Myocyte enhancer factor 2C and its directly-interacting proteins: A review

Martínez-Castilla L, García-Sandoval R, Ballester P, Ferrándiz C, Sanchez MDLP, García-Ponce B, Garay-Arroyo A, R. Álvarez-Buylla E. HDACs MADS-domain protein interaction: a case study of HDA15 and XAL1 in Arabidopsis thaliana

Cellular behavior, cell differentiation and ontogenetic development in eukaryotes result from complex interactions between epigenetic and classic molecular genetic mechanisms, with many of these interactions still to be elucidated. Histone deacetylase enzymes (HDACs) promote the interaction of histones with DNA by compacting the nucleosome, thus causing transcriptional repression. MADS-domain transcription factors are highly conserved in eukaryotes and participate in controlling diverse developmental processes in animals and plants, as well as regulating stress responses in plants. In this work, we focused on finding out putative interactions of Arabidopsis thaliana HDACs and MADS-domain proteins using an evolutionary perspective combined with bioinformatics analyses and testing the more promising predicted interactions through classic molecular biology tools. Through bioinformatic analyses, we found similarities between HDACs proteins from different organisms, which allowed us to predict a putative protein-protein interaction between the Arabidopsis thaliana deacetylase HDA15 and the MADS-domain protein XAANTAL1 (XAL1). The results of two-hybrid and Bimolecular Fluorescence Complementation analysis demonstrated in vitro and in vivo HDA15-XAL1 interaction in the nucleus. Likely, this interaction might regulate developmental processes in plants as is the case for this type of interaction in animals.

Whole genome sequencing reveals that five genes are related to BW trait in sheep

BW is an important economic trait in sheep that influences growth and development. Currently, most studies have used a single approach to screen genes associated with BW traits in sheep. To address this limitation, we conducted a genome-wide association study (GWAS) covering four different BW periods: birth, weaning, 6 months, and 12 months. Five new candidate genes: MAP3K1, ANKRD55, ABCB1, MEF2C and TRNAW-CCA-87 were screened using a combination of GWAS and quantitative trait loci analysis in sheep. Additionally, five genes were subjected to Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. These genes were primarily enriched in pathways related to growth hormone and energy metabolism. The results demonstrated that the above genes potentially influenced the growth and development of sheep. The five new candidate genes are closely related to the BW trait in sheep, which will be valuable for understanding the genetic mechanisms underlying BW traits and for guiding sheep breeding.

Dystrophin deficiency impairs cell junction formation during embryonic myogenesis from pluripotent stem cells

Mutations in the DMD gene lead to Duchenne muscular dystrophy (DMD), a severe neuromuscular disorder affecting young boys as they acquire motor functions. DMD is typically diagnosed at 2-4 years of age, but the absence of dystrophin has negative impacts on skeletal muscles before overt symptoms appear in patients, which poses a serious challenge in current standards of care. Here, we investigated the consequences of dystrophin deficiency during skeletal muscle development. We used single-cell transcriptome profiling to characterize the myogenic trajectory of human pluripotent stem cells and showed that DMD cells bifurcate to an alternative branch when they reach the somite stage. Dystrophin deficiency was linked to marked dysregulations of cell junction proteins involved in the cell state transitions characteristic of embryonic somitogenesis. Altogether, this work demonstrates that in vitro, dystrophin deficiency has deleterious effects on cell-cell communication during myogenic development, which should be considered in future therapeutic strategies for DMD.

MEF2C Directly Interacts with Pre-miRNAs and Distinct RNPs to Post-Transcriptionally Regulate miR-23a-miR-27a-miR-24-2 microRNA Cluster Member Expression

Transcriptional regulation constitutes a key step in gene expression regulation. Myocyte enhancer factor 2C (MEF2C) is a transcription factor of the MADS box family involved in the early development of several cell types, including muscle cells. Over the last decade, a novel layer of complexity modulating gene regulation has emerged as non-coding RNAs have been identified, impacting both transcriptional and post-transcriptional regulation. microRNAs represent the most studied and abundantly expressed subtype of small non-coding RNAs, and their functional roles have been widely documented. On the other hand, our knowledge of the transcriptional and post-transcriptional regulatory mechanisms that drive microRNA expression is still incipient. We recently demonstrated that MEF2C is able to transactivate the long, but not short, regulatory element upstream of the miR-23a-miR-27a-miR-24-2 transcriptional start site. However, MEF2C over-expression and silencing, respectively, displayed distinct effects on each of the miR-23a-miR-27a-miR-24-2 mature cluster members without affecting pri-miRNA expression levels, thus supporting additional MEF2C-driven regulatory mechanisms. Within this study, we demonstrated a complex post-transcriptional regulatory mechanism directed by MEF2C in the regulation of miR-23a-miR-27a-miR-24-2 cluster members, distinctly involving different domains of the MEF2C transcription factor and the physical interaction with pre-miRNAs and Ksrp, HnRNPa3 and Ddx17 transcripts.

Dystrophin deficiency impairs cell junction formation during embryonic myogenesis

Mutations in the DMD gene lead to Duchenne muscular dystrophy, a severe X-linked neuromuscular disorder that manifests itself as young boys acquire motor functions. DMD is typically diagnosed at 2 to 4 years of age, but the absence of dystrophin negatively impacts muscle structure and function before overt symptoms appear in patients, which poses a serious challenge in the optimization of standards of care. In this report, we investigated the early consequences of dystrophin deficiency during skeletal muscle development. We used single-cell transcriptome profiling to characterize the myogenic trajectory of human pluripotent stem cells and showed that DMD cells bifurcate to an alternative branch when they reach the somite stage. Here, dystrophin deficiency was linked to marked dysregulations of cell junction protein families involved in the cell state transitions characteristic of embryonic somitogenesis. Altogether, this work demonstrates that in vitro, dystrophin deficiency has deleterious effects on cell-cell communication during myogenic development, which should be considered in future therapeutic strategies for DMD.

