Anxiolytic and Anxiogenic? How the Transcription Factor MEF2 Might Explain the Manifold Behavioral Effects of Oxytocin

The neuromodulator oxytocin, since its first synthesis by du Vigneaud in 1953, has mainly been associated with beneficial physiological effects, as well as positive social and emotional behaviors. This overall positive picture of oxytocin as the "love-, cuddle-, or bonding-hormone" has repeatedly been challenged since then. Oxytocin-induced effects that would be perceived as negative by the individual, such as increased anxiety or potentiation of stress-induced ACTH release, as well as the regulation of negative approach-related emotions, such as envy and schadenfreude (gloating) have been described. The general consent is that oxytocin, instead of acting unidirectional, induces changes in the salience network to shift the emphasis of emotional contexts, and therefore can, e.g., produce both anxiolytic as well as anxiogenic behavioral outcomes. However, the underlying mechanisms leading to alterations in the salience network are still unclear. With the aim to understand the manifold effects of oxytocin on a cellular/molecular level, a set of oxytocin receptor-coupled signaling cascades and downstream effectors regulating transcription and translation has been identified. Those oxytocin-driven effectors, such as MEF2 and CREB, are known modulators of the neuronal and glial cytoarchitecture. We hypothesize that, by determining cellular morphology and connectivity, MEF2 is one of the key factors that might contribute to the diverse behavioral effects of oxytocin.

Myocyte enhancer factor 2A promotes proliferation and its inhibition attenuates myogenic differentiation via myozenin 2 in bovine skeletal muscle myoblast

Myocyte enhancer factor 2A (MEF2A) is widely distributed in various tissues or organs and plays crucial roles in multiple biological processes. To examine the potential effects of MEF2A on skeletal muscle myoblast, the functional role of MFE2A in myoblast proliferation and differentiation was investigated. In this study, we found that the mRNA expression level of Mef2a was dramatically increased during the myogenesis of bovine skeletal muscle primary myoblast. Overexpression of MEF2A significantly promoted myoblast proliferation, while knockdown of MEF2A inhibited the proliferation and differentiation of myoblast. RT-PCR and western blot analysis revealed that this positive effect of MEF2A on the proliferation of myoblast was carried out by triggering cell cycle progression by activating CDK2 protein expression. Besides, MEF2A was found to be an important transcription factor that bound to the myozenin 2 (MyoZ2) proximal promoter and performed upstream of MyoZ2 during myoblast differentiation. This study provides the first experimental evidence that MEF2A is a positive regulator in skeletal muscle myoblast proliferation and suggests that MEF2A regulates myoblast differentiation via regulating MyoZ2.

Pokemon promotes the invasiveness of hepatocellular carcinoma by enhancing MEF2D transcription

BACKGROUND

Pokemon, a master oncogene crucial for the tumorigenicity and progression of a variety of cancers, has been demonstrated to enhance the proliferation and survival of hepatocellular carcinoma (HCC). However, the contribution of Pokemon to the invasiveness of HCC has not yet been studied.

METHODS

In this study, we employed HCC cells to investigate the role of Pokemon in the invasion of HCC with multidisciplinary approaches.

RESULTS

Pokemon overexpression was found to be closely associated with invasion and intrahepatic metastasis of HCC in clinical specimens. Suppression of Pokemon attenuated the invasion of HCC cells by in vitro transwell and wound-healing assays. Myocyte enhancer factor 2D (MEF2D), an oncogene that can promote the invasiveness of HCC, was found to be underexpressed during Pokemon silencing in HCC cells. Restoration of MEF2D abolished the effect of Pokemon downregulation on the migration of HCC cells. Further experiments verified that Pokemon binds two putative recognition sites located within the upstream region of the MEF2D promoter and enhances its transcription. The association between Pokemon and MEF2D was further confirmed in HCC specimens. Animal experiments further confirmed that Pokemon downregulation attenuated the metastasis of HCC cells in mice.

CONCLUSION

Collectively, Pokemon was found to enhance the migration and invasion of HCC by increasing MEF2D expression. Thus, targeting Pokemon and MEF2D may be an effective strategy to suppress the metastasis of HCC.

Macrophage migration inhibitory factor promotes expression of GLUT4 glucose transporter through MEF2 and Zac1 in cardiomyocytes

OBJECTIVE

Evidence shows that both macrophage migration inhibitory factor (MIF) and GLUT4 glucose transporter are involved in diabetic cardiomyopathy (DCM), but it remains largely unknown whether and how MIF regulates GLUT4 expression in cardiomyocytes. The present study aims to investigate the mechanism underlying the modulation of GLUT4 by MIF in cardiomyocytes.

