Histone demethylase KDM5A is transactivated by the transcription factor C/EBPβ and promotes preadipocyte differentiation by inhibiting Wnt/β-catenin signaling

Hepatic Klf10-Fh1 axis promotes exercise-mediated amelioration of NASH in mice

Exercise is an effective non-pharmacological strategy for the treatment of nonalcoholic steatohepatitis (NASH), but the underlying mechanism needs further investigation. Kruppel-like factor 10 (Klf10) is a transcriptional factor that is expressed in multiple tissues including liver, whose role in NASH is not well defined. In our study, exercise induces hepatic Klf10 expression through the cAMP/PKA/CREB pathway. Hepatocyte-specific knockout of Klf10 (Klf10LKO) increases lipid accumulation, cell death, inflammation and fibrosis in NASH diet-fed mice and reduces the protective effects of treadmill exercise against NASH, while hepatocyte-specific overexpression of Klf10 (Klf10LTG) works in concert with exercise to reduce NASH in mice. Mechanistically, Klf10 promotes the expression of fumarate hydratase 1 (Fh1), thereby reducing fumarate accumulation in hepatocytes. This decreases the trimethyl (me3) levels of histone 3 lysine 4 (H3K4me3) on lipogenic genes promoters to attenuate lipogenesis, thus ameliorating free fatty acids (FFAs)-induced hepatocytes steatosis, apoptosis, insulin resistance and blunting dysfunctional hepatocytes-mediated activation of macrophages and hepatic stellate cells. Therefore, by regulating the Fh1/fumarate/H3K4me3 pathway, Klf10 acts as a downstream effector of exercise to combat NASH.

KDM5 family as therapeutic targets in breast cancer: Pathogenesis and therapeutic opportunities and challenges

Breast cancer (BC) is the most frequent malignant cancer diagnosis and is a primary factor for cancer deaths in women. The clinical subtypes of BC include estrogen receptor (ER) positive, progesterone receptor (PR) positive, human epidermal growth factor receptor 2 (HER2) positive, and triple-negative BC (TNBC). Based on the stages and subtypes of BC, various treatment methods are available with variations in the rates of progression-free disease and overall survival of patients. However, the treatment of BC still faces challenges, particularly in terms of drug resistance and recurrence. The study of epigenetics has provided new ideas for treating BC. Targeting aberrant epigenetic factors with inhibitors represents a promising anticancer strategy. The KDM5 family includes four members, KDM5A, KDM5B, KDM5C, and KDMD, all of which are Jumonji C domain-containing histone H3K4me2/3 demethylases. KDM5 proteins have been extensively studied in BC, where they are involved in suppressing or promoting BC depending on their specific upstream and downstream pathways. Several KDM5 inhibitors have shown potent BC inhibitory activity in vitro and in vivo, but challenges still exist in developing KDM5 inhibitors. In this review, we introduce the subtypes of BC and their current therapeutic options, summarize KDM5 family context-specific functions in the pathobiology of BC, and discuss the outlook and pitfalls of KDM5 inhibitors in this disease.

The journey towards physiology and pathology: Tracing the path of neuregulin 4

Neuregulin 4 (Nrg4), an epidermal growth factor (EGF) family member, can bind to and activate the ErbB4 receptor tyrosine kinase. Nrg4 has five different isoforms by alternative splicing and performs a wide variety of functions. Nrg4 is involved in a spectrum of physiological processes including neurobiogenesis, lipid metabolism, glucose metabolism, thermogenesis, and angiogenesis. In pathological processes, Nrg4 inhibits inflammatory factor levels and suppresses apoptosis in inflammatory diseases. In addition, Nrg4 could ameliorate obesity, insulin resistance, and cardiovascular diseases. Furthermore, Nrg4 improves non-alcoholic fatty liver disease (NAFLD) by promoting autophagy, improving lipid metabolism, and inhibiting cell death of hepatocytes. Besides, Nrg4 is closely related to the development of cancer, hyperthyroidism, and some other diseases. Therefore, elucidation of the functional role and mechanisms of Nrg4 will provide a clearer view of the therapeutic potential and possible risks of Nrg4.

The role of Sirtuin 2 in liver - An extensive and complex biological process

Liver disease has become one of the main causes of health issue worldwide. Sirtuin (Sirt) 2 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase, and is expressed in multiple organs including liver, which plays important and complex roles by interacting with various substrates. Physiologically, Sirt2 can improve metabolic homeostasis. Pathologically, Sirt2 can alleviate inflammation, endoplasmic reticulum (ER) stress, promote liver regeneration, maintain iron homeostasis, aggravate fibrogenesis and regulate oxidative stress in liver. In liver diseases, Sirt2 can mitigate fatty liver disease (FLD) including non-alcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (AFLD), but aggravate hepatitis B (HBV) and liver ischemia-reperfusion injury (LIRI). The role of Sirt2 in liver cancer and aging-related liver diseases, however, has not been fully elucidated. In this review, these biological processes regulated by Sirt2 in liver are summarized, which aims to update the function of Sirt2 in liver and to explore the potential role of Sirt2 as a therapeutic target for liver diseases.