Alterations in gene expression and microbiome composition upon calcium-sensing receptor deletion in the mouse esophagus

The calcium-sensing receptor (CaSR), a G protein-coupled receptor, regulates Ca2+ concentration in plasma by regulating parathyroid hormone secretion. In other tissues, it is reported to play roles in cellular differentiation and migration and in secretion and absorption. We reported previously that CaSR can be conditionally deleted in the mouse esophagus. This conditional knockout (KO) (EsoCaSR-/-) model showed a significant reduction in the levels of adherens and tight junction proteins and had a marked buildup of bacteria on the luminal esophageal surface. To further examine the role of CaSR, we used RNA sequencing to determine gene expression profiles in esophageal epithelia of control and EsoCaSR-/-mice RNA Seq data indicated upregulation of gene sets involved in DNA replication and cell cycle in EsoCaSR-/-. This is accompanied by the downregulation of gene sets involved in the innate immune response and protein homeostasis including peptide elongation and protein trafficking. Ingenuity pathway analysis (IPA) demonstrated that these genes are mapped to important biological networks including calcium and Ras homologus A (RhoA) signaling pathways. To further explore the bacterial buildup in EsoCaSR-/- esophageal tissue, 16S sequencing of the mucosal-associated bacterial microbiome was performed. Three bacterial species, g_Rodentibacter, s_Rodentibacter_unclassified, and s_Lactobacillus_hilgardi were significantly increased in EsoCaSR-/-. Furthermore, metagenomic analysis of 16S sequences indicated that pathways related to oxidative phosphorylation and metabolism were downregulated in EsoCaSR-/- tissues. These data demonstrate that CaSR impacts major pathways of cell proliferation, differentiation, cell cycle, and innate immune response in esophageal epithelium. The disruption of these pathways causes inflammation and significant modifications of the microbiome.NEW & NOTEWORTHY Calcium-sensing receptor (CaSR) plays a significant role in maintaining the barrier function of esophageal epithelium. Using RNA sequencing, we show that conditional deletion of CaSR from mouse esophagus causes upregulation of genes involved in DNA replication and cell cycle and downregulation of genes involved in the innate immune response, protein translation, and cellular protein synthesis. Pathway analysis shows disruption of signaling pathways of calcium and actin cytoskeleton. These changes caused inflammation and esophageal dysbiosis.

lncRNA TUG1 as potential novel biomarker for prognosis of cardiovascular diseases

Globally, cardiovascular diseases (CVDs) are among the leading causes of death. In light of the high prevalence and mortality of CVDs, it is imperative to understand the molecules involved in CVD pathogenesis and the signaling pathways that they initiate. This may facilitate the development of more precise and expedient diagnostic techniques, the identification of more effective prognostic molecules and the identification of potential therapeutic targets. Numerous studies have examined the role of lncRNAs, such as TUG1, in CVD pathogenesis in recent years. According to this review article, TUG1 can be considered a biomarker for predicting the prognosis of CVD.

MEF2C and miR-194-5p: New Players in Triple Negative Breast Cancer Tumorigenesis

Among breast cancer (BC) subtypes, the most aggressive is triple negative BC (TNBC), which is prone to metastasis. We previously found that microRNA (miR)-194-5p is downregulated at the early stages of TNBC brain metastasis development. Additionally, the transcription factor myocyte enhancer factor 2 (MEF2)C, a bioinformatically predicted miR-194-5p target, was increasingly expressed throughout TNBC brain metastasis formation and disease severity. However, the contributions of these two players to malignant cells' features remain undetermined. This study aimed at disclosing the role of miR-194-5p and MEF2C in TNBC tumorigenesis. The transfection of 4T1 cells with a silencer for MEF2C or with a pre-miRNA for miR-194-5p was employed to study TNBC cells' phenotypic alterations regarding epithelial and mesenchymal markers, as well as migratory capability alterations. MEF2C-silenced cells presented a decline in both vimentin and cytokeratin expression, whereas the overexpression of miR-194-5p promoted an increase in cytokeratin and a reduction in vimentin, reflecting the acquisition of an epithelial phenotype. Both treatments reduced TNBC cells' migration. These results suggest that MEF2C may determine TNBC cells' invasive properties by partially determining the occurrence of epithelial-mesenchymal transition, while the overexpression of miR-194-5p promotes a decline in TNBC cells' aggressive behavior and reinforces this miRNA's role as a tumor suppressor in TNBC.

Refining patterns of MEF2C effects in white matter microstructure and psychiatric features

Several GWAS reported Myocyte Enhancer Factor 2 C (MEF2C) gene associations with white matter microstructure and psychiatric disorders, and MEF2C involvement in pathways related to neuronal development suggests a common biological factor underlying these phenotypes. We aim to refine the MEF2C effects in the brain relying on an integrated analysis of white matter and psychiatric phenotypes in an extensively characterized sample. This study included 870 Brazilian adults (47% from an attention-deficit/hyperactivity disorder outpatient clinic) assessed through standardized psychiatric interviews, 139 of which underwent a magnetic resonance imaging scan. We evaluated variants in the MEF2C region using two approaches: 1) a gene-wide analysis, which uses the sum of polymorphism effects, and 2) SNP analyses, restricted to the independent variants within the gene. The outcomes included psychiatric phenotypes and fractional anisotropy for brain images. Results: The gene-wide analyses pointed to a nominal association between MEF2C and the Temporal Portion of the Superior Longitudinal Fasciculus (SLFTEMP). The SNP analysis identified four independent variants significantly associated with SLFTEMP and one (rs4218438) with Substance Use Disorder. Our findings showing specific associations of MEF2C variants with temporal-frontal circuitry components may help to elucidate how the MEF2C gene underlies a broad range of psychiatric phenotypes since these regions are relevant to executive and cognitive functions.

Integrative Bioinformatics Analysis Reveals That miR-524-5p/MEF2C Regulates Bone Metastasis in Prostate Cancer and Breast Cancer

Bone metastases are highly prevalent in patients with advanced prostate cancer and breast cancer and have a serious impact on the survival time and quality of life of these patients. It has been reported that microRNAs (miRNAs) are expressed abnormally in different types of cancer and metastases. However, it remains unknown whether the underlying miRNAs are associated with prostate and breast cancer bone metastasis. Differentially expressed miRNAs (DE-miRNAs) and their potential targets in the metastatic process were identified by bioinformatics analysis. Additionally, qPCR confirmed that the miR-524-5p expression was downregulated in prostate and breast cancer cells. The overexpression of miR-524-5p restrained cell proliferation, invasion, and metastasis in prostate and breast cancer cells. Meanwhile, miR-524-5p could target and inhibit the expression of MEF2C, which was verified by a luciferase assay. In conclusion, our data strongly suggest that downregulation of miR-524-5p appears to be a precocious event in prostate and breast cancer, and the miR-524-5p/MEF2C axis plays a novel role in bone metastases from prostate and breast cancers.

Gene expression and transcriptional regulation driven by transcription factors involved in congenital heart defects

BACKGROUND

Congenital heart disease (CHD) is one of the most important birth defects caused by more than one mutated gene. Mutations in the genes could cause different types of congenital heart defects including atrial septal defect (ASD), tetralogy of Fallot (TOF), and ventricular septal defect (VSD).

