Brahma-related gene 1 bridges epigenetic regulation of proinflammatory cytokine production to steatohepatitis in mice

Chromatin accessibility: biological functions, molecular mechanisms and therapeutic application

The dynamic regulation of chromatin accessibility is one of the prominent characteristics of eukaryotic genome. The inaccessible regions are mainly located in heterochromatin, which is multilevel compressed and access restricted. The remaining accessible loci are generally located in the euchromatin, which have less nucleosome occupancy and higher regulatory activity. The opening of chromatin is the most important prerequisite for DNA transcription, replication, and damage repair, which is regulated by genetic, epigenetic, environmental, and other factors, playing a vital role in multiple biological progresses. Currently, based on the susceptibility difference of occupied or free DNA to enzymatic cleavage, solubility, methylation, and transposition, there are many methods to detect chromatin accessibility both in bulk and single-cell level. Through combining with high-throughput sequencing, the genome-wide chromatin accessibility landscape of many tissues and cells types also have been constructed. The chromatin accessibility feature is distinct in different tissues and biological states. Research on the regulation network of chromatin accessibility is crucial for uncovering the secret of various biological processes. In this review, we comprehensively introduced the major functions and mechanisms of chromatin accessibility variation in different physiological and pathological processes, meanwhile, the targeted therapies based on chromatin dynamics regulation are also summarized.

Direct degradation and stabilization of proteins: New horizons in treatment of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is featured with excessive hepatic lipid accumulation and its global prevalence is soaring. Nonalcoholic steatohepatitis (NASH), the severe systemic inflammatory subtype of NAFLD, is tightly associated with metabolic comorbidities, and the hepatocytes manifest severe inflammation and ballooning. Currently the therapeutic options for treating NASH are limited. Potent small molecules specifically intervene with the signaling pathways that promote pathogenesis of NASH. Nevertheless they have obvious adverse effects and show long-term ineffectiveness in clinical trials. It poses the fundamental question to efficiently and safely inhibit the pathogenic processes. Targeted protein degradation (TPD) belongs to the direct degradation strategies and is a burgeoning strategy. It utilizes the small molecules to bind to the target proteins and recruit the endogenous proteasome, lysosome and autophagosome-mediated degradation machineries. They effectively and specifically degrade the target proteins. It has exhibited promising therapeutic effects in treatment of cancer, neurodegenerative diseases and other diseases in a catalytic manner at low doses. We critically discuss the principles of multiple direct degradation strategies, especially PROTAC and ATTEC. We extensively analyze their emerging application in degradation of excessive pathogenic proteins and lipid droplets, which promote the progression of NASH. Moreover, we discuss the opposite strategy that utilizes the small molecules to recruit deubiquinases to stabilize the NASH/MASH-suppressing proteins. Their advantages, limitations, as well as the solutions to address the limitations have been analyzed. In summary, the innovative direct degradation strategies provide new insights into design of next-generation therapeutics to combat NASH with optimal safety paradigm and efficiency.

Hepatocellular Brg1 promotes CCl4-induced liver inflammation, ECM accumulation and fibrosis in mice

INTRODUCTION

Hepatic fibrosis is a progressive pathological process involving the exhaustion of hepatocellular regenerative capacity and ultimately leading to the development of cirrhosis and even hepatocellular carcinoma. Brg1, the core subunit of the SWI/SNF chromatin-remodeling complex, was recently identified as important for liver regeneration. This study investigates the role of Brg1 in hepatic fibrosis development.

METHODS

Hepatocyte-specific Brg1 knockout mice were generated and injected with carbon tetrachloride (CCl4) for 4, 6, 8, and 12 weeks to induce liver fibrosis. Afterwards, liver fibrosis and liver damage were assessed.

RESULTS

Brg1 expression was significantly increased in the fibrotic liver tissue of wild-type mice, as compared to that of untreated wild-type mice. The livers of the Brg1 knockout animals showed reduced liver inflammation, extracellular matrix accumulation, and liver fibrosis. TNF-α and NF-κB-mediated inflammatory response was reduced in Brg1 knockout animals.

CONCLUSION

Brg1 promotes the progression of liver fibrosis in mice and may therefore be used as a potential therapeutic target for treating patients with liver fibrosis due to chronic injury.

Accumulation of endogenous adenosine improves cardiomyocyte metabolism via epigenetic reprogramming in an ischemia-reperfusion model

Adenosine kinase (ADK) plays the major role in cardiac adenosine metabolism, so that inhibition of ADK increases myocardial adenosine levels. While the cardioprotective actions of extracellular adenosine against ischemia/reperfusion (I/R) are well-established, the role of cellular adenosine in protection against I/R remains unknown. Here we investigated the role of cellular adenosine in epigenetic regulation on cardiomyocyte gene expression, glucose metabolism and tolerance to I/R. Evans blue/TTC staining and echocardiography were used to assess the extent of I/R injury in mice. Glucose metabolism was evaluated by positron emission tomography and computed tomography (PET/CT). Methylated DNA immunoprecipitation (MeDIP) and bisulfite sequencing PCR (BSP) were used to evaluate DNA methylation. Lentiviral/adenovirus transduction was used to overexpress DNMT1, and the OSI-906 was administered to inhibit IGF-1. Cardiomyocyte-specific ADK/IGF-1-knockout mice were used for mechanistic experiments.Cardiomyocyte-specific ADK knockout enhanced glucose metabolism and ameliorated myocardial I/R injury in vivo. Mechanistically, ADK deletion caused cellular adenosine accumulation, decreased DNA methyltransferase 1 (DNMT1) expression and caused hypomethylation of multiple metabolic genes, including insulin growth factor 1 (IGF-1). DNMT1 overexpression abrogated these beneficial effects by enhancing apoptosis and decreasing IGF-1 expression. Inhibition of IGF-1 signaling with OSI-906 or genetic knocking down of IGF-1 also abrogated the cardioprotective effects of ADK knockout, revealing the therapeutic potential of increasing IGF-1 expression in attenuating myocardial I/R injury. In conclusion, the present study demonstrated that cardiomyocyte ADK deletion ameliorates myocardial I/R injury via epigenetic upregulation of IGF-1 expression via the cardiomyocyte adenosine/DNMT1/IGF-1 axis.

Targeting the chromatin remodeling protein BRG1 in liver fibrosis: Mechanism and translational potential

AIMS

Liver fibrosis is characterized by excessive deposition of extracellular matrix (ECM) proteins in the interstitia. Hepatic stellate cells (HSCs) are considered the major source for ECM-producing myofibroblasts contributing to liver fibrosis. The molecular mechanism whereby HSC-myofibroblast transition is regulated remains incompletely understood. We investigated the involvement of BRG1, a chromatin remodeling protein, in this process.

METHODS

Rosa26-Smarca4 mice were crossed to Lrat-Cre mice to generate HSC-specific BRG1 transgenic mice. Liver fibrosis was induced by bile duct ligation (BDL) or injection with carbon tetrachloride (CCl4).

RESULTS

We report here that over-expression of BRG1 promoted HSC-myofibroblast transition in vitro. More importantly, the BRG1 transgenic mice displayed amplification of liver fibrogenesis, induced by BDL or CCl4 injection, compared to the wild type littermates. On the contrary, BRG1 inhibition by a small-molecule compound (PFI-3) attenuated HSC-myofibroblast transition in vitro and ameliorated liver fibrosis in a dose-dependent manner in mice. RNA-seq analysis showed that PFI-3 treatment preferentially influenced the expression of ECM genes in activated HSCs.

CONCLUSION

Our data provide strong evidence that BRG1 plays an important role in HSC-myofibroblast transition and suggest that targeting BRG1 could be considered as a reasonable strategy for the intervention of liver fibrosis.

