BET-inhibition by JQ1 alleviates streptozotocin-induced diabetic cardiomyopathy

Up-regulation of BRD4 contributes to gestational diabetes mellitus-induced cardiac hypertrophy in offspring by promoting mitochondria dysfunction in sex-independent manner

Gestational diabetes mellitus (GDM) is associated with cardiovascular disease in postnatal life. The current study tested the hypothesis that GDM caused the cardiac hypertrophy in fetal (ED18.5), postnatal day 7 (PD7), postnatal day 21 (PD21) and postnatal day 90 (PD90) offspring by upregulation of BRD4 and mitochondrial dysfunction. Pregnant mice were divided into control and GDM groups. Hearts were isolated from ED18.5, PD7, PD21 and PD90. GDM increased the body weight (BW) and heart weight (HW) in ED18.5 and PD7, but not PD21 and PD90 offspring. However, HW/BW ratio was increased in all ages of GDM offspring compared to control group. Electron microscopy showed disorganized myofibrils, mitochondrial swelling, vacuolization, and cristae disorder in GDM offspring. GDM resulted in myocardial hypertrophy in offspring, which persisted from fetus to adult in a sex-independent manner. Echocardiography analysis revealed that GDM caused diastolic dysfunction, but had no effect on systolic function. Meanwhile, myocardial BRD4 was significantly upregulated in GDM offspring and BRD4 inhibition by JQ1 alleviated GDM-induced myocardial hypertrophy in offspring. Co-immunoprecipitation showed that BRD4 interacted with DRP1 and there was an increase of BRD4 and DRP1 interaction in GDM offspring. Furthermore, GDM caused the accumulation of damaged mitochondria in hearts from all ages of offspring, including mitochondrial fusion fission imbalance (upregulation of DRP1, and downregulation of MFN1, MFN2 and OPA1) and myocardial mitochondrial ROS accumulation, which was reversed by JQ1. These results suggested that the upregulation of BRD4 is involved in GDM-induced myocardial hypertrophy in the offspring through promoting mitochondrial damage in a gender-independent manner.

Regulation of programmed cell death by Brd4

Epigenetic factor Brd4 has emerged as a key regulator of cancer cell proliferation. Targeted inhibition of Brd4 suppresses growth and induces apoptosis of various cancer cells. In addition to apoptosis, Brd4 has also been shown to regulate several other forms of programmed cell death (PCD), including autophagy, necroptosis, pyroptosis, and ferroptosis, with different biological outcomes. PCD plays key roles in development and tissue homeostasis by eliminating unnecessary or detrimental cells. Dysregulation of PCD is associated with various human diseases, including cancer, neurodegenerative and infectious diseases. In this review, we discussed some recent findings on how Brd4 actively regulates different forms of PCD and the therapeutic potentials of targeting Brd4 in PCD-related human diseases. A better understanding of PCD regulation would provide not only new insights into pathophysiological functions of PCD but also provide new avenues for therapy by targeting Brd4-regulated PCD.

The importance of caveolin as a target in the prevention and treatment of diabetic cardiomyopathy

The diabetic population has been increasing in the past decades and diabetic cardiomyopathy (DCM), a pathology that is defined by the presence of cardiac remodeling and dysfunction without conventional cardiac risk factors such as hypertension and coronary heart diseases, would eventually lead to fatal heart failure in the absence of effective treatment. Impaired insulin signaling, commonly known as insulin resistance, plays an important role in the development of DCM. A family of integral membrane proteins named caveolins (mainly caveolin-1 and caveolin-3 in the myocardium) and a protein hormone adiponectin (APN) have all been shown to be important for maintaining normal insulin signaling. Abnormalities in caveolins and APN have respectively been demonstrated to cause DCM. This review aims to summarize recent research findings of the roles and mechanisms of caveolins and APN in the development of DCM, and also explore the possible interplay between caveolins and APN.

