Severe Hypomyelination and Developmental Defects Are Caused in Mice Lacking Protein Arginine Methyltransferase 1 (PRMT1) in the Central Nervous System

Protein Arginine Methyltransferases from Regulatory Function to Clinical Implication in Central Nervous System

Arginine methylation, catalyzed by protein arginine methyltransferases (PRMTs), is a regulatory key mechanism involved in various cellular processes such as gene expression, RNA processing, DNA damage repair. Increasing evidence highlights the crucial role of PRMTs in human diseases, including cancer, cardiovascular and metabolic diseases. Here, this review focuses on the latest findings regarding PRMTs in the central nervous system (CNS), emphasizing their regulatory roles in neural stem cells, neurons, and glial cells. Additionally, we examine the connection between PRMTs dysregulation and neurological diseases affecting the CNS, including brain tumors, neurodegenerative diseases, and neurodevelopmental disorders. Therefore, this review aims to deepen our understanding of PRMTs-mediated arginine methylation in CNS and open avenues for developing novel therapeutic strategies for neurological diseases.

PRMT1 Promotes the Self-renewal of Leukemia Stem Cells by Regulating Protein Synthesis

The application of tyrosine kinase inhibitors (TKIs) has revolutionized the management of chronic myeloid leukemia (CML). However, disease relapse and progression particularly due to persistent leukemia stem cells (LSCs) remain a big challenge in the clinic. Therefore, validation of the therapeutic vulnerability in LSCs is urgently needed. This study verifies the critical role of protein arginine methyltransferase 1 (PRMT1) in the maintenance of CML LSCs. It is found that PRMT1 promotes the survival and serially plating abilities of human primary CML LSCs. Genetic deletion of Prmt1 significantly delays the leukemogenesis and impairs the self-renewal of LSCs in BCR-ABL-driven CML mice. PRMT1 regulates LSCs and leukemia development depending on its methyltransferase activity. Pharmacological inhibition of PRMT1 activity by MS023 remarkably eliminates LSCs and prolongs the survival of CML mice. Mechanistical studies reveal that PRMT1 promotes transcriptional activation of ribosomal protein L29 (RPL29) via catalyzing asymmetric dimethylation of histone H4R3 (H4R3me2a) at its gene promoter region. PRMT1 augments the global protein synthesis via RPL29 in CML LSCs. Taken together, the findings provide new evidence that histone arginine methylation modification regulates protein synthesis in LSCs and highlight PRMT1 as a valuable druggable target for patients with CML.

Basic Epigenetic Mechanisms

The human genome consists of 23 chromosome pairs (22 autosomes and one pair of sex chromosomes), with 46 chromosomes in a normal cell. In the interphase nucleus, the 2 m long nuclear DNA is assembled with proteins forming chromatin. The typical mammalian cell nucleus has a diameter between 5 and 15 μm in which the DNA is packaged into an assortment of chromatin assemblies. The human brain has over 3000 cell types, including neurons, glial cells, oligodendrocytes, microglial, and many others. Epigenetic processes are involved in directing the organization and function of the genome of each one of the 3000 brain cell types. We refer to epigenetics as the study of changes in gene function that do not involve changes in DNA sequence. These epigenetic processes include histone modifications, DNA modifications, nuclear RNA, and transcription factors. In the interphase nucleus, the nuclear DNA is organized into different structures that are permissive or a hindrance to gene expression. In this chapter, we will review the epigenetic mechanisms that give rise to cell type-specific gene expression patterns.

Association Analysis of METTL23 Gene Polymorphisms with Reproductive Traits in Kele Pigs

Methyltransferase-like 23 (METTL23) is a kind of RNA methyltransferase that catalyzes the methylation transfer to the N6-adenosine of RNA, serving as one of the key mediators in this process. However, the METTL23 gene has been poorly researched in pigs. In this study, we investigated the genetic effects of METTL23 single-nucleotide polymorphism(SNPs) on reproductive traits in Kele pigs. The DNA was extracted from 228 healthy multiparous Kele sows, and Sanger sequencing revealed three SNPs, g.4804958 G > T (intron 2), g.4805082 C > T (exon 2), and g.4806821 A > G (exon 3). The polymorphism information content (PIC) for each SNP was 0.264, 0.25, and 0.354, indicating moderate polymorphism (0.25 < PIC < 0.5) and providing genetic information. Linkage disequilibrium analysis showed no strong linkage disequilibrium between the three SNPs. The association analysis revealed that in the SNP g.4804958 G > T individuals with the GG genotype had a significantly higher number of piglets born alive, litter birth weight, number of weaned piglets, and weaning litter weight compared to those with the TT genotype (p < 0.05). Individuals with the GG genotype in the SNP g.4806821 A > G group had significantly higher litter birth weight and average birth weight than those with the AA genotype (p < 0.05). The H4H4 diplotype showed significant effects on the number of piglets born alive, litter birth weight, number of weaned piglets, weaning litter weight, and weaning weight (p < 0.05). Together, the METTL23 gene could be used as a candidate gene for the selection of reproductive traits in Kele pigs.

Protein arginine methyltransferase 1 is required for the maintenance of adult small intestinal and colonic epithelial cell homeostasis

The vertebrate adult intestinal epithelium has a high self-renewal rate driven by intestinal stem cells (ISCs) in the crypts, which play central roles in maintaining intestinal integrity and homeostasis. However, the underlying mechanisms remain elusive. Here we showed that protein arginine methyltransferase 1 (PRMT1), a major arginine methyltransferase that can also function as a transcription co-activator, was highly expressed in the proliferating cells of adult mouse intestinal crypts. Intestinal epithelium-specific knockout of PRMT1, which ablates PRMT1 gene starting during embryogenesis, caused distinct, region-specific effects on small intestine and colon: increasing and decreasing the goblet cell number in the small intestinal and colonic crypts, respectively, leading to elongation of the crypts in small intestine but not colon, while increasing crypt cell proliferation in both regions. We further generated a tamoxifen-inducible intestinal epithelium-specific PRMT1 knockout mouse model and found that tamoxifen-induced knockout of PRMT1 in the adult mice resulted in the same region-specific intestinal phenotypes. Thus, our studies have for the first time revealed that the epigenetic enzyme PRMT1 has distinct, region-specific roles in the maintenance of intestinal epithelial architecture and homeostasis, although PRMT1 may influence intestinal development.

Critical Roles of Protein Arginine Methylation in the Central Nervous System

A remarkable post-transitional modification of both histones and non-histone proteins is arginine methylation. Methylation of arginine residues is crucial for a wide range of cellular process, including signal transduction, DNA repair, gene expression, mRNA splicing, and protein interaction. Arginine methylation is modulated by arginine methyltransferases and demethylases, like protein arginine methyltransferase (PRMTs) and Jumonji C (JmjC) domain containing (JMJD) proteins. Symmetric dimethylarginine and asymmetric dimethylarginine, metabolic products of the PRMTs and JMJD proteins, can be changed by abnormal expression of these proteins. Many pathologies including cancer, inflammation and immune responses have been closely linked to aberrant arginine methylation. Currently, the majority of the literature discusses the substrate specificity and function of arginine methylation in the pathogenesis and prognosis of cancers. Numerous investigations on the roles of arginine methylation in the central nervous system (CNS) have so far been conducted. In this review, we display the biochemistry of arginine methylation and provide an overview of the regulatory mechanism of arginine methyltransferases and demethylases. We also highlight physiological functions of arginine methylation in the CNS and the significance of arginine methylation in a variety of neurological diseases such as brain cancers, neurodegenerative diseases and neurodevelopmental disorders. Furthermore, we summarize PRMT inhibitors and molecular functions of arginine methylation. Finally, we pose important questions that require further research to comprehend the roles of arginine methylation in the CNS and discover more effective targets for the treatment of neurological diseases.