Stachydrine Hydrochloride Regulates the NOX2-ROS-Signaling Axis in Pressure-Overload-Induced Heart Failure

Our previous studies revealed the protection of stachydrine hydrochloride (STA) against cardiopathological remodeling. One of the underlying mechanisms involves the calcium/calmodulin-dependent protein kinase Ⅱ (CaMKII). However, the way STA influences CaMKII needs to be further investigated. The nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2)-coupled reactive oxygen species (ROS) overproduction putatively induces the oxidative activation of CaMKII, resulting in the occurrence of pathological cardiac remodeling and dysfunction in experimental models of mice. Thus, in this study, we assessed the role of the NOX2-ROS signal axis in STA cardioprotection. The transverse aortic constriction (TAC)-induced heart failure model of mice, the phenylephrine-induced hypertrophic model of neonatal rat primary cardiomyocytes, and the H2O2-induced oxidative stress models of adult mouse primary cardiomyocytes and H9c2 cells were employed. The echocardiography and histological staining were applied to assess the cardiac effect of STA (6 mg/kg/d or 12 mg/kg/d), which was given by gavage. NOX2, ROS, and excitation-contraction (EC) coupling were detected by Western blotting, immunofluorescence, and calcium transient-contraction synchronous recordings. ROS and ROS-dependent cardiac fibrosis were alleviated in STA-treated TAC mice, demonstrating improved left ventricular ejection fraction and hypertrophy. In the heart failure model of mice and the hypertrophic model of cardiomyocytes, STA depressed NOX2 protein expression and activation, as shown by inhibited translocation of its phosphorylation, p67phox and p47phox, from the cytoplasm to the cell membrane. Furthermore, in cardiomyocytes under oxidative stress, STA suppressed NOX2-related cytosolic Ca2+ overload, enhanced cell contractility, and decreased Ca2+-dependent regulatory protein expression, including CaMKⅡ and Ryanodine receptor calcium release channels. Cardioprotection of STA against pressure overload-induced pathological cardiac remodeling correlates with the NOX2-coupled ROS signaling cascade.

Targetable Brg1-CXCL14 axis contributes to alcoholic liver injury by driving neutrophil trafficking

Alcoholic liver disease (ALD) accounts for a large fraction of patients with cirrhosis and hepatocellular carcinoma. In the present study we investigated the involvement of Brahma-related gene 1 (Brg1) in ALD pathogenesis and implication in ALD intervention. We report that Brg1 expression was elevated in mouse models of ALD, in hepatocyte exposed to alcohol, and in human ALD specimens. Manipulation of Brg1 expression in hepatocytes influenced the development of ALD in mice. Flow cytometry showed that Brg1 deficiency specifically attenuated hepatic infiltration of Ly6G⁺ neutrophils in the ALD mice. RNA-seq identified C-X-C motif chemokine ligand 14 (CXCL14) as a potential target for Brg1. CXCL14 knockdown alleviated whereas CXCL14 over-expression enhanced ALD pathogenesis in mice. Importantly, pharmaceutical inhibition of Brg1 with a small-molecule compound PFI-3 or administration of an antagonist to the CXCL14 receptor ameliorated ALD pathogenesis in mice. Finally, a positive correlation between Brg1 expression, CXCL14 expression, and neutrophil infiltration was detected in ALD patients. In conclusion, our data provide proof-of-concept for targeting the Brg1-CXCL14 axis in ALD intervention.

Dnmt1/Tet2-mediated changes in Cmip methylation regulate the development of nonalcoholic fatty liver disease by controlling the Gbp2-Pparγ-CD36 axis

Dynamic alteration of DNA methylation leads to various human diseases, including nonalcoholic fatty liver disease (NAFLD). Although C-Maf-inducing protein (Cmip) has been reported to be associated with NAFLD, its exact underlying mechanism remains unclear. Here, we aimed to elucidate this mechanism in NAFLD in vitro and in vivo. We first identified alterations in the methylation status of the Cmip intron 1 region in mouse liver tissues with high-fat high-sucrose diet-induced NAFLD. Knockdown of DNA methyltransferase (Dnmt) 1 significantly increased Cmip expression. Chromatin immunoprecipitation assays of AML12 cells treated with oleic and palmitic acid (OPA) revealed that Dnmt1 was dissociated and that methylation of H3K27me3 was significantly decreased in the Cmip intron 1 region. Conversely, the knockdown of Tet methylcytosine dioxygenase 2 (Tet2) decreased Cmip expression. Following OPA treatment, the CCCTC-binding factor (Ctcf) was recruited, and H3K4me3 was significantly hypermethylated. Intravenous Cmip siRNA injection ameliorated NAFLD pathogenic features in ob/ob mice. Additionally, Pparγ and Cd36 expression levels were dramatically decreased in the livers of ob/ob mice administered siCmip, and RNA sequencing revealed that Gbp2 was involved. Gbp2 knockdown also induced a decrease in Pparγ and Cd36 expression, resulting in the abrogation of fatty acid uptake into cells. Our data demonstrate that Cmip and Gbp2 expression levels are enhanced in human liver tissues bearing NAFLD features. We also show that Dnmt1-Trt2/Ctcf-mediated reversible modulation of Cmip methylation regulates the Gbp2-Pparγ-Cd36 signaling pathway, indicating the potential of Cmip as a novel therapeutic target for NAFLD.

Multiomics analysis of the impact of polychlorinated biphenyls on environmental liver disease in a mouse model

Exposure to high fat diet (HFD) and persistent organic pollutants including polychlorinated biphenyls (PCBs) is associated with liver injury in human populations and non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) in animal models. Previously, exposure of HFD-fed male mice to the non-dioxin-like (NDL) PCB mixture Aroclor1260, dioxin-like (DL) PCB126, or Aroclor1260 + PCB126 co-exposure caused toxicant-associated steatohepatitis (TASH) and differentially altered the liver proteome. Here unbiased mRNA and miRNA sequencing (mRNA- and miRNA- seq) was used to identify biological pathways altered in these liver samples. Fewer transcripts and miRs were up- or down- regulated by PCB126 or Aroclor1260 compared to the combination, suggesting that crosstalk between the receptors activated by these PCBs amplifies changes in the transcriptome. Pathway enrichment analysis identified "positive regulation of Wnt/β-catenin signaling" and "role of miRNAs in cell migration, survival, and angiogenesis" for differentially expressed mRNAs and miRNAs, respectively. We evaluated the five miRNAs increased in human plasma with PCB exposure and suspected TASH and found that miR-192-5p was increased with PCB exposure in mouse liver. Although we observed little overlap between differentially expressed mRNA transcripts and proteins, biological pathway-relevant PCB-induced miRNA-mRNA and miRNA-protein inverse relationships were identified that may explain protein changes. These results provide novel insights into miRNA and mRNA transcriptome changes playing direct and indirect roles in the functional protein pathways in PCB-related hepatic lipid accumulation, inflammation, and fibrosis in a mouse model of TASH and its relevance to human liver disease in exposed populations.

Epigenetic Reprogramming of the Inflammatory Response in Obesity and Type 2 Diabetes

For the past several decades, the prevalence of obesity and type 2 diabetes (T2D) has continued to rise on a global level. The risk contributing to this pandemic implicates both genetic and environmental factors, which are functionally integrated by epigenetic mechanisms. While these conditions are accompanied by major abnormalities in fuel metabolism, evidence indicates that altered immune cell functions also play an important role in shaping of obesity and T2D phenotypes. Interestingly, these events have been shown to be determined by epigenetic mechanisms. Consistently, recent epigenome-wide association studies have demonstrated that immune cells from obese and T2D individuals feature specific epigenetic profiles when compared to those from healthy subjects. In this work, we have reviewed recent literature reporting epigenetic changes affecting the immune cell phenotype and function in obesity and T2D. We will further discuss therapeutic strategies targeting epigenetic marks for treating obesity and T2D-associated inflammation.

