Gene Expression In Cardiac Myocytes Research Articles

NFĸB signaling drives myocardial injury via CCR2+ macrophages in a preclinical model of arrhythmogenic cardiomyopathy.

Nuclear factor κ-B (NFκB) is activated in iPSC-cardiac myocytes from patients with arrhythmogenic cardiomyopathy (ACM) under basal conditions, and inhibition of NFκB signaling prevents disease in Dsg2mut/mut mice, a robust mouse model of ACM. Here, we used genetic approaches and single-cell RNA-Seq to define the contributions of immune signaling in cardiac myocytes and macrophages in the natural progression of ACM using Dsg2mut/mut mice. We found that NFκB signaling in cardiac myocytes drives myocardial injury, contractile dysfunction, and arrhythmias in Dsg2mut/mut mice. NFκB signaling in cardiac myocytes mobilizes macrophages expressing C-C motif chemokine receptor-2 (CCR2+ cells) to affected areas within the heart, where they mediate myocardial injury and arrhythmias. Contractile dysfunction in Dsg2mut/mut mice is caused both by loss of heart muscle and negative inotropic effects of inflammation in viable muscle. Single nucleus RNA-Seq and cellular indexing of transcriptomes and epitomes (CITE-Seq) studies revealed marked proinflammatory changes in gene expression and the cellular landscape in hearts of Dsg2mut/mut mice involving cardiac myocytes, fibroblasts, and CCR2+ macrophages. Changes in gene expression in cardiac myocytes and fibroblasts in Dsg2mut/mut mice were dependent on CCR2+ macrophage recruitment to the heart. These results highlight complex mechanisms of immune injury and regulatory crosstalk between cardiac myocytes, inflammatory cells, and fibroblasts in the pathogenesis of ACM.

Histone Deacetylase 6 Inhibitor JS28 Prevents Pathological Gene Expression in Cardiac Myocytes.

BackgroundEpigenetic modulators have been proposed as promising new drug targets to treat adverse remodeling in heart failure. Here, we evaluated the potential of 4 epigenetic drugs, including the recently developed histone deacetylase 6 (HDAC6) inhibitor JS28, to prevent endothelin‐1 induced pathological gene expression in cardiac myocytes and analyzed the chromatin binding profile of the respective inhibitor targets.Methods and ResultsCardiac myocytes were differentiated and puromycin‐selected from mouse embryonic stem cells and treated with endothelin‐1 to induce pathological gene expression (938 differentially expressed genes, q<0.05). Dysregulation of gene expression was at least in part prevented by epigenetic inhibitors, including the pan‐BRD (bromodomain‐containing protein) inhibitor bromosporine (290/938 genes), the BET (bromodomain and extraterminal) inhibitor JQ1 (288/938), the broad‐spectrum HDAC inhibitor suberoylanilide hydroxamic acid (227/938), and the HDAC6 inhibitor JS28 (210/938). Although the 4 compounds were similarly effective toward pathological gene expression, JS28 demonstrated the least adverse effects on physiological gene expression. Genome‐wide chromatin binding profiles revealed that HDAC6 binding sites were preferentially associated with promoters of genes involved in RNA processing. In contrast, BRD4 binding was associated with genes involved in core cardiac myocyte functions, for example, myocyte contractility, and showed enrichment at enhancers and intronic regions. These distinct chromatin binding profiles of HDAC6 and BRD4 might explain the different effects of their inhibitors on pathological versus physiological gene expression.ConclusionsIn summary, we demonstrated, that the HDAC6 inhibitor JS28 effectively prevented the adverse effects of endothelin‐1 on gene expression with minor impact on physiological gene expression in cardiac myocytes. Selective HDAC6 inhibition by JS28 appears to be a promising strategy for future evaluation in vivo and potential translation into clinical application.