Cdo1-Camkk2-AMPK axis confers the protective effects of exercise against NAFLD in mice

Exercise is an effective non-pharmacological strategy for ameliorating nonalcoholic fatty liver disease (NAFLD), but the underlying mechanism needs further investigation. Cysteine dioxygenase type 1 (Cdo1) is a key enzyme for cysteine catabolism that is enriched in liver, whose role in NAFLD remains poorly understood. Here, we show that exercise induces the expression of hepatic Cdo1 via the cAMP/PKA/CREB signaling pathway. Hepatocyte-specific knockout of Cdo1 (Cdo1LKO) decreases basal metabolic rate of the mice and impairs the effect of exercise against NAFLD, whereas hepatocyte-specific overexpression of Cdo1 (Cdo1LTG) increases basal metabolic rate of the mice and synergizes with exercise to ameliorate NAFLD. Mechanistically, Cdo1 tethers Camkk2 to AMPK by interacting with both of them, thereby activating AMPK signaling. This promotes fatty acid oxidation and mitochondrial biogenesis in hepatocytes to attenuate hepatosteatosis. Therefore, by promoting hepatic Camkk2-AMPK signaling pathway, Cdo1 acts as an important downstream effector of exercise to combat against NAFLD.

Domain architecture and protein-protein interactions regulate KDM5A recruitment to the chromatin

Tri-methylation of Histone 3 lysine 4 (H3K4) is an important epigenetic modification whose deposition and removal can affect the chromatin at structural and functional levels. KDM5A is one of the four known H3K4-specific demethylases. It is a part of the KDM5 family, which is characterized by a catalytic Jumonji domain capable of removing H3K4 di- and tri-methylation marks. KDM5A has been found to be involved in multiple cellular processes such as differentiation, metabolism, cell cycle, and transcription. Its link to various diseases, including cancer, makes KDM5A an important target for drug development. However, despite several studies outlining its significance in various pathways, our lack of understanding of its recruitment and function at the target sites on the chromatin presents a challenge in creating effective and targeted treatments. Therefore, it is essential to understand the recruitment mechanism of KDM5A to chromatin, and its activity therein, to comprehend how various roles of KDM5A are regulated. In this review, we discuss how KDM5A functions in a context-dependent manner on the chromatin, either directly through its structural domain, or through various interacting partners, to bring about a diverse range of functions.

Exercise-regulated white adipocyte differentitation: An insight into its role and mechanism

White adipocytes play a key role in the regulation of fat mass amount and energy balance. An appropriate level of white adipocyte differentiation is important for maintaining metabolic homeostasis. Exercise, an important way to improve metabolic health, can regulate white adipocyte differentiation. In this review, the effect of exercise on the differentiation of white adipocytes is summarized. Exercise could regulate adipocyte differentiation in multiple ways, such as exerkines, metabolites, microRNAs, and so on. The potential mechanism underlying the role of exercise in adipocyte differentiation is also reviewed and discussed. In-depth investigation of the role and mechanism of exercise in white adipocyte differentiation would provide new insights into exercise-mediated improvement of metabolism and facilitate the application of exercise-based strategy against obesity.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

HIGD1A links SIRT1 activity to adipose browning by inhibiting the ROS/DNA damage pathway

Energy-dissipating adipocytes have the potential to improve metabolic health. Here, we identify hypoxia-induced gene domain protein-1a (HIGD1A), a mitochondrial inner membrane protein, as a positive regulator of adipose browning. HIGD1A is induced in thermogenic fats by cold exposure. Peroxisome proliferator-activated receptor gamma (PPARγ) transactivates HIGD1A expression synergistically with peroxisome proliferators-activated receptor γ coactivator α (PGC1α). HIGD1A knockdown inhibits adipocyte browning, whereas HIGD1A upregulation promotes the browning process. Mechanistically, HIGD1A deficiency impairs mitochondrial respiration to increase reactive oxygen species (ROS) level. This increases NAD⁺ consumption for DNA damage repair and curtails the NAD⁺/NADH ratio, which inhibits sirtuin1 (SIRT1) activity, thereby compromising adipocyte browning. Conversely, overexpression of HIGD1A blunts the above process to promote adaptive thermogenesis. Furthermore, mice with HIGD1A knockdown in inguinal and brown fat have impaired thermogenesis and are prone to diet-induced obesity (DIO). Overexpression of HIGD1A favors adipose tissue browning, ultimately preventing DIO and metabolic disorders. Thus, the mitochondrial protein HIGD1A links SIRT1 activity to adipocyte browning by inhibiting ROS levels.

