Gene Expression In Cardiac Hypertrophy Research Articles

Identification of HuR‐dependent gene expression in cardiac hypertrophy

HuR is a widely expressed RNA binding protein that interacts with specific AU‐rich domains in target mRNAs and regulates their expression by modulating stability and/or translation. RNA binding proteins such as HuR are becoming recognized as potential mediators of cardiac physiology and pathology but the role of HuR in cardiac hypertrophy is largely unknown. Our results show that HuR undergoes cytoplasmic translocation, indicative of its activation, in hypertrophic cardiac myocytes and is necessary for hypertrophic cell growth. Using an inducible cardiomyocyte‐specific HuR deletion mouse (iCM‐HuR−/−), we have shown that cardiac specific deletion of HuR significantly reduces hypertrophy compared to wild‐type mice at 8 weeks post‐transverse aortic constriction (TAC). More importantly, the iCM‐HuR−/− mice exhibited significantly preserved ejection fraction, reduced chamber dilation, and less fibrosis compared to WT at 8 weeks post‐TAC. To elucidate the downstream target genes of of HuR in the heart and identify potential mechanisms by which HuR deletion reduces pathological cardiac hypertrophy, we used RNA‐seq to identify HuR‐dependent gene expression in the setting of cardiac hypertrophy. Using the NIH DAVID Functional Annotation Tool, our results indicate a significant increase in genes promoting anti‐apoptotic Akt signaling in hearts from iCM‐HuR−/− mice following TAC. However, since HuR binding typically stabilizes target mRNA, we observed a much larger number of significantly down‐regulated mRNA transcripts in iCM‐HuR−/− mice. Among these were genes involved in key cellular growth processes such as muscle cell differentiation, cell proliferation, cell cycle, and positive regulation of transcription. Thus, our results suggest that HuR deletion protects the heart from pathological cardiac hypertrophy by promoting pro‐survival Akt signaling while decreasing the expression of genes involved in cell growth and differentiation.Support or Funding InformationThis work was partially funded by an American Heart Association Scientist Development Grant and NIH R01 HL132111 (MT).

SWI/SNF chromatin remodeling enzymes are associated with cardiac hypertrophy in a genetic rat model of hypertension

Pathological cardiac hypertrophy is characterized by a sustained increase in cardiomyocyte size and re-activation of the fetal cardiac gene program. Previous studies implicated SWI/SNF chromatin remodeling enzymes as regulators of the fetal cardiac gene program in surgical models of cardiac hypertrophy. Although hypertension is a common risk factor for developing cardiac hypertrophy, there has not yet been any investigation into the role of SWI/SNF enzymes in cardiac hypertrophy using genetic models of hypertension. In this study, we tested the hypothesis that components of the SWI/SNF complex are activated and recruited to promoters that regulate the fetal cardiac gene program in hearts that become hypertrophic as a result of salt induced hypertension. Utilizing the Dahl salt-sensitive (S) rat model, we found that the protein levels of several SWI/SNF subunits required for heart development, Brg1, Baf180, and Baf60c, are elevated in hypertrophic hearts from S rats fed a high salt diet compared with normotensive hearts from Dahl salt-resistant (R) rats fed the same diet. Furthermore, we detected significantly higher levels of SWI/SNF subunit enrichment as well as evidence of more accessible chromatin structure on two fetal cardiac gene promoters in hearts from S rats compared with R rats. Our data implicate SWI/SNF chromatin remodeling enzymes as regulators of gene expression in cardiac hypertrophy resulting from salt induced hypertension. Thus we provide novel insights into the epigenetic mechanisms by which salt induced hypertension leads to cardiac hypertrophy.

Chronomics of Pressure Overload–Induced Cardiac Hypertrophy in Mice Reveals Altered Day/Night Gene Expression and Biomarkers of Heart Disease

There is critical demand in contemporary medicine for gene expression markers in all areas of human disease, for early detection of disease, classification, prognosis, and response to therapy. The integrity of circadian gene expression underlies cardiovascular health and disease; however time-of-day profiling in heart disease has never been examined. We hypothesized that a time-of-day chronomic approach using samples collected across 24-h cycles and analyzed by microarrays and bioinformatics advances contemporary approaches, because it includes sleep-time and/or wake-time molecular responses. As proof of concept, we demonstrate the value of this approach in cardiovascular disease using a murine Transverse Aortic Constriction (TAC) model of pressure overload–induced cardiac hypertrophy in mice. First, microarrays and a novel algorithm termed DeltaGene were used to identify time-of-day differences in gene expression in cardiac hypertrophy 8 wks post-TAC. The top 300 candidates were further analyzed using knowledge-based platforms, paring the list to 20 candidates, which were then validated by real-time polymerase chain reaction (RTPCR). Next, we tested whether the time-of-day gene expression profiles could be indicative of disease progression by comparing the 1- vs. 8-wk TAC. Lastly, since protein expression is functionally relevant, we monitored time-of-day cycling for the analogous cardiac proteins. This approach is generally applicable and can lead to new understanding of disease. (Author correspondence: tmartino@uoguelph.ca)

