Transcription factor Yin Yang 1 represses fetal troponin I gene expression in neonatal myocardial cells

Decreased intranuclear cardiac troponin I impairs cardiac autophagy through FOS/ATG5 in ageing hearts

In our previous study, intranuclear cardiac troponin I (cTnI) may function as a co-factor of Yin Yang 1(YY1). Here, we aimed to explore the role of intranuclear cTnI in ageing hearts. Nuclear translocation of cTnI was demonstrated using Western blot and immunofluorescence. The potential nuclear localization sequences (NLSs) of cTnI were predicted by a web server and then verified in 293T cells by putative NLS-eGFP-GST and NLS-mutant transfection. The ratio of Nuclear cTnI/ Total cTnI (Nu/T) decreased significantly in ageing hearts, accompanied with ATG5-decline-related impaired cardiac autophagy. RNA sequencing was performed in cTnI knockout hearts. The differential expressed genes (DEGs) were analysed by overlapping with YY1 ChIP-sequencing data. cTnI gain and loss experiments in vitro determined those filtered DEGs' expression levels. A strong correlation was found between expression patterns cTnI and FOS. Using ChIP-q-PCR, we demonstrated that specific binding DNA sequences of cTnI were enriched in the FOS promoter -299 to -157 region. It was further verified that pcDNA3.1 (-)-cTnI could increase the promoter activity of FOS by using luciferase report assay. At last, we found that FOS can regulate the ATG5 (autophagy-related gene 5) gene by using a luciferase report assay. Taken together, our results indicate that decreased intranuclear cTnI in ageing hearts may cause impaired cardiac autophagy through the FOS/ATG5 pathway.

Intranuclear cardiac troponin I plays a functional role in regulating Atp2a2 expression in cardiomyocytes

In the past studies, it is shown that cardiac troponin I (cTnI, encoded by TNNI3), as a cytoplasmic protein, is an inhibitory subunit in troponin complex, and involves in cardiomyocyte diastolic regulation. Here, we assessed a novel role of cTnI as a nucleoprotein. Firstly, the nuclear translocation of cTnI was found in mouse, human fetuses and rat heart tissues. In addition, there were differences in percentage of intranuclear cTnI in different conditions. Based on weighted gene co-expression network analyses (WGCNA) and verification in cell experiments, a strong expression correlation was found between TNNI3 and Atp2a2, which encodes sarco-endoplasmic reticulum Ca²⁺ ATPase isoform 2a (SERCA2a), and involves in ATP hydrolysis and Ca²⁺ transient. TNNI3 gain and loss caused Atpa2a2 increase/decrease in a dose-dependent manner both in mRNA and protein levels, in vivo and in vitro. By using ChIP-sequence we demonstrated specific binding DNA sequences of cTnI were enriched in ATP2a2 promoter −239∼–889 region and the specific binding sequence motif of cTnI was analyzed by software as "CCAT", which has been reported to be required for YY1 binding to the promoter region of YY1-related genes. Moreover, it was further verified that pcDNA3.1 (−)-TNNI3 could express cTnI proteins and increase the promoter activity of Atp2a2 through luciferase report assay. In the end, we evaluated beat frequencies, total ATP contents, Ca²⁺ transients in TNNI3-siRNA myocardial cells. These findings indicated, for the first time, cTnI may regulate Atp2a2 in cardiomyocytes as a co-regulatory factor and participate in the regulation of intracellular Ca ions.

Gon4l/Udu regulates cardiomyocyte proliferation and maintenance of ventricular chamber identity during zebrafish development

