New polymorphisms in human MEF2C gene as potential modifier of hypertrophic cardiomyopathy

Feline hypertrophic cardiomyopathy: reduced microvascular density and involvement of CD34+ interstitial cells

The sequence of pathological events in feline hypertrophic cardiomyopathy (fHCM) is still largely unknown, although we know that fHCM is characterized by interstitial remodeling in a macrophage-driven pro-inflammatory environment and that myocardial ischemia might contribute to its progression. This study aimed to gain further insights into the structural changes associated with interstitial remodeling in fHCM with special focus on the myocardial microvasculature and the phenotype of the interstitial cells. Twenty-eight hearts (16 hearts with fHCM and 12 without cardiac disease) were evaluated in the current study, with immunohistochemistry, RNA-in situ hybridization, and transmission electron microscopy. Morphometrical evaluations revealed a statistically significant lower microvascular density in fHCM. This was associated with structural alterations in capillaries that go along with a widening of the interstitium due to the accumulation of edema fluid, collagen fibers, and mononuclear cells that also proliferated locally. The interstitial cells were mainly of fibroblastic or vascular phenotype, with a substantial contribution of predominantly resident macrophages. A large proportion expressed CD34 mRNA, which suggests a progenitor cell potential. Our results indicate that microvascular alterations are key events in the pathogenesis of fHCM and that myocardial interstitial cell populations with CD34+ phenotype play a role in the pathogenesis of the disease.

Identification of a novel mutation in MEF2C gene in an atypical patient with frontotemporal lobar degeneration

The MEF2C gene encodes a transcription factor known to play a crucial role in molecular pathways affecting neuronal development. MEF2C mutations were described as a genetic cause of developmental disease (MRD20), and several reports sustain its involvement in dementia-related conditions, such as Alzheimer's disease and amyotrophic lateral sclerosis. These pathologies and frontotemporal degeneration (FTLD) are thought to share common physiopathological pathways. In this exploratory study, we searched for alterations in the DNA sequence of exons and boundaries, including 5'- and 3'-untranslated regions (5'UTR, 3'UTR), of MEF2C gene in 11 patients with clinical phenotypes related with MRD20 or FTLD. We identified a heterozygous deletion of 13 nucleotides in the 5'UTR region of a 69 years old FTLD patient. This alteration was absent in 200 healthy controls, suggesting a contribution to this patient's disease phenotype. In silico analysis of the mutated sequence indicated changes in mRNA secondary structure and stability, thus potentially affecting MEF2C protein levels. Furthermore, in vitro functional analysis of this mutation revealed that the presence of this deletion abolished the transcriptional activity of the gene in human embryonic cells and rat brain neurons, probably by modifying MEF2C expression. Altogether, our results provide evidence for the involvement of MEF2C in FTLD manifesting with seizures.

Knockdown of TUG1 rescues cardiomyocyte hypertrophy through targeting the miR-497/MEF2C axis

The aim of this study was to investigate the detailed role and molecular mechanism of long noncoding RNA (lncRNA) taurine upregulated gene 1 (TUG1) in cardiac hypertrophy. Cardiac hypertrophy was established by transverse abdominal aortic constriction (TAC) in vivo or angiotensin II (Ang II) treatment in vitro. Levels of lncRNA TUG1, miR-497 and myocyte enhancer factor 2C (MEF2C) mRNA were assessed by quantitative reverse transcriptase PCR (qRT-PCR). Western blot assay was performed to determine the expression of MEF2C protein. The endogenous interactions among TUG1, miR-497 and MEF2C were confirmed by dual-luciferase reporter and RNA immunoprecipitation assays. Our data indicated that TUG1 was upregulated and miR-497 was downregulated in the TAC rat model and Ang II-induced cardiomyocytes. TUG1 knockdown or miR-497 overexpression alleviated the hypertrophy induced by Ang II in cardiomyocytes. Moreover, TUG1 acted as a sponge of miR-497, and MEF2C was directly targeted and repressed by miR-497. miR-497 overexpression mediated the protective role of TUG1 knockdown in Ang II-induced cardiomyocyte hypertrophy. MEF2C was a functional target of miR-497 in regulating Ang II-induced cardiomyocyte hypertrophy. In addition, TUG1 regulated MEF2C expression through sponging miR-497. Knockdown of TUG1 rescued Ang II-induced hypertrophy in cardiomyocytes at least partly through targeting the miR-497/MEF2C axis, highlighting a novel promising therapeutic target for cardiac hypertrophy treatment.

