Dedicator of cytokinesis 2 in pleural fibrosis

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Pleural fibrosis is the scarring of the pleura resulting in restrictive lung disease and impaired lung function. The pathophysiological mechanism of pleural fibrosis is unclear. The interactions between resident and inflammatory cells, profibrotic mediators and coagulation factors, and fibrinolytic pathways are integral to pleural remodeling and fibrosis. Increasing evidence affirm the critical role of pleural mesothelial cells (PMCs) in pleural fibrosis development, mainly through a process termed mesothelial to mesenchymal transition (MesoMT). MesoMT is characterized by increased expression of α-smooth muscle actin (α-SMA)/collagen 1 (Col-1)/fibronectin (FN), and enhanced cell migration/invasion. Currently, there are no pharmacologic treatments for this disease. Therefore, identification of novel targets and therapeutic strategies is an important goal for the public health. However, there is a fundamental knowledge gap in mechanisms controlling MesoMT during pleural fibrosis. Our preliminary data strongly support that dedicator of cytokinesis 2 (DOCK2) is a crucial regulator of MesoMT to promote pleural fibrosis. In primary human PMCs (HPMCs), DOCK2 was induced by the potent MesoMT inducer TGF-β. DOCK2 knockdown blocked TGFβ-induced MesoMT maker expression and cell migration. Snail as a transcriptional factor controlling epithelial to mesenchymal transition was found critical in TGF-β-induced MesoMT. DOCK2 knockdown inhibited TGF-β-induced Snail expression and activation of Smad2/3 and NF-κB signaling, which have been shown to upregulate Snail expression in various cell types. In addition, we found that DOCK2 was dramatically induced in the fibrotic pleura of human pleuritis patients and in pleural fibrosis models induced by Streptococcus pneumoniae (Strep), carbon black/bleomycin (CBB), and TGF-β. DOCK2 knockout mice were significantly protected from Strep-induced pleural fibrosis. Based on these findings, our overall hypothesis is that DOCK2 mediates MesoMT and increases PMC migration/invasion to promote pleural fibrosis, which will be tested in three specific aims. In Aim 1, we will determine if DOCK2 promotes pleural MesoMT via upregulation of Snail. Further, we will test whether DOCK2 increases Snail through activating Smad2/3 and NF-κB signaling. In Aim 2, we will test if DOCK2 promote pleural MesoMT with increased cell migration/invasion. Specifically, we will determine if DOCK2 mediates TGF-β-induced cytoskeletal reorganization, migration/invasion via activating Rac1. In Aim 3, we will test the hypothesis that DOCK2 knockout blocks pleural fibrosis via inhibiting MesoMT in vivo. We will determine if general and mesothelial cell-specific DOCK2 knockout mice are protected from Strep, CBB, and TGF-β induced pleural fibrosis through suppressing MesoMT in vivo. Completion of the proposed studies will establish the pivotal role and mechanisms of DOCK2 in promoting pleural fibrosis by regulating MesoMT, which may ultimately contribute to the identification of novel targeted therapies for this important but refractory clinical problem.