Comprehensive analysis of differences of N6-methyladenosine RNA methylomes between high-fat-fed and normal mouse livers

Mettl3-m6A-YTHDF1 axis promotion of mitochondrial dysfunction in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

N6-methyladenosine (m6A) mRNA modification and mitochondrial function hold paramount importance in the advancement of metabolic dysfunction-associated steatotic liver disease (MASLD).

AIM

The aim of this study was to elucidate the impact of m6A on hepatic mitochondrial dysfunction and provide a novel perspective for a more comprehensive understanding of the pathogenesis of MASLD.

METHODS

High-throughput screening methods were used to identify the underlying transcriptome and proteome changes in MASLD model mice. Western blotting, blue native gel electrophoresis (BNGE), dot blot, and Seahorse analyses were conducted to identify and validate the underlying regulatory mechanisms of m6A on mitochondria.

RESULTS

In vivo, abnormal m6A modification in MASLD was attributed to the upregulation of methyltransferase like 3 (Mettl3) and the downregulation of YTH N6-methyladenosine RNA binding protein 1 (YTHDF1) induced by high-fat foods. In vitro, knockdown of Mettl3 inhibited hepatic oxidative phosphorylation (OXPHOS) and the mitochondrial respiratory chain (MRC), while overexpression of Mettl3 promoted these processes. However, knockout of the reader protein YTHDF1, which plays a crucial role in the m6A modification process, counteracted the effect of Mettl3 and suppressed mitochondrial OXPHOS.

CONCLUSIONS

In MASLD, damage to the MRC may be regulated by the Mettl3-m6A-YTHDF1 axis, particularly by the role of YTHDF1. Modulation of the Mettl3-m6A-YTHDF1 axis has the potential to improve mitochondrial function, alleviate MASLD symptoms, and decrease the likelihood of disease progression.

YTHDC2 mediated RNA m6A modification contributes to PM2.5-induced hepatic steatosis

Exposure to fine particulate matter (PM2.5) is a significant risk factor for hepatic steatosis. The N6-methyladenosine (m6A) is implicated in metabolic disturbances triggered by exogenous environmental factors. However, the role of m6A in mediating PM2.5-induced hepatic steatosis remains unclear. Herein, male C57BL/6J mice were subjected to PM2.5 exposure throughout the entire heating season utilizing a real-ambient PM2.5 whole-body inhalation exposure system. Concurrently, HepG2 cell models exposed to PM2.5 were developed to delve the role of m6A methylation modification. Following PM2.5 exposure, significant hepatic lipid accumulation and elevated global m6A level were observed both in vitro and in vivo. The downregulation of YTHDC2, an m6A-binding protein, might contribute to this alteration. In vitro studies revealed that lipid-related genes CEPT1 and YWHAH might be targeted by m6A modification. YTHDC2 could bind to CDS region of them and increase their stability. Exposure to PM2.5 shortened mRNA lifespan and suppressed the expression of CEPT1 and YWHAH, which were reversed to baseline or higher level upon the enforced expression of YTHDC2. Consequently, our findings indicate that PM2.5 induces elevated m6A methylation modification of CEPT1 and YWHAH by downregulating YTHDC2, which in turn mediates the decrease in the mRNA stabilization and expression of these genes, ultimately resulting in hepatic steatosis.

Insight into the regulatory mechanism of m6A modification: From MAFLD to hepatocellular carcinoma

In recent years, there has been a significant increase in the incidence of metabolic-associated fatty liver disease (MAFLD), which has been attributed to the increasing prevalence of type 2 diabetes mellitus (T2DM) and obesity. MAFLD affects more than one-third of adults worldwide, making it the most prevalent liver disease globally. Moreover, MAFLD is considered a significant risk factor for hepatocellular carcinoma (HCC), with MAFLD-related HCC cases increasing. Approximately 1 in 6 HCC patients are believed to have MAFLD, and nearly 40 % of these HCC patients do not progress to cirrhosis, indicating direct transformation from MAFLD to HCC. N6-methyladenosine (m6A) is commonly distributed in eukaryotic mRNA and plays a crucial role in normal development and disease progression, particularly in tumors. Numerous studies have highlighted the close association between abnormal m6A modification and cellular metabolic alterations, underscoring its importance in the onset and progression of MAFLD. However, the specific impact of m6A modification on the progression of MAFLD to HCC remains unclear. Can targeting m6A effectively halt the progression of MAFLD-related HCC? In this review, we investigated the pivotal role of abnormal m6A modification in the transition from MAFLD to HCC, explored the potential of m6A modification as a therapeutic target for MAFLD-related HCC, and proposed possible directions for future investigations.

Crosstalk between Epigenetics and Metabolic Reprogramming in Metabolic Dysfunction-Associated Steatotic Liver Disease-Induced Hepatocellular Carcinoma: A New Sight

Epigenetic and metabolic reprogramming alterations are two important features of tumors, and their reversible, spatial, and temporal regulation is a distinctive hallmark of carcinogenesis. Epigenetics, which focuses on gene regulatory mechanisms beyond the DNA sequence, is a new entry point for tumor therapy. Moreover, metabolic reprogramming drives hepatocellular carcinoma (HCC) initiation and progression, highlighting the significance of metabolism in this disease. Exploring the inter-regulatory relationship between tumor metabolic reprogramming and epigenetic modification has become one of the hot directions in current tumor metabolism research. As viral etiologies have given way to metabolic dysfunction-associated steatotic liver disease (MASLD)-induced HCC, it is urgent that complex molecular pathways linking them and hepatocarcinogenesis be explored. However, how aberrant crosstalk between epigenetic modifications and metabolic reprogramming affects MASLD-induced HCC lacks comprehensive understanding. A better understanding of their linkages is necessary and urgent to improve HCC treatment strategies. For this reason, this review examines the interwoven landscape of molecular carcinogenesis in the context of MASLD-induced HCC, focusing on mechanisms regulating aberrant epigenetic alterations and metabolic reprogramming in the development of MASLD-induced HCC and interactions between them while also updating the current advances in metabolism and epigenetic modification-based therapeutic drugs in HCC.

Landscape of transcriptome-wide m6A modification in diabetic liver reveals rewiring of PI3K-Akt signaling after physical exercise

AIM

Type 2 diabetes mellitus (T2DM) is one of the most common diseases, and epigenetic modification N6-methyladenosine (m6A) is essential for transcriptional modulation involved in its development. However, the precise role and landscape of transcriptome-wide m6A alterations in molecular adaptations after physical exercise have yet to be fully elucidated.

METHODS

Four-week-old male C57BL/6J mice received a high-fat diet (HFD) for 12 weeks to establish a diabetic state, and HFD mice were simultaneously subjected to physical exercise (HFD + EX). The hepatic RNA m6A methylome was examined, the conjoint MeRIP-seq and RNA-seq was performed, and the exercise-modulated genes were confirmed.

RESULTS

Physical exercise significantly ameliorates liver metabolic disorder and triggers a dynamic change in hepatic RNA m6A. By analyzing the distribution of m6A in transcriptomes, an abundance of m6A throughout mRNA transcripts and a pattern of conserved m6A after physical exercise was identified. It is noteworthy that conjoint MeRIP-seq and RNA-seq data revealed that both differentially methylated genes and differentially expressed genes were enriched in all stages of the PI3K-Akt signaling pathway, in particular the upstream nodes of this pathway, which are considered a valuable therapeutic target for T2DM. Moreover, in vivo and in vitro analyses showed that exercise-mediated methyltransferase Rbm15 positively regulated the expression of two upstream genes (Itga3 and Fgf21) in an m6A-dependent manner.