Sphingolipid Mediators of Myocardial Pathology

Cardiomyopathy is the leading cause of mortality worldwide. While the causes of cardiomyopathy continue to be elucidated, current evidence suggests that aberrant bioactive lipid signaling plays a crucial role as a component of cardiac pathophysiology. Sphingolipids have been implicated in the pathophysiology of cardiovascular disease, as they regulate numerous cellular processes that occur in primary and secondary cardiomyopathies. Experimental evidence gathered over the last few decades from both in vitro and in vivo model systems indicates that inhibitors of sphingolipid synthesis attenuate a variety of cardiomyopathic symptoms. In this review, we focus on various cardiomyopathies in which sphingolipids have been implicated and the potential therapeutic benefits that could be gained by targeting sphingolipid metabolism.

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.

Rare genetic variants in GATA transcription factors in patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a very heterogeneous disease. Although primarily caused by mutations in genes encoding sarcomeric proteins, other genes might explain that heterogeneity. Potential candidate genes are GATA transcription factors that regulate the expression of proteins associated with HCM. Exons of GATA2, GATA4, and GATA6 genes were sequenced in 212 patients with unrelated HCM previously analyzed for genes encoding the most frequently mutated sarcomeric proteins. Functional effects of variants were predicted by in silico analyses. 3 potentially pathogenic variants were identified: c.-77G>A in GATA2, p.Ala343Thr (rs370588269) in GATA4, and p.Pro555Ala (rs146243018) in GATA6 Multivariate analyses showed that angina was more frequent in patients carrying sarcomeric and GATA rare variants (55% vs 23.2% in non-carriers of GATA rare variants, OR (95% CI) 7.12 (1.23 to 41.27), p=0.029). Among patients without a known causal mutation, GATA rare variants were associated with a greater maximum posterior wall thickness (16.4±4.4 vs 14.0±3.1 mm in non-carriers, p=0.021). Thus, variants having a putative effect on GATA genes would alter the expression of their target genes and could modify the hypertrophic response. Therefore, although relatively infrequent in patients with HCM, they may represent a novel insight into the molecular mechanisms related to the pathogenesis of HCM.

Study of bovine gene: the temporal-spatial expression patterns, polymorphism and association analysis with meat production traits

The gene () encodes a transcription factor belonging to the MEF2 family that plays an important role in myogenesis by transcriptional regulation of genes involved in skeletal muscle growth and development. Despite the established importance of the factors in the muscular growth and development, the temporal-spatial expression and biological function of have not been reported in cattle. The aim of this study was to analyze the level of expression in the developing longissimus dorsi muscle (LM) of 4 cattle breeds (Polish Holstein-Friesian [HF], Limousine [LIM], Hereford [HER], Polish Red [PR]), differing in terms of meat production and utility type, at 6, 9, and 12 mo of age. The genetic polymorphism and expression patterns in 6 tissues (heart, spleen, liver, semitendinosus muscle [ST], gluteus medius muscle [GM], and LM) were also investigated. The results showed that mRNA was expressed at a high level in adult skeletal and cardiac muscles. Moreover, expression was markedly greater in the GM than in the LM ( 0.05) and ST ( 0.01). An age-dependent and breed-specific comparison of mRNA level in skeletal muscle of HF, LIM, HER, and PR bulls showed that age was significant differentiating factor of transcript/protein abundance in the LM of HER and LIM ( 0.001) compared to HF and PR, for which the differences in mRNA level were not significant ( > 0.05). Regarding the breed effect on the expression, significantly greater mRNA/protein level was noticed in the LM of 9 and 12 mo-old HER than of LIM ( 0.01), HF ( 0.001), and PR ( 0.001). Four novel SNP, namely, (promoter), (exon 7), (exon 8), and (3'UTR), were identified. We found that 3'UTR variant, situated within the seed region of the miR-5187-3p and miR-6931-5p binding sites, was associated with the level of mRNA/protein in LM of 12-mo-old HF bulls. In addition, we observed a significant association between some carcass quality traits, including meat and carcass fatness quality traits, and various 3'UTR genotypes in the investigated population of HF cattle. Our finding provides new evidence of the significant role in the postnatal muscle growth and development in cattle, and indicates that can be a promising molecular marker for carcass quality-related traits in adult cattle.