Control of Fibrotic Gene Expression in Cardiac Myocytes and Fibroblasts via the Rap1 GTPase

Fibrosis describes the excessive deposition of extracellular matrix components by cardiac myofibroblasts (CFs), a process which frequently promotes the adverse effects of pathological conditions damaging cardiac muscle, such as myocardial infarction and arrhythmogenic cardiomyopathy. Roughly 1 million Americans suffer a myocardial infarction each year, after which necrotic cardiac myocytes (CMs) are replaced by CF‐derived extracellular matrix (ECM), in response to (a) biochemical signaling cues from necrotic CMs and (b) mechanical cues from the contracting myocardium and ventricle cavity pressure. Accumulation of ECM proteins (such as collagen) within the infarct scar is initially critical to prevent further tissue damage, but chronic and excessive collagen deposition is detrimental to regeneration of CMs and healing of the myocardium. While the physiological outcomes of cardiac fibrosis are well studied, the biochemical and mechano‐responsive signaling mechanisms which regulate fibrotic gene expression remain poorly investigated. The RhoA GTPase signaling pathway has been shown to play a central role in regulating fibrotic gene expression and is activated via many different pro‐fibrotic signaling factors and biomechanical stimuli (i.e., changes in ECM composition, organization and rigidity). The GTPase Rap1 is also very well‐known to mediate both inside‐out and outside‐in signaling via attachment of integrins to ECM proteins. In certain contexts, Rap1 has also been shown to antagonize RhoA signaling, but very little is known about its role in fibrotic gene expression. We therefore hypothesized that expression of Rap1 would inhibit fibrotic gene expression in cardiac myocytes and fibroblasts. Expression of either wildtype (WT) or constitutively active (63E) GFP‐tagged Rap1A constructs in cardiac fibroblasts resulted in a dramatic decrease in mRNA levels of ACTA2 (smooth muscle alpha‐actin), a commonly used marker of myofibroblast activation. Further, expression of WT or 63E Rap1A in either cardiac myocytes or fibroblasts resulted in a significant decrease in mRNA levels of ECM proteins (such as COL1A1, COL3A1, COL4A1 and FN1), as well as other common markers of fibrotic gene expression (CTGF and EGR1). Taken together, these data indicate that Rap1 signaling inhibits fibrotic gene expression and myofibroblast activation. Interestingly, expression of WT or 63E Rap1A in cardiac fibroblasts caused a dramatic increase in inflammatory markers (such as TNF, IL6, NFKB1A) and matrix remodeling enzymes (MMP3 and MMP9), genes which have been shown to play a role in increasing collagen turnover, reducing ECM rigidity/stiffness and repair of damaged myocardial tissue. Altogether, these data point to a significant role for Rap1 GTPase in reducing fibrotic gene expression and myofibroblast activation and suggest possible new therapeutic strategies to combat the damaging effects of cardiac fibrosis.

Effects of tamoxifen inducible MerCreMer on gene expression in cardiac myocytes in mice.

The Cre-LoxP technology, including the tamoxifen (TAM) inducible MerCreMer (MCM), is increasingly used to delineate gene function, understand the disease mechanisms, and test therapeutic interventions. We set to determine the effects of TAM-MCM on cardiac myocyte transcriptome.Expression of the MCM was induced specifically in cardiac myocytes upon injection of TAM to myosin heavy chain 6-MCM (Myh6-Mcm) mice for 5 consecutive days. Cardiac function, myocardial histology, and gene expression (RNA-sequencing) were analyzed 2 weeks after TAM injection. A total of 346 protein coding genes (168 up- and 178 down-regulated) were differentially expressed. Transcript levels of 85 genes, analyzed by a reverse transcription-polymerase chain reaction in independent samples, correlated with changes in the RNA-sequencing data. The differentially expressed genes were modestly enriched for genes involved in the interferon response and the tumor protein 53 (TP53) pathways. The changes in gene expression were relatively small and mostly transient and had no discernible effects on cardiac function, myocardial fibrosis, and apoptosis or induction of double-stranded DNA breaks.Thus, TAM-inducible activation of MCM alters cardiac myocytes gene expression, provoking modest and transient interferon and DNA damage responses without exerting other discernible phenotypic effects. Thus, the effects of TAM-MCM on gene expression should be considered in discerning the bona fide changes that result from the targeting of the gene of interest.

