METTL3 inhibition ameliorates liver damage in mouse with hepatitis B virus-associated acute-on-chronic liver failure by regulating miR-146a-5p maturation

Small Extracellular Vesicles Promote HBV Replication via METTL3-IGF2BP2-Mediated m6A Modification

BACKGROUND

The roles of small extracellular vesicles (sEVs) and mRNA modifications in regulating hepatitis B virus (HBV) transmission, replication, and related disease progression have received considerable attention. However, the mechanisms through which methyltransferase-like 3 (METTL3) and insulin-like growth factor 2 (IGF2BP2), key genes that mediate m6A modifications, regulate HBV replication in sEVs remain poorly understood. Therefore, this study investigated the molecular mechanisms through which the key molecules (METTL3 and IGF2BP2) in sEVs mediate m6A epigenetic modification to regulate HBV replication.

METHODS

Small extracellular vesicles were extracted from the supernatants of HepG2.2.15 and HepG2 cells via ultracentrifugation, followed by purification with hepatitis B virus surface antigen (HepBsAg) immunomagnetic beads. The sEVs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and Western blotting (WB). Methylation enrichment in the two types of sEVs was analyzed by dot blotting and quantitative reverse transcription-PCR (RT-qPCR). The cells were treated with HepG2.2.15-sEVs transfected with either the METTL3 plasmid, METTL3 siRNA, the IGF2BP2 plasmid, or the IGF2BP2 siRNA. After 48 h, the expression of METTL3, IGF2BP2, and HBV DNA expressions were assessed via dot blotting, quantitative-PCR (qPCR), RT-qPCR, and WB. Co-immunoprecipitation (co-IP) was performed to investigate the interactions between METTL3 and IGF2BP2.

RESULTS

By conducting TEM, DLS, and WB analyses, we confirmed that the isolated sEVs exhibited typical characteristics. HepG2.2.15-derived sEVs presented elevated levels of m6A modifications, with increased METTL3 and IGF2BP2 mRNA and protein expression levels, respectively (p < 0.05). In the overexpression (OE)-METTL3 group, the expression levels of HBV pregenomic RNA (HBV pgRNA), HBV DNA, HBV relaxed circular DNA (HBV rcDNA), HBV covalently closed circular DNA (HBV cccDNA), HBsAg, hepatitis B virus core antigen (HBcAg), and hepatitis B virus e antigen (HBeAg) were significantly elevated compared to those in the control group (p < 0.01). In contrast, results for the small interfering (SI)-METTL3 group were the opposite. Similarly, in the OE-IGF2BP2 group, HBV pgRNA, HBV DNA, HBV rcDNA, HBV cccDNA, HBsAg, HBcAg, and HBeAg expression were greater than in the control group (p < 0.05), whereas the opposite results were recorded in the SI-IGF2BP2 group. Co-immunoprecipitation confirmed that METTL3 and IGF2BP2 interact synergistically.

CONCLUSION

Small extracellular vesicles increase METTL3 and IGF2BP2 expression, synergistically promoting HBV replication by regulating m6A modification levels.

METTL3: a multifunctional regulator in diseases

N6-methyladenosine (m6A) methylation is the most prevalent and abundant internal modification of mRNAs and is catalyzed by the methyltransferase complex. Methyltransferase-like 3 (METTL3), the best-known m6A methyltransferase, has been confirmed to function as a multifunctional regulator in the reversible epitranscriptome modulation of m6A modification according to follow-up studies. Accumulating evidence in recent years has shown that METTL3 can regulate a variety of functional genes, that aberrant expression of METTL3 is usually associated with many pathological conditions, and that its expression regulatory mechanism is related mainly to its methyltransferase activity or mRNA posttranslational modification. In this review, we discuss the regulatory functions of METTL3 in various diseases, including metabolic diseases, cardiovascular diseases, and cancer. We focus mainly on recent progress in identifying the downstream target genes of METTL3 and its underlying molecular mechanisms and regulators in the above systems. Studies have revealed that the use of METTL3 as a therapeutic target and a new diagnostic biomarker has broad prospects. We hope that this review can serve as a reference for further studies.