Trans-activation of eotaxin-1 by Brg1 contributes to liver regeneration

Infiltration of eosinophils is associated with and contributes to liver regeneration. Chemotaxis of eosinophils is orchestrated by the eotaxin family of chemoattractants. We report here that expression of eotaxin-1 (referred to as eotaxin hereafter), but not that of either eotaxin-2 or eotaxin-3, were elevated, as measured by quantitative PCR and ELISA, in the proliferating murine livers compared to the quiescent livers. Similarly, exposure of primary murine hepatocytes to hepatocyte growth factor (HGF) stimulated eotaxin expression. Liver specific deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated eosinophil infiltration and down-regulated eotaxin expression in mice. Brg1 deficiency also blocked HGF-induced eotaxin expression in cultured hepatocytes. Further analysis revealed that Brg1 could directly bind to the proximal eotaxin promoter to activate its transcription. Mechanistically, Brg1 interacted with nuclear factor kappa B (NF-κB)/RelA to activate eotaxin transcription. NF-κB knockdown or pharmaceutical inhibition disrupted Brg1 recruitment to the eotaxin promoter and blocked eotaxin induction in hepatocytes. Adenoviral mediated over-expression of eotaxin overcame Brg1 deficiency caused delay in liver regeneration in mice. On the contrary, eotaxin depletion with RNAi or neutralizing antibodies retarded liver regeneration in mice. More important, Brg1 expression was detected to be correlated with eotaxin expression and eosinophil infiltration in human liver specimens. In conclusion, our data unveil a novel role of Brg1 as a regulator of eosinophil trafficking by activating eotaxin transcription.

Dual Regulation of Tank Binding Kinase 1 by BRG1 in Hepatocytes Contributes to Reactive Oxygen Species Production

Excessive accumulation of reactive oxygen species (ROS) is considered a major culprit for the pathogenesis of non-alcoholic fatty liver disease (NAFLD). We have previously shown that deletion of Brahma related gene 1 (BRG1) mitigated NAFLD in mice in part by attenuating ROS production in hepatocyte. Here we report that BRG1 deletion led to simultaneous down-regulation in expression and phosphorylation of tank binding kinase 1 (TBK1) in vivo and in vitro. On the one hand, BRG1 interacted with AP-1 to bind to the TBK1 promoter and directly activated TBK1 transcription in hepatocytes. On the other hand, BRG1 interacted with Sp1 to activate the transcription of c-SRC, a tyrosine kinase essential for TBK1 phosphorylation. Over-expression of c-SRC and TBK1 corrected the deficiency in ROS production in BRG1-null hepatocytes whereas depletion of TBK1 or c-SRC attenuated ROS production. In conclusion, our data suggest that dual regulation of TBK1 activity, at the transcription level and the post-transcriptional level, by BRG1 may constitute an important mechanism underlying excessive ROS production in hepatocytes.

Binding specificity and function of the SWI/SNF subunit SMARCA4 bromodomain interaction with acetylated histone H3K14

Bromodomains (BD) are conserved reader modules that bind acetylated lysine residues on histones. Although much has been learned regarding the in vitro properties of these domains, less is known about their function within chromatin complexes. SWI/SNF chromatin-remodeling complexes modulate transcription and contribute to DNA damage repair. Mutations in SWI/SNF subunits have been implicated in many cancers. Here we demonstrate that the BD of Caenorhabditis elegans SMARCA4/BRG1, a core SWI/SNF subunit, recognizes acetylated lysine 14 of histone H3 (H3K14ac), similar to its Homo sapiens ortholog. We identify the interactions of SMARCA4 with the acetylated histone peptide from a 1.29 Å-resolution crystal structure of the CeSMARCA4 BD-H3K14ac complex. Significantly, most of the SMARCA4 BD residues in contact with the histone peptide are conserved with other proteins containing family VIII bromodomains. Based on the premise that binding specificity is conserved among bromodomain orthologs, we propose that loop residues outside of the binding pocket position contact residues to recognize the H3K14ac sequence. CRISPR-Cas9-mediated mutations in the SMARCA4 BD that abolish H3K14ac binding in vitro had little or no effect on C. elegans viability or physiological function in vivo. However, combining SMARCA4 BD mutations with knockdown of the SWI/SNF accessory subunit PBRM-1 resulted in severe developmental defects in animals. In conclusion, we demonstrated an essential function for the SWI/SNF bromodomain in vivo and detected potential redundancy in epigenetic readers in regulating chromatin remodeling. These findings have implications for the development of small-molecule BD inhibitors to treat cancers and other diseases.

Epigenetic Remodeling in Obesity-Related Vascular Disease

Significance: The prevalence of obesity and cardiometabolic phenotypes is alarmingly increasing across the globe and is associated with atherosclerotic vascular complications and high mortality. In spite of multifactorial interventions, vascular residual risk remains high in this patient population, suggesting the need for breakthrough therapies. The mechanisms underpinning obesity-related vascular disease remain elusive and represent an intense area of investigation. Recent Advances: Epigenetic modifications-defined as environmentally induced chemical changes of DNA and histones that do not affect DNA sequence-are emerging as a potent modulator of gene transcription in the vasculature and might significantly contribute to the development of obesity-induced endothelial dysfunction. DNA methylation and histone post-translational modifications cooperate to build complex epigenetic signals, altering transcriptional networks that are implicated in redox homeostasis, mitochondrial function, vascular inflammation, and perivascular fat homeostasis in patients with cardiometabolic disturbances. Critical Issues: Deciphering the epigenetic landscape in the vasculature is extremely challenging due to the complexity of epigenetic signals and their function in regulating transcription. An overview of the most important epigenetic pathways is required to identify potential molecular targets to treat or prevent obesity-related endothelial dysfunction and atherosclerotic disease. This would enable the employment of precision medicine approaches in this setting. Future Directions: Current and future research efforts in this field entail a better definition of the vascular epigenome in obese patients as well as the unveiling of novel, cell-specific chromatin-modifying drugs that are able to erase specific epigenetic signals that are responsible for maladaptive transcriptional alterations and vascular dysfunction in obese patients. Antioxid. Redox Signal. 34, 1165-1199.

Myocardin-related transcription factor A (MRTF-A) regulates integrin beta 2 transcription to promote macrophage infiltration and cardiac hypertrophy in mice

AIMS

Macrophage-mediated inflammatory response represents a key pathophysiological process in a host of cardiovascular diseases including heart failure. Regardless of etiology, heart failure is invariably preceded by cardiac hypertrophy. In the present study we investigated the effect of macrophage-specific deletion of myocardin-related transcription factor A (MRTF-A) on cardiac hypertrophy and the underlying mechanism.

METHODS AND RESULTS

We report that when subjected to transverse aortic constriction (TAC), macrophage MRTF-A conditional knockout (CKO) mice developed a less severe phenotype of cardiac hypertrophy compared to wild type (WT) littermates and were partially protected from the loss of heart function. In addition, there was less extensive cardiac fibrosis in the CKO mice than WT mice following the TAC procedure. Further analysis revealed that cardiac inflammation, as assessed by levels of pro-inflammatory cytokines and chemokines, was dampened in CKO mice paralleling reduced infiltration of macrophages in the heart. Mechanistically, MRTF-A deficiency attenuated the expression of integrin beta 2 (ITGB2/CD18) in macrophage thereby disrupting adhesion of macrophages to vascular endothelial cells. MRTF-A was recruited by Sp1 to the ITGB2 promoter and cooperated with Sp1 to activate ITGB2 transcription in macrophages. Administration of a CD18 blocking antibody attenuated TAC induced cardiac hypertrophy in mice. Interaction between MRTF-A and the histone demethylase KDM3A likely contributed to IGTB2 transcription and consequently adhesion of macrophages to endothelial cells.

CONCLUSIONS

Our data suggest that MRTF-A may regulate macrophage trafficking and contribute to the pathogenesis of cardiac hypertrophy by activating ITGB2 transcription.

BRG1 Mediates Nephronectin Activation in Hepatocytes to Promote T Lymphocyte Infiltration in ConA-Induced Hepatitis

Fulminant hepatitis (FH) is a major cause of acute liver failure. Concanavalin A (ConA) belongs to the lectin family and is frequently used as an inducer of FH in animal models. ConA induced FH is characterized by massive accumulation of T lymphocytes in the liver. A host of chemoattractive substances are known to promote T cell homing to the liver during acute hepatitis. Here we investigated the involvement of Brahma-related gene 1 (BRG1), a chromatin remodeling protein, in FH. BRG1-flox mice were crossed to Alb-Cre mice to generate hepatocyte conditional BRG1 knockout (LKO) mice. The mice were peritoneally injected with a single dose of ConA to induce FH. BRG1 deficiency mitigated ConA-induced FH in mice. Consistently, there were fewer T lymphocyte infiltrates in the LKO livers compared to the wild type (WT) livers paralleling downregulation of T cell specific cytokines. Further analysis revealed that BRG1 deficiency repressed the expression of several chemokines critical for T cell homing including nephronectin (Npnt). BRG1 knockdown blocked the induction of Npnt in hepatocytes and attenuated T lymphocyte migration in vitro, which was reversed by the addition of recombinant nephronectin. Mechanistically, BRG1 interacted with β-catenin to directly bind to the Npnt promoter and activate Npnt transcription. Importantly, a positive correlation between infiltration of CD3⁺ T lymphocyes and nephronectin expression was detected in human acute hepatitis biopsy specimens. In conclusion, our data identify a novel role for BRG1 as a promoter of T lymphocyte trafficking by activating Npnt transcription in hepatocytes. Targeting the BRG1-Npnt axis may yield novel therapeutic solutions for FH.