Vertebrate heart development requires spatiotemporal regulation of gene expression to specify cardiomyocytes, increase the cardiomyocyte population through proliferation, and to establish and maintain atrial and ventricular cardiac chamber identities. The evolutionarily conserved chromatin factor Gon4-like (Gon4l), encoded by the zebrafish ugly duckling (udu) locus, has previously been implicated in cell proliferation, cell survival, and specification of mesoderm-derived tissues including blood and somites, but its role in heart formation has not been studied. Here we report two distinct roles of Gon4l/Udu in heart development: regulation of cell proliferation and maintenance of ventricular identity. We show that zygotic loss of udu expression causes a significant reduction in cardiomyocyte number at one day post fertilization that becomes exacerbated during later development. We present evidence that the cardiomyocyte deficiency in udu mutants results from reduced cell proliferation, unlike hematopoietic deficiencies attributed to TP53-dependent apoptosis. We also demonstrate that expression of the G1/S-phase cell cycle regulator, cyclin E2 (ccne2), is reduced in udu mutant hearts, and that the Gon4l protein associates with regulatory regions of the ccne2 gene during early embryogenesis. Furthermore, udu mutant hearts exhibit a decrease in the proportion of ventricular cardiomyocytes compared to atrial cardiomyocytes, concomitant with progressive reduction of nkx2.5 expression. We further demonstrate that udu and nkx2.5 interact to maintain the proportion of ventricular cardiomyocytes during development. However, we find that ectopic expression of nkx2.5 is not sufficient to restore ventricular chamber identity suggesting that Gon4l regulates cardiac chamber patterning via multiple pathways. Together, our findings define a novel role for zygotically-expressed Gon4l in coordinating cardiomyocyte proliferation and chamber identity maintenance during cardiac development.

Yin-Yang 1 transcription factor modulates ST2 expression during adverse cardiac remodeling post-myocardial infarction

BACKGROUND

The cardioprotective effects of metformin remain poorly defined. Interleukin (IL)-33/ST2L signaling is a novel cardioprotective pathway, which is antagonized by the soluble isoform sST2. No data exist about the regulation of ST2 expression. This study aimed to evaluate the pathophysiological implication of Yin-Yang 1 (Yy1) transcription factor in cardiac remodeling and the expression of the soluble ST2 isoform.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in Wistar rats randomly receiving metformin or saline solution by permanent ligation of the left anterior coronary artery. In addition, a model of cardiomyocyte "biochemical strain" was used. Metformin administration improved post-MI cardiac remodeling, an effect that was associated with increased IL-33 and reduced sST2 levels in the myocardium. The anti-remodeling effects of metformin were also associated with a decrease in the transcription factor Yy1 intranuclear level and lower levels of phosphorylated HDAC4 within the cytoplasmic space. These effects were also observed in a cardiomyocyte biochemical strain model, where Yy1 silencing or HDAC4 inhibition blocked sST2 production in cardiomyocytes. Metformin blocked the HDAC4 phosphorylation induced by MI, preventing its export from the nucleus to the cytosol. The presence of dephosphorylated HDAC4 in the nucleus acted as a co-repressor of Yy1, repressing sST2 expression.

CONCLUSION

The transcription factor Yy1 regulates sST2 expression, and repression of Yy1 by metformin results in lower levels of sST2 that are associated with favorable myocardial remodeling. The manipulation of YY1 or its co-repressor HDAC4 emerge as new targets to modulate ST2/IL33 signaling and prevent adverse cardiac remodeling.

Epigenetic regulation of cardiac myofibril gene expression during heart development

Cardiac gene expression regulation is controlled not only by genetic factors but also by environmental, i.e., epigenetic factors. Several environmental toxic effects such as oxidative stress and ischemia can result in abnormal myofibril gene expression during heart development. Troponin, one of the regulatory myofibril proteins in the heart, is a well-known model in study of cardiac gene regulation during the development. In our previous studies, we have demonstrated that fetal form troponin I (ssTnI) expression in the heart is partially regulated by hormones, such as thyroid hormone. In the present study, we have explored the epigenetic role of histone modification in the regulation of ssTnI expression. Mouse hearts were collected at different time of heart development, i.e., embryonic day 15.5, postnatal day 1, day 7, day 14 and day 21. Levels of histone H3 acetylation (acH3) and histone H3 lysine 9 trimethylation (H3K9me(3)) were detected using chromatin immunoprecipitation assays in slow upstream regulatory element (SURE) domain (TnI slow upstream regulatory element), 300-bp proximal upstream domain and the first intron of ssTnI gene, which are recognized as critical regions for ssTnI regulation. We found that the levels of acH3 on the SURE region were gradually decreased, corresponding to a similar decrease of ssTnI expression in the heart, whereas the levels of H3K9me(3) in the first intron of ssTnI gene were gradually increased. Our results indicate that both histone acetylation and methylation are involved in the epigenetic regulation of ssTnI expression in the heart during the development, which are the targets for environmental factors.