Negative Regulation of LINC01013 by METTL3 and YTHDF2 Enhances the Osteogenic Differentiation of Senescent Pre-Osteoblast Cells Induced by Hydrogen Peroxide

Senescent pre-osteoblasts have a reduced ability to differentiate, which leads to a reduction in bone formation. It is critical to identify the keys that regulate the differentiation fate of senescent pre-osteoblasts. LINC01013 has an essential role in cell stemness, differentiation, and senescence regulation. This study aims to examine the role and mechanism of LINC01013 in regulating osteogenic differentiation in senescent human embryonic osteoblast cell line (hFOB1.19) cells induced by hydrogen peroxide (H2O2). The results show that LINC01013 decreased alkaline phosphatase activity, mineralization of hFOB1.19 cells in vitro, and the expression of collagen II, osteocalcin, and bone sialoprotein. LINC01013 knockdown enhances the osteogenesis of hFOB1.19 cells and rescues osteogenic differentiation impaired by H2O2. METTL3 negatively regulates LINC01013 expression, enhancing hFOB1.19 cells' osteogenesis in vitro and in vivo. METTL3 overexpression can enhance hFOB1.19 cells' osteogenic differentiation impaired by H2O2. YTHDF2 promotes LINC01013 decay, facilitating osteogenic differentiation. YTHDF2 overexpression rescues hFOB1.19 cells osteogenic differentiation impaired by H2O2. Taken together, METTL3 upregulates osteogenic differentiation by inhibiting LINC01013, and YTHDF2 accelerates LINC01013 degradation, reducing its inhibitory effect. This study highlights LINC01013 as a key regulator in the fate switching process of senescent hFOB1.19 cells, impacting osteogenic differentiation.

N6-Methyladenosine in Cell-Fate Determination of BMSCs: From Mechanism to Applications

The methylation of adenosine base at the nitrogen-6 position is referred to as "N6-methyladenosine (m6A)" and is one of the most prevalent epigenetic modifications in eukaryotic mRNA and noncoding RNA (ncRNA). Various m6A complex components known as "writers," "erasers," and "readers" are involved in the function of m6A. Numerous studies have demonstrated that m6A plays a crucial role in facilitating communication between different cell types, hence influencing the progression of diverse physiological and pathological phenomena. In recent years, a multitude of functions and molecular pathways linked to m6A have been identified in the osteogenic, adipogenic, and chondrogenic differentiation of bone mesenchymal stem cells (BMSCs). Nevertheless, a comprehensive summary of these findings has yet to be provided. In this review, we primarily examined the m6A alteration of transcripts associated with transcription factors (TFs), as well as other crucial genes and pathways that are involved in the differentiation of BMSCs. Meanwhile, the mutual interactive network between m6A modification, miRNAs, and lncRNAs was intensively elucidated. In the last section, given the beneficial effect of m6A modification in osteogenesis and chondrogenesis of BMSCs, we expounded upon the potential utility of m6A-related therapeutic interventions in the identification and management of human musculoskeletal disorders manifesting bone and cartilage destruction, such as osteoporosis, osteomyelitis, osteoarthritis, and bone defect.

METTL14-mediated N6-methyladenosine modification induces the ferroptosis of hypoxia/reoxygenation-induced cardiomyocytes

BACKGROUND

Hypoxia/reoxygenation (H/R) induces cardiomyocyte ferroptosis, a core remodeling event in myocardial ischemia/reperfusion injury. Methyltransferase-like 14 (METTL14) emerges as a writer of N6-methyladenosine (m6A) modification. This study was conducted to decipher the role of METTL14 in H/R-induced cardiomyocyte ferroptosis.

METHODS

Mouse cardiomyocytes HL-1 were cultured and underwent H/R treatment. The degree of ferroptosis after H/R treatment was appraised by the cell counting kit-8 assay, assay kits (ROS/GSH/Fe2+), and Western blotting (GPX4/ACSL4). The intracellular expressions of METTL14, pri-miR-146a-5p, miR-146a-5p, or adaptor protein phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1) were examined by real-time quantitative polymerase chain reaction or Western blotting, with m6A quantification analysis and RNA immunoprecipitation to determine the total m6A level and the expression of pri-miR-146a-5p bound to DiGeorge critical region 8 (DGCR8) and m6A-modified pri-miR-146a-5p. The binding of miR-146a-5p to APPL1 was testified by the dual-luciferase assay.

RESULTS

H/R treatment induced cardiomyocyte ferroptosis (increased ROS, Fe2+, and ACSL4 and decreased GSH and GPX4) and upregulated METTL14 expression. METTL14 knockdown attenuated H/R-induced cardiomyocyte ferroptosis. METTL14 induced the recognition of pri-miR-146a-5p by DGCR8 by increasing m6A modification on pri-miR-146a-5p, which promoted the conversion of pri-miR-146a-5p into miR-146a-5p and further repressed APPL1 transcription. miR-146a-5p upregulation or APPL1 downregulation limited the inhibitory effect of METTL14 downregulation on H/R-induced cardiomyocyte ferroptosis.

