Genetic deficiency of the transcription factor NFAT1 confers protection against fibrogenic responses independent of immune influx.

Idiopathic pulmonary fibrosis (IPF) is marked by unremitting matrix deposition and architectural distortion. Multiple profibrotic pathways contribute to the persistent activation of mesenchymal cells (MCs) in fibrosis, highlighting the need to identify and target common signaling pathways. The transcription factor nuclear factor of activated T cells 1 (NFAT1) lies downstream of second messenger calcium signaling and has been recently shown to regulate key profibrotic mediator autotaxin (ATX) in lung MCs. Herein, we investigate the role of NFAT1 in regulating fibroproliferative responses during the development of lung fibrosis. Nfat1-/--deficient mice subjected to bleomycin injury demonstrated improved survival and protection from lung fibrosis and collagen deposition as compared with bleomycin-injured wild-type (WT) mice. Chimera mice, generated by reconstituting bone marrow cells from WT or Nfat1-/- mice into irradiated WT mice (WT→WT and Nfat1-/-→WT), demonstrated no difference in bleomycin-induced fibrosis, suggesting immune influx-independent fibroprotection in Nfat1-/- mice. Examination of lung tissue and flow sorted lineageneg/platelet-derived growth factor receptor alpha (PDGFRα)pos MCs demonstrated decreased MC numbers, proliferation [↓ cyclin D1 and 5-ethynyl-2'-deoxyuridine (EdU) incorporation], myofibroblast differentiation [↓ α-smooth muscle actin (α-SMA)], and survival (↓ Birc5) in Nfat1-/- mice. Nfat1 deficiency abrogated ATX expression in response to bleomycin in vivo and MCs derived from Nfat1-/- mice demonstrated decreased ATX expression and migration in vitro. Human IPF MCs demonstrated constitutive NFAT1 activation, and regulation of ATX in these cells by NFAT1 was confirmed using pharmacological and genetic inhibition. Our findings identify NFAT1 as a critical mediator of profibrotic processes, contributing to dysregulated lung remodeling and suggest its targeting in MCs as a potential therapeutic strategy in IPF.NEW & NOTEWORTHY Idiopathic pulmonary fibrosis (IPF) is a fatal disease with hallmarks of fibroblastic foci and exuberant matrix deposition, unknown etiology, and ineffective therapies. Several profibrotic/proinflammatory pathways are implicated in accelerating tissue remodeling toward a honeycombed end-stage disease. NFAT1 is a transcriptional factor activated in IPF tissues. Nfat1-deficient mice subjected to chronic injury are protected against fibrosis independent of immune influxes, with suppression of profibrotic mesenchymal phenotypes including proliferation, differentiation, resistance to apoptosis, and autotaxin-related migration.

MNK-driven eIF4E phosphorylation regulates the fibrogenic transformation of mesenchymal cells and chronic lung allograft dysfunction.

Tissue fibrosis remains unamenable to meaningful therapeutic interventions and is the primary cause of chronic graft failure after organ transplantation. Eukaryotic translation initiation factor (eIF4E), a key translational regulator, serves as convergent target of multiple upstream profibrotic signaling pathways that contribute to mesenchymal cell (MC) activation. Here, we investigate the role of MAP kinase-interacting serine/threonine kinase-induced (MNK-induced) direct phosphorylation of eIF4E at serine 209 (Ser209) in maintaining fibrotic transformation of MCs and determine the contribution of the MNK/eIF4E pathway to the pathogenesis of chronic lung allograft dysfunction (CLAD). MCs from patients with CLAD demonstrated constitutively higher eIF4E phosphorylation at Ser209, and eIF4E phospho-Ser209 was found to be critical in regulating key fibrogenic protein autotaxin, leading to sustained ß-catenin activation and profibrotic functions of CLAD MCs. MNK1 signaling was upregulated in CLAD MCs, and genetic or pharmacologic targeting of MNK1 activity inhibited eIF4E phospho-Ser209 and profibrotic functions of CLAD MCs in vitro. Treatment with an MNK1/2 inhibitor (eFT-508) abrogated allograft fibrosis in an orthotopic murine lung-transplant model. Together these studies identify what we believe is a previously unrecognized MNK/eIF4E/ATX/ß-catenin signaling pathway of fibrotic transformation of MCs and present the first evidence, to our knowledge, for the utility of MNK inhibitors in fibrosis.