The versatile role of Serpina3c in physiological and pathological processes: a review of recent studies

Murine Serpina3c belongs to the family of serine protease inhibitors (Serpins), clade "A" and its human homologue is SerpinA3. Serpina3c is involved in some physiological processes, including insulin secretion and adipogenesis. In the pathophysiological process, the deletion of Serpina3c leads to more severe metabolic disorders, such as aggravated non-alcoholic fatty liver disease (NAFLD), insulin resistance and obesity. In addition, Serpina3c can improve atherosclerosis and regulate cardiac remodeling after myocardial infarction. Many of these processes are directly or indirectly mediated by its inhibition of serine protease activity. Although its function has not been fully revealed, recent studies have shown its potential research value. Here, we aimed to summarize recent studies to provide a clearer view of the biological roles and the underlying mechanisms of Serpina3c.

Beta-adrenergic agonist induces unique transcriptomic signature in inguinal white adipose tissue

Activation of thermogenic adipose tissue depots has been linked to improved metabolism and weight loss. To study the molecular regulation of adipocyte thermogenesis, we performed RNA-Seq on brown adipose tissue (BAT), gonadal white adipose tissue (gWAT), and inguinal white adipose tissue (iWAT) from mice treated with β3-adrenoreceptor agonist CL316,243 (CL). Our analysis revealed diverse transcriptional profile and identified pathways in response to CL treatment. Differentially expressed genes (DEGs) in iWATCL were associated with the upregulation of pathways involved in cellular immune responses and with the upregulation of the browning program. We identified 39 DEGs in beige adipose which included certain heat shock proteins (Hspa1a and Hspa1b), and others suggesting potential associations with browning. Our results highlight transcriptional heterogeneity across adipose tissues and reveal genes specifically regulated in beige adipose, potentially aiding in identifying novel browning pathways.

Drawing a line between histone demethylase KDM5A and KDM5B: their roles in development and tumorigenesis

Distinct epigenetic modifiers ensure coordinated control over genes that govern a myriad of cellular processes. Growing evidence shows that dynamic regulation of histone methylation is critical for almost all stages of development. Notably, the KDM5 subfamily of histone lysine-specific demethylases plays essential roles in the proper development and differentiation of tissues, and aberrant regulation of KDM5 proteins during development can lead to chronic developmental defects and even cancer. In this review, we adopt a unique perspective regarding the context-dependent roles of KDM5A and KDM5B in development and tumorigenesis. It is well known that these two proteins show a high degree of sequence homology, with overlapping functions. However, we provide deeper insights into their substrate specificity and distinctive function in gene regulation that at times divert from each other. We also highlight both the possibility of targeting KDM5A and KDM5B to improve cancer treatment and the limitations that must be overcome to increase the efficacy of current drugs.

Cdo1 promotes PPARγ-mediated adipose tissue lipolysis in male mice

Cysteine dioxygenase 1 (Cdo1) is a key enzyme in taurine synthesis. Here we show that Cdo1 promotes lipolysis in adipose tissue. Adipose-specific knockout of Cdo1 in mice impairs energy expenditure, cold tolerance and lipolysis, exacerbates diet-induced obesity (DIO) and decreases adipose expression of the key lipolytic genes encoding ATGL and HSL, with little effect on adipose taurine levels. White-adipose-specific overexpression of ATGL and HSL blunts the role of adipose Cdo1 deficiency in promoting DIO. Mechanistically, Cdo1 interacts with PPARγ and facilitates the recruitment of Med24, the core subunit of mediator complex, to ATGL and HSL gene promoters, thereby transactivating their expression. Further, mice with transgenic overexpression of Cdo1 show better cold tolerance, ameliorated DIO and higher lipolysis capacity. Thus, we uncover an unexpected and important role of Cdo1 in regulating adipose lipolysis.

Higd1a facilitates exercise-mediated alleviation of fatty liver in diet-induced obese mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common liver disease. Exercise is an effective strategy against NAFLD, but its underlying molecular mechanism is not completely understood.

METHODS

Higd1a, a mitochondrial inner membrane protein, was knocked down or overexpressed in mice livers by tail vein injection of adeno-associated virus (AAV) vectors. High fat diet-induced obese mice were subjected to treadmill training. Alpha mouse liver 12 (AML12) cells were used for in vitro studies.

RESULTS

Higd1a was upregulated in mice livers after treadmill exercise training. Knockdown of Higd1a in diet-induced obese mice livers impaired exercise-mediated alleviation of hepatic steatosis, liver injury and inflammation. On the contrary, hepatic overexpression of Higd1a ameliorated fatty liver, liver injury and inflammation in synergy with exercise. Mechanistically, deficiency of Higd1a in hepatocytes promoted free fatty acids (FFAs)-induced apoptosis and oxidative stress, and elevated the cytosolic level of oxidized mitochondrial DNA (ox-mtDNA) to activate NLRP3 inflammasome and JNK signaling, leading to decreased expression of critical genes involved in fatty acid oxidation (FAO), such as Ppara, Cpt1a and Acadm. Overexpression of Higd1a in hepatocytes blunted the above effects, which ultimately increased FAO genes expression and alleviated fat accumulation in hepatocytes.