CONCLUSION

METTL14 promoted miR-146a-5p expression through the recognition and processing of pri-miR-146a-5p by DGCR8, which repressed APPL1 transcription and triggered H/R-induced cardiomyocyte ferroptosis.

Silencing of GDF11 suppresses hepatocyte apoptosis to relieve LPS/D-GalN acute liver failure

In this paper, we generated a short hairpin RNA growth differentiation factor-11 (sh-GDF11) and evaluated the effects of sh-GDF11 on the pathogenesis of acute liver failure (ALF) in vitro and in vivo. Through bioinformatics study, the key gene related to ALF was assayed. Lipopolysaccharide (LPS) and D-galactoamine (D-GalN) were applied to establish the mouse model of LPS/D-GalN-induced liver injury, and TNF-α and D-Gal were used to construct an in vitro cell model, followed by treatment of sh-GDF11 for analysis of liver cell proliferation. Bioinformatics analysis showed that the protective effect of sh-GDF11 on ALF may be mediated by phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway. The results of in vitro study found that sh-GDF11 could promote cell proliferation and inhibit death by blocking the PI3K/Akt/mTOR signaling pathway. In vivo animal experiments further confirmed that sh-GDF11 could suppress hepatocyte apoptosis by inhibiting the PI3K/Akt/mTOR signaling pathway. sh-GDF11 relieved LPS/D-GalN-induced ALF by blocking the PI3K/Akt/mTOR signaling pathway, emphasizing its critical role in LPS/D-GalN-induced ALF treatment.

Dysregulated microRNAs as a biomarker for diagnosis and prognosis of hepatitis B virus-associated hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a malignancy with a high incidence and fatality rate worldwide. Hepatitis B virus (HBV) infection is one of the most important risk factors for its occurrence and development. Early detection of HBV-associated HCC (HBV-HCC) can improve clinical decision-making and patient outcomes. Biomarkers are extremely helpful, not only for early diagnosis, but also for the development of therapeutics. MicroRNAs (miRNAs), a subset of non-coding RNAs approximately 22 nucleotides in length, have increasingly attracted scientists' attention due to their potential utility as biomarkers for cancer detection and therapy. HBV profoundly impacts the expression of miRNAs potentially involved in the development of hepatocarcinogenesis. In this review, we summarize the current progress on the role of miRNAs in the diagnosis and treatment of HBV-HCC. From a molecular standpoint, we discuss the mechanism by which HBV regulates miRNAs and investigate the exact effect of miRNAs on the promotion of HCC. In the near future, miRNA-based diagnostic, prognostic, and therapeutic applications will make their way into the clinical routine.

The emerging importance role of m6A modification in liver disease

N6-methyladenosine (m6A) modification, as one of the most common types of inner RNA modification in eukaryotes, plays a multifunctional role in normal and abnormal biological processes. This type of modification is modulated by m6A writer, eraser and reader, which in turn impact various processes of RNA metabolism, such as RNA processing, translation, nuclear export, localization and decay. The current academic view holds that m6A modification exerts a crucial role in the post-transcriptional modulation of gene expression, and is involved in multiple cellular functions, developmental and disease processes. However, the potential molecular mechanism and specific role of m6A modification in the development of liver disease have not been fully elucidated. In our review, we summarized the latest research progress on m6A modification in liver disease, and explored how these novel findings reshape our knowledge of m6A modulation of RNA metabolism. In addition, we also illustrated the effect of m6A on liver development and regeneration to prompt further exploration of the mechanism and role of m6A modification in liver physiology and pathology, providing new insights and references for the search of potential therapeutic targets for liver disease.

Predictive Values of Programmed Death-1, CC Chemokine Ligand 20, and Treg/T Helper 17 Cytokines for Patients with Hepatitis B Virus-Related Acute-on-Chronic Liver Failure