The Role of Mitochondrial Abnormalities in Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is defined as the presence in diabetic patients of abnormal cardiac structure and performance (such as left ventricular hypertrophy, fibrosis, and arrhythmia) in the absence of other cardiac risk factors (such as hypertension or coronary artery disease). Although the pathogenesis of DCM remains unclear currently, mitochondrial structural and functional dysfunctions are recognised as a central player in the DCM development. In this review, we focus on the role of mitochondrial dynamics, biogenesis and mitophagy, Ca²⁺ metabolism and bioenergetics in the DCM development and progression. Based on the crucial role of mitochondria in DCM, application of mitochondria-targeting therapies could be effective strategies to slow down the progression of the disease.

Epigenetic Modulation of Gremlin-1/NOTCH Pathway in Experimental Crescentic Immune-Mediated Glomerulonephritis

Crescentic glomerulonephritis is a devastating autoimmune disease that without early and properly treatment may rapidly progress to end-stage renal disease and death. Current immunosuppressive treatment provides limited efficacy and an important burden of adverse events. Epigenetic drugs are a source of novel therapeutic tools. Among them, bromodomain and extraterminal domain (BET) inhibitors (iBETs) block the interaction between bromodomains and acetylated proteins, including histones and transcription factors. iBETs have demonstrated protective effects on malignancy, inflammatory disorders and experimental kidney disease. Recently, Gremlin-1 was proposed as a urinary biomarker of disease progression in human anti-neutrophil cytoplasmic antibody (ANCA)-associated crescentic glomerulonephritis. We have now evaluated whether iBETs could regulate Gremlin-1 in experimental anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS) in mice, a model resembling human crescentic glomerulonephritis. In NTS-injected mice, the iBET JQ1 inhibited renal Gremlin-1 overexpression and diminished glomerular damage, restoring podocyte numbers. Chromatin immunoprecipitation assay demonstrated BRD4 enrichment of the Grem-1 gene promoter in injured kidneys, consistent with Gremlin-1 epigenetic regulation. Moreover, JQ1 blocked BRD4 binding and inhibited Grem-1 gene transcription. The beneficial effect of iBETs was also mediated by modulation of NOTCH pathway. JQ1 inhibited the gene expression of the NOTCH effectors Hes-1 and Hey-1 in NTS-injured kidneys. Our results further support the role for epigenetic drugs, such as iBETs, in the treatment of rapidly progressive crescentic glomerulonephritis.

Discovery of novel 4-phenylquinazoline-based BRD4 inhibitors for cardiac fibrosis

Bromodomain containing protein 4 (BRD4), as an epigenetic reader, can specifically bind to the acetyl lysine residues of histones and has emerged as an attractive therapeutic target for various diseases, including cancer, cardiac remodeling and heart failure. Herein, we described the discovery of hit 5 bearing 4-phenylquinazoline skeleton through a high-throughput virtual screen using 2,003,400 compound library (enamine). Then, structure-activity relationship (SAR) study was performed and 47 new 4-phenylquinazoline derivatives toward BRD4 were further designed, synthesized and evaluated, using HTRF assay set up in our lab. Eventually, we identified compound C-34, which possessed better pharmacokinetic and physicochemical properties as well as lower cytotoxicity against NRCF and NRCM cells, compared to the positive control JQ1. Using computer-based molecular docking and cellular thermal shift assay, we further verified that C-34 could target BRD4 at molecular and cellular levels. Furthermore, treatment with C-34 effectively alleviated fibroblast activation in vitro and cardiac fibrosis in vivo, which was correlated with the decreased expression of BRD4 downstream target c-MYC as well as the depressed TGF-β1/Smad2/3 signaling pathway. Taken together, our findings indicate that novel BRD4 inhibitor C-34 tethering a 4-phenylquinazoline scaffold can serve as a lead compound for further development to treat fibrotic cardiovascular disease.

Epigenetics-based therapeutics for myocardial fibrosis

Myocardial fibrosis (MF) is a reactive remodeling process in response to myocardial injury. It is mainly manifested by the proliferation of cardiac muscle fibroblasts and secreting extracellular matrix (ECM) proteins to replace damaged tissue. However, the excessive production and deposition of extracellular matrix, and the rising proportion of type I and type III collagen lead to pathological fibrotic remodeling, thereby facilitating the development of cardiac dysfunction and eventually causing heart failure with heightened mortality. Currently, the molecular mechanisms of MF are still not fully understood. With the development of epigenetics, it is found that epigenetics controls the transcription of pro-fibrotic genes in MF by DNA methylation, histone modification and noncoding RNAs. In this review, we summarize and discuss the research progress of the mechanisms underlying MF from the perspective of epigenetics, including the newest m6A modification and crosstalk between different epigenetics in MF. We also offer a succinct overview of promising molecules targeting epigenetic regulators, which may provide novel therapeutic strategies against MF.