CONCLUSION

These results identify a Higd1a-mediated inhibition of cytosolic ox-mtDNA/NLRP3 inflammasomes/JNK pathway that facilitates exercise-mediated alleviation of hepatosteatosis.

The functional role of Higd1a in mitochondrial homeostasis and in multiple disease processes

Higd1a is a conserved gene in evolution which is widely expressed in many tissues in mammals. Accumulating evidence has revealed multiple functions of Higd1a, as a mitochondrial inner membrane protein, in the regulation of metabolic homeostasis. It plays an important role in anti-apoptosis and promotes cellular survival in several cell types under hypoxic condition. And the survival of porcine Sertoli cells facilitated by Higd1a helps to support reproduction. In some cases, Higd1a can serve as a sign of metabolic stress. Over the past several years, a considerable amount of studies about how tumor fate is determined and how cancerous proliferation is regulated by Higd1a have been performed. In this review, we summarize the physiological functions of Higd1a in metabolic homeostasis and its pathophysiological roles in distinct diseases including cancer, nonalcoholic fatty liver disease (NAFLD), type II diabetes and mitochondrial diseases. The prospect of Higd1a with potential to preserve mammal health is also discussed. This review might pave the way for Higd1a-based research and application in clinical practice.

SERPINA3C ameliorates adipose tissue inflammation through the Cathepsin G/Integrin/AKT pathway

Objective

Due to the increasing prevalence of obesity and insulin resistance, there is an urgent need for better treatment of obesity and its related metabolic disorders. This study aimed to elucidate the role of SERPINA3C, an adipocyte secreted protein, in obesity and related metabolic disorders.

Methods

Male wild type (WT) and knockout (KO) mice were fed with high-fat diet (HFD) for 16 weeks, adiposity, insulin resistance, and inflammation were assessed. AAV-mediated overexpression of SERPINA3C was injected locally in inguinal white adipose tissue (iWAT) to examine the effect of SERPINA3C. In vitro analyses were conducted in 3T3-L1 adipocytes to explore the molecular pathways underlying the function of SERPINA3C.

Results

Functional exploration of the SERPINA3C knockout mice revealed that SERPINA3C deficiency led to an impaired metabolic phenotype (more severe obesity, lower metabolic rates, worse glucose intolerance and insulin insensitivity), which was associated with anabatic inflammation and apoptosis of white adipose tissues. Consistent with these results, overexpression of SERPINA3C in inguinal adipose tissue protected mice against diet-induced obesity and metabolic disorders with less inflammation and apoptosis in adipose tissue. Mechanistically, SERPINA3C inhibited Cathepsin G activity, acting as a serine protease inhibitor, which blocked Cathepsin G-mediated turnover of α5/β1 Integrin protein. Then, the preserved integrity (increase) of α5/β1 Integrin signaling activated AKT to decrease JNK phosphorylation, thereby inhibiting inflammation and promoting insulin sensitivity in adipocytes.

Conclusions/interpretation

These findings demonstrate a previously unknown SERPINA3C/Cathepsin G/Integrin/AKT pathway in regulating adipose tissue inflammation, and suggest the therapeutic potential of targeting SERPINA3C/Cathepsin G axis in adipose tissue for the treatment of obesity and metabolic diseases.

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SERPINA3C deletion aggravated HFD-induced obesity, insulin resistance and inflammation in mice.

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Overexpression of SERPINA3C in iWAT alleviated HFD-induced obesity, insulin resistance and inflammation.

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SERPINA3C relieved adipose inflammation by inhibiting Cathepsin G-mediated turnover of Integrin α5/β1 to activate AKT.

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The SERPINA3C/Cathepsin G axis in adipose might be a potential therapeutic target for type 2 diabetes and obesity.

Regulatory mechanisms of the early phase of white adipocyte differentiation: an overview

The adipose organ comprises two main fat depots termed white and brown adipose tissues. Adipogenesis is a process leading to newly differentiated adipocytes starting from precursor cells, which requires the contribution of many cellular activities at the genome, transcriptome, proteome, and metabolome levels. The adipogenic program is accomplished through two sequential phases; the first includes events favoring the commitment of adipose tissue stem cells/precursors to preadipocytes, while the second involves mechanisms that allow the achievement of full adipocyte differentiation. While there is a very large literature about the mechanisms involved in terminal adipogenesis, little is known about the first stage of this process. Growing interest in this field is due to the recent identification of adipose tissue precursors, which include a heterogenous cell population within different types of adipose tissue as well as within the same fat depot. In addition, the alteration of the heterogeneity of adipose tissue stem cells and of the mechanisms involved in their commitment have been linked to adipose tissue development defects and hence to the onset/progression of metabolic diseases, such as obesity. For this reason, the characterization of early adipogenic events is crucial to understand the etiology and the evolution of adipogenesis-related pathologies, and to explore the adipose tissue precursors’ potential as future tools for precision medicine.