Functional Implications of Protein Arginine Methyltransferases (PRMTs) in Neurodegenerative Diseases

During the aging of the global population, the prevalence of neurodegenerative diseases will be continuously growing. Although each disorder is characterized by disease-specific protein accumulations, several common pathophysiological mechanisms encompassing both genetic and environmental factors have been detected. Among them, protein arginine methyltransferases (PRMTs), which catalyze the methylation of arginine of various substrates, have been revealed to regulate several cellular mechanisms, including neuronal cell survival and excitability, axonal transport, synaptic maturation, and myelination. Emerging evidence highlights their critical involvement in the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal dementia-amyotrophic lateral sclerosis (FTD-ALS) spectrum, Huntington's disease (HD), spinal muscular atrophy (SMA) and spinal and bulbar muscular atrophy (SBMA). Underlying mechanisms include the regulation of gene transcription and RNA splicing, as well as their implication in various signaling pathways related to oxidative stress responses, apoptosis, neuroinflammation, vacuole degeneration, abnormal protein accumulation and neurotransmission. The targeting of PRMTs is a therapeutic approach initially developed against various forms of cancer but currently presents a novel potential strategy for neurodegenerative diseases. In this review, we discuss the accumulating evidence on the role of PRMTs in the pathophysiology of neurodegenerative diseases, enlightening their pathogenesis and stimulating future research.

Epigenetic and integrative cross-omics analyses of cerebral white matter hyperintensities on MRI

Cerebral white matter hyperintensities on MRI are markers of cerebral small vessel disease, a major risk factor for dementia and stroke. Despite the successful identification of multiple genetic variants associated with this highly heritable condition, its genetic architecture remains incompletely understood. More specifically, the role of DNA methylation has received little attention. We investigated the association between white matter hyperintensity burden and DNA methylation in blood at ∼450 000 cytosine-phosphate-guanine (CpG) sites in 9732 middle-aged to older adults from 14 community-based studies. Single CpG and region-based association analyses were carried out. Functional annotation and integrative cross-omics analyses were performed to identify novel genes underlying the relationship between DNA methylation and white matter hyperintensities. We identified 12 single CpG and 46 region-based DNA methylation associations with white matter hyperintensity burden. Our top discovery single CpG, cg24202936 (P = 7.6 × 10-8), was associated with F2 expression in blood (P = 6.4 × 10-5) and co-localized with FOLH1 expression in brain (posterior probability = 0.75). Our top differentially methylated regions were in PRMT1 and in CCDC144NL-AS1, which were also represented in single CpG associations (cg17417856 and cg06809326, respectively). Through Mendelian randomization analyses cg06809326 was putatively associated with white matter hyperintensity burden (P = 0.03) and expression of CCDC144NL-AS1 possibly mediated this association. Differentially methylated region analysis, joint epigenetic association analysis and multi-omics co-localization analysis consistently identified a role of DNA methylation near SH3PXD2A, a locus previously identified in genome-wide association studies of white matter hyperintensities. Gene set enrichment analyses revealed functions of the identified DNA methylation loci in the blood-brain barrier and in the immune response. Integrative cross-omics analysis identified 19 key regulatory genes in two networks related to extracellular matrix organization, and lipid and lipoprotein metabolism. A drug-repositioning analysis indicated antihyperlipidaemic agents, more specifically peroxisome proliferator-activated receptor-alpha, as possible target drugs for white matter hyperintensities. Our epigenome-wide association study and integrative cross-omics analyses implicate novel genes influencing white matter hyperintensity burden, which converged on pathways related to the immune response and to a compromised blood-brain barrier possibly due to disrupted cell-cell and cell-extracellular matrix interactions. The results also suggest that antihyperlipidaemic therapy may contribute to lowering risk for white matter hyperintensities possibly through protection against blood-brain barrier disruption.

Discovery of cysteine-targeting covalent histone methyltransferase inhibitors

Post-translational methylation of histone lysine or arginine residues by histone methyltransferases (HMTs) plays crucial roles in gene regulation and diverse physiological processes and is implicated in a plethora of human diseases, especially cancer. Therefore, histone methyltransferases have been increasingly recognized as potential therapeutic targets. Consequently, the discovery and development of histone methyltransferase inhibitors have been pursued with steadily increasing interest over the past decade. However, the disadvantages of limited clinical efficacy, moderate selectivity, and propensity for acquired resistance have hindered the development of HMTs inhibitors. Targeted covalent modification represents a proven strategy for kinase drug development and has gained increasing attention in HMTs drug discovery. In this review, we focus on the discovery, characterization, and biological applications of covalent inhibitors for HMTs with emphasis on advancements in the field. In addition, we identify the challenges and future directions in this fast-growing research area of drug discovery.

Regulation of neural stem cell proliferation and survival by protein arginine methyltransferase 1

Protein arginine methyltransferase 1 (PRMT1), a major type I arginine methyltransferase in mammals, methylates histone and non-histone proteins to regulate various cellular functions, such as transcription, DNA damage response, and signal transduction. PRMT1 is highly expressed in neural stem cells (NSCs) and embryonic brains, suggesting that PRMT1 is essential for early brain development. Although our previous reports have shown that PRMT1 positively regulates oligodendrocyte development, it has not been studied whether PRMT1 regulates NSC proliferation and its survival during development. To examine the role of PRMT1 in NSC activity, we cultured NSCs prepared from embryonic mouse forebrains deficient in PRMT1 specific for NSCs and performed neurosphere assays. We found that the primary neurospheres of PRMT1-deficient NSCs were small and the number of spheres was decreased, compared to those of control NSCs. Primary neurospheres deficient in PRMT1 expressed an increased level of cleaved caspase-3, suggesting that PRMT1 deficiency-induced apoptosis. Furthermore, p53 protein was significantly accumulated in PRMT1-deficient NSCs. In parallel, p53-responsive pro-apoptotic genes including Pmaip1 and Perp were upregulated in PRMT1-deficient NSCs. p53-target p21 mRNA and its protein levels were shown to be upregulated in PRMT1-deficient NSCs. Moreover, the 5-bromo-2'-deoxyuridine (BrdU) incorporation assay showed that the loss of PRMT1 led to cell cycle defects in the embryonic NSCs. In contrast to the above in vitro observations, NSCs normally proliferated and survived in the fetal brains of NSC-specific PRMT1-deficient mice. We also found that Lama1, which encodes the laminin subunit α1, was significantly upregulated in the embryonic brains of PRMT1-deficient mice. These data implicate that extracellular factors provided by neighboring cells in the microenvironment gave a trophic support to NSCs in the PRMT1-deficient brain and recovered NSC activity to maintain brain homeostasis. Our study implies that PRMT1 plays a cell-autonomous role in the survival and proliferation of embryonic NSCs.

Protein arginine methyltransferase 1 in the generation of immune megakaryocytes: A perspective review

Megakaryocytes (Mks) in bone marrow are heterogeneous in terms of polyploidy. They not only produce platelets but also support the self-renewal of hematopoietic stem cells and regulate immune responses. Yet, how the diverse functions are generated from the heterogeneous Mks is not clear at the molecular level. Advances in single-cell RNA seq analysis from several studies have revealed that bone marrow Mks are heterogeneous and can be clustered into 3 to 4 subpopulations: a subgroup that is adjacent to the hematopoietic stem cells, a subgroup expressing genes for platelet biogenesis, and a subgroup expressing immune-responsive genes, the so-called immune Mks that exist in both humans and mice. Immune Mks are predominantly in the low-polyploid (≤8 N nuclei) fraction and also exist in the lung. Protein arginine methyltransferase 1 (PRMT1) expression is positively correlated with the expression of genes involved in immune response pathways and is highly expressed in immune Mks. In addition, we reported that PRMT1 promotes the generation of low-polyploid Mks. From this perspective, we highlighted the data suggesting that PRMT1 is essential for the generation of immune Mks via its substrates RUNX1, RBM15, and DUSP4 that we reported previously. Thus, we suggest that protein arginine methylation may play a critical role in the generation of proinflammatory platelet progeny from immune Mks, which may affect many immune, thrombotic, and inflammatory disorders.