Exercise restores dysregulated gene expression in a mouse model of arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (ACM) is a myocardial disease caused mainly by mutations in genes encoding desmosome proteins ACM patients present with ventricular arrhythmias, cardiac dysfunction, sudden cardiac death, and a subset with fibro-fatty infiltration of the right ventricle predominantly. Endurance exercise is thought to exacerbate cardiac dysfunction and arrhythmias in ACM. The objective was to determine the effects of treadmill exercise on cardiac phenotype, including myocyte gene expression in myocyte-specific desmoplakin (Dsp) haplo-insufficient (Myh6-Cre:DspW/F) mice. Three months old sex-matched wild-type (WT) and Myh6-Cre:DspW/F mice with normal cardiac function, as assessed by echocardiography, were randomized to regular activity or 60 min of daily treadmill exercise (5.5 kJ work per run). Cardiac myocyte gene expression, cardiac function, arrhythmias, and myocardial histology, including apoptosis, were analysed prior to and after 3 months of routine activity or treadmill exercise. Fifty-seven and 781 genes were differentially expressed in 3- and 6-month-old Myh6-Cre:DspW/F cardiac myocytes, compared to the corresponding WT myocytes, respectively. Genes encoding secreted proteins (secretome), including inhibitors of the canonical WNT pathway, were among the most up-regulated genes. The differentially expressed genes (DEGs) predicted activation of epithelial-mesenchymal transition (EMT) and inflammation, and suppression of oxidative phosphorylation pathways in the Myh6-Cre:DspW/F myocytes. Treadmill exercise restored transcript levels of two-third (492/781) of the DEGs and the corresponding dysregulated transcriptional and biological pathways, including EMT, inflammation, and secreted inhibitors of the canonical WNT. The changes were associated with reduced myocardial apoptosis and eccentric cardiac hypertrophy without changes in cardiac function. Treadmill exercise restored transcript levels of the majority of dysregulated genes in cardiac myocytes, reduced myocardial apoptosis, and induced eccentric cardiac hypertrophy without affecting cardiac dysfunction in a mouse model of ACM. The findings suggest that treadmill exercise has potential beneficial effects in a subset of cardiac phenotypes in ACM.

Mechanical regulation of gene expression in cardiac myocytes and fibroblasts.

The intact heart undergoes complex and multiscale remodelling processes in response to altered mechanical cues. Remodelling of the myocardium is regulated by a combination of myocyte and non-myocyte responses to mechanosensitive pathways, which can alter gene expression and therefore function in these cells. Cellular mechanotransduction and its downstream effects on gene expression are initially compensatory mechanisms during adaptations to the altered mechanical environment, but under prolonged and abnormal loading conditions, they can become maladaptive, leading to impaired function and cardiacpathologies. In this Review, we summarize mechanoregulated pathways in cardiac myocytes and fibroblasts that lead to altered gene expression and cell remodelling under physiological and pathophysiological conditions. Developments in systems modelling of the networks that regulate gene expression in response to mechanical stimuli should improve integrative understanding of their roles in vivo and help to discover new combinations of drugs and device therapies targeting mechanosignalling in heart disease.

Preface: The First International Symposium on Biomechanics and Mechanobiology in Cardiovascular System

Preface: The First International Symposium on Biomechanics and Mechanobiology in Cardiovascular System

Systems Modeling of Cardiomyocyte Mechanobiology

In this article, we summarize our systems model of cardiomyocyte mechano-signaling published in PLoS Computational Biology and discuss new approaches to extending these models to predict cardiac myocyte gene expression in response to stretch.