Genome-wide identification and expression profiling analysis of Wnt family genes affecting adipocyte differentiation in cattle

The Wnt family features conserved glycoproteins that play roles in tissue regeneration, animal development and cell proliferation and differentiation. For its functional diversity and importance, this family has been studied in several species, but not in the Bovinae. Herein we identified 19 Wnt genes in cattle, and seven other species of Bovinae, and described their corresponding protein properties. Phylogenetic analysis clustered the 149 Wnt proteins in Bovinae, and 38 Wnt proteins from the human and mouse into 12 major clades. Wnt genes from the same subfamilies shared similar protein motif compositions and exon–intron patterns. Chromosomal distribution and collinearity analysis revealed that they were conservative in cattle and five species of Bovinae. RNA-seq data analysis indicated that Wnt genes exhibited tissue-specific expression in cattle. qPCR analysis revealed a unique expression pattern of each gene during bovine adipocytes differentiation. Finally, the comprehensive analysis indicated that Wnt2B may regulate adipose differentiation by activating FZD5, which is worthy of further study. Our study presents the first genome-wide study of the Wnt gene family in Bovinae, and lays the foundation for further functional characterization of this family in bovine adipocytes differentiation.

Pharmacological inhibition of KDM5A for cancer treatment

Lysine-specific demethylase 5A (KDM5A, also named RBP2 or JARID1A) is a demethylase that can remove methyl groups from histones H3K4me1/2/3. It is aberrantly expressed in many cancers, where it impedes differentiation and contributes to cancer cell proliferation, cell metastasis and invasiveness, drug resistance, and is associated with poor prognosis. Pharmacological inhibition of KDM5A has been reported to significantly attenuate tumor progression in vitro and in vivo in a range of solid tumors and acute myeloid leukemia. This review will present the structural aspects of KDM5A, its role in carcinogenesis, a comparison of currently available approaches for screening KDM5A inhibitors, a classification of KDM5A inhibitors, and its potential as a drug target in cancer therapy.

Genistein regulates adipogenesis by blocking the function of adenine nucleotide translocase-2 in the mitochondria

Genistein exerts anti-adipogenic effects, but its target molecules remain unclear. Here, we delineated the molecular mechanism underlying the anti-adipogenic effect of genistein. A pulldown assay using genistein-immobilized beads identified adenine nucleotide translocase-2 as a genistein-binding protein in adipocytes. Adenine nucleotide translocase-2 exchanges ADP/ATP through the mitochondrial inner membrane. Similar to the knockdown of adenine nucleotide translocase-2, genistein treatment decreased ADP uptake into the mitochondria and ATP synthesis. Genistein treatment and adenine nucleotide translocase-2 knockdown suppressed adipogenesis and increased phosphorylation of AMP-activated protein kinase. Adenine nucleotide translocase-2 knockdown reduced the transcriptional activity of CCAAT/enhancer-binding protein β, whereas AMP-activated protein kinase inhibition restored the suppression of adipogenesis by adenine nucleotide translocase-2 knockdown. These results indicate that genistein interacts directly with adenine nucleotide translocase-2 to suppress its function. The downregulation of adenine nucleotide translocase-2 reduces the transcriptional activity of CCAAT/enhancer-binding protein β via activation of AMP-activated protein kinase, which consequently represses adipogenesis.

Bivalent Regulation and Related Mechanisms of H3K4/27/9me3 in Stem Cells

The "bivalent domain" is a unique histone modification region consisting of two histone tri-methylation modifications. Over the years, it has been revealed that the maintenance and dynamic changes of the bivalent domains play a vital regulatory role in the differentiation of various stem cell systems, as well as in other cells, such as immunomodulation. Tri-methylation modifications involved in the formation of the bivalent domains are interrelated and mutually regulated, thus regulating many life processes of cells. Tri-methylation of histone H3 at lysine 4 (H3K4me3), tri-methylation of histone H3 at lysine 9 (H3K9me3) and tri-methylation of histone H3 at lysine 27 (H3K27me3) are the main tri-methylation modifications involved in the formation of bivalent domains. The three form different bivalent domains in pairs. Furthermore, it is equally clear that H3K4me3 is a positive regulator of transcription and that H3K9me3/H3K27me3 are negative regulators. Enzymes related to the regulation of histone methylation play a significant role in the "homeostasis" and "breaking homeostasis" of the bivalent domains. Bivalent domains regulate target genes, upstream transcription, downstream targeting regulation and related cytokines during the establishment and breakdown of homeostasis, and exert the specific regulation of stem cells. Indeed, a unified mechanism to explain the bivalent modification in all stem cells has been difficult to define, and whether the bivalent modification is antagonistic in inducing the differentiation of homologous stem cells is controversial. In this review, we focus on the different bivalent modifications in several key stem cells and explore the main mechanisms and effects of these modifications involved. Finally, we discussed the close relationship between bivalent domains and immune cells, and put forward the prospect of the application of bivalent domains in the field of stem cells.