PRMT1 is required for the generation of MHC-associated microglia and remyelination in the central nervous system

PRMT1 regulates MHC-associated microglia cluster during de/remyelination.

Remyelination failure in multiple sclerosis leads to progressive demyelination and inflammation, resulting in neurodegeneration and clinical decline. Microglia are innate immune cells that can acquire a regenerative phenotype to promote remyelination, yet little is known about the regulators controlling the regenerative microglia activation. Herein, using a cuprizone (CPZ)-diet induced de- and remyelination mice model, we identify PRMT1 as a driver for MHC-associated microglia population required for remyelination in the central nervous system. The loss of PRMT1, but not PRMT5, in microglia resulted in impairment of the remyelination with a reduction of oligoprogenitor cell number and prolonged microgliosis and astrogliosis. Using single-cell RNA sequencing, we found eight distinct microglial clusters during the CPZ diet, and PRMT1 depleted microglia hindered the formation of the MHC-associated cluster, expressing MHCII and CD11c. Mechanistically, PRMT1-KO microglia displayed reduced the H3K27ac peaks at the promoter regions of the MHC- and IFN-associated genes and further suppressed gene expression during CPZ diet. Overall, our findings demonstrate that PRMT1 is a critical regulator of the MHC- and IFN-associated microglia, necessary for central nervous system remyelination.

Neuroblasts contribute to oligodendrocytes generation upon demyelination in the adult mouse brain

After demyelinating insult, the neuronal progenitors of the adult mouse sub-ventricular zone (SVZ) called neuroblasts convert into oligodendrocytes that participate to the remyelination process. We use this rare example of spontaneous fate conversion to identify the molecular mechanisms governing these processes. Using in vivo cell lineage and single cell RNA-sequencing, we demonstrate that SVZ neuroblasts fate conversion proceeds through formation of a non-proliferating transient cellular state co-expressing markers of both neuronal and oligodendrocyte identities. Transition between the two identities starts immediately after demyelination and occurs gradually, by a stepwise upregulation/downregulation of key TFs and chromatin modifiers. Each step of this fate conversion involves fine adjustments of the transcription and translation machineries as well as tight regulation of metabolism and migratory behaviors. Together, these data constitute the first in-depth analysis of a spontaneous cell fate conversion in the adult mammalian CNS.

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NB can contribute to myelin repair by converting into oligodendrocytes

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NB fate conversion occurs gradually, through formation of an intermediate cell type

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NB fate conversion does not involve reversion toward a pluripotent state

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NB fate conversion seems to involve EMT-related mechanisms and metabolic changes

PRMT5 Interacting Partners and Substrates in Oligodendrocyte Lineage Cells

The protein arginine methyl transferase PRMT5 is an enzyme expressed in oligodendrocyte lineage cells and responsible for the symmetric methylation of arginine residues on histone tails. Previous work from our laboratory identified PRMT5 as critical for myelination, due to its transcriptional regulation of genes involved in survival and early stages of differentiation. However, besides its nuclear localization, PRMT5 is found at high levels in the cytoplasm of several cell types, including oligodendrocyte progenitor cells (OPCs) and yet, its interacting partners in this lineage, remain elusive. By using mass spectrometry on protein eluates from extracts generated from primary oligodendrocyte lineage cells and immunoprecipitated with PRMT5 antibodies, we identified 1196 proteins as PRMT5 interacting partners. These proteins were related to molecular functions such as RNA binding, ribosomal structure, cadherin and actin binding, nucleotide and protein binding, and GTP and GTPase activity. We then investigated PRMT5 substrates using iTRAQ-based proteomics on cytosolic and nuclear protein extracts from CRISPR-PRMT5 knockdown immortalized oligodendrocyte progenitors compared to CRISPR-EGFP controls. This analysis identified a similar number of peptides in the two subcellular fractions and a total number of 57 proteins with statistically decreased symmetric methylation of arginine residues in the CRISPR-PRMT5 knockdown compared to control. Several PRMT5 substrates were in common with cancer cell lines and related to RNA processing, splicing and transcription. In addition, we detected ten oligodendrocyte lineage specific substrates, corresponding to proteins with high expression levels in neural tissue. They included: PRC2C, a proline-rich protein involved in methyl-RNA binding, HNRPD an RNA binding protein involved in regulation of RNA stability, nuclear proteins involved in transcription and other proteins related to migration and actin cytoskeleton. Together, these results highlight a cell-specific role of PRMT5 in OPC in regulating several other cellular processes, besides RNA splicing and metabolism.

Protein Arginine Methyltransferases in Neuromuscular Function and Diseases

Neuromuscular diseases (NMDs) are characterized by progressive loss of muscle mass and strength that leads to impaired body movement. It not only severely diminishes the quality of life of the patients, but also subjects them to increased risk of secondary medical conditions such as fall-induced injuries and various chronic diseases. However, no effective treatment is currently available to prevent or reverse the disease progression. Protein arginine methyltransferases (PRMTs) are emerging as a potential therapeutic target for diverse diseases, such as cancer and cardiovascular diseases. Their expression levels are altered in the patients and molecular mechanisms underlying the association between PRMTs and the diseases are being investigated. PRMTs have been shown to regulate development, homeostasis, and regeneration of both muscle and neurons, and their association to NMDs are emerging as well. Through inhibition of PRMT activities, a few studies have reported suppression of cytotoxic phenotypes observed in NMDs. Here, we review our current understanding of PRMTs' involvement in the pathophysiology of NMDs and potential therapeutic strategies targeting PRMTs to address the unmet medical need.

Protein arginine methylation: from enigmatic functions to therapeutic targeting

Protein arginine methyltransferases (PRMTs) are emerging as attractive therapeutic targets. PRMTs regulate transcription, splicing, RNA biology, the DNA damage response and cell metabolism; these fundamental processes are altered in many diseases. Mechanistically understanding how these enzymes fuel and sustain cancer cells, especially in specific metabolic contexts or in the presence of certain mutations, has provided the rationale for targeting them in oncology. Ongoing inhibitor development, facilitated by structural biology, has generated tool compounds for the majority of PRMTs and enabled clinical programmes for the most advanced oncology targets, PRMT1 and PRMT5. In-depth mechanistic investigations using genetic and chemical tools continue to delineate the roles of PRMTs in regulating immune cells and cancer cells, and cardiovascular and neuronal function, and determine which pathways involving PRMTs could be synergistically targeted in combination therapies for cancer. This research is enhancing our knowledge of the complex functions of arginine methylation, will guide future clinical development and could identify new clinical indications.

Arginine methylation of METTL14 promotes RNA N6-methyladenosine modification and endoderm differentiation of mouse embryonic stem cells

RNA N6-methyladenosine (m6A), the most abundant internal modification of mRNAs, plays key roles in human development and health. Post-translational methylation of proteins is often critical for the dynamic regulation of enzymatic activity. However, the role of methylation of the core methyltransferase METTL3/METTL14 in m6A regulation remains elusive. We find by mass spectrometry that METTL14 arginine 255 (R255) is methylated (R255me). Global mRNA m6A levels are greatly decreased in METTL14 R255K mutant mouse embryonic stem cells (mESCs). We further find that R255me greatly enhances the interaction of METTL3/METTL14 with WTAP and promotes the binding of the complex to substrate RNA. We show that protein arginine N-methyltransferases 1 (PRMT1) interacts with and methylates METTL14 at R255, and consistent with this, loss of PRMT1 reduces mRNA m6A modification globally. Lastly, we find that loss of R255me preferentially affects endoderm differentiation in mESCs. Collectively, our findings show that arginine methylation of METTL14 stabilizes the binding of the m6A methyltransferase complex to its substrate RNA, thereby promoting global m6A modification and mESC endoderm differentiation. This work highlights the crosstalk between protein methylation and RNA methylation in gene expression.

