EZH2 as a Potential Target for NAFLD Therapy

Unraveling the relationship between histone methylation and nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) poses a significant health challenge in modern societies due to shifts in lifestyle and dietary habits. Its complexity stems from genetic predisposition, environmental influences, and metabolic factors. Epigenetic processes govern various cellular functions such as transcription, chromatin structure, and cell division. In NAFLD, these epigenetic tendencies, especially the process of histone methylation, are intricately intertwined with fat accumulation in the liver. Histone methylation is regulated by different enzymes like methyltransferases and demethylases and influences the expression of genes related to adipogenesis. While early-stage NAFLD is reversible, its progression to severe stages becomes almost irreversible. Therefore, early detection and intervention in NAFLD are crucial, and understanding the precise role of histone methylation in the early stages of NAFLD could be vital in halting or potentially reversing the progression of this disease.

Molecular mechanism and therapeutic significance of essential amino acids in metabolically associated fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), also known as metabolically associated fatty liver disease (MAFLD), is a systemic metabolic disease characterized by lipid accumulation in the liver, lipid toxicity, insulin resistance, intestinal dysbiosis, and inflammation that can progress from simple steatosis to nonalcoholic steatohepatitis (NASH) and even cirrhosis or cancer. It is the most prevalent illness threatening world health. Currently, there are almost no approved drug interventions for MAFLD, mainly dietary changes and exercise to control weight and regulate metabolic disorders. Meanwhile, the metabolic pathway involved in amino acid metabolism also influences the onset and development of MAFLD in the body, and most amino acid metabolism takes place in the liver. Essential amino acids are those amino acids that must be supplemented from outside the diet and that cannot be synthesized in the body or cannot be synthesized at a rate sufficient to meet the body's needs, including leucine, isoleucine, valine (collectively known as branched-chain amino acids), tryptophan, phenylalanine (which are aromatic amino acids), histidine, methionine, threonine and lysine. The metabolic balance of the body is closely linked to these essential amino acids, and essential amino acids are closely linked to the pathophysiological process of MAFLD. In this paper, we will focus on the metabolism of essential amino acids in the body and further explore the therapeutic strategies for MAFLD based on the studies conducted in recent years.

Histone demethylase KDM1A promotes hepatic steatosis and inflammation by increasing chromatin accessibility in NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease without specific Food and Drug Administration-approved drugs. Recent advances suggest that chromatin remodeling and epigenetic alteration contribute to the development of NAFLD. The functions of the corresponding molecular modulator in NAFLD, however, are still elusive. KDM1A, commonly known as lysine-specific histone demethylase 1, has been reported to increase glucose uptake in hepatocellular carcinoma. In addition, a recent study suggests that inhibition of KDM1A reduces lipid accumulation in primary brown adipocytes. We here investigated the role of KDM1A, one of the most important histone demethylases, in NAFLD. In this study, we observed a significant upregulation of KDM1A in NAFLD mice, monkeys, and humans compared to the control group. Based on these results, we further found that the KDM1A can exacerbate lipid accumulation and inflammation in hepatocytes and mice. Mechanistically, KDM1A exerted its effects by elevating chromatin accessibility, subsequently promoting the development of NAFLD. Furthermore, the mutation of KDM1A blunted its capability to promote the development of NAFLD. In summary, our study discovered that KDM1A exacerbates hepatic steatosis and inflammation in NAFLD via increasing chromatin accessibility, further indicating the importance of harnessing chromatin remodeling and epigenetic alteration in combating NAFLD. KDM1A might be considered as a potential therapeutic target in this regard.

Targeting EZH2 regulates the biological characteristics of glioma stem cells via the Notch1 pathway

Glioma is the most common malignant brain tumor, and its behavior is closely related to the presence of glioma stem cells (GSCs). We found that the enhancer of zeste homolog 2 (EZH2) is highly expressed in glioma and that its expression is correlated with the prognosis of glioblastoma multiforme (GBM) in two databases: The Cancer Genome Atlas and the Chinese Glioma Genome Atlas. Additionally, EZH2 is known to regulate the stemness-associated gene expression, proliferation, and invasion ability of GSCs, which may be achieved through the activation of the STAT3 and Notch1 pathways. Furthermore, we demonstrated the effect of the EZH2-specific inhibitor GSK126 on GSCs; these results not only corroborate our hypothesis, but also provide a potential novel treatment approach for glioma.