Targeting chromatin dysregulation in organ fibrosis

Fibrosis leads to destruction of organ architecture accompanied by chronic inflammation and loss of function. Fibrosis affects nearly every organ in the body and accounts for ∼45% of total deaths worldwide. Over the past decade, tremendous progress has been made in understanding the basic mechanisms leading to organ fibrosis. However, we are limited with therapeutic options and there is a significant need to develop highly effective anti-fibrotic therapies. Recent advances in sequencing technologies have advanced the burgeoning field of epigenetics towards molecular understanding at a higher resolution. Here we provide a comprehensive review of the recent advances in chromatin regulatory processes, specifically DNA methylation, post-translational modification of histones, and chromatin remodeling complexes in kidney, liver and lung fibrosis. Although this research field is young, we discuss new strategies for potential therapeutic interventions for treating organ fibrosis.

Transcriptional Activation of Matricellular Protein Spondin2 (SPON2) by BRG1 in Vascular Endothelial Cells Promotes Macrophage Chemotaxis

The matricellular protein SPON2 plays diverse roles in the development of cardiovascular diseases. SPON2 is expressed in endothelial cells, but its transcription regulation in the context of atherogenesis remains incompletely appreciated. Here we report that SPON2 expression was up-regulated by pro-atherogenic stimuli (oxLDL and TNF-α) in vascular endothelia cells. In addition, endothelial SPON2 was elevated in Apoe^–/– mice fed on a Western diet compared to the control mice. Induction of SPON2 in endothelial cells by pro-atherogenic stimuli was mediated by BRG1, a chromatin remodeling protein, both in vitro and in vivo. Further analysis revealed that BRG1 interacted with the sequence-specific transcription factor Egr-1 to activate SPON2 transcription. BRG1 contributed to SPON2 trans-activation by modulating chromatin structure surrounding the SPON2 promoter. Functionally, activation of SPON2 transcription by the Egr-1/BRG1 complex provided chemoattractive cues for macrophage trafficking. SPON2 depletion abrogated the ability of BRG1 or Egr-1 to stimulate endothelial derived chemoattractive cue for macrophage migration. On the contrary, recombinant SPON2 rescued endothelial chemo-attractability in the absence of BRG1 or Egr-1. In conclusion, our data have identified a novel transcriptional cascade in endothelial cells that may potentially promote macrophage recruitment and vascular inflammation leading to atherogenesis.

New Mechanisms of Vascular Dysfunction in Cardiometabolic Patients: Focus on Epigenetics

Epigenetic processing takes centre stage in cardiometabolic diseases (obesity, metabolic syndrome, type 2 diabetes, hypertension), where it participates in adiposity, inflammation, endothelial dysfunction, vascular insulin resistance and atherosclerosis. Epigenetic modifications, defined as heritable changes in gene expression that do not entail mutation in the DNA sequence, are mainly induced by environmental stimuli (stress, pollution, cigarette smoking) and are gaining considerable interest due to their causal role in cardiovascular disease, and their amenability to pharmacological intervention. Importantly, epigenetic modifications acquired during life can be transmitted to the offspring and exert their biological effects across multiple generations. Indeed, such transgenerational transmission of epigenetic signals may contribute to anticipating cardiovascular and metabolic disease phenotypes already in children and young adults. A deeper understanding of environmental factors and their effects on the epigenetic machinery and transcriptional programs is warranted to develop effective mechanism-based therapeutic strategies. The clinical application of epigenetic drugs-also known as "epi-drugs"-is currently exploding in the field of cardiovascular disease. The present review describes the main epigenetic networks underlying cardiometabolic alterations and sheds light on specific points of intervention for pharmacological reprogramming in this setting.

Brahma Related Gene 1 (Brg1) Regulates Cellular Cholesterol Synthesis by Acting as a Co-factor for SREBP2

Hepatocyte is a hub for cholesterol metabolism. Augmented synthesis of cholesterol in the liver is associated with hypercholesterolemia and contributes to the pathogenesis of a host of cardiovascular and metabolic diseases. Sterol response element binding protein 2 (SREBP2) regulates hepatic cholesterol metabolism by activating the transcription of rate-limiting enzymes in the cholesterol biosynthesis pathway. The underlying epigenetic mechanism is not well understood. We report here that mice with hepatocyte-specific knockout (CKO) of Brg1, a chromatin remodeling protein, exhibit reduced levels of hepatic cholesterol compared to the wild type (WT) littermates when placed on a high-fact diet (HFD) or a methionine-and-choline-deficient diet (MCD). Down-regulation of cholesterol levels as a result of BRG1 deficiency was accompanied by attenuation of cholesterogenic gene transcription. Likewise, BRG1 knockdown in hepatocytes markedly suppressed the induction of cholesterogenic genes by lipid depletion formulas. Brg1 interacted with SREBP2 and was recruited by SREBP2 to the cholesterogenic gene promoters. Reciprocally, Brg1 deficiency dampened the occupancies of SREBP2 on target promoters likely through modulating H3K9 methylation on the cholesterogenic gene promoters. Mechanistically, Brg1 recruited the H3K9 methyltransferase KDM3A to co-regulate pro-cholesterogenic transcription. KDM3A silencing dampened the cholesterogenic response in hepatocytes equivalent to Brg1 deficiency. In conclusion, our data demonstrate a novel epigenetic pathway that contributes to SREBP2-dependent cholesterol synthesis in hepatocytes.

ARRB1 inhibits non-alcoholic steatohepatitis progression by promoting GDF15 maturation

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is associated with the dysregulation of lipid metabolism and hepatic inflammation. The causal mechanism underlying NASH is not fully elucidated. This study investigated the role of β-Arrestin1 (ARRB1) in the progression of NASH.

METHODS

Liver tissue from patients with NASH and controls were obtained to evaluate ARRB1 expression. NASH models were established in Arrb1-knockout and wild-type mice fed either a high-fat diet (HFD) for 26 weeks or a methionine/choline-deficient (MCD) diet for 6 weeks.

RESULTS

ARRB1 expression was reduced in liver samples from patients with NASH. Reduced Arrb1 levels were also detected in murine NASH models. Arrb1 deficiency accelerated steatohepatitis development in HFD-/MCD-fed mice (accompanied by the upregulation of lipogenic genes and downregulation of β-oxidative genes). Intriguingly, ARRB1 was found to interact with growth differentiation factor 15 (GDF15) and facilitated the transportation of GDF15 precursor (pro-GDF15) to the Golgi apparatus for cleavage and maturation. Treatment with recombinant GDF15 ablated the lipid accumulation in the presence of Arrb1 deletion both in vitro and in vivo. Re-expression of Arrb1 in the NASH models ameliorated the liver disease, and this effect was greater in the presence of pro-GDF15 overexpression. By contrast, the effect of pro-GDF15 overexpression alone was impaired in Arrb1-deficient mice. In addition, the severity of liver disease in patients with NASH was negatively correlated with ARRB1 expression.

CONCLUSION

ARRB1 acts as a vital regulator in the development of NASH by facilitating the translocation of GDF15 to the Golgi apparatus and its subsequent maturation. Thus, ARRB1 is a potential therapeutic target for the treatment of NASH.

LAY SUMMARY

Non-alcoholic steatohepatitis (NASH) is associated with the progressive dysfunction of lipid metabolism and a consequent inflammatory response. Decreased ARRB1 is observed in patients with NASH and murine NASH models. Re-expression of Arrb1 in the murine NASH model ameliorated liver disease, an effect which was more pronounced in the presence of pro-GDF15 overexpression, highlighting a promising strategy for NASH therapy.