Protein arginine methyltransferases: promising targets for cancer therapy

Protein methylation, a post-translational modification (PTM), is observed in a wide variety of cell types from prokaryotes to eukaryotes. With recent and rapid advancements in epigenetic research, the importance of protein methylation has been highlighted. The methylation of histone proteins that contributes to the epigenetic histone code is not only dynamic but is also finely controlled by histone methyltransferases and demethylases, which are essential for the transcriptional regulation of genes. In addition, many nonhistone proteins are methylated, and these modifications govern a variety of cellular functions, including RNA processing, translation, signal transduction, DNA damage response, and the cell cycle. Recently, the importance of protein arginine methylation, especially in cell cycle regulation and DNA repair processes, has been noted. Since the dysregulation of protein arginine methylation is closely associated with cancer development, protein arginine methyltransferases (PRMTs) have garnered significant interest as novel targets for anticancer drug development. Indeed, several PRMT inhibitors are in phase 1/2 clinical trials. In this review, we discuss the biological functions of PRMTs in cancer and the current development status of PRMT inhibitors in cancer therapy.

The Role of Protein Arginine Methylation as Post-Translational Modification on Actin Cytoskeletal Components in Neuronal Structure and Function

The brain encompasses a complex network of neurons with exceptionally elaborated morphologies of their axonal (signal-sending) and dendritic (signal-receiving) parts. De novo actin filament formation is one of the major driving and steering forces for the development and plasticity of the neuronal arbor. Actin filament assembly and dynamics thus require tight temporal and spatial control. Such control is particularly effective at the level of regulating actin nucleation-promoting factors, as these are key components for filament formation. Arginine methylation represents an important post-translational regulatory mechanism that had previously been mainly associated with controlling nuclear processes. We will review and discuss emerging evidence from inhibitor studies and loss-of-function models for protein arginine methyltransferases (PRMTs), both in cells and whole organisms, that unveil that protein arginine methylation mediated by PRMTs represents an important regulatory mechanism in neuritic arbor formation, as well as in dendritic spine induction, maturation and plasticity. Recent results furthermore demonstrated that arginine methylation regulates actin cytosolic cytoskeletal components not only as indirect targets through additional signaling cascades, but can also directly control an actin nucleation-promoting factor shaping neuronal cells—a key process for the formation of neuronal networks in vertebrate brains.

Oligodendroglial Epigenetics, from Lineage Specification to Activity-Dependent Myelination

Oligodendroglial cells are the myelinating cells of the central nervous system. While myelination is crucial to axonal activity and conduction, oligodendrocyte progenitor cells and oligodendrocytes have also been shown to be essential for neuronal support and metabolism. Thus, a tight regulation of oligodendroglial cell specification, proliferation, and myelination is required for correct neuronal connectivity and function. Here, we review the role of epigenetic modifications in oligodendroglial lineage cells. First, we briefly describe the epigenetic modalities of gene regulation, which are known to have a role in oligodendroglial cells. We then address how epigenetic enzymes and/or marks have been associated with oligodendrocyte progenitor specification, survival and proliferation, differentiation, and finally, myelination. We finally mention how environmental cues, in particular, neuronal signals, are translated into epigenetic modifications, which can directly influence oligodendroglial biology.

Arginine Methylation in Brain Tumors: Tumor Biology and Therapeutic Strategies

Protein arginine methylation is a common post-translational modification that plays a pivotal role in cellular regulation. Protein arginine methyltransferases (PRMTs) catalyze the modification of target proteins by adding methyl groups to the guanidino nitrogen atoms of arginine residues. Protein arginine methylation takes part in epigenetic and cellular regulation and has been linked to neurodegenerative diseases, metabolic diseases, and tumor progression. Aberrant expression of PRMTs is associated with the development of brain tumors such as glioblastoma and medulloblastoma. Identifying PRMTs as plausible contributors to tumorigenesis has led to preclinical and clinical investigations of PRMT inhibitors for glioblastoma and medulloblastoma therapy. In this review, we discuss the role of arginine methylation in cancer biology and provide an update on the use of small molecule inhibitors of PRMTs to treat glioblastoma, medulloblastoma, and other cancers.

Roles of protein arginine methyltransferase 1 (PRMT1) in brain development and disease

BACKGROUND

Protein arginine methyltransferase 1 (PRMT1), a major type I arginine methyltransferase in mammals, methylates histone and non-histone proteins to regulate various cellular functions such as transcription, DNA damage response, and signal transduction.

SCOPE OF REVIEW

This review summarizes previous and recent studies on PRMT1 functions in major cell types of the central nervous system. We also discuss the potential involvement of PRMT1 in neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal dementia. Also, we raise key questions that must be addressed in the future to more precisely understand the roles of PRMT1.

MAJOR CONCLUSIONS

Recent studies revealed that PRMT1 is essential for the development of neurons, astrocytes, and oligodendrocytes, although further investigation using cell type-specific PRMT1-deficient animals is required. In addition, the relevance of PRMT1 in neurodegenerative diseases will continue to be a hot topic.

GENERAL SIGNIFICANCE

PRMT1 is important for neural development and neurodegenerative diseases.

Loss of PRMT1 in the central nervous system (CNS) induces reactive astrocytes and microglia during postnatal brain development

PRMT1, a major arginine methyltransferase, plays critical roles in transcription, DNA damage response, and cell proliferation. Although we have previously discovered the crucial roles of PRMT1 for oligodendrocyte lineage progression in the central nervous system of neural stem cell-specific PRMT1 conditional knockout (PRMT1-CKO) mice, the context of other glial cell states that may cause the hypomyelination phenotype in PRMT1-CKO mice has not been explored so far. Here, we performed RNA-seq of the neonatal cortices of PRMT1-CKO mice to reveal overall gene expression changes and show the up-regulation of inflammatory signaling which is generally mediated by astrocytes and microglia in advance of the myelination defects. In particular, qRT-PCR analyses revealed Interleukin-6 (Il-6), a major central nervous system cytokine, was dramatically increased in the PRMT1-CKO brains. The gene expression changes led to augmentation of glial fibrillary acidic protein and Vimentin protein levels in PRMT1-CKO mice, showing severe reactive astrogliosis after birth. We further show that IBA1-positive and CD68-positive activated microglia were increased in PRMT1-CKO mice, in spite of intact Prmt1 gene expression in purified microglia from the mutant mice. Our results indicate that PRMT1 loss in the neural stem cell lineage causes disruptive changes in all glial types perturbing postnatal brain development and myelination.

Transcriptional regulation by methyltransferases and their role in the heart: highlighting novel emerging functionality

Methyltransferases are a superfamily of enzymes that transfer methyl groups to proteins, nucleic acids, and small molecules. Traditionally, these enzymes have been shown to carry out a specific modification (mono-, di-, or trimethylation) on a single, or limited number of, amino acid(s). The largest subgroup of this family, protein methyltransferases, target arginine and lysine side chains of histone molecules to regulate gene expression. Although there is a large number of functional studies that have been performed on individual methyltransferases describing their methylation targets and effects on biological processes, no analyses exist describing the spatial distribution across tissues or their differential expression in the diseased heart. For this review, we performed tissue profiling in protein databases of 199 confirmed or putative methyltransferases to demonstrate the unique tissue-specific expression of these individual proteins. In addition, we examined transcript data sets from human heart failure patients and murine models of heart disease to identify 40 methyltransferases in humans and 15 in mice, which are differentially regulated in the heart, although many have never been functionally interrogated. Lastly, we focused our analysis on the largest subgroup, that of protein methyltransferases, and present a newly emerging phenomenon in which 16 of these enzymes have been shown to play dual roles in regulating transcription by maintaining the ability to both activate and repress transcription through methyltransferase-dependent or -independent mechanisms. Overall, this review highlights a novel paradigm shift in our understanding of the function of histone methyltransferases and correlates their expression in heart disease.

