Wang, Faping

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with limited survival. Janus kinases (JAKs), tyrosine kinases that transduce cytokine-mediated signals, are known to be involved, but their specific roles in lung fibrosis are not well defined. In this study, the interactions between JAK1/signal transducers and activators of transcription (STAT)3 signaling and transforming growth factor-beta (TGF-β)-induced fibroblast responses were investigated using both pharmacological and siRNA approaches in human normal and IPF-derived lung fibroblasts. We found that JAK1 directly interacts with the TGF-β receptor I subunit (TβRI), and silencing JAK1 promotes myofibroblast transdifferentiation. However, the suppression of JAK1 signaling in vitro and in vivo using an inhibitor (upadacitinib) did not alter lung fibroblast activation or fibrosis development. STAT3 was constitutively active in cultured primary lung fibroblasts; this STAT3 activation required JAK1 and repressed myofibroblast transdifferentiation. Loss of phosphorylated STAT3 following transcriptional JAK1 silencing promoted myofibroblast transdifferentiation. In contrast, transcriptional silencing of unphosphorylated STAT3 suppressed TGF-β signaling, decreased SMAD3 activation, and reduced myofibroblast transdifferentiation and ECM production. Taken together, these observations support a role for JAK1/STAT3 as a direct regulator of TGF-β signaling in lung fibroblasts. Modulation of JAK1/STAT3 signaling in lung fibroblasts represents a noncanonical approach to regulating TGF-β-induced fibrosis and suggests the potential for a novel approach to treat pulmonary fibrosis.

Abstract Idiopathic pulmonary fibrosis (IPF) and rheumatoid arthritis‐associated interstitial lung disease (RA‐ILD) are two fibrotic interstitial lung diseases that share the usual interstitial pneumonia (UIP) injury pattern. Here, we report that RNA sequencing of lung biopsies from patients with RA‐ILD and IPF revealed shared and distinct disease‐causing pathways. Analysis of transcriptomic data identified a JAK2 related JAK/STAT signaling pathway gene signature that distinguishes RA‐UIP from idiopathic UIP. This was further confirmed by immunohistostaining, which identified JAK2 phosphorylation with two distinct forms of activation: a cytoplasmic form of JAK2 activation in most IPF cases (13/20) and a nuclear form of p‐JAK2 in RA‐UIP (5/5) and a minority of IPF (6/20) cases. Further immunohistostaining identified STAT5A&B as the downstream transcriptional activator for JAK2‐mediated canonical signal transduction and phosphorylation of Tyr41 on histone H3 (H3Y41ph) as the downstream epigenetic regulation site for JAK2‐mediated noncanonical signal transduction. Gene Set Enrichment Analysis (GSEA) of the RNA‐Seq data further supported this shared pathogenic mechanism for the two diseases with the enrichment of STAT5A&B target gene sets as well as the JAK2 regulated H3Y41ph target gene set. This regulatory role of JAK2 in the pathogenesis of pulmonary fibrosis was further demonstrated by the attenuation of bleomycin‐induced murine pulmonary fibrosis using a JAK2‐selective pharmacological inhibitor CEP33779. In vitro studies with normal and IPF derived lung fibroblasts revealed a central role for JAK2 as an essential intermediary molecule in TGF‐β‐mediated myofibroblast trans‐differentiation, proliferation, and extracellular matrix protein production. These observations support a crucial role for JAK2 as an intermediary molecule in fibrotic lung disease development.