The effects of epigenetic modification on the occurrence and progression of liver diseases and the involved mechanism

Introduction: Epigenetic modification is a type of gene expression and regulation that does not involve changes in DNA sequences. An increasing number of studies have proven that epigenetic modifications play an important role in the occurrence and progression of liver diseases through the gene regulation and protein expressions of hepatocellular lipid metabolism, inflammatory reaction, cell proliferation, and activation, etc.Areas covered: In this study, we elaborated and analyzed the underlying functional mechanism of epigenetic modification in alcoholic liver disease (ALD), nonalcoholic fatty liver disease (NAFLD), liver fibrosis (LF), viral hepatitis, hepatocellular carcinoma (HCC), and research progress of recent years.Expert opinion: The further understanding of epigenetic mechanisms that can regulate gene expression and cell phenotype leads to new insights in epigenetic control of chronic liver disease. Currently, hepatologists are exploring the role of DNA methylation, histone/chromatin modification, and non-coding RNA in specific liver pathology. These findings have led to advances in direct epigenetic biomarker testing of patient tissue or body fluid specimens, as well as quantitative analysis. Based on these findings, drug validation of some targets involved in the epigenetic mechanism of liver disease is gradually being carried out clinically.

Activation of Galectin-3 (LGALS3) Transcription by Injurious Stimuli in the Liver Is Commonly Mediated by BRG1

Galectin-3 (encoded by LGALS3) is a glycan-binding protein that regulates a diverse range of pathophysiological processes contributing to the pathogenesis of human diseases. Previous studies have found that galectin-3 levels are up-regulated in the liver by a host of different injurious stimuli. The underlying epigenetic mechanism, however, is unclear. Here we report that conditional knockout of Brahma related gene (BRG1), a chromatin remodeling protein, in hepatocytes attenuated induction of galectin-3 expression in several different animal models of liver injury. Similarly, BRG1 depletion or pharmaceutical inhibition in cultured hepatocytes suppressed the induction of galectin-3 expression by treatment with LPS plus free fatty acid (palmitate). Further analysis revealed that BRG1 interacted with AP-1 to bind to the proximal galectin-3 promoter and activate transcription. Mechanistically, DNA demethylation surrounding the galectin-3 promoter appeared to be a rate-limiting step in BRG1-mediated activation of galectin-3 transcription. BRG1 recruited the DNA 5-methylcytosine dioxygenase TET1 to the galectin-3 to promote active DNA demethylation thereby activating galectin-3 transcription. Finally, TET1 silencing abrogated induction of galectin-3 expression by LPS plus palmitate in cultured hepatocytes. In conclusion, our data unveil a novel epigenetic pathway that contributes to injury-associated activation of galectin-3 transcription in hepatocytes.

The Burden of Hepatocellular Carcinoma in Non-Alcoholic Fatty Liver Disease: Screening Issue and Future Perspectives

In recent decades, non-alcoholic fatty liver disease (NAFLD) has become the most common liver disease in the Western world, and the occurrence of its complications, such as hepatocellular carcinoma (HCC), has rapidly increased. Obesity and diabetes are considered not only the main triggers for the development of the disease, but also two independent risk factors for HCC. Single nucleotide polymorphisms (such as PNPLA3, TM6SF2 and MBOAT7) are related to the susceptibility to the development of HCC and its progression. Therefore, an appropriate follow-up of these patients is needed for the early diagnosis and treatment of HCC. To date, international guidelines recommend the use of ultrasonography with or without alpha-fetoprotein (AFP) in patients with advanced fibrosis. Furthermore, the use of non-invasive tools could represent a strategy to implement surveillance performance. In this review, we analyzed the main risk factors of NAFLD-related HCC, the validated screening methods and the future perspectives.

Megakaryocytic Leukemia 1 Bridges Epigenetic Activation of NADPH Oxidase in Macrophages to Cardiac Ischemia-Reperfusion Injury

BACKGROUND

Excessive accumulation of reactive oxygen species (ROS), catalyzed by the NADPH oxidases (NOX), is involved in the pathogenesis of ischemia-reperfusion (IR) injury. The underlying epigenetic mechanism remains elusive.

METHODS

We evaluated the potential role of megakaryocytic leukemia 1 (MKL1), as a bridge linking epigenetic activation of NOX to ROS production and cardiac ischemia-reperfusion injury.

RESULTS

Following IR injury, MKL1-deficient (knockout) mice exhibited smaller myocardial infarction along with improved heart function compared with wild-type littermates. Similarly, pharmaceutical inhibition of MKL1 with CCG-1423 also attenuated myocardial infarction and improved heart function in mice. Amelioration of IR injury as a result of MKL1 deletion or inhibition was accompanied by reduced ROS in vivo and in vitro. In response to IR, MKL1 levels were specifically elevated in macrophages, but not in cardiomyocytes, in the heart. Of note, macrophage-specific deletion (MϕcKO), instead of cardiomyocyte-restricted ablation (CMcKO), of MKL1 in mice led to similar improvements of infarct size, heart function, and myocardial ROS generation. Reporter assay and chromatin immunoprecipitation assay revealed that MKL1 directly bound to the promoters of NOX genes to activate NOX transcription. Mechanistically, MKL1 recruited the histone acetyltransferase MOF (male absent on the first) to modify the chromatin structure surrounding the NOX promoters. Knockdown of MOF in macrophages blocked hypoxia/reoxygenation-induced NOX transactivation and ROS accumulation. Of importance, pharmaceutical inhibition of MOF with MG149 significantly downregulated NOX1/NOX4 expression, dampened ROS production, and normalized myocardial function in mice exposed to IR injury. Finally, administration of a specific NOX1/4 inhibitor GKT137831 dampened ROS generation and rescued heart function after IR in mice.

CONCLUSIONS

Our data delineate an MKL1-MOF-NOX axis in macrophages that contributes to IR injury, and as such we have provided novel therapeutic targets in the treatment of ischemic heart disease.

Serum response factor (SRF) promotes ROS generation and hepatic stellate cell activation by epigenetically stimulating NCF1/2 transcription

Activation of hepatic stellate cells (HSC) is a hallmark event in liver fibrosis. Accumulation of reactive oxygen species (ROS) serves as a driving force for HSC activation. The regulatory subunits of the NOX complex, NCF1 (p47phox) and NCF2 (p67phox), are up-regulated during HSC activation contributing to ROS production and liver fibrosis. The transcriptional mechanism underlying NCF1/2 up-regulation is not clear. In the present study we investigated the role of serum response factor (SRF) in HSC activation focusing on the transcriptional regulation of NCF1/2. We report that compared to wild type littermates HSC-conditional SRF knockout (CKO) mice exhibited a mortified phenotype of liver fibrosis induced by thioacetamide (TAA) injection or feeding with a methionine-and-choline deficient diet (MCD). More importantly, SRF deletion attenuated ROS levels in HSCs in vivo. Similarly, SRF knockdown in cultured HSCs suppressed ROS production in vitro. Further analysis revealed that SRF deficiency resulted in repression of NCF1/NCF2 expression. Mechanistically, SRF regulated epigenetic transcriptional activation of NCF1/NCF2 by interacting with and recruiting the histone acetyltransferase KAT8 during HSC activation. In conclusion, we propose that SRF integrates transcriptional activation of NCF1/NCF2 and ROS production to promote liver fibrosis.