Convergent epigenetic regulation of glial plasticity in myelin repair and brain tumorigenesis: A focus on histone modifying enzymes

Brain regeneration and tumorigenesis are complex processes involving in changes in chromatin structure to regulate cellular states at the molecular and genomic level. The modulation of chromatin structure dynamics is critical for maintaining progenitor cell plasticity, growth and differentiation. Oligodendrocyte precursor cells (OPC) can be differentiated into mature oligodendrocytes, which produce myelin sheathes to permit saltatory nerve conduction. OPCs and their primitive progenitors such as pri-OPC or pre-OPC are highly adaptive and plastic during injury repair or brain tumor formation. Recent studies indicate that chromatin modifications and epigenetic homeostasis through histone modifying enzymes shape genomic regulatory landscape conducive to OPC fate specification, lineage differentiation, maintenance of myelin sheaths, as well as brain tumorigenesis. Thus, histone modifications can be convergent mechanisms in regulating OPC plasticity and malignant transformation. In this review, we will focus on the impact of histone modifying enzymes in modulating OPC plasticity during normal development, myelin regeneration and tumorigenesis.

Post-translational modifications of the Fragile X Mental Retardation Protein in neuronal function and dysfunction

The Fragile X Mental Retardation Protein (FMRP) is an RNA-binding protein essential to the regulation of local translation at synapses. In the mammalian brain, synapses are constantly formed and eliminated throughout development to achieve functional neuronal networks. At the molecular level, thousands of proteins cooperate to accomplish efficient neuronal communication. Therefore, synaptic protein levels and their functional interactions need to be tightly regulated. FMRP generally acts as a translational repressor of its mRNA targets. FMRP is the target of several post-translational modifications (PTMs) that dynamically regulate its function. Here we provide an overview of the PTMs controlling the FMRP function and discuss how their spatiotemporal interplay contributes to the physiological regulation of FMRP. Importantly, FMRP loss-of-function leads to Fragile X syndrome (FXS), a rare genetic developmental condition causing a range of neurological alterations including intellectual disability (ID), learning and memory impairments, autistic-like features and seizures. Here, we also explore the possibility that recently reported missense mutations in the FMR1 gene disrupt the PTM homoeostasis of FMRP, thus participating in the aetiology of FXS. This suggests that the pharmacological targeting of PTMs may be a promising strategy to develop innovative therapies for patients carrying such missense mutations.

SCYL1 arginine methylation by PRMT1 is essential for neurite outgrowth via Golgi morphogenesis

Arginine methylation is a common posttranslational modification that modulates protein function. SCY1-like pseudokinase 1 (SCYL1) is crucial for neuronal functions and interacts with γ₂-COP to form coat protein complex I (COPI) vesicles that regulate Golgi morphology. However, the molecular mechanism by which SCYL1 is regulated remains unclear. Here, we report that the γ₂-COP-binding site of SCYL1 is arginine-methylated by protein arginine methyltransferase 1 (PRMT1) and that SCYL1 arginine methylation is important for the interaction of SCYL1 with γ₂-COP. PRMT1 was colocalized with SCYL1 in the Golgi fraction. Inhibition of PRMT1 suppressed axon outgrowth and dendrite complexity via abnormal Golgi morphology. Knockdown of SCYL1 by small interfering RNA (siRNA) inhibited axon outgrowth, and the inhibitory effect was rescued by siRNA-resistant SCYL1, but not SCYL1 mutant, in which the arginine methylation site was replaced. Thus, PRMT1 regulates Golgi morphogenesis via SCYL1 arginine methylation. We propose that SCYL1 arginine methylation by PRMT1 contributes to axon and dendrite morphogenesis in neurons.

Epigenetic regulation of oligodendrocyte myelination in developmental disorders and neurodegenerative diseases

Oligodendrocytes are the critical cell types giving rise to the myelin nerve sheath enabling efficient nerve transmission in the central nervous system (CNS). Oligodendrocyte precursor cells differentiate into mature oligodendrocytes and are maintained throughout life. Deficits in the generation, proliferation, or differentiation of these cells or their maintenance have been linked to neurological disorders ranging from developmental disorders to neurodegenerative diseases and limit repair after CNS injury. Understanding the regulation of these processes is critical for achieving proper myelination during development, preventing disease, or recovering from injury. Many of the key factors underlying these processes are epigenetic regulators that enable the fine tuning or reprogramming of gene expression during development and regeneration in response to changes in the local microenvironment. These include chromatin remodelers, histone-modifying enzymes, covalent modifiers of DNA methylation, and RNA modification-mediated mechanisms. In this review, we will discuss the key components in each of these classes which are responsible for generating and maintaining oligodendrocyte myelination as well as potential targeted approaches to stimulate the regenerative program in developmental disorders and neurodegenerative diseases.

GC-MS and LC-MS/MS pilot studies on the guanidine (NG)-dimethylation in native, asymmetrically and symmetrically NG-dimethylated arginine-vasopressin peptides and proteins in human red blood cells

Protein-arginine methyltransferases catalyze the methylation of the guanidine (N^G) group of proteinic L-arginine (Arg) to produce monomethyl and dimethylarginine proteins. Their proteolysis releases the free amino acids monomethylarginine (MMA), symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA), respectively. MMA, SDMA and ADMA are inhibitors of the nitric oxide synthase (NOS) activity. High circulating and low urinary concentrations of ADMA and SDMA are considered risk factors in the cardiovascular and renal systems, mainly due to their inhibitory action on NOS activity. Identity, biological activity and concentration of N^G-methylated proteins are largely unknown. The present study addressed these issues by using GC-MS and LC-MS/MS approaches. GC-MS was used to quantify free ADMA released by classical HCl-catalyzed hydrolysis of three synthetic Arg-vasopressin (V) peptides and of unknown endogenous N^G-dimethylated proteins. The cyclic (c) disulfide forms of Arg-vasopressin analogs, i.e., Arg-vasopressin (cV-Arg-Gly-NH₂), asymmetrically N^G-dimethylated vasopressin (cV-ADMA-Gly-NH₂) and symmetrically N^G-dimethylated vasopressin (cV-SDMA-Gly-NH₂) were used as model peptides in quantitative GC-MS analyses of ADMA, SDMA and other expected amino acids from the hydrolyzed Arg-vasopressin analogs. cV-ADMA-Gly-NH₂ and cV-SDMA-Gly-NH₂ were discriminated from cV-Arg-Gly-NH₂ by LC-MS and LC-MS/MS, yet they were indistinguishable from each other. The same applies to the respective open (o) reduced and di-S-acetamide forms of oV-ADMA-Gly-NH₂, oV-SDMA-Gly-NH₂ and oV-Arg-Gly-NH₂. Our LC-MS and LC-MS/MS studies suggest that the Arg-vasopressin analogs form [(M-H)]⁺ and [(M-H)+H]⁺ in the positive ESI mode and undergo in part conversion of their terminal Gly-NH₂ (NH₂, 16 Da) group to Gly-OH (OH, 17 Da). The product ion mass spectra of the di-S-acetamide forms are complex and contain several intense mass fragments differing by 1 Da. cV-ADMA-Gly-NH₂ and cV-SDMA-Gly-NH₂ induced platelet aggregation in platelet-rich human plasma with moderately different initial velocity and maximal aggregation rates compared to cV-Arg-Gly-NH₂. Previous studies showed that human red blood cells are rich in large (>50 kDa) ADMA-containing proteins of unknown identity. Our LC-MS/MS proteomic study identified several membrane and cytosolic erythrocytic N^G-dimethylated proteins, including spectrin-α (280 kDa), spectrin-β (247 kDa) and protein 4.1 (80 kDa). Being responsible for the stability of the erythrocyte membrane, the newly identified main targets for N^G-dimethylation in human erythrocytes should be given a closer look in erythrocytic diseases like hereditary spherocytosis.