OBJECTIVES

Cardiac transcription factors are key players for heart development and are actively involved in controlling stress regulation of the heart. Transcription factors are sequence-specific DNA binding proteins that control the process of transcription and work in a synergistic manner. We aim to characterize core cardiac transcription factors including NKX2-5, TBX, SRF, GATA4, and MEF2, which encode homeobox and MADS domain and play a crucial role in heart development.

METHODS

In this study, we have explored the important transcription factors involved in cardiac development and genes controlling the expression and regulation process by using the bioinformatics approach.

RESULTS

We have predicted the orthologs and homologs based on their evolutionary history, conserved protein domains, functional sites, and 3D structures for better understanding and presentation of factors responsible for causing CHD. Results showed the importance of these transcription factors for normal heart functioning and development.

CONCLUSION

Understanding the molecular pathways and genetic basis of CHD will help to open a new door for the treatment of patients with cardiac defects.

A high-quality assembly reveals genomic characteristics, phylogenetic status, and causal genes for leucism plumage of Indian peafowl

BACKGROUND

The dazzling phenotypic characteristics of male Indian peafowl (Pavo cristatus) are attractive both to the female of the species and to humans. However, little is known about the evolution of the phenotype and phylogeny of these birds at the whole-genome level. So far, there are no reports regarding the genetic mechanism of the formation of leucism plumage in this variant of Indian peafowl.

RESULTS

A draft genome of Indian peafowl was assembled, with a genome size of 1.05 Gb (the sequencing depth is 362×), and contig and scaffold N50 were up to 6.2 and 11.4 Mb, respectively. Compared with other birds, Indian peafowl showed changes in terms of metabolism, immunity, and skeletal and feather development, which provided a novel insight into the phenotypic evolution of peafowl, such as the large body size and feather morphologies. Moreover, we determined that the phylogeny of Indian peafowl was more closely linked to turkey than chicken. Specifically, we first identified that PMEL was a potential causal gene leading to the formation of the leucism plumage variant in Indian peafowl.

CONCLUSIONS

This study provides an Indian peafowl genome of high quality, as well as a novel understanding of phenotypic evolution and phylogeny of Indian peafowl. These results provide a valuable reference for the study of avian genome evolution. Furthermore, the discovery of the genetic mechanism for the development of leucism plumage is both a breakthrough in the exploration of peafowl plumage and also offers clues and directions for further investigations of the avian plumage coloration and artificial breeding in peafowl.

Activin A Causes Muscle Atrophy through MEF2C-Dependent Impaired Myogenesis

Activin A (ActA) is considered to play a major role in cancer-induced cachexia (CC). Indeed, circulating ActA levels are elevated and predict survival in patients with CC. However, the mechanisms by which ActA mediates CC development and in particular skeletal muscle (SM) atrophy in humans are not yet fully understood. In this work, we aimed to investigate the effects of ActA on human SM and in mouse models of CC. We used a model of human muscle cells in culture to explore how ActA acts towards human SM. In this model, recombinant ActA induced myotube atrophy associated with the decline of MyHC-β/slow, the main myosin isoform in human muscle cells studied. Moreover, ActA inhibited the expression and activity of MEF2C, the transcription factor regulating MYH7, the gene which codes for MyHC-β/slow. This decrease in MEF2C was involved in the decline of MyHC-β/slow expression, since inhibition of MEF2C by a siRNA leads to the decrease in MyHC-β/slow expression. The relevance of this ActA/MEF2C pathway in vivo was supported by the parallel decline of MEF2C expression and SM mass, which are both blunted by ActA inhibition, in animal models of CC. In this work, we showed that ActA is a potent negative regulator of SM mass by inhibiting MyHC-β/slow synthesis through downregulation of MEF2C. This observation highlights a novel interaction between ActA signaling and MEF2C transcriptional activity which contributes to SM atrophy in CC models.

Molecular mechanisms governing circulating immune cell heterogeneity across different species revealed by single-cell sequencing

BACKGROUND

Immune cells play important roles in mediating immune response and host defense against invading pathogens. However, insights into the molecular mechanisms governing circulating immune cell diversity among multiple species are limited.

METHODS

In this study, we compared the single-cell transcriptomes of immune cells from 12 species. Distinct molecular profiles were characterized for different immune cell types, including T cells, B cells, natural killer cells, monocytes, and dendritic cells.

RESULTS

Our data revealed the heterogeneity and compositions of circulating immune cells among 12 different species. Additionally, we explored the conserved and divergent cellular crosstalks and genetic regulatory networks among vertebrate immune cells. Notably, the ligand and receptor pair VIM-CD44 was highly conserved among the immune cells.

CONCLUSIONS

This study is the first to provide a comprehensive analysis of the cross-species single-cell transcriptome atlas for peripheral blood mononuclear cells (PBMCs). This research should advance our understanding of the cellular taxonomy and fundamental functions of PBMCs, with important implications in evolutionary biology, developmental biology, and immune system disorders.

Inhibition of miR-218-5p reduces myocardial ischemia-reperfusion injury in a Sprague-Dawley rat model by reducing oxidative stress and inflammation through MEF2C/NF-κB pathway

Following myocardial ischemia, myocardial reperfusion injury causes oxidative stress (OS) and inflammation, leading to myocardial cell apoptosis and necrosis. Recently, emerging studies have shown that microRNAs (miRNAs) contribute to the pathophysiology associated with myocardial ischemia-reperfusion (I/R). In this study, we conducted both in-vitro and in-vivo experiments to explore the role of miR-218-5p in ischemia-reperfusion (I/R)- or oxygen and glucose deprivation/reperfusion (OGD/R)-mediated cardiomyocyte injury. A total 44 Sprague-Dawley (SD) rats were used, and randomly divided into four groups, control group (n = 11), miR-218-5p-in group (n = 11), I/R group (n = 11), I/R + miR-218-5p-in group (n = 11). Our data showed that miR-218-5p was overexpressed in H9C2 cardiomyocytes under OGD/R treatment. miR-218-5p inhibition reduced the lactate dehydrogenase (LDH) activity and the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD), as well as the expression of tumor necrosis factor alpha (TNF-α), interleukin (IL-1β), and IL-6. Oppositely, miR-218-5p overexpression aggravated OGD/R-mediated damage on H9C2 cells, whereas nuclear factor kappa B (NF-κB) pathway inhibition or myocyte enhancer factor 2C (MEF2C) upregulation reversed miR-218-5p mimics-mediated effects. Bioinformatics analysis predicted that miR-218-5p targeted and dampened its expression, which was testified by the dual-luciferase reporter assay and RNA pull-down assay. In vivo, inhibiting miR-218-5p declined LDH activities and ROS, MDA and SOD levels in rat myocardial tissues under I/R injury, alleviated myocardial fibrosis and inflammatory reactions, and reduced myocardial infarction area. Overall, inhibition of miR-218-5p choked oxidative stress and inflammation in myocardial I/R injury via targeting MEF2C/NF-κB axis, thus relieving the disease progression.