The emerging role of KDM5A in human cancer

Histone methylation is a key posttranslational modification of chromatin, and its dysregulation affects a wide array of nuclear activities including the maintenance of genome integrity, transcriptional regulation, and epigenetic inheritance. Variations in the pattern of histone methylation influence both physiological and pathological events. Lysine-specific demethylase 5A (KDM5A, also known as JARID1A or RBP2) is a KDM5 Jumonji histone demethylase subfamily member that erases di- and tri-methyl groups from lysine 4 of histone H3. Emerging studies indicate that KDM5A is responsible for driving multiple human diseases, particularly cancers. In this review, we summarize the roles of KDM5A in human cancers, survey the field of KDM5A inhibitors including their anticancer activity and modes of action, and the current challenges and potential opportunities of this field.

Running Against the Wnt: How Wnt/β-Catenin Suppresses Adipogenesis

Mesenchymal stem cells (MSCs) give rise to adipocytes, osteocytes, and chondrocytes and reside in various tissues, including bone marrow and adipose tissue. The differentiation choices of MSCs are controlled by several signaling pathways, including the Wnt/β-catenin signaling. When MSCs undergo adipogenesis, they first differentiate into preadipocytes, a proliferative adipocyte precursor cell, after which they undergo terminal differentiation into mature adipocytes. These two steps are controlled by the Wnt/β-catenin pathway, in such a way that when signaling is abrogated, the next step in adipocyte differentiation can start. This sequence suggests that the main role of Wnt/β-catenin signaling is to suppress differentiation while increasing MSC and preadipocytes cell mass. During later steps of MSC differentiation, however, active Wnt signaling can promote osteogenesis instead of keeping the MSCs undifferentiated and proliferative. The exact mechanisms behind the various functions of Wnt signaling remain elusive, although recent research has revealed that during lineage commitment of MSCs into preadipocytes, Wnt signaling is inactivated by endogenous Wnt inhibitors. In part, this process is regulated by histone-modifying enzymes, which can lead to increased or decreased Wnt gene expression. The role of Wnt in adipogenesis, as well as in osteogenesis, has implications for metabolic diseases since Wnt signaling may serve as a therapeutic target.

KLF2 Inhibits Chicken Preadipocyte Differentiation at Least in Part via Directly Repressing PPARγ Transcript Variant 1 Expression

Peroxisome proliferator-activated receptor gamma (PPARγ) is the master regulatory factor of preadipocyte differentiation. As a result of alternative splicing and alternative promoter usage, PPARγ gene generates multiple transcript variants encoding two protein isoforms. Krüppel-like factor 2 (KLF2) plays a negative role in preadipocyte differentiation. However, its underlying mechanism remains incompletely understood. Here, we demonstrated that KLF2 inhibited the P1 promoter activity of the chicken PPARγ gene. Bioinformatics analysis showed that the P1 promoter harbored a conserved putative KLF2 binding site, and mutation analysis showed that the KLF2 binding site was required for the KLF2-mediated transcription inhibition of the P1 promoter. ChIP, EMSA, and reporter gene assays showed that KLF2 could directly bind to the P1 promoter regardless of methylation status and reduced the P1 promoter activity. Consistently, histone modification analysis showed that H3K9me2 was enriched and H3K27ac was depleted in the P1 promoter upon KLF2 overexpression in ICP1 cells. Furthermore, gene expression analysis showed that KLF2 overexpression reduced the endogenous expression of PPARγ transcript variant 1 (PPARγ1), which is driven by the P1 promoter, in DF1 and ICP1 cells, and that the inhibition of ICP1 cell differentiation by KLF2 overexpression was accompanied by the downregulation of PPARγ1 expression. Taken together, our results demonstrated that KLF2 inhibits chicken preadipocyte differentiation at least inpart via direct downregulation of PPARγ1 expression.

Epigenetic regulation of adipogenesis by histone-modifying enzymes

Many studies investigating the transcriptional control of adipogenesis have been published so far; recently the research is focusing on the role of epigenetic mechanisms in regulating the process of adipocyte development. Histone-modifying enzymes and the histone tails post-transcriptional modifications catalyzed by them, are fundamentally involved in the epigenetic regulation of adipogenesis. In our review, we will discuss recent advances in epigenomic regulation of adipogenesis with a focus on histone-modifying enzymes implicated in the various phases of adipocytes differentiation process from mesenchymal stem cells to mature adipocytes. Understanding adipogenesis, may provide new ways to treat obesity and related metabolic diseases.