Knockdown of zebrafish YY1a can downregulate the phosphatidylserine (PS) receptor expression, leading to induce the abnormal brain and heart development

Background

Yin Yang 1 (YY1) is a ubiquitously expressed GLI-Kruppel zinc finger-containing transcriptional regulator. YY1 plays a fundamental role in normal biologic processes such as embryogenesis, differentiation, and cellular proliferation. YY1 effects on the genes involved in these processes are mediated via initiation, activation, or repression of transcription depending upon the context in which it binds. The role of the multifunctional transcription factor Yin Yang 1 (YY1) in tissue development is poorly understood. In the present, we investigated YY1a role in developing zebrafish on PSR-mediated apoptotic cell engulfment during organic morphogenesis.

Results

YY1a is first expressed 0.5 h post-fertilization (hpf), in the whole embryo 12 hpf, and in brain, eyes, and heart 72 hpf by in situ hybridization assay. The nucleotide sequence of zebrafish YY1a transcription factor (clone zfYY1a; HQ 166834) was found to be similar to that of zebrafish YY1a (99 % sequence identity; NM 212617). With the loss-of-function assay, YY1a knockdown by a morpholino oligonucleotide led to downregulation of the phosphatidylserine engulfing receptor zfPSR during embryonic segmentation and to the accumulation of a large number of dead apoptotic cells throughout the entire early embryo, especially in the posterior area. Up to 24 hpf, these cells interfered with embryonic cell migration and cell-cell interactions that normally occur in the brain, heart, eye, and notochord. Finally, with gain-of-function assay, defective morphants could be rescued by injecting both YY1a mRNA and PSR mRNA and trigger resumption of normal development.

Conclusions

Taken together, our results suggest that YY1a regulates PS receptor expression that linked to function of PSR-phagocyte mediated apoptotic cell engulfment during development, especially the development of organs such as the brain and heart. YY1a/PSR-mediated engulfing system may involve in diseases.

DNA methylation regulates mouse cardiac myofibril gene expression during heart development

Background

It is well known that epigenetic modifications play an important role in controlling the regulation of gene expression during the development. Our previous studies have demonstrated that the expression of fetal troponin I gene (also called slow skeletal troponin I, ssTnI) is predominated in the fetal stage, reduced after birth and disappeared in the adulthood. The mechanism underlying the developmentally related ssTnI gene regulation is not clear. In this study, we have explored the epigenetic role of DNA methylation in the regulation of ssTnI expression in the heart during the development.

Results

The DNA methylation levels of CpG island and CpG dinucleotides region were detected using methylation specific PCR (MSP) and bisulfite sequence PCR (BSP) in 2000 bp upstream and 100 bp upstream of ssTnI gene promoter. Real time RT-PCR and Western blot were used to detect ssTnI mRNA and protein expression levels. We found that DNA methylation levels of the CpG dinucleotides region in ssTnI gene promoter were increased with the development, corresponding to a decreased expression of ssTnI gene in mouse heart. However the DNA methylation levels of CpG islands in this gene were not changed during the development. Application of a methylation inhibitor, 5-Azacytidine, in cultured myocardial cells partially prevented the decline of ssTnI expression.

Conclusion

Our results indicate that DNA methylation, as an epigenetic intervention, plays a role in the regulation of the fetal TnI gene expression in the heat during the development.

Transgenic over-expression of YY1 induces pathologic cardiac hypertrophy in a sex-specific manner

YY1 can activate or repress transcription of various genes. In cardiac myocytes in culture YY1 has been shown to regulate expression of several genes involved in myocyte pathology. YY1 can also acutely protect the heart against detrimental changes in gene expression. In this study we show that cardiac over-expression of YY1 induces pathologic cardiac hypertrophy in male mice, measured by changes in gene expression and lower ejection fraction/fractional shortening. In contrast, female animals are protected against pathologic gene expression changes and cardiac dysfunction. Furthermore, we show that YY1 regulates, in a sex-specific manner, the expression of mammalian enable (Mena), a factor that regulates cytoskeletal actin dynamics and whose expression is increased in several models of cardiac pathology, and that Mena expression in humans with heart failure is sex-dependent. Finally, we show that sex differences in YY1 expression are also observed in human heart failure. In summary, this is the first work to show that YY1 has a sex-specific effect in the regulation of cardiac pathology.