miR-194-Loaded Gelatin Nanospheres Target MEF2C to Suppress Muscle Atrophy in a Mechanical Unloading Model

Muscle atrophy usually occurs under mechanical unloading, which increases the risk of injury to reduce the functionality of the moving system, while there is still no effective therapy until now. It was found that miR-194 was significantly downregulated in a muscle atrophy model, and its target protein was the myocyte enhancer factor 2C (MEF2C). miR-194 could promote muscle differentiation and also inhibit ubiquitin ligases, thus miR-194 could be used as a nucleic acid drug to treat muscle atrophy, whereas miRNA was unstable in vivo, limiting its application as a therapeutic drug. A gelatin nanosphere (GN) delivery system was applied for the first time to load exogenous miRNA here. Exogenous miR-194 was loaded in GNs and injected into the muscle atrophy model. It demonstrated that the muscle fiber cross-sectional area, in situ muscle contractile properties, and myogenic markers were increased significantly after treatment. It proposed miR-194 loaded in GNs as an effective treatment for muscle atrophy by promoting muscle differentiation and inhibiting ubiquitin ligase activity. Moreover, the developed miRNA delivery system, taking advantage of its tunable composition, degradation rate, and capacity to load various drug molecules with high dosage, is considered a promising platform to achieve precise treatment of muscle atrophy-related diseases.

MEF2C silencing downregulates NF2 and E-cadherin and enhances Erastin-induced ferroptosis in meningioma

BACKGROUND

Ferroptosis, a programmed cell death characterized by lipid peroxidation, is implicated in various diseases including cancer. Although cell density-dependent E-cadherin and Merlin/Neurofibromin (NF2) loss can modulate ferroptosis, the role of ferroptosis and its potential link to NF2 status and E-cadherin expression in meningioma remain unknown.

METHODS

Relationship between ferroptosis modulators expression and NF2 mutational status was examined in 35 meningiomas (10 NF2 loss and 25 NF2 wildtype). The impact of NF2 and E-cadherin on ferroptosis were examined by LDH release, lipid peroxidation and western blot assays in IOMM-Lee, CH157 and patient-derived meningioma cell models. Luciferase reporter and chromatin immunoprecipitation assays were used to assess the ability of MEF2C (myocyte enhancer factor 2C) to drive expression of NF2 and CDH1 (E-cadherin). Therapeutic efficacy of Erastin-induced ferroptosis was tested in xenograft mouse models.

RESULTS

Meningioma cells with NF2 inactivation were susceptible to Erastin-induced ferroptosis. Meningioma cells grown at higher density increased expression of E-Cadherin, which suppressed Erastin-induced ferroptosis. Maintaining NF2 and E-cadherin inhibited ferroptosis-related lipid peroxidation and meningioma cell death. MEF2C was found to drive the expression of both NF2 and E-cadherin. MEF2C silencing enhanced Erastin-induced ferroptotic meningioma cell death and lipid peroxidation levels in vitro, which was limited by forced expression of MEF2C targets, NF2 and E-Cadherin. In vivo, anti-meningioma effect of Erastin was augmented by MEF2C knockdown and was counteracted by NF2 or E-Cadherin.

CONCLUSIONS

NF2 loss and low E-cadherin create susceptibility to ferroptosis in meningioma. MEF2C could be a new molecular target in ferroptosis-inducing therapies for meningioma.

Myocyte Enhancer Factor 2C as a New Player in Human Breast Cancer Brain Metastases

Myocyte enhancer factor 2C (MEF2C) is increasingly expressed in mice along with breast cancer brain metastases (BCBM) development. We aim to ascertain MEF2C expression in human BCBM, establish the relationship with disease severity, disclose the involvement of vascular endothelial growth factor receptor-2 (VEGFR-2) and β-catenin, also known as KDR and CTNNB1, respectively, and investigate if matched primary tumors express the protein. We studied resected BCBM for the expression of MEF2C, VEGFR-2, and ß-catenin, as well as proliferation (Ki-67) and epithelial (pan Cytokeratin) markers, and related experimental and clinical data. MEF2C expression was further assessed in matched primary tumors and non-BCBM samples used as controls. MEF2C expression was observed in BCBM, but not in controls, and was categorized into three phenotypes (P): P1, with extranuclear location; P2, with extranuclear and nuclear staining, and P3, with nuclear location. Nuclear translocation increased with metastases extension and Ki-67-positive cells number. P1 was associated with higher VEFGR-2 plasma membrane immunoreactivity, whereas P2 and P3 were accompanied by protein dislocation. P1 was accompanied by β-catenin membrane expression, while P2 and P3 exhibited β-catenin nuclear translocation. Primary BC samples expressed MEF2C in mammary ducts and scattered cells in the parenchyma. MEF2C emerges as a player in BCBM associated with disease severity and VEGFR-2 and β-catenin signaling.

Type I interferon response-related microglial Mef2c deregulation at the onset of Alzheimer's pathology in 5×FAD mice

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder with multifactorial etiology. The role of microglia in the pathogenesis of AD has been increasingly recognized in recent years; however, the detailed mechanisms shaping microglial phenotypes in AD-relevant pathological settings remain largely unresolved. Myocyte-specific enhancer factor 2C (Mef2C) is a transcription factor with versatile functions. Recent studies have attributed aging-related microglial changes to type I interferon (IFN-I)-associated Mef2C deregulation. In view of the close relationship between brain aging and AD, it is of great interest to determine microglial Mef2C changes in AD-related conditions. In this study, we have found that suppressed Mef2C nuclear translocation was an early and prominent microglial phenotype in a mouse model of brain amyloidosis (5×FAD mice), which exacerbated with age. Echoing the early Mef2C deregulation and its association with microglial activation, transcriptional data showed elicited IFN-I response in microglia from young 5×FAD mice. Amyloid beta 42 (Aβ42) in its oligomeric forms promoted Mef2C deregulation in microglia on acute organotypic brain slices with augmented microglial activation and synapse elimination via microglial phagocytosis. Importantly, these oligomeric Aβ42-mediated microglial changes were substantially attenuated by blocking IFN-I signaling. The simplest interpretation of the results is that Mef2C, concurring with activated IFN-I signaling, constitutes early microglial changes in AD-related conditions. In addition to the potential contribution of Mef2C deregulation to the development of microglial phenotypes in AD, Mef2C suppression in microglia may serve as a potential mechanistic pathway linking brain aging and AD.

