Epithelial Reprogramming Underpinning Euplastic versus Dysplastic Repair

About This Grant

PROJECT SUMMARY Lung possesses a remarkable ability to regenerate and restore normal lung function after severe acute injury. However, in the case of chronic injuries, the lung epithelial stem/progenitors fail to restore normal lung function and contribute to a pathologic regeneration, amounting to regenerative failure that typifies chronic restrictive lung diseases like Idiopathic Pulmonary Fibrosis (IPF). Both airway and alveolar epithelial stem cells are capable of differentiating into type 1 and type 2 alveolar epithelial cells (AT1 and AT2, respectively) via a series of intermediate cell states. During normal injury resolution, like in acute injuries in human lungs and murine models, both airway and alveolar epithelial stem cells go through a euplastic intermediate cell (EIC) state to eventually differentiate into alveolar epithelial cells (AT1 and AT2s). However, in chronic lung diseases like IPF or animal models of chronic fibrotic injury, the stem cells progress through EICs and differentiate further into aberrant basal-like dysplastic intermediate cell (DIC) state that result maladaptive regeneration and honeycomb-like cystic structures. Currently, we lack understanding of the signaling mechanisms that control the balance between euplastic and dysplastic regenerative cell states. This is especially relevant in a histologically heterogeneous disease like IPF where the balance between euplastic and dysplastic repair is a key indicator of disease severity. To this end, we discovered that EICs and DICs are spatially distributed in relation to severity of remodeling and state of microenvironment niche signals. EICs are often found in areas of active but mild injury and are associated with mesenchymal cells that secrete pro-regenerative growth factors such as NRG1 that activated ErbB3/STAT3 signaling. On the other hand, DICs are associated with Collagenhigh/CTHRC1high pro-fibrotic mesenchymal cells found in actively remodeling regions. Furthermore, our preliminary data suggests that intermediate filaments such as cytokeratin 17 (KRT17) and Vimentin play an integral role in the switch from EIC to DIC. Therefore, we will test the hypothesis that spatially restricted microenvironment cues activation of distinct signaling pathways in activated epithelial progenitors to determine euplastic versus dysplastic regenerative trajectories in the following three aims: Aim 1: Define the role of NRG1/ErbB3 signaling in euplastic alveolar regeneration. Aim 2: Determine the role of TGFβ1/KRT17 signaling axis in dysplastic alveolar regeneration during chronic injury. Aim 3: Identify spatial cues required for euplastic to dysplastic regenerative switch. We will use newly established animal models of chronic injury, cell-specific in vivo conditional knockout of relevant candidate genes, in vitro co- culture techniques modeling human euplastic and dysplastic repair to test specific signaling components of NRG1/ErbB3 signaling and TGFβ1/KRT17 signaling. Finally, using a novel in silico approach, we will build an integrated mouse PF and human IPF spatiotemporal signaling map of progressive fibrosis. Together, successful completion of this proposal will build a comprehensive model of niche-influenced signaling crosstalk governing epithelial plasticity and reveal novel therapeutic targets for treating fibrotic disorders.