Expression of sarcomeric tropomyosin in striated muscles in axolotl treated with shz-1, a small cardiogenic molecule

We evaluated the effect of shz-1, a cardiogenic molecule, on the expression of various tropomyosin (TM) isoforms in the Mexican axolotl (Ambystoma mexicanum) hearts. qRT-PCR data show a ~1.5-fold increase in cardiac transcripts of the Nkx2.5 gene, which plays a crucial role in cardiogenesis in vertebrates. Shz-1 augments the expression of transcripts of the total sarcomeric TPM1 (both TPM1α & TPM1κ) and sarcomeric TPM4α. In order to understand the mechanism by which shz-1 augments the expression of sarcomeric TPM transcription in axolotl hearts, we transfected C2C12 cells with pGL3.axolotl. We transfected C2C12 cells with pGL3-axolotl TPM4 promoter constructs containing the firefly luciferase reporter gene. The transfected C2C12 cells were grown in the absence or presence of shz-1 (5 μM). Subsequently, we determined the firefly luciferase activity in the extracts of transfected cells. The results suggest that shz-1 activates the axolotl TPM4 promoter-driven ectopic expression in C2C12 cells. Also, we transfected C2C12 cells with a pGL3.1 vector containing the promoter of the mouse skeletal muscle troponin-I and observed a similar increase in the luciferase activity in shz-1-treated cells. We conclude that shz-1 activates the promoters of a variety of genes including axolotl TPM4. We have quantified the expression of the total sarcomeric TPM1 and observed a 1.5-fold increase in treated cells. Western blot analyses with CH1 monoclonal antibody specific for sarcomeric isoforms show that shz-1 does not increase the expression of TM protein in axolotl hearts, whereas it does in C2C12 cells. These findings support our hypothesis that cardiac TM expression in axolotl undergoes translational control.

Gene expression profiles in engineered cardiac tissues respond to mechanical loading and inhibition of tyrosine kinases

Engineered cardiac tissues (ECTs) are platforms to investigate cardiomyocyte maturation and functional integration, the feasibility of generating tissues for cardiac repair, and as models for pharmacology and toxicology bioassays. ECTs rapidly mature in vitro to acquire the features of functional cardiac muscle and respond to mechanical load with increased proliferation and maturation. ECTs are now being investigated as platforms for in vitro models for human diseases and for pharmacologic screening for drug toxicities. We tested the hypothesis that global ECT gene expression patterns are complex and sensitive to mechanical loading and tyrosine kinase inhibitors similar to the maturing myocardium. We generated ECTs from day 14.5 rat embryo ventricular cells, as previously published, and then conditioned constructs after 5 days in culture for 48 h with mechanical stretch (5%, 0.5 Hz) and/or the p38 MAPK (p38 mitogen-activated protein kinase) inhibitor BIRB796. RNA was isolated from individual ECTs and assayed using a standard Agilent rat 4 × 44k V3 microarray and Pathway Analysis software for transcript expression fold changes and changes in regulatory molecules and networks. Changes in expression were confirmed by quantitative-polymerase chain reaction (q-PCR) for selected regulatory molecules. At the threshold of a 1.5-fold change in expression, stretch altered 1559 transcripts, versus 1411 for BIRB796, and 1846 for stretch plus BIRB796. As anticipated, top pathways altered in response to these stimuli include cellular development, cellular growth and proliferation; tissue development; cell death, cell signaling, and small molecule biochemistry as well as numerous other pathways. Thus, ECTs display a broad spectrum of altered gene expression in response to mechanical load and/or tyrosine kinase inhibition, reflecting a complex regulation of proliferation, differentiation, and architectural alignment of cardiomyocytes and noncardiomyocytes within ECT.

Sumoylation and regulation of cardiac gene expression

Sumoylation is a posttranslational modification process in which SUMO proteins are covalently and reversibly conjugated to their targets via enzymatic cascade reactions. Since the discovery of SUMO-1 in 1996, the SUMO pathway has garnered increased attention due to its role in a number of important biological activities such as cell cycle progression, epigenetic modulation, signal transduction, and DNA replication/repair, as well as its potential implication in human pathogenesis such as in cancer development and metastasis, neurodegenerative disorders and craniofacial defects. The role of the SUMO pathway in regulating cardiogenic gene activity, development and/or disorders is just emerging. Our review is based on recent advances that highlight the regulation of cardiac gene activity in cardiac development and disease by the SUMO conjugation pathway.