Cellular senescence primes liver fibrosis regression through Notch-EZH2

Cellular senescence plays a pivotal role in wound healing. At the initiation of liver fibrosis regression, accumulated senescent cells were detected and genes of senescence were upregulated. Flow cytometry combined with single-cell RNA sequencing analyses revealed that most of senescent cells were liver nonparenchymal cells. Removing senescent cells by dasatinib and quercetin (DQ), alleviated hepatic cellular senescence, impeded fibrosis regression, and disrupted liver sinusoids. Clearance of senescent cells not only decreased senescent macrophages but also shrank the proportion of anti-inflammatory M2 macrophages through apoptotic pathway. Subsequently, macrophages were depleted by clodronate, which diminished hepatic senescent cells and impaired fibrosis regression. Mechanistically, the change of the epigenetic regulator enhancer of zeste homolog2 (EZH2) accompanied with the emergence of hepatic senescent cells while liver fibrosis regressed. Blocking EZH2 signaling by EPZ6438 reduced hepatic senescent cells and macrophages, decelerating liver fibrosis regression. Moreover, the promoter region of EZH2 was transcriptionally suppressed by Notch-Hes1 (hairy and enhancer of split 1) signaling. Disruption of Notch in macrophages using Lyz2 (lysozyme 2) Cre-RBP-J (recombination signal binding protein Jκ) f/f transgenic mice, enhanced hepatic cellular senescence, and facilitated fibrosis regression by upregulating EZH2 and blocking EZH2 abrogated the above effects caused by Notch deficiency. Ultimately, adopting Notch inhibitor Ly3039478 or exosome-mediated RBP-J decoy oligodeoxynucleotides accelerated liver fibrosis regression by augmenting hepatic cellular senescence.

Histone Modifications in NAFLD: Mechanisms and Potential Therapy

Nonalcoholic fatty liver disease (NAFLD) is a progressive condition that encompasses a spectrum of liver disorders, beginning with the simple steatosis, progressing to nonalcoholic steatohepatitis (NASH), and possibly leading to more severe diseases, including liver cirrhosis and hepatocellular carcinoma (HCC). In recent years, the prevalence of NAFLD has increased due to a shift towards energy-dense dietary patterns and a sedentary lifestyle. NAFLD is also strongly associated with metabolic disorders such as obesity and hyperlipidemia. The progression of NAFLD could be influenced by a variety of factors, such as diet, genetic factors, and even epigenetic factors. In contrast to genetic factors, epigenetic factors, including histone modifications, exhibit dynamic and reversible features. Therefore, the epigenetic regulation of the initiation and progression of NAFLD is one of the directions under intensive investigation in terms of pathogenic mechanisms and possible therapeutic interventions. This review aims to discuss the possible mechanisms and the crucial role of histone modifications in the framework of epigenetic regulation in NAFLD, which may provide potential therapeutic targets and a scientific basis for the treatment of NAFLD.

EZH2 can be used as a therapeutic agent for inhibiting endothelial dysfunction

Enhancer of zeste homolog 2 (EZH2) is a catalytic subunit of polycomb repressor complex 2 and plays important roles in endothelial cell homeostasis. EZH2 functionally methylates lysine 27 of histone H3 and represses gene expression through chromatin compaction. EZH2 mediates the effects of environmental stimuli by regulating endothelial functions, such as angiogenesis, endothelial barrier integrity, inflammatory signaling, and endothelial mesenchymal transition. Numerous studies have been conducted to determine the significance of EZH2 in endothelial function. The aim of this review is to provide a concise summary of the roles EZH2 plays in endothelial function and elucidate its therapeutic potential in cardiovascular diseases.

The roles of EZH2 in cancer and its inhibitors

The enhancer of zeste homolog 2 (EZH2) is encoded by the Enhancer of zeste 2 polycomb repressive complex 2 subunit gene. EZH2 is involved in the cell cycle, DNA damage repair, cell differentiation, autophagy, apoptosis, and immunological modulation. The main function of EZH2 is to catalyze the methylation of H3 histone of H3K27Me3, which inhibits the transcription of target genes, such as tumor suppressor genes. EZH2 also forms complexes with transcriptions factors or directly binds to the promoters of target genes, leading to regulate gene transcriptions. EZH2 has been as a prominent target for cancer therapy and a growing number of potential targeting medicines have been developed. This review summarized the mechanisms that EZH2 regulates gene transcription and the interactions between EZH2 and important intracellular signaling molecules (Wnt, Notch, MEK, Akt) and as well the clinical applications of EZH2-targeted drugs.

