Epithelial-Mesenchymal Interactions in Fibrosis Resolution

Project Summary Pulmonary fibrosis (PF) remains a major and growing medical burden with unsatisfactory therapeutic options that fail to reverse established disease. Our prior work has identified that YAP/TAZ activation in fibroblasts is a central feature of the pathological feedback loop that propagates progression of PF. In the prior funding cycle, we identified Dopamine D1 receptor (D1R) agonism as a strategy to inactivate YAP/TAZ selectively in lung fibroblasts, leading to accelerated resolution of experimental pulmonary fibrosis in mice in part by switching lung fibroblasts from matrix depositing to matrix degrading state. Moreover, we demonstrated that the lungs of individuals with PF exhibit a deficit in expression of DOPA decarboxylase (DDC), the enzyme that catalyzes conversion of L-DOPA into bioactive dopamine. These studies lead us to propose that restoration of endogenous local dopamine levels in the lung is an essential trigger for the matrix degradation and fibrosis clearance that is essential to successful repair of the lung, but is impaired in PF. Our preliminary data show that Ddc transcripts are transiently depressed in lung tissue of young mice following bleomycin injury and rise during fibrosis resolution, whereas aged mice exhibited sustained reductions in Ddc that parallel persistent fibrosis. Moreover, small molecule inhibition of Ddc enzymatic activity or the D1R from day 21 to 42 post- bleomycin in young mice ablates the spontaneous resolution of lung fibrosis, demonstrating the essential role for dopamine signaling in fibrosis resolution. In addition, we find that dopamine is detectable in supernatants of precision cut lung slices and is diminished in slices cultured from fibrotic lungs, confirming the local synthesis of dopamine within the lung. Based on these findings, we propose to test the central hypothesis that epithelial dopamine synthesis is essential to fibrosis resolution and that restoration of normal dopamine levels in PF lung tissue can promote collagen resorption and repair of the lung. We will test this hypothesis in three aims spanning non-resolving mouse models of pulmonary fibrosis as well as ex vivo models of mouse and human lung tissues. To define the functional roles of dopamine signaling we will leverage both cell-specific conditional genetic models as well as well-characterized small molecule inhibitors and dopamine agonists in these systems. Together our studies will define the cellular sources and regulatory systems that control dopamine bioavailability during normal lung repair, and will delineate how this repair system fails in human PF. These studies may reveal new therapeutic approaches to promote fibrosis resolution and lung repair.