CONCLUSION

These findings highlight the pivotal role of the exercise-induced m6A epigenetic network and contribute insights into the intricate epigenetic mechanism underlying insulin signaling.

m6A RNA Methylation and Implications for Hepatic Lipid Metabolism

This review presents a summary of recent progress in research on the N6-methyladenosine (m6A) modification and regulatory roles in hepatic lipid metabolism. As the most abundant internal modification of eukaryotic RNA, the m6A modification is a dynamic and reversible process of the m6A enzyme system, which includes writers, erasers, and readers. m6A methylation depressed lipid synthesis and facilitated lipolysis in liver. The depletion of m6A methyltransferase Mettl14/Mettl3 raised fatty acid synthase (FAS), stearoyl-CoA desaturase-1 (SCD1), acetyl-CoA carboxylase (ACC), and elongase of very long chain fatty acids 6 (ELOVL6) in rodent liver, causing increases in liver weight, triglyceride (TG) production, and content in hepatocytes. FTO catalyzed m6A demethylation and the suppression m6A reader YTHDC2 promoted hepatocellular TG generation and hepatic steatosis in C57BL/6 mice through sterol regulatory element-binding protein 1c (SREBP-1c) signaling pathway, which upregulated the lipogenic genes FAS, SCD1, ACC, recombinant acetyl coenzyme a carboxylase alpha, and cell death-inducing DNA fragmentation factor-like effector C (CIDEC). Furthermore, FTO overexpression did not only enhance mitochondrial fusion to impair mitochondrial function and lipid oxidation but also promoted lipid peroxidation, accompanied by excessive TG in hepatocytes and rodent liver. Elevated m6A modification potently suppressed hepatic lipid accumulation, while the shrinkage of m6A modification arose hepatic lipid deposition. These findings have highlighted the beneficial role of m6A RNA methylation in hepatic lipid metabolism, potentially protecting liver from lipid metabolic disorders.

N6-methyladenosine (m6A) modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the deadliest cancers of human, the tumor-related death of which ranks third among the common malignances. N6-methyladenosine (m6A) methylation, the most abundant internal modification of RNA in mammals, participates in the metabolism of mRNA and interrelates with ncRNAs. In this paper, we overviewed the complex function of m6A regulators in HCC, including regulating the tumorigenesis, progression, prognosis, stemness, metabolic reprogramming, autophagy, ferroptosis, drug resistance and tumor immune microenvironment (TIME). Furthermore, we elucidated the interplay between m6A modification and non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). Finally, we summarized the potential of m6A regulators as diagnostic biomarkers. What's more, we reviewed the inhibitors targeting m6A enzymes as promising therapeutic targets of HCC. We aimed to help understand the function of m6A methylation in HCC systematically and comprehensively so that more effective strategies for HCC treatment will be developed.

The role of m6A modification in type 2 diabetes: A systematic review and integrative analysis

This study focuses on the latest developments in the studies of m6A modification and provides an up-to-date summary of the association between m6A modification and type 2 diabetes (T2D). The possible mechanisms of m6A related to T2D were summarized by literature review. The differentially expressed genes (DEGs) of m6A methylase in T2D were analyzed from 12 datasets in Gene Expression Omnibus (GEO). The associations between m6A level and T2D were explored in four electronic databases, including PubMed, EmBase, Web of Science and CNKI. Standard mean difference (SMD) and 95 % confidence interval (95 %CI) was calculated to assess the total effect in integrative analysis. Differential expression genes detected in at least three of six tissues were ZC3H13, YTHDC1/2, and IGF2BP2. LRPPRC were differentially expressed in five tissues except in arterial tissue. A total of 6 studies were included for integrative analysis. The mean m6A levels were significantly lower in T2D than those in normal controls (SMD = -1.35, 95 %CI: -2.58 to -0.11). This systematic review and integrative analysis summarize the previous studies on the association between m6A modification and T2D and the possible role of m6A modification in the progression of T2D, such as abnormal blood glucose, abnormal pancreatic β-cell function, insulin resistance, and abnormal lipid metabolism. The integrative analysis showed that decreased level of m6A was associated with T2D. These findings provide new targets for early detection and treatment for T2D.

Identification of m6A-associated autophagy genes in non-alcoholic fatty liver

Background

Studies had shown that autophagy was closely related to nonalcoholic fat liver disease (NAFLD), while N6-methyladenosine (m6A) was involved in the regulation of autophagy. However, the mechanism of m6A related autophagy in NAFLD was unclear.

Methods

The NAFLD related datasets were gained via the Gene Expression Omnibus (GEO) database, and we also extracted 232 autophagy-related genes (ARGs) and 37 m6A. First, differentially expressed ARGs (DE-ARGs) and differentially expressed m6A (DE-m6A) were screened out by differential expression analysis. DE-ARGs associated with m6A were sifted out by Pearson correlation analysis, and the m6A-ARGs relationship pairs were acquired. Then, autophagic genes in m6A-ARGs pairs were analyzed for machine learning algorithms to obtain feature genes. Further, we validated the relationship between feature genes and NAFLD through quantitative real-time polymerase chain reaction (qRT-PCR), Western blot (WB). Finally, the immuno-infiltration analysis was implement, and we also constructed the TF-mRNA and drug-gene networks.

Results

There were 19 DE-ARGs and four DE-m6A between NAFLD and normal samples. The three m6A genes and five AGRs formed the m6A-ARGs relationship pairs. Afterwards, genes obtained from machine learning algorithms were intersected to yield three feature genes (TBK1, RAB1A, and GOPC), which showed significant positive correlation with astrocytes, macrophages, smooth muscle, and showed significant negative correlation with epithelial cells, and endothelial cells. Besides, qRT-PCR and WB indicate that TBK1, RAB1A and GOPC significantly upregulated in NAFLD. Ultimately, we found that the TF-mRNA network included FOXP1-GOPC, ATF1-RAB1A and other relationship pairs, and eight therapeutic agents such as R-406 and adavosertib were predicted based on the TBK1.

Conclusion

The study investigated the potential molecular mechanisms of m6A related autophagy feature genes (TBK1, RAB1A, and GOPC) in NAFLD through bioinformatic analyses and animal model validation. However, it is critical to note that these findings, although consequential, demonstrate correlations rather than cause-and-effect relationships. As such, more research is required to fully elucidate the underlying mechanisms and validate the clinical relevance of these feature genes.

Molecular mechanisms in MASLD/MASH-related HCC

Liver cancer is the third leading cause of cancer-related deaths and ranks as the sixth most prevalent cancer type globally. NAFLD or metabolic dysfunction-associated steatotic liver disease, and its more severe manifestation, NASH or metabolic dysfunction-associated steatohepatitis (MASH), pose a significant global health concern, affecting approximately 20%-25% of the population. The increased prevalence of metabolic dysfunction-associated steatotic liver disease and MASH is parallel to the increasing rates of obesity-associated metabolic diseases, including type 2 diabetes, insulin resistance, and fatty liver diseases. MASH can progress to MASH-related HCC (MASH-HCC) in about 2% of cases each year, influenced by various factors such as genetic mutations, carcinogen exposure, immune microenvironment, and microbiome. MASH-HCC exhibits distinct molecular and immune characteristics compared to other causes of HCC and affects both men and women equally. The management of early to intermediate-stage MASH-HCC typically involves surgery and locoregional therapies, while advanced HCC is treated with systemic therapies, including anti-angiogenic therapies and immune checkpoint inhibitors. In this comprehensive review, we consolidate previous research findings while also providing the most current insights into the intricate molecular processes underlying MASH-HCC development. We delve into MASH-HCC-associated genetic variations and somatic mutations, disease progression and research models, multiomics analysis, immunological and microenvironmental impacts, and discuss targeted/combined therapies to overcome immune evasion and the biomarkers to recognize treatment responders. By furthering our comprehension of the molecular mechanisms underlying MASH-HCC, our goal is to catalyze the advancement of more potent treatment strategies, ultimately leading to enhanced patient outcomes.

Progress of epigenetic modification of SATB2 gene in the pathogenesis of non-syndromic cleft lip and palate

Non-syndromic Cleft Lip and Palate (NSCLP) is one of the most common congenital craniofacial malformations. However, there is no enough knowledge about its mechanism, even through many relevant studies verify that cleft lip and palate is caused by interactions between environmental and genetic factors. SATB2 gene is one of the most common candidate genes of NSCLP, and the development of epigenetics provides a new direction on pathogenesis of cleft lip and palate. This review summarizes SATB2 gene in the pathogenesis of non-syndromic cleft lip and palate, expecting to provide strategies to prevent and treat cleft and palate in the future.

N6-methyladenosine RNA modification in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, influencing numerous regulatory axes and extrahepatic vital organs. The molecular mechanisms that lead to the progression of NAFLD remain unclear and knowledge on the pathways causing hepatocellular damage followed by lipid accumulation is limited. Recently, a number of studies have shown that mRNA N6-methyladenosine (m6A) modification contributes to the progression of NAFLD. In this review, we summarize current knowledge on m6A modification in the metabolic processes associated with NAFLD and discuss the challenges of and prospects for therapeutic avenues based on m6A regulation for the treatment of liver disease.