Genotypes and Phenotypes of MEF2C Haploinsufficiency Syndrome: New Cases and Novel Point Mutations

Aim: MEF2C haploinsufficiency syndrome (MCHS) is a severe neurodevelopmental disorder. We describe the clinical phenotypes and genotypes of seven patients with MCHS to enhance the understanding of clinical manifestations and genetic alterations associated with MCHS. Method: Seven patients (6 females and 1 male, aged between 2 years 5 months and 6 years) who had MEF2C mutations, and their parents underwent trio-based whole-exome sequencing; subsequently, their clinical features were assessed. A literature review of patients with MCHS was performed by searching the PubMed and Online Mendelian Inheritance in Man databases. Results: Seven mutations were identified, of which six were unreported in the past; of the reported cases, five patients had de novo mutations but two had an undefined inheritance pattern. All patients presented delays in developmental milestones, severe intellectual disabilities and lack of speech. Six patients exhibited infantile hypotonia, five patients experienced stereotypic movements and were unable to walk, four patients exhibited poor eye contact indicative of autism and two showed poor performance. While six patients experienced seizure, five among them became seizure free after receiving anti-seizure medicine. Three patients showed a regression in their development, whereas the mothers of two patients exhibited mosaicism but were healthy without any abovementioned symptoms. Interpretation: Regression was not a common phenomenon but occurred in MCHS. The prognosis of MCHS patients with epilepsy was good, but most patients can achieve a seizure-free status. Healthy people may have low-level mosaicism and carry a pathogenic MEF2C mutation.

Prothrombotic effects of high uric acid in mice via activation of MEF2C-dependent NF-κB pathway by upregulating let-7c

Serum uric acid is reportedly associated with thrombosis development. However, still unclear is the mechanism of high uric acid in thrombosis with the involvement of let-7c. In an aim to fill this void, we conducted this study by treating mice and human umbilical vein endothelial cells with high uric acid. Analysis indicated that let-7c was upregulated in hyperuricemia patients as well as in mice and human umbilical vein endothelial cells treated with high uric acid. Furthermore, high uric acid inhibited myocyte enhancer factor-2C, but activated nuclear factor-kappa B pathway in human umbilical vein endothelial cells. Then the targeting relationship between let-7c and myocyte enhancer factor-2C was verified. On the one hand, high uric acid shortened activated partial thromboplastin time and prothrombin time of mice and declined tissue plasminogen activator level. Additionally, the treatment prolonged thrombin time and elevated the levels of thrombosis related molecules or proteins such as Fibrinogen and D-dimer. Nevertheless, these alternations could be reversed by inhibition of let-7c and nuclear factor-kappa B pathway or overexpressing myocyte enhancer factor-2C. To sum up, our results uncovered the pro-thrombotic effect of high uric acid in mice by activating myocyte enhancer factor-2C-dependent nuclear factor-kappa B pathway via let-7c upregulation.

The role of histone deacetylase 4 during chondrocyte hypertrophy and endochondral bone development

Chondrocyte hypertrophy represents a crucial turning point during endochondral bone development. This process is tightly regulated by various factors, constituting a regulatory network that maintains normal bone development. Histone deacetylase 4 (HDAC4) is the most well-characterized member of the HDAC class IIa family and participates in different signalling networks during development in various tissues by promoting chromatin condensation and transcriptional repression. Studies have reported that HDAC4-null mice display premature ossification of developing bones due to ectopic and early-onset chondrocyte hypertrophy. Overexpression of HDAC4 in proliferating chondrocytes inhibits hypertrophy and ossification of developing bones, which suggests that HDAC4, as a negative regulator, is involved in the network regulating chondrocyte hypertrophy. Overall, HDAC4 plays a key role during bone development and disease. Thus, understanding the role of HDAC4 during chondrocyte hypertrophy and endochondral bone formation and its features regarding the structure, function, and regulation of this process will not only provide new insight into the mechanisms by which HDAC4 is involved in chondrocyte hypertrophy and endochondral bone development, but will also create a platform for developing a therapeutic strategy for related diseases.

Cite this article:Bone Joint Res. 2020;9(2):82–89.

MicroRNA regulatory networks in the pathogenesis of sarcopenia

Sarcopenia is an age‐related disease characterized by disturbed homeostasis of skeletal muscle, leading to a decline in muscle mass and function. Loss of muscle mass and strength leads to falls and fracture, and is often accompanied by other geriatric diseases, including osteoporosis, frailty and cachexia, resulting in a general decrease in quality of life and an increase in mortality. Although the underlying mechanisms of sarcopenia are still not completely understood, there has been a marked improvement in the understanding of the pathophysiological changes leading to sarcopenia in recent years. The role of microRNAs (miRNAs), especially, has been clearer in skeletal muscle development and homeostasis. miRNAs form part of a gene regulatory network and have numerous activities in many biological processes. Intervention based on miRNAs may develop into an innovative treatment strategy to conquer sarcopenia. This review is divided into three sections: firstly, the latest understanding of the pathogenesis of sarcopenia is summarized; secondly, increasing evidence for the involvement of miRNAs in the regulation of muscle quantity or quality and muscle homeostasis is highlighted; and thirdly, the possibilities and limitations of miRNAs as a treatment for sarcopenia are explored.

Downregulation of circulating miR 802-5p and miR 194-5p and upregulation of brain MEF2C along breast cancer brain metastasization

Breast cancer brain metastases (BCBMs) have been underinvestigated despite their high incidence and poor outcome. MicroRNAs (miRNAs), and particularly circulating miRNAs, regulate multiple cellular functions, and their deregulation has been reported in different types of cancer and metastasis. However, their signature in plasma along brain metastasis development and their relevant targets remain undetermined. Here, we used a mouse model of BCBM and next‐generation sequencing (NGS) to establish the alterations in circulating miRNAs during brain metastasis formation and development. We further performed bioinformatics analysis to identify their targets with relevance in the metastatic process. We additionally analyzed human resected brain metastasis samples of breast cancer patients for target expression validation. Breast cancer cells were injected in the carotid artery of mice to preferentially induce metastasis in the brain, and samples were collected at different timepoints (5 h, 3, 7, and 10 days) to follow metastasis development in the brain and in peripheral organs. Metastases were detected from 7 days onwards, mainly in the brain. NGS revealed a deregulation of circulating miRNA profile during BCBM progression, rising from 18% at 3 days to 30% at 10 days following malignant cells’ injection. Work was focused on those altered prior to metastasis detection, among which were miR‐802‐5p and miR‐194‐5p, whose downregulation was validated by qPCR. Using targetscan and diana tools, the transcription factor myocyte enhancer factor 2C (MEF2C) was identified as a target for both miRNAs, and its expression was increasingly observed in malignant cells along brain metastasis development. Its upregulation was also observed in peritumoral astrocytes pointing to a role of MEF2C in the crosstalk between tumor cells and astrocytes. MEF2C expression was also observed in human BCBM, validating the observation in mouse. Collectively, downregulation of circulating miR‐802‐5p and miR‐194‐5p appears as a precocious event in BCBM and MEF2C emerges as a new player in brain metastasis development.