An interaction between MKL1, BRG1, and C/EBPβ mediates palmitate induced CRP transcription in hepatocytes

Non-alcoholic steatohepatitis (NASH) is one of the most predominant disorders in metabolic syndrome. Induction of pro-inflammatory mediators in hepatocytes exposed to free fatty acids represents a hallmark event during NASH pathogenesis. C-reactive protein (CRP) is a prototypical pro-inflammatory mediator. In the present study, we investigated the mechanism by which megakaryocytic leukemia 1 (MKL1) mediates palmitate (PA) induced CRP transcription in hepatocytes. We report that over-expression of MKL1, but not MKL2, activated the CRP promoter whereas depletion or inhibition of MKL1 repressed the CRP promoter. MKL1 potentiated the induction of the CRP promoter activity by PA treatment. Importantly, MKL1 knockdown by siRNA or pharmaceutical inhibition by CCG-1423 attenuated the induction of endogenous CRP expression in hepatocytes. Similarly, primary hepatocytes isolated from wild type (WT) mice produced more CRP than those isolated from MKL1 deficient (KO) mice when stimulated with PA. Mechanistically, the sequence-specific transcription factor CCAAT-enhancer-binding protein (C/EBPβ) interacted with MKL1 and recruited MKL1 to activate CRP transcription. Reciprocally, MKL1 modulated C/EBPβ activity by recruiting the chromatin remodeling protein BRG1 to the CRP promoter to alter histone modifications. In conclusion, our data delineate a novel epigenetic mechanism underlying augmented hepatic inflammation during NASH pathogenesis.

Endothelial-specific deletion of Brahma-related gene 1 (BRG1) assuages unilateral ureteral obstruction induced renal injury in mice

Renal homeostasis is regulated by the interplay among different cell types in the kidneys including endothelial cells. In the present study we investigated the phenotypic regulation of endothelial cells by BRG1, a chromatin remodeling protein, in a mouse model of obstructive nephropathy (ON). We report that endothelial-specific deletion of BRG1 attenuated renal inflammation induced by unilateral ureteral tract obstruction (UUO) in mice, as evidenced by down-regulation of pro-inflammatory cytokines and diminished infiltration of immune cells. Moreover, endothelial BRG1 deficiency suppressed UUO-induced renal fibrosis in mice as measured by expression of pro-fibrogenic genes, picrosirius red staining of collagenous tissues, and quantification of hydroxylproline levels. Mechanistically, BRG1 activated the transcription of adhesion molecules and chemokines in endothelial cells by recruiting histone modifying enzymes leading to macrophage adhesion and chemotaxis. In conclusion, we propose that epigenetic regulation of endothelial function by BRG1 may play an active role in ON pathogenesis.

MKL1 mediates TNF-α induced pro-inflammatory transcription by bridging the crosstalk between BRG1 and WDR5

Tumor necrosis factor alpha (TNF-α) is a cytokine that can potently stimulate the synthesis of a range of pro-inflammatory mediators in macrophages. The underlying epigenetic mechanism, however, is underexplored. Here we report that the transcriptional modulator megakaryocytic leukemia 1 (MKL1) is associated with a histone H3K4 methyltransferase activity. Re-ChIP assay suggests that MKL1 interacts with and recruits WDR5, a component of the COMPASS complex responsible for H3K4 methylation, to the promoter regions of pro-inflammatory genes in macrophages treated with TNF-α. WDR5 enhances the ability of MKL1 to stimulate the promoter activities of pro-inflammatory genes. In contrast, silencing of WDR5 attenuates TNF-α induced production of pro-inflammatory mediators and erases the H3K4 methylation from the gene promoters. Of interest, the chromatin remodeling protein BRG1 also plays an essential role in maintaining H3K4 methylation on MKL1 target promoters by interacting with WDR5. MKL1 knockdown disrupts the interaction between BRG1 and WDR5. Together, our data illustrate a role for MKL1 in moderating the crosstalk between BRG1 and WDR5 to activate TNF-α induced pro-inflammatory transcription in macrophages.

A Cross Talk Between BRG1 and Males Absent on the First Contributes to Reactive Oxygen Species Production in a Mouse Model of Nonalcoholic Steatohepatitis

Aims: Accumulation of reactive oxygen species (ROS) in hepatocytes in response to excessive nutrients and the ensuing liver damages caused by ROS constitute a key pathophysiological event in nonalcoholic steatohepatitis (NASH). In the present study, we investigated the epigenetic mechanism underlying ROS production in NASH pathogenesis. Results: NASH was induced by feeding the mice with a methionine-and-choline-deficient (MCD) diet for 4 weeks. Compared with the control mice (wild type [WT]), mice with hepatocyte-specific deletion of Brg1 (HepcKO), a core component of the mammalian chromatin remodeling complex, developed a less severe form of NASH when fed on the MCD diet. Importantly, ROS levels were attenuated in HepcKO mice as opposed to WT mice. Brahma-related gene 1 (Brg1) deficiency downregulated the transcription of NADPH oxidases (NOX1, NOX2, and NOX4) both in vivo and in vitro. Mechanistically, Brg1 deletion rendered a more repressive chromatin structure surrounding the NOX promoters as characterized by reduced levels of acetylated histones. In addition, Brg1 interacted with the histone H4K16 acetyltransferase males absent on the first (MOF) to activate NOX transcription. MOF knockdown by small interfering RNA or pharmaceutical inhibition by MG149 suppressed NOX transcription and ameliorated ROS levels. Innovation: Our data highlight a novel epigenetic mechanism through which Brg1 and MOF cooperate to regulate ROS production in hepatocytes in response to pro-NASH stimuli. Conclusion: A cross talk between Brg1 and MOF epigenetically activates NOX transcription and elevates ROS synthesis contributing to NASH pathogenesis.

Interplay between early-life malnutrition, epigenetic modulation of the immune function and liver diseases

Early-life nutrition plays a critical role in fetal growth and development. Food intake absence and excess are the two main types of energy malnutrition that predispose to the appearance of diseases in adulthood, according to the hypothesis of 'developmental origins of health and disease'. Epidemiological data have shown an association between early-life malnutrition and the metabolic syndrome in later life. Evidence has also demonstrated that nutrition during this period of life can affect the development of the immune system through epigenetic mechanisms. Thus, epigenetics has an essential role in the complex interplay between environmental factors and genetics. Altogether, this leads to the inflammatory response that is commonly seen in non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome. In conjunction, DNA methylation, covalent modification of histones and the expression of non-coding RNA are the epigenetic phenomena that affect inflammatory processes in the context of NAFLD. Here, we highlight current understanding of the mechanisms underlying developmental programming of NAFLD linked to epigenetic modulation of the immune system and environmental factors, such as malnutrition.

lncRNA MALAT1 binds chromatin remodeling subunit BRG1 to epigenetically promote inflammation-related hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one type of cancers whose carcinogenesis and progression are closely related to chronic inflammation. Identifying the molecular mechanisms for inflammation-related HCC progression will contribute to improve the efficacy of current therapeutics for HCC patients. Many kinds of epigenetic factors, including long non-coding RNAs (lncRNAs), have been discovered to be important in HCC growth and metastasis. However, how the lncRNAs promote HCC progression and what's the application of lncRNA silencing in vivo in suppressing HCC remain to be further investigated. Here, we found that lncRNA metastasis associated lung adenocarcinoma transcript1 (MALAT1) was upregulated in HCC tumor tissues, and knockdown of MALAT1 suppressed proliferation, cell cycle and invasion of HCC cells in response to lipopolysaccharide (LPS) stimulation. Knockdown of MALAT1 significantly inhibited LPS-induced pro-inflammatory mediators IL-6 and CXCL8 expression in HCC cells, which could be restored by overexpressing MALAT1. Mechanistically, MALAT1 recruited Brahma-related gene 1 (BRG1), a catalytic subunit of chromatin remodeling complex switching/sucrose non-fermentable (SWI/SNF), to the promoter region of IL-6 and CXCL8, and thus facilitated NF-κB to induce the expression of these inflammatory factors. Importantly, in vivo silencing of MALAT1 in HCC tissues inhibited growth of HCC xenografts, and also suppressed the expression of pro-inflammatory factors in HCC tissues accordingly. Our results demonstrate that MALAT1 promotes HCC progression by binding BRG1 to epigenetically enhance inflammatory response in HCC tissues, and silencing of MALAT1 may be a potential approach to the treatment of HCC.