Alternative splicing: a bridge connecting NAFLD and HCC

Non-alcoholic fatty liver disease (NAFLD) is becoming the most important risk factor for hepatocellular carcinoma (HCC). Understanding the progression of benign diseases to HCC is crucial for early prevention and reversal of malignant transformation. Alternative splicing (AS) of RNA plays a role in the pathogenicity, initiation, and transformation of liver disease. We summarize the changes or mutations in the activity of splicing factors in NAFLD and HCC, as well as the impact of AS mediated by epigenetic modifications such as DNA methylation, RNA methylation, histone modification, and protein phosphorylation on liver cell fate. We also summarize therapeutic methods and drugs that are helpful for treating NAFLD, HCC, and the early stages of NAFLD progression to HCC.

Changes in m6A in Steatotic Liver Disease

Fatty liver disease is one of the major causes of morbidity and mortality worldwide. Fatty liver includes non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH), now replaced by a consensus group as metabolic dysfunction-associated steatotic liver disease (MASLD). While excess nutrition and obesity are major contributors to fatty liver, the underlying mechanisms remain largely unknown and therapeutic interventions are limited. Reversible chemical modifications in RNA are newly recognized critical regulators controlling post-transcriptional gene expression. Among these modifications, N6-methyladenosine (m6A) is the most abundant and regulates transcript abundance in fatty liver disease. Modulation of m6A by readers, writers, and erasers (RWE) impacts mRNA processing, translation, nuclear export, localization, and degradation. While many studies focus on m6A RWE expression in human liver pathologies, limitations of technology and bioinformatic methods to detect m6A present challenges in understanding the epitranscriptomic mechanisms driving fatty liver disease progression. In this review, we summarize the RWE of m6A and current methods of detecting m6A in specific genes associated with fatty liver disease.

Metabolo-epigenetic interplay provides targeted nutritional interventions in chronic diseases and ageing

Epigenetic modifications are chemical modifications that affect gene expression without altering DNA sequences. In particular, epigenetic chemical modifications can occur on histone proteins -mainly acetylation, methylation-, and on DNA and RNA molecules -mainly methylation-. Additional mechanisms, such as RNA-mediated regulation of gene expression and determinants of the genomic architecture can also affect gene expression. Importantly, depending on the cellular context and environment, epigenetic processes can drive developmental programs as well as functional plasticity. However, misbalanced epigenetic regulation can result in disease, particularly in the context of metabolic diseases, cancer, and ageing. Non-communicable chronic diseases (NCCD) and ageing share common features including altered metabolism, systemic meta-inflammation, dysfunctional immune system responses, and oxidative stress, among others. In this scenario, unbalanced diets, such as high sugar and high saturated fatty acids consumption, together with sedentary habits, are risk factors implicated in the development of NCCD and premature ageing. The nutritional and metabolic status of individuals interact with epigenetics at different levels. Thus, it is crucial to understand how we can modulate epigenetic marks through both lifestyle habits and targeted clinical interventions -including fasting mimicking diets, nutraceuticals, and bioactive compounds- which will contribute to restore the metabolic homeostasis in NCCD. Here, we first describe key metabolites from cellular metabolic pathways used as substrates to "write" the epigenetic marks; and cofactors that modulate the activity of the epigenetic enzymes; then, we briefly show how metabolic and epigenetic imbalances may result in disease; and, finally, we show several examples of nutritional interventions - diet based interventions, bioactive compounds, and nutraceuticals- and exercise to counteract epigenetic alterations.

U-shaped association between serum IGF2BP3 and T2DM: A cross-sectional study in Chinese population

OBJECTIVE

To clarify the expression of N6-methyladenosine (m⁶ A) modulators involved in the pathogenesis of type 2 diabetes mellitus (T2DM). We further explored the association of serum insulin-like growth factor 2 mRNA-binding proteins 3 (IGF2BP3) levels and odds of T2DM in a high-risk population.

METHODS

The gene expression data set GSE25724 was obtained from the Gene Expression Omnibus, and a cluster heatmap was generated by using the R package ComplexHeatmap. Differential expression analysis for 13 m⁶ A RNA methylation regulators between nondiabetic controls and T2DM subjects was performed using an unpaired t test. A cross-sectional design, including 393 subjects (131 patients with newly diagnosed T2DM, 131 age- and sex-matched subjects with prediabetes, and 131 healthy controls), was carried out. The associations between serum IGF2BP3 concentrations and T2DM were modeled by restricted cubic spline and logistic regression models.

RESULTS

Two upregulated (IGF2BP2 and IGF2BP3) and 5 downregulated (methyltransferase-like 3 [METTL3], alkylation repair homolog protein 1 [ALKBH1], YTH domain family 2 [YTHDF2], YTHDF3, and heterogeneous nuclear ribonucleoprotein [HNRNPC]) m⁶ A-related genes were found in islet samples of T2DM patients. A U-shaped association existed between serum IGF2BP3 levels and odds of T2DM according to cubic natural spline analysis models, after adjustment for body mass index, waist circumference, diastolic blood pressure, total cholesterol, and triglyeride. Multivariate logistic regression showed that progressively higher odds of T2DM were observed when serum IGF2BP3 levels were below 0.62 ng/mL (odds ratio 3.03 [95% confidence interval 1.23-7.47]) in model 4.

CONCLUSION

Seven significantly altered m⁶ A RNA methylation genes were identified in T2DM. There was a U-shaped association between serum IGF2BP3 levels and odds of T2DM in the general Chinese adult population. This study provides important evidence for further examination of the role of m⁶ A RNA methylation, especially serum IGF2BP3 in T2DM risk assessment.

Roles of RNA m6A modification in nonalcoholic fatty liver disease

NAFLD is a series of liver disorders, and it has become the most prevalent hepatic disease to date. However, there are no approved and effective pharmaceuticals for NAFLD owing to a poor understanding of its pathological mechanisms. While emerging studies have demonstrated that m6A modification is highly associated with NAFLD. In this review, we summarize the general profile of NAFLD and m6A modification, and the role of m6A regulators including erasers, writers, and readers in NAFLD. Finally, we also highlight the clinical significance of m6A in NAFLD.

N6-methyladenosine in macrophage function: a novel target for metabolic diseases

N6-methyladenosine (m⁶A) is one of the most prevalent internal transcriptional modifications. Evidence has highlighted changes in m⁶A in metabolic disorders and various metabolic diseases. However, the precise mechanisms of these m⁶A changes in such conditions are not understood. Macrophages are crucial for the innate immune system and exert either beneficial or harmful roles in metabolic disease. Notably, m⁶A was found to be closely related to macrophage phenotype and dysfunction. In this review, we summarize m⁶A in macrophage function from the perspective of macrophage development, activation, and polarization, pyroptosis, and metabolic disorders. Furthermore, we discuss how m⁶A-mediated macrophage function affects metabolic diseases, including atherosclerosis and nonalcoholic fatty liver disease (NAFLD). Finally, we discuss challenges and prospects for m⁶A in macrophage and metabolic diseases with the aim of providing guidance for the treatment of metabolic diseases.

Insights into the role of nucleotide methylation in metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disease characterized by fatty infiltration of the liver. In recent years, the MAFLD incidence rate has risen and emerged as a serious public health concern. MAFLD typically progresses from the initial hepatocyte steatosis to steatohepatitis and then gradually advances to liver fibrosis, which may ultimately lead to cirrhosis and carcinogenesis. However, the potential evolutionary mechanisms still need to be clarified. Recent studies have shown that nucleotide methylation, which was directly associated with MAFLD's inflammatory grading, lipid synthesis, and oxidative stress, plays a crucial role in the occurrence and progression of MAFLD. In this review, we highlight the regulatory function and associated mechanisms of nucleotide methylation modification in the progress of MAFLD, with a particular emphasis on its regulatory role in the inflammation of MAFLD, including the regulation of inflammation-related immune and metabolic microenvironment. Additionally, we summarize the potential value of nucleotide methylation in the diagnosis and treatment of MAFLD, intending to provide references for the future investigation of MAFLD.