Loss of Frataxin activates the iron/sphingolipid/PDK1/Mef2 pathway in mammals

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by mutations in Frataxin (FXN). Loss of FXN causes impaired mitochondrial function and iron homeostasis. An elevated production of reactive oxygen species (ROS) was previously proposed to contribute to the pathogenesis of FRDA. We recently showed that loss of frataxin homolog (fh), a Drosophila homolog of FXN, causes a ROS independent neurodegeneration in flies (Chen et al., 2016). In fh mutants, iron accumulation in the nervous system enhances the synthesis of sphingolipids, which in turn activates 3-phosphoinositide dependent protein kinase-1 (Pdk1) and myocyte enhancer factor-2 (Mef2) to trigger neurodegeneration of adult photoreceptors. Here, we show that loss of Fxn in the nervous system in mice also activates an iron/sphingolipid/PDK1/Mef2 pathway, indicating that the mechanism is evolutionarily conserved. Furthermore, sphingolipid levels and PDK1 activity are also increased in hearts of FRDA patients, suggesting that a similar pathway is affected in FRDA.

MEF2C orthologues from zebrafish: Evolution, expression and promoter regulation

MEF2C is a crucial transcription factor for cranial neural crest cells development. An abnormal expression of this protein leads to severe abnormalities in craniofacial features. Recently, a human disease (MRD20) was described as a consequence of MEF2C haploinsufficiency. These patients show severe developmental delay, intellectual disability and dysmorphic features. Zebrafish presents two MEF2C orthologues, mef2ca and mef2cb. In this study we demonstrate a highly conserved pattern of chromosome localization for MEF2C between human and zebrafish, a similar protein sequence and tissue expression profile. We have focused our functional analysis on the zebrafish orthologue mef2cb. We identified three new exons through 5' RACE and described two new transcriptional start sites (TSS). These alternative TSS reflect the occurrence of two alternative promoters differentially regulated by nuclear factors related to craniofacial or neuronal development such as Sox9b, Sox10 and Runx2. We also predict that mef2cb gene may be post transcriptionally regulated by analysing the structure of its 5' UTR region, conserved throughout evolution. Our study provides new insights in MEF2C conservation and provides the first evidence of mef2cb regulation by both transcriptional and post transcriptional mechanisms, thus contributing to validate zebrafish as a good model for future studies concerning MEF2C dependent pathologies.

Construction of microRNA and transcription factor regulatory network based on gene expression data in cardiomyopathy

Background

Cardiomyopathy is a progressive myocardial disorder. Here, we attempted to reveal the possible mechanism of cardiomyopathy at the transcription level with the roles of microRNAs (miRNAs) and transcription factors (TFs) taken into account.

Method

We firstly identified differentially expressed genes (DEGs) between cardiomyopathy patients and controls with data from the gene expression omnibus (GEO) database. DEGs were associated with the canonical pathways, molecular and cellular functions, physiological system development and function in the Ingenuity Knowledge Base by using the Ingenuity Pathway Analysis (IPA) software. TFs and miRNAs that DEGs significantly enriched were identified and a double-factor regulatory network was constructed.

Results

A total of 1,680 DEGs were identified. The DEGs were enriched for various pathways, with glucocorticoid receptor signaling as the most significant. A double-factor regulatory network was constructed, including seven TFs and two miRNAs. A subnetwork under the regulation of MEF2C and SRF was also constructed to illustrate their regulatory effects on cardiac functions.

Conclusion

Our results may provide new understanding of cardiomyopathy and may facilitate further therapeutic studies.

Postnatal expression patterns and polymorphism analysis of the bovine myocyte enhancer factor 2C (Mef2C) gene

The aim of this study was to analyze the level of expression of the Mef2C gene in the developing bovine longissimus dorsi (LD) muscle (at 6, 9 and 12months of age) and to evaluate differences in expression among Polish Holstein-Friesian (HO) and Limousine (LM) bulls. Moreover, the expression patterns of Mef2C in different tissues were determined. The results showed that Mef2C mRNA was expressed at a high level in adult skeletal and cardiac muscles. Moreover, Mef2C expression was markedly lower in the semitendinosus (ST) than in the gluteus medius (GM) and LD muscles. A relatively higher Mef2C mRNA and MEF2C protein level was estimated in the muscles of HO bulls at the age of 12months in comparison with its lower expression in LM bulls. Furthermore, we found that the Mef2C promoter variant (GU211004:g.-1606C>T) does not affect the level of mRNA in the LD and ST muscles of 12-month-old HO bulls.