JMJD2C triggers the growth of multiple myeloma cells via activation of β‑catenin

Emerging evidence has indicated that histone modification and its related regulators are involved in the progression of multiple myeloma (MM) cells. In the present study, the expression of Jumonji C domain‑containing 2 (JMJD2) was examined in both MM tissues and healthy controls. The roles of JMJD2C in the progression of MM were further investigated. The results revealed that the expression of JMJD2C, but not that of JMJD2A or JMJD2B, was increased in MM tissues compared with the healthy controls. The overexpression of JMJD2C significantly increased the in vitro growth of MM cells. The inhibitor of the β‑catenin signaling pathway significantly attenuated the JMJD2C‑induced growth of MM cells. Mechanistical analyses indicated that JMJD2C increased the transcription of β‑catenin in MM cells, which may be due to the fact that JMJD2C can directly bind with the promoter of β‑catenin. Furthermore, JMJD2C activated β‑catenin in MM cells via a GSK3β‑dependent manner, which was evidenced by the results demonstrating that the overexpression of GSK3β attenuated the JMJD2C‑induced decrease in the phosphorylation of β‑catenin. On the whole, the findings of the present study demonstrated that JMJD2C promotes the malignancy of MM via the activation of the β‑catenin pathway. These results suggested that JMJD2C may be a potential target for MM treatment.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Expression and Function of WNT6: From Development to Disease

WNT family member 6 (WNT6) is a member of the highly conserved WNT protein family. It plays an essential role in the normal development process, not only in embryonic morphogenesis, but also in post-natal homeostasis. WNT6 functions in mice and humans. This review summarizes the current findings on the biological functions of WNT6, describing its involvement in regulating embryogenesis, decidualization, and organ development. Aberrant WNT6 signaling is related to various pathologies, such as promoting cancer development, lung tuberculosis, and kidney fibrosis and improving the symptoms of Rett syndrome (RTT). Thus, due to its various functions, WNT6 has great potential for in-depth research. This work not only describes the signaling mechanism and function of WNT6 under physiological and pathological conditions, but also provides a theoretical basis for targeted therapy.

Morolic Acid 3-O-Caffeate Inhibits Adipogenesis by Regulating Epigenetic Gene Expression

Obesity causes a wide range of metabolic diseases including diabetes, cardiovascular disease, and kidney disease. Thus, plenty of studies have attempted to discover naturally derived compounds displaying anti-obesity effects. In this study, we evaluated the inhibitory effects of morolic acid 3-O-caffeate (MAOC), extracted from Betula schmidtii, on adipogenesis. Treatment of 3T3-L1 cells with MAOC during adipogenesis significantly reduced lipid accumulation and decreased the expression of adiponectin, a marker of mature adipocytes. Moreover, the treatment with MAOC only during the early phase (day 0-2) sufficiently inhibited adipogenesis, comparable with the inhibitory effects observed following MAOC treatment during the whole processes of adipogenesis. In the early phase of adipogenesis, the expression level of Wnt6, which inhibits adipogenesis, increased by MAOC treatment in 3T3-L1 cells. To identify the gene regulatory mechanism, we assessed alterations in histone modifications upon MAOC treatment. Both global and local levels on the Wnt6 promoter region of histone H3 lysine 4 trimethylation, an active transcriptional histone marker, increased markedly by MAOC treatment in 3T3-L1 cells. Our findings identified an epigenetic event associated with inhibition of adipocyte generation by MAOC, suggesting its potential as an efficient therapeutic compound to cure obesity and metabolic diseases.

Molecular mechanisms of KDM5A in cellular functions: Facets during development and disease

Gene expression is influenced at many layers by a fine-tuned crosstalk between multiple extrinsic signalling pathways and intrinsic regulatory molecules that respond to environmental stimuli. Epigenetic modifiers like DNA methyltransferases, histone modifying enzymes and chromatin remodellers are reported to act as triggering factors in many scenarios by exhibiting their control over most of the cellular processes. These epigenetic players can either directly regulate gene expression or interact with some effector molecules that harmonize the expression of downstream genes. One such epigenetic regulator which exhibits multifaceted regulation over gene expression is KDM5A. It is classically a transcriptional repressor acting as H3K4me3 demethylase, but also is reported to act as an activator in many contexts either by loss of activity due to inhibition manifested by other interacting proteins or by downregulating the negative players of a given physiological process thereby escalating the framework. Through this review, we draw attention to the remarkable modes of functioning laid by KDM5A on transcriptional and translational processes, affecting gene expression during differentiation and development and finally summing up on role in disease causation (Fig. 1). We also shed light on different orthologs of KDM5A and their organism specific roles, along with comparison of the sequence similarity to extrapolate some unanswered questions about this protein.