Relocation of Calmodulin in Hypertrophic Neonatal Cardiomyocytes

An increasing body of evidence suggests that calmodulin (CaM) signaling is involved in the regulation of gene expression in cardiac hypertrophy (HT). According to recent report (Yamaguchi et al, 2007) mice expressing RyR2 mutant, that cannot bind CaM, develops cardiac HT. In an attempt to gain further insight into the role of RyR2-bound CaM in the process of development of HT, we have induced HT in neonatal rat cardiomyocytes by endothelin-1 (ET-1), and found distinct differences between the hypertrophied cells and control cells in several aspects. (1) The immuno-stain with anti-CaM antibody is chiefly localized in the cytoplasm of the control cells; whereas, in the HT cells, the stain is accumulated chiefly in the nucleus. (2) The cross linking/Western blot analysis shows that CaM is cross-linked with the RyR2 in control cells, but not in the HT cells. (3) We have prepared fluorescently labeled CaM by conjugating C34 mutant of CaM with Alexa 546, and introduced it into the myocytes using Bioporter. The exogenously introduced CaM-alexa is localized mainly in the cytoplasmic region in control cells, but within the nucleus in the HT cells. These findings suggest that stimulation of the neonatal cardiomyocytes with ET-1 dissociates RyR2-bound CaM from the receptor, then the dissociated CaM translocates to the nucleus to activate the HT gene program. In support of this conclusion, dantrolene (a specific blocker of RyR Ca2+ channel) inhibited HT in the ET-1-treated cells; at the same time prevented CaM translocation to the nucleus. Furthermore, an antibody raised against the CaM binding domain of RyR2, which was introduced into the cell via Bioporter, also prevented HT in the ET-1-treated cells. (Supported by HL072841)

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Loss of the Normal Epicardial to Endocardial Gradient of cftr mRNA Expression in the Hypertrophied Rabbit Left Ventricle

The electrical instability of hypertrophied and failing hearts is caused by delayed repolarisation, which is thought to be due in part to altered levels and/or patterns of expression of ion channel genes. The aim of this study was to investigate changes in the levels and pattern of cystic fibrosis transmembrane conductance regulator (cftr) mRNA expression in a combined pressure and volume overload model of heart failure in the rabbit, using in situ mRNA hybridisation. There was a decrease in cftr mRNA expression, primarily due to a decrease in epicardial expression and, hence, loss of the normal epicardial to endocardial gradient of cftr mRNA expression in the rabbit left ventricle. In contrast there was an increase in atrial natriuretic factor (anf) mRNA expression in the hypertrophied hearts with preferential reexpression in subendocardial regions. The patterns of both cftr and anf mRNA expression in the hypertrophied hearts were similar to those seen in embryonic hearts. This suggests that the reversion to an embryonic pattern of gene expression in cardiac hypertrophy applies to ion channel genes. The loss of the normal transmural gradient of repolarising ion channels is likely to contribute to instability of repolarisation in the hypertrophied heart and hence increased risk of cardiac arrhythmias in patients with heart failure.

Attenuation of changes in sarcoplasmic reticular gene expression in cardiac hypertrophy by propranolol and verapamil.