Angiotensin II induced CSF1 transcription is mediated by a crosstalk between different epigenetic factors in vascular endothelial cells

Endothelium-derived colony stimulating factor (CSF1) plays a key role in a range of human pathologies. Angiotensin II (Ang II) has been documented to stimulate CSF1 transcription although the underlying epigenetic mechanism remains unclear. Here we report that induction of CSF1 transcription by Ang II in vascular endothelial cells paralleled alterations of signature histone modifications surrounding the CSF1 promoter. Specifically, ChIP assays indicated that there was a simultaneous up-regulation of both acetylated H3 and trimethylated H3K4, indicative of transcriptional activation, and down-regulation of dimethyl H3K9, implicated in transcriptional repression, surrounding the proximal CSF1 promoter. Further analysis revealed that silencing of brahma related gene 1 (BRG1), a chromatin remodeling protein, abrogated CSF1 induction by Ang II. In the meantime, BRG1 silencing erased H3 acetylation and H3K4 trimethylation and restored H3K9 dimethylation. Mechanistically, BRG1 interacted with and recruited SET1A, a histone H3K4 methyltransferase, and JMJD1A, a histone H3K9 demethylase, to the CSF1 promoter to alter chromatin structure thereby promoting CSF1 trans-activation in response to Ang II stimulation. Knockdown of either SET1A or JMJD1A blocked CSF1 induction by Ang II. Finally, we demonstrate that the crosstalk between BRG1 and histone modifying enzymes was mediated by the transcription factor AP-1. In conclusion, our data unveil a novel epigenetic mechanism whereby a BRG1-centered complex mediates transcriptional activation of CSF1 by Ang II in vascular endothelial cells.

Epigenetic processing in cardiometabolic disease

Albeit a consistent body of evidence supports the notion that genes influence cardiometabolic features and outcomes, the "non-genetic regulation" of this process is gaining increasing attention. Plastic chemical changes of DNA/histone complexes - known as epigenetic changes - critically determine gene activity by rapidly modifying chromatin accessibility to transcription factors. In this review, we describe the emerging role of chromatin modifications as fine tuners of gene transcription in adipogenesis, insulin resistance, macrophage polarization, immuno-metabolism, endothelial dysfunction and metabolic cardiomyopathy. Epigenetic processing participates in the dynamic interplay among different organs in the cardiometabolic patient. DNA methylation and post-translational histone modifications in both visceral and subcutaneous adipose tissue enable the transcription of genes implicated in lipo- and adipogenesis, inflammation and insulin resistance. Along the same line, complex networks of chromatin modifying enzymes are responsible for impaired nitric oxide bioavailability and defective insulin signalling in the vasculature, thus leading to reduced capillary recruitment and insulin delivery in the liver, skeletal muscle and adipose tissue. Furthermore, changes in methylation status of IL-4, IFNγ and Forkhead box P3 (Foxp3) gene loci are crucial for the polarization of immune cells, thus leading to adipose tissue inflammation and atherosclerosis. Cell-specific epigenetic information could advance our understanding of cardiometabolic processes, thus leading to individualized risk assessment and personalized therapeutic approaches in patients with cardiometabolic disturbances. The development of new chromatin modifying drugs indicates that targeting epigenetic changes is a promising approach to reduce the burden of cardiovascular disease in this setting.

The chromatin remodeling protein BRG1 regulates APAP-induced liver injury by modulating CYP3A11 transcription in hepatocyte

Acetaminophen (APAP) overdose represents the most frequent cause of acute liver failure. The underlying epigenetic mechanism is not fully understood. In the present study we investigated the mechanism whereby the chromatin remodeling protein brahma related gene 1 (Brg1) regulates APAP induced liver injury in mice. We report that hepatocyte-specific deletion of Brg1 attenuated APAP induced liver injury in mice as evidenced by reduced plasma ALT and AST levels, decreased liver necrosis, amelioration of GSH depletion, and prolonged survival. Brg1 regulated APAP-induced liver injury likely by stimulating the transcription of Cyp3a11, a key cytochrome enzyme involved in APAP metabolism. Immunoprecipitation coupled with DNA affinity microarray identified hepatocyte nuclear factor 4 (HNF4) as a novel binding partner for Brg1. HNF4 recruited Brg1 to the Cyp3a11 promoter and formed a complex with Brg1 to trans-activate Cyp3a11. In contrast, BRG1 deficiency attenuated HNF4 binding to the Cyp3a11 promoter and dampened Cyp3a11 transcription. Therefore, our data suggest that Brg1 might play an essential role mediating APAP induced liver injury in vivo.

Brg1 deficiency in vascular endothelial cells blocks neutrophil recruitment and ameliorates cardiac ischemia-reperfusion injury in mice

BACKGROUND

Increased neutrophil infiltration and the ensuing inflammatory response represent a hallmark event in cardiac ischemia-reperfusion injury (IRI). It remains poorly defined how the epigenetic machinery contributes to this process.

METHODS AND RESULTS

Here we report that mice with endothelial specific deletion of brahma related gene 1 (BRG1), a chromatin remodeling protein, exhibited amelioration when subjected to cardiac ischemia-reperfusion as evidenced by a reduction in infarct size as well as better recovery of heart function. Endothelial BRG1 deficiency also attenuated cardiac fibrosis following IRI when compared to wild type littermates. Interestingly, ablation of BRG1 in the endothelium suppressed neutrophil infiltration and down-regulated the levels of pro-inflammatory mediators in the heart following IRI. Further studies revealed that BRG1 activated the transcription of PODOCALYXIN (PODXL), an L-SELECTIN ligand crucial for neutrophil adhesion, in vascular endothelial cells in response to hypoxia-reoxygenation (HR). BRG1 knockdown by small interfering RNA abrogated HR-induced PODXL expression and blocked the adhesion of neutrophils to endothelial cells. Mechanistically, BRG1 alters the chromatin structure surrounding the PODXL promoter by interacting with JMJD2B, a histone H3K9 demethylase. Depletion of JMJD2B abrogated PODXL induction by HR and inhibited the adhesion of neutrophils to endothelial cells.

CONCLUSION

Our data suggest that trans-activation of PODXL by the BRG1-JMJD2B complex in endothelial cells may promote neutrophil infiltration and consequently the pathogenesis of cardiac ischemia-reperfusion injury.

Differentially methylated loci in NAFLD cirrhosis are associated with key signaling pathways

Altered DNA methylation events contribute to the pathogenesis and progression of metabolic disorders, including nonalcoholic fatty liver disease (NAFLD). Investigations of global DNA methylation patterns in liver biopsies representing severe NAFLD fibrosis have been limited. We used the HumanMethylation 450K BeadChip to analyze genome-wide methylation in patients with biopsy-proven grade 3/4 NAFLD fibrosis/cirrhosis (N = 14) and age- and sex-matched controls with normal histology (N = 15). We identified 208 CpG islands (CGIs), including 99 hypomethylated and 109 hypermethylated CGIs, showing statistically significant evidence (adjusted P value < 0.05) for differential methylation between cirrhotic and normal samples. Comparison of β values for each CGI to the read count of its corresponding gene obtained from RNA-sequencing analysis revealed negative correlation (adjusted P value < 0.05) for 34 transcripts. These findings provide supporting evidence for a role for CpG methylation in the pathogenesis of NAFLD-related cirrhosis, including confirmation of previously reported differentially methylated CGIs, and contribute new insight into the molecular mechanisms underlying the initiation and progression of liver fibrosis and cirrhosis.

Brahma related gene 1 (Brg1) contributes to liver regeneration by epigenetically activating the Wnt/β-catenin pathway in mice

Liver regeneration is a complicated pathophysiologic process that is regulated by a myriad of signaling pathways and transcription factors. The interaction among these pathways and factors, either cooperatively or antagonistically, may ultimately lead to recovery and restoration of liver function or permanent loss of liver function and liver failure. In the present study, we investigated the mechanism whereby the chromatin remodeling protein brahma related gene 1 (Brg1) regulates liver regeneration in mice. The Smarca4-Flox strain of mice was crossbred with the Alb-Cre strain to generate hepatocyte-specific Brg1 knockout mice. Liver injury was induced by partial hepatectomy (PHx). We report that Brg1 deletion in hepatocyte compromised liver regeneration and dampened survival after PHx in mice. Brg1 interacted with β-catenin to potentiate Wnt signaling and promote hepatocyte proliferation. Mechanistically, Brg1 recruited lysine demethylase 4 (KDM4) to activate β-catenin target genes. Our data suggest that Brg1 might play an essential role maintaining hepatic homeostasis and contributing to liver repair.-Li, N., Kong, M., Zeng, S., Hao, C., Li, M., Li, L., Xu, Z., Zhu, M., Xu, Y. Brahma related gene 1 (Brg1) contributes to liver regeneration by epigenetically activating the Wnt/β-catenin pathway in mice.