Protein Arginine Methyltransferases in Cardiovascular and Neuronal Function

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a type of post-translational modification which is important for numerous cellular processes, including mRNA splicing, DNA repair, signal transduction, protein interaction, and transport. PRMTs have been extensively associated with various pathologies, including cancer, inflammation, and immunity response. However, the role of PRMTs has not been well described in vascular and neurological function. Aberrant expression of PRMTs can alter its metabolic products, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). Increased ADMA levels are recognized as an independent risk factor for cardiovascular disease and mortality. Recent studies have provided considerable advances in the development of small-molecule inhibitors of PRMTs to study their function under normal and pathological states. In this review, we aim to elucidate the particular roles of PRMTs in vascular and neuronal function as a potential target for cardiovascular and neurological diseases.

Protein Arginine Methyltransferase 1 Interacts With PGC1α and Modulates Thermogenic Fat Activation

Protein arginine methyltransferases (PRMTs) are enzymes that regulate the evolutionarily conserved process of arginine methylation. It has been reported that PRMTs are involved in many metabolic regulatory pathways. However, until now, their roles in adipocyte function, especially browning and thermogenesis, have not been evaluated. Even though Prmt1 adipocyte-specific-deleted mice (Prmt1fl/flAQcre) appeared normal at basal level, following cold exposure or β-adrenergic stimulation, impaired induction of the thermogenic program was observed in both the interscapular brown adipose tissue and inguinal white adipose tissue of Prmt1fl/flAQcre mice compared with littermate controls. Different splicing variants of Prmt1 have been reported. Among them, PRMT1 variant 1 and PRMT1 variant 2 (PRMT1V2) are well conserved between humans and mice. Both variants contribute to the activation of thermogenic fat, with PRMT1V2 playing a more dominant role. Mechanistic studies using cultured murine and human adipocytes revealed that PRMT1V2 mediates thermogenic fat activation through PGC1α, a transcriptional coactivator that has been shown to play a key role in mitochondrial biogenesis. To our knowledge, our data are the first to demonstrate that PRMT1 plays a regulatory role in thermogenic fat function. These findings suggest that modulating PRMT1 activity may represent new avenues to regulate thermogenic fat and mediate energy homeostasis. This function is conserved in human primary adipocytes, suggesting that further investigation of this pathway may ultimately lead to therapeutic strategies against human obesity and associated metabolic disorders.

The emergence of protein arginine methyltransferases in skeletal muscle and metabolic disease

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins and thus alter the stability, localization, or activity of the substrate. In doing so, PRMTs mediate a variety of intracellular functions that are essential for survival. Additionally, PRMT dysregulation is involved in a number of the most prevalent health disorders, including cancer and neurodegenerative and cardiovascular diseases, as well as in the aging process. Investigations of PRMT biology in skeletal muscle cells began in 2002, and since then these enzymes have emerged as regulators of skeletal muscle phenotype determination, maintenance, and remodeling. Specifically, more recent in vivo studies have revealed that PRMTs impact multiple aspects of skeletal muscle biology, including satellite cell function and phenotypic plasticity in response to exercise and disuse. Skeletal muscle plays critically important roles in regulating whole body metabolism, and recent investigations have also begun elucidating PRMT expression and function under conditions of metabolic dysfunction. The goals of this review are to 1) summarize the literature on PRMT biology in skeletal muscle with a particular emphasis on the in vivo evidence and 2) survey PRMTs in metabolic disorders, namely, obesity and type 2 diabetes mellitus. We also identify notable knowledge gaps therein and present opportunities to further expand our understanding of these enzymes so critical to health and disease.

Melatonin rescued methotrexate-induced spatial deficit and hyperhomocysteinemia and increased asymmetric dimethylarginine in plasma and dorsal hippocampus in developing rats

AIMS

With the improvement of the survival rates in children acute lymphoblastic leukemia (ALL), some children ALL survivors show impaired cognitive function. Methotrexate (MTX), an essential component in ALL treatment, has been reported to be related to neurologic sequelae and to increased oxidative stress through its interactions with enzymes in the folate pathway. Asymmetric dimethylarginine (ADMA) is the main endogenous inhibitor of nitric oxide synthase, and increased ADMA may result from increased oxidants. Melatonin is an antioxidant; however, its role in MTX neuropathy is not well studied. We developed a rat model mimicking child ALL treatment to explore peripheral and central homocysteine and ADMA regulation after MTX and found potential treatment choice.

MAIN METHODS

Preweaning male Sprague-Dawley rats were used in this study. Experiment 1 evaluated spatial performance in rats with intrathecal (IT) MTX, intraperitoneal (IP) MTX, or combined IT and IP MTX, protocols mimicking ALL treatment in children. Experiment 2 focused on rats with combined IT and IP MTX, evaluating spatial performance and plasma and dorsal hippocampal homocysteine and ADMA levels, their regulation, and the protective effect of melatonin.

KEY FINDINGS

Combined IT and IP MTX treatment caused in spatial deficits in developing rats, and melatonin restored the spatial performance. Alterations in peripheral and central homocysteine and ADMA concentrations and their regulation were found and could be alleviated by melatonin treatment.

SIGNIFICANCES

Combined IP and IT MTX treatment caused spatial deficits in developing rats. Melatonin could restore spatial performance through alleviating the effects on the imbalance of oxidative stress.

From OPC to Oligodendrocyte: An Epigenetic Journey

Oligodendrocytes provide metabolic and functional support to neuronal cells, rendering them key players in the functioning of the central nervous system. Oligodendrocytes need to be newly formed from a pool of oligodendrocyte precursor cells (OPCs). The differentiation of OPCs into mature and myelinating cells is a multistep process, tightly controlled by spatiotemporal activation and repression of specific growth and transcription factors. While oligodendrocyte turnover is rather slow under physiological conditions, a disruption in this balanced differentiation process, for example in case of a differentiation block, could have devastating consequences during ageing and in pathological conditions, such as multiple sclerosis. Over the recent years, increasing evidence has shown that epigenetic mechanisms, such as DNA methylation, histone modifications, and microRNAs, are major contributors to OPC differentiation. In this review, we discuss how these epigenetic mechanisms orchestrate and influence oligodendrocyte maturation. These insights are a crucial starting point for studies that aim to identify the contribution of epigenetics in demyelinating diseases and may thus provide new therapeutic targets to induce myelin repair in the long run.

Essential Role of Protein Arginine Methyltransferase 1 in Pancreas Development by Regulating Protein Stability of Neurogenin 3

BACKGROUND

Protein arginine methyltransferase 1 (PRMT1) is a major enzyme responsible for the formation of methylarginine in mammalian cells. Recent studies have revealed that PRMT1 plays important roles in the development of various tissues. However, its role in pancreas development has not yet been elucidated.

METHODS

Pancreatic progenitor cell-specific Prmt1 knock-out (Prmt1 PKO) mice were generated and characterized for their metabolic and histological phenotypes and their levels of Neurog3 gene expression and neurogenin 3 (NGN3) protein expression. Protein degradation assays were performed in mPAC cells.