The effects of propranolol and verapamil on contractile dysfunction, subcellular remodeling and changes in gene expression in cardiac hypertrophy due to pressure overload were examined. Rats were subjected to banding of the abdominal aorta and then treated with either propranolol (10 mg/kg daily), verapamil (5 mg/kg daily) or vehicle for 8 weeks after the surgery. Depression of the left ventricular function in the hypertrophied heart was associated with decreases in myofibrillar and myosin Ca2+ ATPase activities as well as Ca2+-pump and Ca2+-release activities of the sarcoplasmic reticulum (SR). The level of alpha-myosin heavy chain (alpha-MHC) mRNA was decreased while that of beta-MHC mRNA was increased in the pressure-overloaded heart. The level of SR Ca2+-pump ATPase (SERCA2) mRNA and protein content for SERCA2 were decreased in the pressure overloaded heart. Treatment of the hypertrophied animals with propranolol or verapamil resulted in preservation of the left ventricular function and prevention of the subcellular alterations. Shift in the alpha- and beta-MHC mRNA levels and changes in the expression in SERCA2 mRNA level and protein content were also attenuated by these treatments. The results suggest that blockade of beta-adrenoceptors or voltage-dependent calcium channels normalizes the cardiac gene expression, prevents subcellular remodeling and thus attenuates heart dysfunction in rats with cardiac hypertrophy. Furthermore, both cardiac beta-adrenoceptors and L-type Ca2+-channels may be involved in the genesis of cardiac hypertrophy due to pressure overload.

Regulation of very-low-density lipoprotein receptor in hypertrophic rat heart.

To elucidate the regulation of very-low density-lipoprotein (VLDL) receptor, we have studied its gene expression in the heart of spontaneously hypertensive rats-stroke prone (SHR-SP, an animal model for hypertension-induced cardiac hypertrophy) compared with Wistar-Kyoto rats. RNase protection assay showed that ventricular VLDL receptor mRNA falls to 41% of normal levels at 4 weeks when hypertension is not yet fully developed, and drops further to 14% at 13 weeks, when cardiac hypertrophy is established. Lipoprotein lipase mRNA decreases in parallel with VLDL receptor mRNA. In cultured neonatal rat ventricular cardiomyocytes, VLDL receptor mRNA decreases in parallel with the process of cardiocyte hypertrophy during the 24 hours after treatment with 10-8 mol/L endothelin-1, falling to 40% of the initial value. These results demonstrate that there is downregulation of VLDL receptor gene expression in cardiac hypertrophy both in vivo and in vitro and suggest that the regulation of the VLDL receptor is possibly linked with the switch in energy substrate from lipid to glucose known to occur in cardiac hypertrophy.

Sarcoplasmic reticulum gene expression in cardiac hypertrophy and heart failure.

Sarcoplasmic reticulum gene expression in cardiac hypertrophy and heart failure.

Gene expression in cardiac hypertrophy

Cardiac hypertrophy due to hemodynamic overload is a harbinger of morbidity and mortality in humans. The development of hypertrophy involves both quantitative and qualitative changes in gene expression that are thought to produce an enlarged organ more capable of meeting its new functional requirements. The genes are normal, but the way in which they are regulated is modified. Analysis of these changes and the mechanisms involved are essential if we are to understand the role that hypertrophy plays in the pathogenesis of heart failure.

Regulation of myosin heavy chain (MHC) gene expression in cardiac hypertrophy: Effects of testosterone and cAMP

Regulation of myosin heavy chain (MHC) gene expression in cardiac hypertrophy: Effects of testosterone and cAMP

Altered gene expression in cardiac hypertrophy

Altered gene expression in cardiac hypertrophy

Gene expression in cardiac hypertrophy in rat and human heart muscle.

Changes in the cardiac contents of microsomal RNA and poly(A)-containing mRNA have been examined during induction and regression of heart muscle hypertrophy in rat hearts, as well as possible changes in the subcellular distribution and protein-synthetic activity of cardiac mRNA. In addition, cardiac biopsies from patients with mitral valve diseases were evaluated for their mRNA contents. Induction of heart muscle hypertrophy was accompanied by substantial increases in cardiac microsomal RNA (30-60%) and cardiac mRNA (20-80%). During regression of hypertrophy increased levels of cardiac microsomal RNA and mRNA returned to normal values within 10-16 days. In general, cardiac mRNA levels were lower in human heart muscle than in rat heart muscle. Since the subcellular distribution of the microsomal RNA and of the mRNA as well as the protein-synthetic activity of the mRNA were not changed in the hypertrophied animals as compared with normal animals, and since the cardiac contents of most specific cardiac mRNA species (mRNAs for MHC, MLC1 and MLC2, actin, tropomyosin, troponin-T, myoglobin) increased proportionately, it is concluded that during induction of hypertrophy activation of gene expression occurs and affects the genes coding for the major cardiac proteins to a similar extent. This does, however, not exclude the possibility of more specific shifts in isoprotein patterns and in the levels of their corresponding mRNAs. It is proposed that changes in cardiac mRNA levels are the major regulatory factor in causing changes in cardiac protein synthesis rates leading to the induction and regression of cardiac hypertrophy.