MATERIAL AND METHODS

Activations of AKT and AMPK signaling, and expressions of MIF, GLUT4 and the candidate GLUT4 regulation associated transcription factors in the diabetic mouse myocardium were determined. The screened transcription factors mediating MIF-promoted GLUT4 expression were verified by RNA interference (RNAi) and electrophoretic mobility shift assay (EMSA), respectively.

RESULTS

MIF was increased, but GLUT4 was decreased in the diabetic mouse myocardium. MIF could enhance glucose uptake and up-regulate GLUT4 expression in NMVCs. Expressions of transcription factor MEF2A, -2C, -2D and Zac1 were significantly up-regulated in MIF-treated neonatal mouse ventricular cardiomyocytes (NMVCs), and markedly reduced in the diabetic myocardium. Knockdown of MEF2A, -2C, -2D and Zac1 could significantly inhibit glucose uptake and GLUT4 expression in cardiomyocytes. Moreover, EMSA results revealed that transcriptional activities of MEF2 and Zac1 were significantly increased in MIF-treated NMVCs. AMPK signaling was activated in MIF-stimulated NMVCs, and AMPK activator AICAR could enhance MEF2A, -2C, -2D, Zac1 and GLUT4 expression. Additionally, MIF effects were inhibited by an AMPK inhibitor compound C and siRNA targeting MIF receptor CD74, suggesting the involvement of CD74-dependent AMPK activation.

CONCLUSIONS

Transcription factor MEF2 and Zac1 mediate MIF-induced GLUT4 expression through CD74-dependent AMPK activation in cardiomyocytes.

A traditional Chinese medicine, Lujiao prescription, as a potential therapy for hypertrophic cardiomyocytes by acting on histone acetylation

BACKGROUND

Chronic heart failure (CHF) is a complex clinical syndrome, and a serious stage of various heart diseases. Dysfunction of histone acetylation is involved in pathogenesis of CHF. Lujiao is a clinical and traditional prescription that has been previously used in the treatment of heart failure. The objective of our study was to explore the effects of traditional Chinese Medicine intervention with Lujiao prescription on hypertrophic cardiomyocytes with histone acetylation abnormality.

METHODS

Myocardial cells from neonatal rats were stimulated via phenylephrine (PE) and then randomly divided into seven groups: normal group (without any treatment), model group (treated with saline), TSA group (treated with trichostatin A), perindopril group (treated with perindopril), and the high, medium, and low dose of Lujiao groups (treated with 2.4 g/mL, 1.2 g/mL, and 0.6 g/mL of Lujiao, respectively). The test drug of perindopril group or Lujiao group was derived from serum after drug treatment in rats. Real-time polymerase chain reaction and Western blot were performed to analyze expression of myocyte enhancer factor 2 (MEF-2), α-major histocompatibility complex (MHC), and β-MHC and acetylation level of histone H3.

RESULTS

Expressions of MEF-2 and β-MHC were significantly increased after PE treatment and decreased after drug treatment. Expression of α-MHC mRNA was significantly reduced after PE treatment and increased after being treated with Lujiao prescription, perindopril, and TSA. The acetylation level of histone H3 decreased in rat myocardial cells stimulated by PE 48 for hours and this decrease was reversed after treatment with high and medium doses of Lujiao prescription, perindopril and TSA.

CONCLUSION

Histone acetylation-MEF-2-α-MHC/β-MHC axis was discovered in myocardial hypertrophy, and intervention of Lujiao prescription exhibited good effects.

Severe myopathy in mice lacking the MEF2/SRF-dependent gene leiomodin-3

Maintenance of skeletal muscle structure and function requires a precise stoichiometry of sarcomeric proteins for proper assembly of the contractile apparatus. Absence of components of the sarcomeric thin filaments causes nemaline myopathy, a lethal congenital muscle disorder associated with aberrant myofiber structure and contractility. Previously, we reported that deficiency of the kelch-like family member 40 (KLHL40) in mice results in nemaline myopathy and destabilization of leiomodin-3 (LMOD3). LMOD3 belongs to a family of tropomodulin-related proteins that promote actin nucleation. Here, we show that deficiency of LMOD3 in mice causes nemaline myopathy. In skeletal muscle, transcription of Lmod3 was controlled by the transcription factors SRF and MEF2. Myocardin-related transcription factors (MRTFs), which function as SRF coactivators, serve as sensors of actin polymerization and are sequestered in the cytoplasm by actin monomers. Conversely, conditions that favor actin polymerization de-repress MRTFs and activate SRF-dependent genes. We demonstrated that the actin nucleator LMOD3, together with its stabilizing partner KLHL40, enhances MRTF-SRF activity. In turn, SRF cooperated with MEF2 to sustain the expression of LMOD3 and other components of the contractile apparatus, thereby establishing a regulatory circuit to maintain skeletal muscle function. These findings provide insight into the molecular basis of the sarcomere assembly and muscle dysfunction associated with nemaline myopathy.