BRD4 inhibition by JQ1 prevents high-fat diet-induced diabetic cardiomyopathy by activating PINK1/Parkin-mediated mitophagy in vivo

BRD4 is a member of the BET family of epigenetic regulators. Inhibition of BRD4 by the selective bromodomain inhibitor JQ1, alleviates thoracic aortic constriction-induced cardiac hypertrophy and heart failure. However, whether BRD4 inhibition by JQ1 has therapeutic effect on diabetic cardiomyopathy, a major cause of heart failure in patients with Type 2 diabetes, remains unknown. Here, we discover a novel link between BRD4 and PINK1/Parkin-mediated mitophagy during diabetic cardiomyopathy. Upregulation of BRD4 in diabetic mouse hearts inhibits PINK1/Parkin-mediated mitophagy, resulting in accumulation of damaged mitochondria and subsequent impairment of cardiac structure and function. BRD4 inhibition by JQ1 improves mitochondrial function, and repairs the cardiac structure and function of the diabetic heart. These effects depended on rewiring of the BRD4-driven transcription and repression of PINK1. Deletion of Pink1 suppresses mitophagy, exacerbates cardiomyopathy, and abrogates the therapeutic effect of JQ1 on diabetic cardiomyopathy. Our results illustrate a valid therapeutic strategy for treating diabetic cardiomyopathy by inhibition of BRD4.

Epigenetic Modifiers as Potential Therapeutic Targets in Diabetic Kidney Disease

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications-histone methylation, acetylation and crotonylation-in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of β-hydroxybutyrate, a molecule that generates a specific histone modification, β-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio- and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.

Specific Inhibition of CYP4A Alleviates Myocardial Oxidative Stress and Apoptosis Induced by Advanced Glycation End-Products

High exposure to advanced glycation end-products (AGEs) may induce cardiotoxicity. However, the effects and mechanisms remain to be further clarified. CYP4A plays an important role in the pathophysiological process of myocardial abnormalities by modulating oxidative stress and apoptosis (OS/Apop) signaling pathway. The present work aimed to investigate whether CYP4A mediates AGEs-induced myocardial injury. AGEs solution was administered intragastrically to C57BL/6 mice for 60 days, while the specific inhibitor of CYP4A, HET0016, was given from the 47th day via intraperitoneal injection for 2 weeks. Levels of OS/Apop in heart tissue were measured. The effects on the cell viability and apoptosis were detected in primary rat cardiomyocytes. To further investigate the mechanism, H9c2 cells were treated with HET0016 or small interfering RNAs (siRNAs) against CYP4a mRNA before incubation with AGEs. Exposure to AGEs led to significantly increased expression of CYP4A and levels of OS/Apop in heart and H9c2 cells both in vivo and in vitro. The OS/Apop pathway was activated with increased expression of NOX2, p-JNK, and cleaved caspase-3 (c-caspase-3) and decreased expression of p-Akt and Bcl-xL both in vivo and in vitro. Specific CYP4A suppression by HET0016 or siRNA exerted significant protective effects by attenuating AGEs-induced OS/Apop pathways in vitro. Our results demonstrate that specific inhibition of CYP4A might be a potential therapeutic option for myocardial injury induced by AGEs.

Drugging transcription in heart failure

Advances in our understanding of the basic biology and biochemistry of chromatin structure and function at genome scales has led to tremendous growth in the fields of epigenomics and transcriptional biology. While it has long been appreciated that transcriptional pathways are dysregulated in failing hearts, only recently has the idea of disrupting altered transcription by targeting chromatin-associated proteins been explored. Here, we provide a brief overview of efforts to drug transcription in the context of heart failure, focusing on the bromo- and extra-terminal domain (BET) family of chromatin co-activator proteins.