Inhibition of BRD4 Reduces Neutrophil Activation and Adhesion to the Vascular Endothelium Following Ischemia Reperfusion Injury

Abstract

Renal ischemia reperfusion injury (IRI) is associated with inflammation, including neutrophil infiltration that exacerbates the initial ischemic insult. The molecular pathways involved are poorly characterized and there is currently no treatment. We performed an in silico analysis demonstrating changes in NFκB-mediated gene expression in early renal IRI. We then evaluated NFκB-blockade with a BRD4 inhibitor on neutrophil adhesion to endothelial cells in vitro, and tested BRD4 inhibition in an in vivo IRI model. BRD4 inhibition attenuated neutrophil adhesion to activated endothelial cells. In vivo, IRI led to increased expression of cytokines and adhesion molecules at 6 h post-IRI with sustained up-regulated expression to 48 h post-IRI. These effects were attenuated, in part, with BRD4 inhibition. Absolute neutrophil counts increased significantly in the bone marrow, blood, and kidney 24 h post-IRI. Activated neutrophils increased in the blood and kidney at 6 h post-IRI and remained elevated in the kidney until 48 h post-IRI. BRD4 inhibition reduced both total and activated neutrophil counts in the kidney. IRI-induced tubular injury correlated with neutrophil accumulation and was reduced by BRD4 inhibition. In summary, BRD4 inhibition has important systemic and renal effects on neutrophils, and these effects are associated with reduced renal injury.

Recent Approaches to Targeting Canonical NFκB Signaling in the Early Inflammatory Response to Renal IRI

“…79 Similarly, Reid et al studied the effects of MS417, a BRD4-specific inhibitor designed to inhibit BRD4 from interacting with RelA, thus inhibiting NFkB-mediated transcription. 24,84 After IRI, mice treated with MS417 had reduced recruitment and activation of neutrophils in the kidney tissue and reduced tubular injury. 24 In another approach, Zhao et al treated rats with total flavonoids which activate silent information regulator factor 2-related enzyme 1 (sirt1), a histone deacetylase that targets RelA at lysine 310 in the nucleus.…”

“…However, particular considerations are required in regard to BRD4 inhibitors because these compounds may have broader effects on gene expression beyond the inhibition of NFkB. 24,[87][88][89]…”

“…In the setting of IRI, NF κ B plays a key role in modulating the immune response after IRI. 21,24 NF κ B is activated after IRI by an array of stimuli, including PRRs and cytokines as well as TLRs, B-cell receptors, and T-cell receptors (Figure 1A). 25 The activation leads to ubiquitin-dependent degradation of the inhibitor protein, I κ B α , through phosphorylation by the I κ K complex (composed of IKK α , IKK β , and IKK γ ).…”

“…Targeting NFkB in the Nucleus Investigators have also explored the effects of targeting NFkB within the nucleus after IRI (Figure 1D). 24,[77][78][79][80] Ubiquitination of IkBa and its subsequent degradation lead to the nuclear translocation of canonical NFkB transcription factors where they bind to NFkB consensus sequences in gene promoter regions to stimulate gene transcription. 22 In this regard, Zhang et al explored the role of miR-181d in NFkB activation.…”

BRD4 Inhibition Protects Against Myocardial Ischemia/Reperfusion Injury by Suppressing Inflammation and Oxidative Stress Through the PI3K/AKT Signaling Pathway

“…BRD4 inhibition has been demonstrated to reduce neutrophil recruitment and activation and decrease inflammatory gene expression in primary tubule cells. 19 Zhu et al reported that the elevated IL-1β, TNF-α, and phosphorylated NF-κB levels in Ang II-incubated cardiomyocytes could be reduced by shBRD4. 9 In a mouse model of heart failure, BRD4 inhibition with JQ1 blocks the transactivation of proinflammatory transcription factors.…”