EZH2 Methyltransferase Regulates Neuroinflammation and Neuropathic Pain

Recent studies by us and others have shown that enhancer of zeste homolog-2 (EZH2), a histone methyltransferase, in glial cells regulates the genesis of neuropathic pain by modulating the production of proinflammatory cytokines and chemokines. In this review, we summarize recent advances in this research area. EZH2 is a subunit of polycomb repressive complex 2 (PRC2), which primarily serves as a histone methyltransferase to catalyze methylation of histone 3 on lysine 27 (H3K27), ultimately resulting in transcriptional repression. Animals with neuropathic pain exhibit increased EZH2 activity and neuroinflammation of the injured nerve, spinal cord, and anterior cingulate cortex. Inhibition of EZH2 with DZNep or GSK-126 ameliorates neuroinflammation and neuropathic pain. EZH2 protein expression increases upon activation of Toll-like receptor 4 and calcitonin gene-related peptide receptors, downregulation of miR-124-3p and miR-378 microRNAs, or upregulation of Lncenc1 and MALAT1 long noncoding RNAs. Genes suppressed by EZH2 include suppressor of cytokine signaling 3 (SOCS3), nuclear factor (erythroid-derived 2)-like-2 factor (NrF2), miR-29b-3p, miR-146a-5p, and brain-specific angiogenesis inhibitor 1 (BAI1). Pro-inflammatory mediators facilitate neuronal activation along pain-signaling pathways by sensitizing nociceptors in the periphery, as well as enhancing excitatory synaptic activities and suppressing inhibitory synaptic activities in the CNS. These studies collectively reveal that EZH2 is implicated in signaling pathways known to be key players in the process of neuroinflammation and genesis of neuropathic pain. Therefore, targeting the EZH2 signaling pathway may open a new avenue to mitigate neuroinflammation and neuropathic pain.

Methionine cycle in nonalcoholic fatty liver disease and its potential applications

As a chronic metabolic disease affecting epidemic proportions worldwide, the pathogenesis of Nonalcoholic Fatty Liver Disease (NAFLD) is not clear yet. There is also a lack of precise biomarkers and specific medicine for the diagnosis and treatment of NAFLD. Methionine metabolic cycle, which is critical for the maintaining of cellular methylation and redox state, is involved in the pathophysiology of NAFLD. However, the molecular basis and mechanism of methionine metabolism in NAFLD are not completely understood. Here, we mainly focus on specific enzymes that participates in methionine cycle, to reveal their interconnections with NAFLD, in order to recognize the pathogenesis of NAFLD from a new angle and at the same time, explore the clinical characteristics and therapeutic strategies.

LncRNA MEG3 up-regulates SIRT6 by ubiquitinating EZH2 and alleviates nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a global health threat. Here, we presented the significant role of a novel signaling axis comprising long non-coding RNA maternally expressed gene 3 (MEG3), enhancer of zeste homolog 2 (EZH2), and sirtuin 6 (SIRT6) in controlling lipid accumulation, inflammation, and the progression of NAFLD. Mice fed with high-fat diet (HFD) were established as in vitro and in vivo NAFLD models, respectively. Lipid accumulation was measured by oil red O staining and assays for triglycerides or cholesterol. Inflammation was examined by ELISA for pro-inflammatory cytokines. Gene expressions were examined by RT-qPCR or Western blot. Interactions between key signaling molecules were examined by combining expressional analysis, RNA immunoprecipitation, cycloheximide stability assay, co-immunoprecipitation, and chromatin immunoprecipitation. MEG3 level was reduced in FFA-challenged hepatocytes or liver from HFD-fed mice, and the reduction paralleled the severity of NAFLD in clinic. Overexpressing MEG3 suppressed FFA-induced lipid accumulation or inflammation in hepatocytes. By promoting the ubiquitination and degradation of EZH2, MEG3 upregulated SIRT6, an EZH2 target. SIRT6 essentially mediated the protective effects of MEG3 in hepatocytes. Consistently, overexpressing MEG3 alleviated HFD-induced NAFLD in vivo. By controlling the expressions of genes involved in lipid metabolism and inflammation, the MEG3/EZH2/SIRT6 axis significantly suppressed lipid accumulation and inflammation in vitro, and NAFLD development in vivo. Therefore, boosting MEG3 level may benefit the treatment of NAFLD.

