufficient for either. In Aim 2, I will evaluate the necessity of Muc5b in fibrosis, and determine whether effects of Muc5b on fibrosis are epithelial-cell intrinsic. These Aims address significant gaps in our knowledge of IPF pathogenesis, particularly where epithelia are concerned, and may lead to novel therapies. Training received during this novel project will enhance my understanding of molecular biology, and, paired with specific coursework in bioinformatics, will enable me to focus on functional genetic approaches to interstitial lung disease.