Background: This study aimed to explore the correlations of programmed death-1 (PD-1) and CC chemokine ligand 20 (CCL20) with Treg/T helper 17 (Th17) balance in patients with HBV-ACLF. Methods: In this cross-sectional study, 50 patients with HBV-ACLF and 50 cases with chronic hepatitis B (CHB) diagnosed from February 2021 to February 2022 were selected, and another 50 healthy volunteers who received physical examinations in the same period were selected as a control group. The expression levels of PD-1, CCL20, and Treg/Th17 cytokines were detected by Western blotting, immunoturbidimetry, and enzyme-linked immunosorbent assay (ELISA), respectively. The correlations of PD-1 and CCL20 with Treg/Th17 cytokines were explored by Pearson analysis. The predictive values of PD-1, CCL20, and Treg/Th17 cytokines for the prognosis of HBV-ACLF patients were analyzed. Results: The expression levels of PD-1 and CCL20 were higher in the HBV-ACLF group than in the CHB and control groups (P < 0.05). Severe HBV-ACLF patients had higher levels of PD-1 and CCL20 compared with mild and moderate HBV-ACLF patients (P < 0.05). Hepatitis B virus-related acute-on-chronic liver failure patients with poor prognosis had higher levels of PD-1 and CCL20 than those with good prognosis (P < 0.05). The levels of transforming growth factor β (TGF-β), interleukin 10 (IL-10), IL-23, and tumor necrosis factor α (TNF-α) were higher in the HBV-ACLF group than in the CHB and control groups (P < 0.05). The levels of PD-1 and CCL20 in the HBV-ACLF group were positively correlated with those of Treg/Th17 cytokines (TGF-β, IL-10, IL-23, and TNF-α; P < 0.05). The combined detection of PD-1, CCL20, and Treg/Th17 cytokines had higher sensitivity and lower specificity than single detection in predicting the prognosis of HBV-ACLF patients (P < 0.05). Conclusions: The expression levels of PD-1 and CCL20 are higher in HBV-ACLF patients, being correlated with Treg/Th17 balance. The combined detection of PD-1, CCL20, and Treg/Th17 cytokines has a higher value for predicting the prognosis of HBV-ACLF patients.

METTL16 regulates m6A methylation on chronic hepatitis B associated gene HLA-DPB1 involved in liver fibrosis

The role of genetic factors in the occurrence and progression of CHB (CHB) is still not fully explored. In recent years, genome-wide association studies on CHB patients have demonstrated that a large number of CHB-associated single nucleotide polymorphisms exist in the gene intron, which may regulate expression at the transcriptional level. Modification of RNA m6A methylation is one of the key mechanisms regulating gene expression. Here we show that METTL16, an m6A regulator involved in mRNA intron splicing, is differentially expressed in CHB the tissue of patients who has definite diagnosis of mild and severe fibrosis. At the same time, there are also significant differences in the expression of CHB-associated genes such as HLA-DPA1 and HLA-DPB1. The expression of HLA-DPB1 is related to METTL16. Furthermore, analyses of RNA binding of METTL16 and HLA-DPB1 show that the silencing of METTL16 in astrocytes downregulates m6A and expression of HLA-DPB1. In conclusion, METTL16 participates in the progression of CHB fibrosis by regulating the m6A level and expression of HLA-DPB1.

METTL3 Attenuates Inflammation in Fusarium solani-Induced Keratitis via the PI3K/AKT Signaling Pathway

Purpose

Our previous investigations revealed a significant role of methyltransferase-like 3 (METTL3)-mediated N6-methyladenosine (m6A) modification in the development of corneal inflammation in Fusarium infection, but the exact mechanism is unknown. Therefore, this research aimed to explore how METTL3 affects the inflammatory process of fungal keratitis (FK) in mice.

Methods

We established in vitro and in vivo models by inoculating mice and primary corneal stromal cells with F. solani. METTL3 expression was confirmed by real-time quantitative polymerase chain reaction, immunofluorescence, and western blotting. After that, siRNAMETTL3 and AAV-sh-METTL3 were transfected into cells and mice to explore the role of METTL3 in the PI3K/AKT signaling pathway and inflammation. PI3K, p-PI3K, AKT, and p-AKT expression was analyzed by western blotting. Viability of corneal stromal cells was measured using a Cell Counting Kit-8 (CCK-8). Additionally, we detected interleukin (IL)-6, IL-1β, and tumor necrosis factor alpha (TNF-α) levels in corneal tissues and analyzed the role of METTL3 in inflammation in FK using slit-lamp biomicroscopy and hematoxylin and eosin staining.

Results

Here, our results show that METTL3 increased in mouse FK, and the expression of p-PI3K and p-AKT decreased when METTL3 was downregulated. We also found that knockdown of METTL3 expression attenuated the inflammatory response and decreased TNF-α, IL-1β, and IL-6 expression in corneal-infected mice. Furthermore, inhibition of the PI3K/AKT pathway attenuated the inflammatory response of FK, decreased the expression of the above inflammatory factors, and enhanced the viability of corneal stromal cells.

Conclusions

Based on the study results, METTL3 downregulation attenuates Fusarium-induced corneal inflammation via the PI3K/AKT signaling pathway.