Systems Mechanobiology of Cardiac Myocytes

Cardiac myocytes are sensitive to specific and distinct mechanical stimuli. We examined the effect of the major axis of biaxial mechanical stretch on cardiac myocyte gene expression and reconstructed a stretch signaling model to identify pathways and transcription factors regulating these responses. Neonatal cardiac myocytes were cultured on a micropatterned substrate, and the primary stretch axis was applied either parallel or transverse to the myofibril direction. RNA sequencing (RNA-Seq) after acute myocyte stretch showed a more robust response to longitudinal than to transverse stretch. After 30 minutes of stretch, 53 and 168 genes were significantly up- or down-regulated by transverse or longitudinal stretch, respectively. After 4 hours, the number of differentially expressed genes increased to 795 with longitudinal stretch but only 35 with transverse stretch. Genes regulated by both stretches showed significant enrichment of transcription factor activity and protein kinase activity, whereas longitudinal but not transverse stretch specifically activated genes involved in sarcomere organization and cytoskeletal protein binding. Network analysis using logic-based signaling model constructed from published data identified serum response factor (SRF) and myocyte enhancer factor-2 (MEF2) as critical regulators of longitudinal stretch-induced changes mediated by protein kinase C (PKC). cAMP response element-binding protein (CREB) was found to be activated by both longitudinal and transverse stretch. Inhibitor experiments were used to validate these model predictions. Cardiac myocytes activate different pathways in response to transverse and longitudinal mechanical strain; these responses may underlie differential whole organ responses to pressure versus volume overload.

Deciphering the Epigenetic Code of Cardiac Myocyte Transcription.

Epigenetic mechanisms are crucial for cell identity and transcriptional control. The heart consists of different cell types, including cardiac myocytes, endothelial cells, fibroblasts, and others. Therefore, cell type-specific analysis is needed to gain mechanistic insight into the regulation of gene expression in cardiac myocytes. Although cytosolic mRNA represents steady-state levels, nuclear mRNA more closely reflects transcriptional activity. To unravel epigenetic mechanisms of transcriptional control, cell type-specific analysis of nuclear mRNA and epigenetic modifications is crucial. The aim was to purify cardiac myocyte nuclei from hearts of different species by magnetic- or fluorescent-assisted sorting and to determine the nuclear and cellular RNA expression profiles and epigenetic marks in a cardiac myocyte-specific manner. Frozen cardiac tissue samples were used to isolate cardiac myocyte nuclei. High sorting purity was confirmed for cardiac myocyte nuclei isolated from mice, rats, and humans. Deep sequencing of nuclear RNA revealed a major fraction of nascent, unspliced RNA in contrast to results obtained from purified cardiac myocytes. Cardiac myocyte nuclear and cellular RNA expression profiles showed differences, especially for metabolic genes. Genome-wide maps of the transcriptional elongation mark H3K36me3 were generated by chromatin-immunoprecipitation. Transcriptome and epigenetic data confirmed the high degree of cardiac myocyte-specificity of our protocol. An integrative analysis of nuclear mRNA and histone mark occurrence indicated a major impact of the chromatin state on transcriptional activity in cardiac myocytes. This study establishes cardiac myocyte-specific sorting of nuclei as a universal method to investigate epigenetic and transcriptional processes in cardiac myocytes of different origins. These data sets provide novel insight into cardiac myocyte transcription.

Inhibition of p300-HAT results in a reduced histone acetylation and down-regulation of gene expression in cardiac myocytes