Polychlorinated biphenyls alter hepatic m6A mRNA methylation in a mouse model of environmental liver disease

Exposure to polychlorinated biphenyls (PCBs) has been associated with liver injury in human cohorts and with nonalcoholic steatohepatitis (NASH) in mice fed a high fat diet (HFD). N (6)-methyladenosine (m6A) modification of mRNA regulates transcript fate, but the contribution of m6A modification on the regulation of transcripts in PCB-induced steatosis and fibrosis is unknown. This study tested the hypothesis that PCB and HFD exposure alters the levels of m6A modification in transcripts that play a role in NASH in vivo. Male C57Bl6/J mice were fed a HFD (12 wks) and administered a single oral dose of Aroclor1260, PCB126, or Aroclor1260 + PCB126. Genome-wide identification of m6A peaks was accomplished by m6A mRNA immunoprecipitation sequencing (m6A-RIP) and the mRNA transcriptome identified by RNA-seq. Exposure of HFD-fed mice to Aroclor1260 decreased the number of m6A peaks and m6A-containing genes relative to PCB vehicle control whereas PCB126 or the combination of Aroclor1260 + PCB126 increased m6A modification frequency. ∼41% of genes had one m6A peak and ∼49% had 2-4 m6A peaks. 117 m6A peaks were common in the four experimental groups. The Aroclor1260 + PCB126 exposure group showed the highest number (52) of m6A-peaks. qRT-PCR confirmed enrichment of m6A-containing fragments of the Apob transcript with PCB exposure. A1cf transcript abundance, m6A peak count, and protein abundance was increased with Aroclor1260 + PCB126 co-exposure. Irrespective of the PCB type, all PCB groups exhibited enriched pathways related to lipid/lipoprotein metabolism and inflammation through the m6A modification. Integrated analysis of m6A-RIP-seq and mRNA-seq identified 242 differentially expressed genes (DEGs) with increased or reduced number of m6A peaks. These data show that PCB exposure in HFD-fed mice alters the m6A landscape offering an additional layer of regulation of gene expression affecting a subset of gene responses in NASH.

Overview of distinct 5-methylcytosine profiles of messenger RNA in normal and knock-down NSUN2 colorectal cancer cells

Background: Colorectal cancer (CRC) is a harmful cancer with high morbidity and poor prognosis. There is growing evidence that RNA methylation is closely related to the occurrence of cancer and its malignant biological behavior. N6-methyladenosine (m⁶A) methylation is the most common RNA modification in eukaryotes, and its multiple regulatory mechanisms in CRC have been elucidated from multiple perspectives. At the same time, the role of 5-methylcytosine (m5C), another important and widely distributed methylation modification, in CRC is far from being elucidated. Methods: In this study, we used RNA immunoprecipitation sequencing combined with bioinformatics methods to identify the m5C peaks on messenger RNA (mRNA) in HCT15 cells and sh-NSUN2 HCT15 cells, understand which transcripts are modified by m5C, and characterize the distribution of m5C modifications. In addition, we performed further bioinformatics analysis of the detected data to initially clarify the potential function of these m5C-modified transcripts. Results: We found significant differences in the distribution of m5C between HCT15 cells and sh-NSUN2 HCT15 cells, suggesting that m5C is likely to play a key role in the occurrence and development of CRC. Furthermore, Gene Ontology (GO) enrichment analysis showed that genes altered by m5C were mainly enriched in phylogeny, synaptic membrane, and transcription factor binding. The Kyoto Encyclopedia of Genes and Genomes (KEGG)pathway analysis showed that the genes altered by m5C are enriched in ECM receptor interaction pathway, the circadian pathway, and the cAMP signaling pathway. Conclusion: Here, our study preliminarily revealed the different distribution patterns of m5C between HCT15 cell and sh-NSUN2 HCT15 cell. Our results open a new window to understand the role of m5C RNA methylation of mRNA in the development of CRC.

Novel insights into the N6-methyladenosine RNA modification and phytochemical intervention in lipid metabolism

Epitranscriptome (RNA modification) plays a vital role in a variety of biological events. N6-methyladenosine (m6A) modification is the most prevalent mRNA modification in eukaryotic cells. Dynamic and reversible m6A modification affects the plasticity of epitranscriptome, which plays an essential role in lipid metabolism. In this review, we comprehensively delineated the role and mechanism of m6A modification in the regulation of lipid metabolism in adipose tissue and liver, and summarized phytochemicals that improve lipid metabolism disturbance by targeting m6A regulator, providing potential lead candidates for drug therapeutics. Moreover, we discussed the main challenges and possible future directions in this field.

METTL16-mediated translation of CIDEA promotes non-alcoholic fatty liver disease progression via m6A-dependent manner

Background

As the most prevalent chemical modifications on eukaryotic mRNAs, N6-methyladenosine (m6A) methylation was reported to participate in the regulation of various metabolic diseases. This study aimed to investigate the roles of m6A methylation and methyltransferase-like16 (METTL16) in non-alcoholic fatty liver disease (NAFLD).

Methods

In this study, we used a model of diet-induced NAFLD, maintaining six male C57BL/6J mice on high-fat diet (HFD) to generate hepatic steatosis. The high-throughput sequencing and RNA sequencing were performed to identify the m6A methylation patterns and differentially expressed mRNAs in HFD mice livers. Furthermore, we detected the expression levels of m6A modify enzymes by qRT-PCR in liver tissues, and further investigated the potential role of METTL16 in NAFLD through constructing overexpression and a knockdown model of METTL16 in HepG2 cells.

Results

In total, we confirmed 15,999 m6A recurrent peaks in HFD mice and 12,322 in the control. Genes with differentially methylated m6A peaks were significantly associated with the dysregulated glucolipid metabolism and aggravated hepatic inflammatory response. In addition, we identified five genes (CIDEA, THRSP, OSBPL3, GDF15 and LGALS1) that played important roles in NAFLD progression after analyzing the differentially expressed genes containing differentially methylated m6A peaks. Intriguingly, we found that the expression levels of METTL16 were substantially increased in the NAFLD model in vivo and in vitro, and further confirmed that METTL16 upregulated the expression level of lipogenic genes CIDEA in HepG2 cells.

Conclusions

These results indicate the critical roles of m6A methylation and METTL16 in HFD-induced mice and cell NAFLD models, which broaden people's perspectives on potential m6A-related treatments and biomarkers for NAFLD.

Transcriptome-Wide Study of mRNAs and lncRNAs Modified by m6A RNA Methylation in the Longissimus Dorsi Muscle Development of Cattle-Yak

Cattle-yak is a hybrid F₁ generation of cattle and yak, which has a history of more than 3000 years and has shown better production performance and higher economic benefits than those of yaks. However, up to now, there has been no study on the transcriptome-wide m⁶A methylation profile of bovine skeletal muscle and its potential biological function during muscle development. Here, we observed significant changes in the expression levels of muscle-related marker genes and methylation-related enzymes during the development of cattle-yak, and the overall m⁶A content in the Longissimus dorsi muscle of 18-month-old cattle-yak decreased significantly. A total of 36,602 peaks, 11,223 genes and 8388 lncRNAs were identified in the two groups, including 2989 differential peaks (427 up-regulated peaks and 2562 down-regulated peaks), 1457 differentially expressed genes (833 up-regulated genes and 624 down-regulated genes) and 857 differentially expressed lncRNAs (293 up-regulated lncRNAs and 564 down-regulated lncRNAs). GO and KEGG analysis revealed that they were significantly enriched in some muscle-related pathways (Wnt signaling pathway and MAPK signaling pathway) and high-altitude adaptation-related pathway (HIF-1 signaling pathway). Moreover, m⁶A abundance was positively correlated with gene expression levels, while it was negatively correlated with lncRNA expression levels. This indicates that m⁶A modification played an important role in the Longissimus dorsi muscle development of cattle-yak; however, the regulation mechanism of m⁶A-modified mRNA and lncRNA may be different. This study was the first report of transcriptome-wide m⁶A-modified mRNAs and lncRNAs atlas in the Longissimus dorsi muscle development of cattle-yak, one which will provide new perspectives for genetic improvement in bovines.