RESULTS

Prmt1 PKO mice showed growth retardation and a severely diabetic phenotype. The pancreatic size and β-cell mass were significantly reduced in Prmt1 PKO mice. Proliferation of progenitor cells during the secondary transition was decreased and endocrine cell differentiation was impaired. These defects in pancreas development could be attributed to the sustained expression of NGN3 in progenitor cells. Protein degradation assays in mPAC cells revealed that PRMT1 was required for the rapid degradation of NGN3.

CONCLUSION

PRMT1 critically contributes to pancreas development by destabilizing the NGN3 protein.

Chromatin modification and epigenetic control in functional nerve regeneration

The repair and functional recovery of the nervous system is a highly regulated process that requires the coordination of many different components including the proper myelination of regenerated axons. Dysmyelination and remyelination failures after injury result in defective nerve conduction, impairing normal nervous system functions. There are many convergent regulatory networks and signaling mechanisms between development and regeneration. For instance, the regulatory mechanisms required for oligodendrocyte lineage progression could potentially play fundamental roles in myelin repair. In recent years, epigenetic chromatin modifications have been implicated in CNS myelination and functional nerve restoration. The pro-regenerative transcriptional program is likely silenced or repressed in adult neural cells including neurons and myelinating cells in the central and peripheral nervous systems limiting the capacity for repair after injury. In this review, we will discuss the roles of epigenetic mechanisms, including histone modifications, chromatin remodeling, and DNA methylation, in the maintenance and establishment of the myelination program during normal oligodendrocyte development and regeneration. We also discuss how these epigenetic processes impact myelination and axonal regeneration, and facilitate the improvement of current preclinical therapeutics for functional nerve regeneration in neurodegenerative disorders or after injury.

Roles and regulation of histone methylation in animal development

Histone methylation can occur at various sites in histone proteins, primarily on lysine and arginine residues, and it can be governed by multiple positive and negative regulators, even at a single site, to either activate or repress transcription. It is now apparent that histone methylation is critical for almost all stages of development, and its proper regulation is essential for ensuring the coordinated expression of gene networks that govern pluripotency, body patterning and differentiation along appropriate lineages and organogenesis. Notably, developmental histone methylation is highly dynamic. Early embryonic systems display unique histone methylation patterns, prominently including the presence of bivalent (both gene-activating and gene-repressive) marks at lineage-specific genes that resolve to monovalent marks during differentiation, which ensures that appropriate genes are expressed in each tissue type. Studies of the effects of methylation on embryonic stem cell pluripotency and differentiation have helped to elucidate the developmental roles of histone methylation. It has been revealed that methylation and demethylation of both activating and repressive marks are essential for establishing embryonic and extra-embryonic lineages, for ensuring gene dosage compensation via genomic imprinting and for establishing body patterning via HOX gene regulation. Not surprisingly, aberrant methylation during embryogenesis can lead to defects in body patterning and in the development of specific organs. Human genetic disorders arising from mutations in histone methylation regulators have revealed their important roles in the developing skeletal and nervous systems, and they highlight the overlapping and unique roles of different patterns of methylation in ensuring proper development.

Developmental expression of three prmt genes in Xenopus

Protein arginine methyltransferases (PRMTs) are involved in many cellular processes via the arginine methylation of histone or non-histone proteins. We examined the expression patterns of prmt4, prmt7, and prmt9 during embryogenesis in Xenopus using whole-mount in situ hybridization and quantitative reverse transcription polymerase chain reaction (RT-PCR). Xenopus prmt4 and prmt7 were expressed in the neural crest, brain, and spinal cord, and also detected in the eye, branchial arches, and heart at the tailbud stage. Specific prmt9 signals were not detected in Xenopus embryos until the late tailbud stage when weak expression was observed in the branchial arches. Quantitative RT-PCR indicated that the expressions of prmt4 and prmt7 were up-regulated during the neurula stage, whereas prmt9 maintained its low expression until the late tailbud stage, consistent with the whole-mount in situ hybridization results. Thus, the developmental expression patterns of these three prmt genes in Xenopus embryos provide a basis for further functional study of such genes.

Downregulation of PRMT1 promotes the senescence and migration of a non-MYCN amplified neuroblastoma SK-N-SH cells

Protein arginine methyltransferase 1 (PRMT1) catalyzing the formation of asymmetric dimethylarginines has been implicated in cancer development, metastasis, and prognosis. In this study, we investigated the effects of low PRMT1 levels on a non-MYCN amplified neuroblastoma SK-N-SH cell line. Stable PRMT1-knockdown (PRMT1-KD) cells showed reduced growth rates and cell cycle arrest at G₂/M. They also exhibited senescent phenotypes and increased p53 expression. p21 and PAI-1, which are two p53 downstream targets critical for senescence, were significantly induced in SK-N-SH cells subjected to either PRMT1-KD or inhibitor treatment. The induction was suppressed by a p53 inhibitor and marginal in a p53-null SK-N-AS cell line, suggesting dependence on p53. In general, the DNA damage and ROS levels of the PRMT1-KD SK-N-SH cells were slightly increased. Their migration activity also increased with the induction of PAI-1. Thus, PRMT1 downregulation released the repression of cellular senescence and migration activity in SK-N-SH cells. These results might partially explain the poor prognostic outcome of low PRMT1 in a non-MYCN-amplified cohort and indicate the multifaceted complexity of PRMT1 as a biological regulator of neuroblastoma.

Emerging impacts of biological methylation on genetic information

The central dogma of molecular biology explains the fundamental flow of genetic information for life. Although genome sequence (DNA) itself is a static chemical signature, it includes multiple layers of information composed of mRNA, tRNA, rRNA and small RNAs, all of which are involved in protein synthesis and is passing from parents to offspring via DNA. Methylation is a biologically important modification, because DNA, RNAs and proteins, components of the central dogma, are methylated by a set of methyltransferases. Recent works focused on understanding a variety of biological methylation have shed light on new regulation of cellular functions. In this review, we briefly discuss some of those recent findings of methylation, including DNA, RNAs and proteins.

5-Aminolevulinic acid regulates the immune response in LPS-stimulated RAW 264.7 macrophages

BACKGROUND

Macrophages are crucial players in a variety of inflammatory responses to environmental cues. However, it has been widely reported that macrophages cause chronic inflammation and are involved in a variety of diseases, such as obesity, diabetes, metabolic syndrome, and cancer. In this study, we report the suppressive effect of 5-aminolevulinic acid (ALA), via the HO-1-related system, on the immune response of the LPS-stimulated mouse macrophage cell line RAW264.7.

RESULTS

RAW264.7 cells were treated with LPS with or without ALA, and proinflammatory mediator expression levels and phagocytic ability were assessed. ALA treatment resulted in the attenuation of iNOS and NO expression and the downregulation of proinflammatory cytokines (TNF-α, cyclooxygenase2, IL-1β, IL-6). In addition, ALA treatment did not affect the phagocytic ability of macrophages. To our knowledge, this study is the first to investigate the effect of ALA on macrophage function. Our findings suggest that ALA may have high potential as a novel anti-inflammatory agent.

CONCLUSIONS

In the present study, we showed that exogenous addition of ALA induces HO-1 and leads to the downregulation of NO and some proinflammatory cytokines. These findings support ALA as a promising anti-inflammatory agent.

Inhibiting Arginine Methylation as a Tool to Investigate Cross-Talk with Methylation and Acetylation Post-Translational Modifications in a Glioblastoma Cell Line

Glioblastomas (GBM) are the most common grade 4 brain tumours; patients have very poor prognosis with an average survival of 15 months after diagnosis. Novel research lines have begun to explore aberrant protein arginine methylation (ArgMe) as a possible therapeutic target in GBM and ArgMe inhibitors are currently in clinical trials. Enzymes known as protein arginine methyltransferases (PRMT1-9) can lead to mono- or di-ArgMe, and in the latter case symmetric or asymmetric dimethylation (SDMA and ADMA, respectively). Using the most common GBM cell line, we have profiled the expression of PRMTs, used ArgMe inhibitors as tools to investigate post-translational modifications cross-talk and measured the effect of ArgMe inhibitors on cell viability. We have identified novel SDMA events upon inhibition of ADMA in GBM cells and spheroids. We have observed cross-talk between ADMA and lysine acetylation in GBM cells and platelets. Treatment of GBM cells with furamidine, a PRMT1 inhibitor, reduces cell viability in 2D and 3D models. These data provide new molecular understanding of a disease with unmet clinical needs.