Aims Histone acetylation plays an important role in cardiogenesis, but the underlying mechanism is unclear. In this study, we investigated the relationship between histone hypo-acetylation and the expression of cardiac-specific genes to explore the underlying mechanisms. Main methods Cardiac-specific genes that physically interacted with p300 protein in mouse hearts were analyzed using chromatin immunoprecipitation (ChIP) assays. The cultured mouse neonatal cardiac myocytes were treated with curcumin with different concentrations and durations. The changes of histone acetyltransferase (HAT) activities, histone acetylation, cardiac-specific genes expression, and structure of chromatin were assessed by ELISA, Western blotting, quantitative RT-PCR, and ChIP assays, respectively. Key findings Results from the ChIP assay showed that GATA4, Nkx2.5, and Mef2c physically interacted with p300 protein. After treatment with 30 μM curcumin for 24 h, the HAT activities of cardiac myocytes were inhibited significantly. And the acetylation of whole histone H3 was reduced by 0.3983-fold compared to control groups (P < 0.05). Accordingly, the expression of cardiac-specific genes, GATA4, Nkx2.5, and Mef2c, were significantly down-regulated. Acetylation of histone H3 bound with promoter regions of these genes was significantly reduced. Significance p300 interacts with cardiac-specific genes, GATA4, Nkx2.5 and Mef2c, and inhibition of p300-HAT by curcumin down-regulates their expression through the inhibition of histone H3 acetylation in the promoter regions. This finding indicates that p300-HAT mediated histone H3 acetylation plays an important role in the regulation of cardiac gene expression, which is a novel mechanism of epigenetic regulation in the heart during the development and in case of some congenital heart diseases.

Proteomic comparison of spherical aggregates and adherent cells of cardiac stem cells

Background Previously published papers showed that cardiac stem cells (CSCs) form (cardio)sphere. However, recent studies questioned the significance of the sphere-formation as one of the characteristics of CSCs. We isolated c-kit-positive cardiac stem cells, cultured as bulk (CSC-BC) and characterized them previously. Among them, CSC-BC21 formed an extraordinary number of spheres. Using a clone derived from this bulk culture, we investigated the effect of sphere-formation on differentiation and performed proteomics analysis comparing two statuses, cardiosphere and dish substrate attachment. Methods We performed sphere-forming assay to compare the sphere-forming ability among CSC-BCs. The cloned cells from CSC-BC21, which had distinct sphere-forming ability, were cultured in a differentiation medium (DM) to induce cardiac myocyte differentiation. We performed RT-PCR analysis to investigate if cardiosphere-formation affects cardiac myocyte gene expression level. Furthermore, proteome analysis was performed to compare floating cardiosphere (flCS) and dish-attached cardiosphere-derived cells (daCS). Results One of the cloned cells, CSC-21E expressed higher troponin I message than CSC-BC21. Moreover, the message level of troponin I was enhanced when they had experienced cardiosphere prior to the treatment of myocyte differentiation medium. The change from flCS to daCS accompanied up-regulation of chaperones and down regulation of glycolytic and other metabolic enzymes. Calreticulin and Hsp 90 were among the up-regulated chaperons. Calreticulin is known to be an essential component of cardiogenesis. Conclusion These results suggest that the switch from aggregated sphere to the cell attachment, is important for advancing the cardiac cell differentiation.

Modulation of interleukin signalling and gene expression in cardiac myocytes by endothelin-1

The related inflammatory cytokines, interleukin- (IL-) 1β and IL-33, are both implicated in the response of the heart to injury. They also activate mitogen-activated protein kinases (MAPKs) in cardiac myocytes. The hypertrophic Gq protein-coupled receptor agonist endothelin-1 is a potentially cardioprotective peptide and may modulate the inflammatory response. Endothelin-1 also stimulates (MAPKs) in cardiac myocytes and promotes rapid changes in expression of mRNAs encoding intercellular and intracellular signalling components including receptors for IL-33 (ST2) and phosphoprotein phosphatases. Prior exposure to endothelin-1 may specifically modulate the response to IL-33 and, more globally, influence MAPK activation by different stimuli. Neonatal rat ventricular myocytes were exposed to IL-1β or IL-33 with or without pre-exposure to endothelin-1 (5h) and MAPK activation assessed. IL-33 activated ERK1/2, JNKs and p38-MAPK, but to a lesser degree than IL-1β. Endothelin-1 increased expression of soluble IL-33 receptors (sST2 receptors) which may prevent binding of IL-33 to the cell-surface receptors. However, pretreatment with endothelin-1 only inhibited activation of p38-MAPK by IL-33 with no significant influence on ERK1/2 and a small increase in activation of JNKs. Inhibition of p38-MAPK signalling following pretreatment with endothelin-1 was also detected with IL-1β, H2O2 or tumour necrosis factor α (TNFα) indicating an effect intrinsic to the signalling pathway. Endothelin-1 pretreatment suppressed the increase in expression of IL-6 mRNA induced by IL-1β and decreased the duration of expression of TNFα mRNA. Coupled with the general decrease in p38-MAPK signalling, we conclude that endothelin-1 attenuates the cardiac myocyte inflammatory response, potentially to confer cardioprotection.

