m6A Methylation of Precursor-miR-320/RUNX2 Controls Osteogenic Potential of Bone Marrow-Derived Mesenchymal Stem Cells

The crosstalk between m6A RNA methylation and other epigenetic regulators: a novel perspective in epigenetic remodeling

Epigenetic regulation involves a range of sophisticated processes which contribute to heritable alterations in gene expression without altering DNA sequence. Regulatory events predominantly include DNA methylation, chromatin remodeling, histone modifications, non-coding RNAs (ncRNAs), and RNA modification. As the most prevalent RNA modification in eukaryotic cells, N⁶-methyladenosine (m⁶A) RNA methylation actively participates in the modulation of RNA metabolism. Notably, accumulating evidence has revealed complicated interrelations occurring between m⁶A and other well-known epigenetic modifications. Their crosstalk conspicuously triggers epigenetic remodeling, further yielding profound impacts on a variety of physiological and pathological processes, especially tumorigenesis. Herein, we provide an up-to-date review of this emerging hot area of biological research, summarizing the interplay between m⁶A RNA methylation and other epigenetic regulators, and highlighting their underlying functions in epigenetic reprogramming.

The role of m6A modification in the biological functions and diseases

N⁶-methyladenosine (m6A) is the most prevalent, abundant and conserved internal cotranscriptional modification in eukaryotic RNAs, especially within higher eukaryotic cells. m6A modification is modified by the m6A methyltransferases, or writers, such as METTL3/14/16, RBM15/15B, ZC3H3, VIRMA, CBLL1, WTAP, and KIAA1429, and, removed by the demethylases, or erasers, including FTO and ALKBH5. It is recognized by m6A-binding proteins YTHDF1/2/3, YTHDC1/2 IGF2BP1/2/3 and HNRNPA2B1, also known as "readers". Recent studies have shown that m6A RNA modification plays essential role in both physiological and pathological conditions, especially in the initiation and progression of different types of human cancers. In this review, we discuss how m6A RNA methylation influences both the physiological and pathological progressions of hematopoietic, central nervous and reproductive systems. We will mainly focus on recent progress in identifying the biological functions and the underlying molecular mechanisms of m6A RNA methylation, its regulators and downstream target genes, during cancer progression in above systems. We propose that m6A RNA methylation process offer potential targets for cancer therapy in the future.

MiR-103-3p targets the m6 A methyltransferase METTL14 to inhibit osteoblastic bone formation

Impaired osteoblast function is involved in osteoporosis, and microRNA (miRNA) dysregulation may cause abnormal osteoblast osteogenic activity. However, the influence of miRNA on osteoblast activity and the underlying mechanisms remain elusive. In this study, miR‐103‐3p was found to be negatively correlated with bone formation in bone specimens from elderly women with fractures and ovariectomized (OVX) mice. Additionally, miR‐103‐3p directly targeted Mettl14 to inhibit osteoblast activity, and METTL14‐dependent N⁶‐methyladenosine (m⁶A) methylation inhibited miR‐103‐3p processing by the microprocessor protein DGCR8 and promoted osteoblast activity. Moreover, miR‐103‐3p inhibited bone formation in vivo, and therapeutic inhibition of miR‐103‐3p counteracted the decreased bone formation in OVX mice. Further, METTL14 was negatively correlated with miR‐103‐3p but positively correlated with bone formation in bone specimens from elderly women with fractures and OVX mice. Collectively, our results highlight the critical roles of the miR‐103‐3p/METTL14/m⁶A signaling axis in osteoblast activity, identifying this axis as a potential target for ameliorating osteoporosis.

Biological functions of m6A methyltransferases

M⁶A methyltransferases, acting as a writer in N6-methyladenosine, have attracted wide attention due to their dynamic regulation of life processes. In this review, we first briefly introduce the individual components of m⁶A methyltransferases and explain their close connections to each other. Then, we concentrate on the extensive biological functions of m⁶A methyltransferases, which include cell growth, nerve development, osteogenic differentiation, metabolism, cardiovascular system homeostasis, infection and immunity, and tumour progression. We summarize the currently unresolved problems in this research field and propose expectations for m⁶A methyltransferases as novel targets for preventive and curative strategies for disease treatment in the future.

The epitranscriptome of long noncoding RNAs in metabolic diseases

Long noncoding RNAs (lncRNAs) have abundant content and extensive functions that regulate the expression of genes at multiple levels. Recently, transcriptome-wide analysis confirmed that RNA can undergo various chemical modifications in response to stimulation by the environment that further determine the action mechanisms of RNAs and expand the diversity of the transcriptome. Modifications that occur in lncRNAs can affect their expression and the regulation of downstream molecules by changing the secondary structure, splicing, degradation or molecular stability of lncRNAs. During the development of metabolic diseases, reversible RNA modifications show a complex transcriptional landscape. Although a wide quantity and variety of lncRNA modifications have been identified, the knowledge regarding their underlying actions in alcohol use disorders (AUDs), osteoporosis, obesity, and cardiovascular disease (CVD) is still in its infancy. Herein, we will focus on the epitranscriptomic modifications that occur on lncRNAs and the crosstalk between them that affect metabolic diseases.

