Airway remodeling is resultant of a complex multicellular response associated with a progressive decline of pulmonary function in patients with chronic airway disease. Here, repeated infections with respiratory viruses are linked with airway remodeling through largely unknown mechanisms. Although acute activation of the Toll-like receptor (TLR) 3 pathway by extracellular polyinosinic:polycytidylic acid (poly[I:C]) induces innate signaling through the NF-κB transcription factor in normal human small airway epithelial cells, prolonged (repetitive or tonic) poly(I:C) stimulation produces chronic stress fiber formation, mesenchymal transition, and activation of a fibrotic program. Chronic poly(I:C) stimulation enhanced the expression of core mesenchymal regulators Snail family zinc finger 1, zinc finger E-box binding homeobox, mesenchymal intermediate filaments (vimentin), and extracellular matrix proteins (fibronectin-1), and collagen 1A. This mesenchymal transition was prevented by silencing expression of NF-κB/RelA or administration of a small-molecule inhibitor of the IκB kinase, BMS345541. Acute poly(I:C) exposure in vivo induced profound neutrophilic airway inflammation. When administered repetitively, poly(I:C) resulted in enhanced fibrosis observed by lung micro-computed tomography, second harmonic generation microscopy of optically cleared lung tissue, and by immunohistochemistry. Epithelial flattening, expansion of the epithelial mesenchymal trophic unit, and enhanced Snail family zinc finger 1 and fibronectin 1 expression in airway epithelium were also observed. Repetitive poly(I:C)-induced airway remodeling, fibrosis, and epithelial-mesenchymal transition was inhibited by BMS345541 administration. Based on this novel model of viral inflammation-induced remodeling, we conclude that NF-κB is a major controller of epithelial-mesenchymal transition and pulmonary fibrosis, a finding that has potentially important relevance to airway remodeling produced by repetitive viral infections.

NFκB/RelA triggers innate inflammation by binding to Bromodomain-Containing Protein 4 (BRD4), an atypical histone acetyltransferase (HAT). Although RelA·BRD4 HAT mediates acute neutrophilic inflammation, its role in chronic and functional airway remodeling is not known. We observed that BRD4 is required for TLR3 mediated mesenchymal transition, a cell-state change that is characteristic of remodeling. We therefore tested novel highly selective BRD4 inhibitors, ZL0420 and -0454, on chronic airway remodeling produced by repetitive TLR3 agonist challenges, and compared their efficacy with nonselective BET protein inhibitors, JQ1 and RVX208. We observed that ZL0420 and -0454 more potently reduced poly(I:C)-induced weight loss, fibrosis assessed by micro-CT and second harmonic generation microscopy; these measures correlated with collagen deposition observed in histopathology. Importantly the ZL inhibitors were more effective than that of nonselective BET inhibitors at equivalent doses. The ZL inhibitors had significant effects on lung physiology, reversing TLR3-associated airway hyper responsiveness (AHR) and increasing lung compliance in vivo. At the molecular level, ZL inhibitors reduced elaboration of the TGF β-induced growth program, preventing mucosal mesenchymal transition, disrupting BRD4 HAT activity, and complex formation with RelA. We also observed that ZL0454 treatment blocked poly(I:C)-associated expansion of the αSMA1+/COL1A+ myofibroblast population, and prevented myofibroblast transition in a co-culture system. We conclude that 1) BRD4 is a central effector of mesenchymal transition that results in paracrine activation of myofibroblasts, mechanistically linking innate inflammation to AHR and fibrosis, and 2) highly selective BRD4 inhibitors may be effective in reversing the effects of repetitive airway viral infections on innate inflammation-mediated remodeling.

Myosin Light Chain (MLC) regulates platelet contraction through its phosphorylation by Myosin Light Chain Kinase (MLCK) or dephosphorylation by Myosin Light Chain Phosphatase (MLCP). The correlation between platelet contraction force and levels of MLC phosphorylation is unknown. We investigate the relationship between platelet contraction force and MLC phosphorylation using a novel microelectromechanical (MEMS) based clot contraction sensor (CCS). The MLCK and MLCP pair were interrogated by inhibitors and activators of platelet function. The CCS was fabricated from silicon using photolithography techniques and force was validated over a range of deflection for different chip spring constants. The force of platelet contraction measured by the clot contraction sensor (CCS) was compared to the degree of MLC phosphorylation by Western Blotting (WB) and ELISA. Stimulators of MLC phosphorylation produced higher contraction force, higher phosphorylated MLC signal in ELISA and higher intensity bands in WB. Inhibitors of MLC phosphorylation produced the opposite. Contraction force is linearly related to levels of phosphorylated MLC. Direct measurements of clot contractile force are possible using a MEMS sensor platform and correlate linearly with the degree of MLC phosphorylation during coagulation. Measured force represents the mechanical output of the actin/myosin motor in platelets regulated by myosin light chain phosphorylation.