A novel MEF2C mutation in lymphoid neoplasm diffuse large B-cell lymphoma promotes tumorigenesis by increasing c-JUN expression

Diffuse large B-cell lymphoma (DLBCL) is the most aggressive non-Hodgkin lymphoma (NHL), accounting for about 31% of the newly diagnosed NHL worldwide. Although approximately 60% of patients who initially received a standard R-CHOP treatment likely have a 3-year event-free survival, many patients become refractory or relapsed due to the genetic heterogeneity of this malignancy. Hence, new treatment strategies are urgently needed. MEF2C, a member of the MEF2 transcription factor family gene, plays great important roles involved in the development of various tissues and the pathogenesis of lymphoma. However, the exact functions and molecular mechanisms of MEF2C in DLBCL are not fully investigated. By Sanger sequencing, we identified a novel point mutation of MEF2C at the p.N389 site in DLBCL patient, which was further validated by several DLBCL cell lines. Intriguingly, we found that the p.N389S mutation did not influence MEF2C expression, protein stability, and subcellular distribution, but enhanced its transcriptional activity. Furthermore, we demonstrated that MEF2C p.N389S mutation promotes DLBCL cell proliferation, cellular adhesion, and tumor formation in nude mice. On mechanism, our data revealed that MEF2C p.N389S mutation increases c-JUN expression, and c-JUN regulation mediated the oncogenic function of MEF2C p.N389S mutation on DLBCL cells. Our finding may provide a significant insight into the DLBCL and a compelling therapy target for this disease treatment.

Zebrafish Vestigial Like Family Member 4b Is Required for Valvulogenesis Through Sequestration of Transcription Factor Myocyte Enhancer Factor 2c

A variety of cardiac transcription factors/cofactors, signaling pathways, and downstream structural genes integrate to form the regulatory hierarchies to ensure proper cardiogenesis in vertebrate. Major interaction proteins of the transcription cofactor vestigial like family member 4 (VGLL4) include myocyte enhancer factor 2 (MEF2) and TEA domain transcription factors (TEAD), both of which play important roles in embryonic cardiac development and in adulthood. In this study, we identified that the deficiency of zebrafish vgll4b paralog, a unique family member expressed in developing heart, led to an impaired valve development. Mechanistically, in vgll4b mutant embryos the disruption of Vgll4b-Mef2c complex, rather than that of Vgll4b-Tead complex, resulted in an aberrant expression of krüppel-like factor 2a (klf2a) in endocardium. Such misexpression of klf2a eventually evoked the valvulogenesis defects. Our findings suggest that zebrafish Vgll4b plays an important role in modulating the transcription activity of Mef2c on klf2a during valve development in a blood-flow-independent manner.

The Pathway to Cancer Cachexia: MicroRNA-Regulated Networks in Muscle Wasting Based on Integrative Meta-Analysis

Cancer cachexia is a multifactorial syndrome that leads to significant weight loss. Cachexia affects 50%-80% of cancer patients, depending on the tumor type, and is associated with 20%-40% of cancer patient deaths. Besides the efforts to identify molecular mechanisms of skeletal muscle atrophy-a key feature in cancer cachexia-no effective therapy for the syndrome is currently available. MicroRNAs are regulators of gene expression, with therapeutic potential in several muscle wasting disorders. We performed a meta-analysis of previously published gene expression data to reveal new potential microRNA-mRNA networks associated with muscle atrophy in cancer cachexia. We retrieved 52 differentially expressed genes in nine studies of muscle tissue from patients and rodent models of cancer cachexia. Next, we predicted microRNAs targeting these differentially expressed genes. We also include global microRNA expression data surveyed in atrophying skeletal muscles from previous studies as background information. We identified deregulated genes involved in the regulation of apoptosis, muscle hypertrophy, catabolism, and acute phase response. We further predicted new microRNA-mRNA interactions, such as miR-27a/Foxo1, miR-27a/Mef2c, miR-27b/Cxcl12, miR-27b/Mef2c, miR-140/Cxcl12, miR-199a/Cav1, and miR-199a/Junb, which may contribute to muscle wasting in cancer cachexia. Finally, we found drugs targeting MSTN, CXCL12, and CAMK2B, which may be considered for the development of novel therapeutic strategies for cancer cachexia. Our study has broadened the knowledge of microRNA-regulated networks that are likely associated with muscle atrophy in cancer cachexia, pointing to their involvement as potential targets for novel therapeutic strategies.

Conserved functions of RNA-binding proteins in muscle

Animals require different types of muscle for survival, for example for circulation, motility, reproduction and digestion. Much emphasis in the muscle field has been placed on understanding how transcriptional regulation generates diverse types of muscle during development. Recent work indicates that alternative splicing and RNA regulation are as critical to muscle development, and altered function of RNA-binding proteins causes muscle disease. Although hundreds of genes predicted to bind RNA are expressed in muscles, many fewer have been functionally characterized. We present a cross-species view summarizing what is known about RNA-binding protein function in muscle, from worms and flies to zebrafish, mice and humans. In particular, we focus on alternative splicing regulated by the CELF, MBNL and RBFOX families of proteins. We discuss the systemic nature of diseases associated with loss of RNA-binding proteins in muscle, focusing on mis-regulation of CELF and MBNL in myotonic dystrophy. These examples illustrate the conservation of RNA-binding protein function and the marked utility of genetic model systems in understanding mechanisms of RNA regulation.

PHACTR1 gene polymorphism with the risk of coronary artery disease in Chinese Han population

BACKGROUND

Coronary artery disease (CAD) is the most frequent multifactorial disease worldwide and is characterised by endothelial injury, lipid deposition and coronary artery calcification. The purpose of this study was to determine the allelic and genotypic frequencies of two loci (rs2026458 and rs9349379) of phosphatase and actin regulator 1 (PHACTR1) to the risk of developing CAD in the Chinese Han population.