N6-methyladenosine (m6A) methyltransferase WTAP accelerates the Warburg effect of gastric cancer through regulating HK2 stability

N6-methyladenosine (m6A) is one of the most abundant messenger RNAs modification. Increasing evidence illustrates its critical role on gastric cancer. Here, present research focuses on the potential function of m6A methyltransferase Wilms' tumour 1-associated protein (WTAP) in gastric cancer tumorigenesis. Firstly, m6A immunoprecipitation sequencing analysis (MeRIP-Seq) analysis demonstrated the m6A profile in gastric cancer cells. Both WTAP and the m6A expression were up-regulated in gastric cancer tissue and cells. The high-expression of WTAP was closely correlated with poor prognosis of gastric cancer patients. Functional experiments illustrated that WTAP promoted the proliferation and glycolytic capacity (glucose uptake, lactate production and extracellular acidification rate) in vitro, and the knockdown of WTAP suppressed the tumor growth in vivo. Mechanistically, HK2 was identified to be the target of WTAP using MeRIP-Seq and MeRIP-qPCR. WTAP enhanced the stability of HK2 mRNA through binding with the 3'-UTR m6A site. In conclusion, our results demonstrate the oncogenic role of WTAP and its m6A-mediated regulation on gastric cancer Warburg effect, providing a novel approach and therapeutic target in gastric cancer.

Novel Insights Into the Role of N6-Methyladenosine RNA Modification in Bone Pathophysiology

Thus far, there are more than known 150 modifications to RNA, in which common internal modifications of mRNA include N6-methyladenosine (m6A), N1-methyladenosine, and 5-methylcytosine. Among them, m6A RNA modification is one of the highest abundance modifications in eukaryotes, regulating mechanisms controlling gene expression at the post-transcription level. As an invertible and dynamic epigenetic marker, m6A base modification influences almost all vital biological processes, cellular components, and molecular functions. Once the m6A modification process is abnormal, a series of diseases-including cancer, neurological diseases, and growth disorders-will be caused. Besides, several base modification activities also have been created by noncoding RNAs (ncRNAs), for instance, microRNAs, and circular RNAs, long ncRNAs, which were dynamically regulated during bone and cartilage pathophysiology processes. Therefore, it has now been clear that dynamic modification on coding RNAs and ncRNAs represents a completely new way to modulate genetic information. In this review, we highlight up-to-date progress and applications of m6A RNA modification in bone and cartilage pathophysiology, and we discuss the pathological roles and underlying molecular mechanism of m6A modifications in osteoarthritis and osteoporosis and osteosarcoma pathogenesis.

Effect of total flavonoids of Rhizoma Drynariae in thiram induced cytotoxicity of chondrocyte via BMP-2/Runx2 and IHH/PTHrP expressions

Tibial Dyschondroplasia (TD) is a prevailing skeletal disorder that mainly affects rapidly growing avian species. It results in reduced bone strength, lameness and an increase risk of fragility fractures. Total flavonoids of Rhizoma drynariae (TFRD) have been used as an effective treatment of different bone diseases in humans. The current in vitro study was conducted to explore the therapeutic effect of TFRD on thiram-induced cytotoxicity in avian growth plate cells via bone morphogenetic protein-2/runt related transcription factor-2 (BMP-2/Runx2) and Indian hedgehog/Parathyroid hormone-related peptide (IHH/PTHrP) expressions. Chondrocytes were isolated, cultured and refined from chicken's tibial growth plates in a special medium. Then chondrocytes were treated with sublethal thiram having less concentration (2.5 μg/mL) to induce cytotoxicity of chondrocyte, and then treated with providential doses (100 μg/mL) of TFRD. Thiram caused distorted morphology of chondrocytes, nuclei appeared disintegration or lysed along with decreased expressions of BMP-2/Runx2 and IHH/PTHrP. TFRD administration not only enhanced the viability of chondrocytes by itself, but also well restored the damage caused by thiram on growth plate chondrocytes by significantly up-regulating the expressions of BMP-2/Runx2 and IHH/PTHrP. Therefore, this study provides a novel insight into the further treatment of TD and other skeletal ailments and lays the foundation for prevention and treatment.

