BRD4‐MK2 signaling: target for Crohn’s Disease‐associated fibrosis

Abstract

IntroductionFibrosis is the major complication of Crohn’s disease (CD). No targeted therapies are currently available to revert CD‐associated fibrosis. While inflammatory mechanisms in CD have been extensively investigated, understanding the pathogenesis of fibrosis is relatively limited. Mesenchymal cells are the major effectors in profibrotic processes in CD. A dramatic increase in α‐SMA expressing subsets of mesenchymal cells, also known as myofibroblasts (MF), is among the main hallmarks of profibrotic changes in CD. Mitogen‐activated protein kinase‐activated protein kinase 2 (MK2) is involved in the increase of α‐SMAexpression by MFs. Along with an increase in MK2 activity in CD we also observed an increase in the bromodomain‐containing Protein 4 (BRD4), an important epigenetic reader. BRD4 is critical for the expression of enhancer‐mediated profibrotic genes and, thus, is a potential novel regulator of MK2. However, the presence of mechanistic link between BRD4 and MK2 activity with respect to profibrotic activation of MFs in CD is unknown. Herein, we tested hypothesis that BRD4 mediated increase in MK2 activity is critical to the profibrotic reprogramming of MFs in CD and this pathway has potential for novel anti‐fibrotic therapy.MethodsHuman normal (N)‐ and CD‐derived MFs were analyzed using RNAseq, cytokine/chemokine multiplex array, FACS, and immunofluorescent microscopy. The T cell transfer murine colitis model relevant to CD was also used in this study.ResultsAn Increase in BRD4 and MK2 expression was observed in primary human CD‐ when compared to N‐MFs and were associated with the expression of the profibrotic genes including Col1α2, α‐SMA, TNC, Fn1, and TGF‐β1. Inhibition of MK2 activity in CD‐MFs with the MK2 specific inhibitor PF‐3644022 and murine MK2 KO MFs showed significantly reduced basal and TGF‐β1‐induced profibrotic gene expression. Use of the BRD4 specific inhibitor ZL0454 significantly reduced MK2 mRNA expression in CD‐MFs Additionally, ex vivo treatment of the CD tissues with ZL0454 also abrogated MK2 expression. Therapeutic use of the BRD4 inhibitor ZL0454 (10 mg/kg, daily for 10 days) in T cell transfer murine colitis significantly decreased MK2 expression and downstream profibrotic responses as measured by collagen deposition and expression of fibrosis‐related genes.ConclusionsOur data suggests that BRD4 positively regulates MK2 expression in CD. Further, BRD4‐MK2 signaling is critical to profibrotic activation of mesenchymal cells in CD and is a potential therapeutic target to reverse CD‐associated fibrosis.