METHODS

A case-control study was conducted including 332 patients with CAD and 119 controls. Genotype analysis was performed by PCR and Sanger sequencing. Genetic model analysis was performed to evaluate the association between single nucleotide polymorphisms and CAD susceptibility using Pearson's χ² test and logistic regression analysis.

RESULTS

The GG genotype of rs9349379 represented 50% and 29% of patients with CAD and controls, respectively (p<0.001). The CC genotype of rs2026458 was more prevalent in the controls than in patients with CAD compared with TT genotype (OR=0.548, 95% CI 0.351 to 0.856, p=0.008). Logistic regression analyses revealed that PHACTR1 rs9349379 GG genotype was significantly associated with increased risk of CAD in the recessive model (OR=2.359, 95% CI 1.442 to 3.862, p=0.001), even after adjusting for age gender, hypertension, type 2 diabetes, hyperlipidaemia and smoking habit. Heterogeneity test proved that rs9349379's risk effects on CAD were more significant among women.

CONCLUSIONS

Our study indicate that the PHACTR1 rs9349379 polymorphism is associated with the increased risk for CAD in the female Chinese Han population.

Cardiovascular development and survival require Mef2c function in the myocardial but not the endothelial lineage

MEF2C is a member of the highly conserved MEF2 family of transcription factors and is a key regulator of cardiovascular development. In mice, Mef2c is expressed in the developing heart and vasculature, including the endothelium. Loss of Mef2c function in germline knockout mice leads to early embryonic demise and profound developmental abnormalities in the cardiovascular system. Previous attempts to uncover the cause of embryonic lethality by specifically disrupting Mef2c function in the heart or vasculature failed to recapitulate the global Mef2c knockout phenotype and instead resulted in relatively minor defects that did not compromise viability or result in significant cardiovascular defects. However, previous studies examined the requirement of Mef2c in the myocardial and endothelial lineages using Cre lines that begin to be expressed after the expression of Mef2c has already commenced. Here, we tested the requirement of Mef2c in the myocardial and endothelial lineages using conditional knockout approaches in mice with Cre lines that deleted Mef2c prior to onset of its expression in embryonic development. We found that deletion of Mef2c in the early myocardial lineage using Nkx2-5^Cre resulted in cardiac and vascular abnormalities that were indistinguishable from the defects in the global Mef2c knockout. In contrast, early deletion of Mef2c in the vascular endothelium using an Etv2::Cre line active prior to the onset of Mef2c expression resulted in viable offspring that were indistinguishable from wild type controls with no overt defects in vascular development, despite nearly complete early deletion of Mef2c in the vascular endothelium. Thus, these studies support the idea that the requirement of MEF2C for vascular development is secondary to its requirement in the heart and suggest that the observed failure in vascular remodeling in Mef2c knockout mice results from defective heart function.

Novel MEF2C point mutations in Chinese patients with Rett (-like) syndrome or non-syndromic intellectual disability: insights into genotype-phenotype correlation

BACKGROUND

MEF2C (Myocyte-specific enhancer factor 2C) has been associated with neurodevelopmental disorders. This study aimed at delineating the clinical profiles of MEF2C gene mutations.

METHODS

In total, 112 Chinese patients with intellectual disability (ID) were recruited, including 44 patients presented with Rett syndrome (RTT) or RTT-like syndrome, and 68 patients with non-syndromic ID. Targeted next-generation sequencing (NGS) was performed. Detailed clinical information was collected.

RESULTS

Five heterozygous MEF2C gene mutations were identified, of which three were novel. The MEF2C mutant rate was 4.5% (5/112) in total, and 6.8% (3/44) in the RTT (-like) cohort. All patients with MEF2C gene mutation presented with cognitive impairment, gross motor delay, speech disorder and autistic features. Four patients had epilepsy, which responded well to antiepileptic drugs. One female was diagnosed with classical RTT, two females with RTT-like syndrome, and two males with non-syndromic ID. Generally, the phenotype of two males with relatively downstream mutations (c.565C > T, p.Arg 189*; c.766C > T, p.Arg 256*) was milder than that of three females with upstream mutations (c.48C > G, p.Asn16Lys; c.334G > T, p.Glu112* and c.403-1G > T).

CONCLUSIONS

Our findings expanded the current understanding of the consequences of MEF2C dysfunctions, especially MEF2C point mutations. MEF2C mutations are associated with a broad clinical spectrum, ranged from classical RTT to non-syndromic ID. Through our study, it can be inferred that there is correlation between the phenotype and MEF2C-genotype, the mutation site. Overall, the MEF2C gene mutational analysis should be performed in ID cohort, especially in patients with features overlapped with RTT.

Covalent CDK7 Inhibitor THZ1 Inhibits Myogenic Differentiation

Covalent CDK7 inhibitor THZ1 is a newly discovered anti-tumor drug.THZ1 affects the function of transcription factor TFIIH by inhibiting CDK7, which in turn affects RNA polymerase II, and ultimately affects transcription initiation. Study found that THZ1 could inhibit proliferation and promote apoptosis of several tumor cell lines. However, there is no report of the potential side effect of THZ1 in normal tissues. In the course of cancer, the muscle consumption of cachexia needs to be supplemented by the differentiation of muscle cells. However, the effect of THZ1 on myogenic differentiation remains unclear. Our study in this article found that THZ1 could both inhibit the differentiation of C2C12 cells and mouse primary myoblasts, also repressing the expression of differentiation-related transcription factors and muscle structural proteins, such as and myogenin, myh3 and MCK. Moreover, THZ1 could inhibit C2C12 cell proliferation and migration, increase its oxidative stress and promote its apoptosis. Our data indicates that THZ1 inhibits myogenic differentiation, suggesting that therapies based on THZ1 might have potential side effects on muscle functions.

MEF2C promotes gefitinib resistance in hepatic cancer cells through regulating MIG6 transcription

Introduction:

Mitogen-inducible gene 6 ( MIG6) holds a special position in epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) resistance. As MIG6 regulates the activity of EGFR signal pathway negatively, high level of MIG6 can increase the EGFR TKI resistance of cancer cells, and limit the therapeutic action of EGFR TKI, such as gefitinib or erlotinib. Therefore, better understanding of the molecular mechanisms underlying the regulation of EGFR TKI resistance holds great value in cancer therapy.

Methods:

In our study, we mainly explored the function of transcription activator, myocyte enhancer factor 2C (MEF2C), on MIG6 expression as well as gefitinib-resistant ability of hepatic cancer cells.