Fusarium infection alters the m6A-modified transcript landscape in the cornea

N6-methyladenosine (m⁶A) is the most common post-transcriptional modification of RNA in eukaryotes that regulates the post-transcriptional expression level of genes without changing the base sequence. The role of m⁶A in fungal keratitis has not yet been elucidated. Here, we aimed to identify m⁶A modification changes and their potential roles in fungal keratitis. The murine model of fungal keratitis was established by inoculating mice with Fusarium solani (F. solani). The overall m⁶A level was detected via an m⁶A RNA methylation assay kit. The expression levels of key m⁶A modification-related genes were estimated by quantitative real-time polymerase chain reaction (PCR). The expression and localization of METTL (methyltransferase like)3, the key component of the m⁶A methyltransferase complex, was determined by immunostaining and Western blotting (WB). Immunoprecipitation methylation microarray was used to describe the changes in m⁶A modification in F. solani-infected corneal tissue. The overall m⁶A level in corneal tissue on the 5th day in the F. solani-treated group was upregulated compared with that in the control group. The demethylase levels were unaltered, but the level of the methylase METTL3 was increased significantly after fungal infection. Additionally, differences were found in m⁶A modifications in 1137 mRNAs, of which 780 were hypermethylated and 357 were hypomethylated. To the best of our knowledge, the present work is the first investigation on the m⁶A modification profiles in experimental fungal keratitis, and it may provide a potential therapeutic target.

Multifaceted Functions and Novel Insight Into the Regulatory Role of RNA N6-Methyladenosine Modification in Musculoskeletal Disorders

RNA modifications have emerged as key regulators of transcript expression in diverse physiological and pathological processes. As one of the most prevalent types of RNA modifications, N⁶-methyladenosine (m⁶A) has become the highlight in modulation of various diseases through interfering RNA splicing, translation, nuclear export, and decay. In many cases, the detailed functions of m⁶A in cellular processes and diseases remain unclear. Notably, recent studies have determined the relationship between m⁶A modification and musculoskeletal disorders containing osteosarcoma, osteoarthritis, rheumatoid arthritis, osteoporosis, etc. Herein, this review comprehensively summarizes the recent advances of m⁶A modification in pathogenesis and progression of musculoskeletal diseases. Specifically, the underlying molecular mechanisms, detection technologies, regulatory functions, clinical implications, and future perspectives of m⁶A in musculoskeletal disorders are discussed, with the aim to provide a novel insight into their association.

m6A RNA Methylation: Ramifications for Gene Expression and Human Health

Cellular transcriptomes are frequently adorned by a variety of chemical modification marks, which in turn have a profound influence on its functioning. Of these modifications, the one which has invited a lot of attention in the recent years is m6A RNA methylation, leading to the development of RNA epigenetics or epitranscriptomics as a frontier research area. m6A RNA methylation is one of the most abundant reversible internal modification seen in cellular RNAs. Studies in the last few years have not only shed light on the molecular machinery involved in m6A RNA methylation but also on the impact of this modification in regulating gene expression and hence biological processes. In this review, we will emphasize the biological impact of this modification in normal organismal development and diseases.

Bioinformatics analysis integrating metabolomics of m6A RNA microarray in intervertebral disc degeneration

Aim: To explore the potential functions and mechanism of N⁶.methyladenosine (m⁶A) abnormality of RNAs in nucleus pulposus from the intervertebral disc degeneration (IDD). Materials & methods: We performed rat model, m⁶A epitranscriptomic microarray, bioinformatics analysis and metabolomics. Results: In IDD, most of the differentially methylated RNAs showed a significant demethylation situation. The competing endogenous RNA network LOC102555094/miR-431/GSK-3β combining downstream Wnt pathway were identified in bioinformatics analysis. For metabolomics, activation of Wnt pathway led to reprogramming of glucose metabolism and enzyme activation of PKM2. Finally, quantitative real-time PCR and methylated RNA immunoprecipitation coupled with quantitative real-time PCR revealed the positive correlation between demethylation of LOC102555094 and expression of both FTO and ZFP217. Conclusion: LOC102555094 might be demethylated by ZFP217, activating FTO and LOC102555094/miR-431/GSK-3β/Wnt played a crucial role in IDD.

Methyltransferase-like 3-mediated N6-methyladenosine modification of miR-7212-5p drives osteoblast differentiation and fracture healing

N6-methyladenosine (m6A) modification has been reported in various diseases and implicated in increasing numbers of biological processes. However, previous studies have not focused on the role of m6A modification in fracture healing. Here, we demonstrated that m6A modifications are decreased during fracture healing and that methyltransferase-like 3 (METTL3) is the main factor involved in the abnormal changes in m6A modifications. Down-regulation of METTL3 promotes osteogenic processes both in vitro and in vivo, and this effect is recapitulated by the suppression of miR-7212-5p maturation. Further studies have shown that miR-7212-5p inhibits osteoblast differentiation in MC3T3-E1 cells by targeting FGFR3. The present study demonstrated an important role of the METTL3/miR-7212-5p/FGFR3 axis and provided new insights on m6A modification in fracture healing.