Mechanism and Therapeutic Opportunities of Histone Modifications in Chronic Liver Disease

Chronic liver disease (CLD) represents a global health problem, accounting for the heavy burden of disability and increased health care utilization. Epigenome alterations play an important role in the occurrence and progression of CLD. Histone modifications, which include acetylation, methylation, and phosphorylation, represent an essential part of epigenetic modifications that affect the transcriptional activity of genes. Different from genetic mutations, histone modifications are plastic and reversible. They can be modulated pharmacologically without changing the DNA sequence. Thus, there might be chances to establish interventional solutions by targeting histone modifications to reverse CLD. Here we summarized the roles of histone modifications in the context of alcoholic liver disease (ALD), metabolic associated fatty liver disease (MAFLD), viral hepatitis, autoimmune liver disease, drug-induced liver injury (DILI), and liver fibrosis or cirrhosis. The potential targets of histone modifications for translation into therapeutics were also investigated. In prospect, high efficacy and low toxicity drugs that are selectively targeting histone modifications are required to completely reverse CLD and prevent the development of liver cirrhosis and malignancy.

Overexpression of miR-101 suppresses collagen synthesis by targeting EZH2 in hypertrophic scar fibroblasts

Background

MicroRNA-101 (miR-101) is a tumor suppressor microRNA (miRNA) and its loss is associated with the occurrence and progression of various diseases. However, the biological function and target of miR-101 in the pathogenesis of hypertrophic scars (HS) remains unknown.

Methods

We harvested HS and paired normal skin (NS) tissue samples from patients and cultured their fibroblasts (HSF and NSF, respectively). We used quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), fluorescence in situ hybridization (FISH), enzyme-linked immunosorbent assays (ELISA) and Western blot analyses to measure mRNA levels and protein expression of miR-101, enhancer of zeste homolog 2 (EZH2), collagen 1 and 3 (Col1 and Col3) and α-smooth muscle actin (α-SMA) in different in vitro conditions. We also used RNA sequencing to evaluate the relevant signaling pathways and bioinformatics analysis and dual-luciferase reporter assays to predict miR-101 targets. We utilized a bleomycin-induced fibrosis mouse model in which we injected miR-101 mimics to evaluate collagen deposition in vivo.

Results

We found low expression of miR-101 in HS and HSF compared to NS and NSF. Overexpressing miR-101 decreased Col1, Col3 and α-SMA expression in HSF. We detected high expression of EZH2 in HS and HSF. Knockdown of EZH2 decreased Col1, Col3 and α-SMA in HSF. Mechanistically, miR-101 targeted the 3′-untranslated region (3′UTR) of EZH2, as indicated by the decreased expression of EZH2. Overexpressing EZH2 rescued miR-101-induced collagen repression. MiR-101 mimics effectively suppressed collagen deposition in the bleomycin-induced fibrosis mouse model.

Conclusions

Our data reveal that miR-101 targets EZH2 in HS collagen production, providing new insight into the pathological mechanisms underlying HS formation.

Epigenetically Mediated Ciliogenesis and Cell Cycle Regulation, and Their Translational Potential

Primary cilia biogenesis has been closely associated with cell cycle progression. Cilia assemble when cells exit the cell cycle and enter a quiescent stage at the post-mitosis phase, and disassemble before cells re-enter a new cell cycle. Studies have focused on how the cell cycle coordinates with the cilia assembly/disassembly process, and whether and how cilia biogenesis affects the cell cycle. Appropriate regulation of the functions and/or expressions of ciliary and cell-cycle-associated proteins is pivotal to maintaining bodily homeostasis. Epigenetic mechanisms, including DNA methylation and histone/chromatin modifications, are involved in the regulation of cell cycle progression and cilia biogenesis. In this review, first, we discuss how epigenetic mechanisms regulate cell cycle progression and cilia biogenesis through the regulation of DNA methylation and chromatin structures, to either promote or repress the transcription of genes associated with those processes and the modification of cytoskeleton network, including microtubule and actin. Next, we discuss the crosstalk between the cell cycle and ciliogenesis, and the involvement of epigenetic regulators in this process. In addition, we discuss cilia-dependent signaling pathways in cell cycle regulation. Understanding the mechanisms of how epigenetic regulators contribute to abnormal cell cycle regulation and ciliogenesis defects would lead to developing therapeutic strategies for the treatment of a wide variety of diseases, such as cancers, polycystic kidney disease (PKD), and other ciliopathy-associated disorders.