RNA m6A modification in liver biology and its implication in hepatic diseases and carcinogenesis

N6-methyladenosine (m6A) is the most prevalent internal modification in eukaryotic RNAs. This modification is regulated by three different factors (writers, erasers, and readers) and affects multiple aspects of RNA metabolism, including RNA splicing, nuclear export, translation, stability and decay. The m6A-mediated modification plays important roles in posttranscriptional regulation of gene expression and mediates a variety of cellular and biological processes. Accordingly, deregulation in m6A modification is closely related to the occurrence and development of human diseases. The liver is the largest digestive and metabolic organ in human and recent studies have shown that m6A modification is importantly implicated in liver cellular and physiological functions and in the pathogenesis of hepatic diseases and cancers. In the current review, we summarize the functions of m6A in RNA metabolism and its roles in liver cell biology and discuss its implication in hepatic diseases and carcinogenesis.

FTO promotes liver inflammation by suppressing m6A mRNA methylation of IL-17RA

Background

Previous studies have demonstrated that inflammation-related interleukin-17 (IL-17) signaling plays a pivotal role in the pathogenesis of non-alcoholic steatohepatitis (NASH)- and alcoholic liver disease (ALD)-induced hepatocellular carcinoma (HCC). However, rare efforts have been intended at implementing the analysis of N6-methyladenosine (m6A) mRNA methylation to elucidate the underpinning function of the IL-17 receptor A (IL-17RA) during the inflammation-carcinogenesis transformation of HCC.

Methods

We performed methylated RNA immunoprecipitation sequencing (MeRIP-seq) using normal, HCC tumor and paired tumor adjacent tissues from patients to investigate the dynamic changes of m6A mRNA methylation in the process of HCC. Additionally, murine non-alcoholic fatty liver disease (NAFLD) model and murine chronic liver injury model were utilized to investigate the role of IL-17RA regulated by m6A mRNA modulator fat mass and obesity-associated (FTO) in chronic hepatic inflammation.

Results

MeRIP-seq revealed the reduction of m6A mRNA methylation of IL-17RA in tumor adjacent tissues with chronic inflammation, suggesting the potential role of IL-17RA in the inflammation-carcinogenesis transformation of HCC. Besides, we demonstrated that FTO, rather than methyltransferase-like 3 (METTL3), methyltransferase-like 14 (METTL14), and alkB homolog 5 (ALKBH5) functions as a main modulator for the decrease of m6A mRNA methylation of IL-17RA via knockdown and overexpression of FTO in vitro and in vivo.

Conclusions

Overall, we elaborated the underlying mechanisms of the increase of IL-17RA resulting in chronic inflammation via the demethylation of FTO in tumor adjacent tissues and demonstrated that targeting the specific m6A modulator FTO may provide an effective treatment for hepatitis patients to prevent the development of HCC.

Global N6-methyladenosine methylation analysis reveals the positive correlation between m6A modification and mRNA abundance during Apostichopus japonicus disease development

N⁶-methyladenosine (m⁶A), the most abundant epitranscriptomic modification in eukaryotic messenger RNA (mRNA), plays important roles in regulation of gene expression for fundamental biological processes and diverse physiological functions, including combating with pathogen infection. Here, we were first profile transcriptome-wide m⁶A sequencing in four stages of skin ulceration syndrome-diseased Apostichopus japonicus following Vibrio splendidus infection, including Control (healthy), Early (small ulcer), Later (extensive ulcer), and Resistant (no ulcer) groups. Our results revealed that three experimental groups were all extensively methylated by m⁶A and the proportion of the m⁶A modified genes were also significantly increased to 28.90% (Early), 27.97% (Later), and 29.98% (Resistant) when compared with Control group (15.15%), indicating m⁶A modification could be induced by V. splendidus infection. Intriguingly, we discovered a positive correlation between the m⁶A methylation level and mRNA abundance, indicating a positive regulatory role of m⁶A in sea cucumber gene expression during V. splendidus infection. Moreover, genes with specific and differentially expressed m⁶A methylation in Later group were both enriched in cell adhesion, while Early and Resistant groups were both mainly involved in DNA conformation change and chromosome organization when compared with Control, suggesting the higher-methylated m⁶A might serve as "conformational marker" and associated to the initiation of related anti-disease genes transcription in order to improve disease resistance of sea cucumber. Subsequently, we selected the pivotal genes enriched in cell adhesion pathway and found that the IggFc-binding protein (FcGBP) and Fibrocystin-L both had higher levels of m⁶A methylation and higher level of mRNA expressions in Later group. Conversely, Fibrinogen C domain-containing protein 1 (F1BCD1) gene presented as an antibacterial role in sea cucumber and showed higher mRNA expression and higher m⁶A methylation in Resistant group and lower mRNA level in Later group. The levels of m⁶A methylation and mRNA abundance of FcGBP and F1BCD1 genes indicates disease occurrence or disease resistant were also verified by MeRIP-qPCR. Overall, our study presents the first comprehensive characterize of dynamic m⁶A methylation modification in the different stages of disease in sea cucumber. These data provide an invaluable resource for future studies of function and biological significance of m⁶A in mRNA in marine invertebrates.

The methyltransferase METTL3-mediated fatty acid metabolism revealed the mechanism of cinnamaldehyde on alleviating steatosis

BACKGROUND

As a primarily N6-methyladenosine methyltransferase, methyltransferase 3 (METTL3) plays a crucial role in nonalcoholic fatty liver disease. However, its regulatory mechanism in steatosis remains unknown.

METHODS

Alpha mouse liver 12 (AML12) cells were induced by free fatty acids (FFA). Triglycerides, lipid droplet assay, and Oil Red O staining were performed to evaluate steatosis. The expression of METTL3 and cytochrome P450 family 4 subfamily f polypeptide 40 (CYP4F40) was measured using Western blotting, real-time quantitative polymerase chain reaction, and dual-luciferase reporter assay. Triglycerides, total cholesterol, almandine aminotransferase, and aspartate aminotransferase were assayed after cinnamaldehyde treatment. Transcriptomics and metabolomics were performed to determine how METTL3 and cinnamaldehyde regulate steatosis.

RESULTS

METTL3 protein level was reduced in FFA-induced steatosis in AML12 cells, and METTL3 knockdown aggravated the steatosis. Cinnamaldehyde alleviated steatosis by increasing METTL3 expression. A combined transcriptomics and metabolomics analysis revealed that METTL3 knockdown reduced CYP4F40 expression and reduced the level of capric acid, gamma-linolenic acid, arachidonic acid, and docosapentaenoic acid. Cinnamaldehyde promoted CYP4F40 expression by increasing METTL3 and increased the levels of capric acid, gamma-linolenic acid, arachidonic acid, and docosapentaenoic acid. Finally, the beneficial effects of cinnamaldehyde on steatosis were reversed after METTL3 knockdown.

CONCLUSIONS

METTL3 knockdown aggravated steatosis in AML12 cells through CYP4F40-mediated fatty acid metabolism, and cinnamaldehyde alleviated steatosis via the METTL3-CYP4F40 pathway.

Transcriptome-Wide Dynamics of m6A Methylation in Tumor Livers Induced by ALV-J Infection in Chickens

Avian Leukosis Virus Subgroup J (ALV-J) is a tumorigenic virus with high morbidity and rapid transmission. N6-methyladenosine (m⁶A) is a common epigenetic modification that may be closely related to the pathogenicity of ALV-J. Currently, there are no reports on whether m⁶A modification is related to ALV-J induced tumor formation. In this study, we used methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) to examine the differences in m⁶A methylation and gene expression in normal livers and ALV-J-induced tumor livers systematically, with functional enrichment and co-expression analysis. The results identified 6,541 m⁶A methylated peaks, mainly enriched in CDS, and more than 83% of the transcripts contained 1-2 m⁶A peaks. For RNA-seq, 1,896 and 1,757 differentially expressed mRNAs and lncRNAs were identified, respectively. Gene enrichment analysis indicated that they may be involved in biological processes and pathways such as immunology-related and apoptosis. Moreover, we identified 17 lncRNAs, commonly existing in differently expressed methylome and transcriptome. Through co-expression analysis, 126 differentially expressed lncRNAs, and 18 potentially m⁶A-related methyltransferases were finally identified and connected, suggesting that m⁶A modifications might affect gene expression of lncRNAs and play a role in ALV-J induced tumor formation. This study provides the first comprehensive description of the m⁶A expression profile in tumor livers induced by ALV-J infection in chickens, which provides a basis for studying the role of m⁶A modification in ALV-J induced tumorigenesis. This study provides clues for studying the epigenetic etiology and pathogenesis of ALV-J.