PRMT1 Deficiency in Mouse Juvenile Heart Induces Dilated Cardiomyopathy and Reveals Cryptic Alternative Splicing Products

Protein arginine methyltransferase 1 (PRMT1) catalyzes the asymmetric dimethylation of arginine residues in proteins and methylation of various RNA-binding proteins and is associated with alternative splicing in vitro. Although PRMT1 has essential in vivo roles in embryonic development, CNS development, and skeletal muscle regeneration, the functional importance of PRMT1 in the heart remains to be elucidated. Here, we report that juvenile cardiomyocyte-specific PRMT1-deficient mice develop severe dilated cardiomyopathy and exhibit aberrant cardiac alternative splicing. Furthermore, we identified previously undefined cardiac alternative splicing isoforms of four genes (Asb2, Fbxo40, Nrap, and Eif4a2) in PRMT1-cKO mice and revealed that eIF4A2 protein isoforms translated from alternatively spliced mRNA were differentially ubiquitinated and degraded by the ubiquitin-proteasome system. These findings highlight the essential roles of PRMT1 in cardiac homeostasis and alternative splicing regulation.

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PRMT1 deficiency in cardiomyocytes causes dilated cardiomyopathy in juvenile mice

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PRMT1-deficient heart shows abnormal alternative splicing patterns

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Previously undefined cardiac splicing events are revealed by transcriptome analysis

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eIF4A2 isoforms are differentially ubiquitinated and degraded

Arginine methylation of SMAD7 by PRMT1 in TGF-β-induced epithelial-mesenchymal transition and epithelial stem-cell generation

The epithelial-to-mesenchymal transdifferentiation (EMT) is crucial for tissue differentiation in development and drives essential steps in cancer and fibrosis. EMT is accompanied by reprogramming of gene expression and has been associated with the epithelial stem-cell state in normal and carcinoma cells. The cytokine transforming growth factor β (TGF-β) drives this program in cooperation with other signaling pathways and through TGF-β-activated SMAD3 as the major effector. TGF-β-induced SMAD3 activation is inhibited by SMAD7 and to a lesser extent by SMAD6, and SMAD6 and SMAD7 both inhibit SMAD1 and SMAD5 activation in response to the TGF-β-related bone morphogenetic proteins (BMPs). We previously reported that, in response to BMP, protein arginine methyltransferase 1 (PRMT1) methylates SMAD6 at the BMP receptor complex, thereby promoting its dissociation from the receptors and enabling BMP-induced SMAD1 and SMAD5 activation. We now provide evidence that PRMT1 also facilitates TGF-β signaling by methylating SMAD7, which complements SMAD6 methylation. We found that PRMT1 is required for TGF-β-induced SMAD3 activation, through a mechanism similar to that of BMP-induced SMAD6 methylation, and thus promotes the TGF-β-induced EMT and epithelial stem-cell generation. This critical mechanism positions PRMT1 as an essential mediator of TGF-β signaling that controls the EMT and epithelial cell stemness through SMAD7 methylation.

Prmt1 regulates craniofacial bone formation upstream of Msx1

Protein arginine methylation has been recently identified as an important form of post-translational modification (PTM). It is carried out by the protein arginine methyltransferase (PRMT) family of enzymes, which in mammals consists of nine members. Among them, PRMT1 is the major arginine methyltransferase and participates in transcription, signal transduction, development and cancer. The function of PRMT1 in craniofacial development remains unclear. We generated Wnt1-Cre;Prmt1^fl/fl mice with cranial neural crest (CNC)-specific deletion of Prmt1 and compared CNC-derived craniofacial bones from newborn control and Wnt1-Cre;Prmt1^fl/fl mice. The size, surface area and volume of the premaxilla, maxilla, palatine bone, frontal bone, and mandible were analyzed using three-dimensional (3D) micro-computed tomography (microCT). We found that Prmt1 deficiency led to alterations in craniofacial bones including the premaxilla, maxilla, palatine bone, frontal bone, and mandible, as well as defects in the incisor and alveolar bone, recapitulating changes seen in Msx1-deficient mice. We further determined that Prmt1 depletion resulted in significant downregulation of Msx1 in calvaria-derived preosteoblast and primordium of frontal bone and mandible. Our study reveals critical roles of PRMT1 in the formation of CNC-derived craniofacial bones and suggests that Prmt1 is an upstream regulator of Msx1 in craniofacial bone development.

The GATA transcription factor ELT-2 modulates both the expression and methyltransferase activity of PRMT-1 in Caenorhabditis elegans

Protein arginine methyltransferase 1 (PRMT1) catalyzes asymmetric arginine dimethylation of cellular proteins and thus modulates various biological processes, including gene regulation, RNA metabolism, cell signaling and DNA repair. Since prmt-1 null mutant completely abolishes asymmetric dimethylarginine in C. elegans, PRMT-1 is thought to play a crucial role in determining levels of asymmetric arginine dimethylation. However, the mechanism underlying the regulation of PRMT-1 activity remains largely unknown. Here, we explored for transcription factors that induce the expression of PRMT-1 by an RNAi screen using transgenic C. elegans harbouring prmt-1 promoter upstream of gfp. Of 529 clones, we identify a GATA transcription factor elt-2 as a positive regulator of Pprmt-1:: gfp expression and show that elt-2 RNAi decreases endogenous PRMT-1 expression at mRNA and protein levels. Nevertheless, surprisingly arginine methylation levels are increased when elt-2 is silenced, implying that erythroid-like transcription factor (ELT)-2 may also have ability to inhibit methyltransferase activity of PRMT-1. Supporting this idea, GST pull-down and co-immunoprecipitation assays demonstrate the interaction between ELT-2 and PRMT-1. Furthermore, we find that ELT-2 interferes with PRMT-1-induced arginine methylation in a dose-dependent manner. Collectively, our results illustrate the two modes of PRMT-1 regulation, which could determine the levels of asymmetric arginine dimethylation in C. elegans.

Gestational changes in PRMT1 expression of murine placentas

INTRODUCTION

In mammals, the placenta is an organ that is required to maintain the development of fetus during pregnancy. Although the proper formation of placenta is in part regulated by the post-translational modifications of proteins, little is known regarding protein arginine methylation during placental development. Here, we characterized developmental expression of protein arginine methyltransferase 1 (PRMT1) in mouse placentas.

METHODS

Expression levels of PRMT1 mRNA and protein in placentas were investigated using the real-time quantitative PCR and Western blot, respectively. Next, the localization of PRMT1 was determined by immunohistochemistry and immunofluorescence analyses. In addition, the levels of methylarginines of placental proteins were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

PRMT1 mRNA and its protein were expressed at highest levels in mid-gestation stages, and their expression showed stepwise decrease in the late gestation. At embryonic (E) day 9, PRMT1 was observed in several different trophoblast cell (TC) subtypes. Furthermore, PRMT1 was mainly expressed in the labyrinth zone of TCs at E13. Finally, total methylarginines of proteins were significantly reduced in late gestation of placentas compared with mid-gestation stages.

DISCUSSION

In this study, we found developmental changes in the placental expression of PRMT1 and in protein arginine methylation status during pregnancy. These findings provide fundamental information regarding placental PRMT1-mediated arginine methylation during the development.