Selective Inhibition of Bromodomain-Containing Protein 4 Reduces Myofibroblast Transdifferentiation and Pulmonary Fibrosis

Abstract

Idiopathic pulmonary fibrosis is a lethal disease driven by myofibroblast expansion. Currently no therapies exist that target the epigenetic mechanisms controlling myofibroblast transdifferentiation, which is responsible for unregulated extracellular matrix (ECM) production. We have recently shown that bromodomain-containing protein 4 (BRD4), an epigenetic regulator that forms a scaffold for nuclear activators and transcription factors, is essential for TGFβ-induced myofibroblast transdifferentiation. However, its role in the development and progression of pulmonary fibrosis in vivo has not been established. Here, we evaluate the hypothesis that BRD4 bromodomain interactions mediate myofibroblast expansion and fibrosing disease in vivo. C57BL/6J mice challenged with intratracheal bleomycin were systemically treated with a selective allosteric inhibitor of the BRD4 bromodomain 1 (BD1), ZL0591 (10 mg/kg), during the established fibrotic phase (14 days post-bleomycin) in a rigorous therapeutic paradigm. Eleven days after initiation of ZL0591 treatment (25 days post-bleomycin), we detected a significant improvement in blood O2 saturation compared to bleomycin/vehicle control. Twenty-eight days post-bleomycin, we observed a reduction in the volumetric Hounsfield Unit (HU) density by micro computed tomography (µCT) in the ZL0591-treated group, as well as a reduction in collagen deposition (hydroxyproline content) and severity of injury (Ashcroft scoring). Myofibroblast transdifferentiation was measured by smooth muscle α-actin (αSMA) staining, indicating a loss of this cell population in the ZL0591-treated group, and corresponded to reduced transcript levels of myofibroblast-associated extracellular matrix genes, tenascin-C and collagen 1α1. We conclude that BRD4 BD1 interactions are critical for myofibroblast transdifferentiation and fibrotic progression in a mouse model of pulmonary fibrosis.

[ 64 Cu]Cu-PEG-FUD peptide for noninvasive and sensitive detection of murine pulmonary fibrosis

“…4A ). Given that HRCT is routinely used as one of the gold standard methods for assessing fibrotic burden and changes over time in the clinic and that μCT serves as a reliable means for assessment of lung fibrosis in the preclinical models of the disease ( 55 – 57 ), we chose to analyze μCT as a measure of overall fibrosis in our experiments. Three days after bleomycin treatment, there was no significant increase of radiodensity observed in the axial lung μCT images of the mice ( P = 0.9755; Fig.…”

“…As already mentioned, the bleomycin-induced model of murine pulmonary injury and fibrosis is one of the most commonly used and well-accepted models for preclinical investigations related to IPF therapeutic ( 57 , 66 , 67 ) and diagnostic development ( 19 , 20 , 30 , 59 ) but is not without challenges. While the bleomycin-induced mouse model is similar to IPF disease in its spatial heterogeneity, it is not characterized by the presence of fibroblastic foci.…”

Semi-automated micro-computed tomography lung segmentation and analysis in mouse models

“…From the related paper [14] , HU bins of [−1000 to −600, −600 to −500, −500 to −400, −400 to −300, −300 to −200, −200 to 0] were used to segment the lung radiodensity when manually selected. Within this HU bin manual segmentation construct, the bleomycin lung injury model demonstrated a right-shifted HU density histogram when the lungs were experimentally driven toward the fibrotic stage; accordingly, through automation, we aimed to replicate that finding in full 3D, with minimal user interactions [21] .…”

“…Segmentation runs automatically with a macro “CT_AutoHU_SelectBin.ijm,” which allows for automated and batch processing of images. There are three modes: (1) for HU bins defined as “Default” (as used in the original papers [ 14 , 21 ], (2) “Mod” with the subranges split for more accuracy, and (3) “Range,” where a max, min, and bin width can be user defined.…”

BRD4 as a Therapeutic Target in Pulmonary Diseases

“…In accord, pulmonary fibrosis, as indicated by collagen I expression, was also largely inhibited by JQ1. Recently, Bernau and colleagues [43] further showed the efficacy of selective inhibition of the BRD4 BD1 domain in reducing myofibroblast differentiation and reversing established pulmonary fibrosis in mice using the BRD4 BD1-selective inhibitor ZL0591.…”