METTL3-m6A-Rubicon axis inhibits autophagy in nonalcoholic fatty liver disease

N6-methyladenosine (m⁶A) mRNA modification plays critical roles in various biological events and is involved in multiple complex diseases. However, the role of m⁶A modification in autophagy in nonalcoholic fatty liver disease (NAFLD) remains largely unknown. Here, we report that m⁶A modification was increased in livers of NAFLD mouse models and in free fatty acid (FFA)-treated hepatocytes, and the abnormal m⁶A modification was attributed to the upregulation of methyltransferase like 3 (METTL3) induced by lipotoxicity. Knockdown of METTL3 promoted hepatic autophagic flux and clearance of lipid droplets (LDs), while overexpression of METTL3 inhibited these processes. Mechanistically, METTL3 directly bound to Rubicon mRNA and mediated the m⁶A modification, while YTH N6-methyladenosine RNA binding protein 1 (YTHDF1), as a partner of METTL3, interacted with the m⁶A-marked Rubicon mRNA and promoted its stability. Subsequently, RUBICON inhibited autophagosome-lysosome fusion and further blocked clearance of LDs. Taken together, our results showed a critical role of METTL3 and YTHDF1 in regulating lipid metabolism via the autophagy pathway and provided a novel insight into m⁶A mRNA methylation in NAFLD.

Analysis of N6-Methyladenosine Methylome in Adenocarcinoma of Esophagogastric Junction

Background: From previous studies, we found that there are more than 100 types of RNA modifications in RNA molecules. m⁶A methylation is the most common. The incidence rate of adenocarcinoma of the esophagogastric junction (AEG) at home and abroad has increased faster than that of stomach cancer at other sites in recent years. Here, we systematically analyze the modification pattern of m⁶A mRNA in adenocarcinoma at the esophagogastric junction.

Methods: m⁶A sequencing, RNA sequencing, and bioinformatics analysis were used to describe the m⁶A modification pattern in adenocarcinoma and normal tissues at the esophagogastric junction.

Results: In AEG samples, a total of 4,775 new m⁶A peaks appeared, and 3,054 peaks disappeared. The unique m6A-related genes in AEG are related to cancer-related pathways. There are hypermethylated or hypomethylated m⁶A peaks in AEG in differentially expressed mRNA transcripts.

Conclusion: This study preliminarily constructed the first m⁶A full transcriptome map of human AEG. This has a guiding role in revealing the mechanism of m⁶A-mediated gene expression regulation.

Integrated Study of Transcriptome-wide m6A Methylome Reveals Novel Insights Into the Character and Function of m6A Methylation During Yak Adipocyte Differentiation

Yak (Bos grunniens) is considered an iconic symbol of Tibet and high altitude, but they suffer from malnutrition during the cold season that challenges the metabolism of energy. Adipocytes perform a crucial role in maintaining the energy balance, and adipocyte differentiation is a complex process involving multiple changes in the expression of genes. N ⁶-methyladenosine (m⁶A) plays a dynamic role in post-transcription gene expression regulation as the most widespread mRNA modification of the higher eukaryotes. However, currently there is no research existing on the m⁶A transcriptome-wide map of bovine animals and their potential biological functions in adipocyte differentiation. Therefore, we performed methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) to determine the distinctions in m⁶A methylation and gene expression during yak adipocyte differentiation. In yak adipocyte and preadipocyte the content of m⁶A and m⁶A-associated enzymes was substantially different. In the two groups, a total of 14,710 m⁶A peaks and 13,388 m⁶A peaks were identified. For the most part, m⁶A peaks were enriched in stop codons, 3'-untranslated regions, and coding regions with consensus motifs of GGACU. The functional enrichment exploration displayed that differentially methylated genes participated in some of the pathways associated with adipogenic metabolism, and several candidate genes (KLF9, FOXO1, ZNF395, and UHRF1) were involved in these pathways. In addition to that, there was a positive association between m⁶A abundance and levels of gene expression, which displayed that m⁶A may play a vital role in modulating gene expression during yak adipocyte differentiation. Further, in the adipocyte group, several methylation gene protein expression levels were significantly higher than in preadipocytes. In short, it can be concluded that the current study provides a comprehensive explanation of the m⁶A features in the yak transcriptome, offering in-depth insights into m⁶A topology and associated molecular mechanisms underlying bovine adipocyte differentiation, which might be helpful for further understanding its mechanisms.

Unique features of the m6A methylome and its response to drought stress in sea buckthorn (Hippophae rhamnoides Linn.)

In plants, recent studies have revealed that N6-methyladenosine (m⁶A) methylation of mRNA has potential regulatory functions of this mRNA modification in many biological processes. m⁶A methyltransferase, m⁶A demethylase and m⁶A-binding proteins can cause differential phenotypes, indicating that m⁶A may have critical roles in the plant. In this study, we depicted the m⁶A map of sea buckthorn (Hippophae rhamnoides Linn.) transcriptome. Similar to A. thaliana, m⁶A sites of sea buckthorn transcriptome is significantly enriched around the stop codon and within 3'-untranslated regions (3'UTR). Gene ontology analysis shows that the m⁶A modification genes are associated with metabolic biosynthesis. In addition, we identified 13,287 different m⁶A peaks (DMPs) between leaf under drought (TR) and control (CK) treatment. It reveals that m⁶A has a high level of conservation and has a positive correlation with mRNA abundance in plants. GO and KEGG enrichment results showed that DMP modification DEGs in TR were particularly associated with ABA biosynthesis. Interestingly, our results showed three m⁶A demethylase (HrALKBH10B, HrALKBH10C and HrALKBH10D) genes were significantly increased following drought stress, which indicated that it may contributed the decreased m⁶A levels. This exhaustive m⁶A map provides a basis and resource for the further functional study of mRNA m⁶A modification in abiotic stress.

N 6-Methyladenosine Methylomic Landscape of Lung Tissues in Murine Acute Allergic Asthma

Allergic asthma is well known as a common respiratory disorder comprising an allergic inflammatory nature and excessive immune characteristic. N ⁶-methyladenosine (m6A) methylation is an RNA epigenetic modification that post-transcriptionally regulates gene expression and function by affecting the RNA fate. Currently, m6A methylation is gaining attention as a mechanism of immunoregulation. However, whether m6A methylation engages the pathological process of asthma remains uncertain. Here, we present the m6A methylomic landscape in the lung tissues of ovalbumin-induced acute asthma mice using MeRIP-seq and RNA-seq. We identified 353 hypermethylated m6A peaks within 329 messenger RNAs (mRNAs) and 150 hypomethylated m6A peaks within 143 mRNAs in the lung tissues of asthmatic mice. These differentially methylated mRNAs were found to be involved in several immune function-relevant signaling pathways. In addition, we predicted 25 RNA-binding proteins that recognize the differentially methylated peak sites by exploring public databases, and the roles of these proteins are mostly related to mRNA biogenesis and metabolism. To further investigate the expression levels of the differentially methylated genes, we performed combined analysis of the m6A methylome and transcriptome data and identified 127 hypermethylated mRNAs (107 high and 20 low expression) and 43 hypomethylated mRNAs with differential expressions (9 high and 34 low expression). Of these, there are a list of mRNAs involved in immune function and regulation. The present results highlight the essential role of m6A methylation in the pathogenesis of asthma.

Advances in RNA Epigenetic Modifications in Hepatocellular Carcinoma and Potential Targeted Intervention Strategies

The current interventions for hepatocellular carcinoma (HCC) are not satisfactory, and more precise targets and promising strategies need to be explored. Recent research has demonstrated the non-negligible roles of RNA epigenetic modifications such as N6-methyladenosine (m6A) and 5-methylcytosine (m5C) in various cancers, including HCC. However, the specific targeting mechanisms are not well elucidated. In this review, we focus on the occurrence and detailed physiopathological roles of multiple RNA modifications on diverse RNAs closely related to the HCC process. In particular, we highlight fresh insights into the impact mechanisms of these posttranscriptional modifications on the whole progression of HCC. Furthermore, we analyzed the possibilities and significance of these modifications and regulators as potential therapeutic targets in HCC treatment, which provides the foundation for exploring targeted intervention strategies. This review will propel the identification of promising therapeutic targets and novel strategies that can be translated into clinical applications for HCC treatment.