Upregulation of insulin-like growth factor-1 gene expression in cardiac myocytes by hypoxia : mechanism for its cardioprotective effect

Upregulation of insulin-like growth factor-1 gene expression in cardiac myocytes by hypoxia : mechanism for its cardioprotective effect

Endothelin-1 regulation of immediate early gene expression in cardiac myocytes: negative feedback regulation of interleukin 6 by Atf3 and Klf2

Endothelin-1 regulation of immediate early gene expression in cardiac myocytes: negative feedback regulation of interleukin 6 by Atf3 and Klf2

Stretch-induced regulation of angiotensinogen gene expression in cardiac myocytes and fibroblasts: Opposing roles of JNK1/2 and p38α MAP kinases

The cardiac renin–angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy, remodeling, and fibroblast proliferation in the hemodynamically overloaded heart. However, the intracellular signaling mechanisms responsible for regulation of angiotensinogen (Ao), a substrate of the RAS system, are largely unknown. Here we report the identification of JNK1/2 as a negative, and p38α as a major positive regulator of Ao gene expression. Isolated neonatal rat ventricular myocytes (NRVM) and fibroblasts (NRFB) plated on deformable membranes coated with collagen IV, were exposed to 20% equiaxial static-stretch (0–24 h). Mechanical stretch initially depressed Ao gene expression (4 h), whereas after 8 h, Ao gene expression increased in a time-dependent manner. Blockade of JNK1/2 with SP600125 increased basal Ao gene expression in NRVM (10.52 ± 1.98 fold, P < 0.001) and NRFB (13.32 ± 2.07 fold, P < 0.001). Adenovirus-mediated expression of wild-type JNK1 significantly inhibited, whereas expression of dominant-negative JNK1 and JNK2 increased basal and stretch-mediated (24 h) Ao gene expression, showing both JNK1 and JNK2 to be negative regulators of Ao gene expression in NRVM and NRFB. Blockade of p38α/β by SB202190 or p38α by SB203580 significantly inhibited stretch-induced (24 h) Ao gene expression, whereas expression of wild-type p38α increased stretch-induced Ao gene expression in both NRVM (8.41 ± 1.50 fold, P < 0.001) and NRFB (3.39 ± 0.74 fold, P < 0.001). Conversely, expression of dominant-negative p38α significantly inhibited stretch response. Moreover, expression of constitutively active MKK6b (E) significantly stimulated Ao gene expression in the absence of stretch, indicating that p38 activation alone is sufficient to induce Ao gene expression. Taken together p38α was demonstrated to be a positive regulator, whereas JNK1/2 was found to be a negative regulator of Ao gene expression. Prolonged stretch diminished JNK1/2 activation, which was accompanied by a reciprocal increase in p38 activation and Ao gene expression. This suggests that a balance in JNK1/2 and p38α activation determines the level of Ao gene expression in myocardial cells.

Gene expression studies on bio‐electrosprayed primary cardiac myocytes

Cardiovascular pathology accounts for the greatest number of mortalities in the western world and thus the development of ex vivo cardiac tissue has vast potential in cardiac therapy. Bio-electrosprays (BES), a recently discovered direct cell engineering protocol, has demonstrated tremendous applicability for regenerative and therapeutic medicine. For bio-electrospraying to be carried forward as a novel method of cardiac tissue engineering, it is important that the process does not adversely affect cellular physiology. Our previous work has shown that bio-electrospraying does not induce cell death, activate intracellular stress pathways or induce DNA damage in primary cardiac myocytes. Here we show for the first time using genome-wide microarray analysis, that bio-electrospraying has no negative effects on global gene expression in cardiac myocytes. Moreover, we show that bio-electrospraying does not lead to endothelial cell activation. These data suggest that BES has minimal effect upon the physiology of cardiac myocytes and endothelial cells and thus paves the way for the development of BES in cardiac tissue engineering.