Results:

Our results indicated that both MEF2C and MIG6 could be upregulated in gefitinib-resistant cancer tissues and cancer cell lines compared with gefitinib-sensitive ones. Chromatin immunoprecipitation assay and dual luciferase assay showed that MEF2C could bind to the MEF2C element in the promoter sequence of MIG6 and promote the transcription of MIG6. This effect increased the gefitinib-resistant ability of cancer cells. Therefore, MEF2C knockdown inhibited the gefitinib resistance and limited the proliferation of hepatic cancer cells in vitro and in vivo, while overexpression of MEF2C showed opposite effect on cancer cell proliferation.

Conclusion:

Our study provides novel insight into the regulation mechanism of MIG6 and suggests potential implications for the therapeutic strategies of gefitinib resistance through inhibiting MEF2C in hepatic cancer cells.

A Novel MEF2C Loss-of-Function Mutation Associated with Congenital Double Outlet Right Ventricle

Congenital heart defect (CHD) represents the most prevalent birth defect, and accounts for substantial morbidity and mortality in humans. Aggregating evidence demonstrates the genetic basis for CHD. However, CHD is a heterogeneous disease, and the genetic determinants underlying CHD in most patients remain unknown. In the present study, a cohort of 186 unrelated cases with CHD and 300 unrelated control individuals were recruited. The coding exons and flanking introns of the MEF2C gene, which encodes a transcription factor crucial for proper cardiovascular development, were sequenced in all study participants. The functional effect of an identified MEF2C mutation was characterized using a dual-luciferase reporter assay system. As a result, a novel heterozygous MEF2C mutation, p.R15C, was detected in an index patient with congenital double outlet right ventricle (DORV) as well as ventricular septal defect. Analysis of the proband's pedigree showed that the mutation co-segregated with CHD with complete penetrance. The missense mutation, which changed the evolutionarily conserved amino acid, was absent in 300 control individuals. Functional deciphers revealed that the mutant MEF2C protein had a significantly decreased transcriptional activity. Furthermore, the mutation significantly reduced the synergistic activation between MEF2C and GATA4, another transcription factor linked to CHD. This study firstly associates MEF2C loss-of-function mutation with DORV in humans, which provides novel insight into the molecular pathogenesis of CHD, suggesting potential implications for genetic counseling and personalized treatment of CHD patients.

Mef2 and the skeletal muscle differentiation program

Mef2 is a conserved and significant transcription factor in the control of muscle gene expression. In cell culture Mef2 synergises with MyoD-family members in the activation of gene expression and in the conversion of fibroblasts into myoblasts. Amongst its in vivo roles, Mef2 is required for both Drosophila muscle development and mammalian muscle regeneration. Mef2 has functions in other cell-types too, but this review focuses on skeletal muscle and surveys key findings on Mef2 from its discovery, shortly after that of MyoD, up to the present day. In particular, in vivo functions, underpinning mechanisms and areas of uncertainty are highlighted. We describe how Mef2 sits at a nexus in the gene expression network that controls the muscle differentiation program, and how Mef2 activity must be regulated in time and space to orchestrate specific outputs within the different aspects of muscle development. A theme that emerges is that there is much to be learnt about the different Mef2 proteins (from different paralogous genes, spliced transcripts and species) and how the activity of these proteins is controlled.

MEF2C loss-of-function mutation associated with familial dilated cardiomyopathy

Background:

The MADS-box transcription factor myocyte enhancer factor 2C (MEF2C) is required for the cardiac development and postnatal adaptation and in mice-targeted disruption of the MEF2C gene results in dilated cardiomyopathy (DCM). However, in humans, the association of MEF2C variation with DCM remains to be investigated.

Methods:

The coding regions and splicing boundaries of the MEF2C gene were sequenced in 172 unrelated patients with idiopathic DCM. The available close relatives of the index patient harboring an identified MEF2C mutation and 300 unrelated, ethnically matched healthy individuals used as controls were genotyped for MEF2C. The functional effect of the mutant MEF2C protein was characterized in contrast to its wild-type counterpart by using a dual-luciferase reporter assay system.

Results:

A novel heterozygous MEF2C mutation, p.Y157X, was detected in an index patient with adult-onset DCM. Genetic screen of the mutation carrier’s family members revealed that the mutation co-segregated with DCM, which was transmitted as an autosomal dominant trait with complete penetrance. The non-sense mutation was absent in 300 control individuals. Functional analyses unveiled that the mutant MEF2C protein had no transcriptional activity. Furthermore, the mutation abolished the synergistic transactivation between MEF2C and GATA4 as well as HAND1, two other transcription factors that have been associated with DCM.

Conclusions:

This study indicates MEF2C as a new gene responsible for human DCM, which provides novel insight into the mechanism underpinning DCM, suggesting potential implications for development of innovative prophylactic and therapeutic strategies for DCM, the most prevalent form of primary myocardial disease.

MEF2C loss-of-function mutation contributes to congenital heart defects

Congenital heart disease (CHD) is the most common type of developmental abnormality in humans, and is a leading cause for substantially increased morbidity and mortality in affected individuals. Increasing studies demonstrates a pivotal role of genetic defects in the pathogenesis of CHD, and presently mutations in more than 60 genes have been associated with CHD. Nevertheless, CHD is of pronounced genetic heterogeneity, and the genetic basis underpinning CHD in a large proportion of patients remains unclear. In the present study, the whole coding exons and splicing donors/acceptors of the MEF2C gene, which codes for a transcription factor essential for normal cardiovascular development, were sequenced in 200 unrelated patients affected with CHD, and a novel heterozygous missense mutation, p.L38P, was identified in an index patient with patent ductus arteriosus (PDA) and ventricular septal defect (VSD). Genetic scan of the mutation carrier's family members available showed that the mutation was present in all affected family members but absent in unaffected family members. Analysis of the proband's pedigree revealed that the mutation co-segregated with PDA, which was transmitted as an autosomal dominant trait with complete penetrance. The mutation changed the amino acid that was completely conserved evolutionarily, and did not exist in 300 unrelated, ethnically-matched healthy individuals used as controls. Functional deciphers by using a dual-luciferase reporter assay system unveiled that the mutant MEF2C protein had a significantly reduced transcriptional activity. Furthermore, the mutation significantly diminished the synergistic activation between MEF2C and GATA4, another cardiac core transcription factor that has been causally linked to CHD. In conclusion, this is the first report on the association of a MEF2C loss-of-function mutation with an increased vulnerability to CHD in humans, which provides novel insight into the molecular mechanisms underlying CHD, implying potential implications for early diagnosis and timely prophylaxis of CHD.