Regulatory role and mechanism of m6A RNA modification in human metabolic diseases

Metabolic diseases caused by disorders in amino acids, glucose, lipid metabolism, and other metabolic risk factors show high incidences in young people, and current treatments are ineffective. N⁶-methyladenosine (m⁶A) RNA modification is a post-transcriptional regulation of gene expression with several effects on physiological processes and biological functions. Recent studies report that m⁶A RNA modification is involved in various metabolic pathways and development of common metabolic diseases, making it a potential disease-specific therapeutic target. This review explores components, mechanisms, and research methods of m⁶A RNA modification. In addition, we summarize the progress of research on m⁶A RNA modification in metabolism-related human diseases, including diabetes, obesity, non-alcoholic fatty liver disease, osteoporosis, and cancer. Furthermore, opportunities and the challenges facing basic research and clinical application of m⁶A RNA modification in metabolism-related human diseases are discussed. This review is meant to enhance our understanding of the molecular mechanisms, research methods, and clinical significance of m⁶A RNA modification in metabolism-related human diseases.

Dietary Patterns Influence Target Gene Expression through Emerging Epigenetic Mechanisms in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) refers to the pathologic buildup of extra fat in the form of triglycerides in liver cells without excessive alcohol intake. NAFLD became the most common cause of chronic liver disease that is tightly associated with key aspects of metabolic disorders, including insulin resistance, obesity, diabetes, and metabolic syndrome. It is generally accepted that multiple mechanisms and pathways are involved in the pathogenesis of NAFLD. Heredity, sedentary lifestyle, westernized high sugar saturated fat diet, metabolic derangements, and gut microbiota, all may interact on a on genetically susceptible individual to cause the disease initiation and progression. While there is an unquestionable role for gene-diet interaction in the etiopathogenesis of NAFLD, it is increasingly apparent that epigenetic processes can orchestrate many aspects of this interaction and provide additional mechanistic insight. Exciting research demonstrated that epigenetic alterations in chromatin can influence gene expression chiefly at the transcriptional level in response to unbalanced diet, and therefore predispose an individual to NAFLD. Thus, further discoveries into molecular epigenetic mechanisms underlying the link between nutrition and aberrant hepatic gene expression can yield new insights into the pathogenesis of NAFLD, and allow innovative epigenetic-based strategies for its early prevention and targeted therapies. Herein, we outline the current knowledge of the interactive role of a high-fat high-calories diet and gene expression through DNA methylation and histone modifications on the pathogenesis of NAFLD. We also provide perspectives on the advancement of the epigenomics in the field and possible shortcomings and limitations ahead.

Integrated analysis of m6A mRNA methylation in rats with monocrotaline-induced pulmonary arterial hypertension

Background: N6-methyladenosine (m⁶A) modification is one of the most common chemical modifications of eukaryotic mRNAs, which play an important role in tumors and cardiovascular disease through regulating mRNA stability, splicing and translation. However, the changes of m⁶A mRNA and m⁶A-related enzymes in pulmonary arterial hypertension (PAH) remain largely unexplored.

Methods: MeRIP-seq was used to identify m⁶A methylation in lung tissues from control and MCT-PAH rats. Western blot and immunofluorescence were used to evaluate expression of m⁶A-related enzymes.

Results: Compared with control group, m⁶A methylation was mainly increased in lung tissues from MCT-PAH rats. The up-methylated coding genes in MCT-PAH rats were primarily enriched in processes associated with inflammation, glycolysis, ECM-receptor interaction and PDGF signal pathway, while genes with down-methylation were enriched in processes associated with TGF-β family receptor members. The expression of FTO and ALKBH5 downregulated, METTL3 and YTHDF1 increased and other methylation modification-related proteins was not significantly changed in MCT-PAH rats lung tissues. Immunofluorescence indicated that expression of FTO decreased and YTHDF1 increased in small pulmonary arteries of MCT-PAH rats.

Conclusion: m⁶A levels and the expression of methylation-related enzymes were altered in PAH rats, in which FTO and YTHDF1 may play a crucial role in m⁶A modification.

Epigenetic regulation of N6-methyladenosine modifications in obesity

Obesity is a serious health issue in the world and is related to a higher risk of suffering metabolic diseases. Understanding the molecular basis of obesity is critical to identify new targets to treat obesity and obesity-associated metabolic diseases. N6-methyladenosine (m6A) modification is the most common form of ribonucleic acid modification, which has attracted increasing interest of researchers in recent years, as it is reported that m6A has vital functions in diseases and everyday life activities. Recent studies showed that m6A modification was decreased in obese adipose tissue, and appeared to play a regulatory role in many obesity-associated biological processes, including adipogenesis, lipid metabolism and insulin resistance. In this review, we discussed the emerging advances in m6A modification in obesity to provide a novel therapeutic strategy for fighting against obesity.

Comprehensive analysis of the translatome reveals the relationship between the translational and transcriptional control in high fat diet-induced liver steatosis

Translational regulation plays a critical role in gene expression. However, there are few genome-wide studies on translational regulation in non-alcoholic fatty liver disease (NAFLD), which is a severe non-communicable epidemic worldwide. In this study, we performed RNC-mRNA (mRNAs bound to ribosome-nascent chain complex) sequencing and mRNA sequencing to probe the translation status of high-fat-diet (HFD) induced mouse fatty liver. Generally, in the HFD group compared to the control group, changes of translation ratios and changes in mRNA abundance had a negative correlation. The relative abundance of RNC-mRNAs and mRNAs were positively correlated, yet the former changed more slowly than the latter. However, the rate of change became more balanced when it came to the livers of mice that were fed the HFD plus lycopene, an antioxidant. This indicated relatively independent roles of translational modulation and transcriptional regulation. Furthermore, many genes were differentially regulated at the transcriptional or translational levels, suggesting a new screening strategy for functional genes. In conclusion, our analysis revealed the different and correlated role of translational control with transcriptional regulation in the HFD-induced mouse fatty liver relative to the control, which indicates critical roles of translational control for liver steatosis; thus, adding a new dimension towards a better understanding and improvement of treatment for NAFLD.

Comprehensive Analysis of Differential m6A RNA Methylomes in the Hippocampus of Cocaine-Conditioned Mice

N6-methyladenosine (m6A) is the most prevalent internal modification found in mRNAs and lncRNA and plays a vital role in posttranscriptional regulation in mammals. m6A is abundant in the nervous system, where it modulates neuronal development and hippocampus-dependent learning and memory. However, the roles of RNAs m6A modification and its related enzymes in cocaine reward are still not fully understood. In this study, we found that the fat mass and obesity-associated gene (FTO) demethylase, but not methyltransferase-like 3 (METTL3) and 14 (METTL14), was downregulated in the hippocampus following cocaine-induced conditioned place preference (CPP), and the level of m6A is notably higher in the hippocampus of cocaine CPP training mice. Using methylated m6A RNA immunoprecipitation sequencing (MeRIP-m6A-seq), we identified a total of 6516 m6A peaks within 4460 mRNAs, and 3083 m6A peaks within 850 lncRNAs were significantly dysregulated. Intriguingly, the altered m6A peaks within mRNAs and lncRNAs were enriched in synapse maturation and localization processes. Our study uncovers a critical role for an m6A epitranscriptomic dysregulation and downregulation of FTO expression in the hippocampus following cocaine-induced CPP.

Profiling of RNA N 6 -Methyladenosine Methylation Reveals the Critical Role of m6A in Chicken Adipose Deposition

One of the main objectives of broiler breeding is to prevent excessive abdominal adipose deposition. The role of RNA modification in adipose deposition is not clear. This study was aimed to map m⁶A modification landscape in chicken adipose tissue. MeRIP-seq was performed to compare the differences in m⁶A methylation pattern between fat and lean broilers. We found that start codons, stop codons, coding regions, and 3′-untranslated regions were generally enriched for m⁶A peaks. The high m⁶A methylated genes (fat birds vs. lean birds) were primarily associated with fatty acid biosynthesis and fatty acid metabolism, while the low m⁶A methylated genes were mainly involved in processes associated with development. Furthermore, we found that the mRNA levels of many genes may be regulated by m⁶A modification. This is the first comprehensive characterization of m⁶A patterns in the chicken adipose transcriptome, and provides a basis for studying the role of m⁶A modification in fat deposition.