Loss of both GATA4 and GATA6 blocks cardiac myocyte differentiation and results in acardia in mice

Despite significant advances in identifying signaling molecules that induce cardiogenesis in mammals, the transcription factors that control the onset of cardiac myocyte gene expression have remained elusive. Candidates include the zinc finger transcription factors GATA binding proteins 4 and 6 (GATA4, GATA6). The individual loss of either protein in mice results in lethality prior to the onset of heart development due to defects in the extra-embryonic endoderm; however, when this extra-embryonic deficiency is circumvented using tetraploid embryo complementation, cardiac myocyte differentiation initiates normally. Here we show that these factors have redundant roles in controlling the onset of cardiac myocyte differentiation. As a consequence, Gata4−/−Gata6−/− embryos completely lack hearts, although second heart field progenitor cells are still generated. Our data support a model whereby GATA4 or GATA6 are essential for expression of the network of transcription factors that regulate the onset of cardiac myocyte gene expression during mammalian development.

Signaling pathways mediating cardiac myocyte gene expression in physiological and stress responses

The contractile cells in the heart (the cardiac myocytes) are terminally differentiated. In response to pathophysiological stresses, cardiac myocytes undergo hypertrophic growth or apoptosis, responses associated with the development of cardiac pathologies. There has been much effort expended in gaining an understanding of the stimuli which promote these responses, and in identifying the intracellular signaling pathways which are activated and potentially involved. These signaling pathways presumably modulate gene and protein expression to elicit the end-stage response. For the regulation of gene expression, the signal may traverse the cytoplasm to modulate nuclear-localized transcription factors as occurs with the mitogen-activated protein kinase or protein kinase B/Akt cascades. Alternatively, the signal may promote translocation of transcription factors from the cytoplasm to the nucleus as is seen with the calcineurin/NFAT and JAK/STAT systems. We present an overview of the principal signaling pathways implicated in the regulation of gene expression in cardiac myocyte pathophysiology, and summarize the current understanding of these pathways, the transcription factors they regulate and the changes in gene expression associated with the development of cardiac pathologies. Finally, we discuss how intracellular signaling and gene expression may be integrated to elicit the overall change in cellular phenotype.

Chemotherapeutic agents and gene expression in cardiac myocytes

It is becoming apparent that anti-cancer chemotherapies are increasingly associated with cardiac dysfunction or even congestive heart failure (Minotti et al., 2004; Eliott, 2006; Suter et al., 2004; Ren, 2005). Our data suggest that one of the contributing factors to the cardiotoxicitiy of these drugs may be the activation of the AhR-response (including the increased expression of Cyp1a1) and/or other detoxification program in cardiac myocytes themselves. The induction of such responses may have secondary effects (e.g. to increase the level of intracellular oxidative stress), which may influence the contractility or even survival of cardiac myocytes. Furthermore, the specific response of cardiac myocytes, both with respect to the metabolizing enzymes and the export channels, potentially differs from other cells (e.g. we failed to detect any increase in expression of other “classical” AhR-responsive genes, Ugt1a1 and Ugt1a6). This could account for, for example, the observation that doxoribicinol (the 13-hydroxy form of doxorubicin) accumulates in cardiac myocytes but not in hepatocytes (Del Tacca et al., 1985; Olson et al., 1988). Given the vulnerability of the heart and the almost irreparable damage that can be done by severe oxidative stress, further studies would seem to be merited specifically on the effects of chemotherapeutic agents on cardiac myocytes.