Inositol 1,4,5 trisphosphate receptor 1 is a key player of human myoblast differentiation

Cytosolic Ca(2+) signals are fundamental for the early and late steps of myoblast differentiation and are, as in many cells, generated by Ca(2+) release from internal stores as well as by plasma membrane Ca(2+) entry. Our recent studies identified the store-operated Ca(2+) channels, Orai1 and TRPC1&C4, as crucial for the early steps of human myogenesis and for the late fusion events. In the present work, we assessed the role of the inositol-1,4,5 tris-phosphate receptor (IP3R) type 1 during human myoblast differentiation. We demonstrated, using siRNA strategy that IP3R1 is required for the expression of muscle-specific transcription factors such as myogenin and MEF2 (myocyte enhancer factor 2), and for the formation of myotubes. The knockdown of IP3R1 strongly reduced endogenous spontaneous Ca(2+) transients, and attenuated store-operated Ca(2+) entry. As well, two Ca(2+)-dependent key enzymes of muscle differentiation, NFAT and CamKII are down-regulated upon siIP3R1 treatment. On the contrary, the overexpression of IP3R1 accelerated myoblasts differentiation. These findings identify Ca(2+) release mediated by IP3R1 as an essential mechanism during the early steps of myoblast differentiation.

[Temporal regulation of transcription factor Mef2c by histone acetylases during cardiogenesis]

OBJECTIVE

To observe the temporal modification of transcription factor Mef2c by histone acetylases (HATs) P300, PCAF, and SRC1 during cardiogenesis and to provide a basis for investigating the pathogenesis of congenital heart disease.

METHODS

The normal heart tissues from embryonic mice (embryonic days 14.5 and 16.5) and neonatal mice (postnatal days 0.5 and 7) were collected. The binding of P300, PCAF, and SRC1 to Mef2c gene and level of histone H3 acetylation in the promoter region of Mef2c were evaluated by chromatin immunoprecipitation assays. Meanwhile, real-time PCR was used to measure the mRNA expression of Mef2c.

RESULTS

P300, PCAF, SRC1 were involved in histone acetylation in the promoter region of Mef2c during cardiogenesis in mice, and binding of P300, PCAF, and SRC1 to the promoter of Mef2c varied significantly in different stages of cardiogenesis (P<0.01). The level of histone H3 acetylation and mRNA expression of Mef2c in the promoter region of Mef2c also varied significantly in different stages of cardiac development (P<0.01). The levels of acetylated H3, Mef2c mRNA, and HATs (P300, PCAF, SRC1) changed over time. They were highest on embryonic day 14.5 (P<0.01), decreased gradually with cardiac development, and were maintained at low levels after birth.

CONCLUSIONS

The mRNA expression of Mef2c varies during cardiogenesis in mice, which indicates that Mef2c plays an important role in the process of cardiac development. Meanwhile, histone acetylation in the promoter region of Mef2c is regulated temporally by HATs P300, PCAF, and SRC1.

Comparative analysis reveals distinct and overlapping functions of Mef2c and Mef2d during cardiogenesis in Xenopus laevis

The family of vertebrate Mef2 transcription factors is comprised of four members named Mef2a, Mef2b, Mef2c, and Mef2d. These transcription factors are regulators of the myogenic programs with crucial roles in development of skeletal, cardiac and smooth muscle cells. Mef2a and Mef2c are essential for cardiac development in mice. In Xenopus, mef2c and mef2d but not mef2a were recently shown to be expressed during cardiogenesis. We here investigated the function of Mef2c and Mef2d during Xenopus laevis cardiogenesis. Knocking down either gene by corresponding antisense morpholino oligonucleotides led to profound heart defects including morphological abnormalities, pericardial edema, and brachycardia. Marker gene expression analyses and rescue experiments revealed that (i) both genes are required for proper cardiac gene expression, (ii) Mef2d can compensate for the loss of Mef2c but not vice versa, and (iii) the γ domain of Mef2c is required for early cardiac development. Taken together, our data provide novel insights into the function of Mef2 during cardiogenesis, highlight evolutionary differences between species and might have an impact on attempts of direct reprogramming.

Protein sumoylation in brain development, neuronal morphology and spinogenesis

Small ubiquitin-like modifiers (SUMOs) are polypeptides resembling ubiquitin that are covalently attached to specific lysine residue of target proteins through a specific enzymatic pathway. Sumoylation is now seen as a key posttranslational modification involved in many biological processes, but little is known about how this highly dynamic protein modification is regulated in the brain. Disruption of the sumoylation enzymatic pathway during the embryonic development leads to lethality revealing a pivotal role for this protein modification during development. The main aim of this review is to briefly describe the SUMO pathway and give an overview of the sumoylation regulations occurring in brain development, neuronal morphology and synapse formation.