Low Molecular Pectin Inhibited the Lipid Accumulation by Upregulation of METTL7B

Inhibition of lipid accumulation is the key step to prevent nonalcoholic fatty liver (NAFL) progressing to nonalcoholic steatohepatitis. We aimed to study the effect of low-molecular-weight citrus pectin (LCP) against lipid accumulation and the underlying mechanism. Oleic acid (OA)-induced lipid deposition in HepG2 cells was applied to mimic in vitro model of lipid accumulation. Oil Red O (ORO) stain result showed lipid accumulation was significantly reduced, and levels of adipose triglyceride lipase (ATGL) and carnitine palmitoyltransferase-1 (CPT-1), involved in triacylglycerol catabolism and fatty acid β-oxidation, detected by RT-qPCR were increased after OA-stimulated HepG2 cells treated with LCP. RNA sequencing analysis identified 740 differentially expressed genes (DEGs) in OA-stimulated HepG2 cells treated with the LCP group (OA+LCP group), and bioinformatics analysis indicated that some DEGs were enriched in lipid metabolism-related processes and pathways. The expression of the top 8 known DEGs in the OA+LCP group was then verified by RT-qPCR, which showed that fold change (abs) of METTL7B was the highest among the 8 candidates. In addition, overexpression of METTL7B in HepG2 cells significantly inhibited the lipid accumulation and enhanced levels of ATGL and CPT-1. In conclusion, LCP inhibited lipid accumulation through the upregulation of METTL7B, and further enhancement of ATGL and CPT-1 levels. LCP is expected to develop as a promising agent to ameliorate fat accumulation in NAFL.

Comprehensive analysis of lncRNAs N6-methyladenosine modification in colorectal cancer

BACKGROUND

Long non-coding RNAs (lncRNAs) and their N6-methyladenosine (M6A) modifications are involved in cancer occurrence and development.

METHODS

lncRNA M6A modification in colorectal cancer (CRC) was comprehensively analyzed for the first time.

RESULTS

M6A levels of lnRNAs in CRC tissues were higher than those in tumor-adjacent normal tissues. A total of 8,332 M6A peaks were detected in 6,690 lncRNAs in CRC tissues. Approximately 91% of the modified lncRNAs had unique M6A modification peaks. A total of 383 lncRNAs were differentially methylated in CRC, of which 48.24% had a length of 1-1,000 bp. Most of these were located on chromosomes 1, 2, 7, 11, 16 and 19; 42.3% were within a sense-overlapping exon. RNA sequencing identified 163 differentially expressed lncRNAs in CRC. GO and KEGG analyses revealed that genes near differentially-methylated or -expressed lncRNAs were associated with CRC occurrence and development. Methylation was positively correlated with lncRNA expression levels in CRC and tumor-adjacent normal tissues. More unmethylated than M6A methylated lncRNA molecules were detected. A competing endogenous RNA (ceRNA) and lncRNA-mRNA expression-regulation network revealed a regulatory relationship between lncRNAs, microRNAs (miRNAs), and mRNAs.

CONCLUSIONS

The findings may help improve our understanding of lncRNA function in colorectal cancer.

IL-37 Confers Anti-Tumor Activity by Regulation of m6A Methylation

N6-methyladenosine (m6A) is a common transcriptomic modification in cancer. Recently, it has been found to be involved in the regulation of non-small cell lung cancer (NSCLC) formation and metastasis. Interleukin 37 (IL-37) plays a crucial protective role in lung cancer. In our previous studies, we found that IL-37 is a potential novel tumor suppressor by inhibiting IL-6 expression to suppress STAT3 activation and decreasing epithelial-to-mesenchymal transition. Moreover, we found that treatment of IL-37 in lung cancer cells induced widespread and dynamic RNA m6A methylation. The effects of RNA m6A methylation of IL-37 treatment require further study. However, the functions of RNA m6A methylation of IL-37 treatment still await elucidation. Using MeRIP-seq and RNA-seq, we uncovered a unique m6A methylation profile in the treatment of IL-37 on the A549 cell line. We also showed the expression of m6A writers METTL3, METTL14, and WTAP and erasers ALKBH5 and FTO in A549 cells and lung cancer tissues after the treatment of IL-37. This study showed that IL-37 could lead to changes in m6A methylation level and related molecule expression level in A546 cells and may downregulate the proliferation by inhibiting Wnt5a/5b pathway in A549 cells. We conclude that IL-37 suppresses tumor growth through regulation of RNA m6A methylation in lung cancer cells.

Analysis of N6-Methyladenosine Methylation Modification in Fructose-Induced Non-Alcoholic Fatty Liver Disease

Improvements in living standards have led to non-alcoholic fatty liver disease (NAFLD), one of the most common chronic liver diseases worldwide. Recent studies have shown that N6-methyladenosine (m6A), a type of RNA modification, is strongly associated with many important biological processes. However, the relationship between m6A methylation modifications and NAFLD remains poorly understood. In the present study, through methylated RNA immunoprecipitation sequencing and RNA transcriptome sequencing in high fructose diet-induced NAFLD mice, we found that hypermethylation-encoding genes were mainly enriched in lipid metabolism processes. We identified 266 overlapping and differentially expressed genes (DEGs) that changed at both the mRNA expression level and m6A modification level. Among them, 193 genes displayed increased expression and m6A modification, indicating that m6A RNA modifications tend to be positively correlated with NAFLD. We further compared the high fructose diet-induced NAFLD mouse model with leptin receptor-deficient mice and found that DEGs enriched in the lipid metabolism pathway were up-regulated in both groups. In contrast, DEGs associated with the immune inflammatory response were up-regulated in the high fructose diet group, but down-regulated in leptin receptor-deficient mice. Taken together, our results demonstrate that m6A methylation modifications may play an important role in the development of NAFLD.

Epigenetics of Hepatic Insulin Resistance

Insulin resistance (IR) is largely recognized as a unifying feature that underlies metabolic dysfunction. Both lifestyle and genetic factors contribute to IR. Work from recent years has demonstrated that the epigenome may constitute an interface where different signals may converge to promote IR gene expression programs. Here, we review the current knowledge of the role of epigenetics in hepatic IR, focusing on the roles of DNA methylation and histone post-translational modifications. We discuss the broad epigenetic changes observed in the insulin resistant liver and its associated pathophysiological states and leverage on the wealth of 'omics' studies performed to discuss efforts in pinpointing specific loci that are disrupted by these changes. We envision that future studies, with increased genomic resolution and larger cohorts, will further the identification of biomarkers of early onset hepatic IR and assist the development of targeted interventions. Furthermore, there is growing evidence to suggest that persistent epigenetic marks may be acquired over prolonged exposure to disease or deleterious exposures, highlighting the need for preventative medicine and long-term lifestyle adjustments to avoid irreversible or long-term alterations in gene expression.

The emerging roles of m6A modification in liver carcinogenesis

The 'epitranscriptome', a collective term for chemical modifications that influence the structure, metabolism, and functions of RNA, has recently emerged as vitally important for the regulation of gene expression. N⁶-methyladenosine (m⁶A), the most prevalent mammalian mRNA internal modification, has been demonstrated to have a pivotal role in almost all vital bioprocesses, such as stem cell self-renewal and differentiation, heat shock or DNA damage response, tissue development, and maternal-to-zygotic transition. Hepatocellular carcinoma (HCC) is prevalent worldwide with high morbidity and mortality because of late diagnosis at an advanced stage and lack of effective treatment strategies. Epigenetic modifications including DNA methylation and histone modification have been demonstrated to be crucial for liver carcinogenesis. However, the role and underlying molecular mechanism of m⁶A in liver carcinogenesis are mostly unknown. In this review, we summarize recent advances in the m⁶A region and how these new findings remodel our understanding of m⁶A regulation of gene expression. We also describe the influence of m⁶A modification on liver carcinoma and lipid metabolism to instigate further investigations of the role of m⁶A in liver biological diseases and its potential application in the development of therapeutic strategies.