Hepatocyte-specific deletion of Brg1 alleviates methionine-and-choline-deficient diet (MCD) induced non-alcoholic steatohepatitis in mice

Uncontrolled inflammatory response and augmented lipid accumulation represent two key pathophysiological events in the pathogenesis of non-alcoholic steatohepatitis (NASH). NF-κB and SREBP1c program transcriptional regulation of cellular inflammatory response and lipid metabolism, respectively. The epigenetic mechanism underlying NF-κB-dependent pro-inflammatory transcription and SREBP1c-dependent pro-lipogenic transcription remains incompletely understood. In the present study we investigated the involvement of Brg1, a chromatin remodeling protein, in NASH pathogenesis in a methionine-and-choline deficient diet (MCD) induced mouse model. Brg1 expression was up-regulated in the liver in mice fed on the MCD diet and in primary hepatocytes exposed to free fatty acids. Liver injury and hepatic inflammation attenuated in hepatocyte-specific Brg1 knockout (CKO) mice fed on the MCD diet compared to the wild type (WT) littermates. Likewise, synthesis of pro-inflammatory mediators was down-regulated in primary hepatocytes isolated from CKO mice compared to WT mice, which resulted in reduced macrophage chemotaxis. Brg1 contributed to the transcription of pro-inflammatory mediators possibly by regulating the interaction between NF-κB and its co-factor MRTF-A. On the other hand, accumulation of triglyceride and cholesterol was ameliorated in MCD-fed CKO mice with a concomitant reduction of SREBP1c target genes. Brg1 interacted with SREBP1c and modulated the transcription of SREB1c target genes in the liver in response to MCD feeding by influencing active histone modifications. In conclusion, targeting Brg1 may yield novel anti-NASH therapeutics by simultaneously normalizing hepatic inflammatory status and metabolic profile in NASH patients.

HDAC4 stimulates MRTF-A expression and drives fibrogenesis in hepatic stellate cells by targeting miR-206

Activation of hepatic stellate cells (HSCs) is a hallmark event during liver fibrogenesis. We have previously shown that the transcriptional modulator MRTF-A contributes to liver fibrosis by programming epigenetic activation of HSCs. In the present study we investigated the mechanism whereby MRTF-A expression is regulated in this process. We report here that MRTF-A protein levels, but not mRNA levels, were up-regulated in vivo in the livers of mice induced to develop hepatic fibrosis. Pro-fibrogenic stimuli (TGF-β and PDGF-BB) also activated MRTF-A expression post-transcriptionally in vitro in cultured HSCs. miR-206 bound to the 3′-UTR of MRTF-A presumably to inhibit translation. miR-206 levels were down-regulated in response to pro-fibrogenic stimuli in vivo and in vitro allowing MRTF-A proteins to accumulate. Mechanistically, histone deacetylase 4 (HDAC4) was induced by pro-fibrogenic stimuli and recruited to the miR-206 promoter to repress miR-206 transcription. HDAC4 stimulated MRTF-A expression and drove fibrogenesis in HSCs in a miR-206 dependent manner. Therefore, our data reveal an HDAC4-miR-206-MRTF-A axis that can play a potentially important role in HSC activation and liver fibrosis.

Protein inhibitor of activated STAT 4 (PIAS4) regulates pro-inflammatory transcription in hepatocytes by repressing SIRT1

Excessive nutrition promotes the pathogenesis of non-alcoholic steatohepatitis (NASH), characterized by the accumulation of pro-inflammation mediators in the liver. In the present study we investigated the regulation of pro-inflammatory transcription in hepatocytes by protein inhibitor of activated STAT 4 (PIAS4) in this process and the underlying mechanisms. We report that expression of the class III deacetylase SIRT1 was down-regulated in the livers of NASH mice accompanied by a simultaneous increase in the expression and binding activity of PIAS4. Exposure to high glucose stimulated the expression PIAS4 in cultured hepatocytes paralleling SIRT1 repression. Estrogen, a known NASH-protective hormone, ameliorated SIRT1 trans-repression by targeting PIAS4. Over-expression of PIAS4 enhanced, while PIAS4 knockdown alleviated, repression of SIRT1 transcription by high glucose. Lentiviral delivery of short hairpin RNA (shRNA) targeting PIAS4 attenuated hepatic inflammation in NASH mice by restoring SIRT1 expression. Mechanistically, PIAS4 promoted NF-κB-mediated pro-inflammatory transcription in a SIRT1 dependent manner. In conclusion, our study indicates that PIAS4 mediated SIRT1 repression in response to nutrient surplus contributes to the pathogenesis of NASH. Therefore, targeting PIAS4 might provide novel therapeutic strategies in the intervention of NASH.

SIRT1 antagonizes liver fibrosis by blocking hepatic stellate cell activation in mice

Hepatic stellate cells (HSCs) are a major source of fibrogenesis in the liver, contributing to cirrhosis. When activated, HSCs transdifferentiate into myofibroblasts and undergo profound functional alterations paralleling an overhaul of the transcriptome, the mechanism of which remains largely undefined. We investigated the involvement of the class III deacetylase sirtuin [silent information regulator 1 (SIRT1)] in HSC activation and liver fibrosis. SIRT1 levels were down-regulated in the livers in mouse models of liver fibrosis, in patients with cirrhosis, and in activated HSCs as opposed to quiescent HSCs. SIRT1 activation halted, whereas SIRT1 inhibition promoted, HSC transdifferentiation into myofibroblasts. Liver fibrosis was exacerbated in mice with HSC-specific deletion of SIRT1 [conditional knockout (cKO)], receiving CCl₄ (1 mg/kg) injection or subjected to bile duct ligation, compared to wild-type littermates. SIRT1 regulated peroxisome proliferator activated receptor γ (PPARγ) transcription by deacetylating enhancer of zeste homolog 2 (EZH2) in quiescent HSCs. Finally, EZH2 inhibition or PPARγ activation ameliorated fibrogenesis in cKO mice. In summary, our data suggest that SIRT1 plays an essential role guiding the transition of HSC phenotypes.-Li, M., Hong, W., Hao, C., Li, L., Wu, D., Shen, A., Lu, J., Zheng, Y., Li, P., Xu, Y. SIRT1 antagonizes liver fibrosis by blocking hepatic stellate cell activation in mice.

BRM/SMARCA2 promotes the proliferation and chemoresistance of pancreatic cancer cells by targeting JAK2/STAT3 signaling

BACKGROUND

BRM is one of two evolutionarily conserved catalytic ATPase subunits of SWI/SNF complexes and plays important role in cell proliferation, linage specification and development, cell adhesion, cytokine responses and DNA repair. BRM is often inactivated in various types of cancer indicating its indispensable roles in oncogenesis but the mechanisms remain poorly understood.

METHODS

BRM expression in clinical pancreatic cancer samples was examined by immunohistochemistry and the correlation with patient survival was analyzed. shRNAs targeting BRM were used to establish stable BRM knockdown BxPC-3 and T3M4 cell lines. Cell viability was assessed by CCK-8 assay. Cell proliferation was measured by EdU incorporation assay, colony formation assay and Ki67 staining. Cell cycle and apoptosis were examined by flow cytometry. Growth and chemosensitivity of xenografts initiating from BRM-deficient cells were evaluated, and in situ apoptosis was detected by TUNEL assay. The status of JAK-STAT3 signaling was examined by real-time PCR and Western blot analysis.

RESULTS

High BRM expression was correlated with worse survival of pancreatic cancer patients. BRM shRNA reduced the proliferation and increased the sensitivity of pancreatic cancer cells to gemcitabine in vivo and in vitro, and these effects are associated with the inhibition of STAT3 phosphorylation and reduced transcription of STAT3 target genes.

CONCLUSION

We reveal a novel mechanism by which BRM could activate JAK2/STAT3 pathway to promote pancreatic cancer growth and chemoresistance. These findings may offer potential therapeutic targets for pancreatic cancer patients with excessive BRM expression.