Exposure to HBCD promotes adipogenesis both in vitro and in vivo by interfering with Wnt6 expression

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant, and a ubiquitous environmental contaminant. However, effects and mechanisms underlying HBCD and the development of obesity remain largely unknown. Here, we investigated the effects and underlying mechanisms of HBCD on adipogenesis. Our results firstly disclosed that both murine 3T3-L1 and human HPA-V preadipocyte exposed to HBCD displayed markedly enhanced adipogenesis, manifesting with increase of triglyceride accumulation and expression of adipogenic marker genes. HBCD was further identified to play roles mainly during early-stage adipogenesis and increased expression of Pparγ, a key adipogenic regulator. Interestingly, HBCD didn't affect early key event mitotic clonal expansion (MCE), expression and activation of early pivotal factor C/EBPβ. In virtue of RNA sequencing, HBCD was further demonstrated to specially block Wnt6 gene expression and inhibited the Wnt/β-catenin pathway at an early stage of adipogenesis. Consistent with cellular finding, C57BL/6 male mice chronically exposed to HBCD exhibited specially increased epididymal white adipose tissue (eWAT) weight gain, elevated expression of master adipogenic genes and down-regulated expression of Wnt6 in eWAT. Taking together, our findings firstly revealed that HBCD promotes adipogenesis in vitro and in vivo by specifically inhibiting Wnt6 expression, presumably connecting exposure of HBCD to the development of obesity.

Taurine-mediated browning of white adipose tissue is involved in its anti-obesity effect in mice

Taurine, a nonprotein amino acid, is widely distributed in almost all animal tissues. Ingestion of taurine helps to improve obesity and its related metabolic disorders. However, the molecular mechanism underlying the protective role of taurine against obesity is not completely understood. In this study, it was found that intraperitoneal treatment of mice with taurine alleviated high-fat diet (HFD)-induced obesity, improved insulin sensitivity, and increased energy expenditure and adaptive thermogenesis of the mice. Meanwhile, administration of the mice with taurine markedly induced the browning of inguinal white adipose tissue (iWAT) with significantly elevated expression of PGC1α, UCP1, and other thermogenic genes in iWAT. In vitro studies indicated that taurine also induced the development of brown-like adipocytes in C3H10T1/2 white adipocytes. Knockdown of PGC1α blunted the role of taurine in promoting the brown-like adipocyte phenotypes in C3H10T1/2 cells. Moreover, taurine treatment enhanced AMPK phosphorylation in vitro and in vivo, and knockdown of AMPKα1 prevented taurine-mediated induction of PGC1α in C3H10T1/2 cells. Consistently, specific knockdown of PGC1α in iWAT of the HFD-fed mice inhibited taurine-induced browning of iWAT, with the role of taurine in the enhancement of adaptive thermogenesis, the prevention of obesity, and the improvement of insulin sensitivity being partially impaired. These results reveal a functional role of taurine in facilitating the browning of white adipose tissue, which depends on the induction of PGC1α. Our studies also suggest a potential mechanism for the protective role of taurine against obesity, which involves taurine-mediated browning of white adipose tissue.

Enhanced acetylation of ATP-citrate lyase promotes the progression of nonalcoholic fatty liver disease

Hepatic steatosis is a hallmark of nonalcoholic fatty liver disease (NAFLD) and is promoted by dysregulated de novo lipogenesis. ATP-citrate lyase (ACLY) is a crucial lipogenic enzyme that is up-regulated in individuals with NAFLD. A previous study has shown that acetylation of ACLY at Lys-540, Lys-546, and Lys-554 (ACLY-3K) increases ACLY protein stability by antagonizing its ubiquitylation, thereby promoting lipid synthesis and cell proliferation in lung cancer cells. But the functional importance of this regulatory mechanism in other cellular or tissue contexts or under other pathophysiological conditions awaits further investigation. Here, we show that ACLY-3K acetylation also promotes ACLY protein stability in AML12 cells, a mouse hepatocyte cell line, and found that the deacetylase sirtuin 2 (SIRT2) deacetylates ACLY-3K and destabilizes ACLY in these cells. Of note, the livers of mice and humans with NAFLD had increased ACLY protein and ACLY-3K acetylation levels and decreased SIRT2 protein levels. Mimicking ACLY-3K acetylation by replacing the three lysines with three glutamines (ACLY-3KQ variant) promoted lipid accumulation both in high glucose-treated AML12 cells and in the livers of high-fat/high-sucrose (HF/HS) diet-fed mice. Moreover, overexpressing SIRT2 in AML12 cells inhibited lipid accumulation, which was more efficiently reversed by overexpressing the ACLY-3KQ variant than by overexpressing WT ACLY. Additionally, hepatic SIRT2 overexpression decreased ACLY-3K acetylation and its protein level and alleviated hepatic steatosis in HF/HS diet-fed mice. Our findings reveal a posttranscriptional mechanism underlying the up-regulation of hepatic ACLY in NAFLD and suggest that the SIRT2/ACLY axis is involved in NAFLD progression.