Myocardial expression of the arginine:glycine amidinotransferase gene is elevated in heart failure and normalized after recovery: potential implications for local creatine synthesis.

BACKGROUND: Combination therapy consisting of mechanical unloading using a left ventricular assist device (LVAD) and pharmacological intervention can promote recovery from end-stage heart failure, but the mechanism is unknown. Preliminary microarray analysis revealed a significant and unexpected decrease in myocardial arginine:glycine amidinotransferase (AGAT) gene expression during recovery in these patients. The aim of this study was to evaluate the expression and role of AGAT expression in heart failure and recovery. METHODS AND RESULTS: We used quantitative real time (TaqMan) polymerase chain reaction to examine myocardial AGAT mRNA expression in implant and explant samples from recovering patients after combination therapy (n=12), end-stage heart failure (ESHF) samples from stable patients undergoing transplantation without LVAD support (n=10), and donor hearts with normal hemodynamic function (n=8). AGAT mRNA expression was significantly elevated in all heart failure patients relative to donors (4.3-fold [P<0.001] and 2.7-fold [P<0.005] in LVAD and ESHF relative to donors, respectively) and returned to normal levels after recovery. AGAT enzyme activity was detectable in both human and rat myocardia and was elevated in heart failure. CONCLUSIONS: Our data highlight local and potentially regulated expression of AGAT activity in the myocardium and suggest a specific response to heart failure involving elevated local creatine synthesis. These findings have implications both for the management of recovery patients undergoing combination therapy and for heart failure in general.

Mapping transcriptional start sites and in silico DNA footprinting.

Determination of a gene's transcriptional start site underlies the identification of the proximal promoter region and thus facilitates the subsequent analysis of components controlling its expression, namely, cis-acting regulatory elements and their cognate binding proteins. It also enables assembly of meaningful reporter constructs to examine promoter function in different cellular contexts. In this chapter, basic protocols for two experimental approaches to transcriptional start site determination are described: primer extension analysis and the ribonuclease protection assay. Consideration is also given to RNA sources, RNA purification, and primer design. The explosion in genomic DNA and mRNA sequence information derived from genomic sequencing projects, expressed sequence tags and microarrays, combined with in silico analysis, such as automated sequence annotation and gene identification algorithms, now provides an alternative source of detailed information on gene structure and expression. Two approaches to the in silico identification of transcription factor binding sites are described.

Myocardial insulin-like growth factor-I gene expression during recovery from heart failure after combined left ventricular assist device and clenbuterol therapy.

BACKGROUND: Patients who undergo mechanical support with a left ventricular assist device (LVAD) exhibit reverse remodeling and in some cases recover from heart failure. We have developed a combination therapy using LVAD support combined with pharmacological therapy to maximize reverse remodeling, followed by the beta2 adrenergic agonist clenbuterol. We recently found that clenbuterol induces insulin-like growth factor I (IGF-I) in cardiac myocytes in vitro. The purpose of this study is to examine IGF-I expression in recovery patients after combination therapy. METHODS AND RESULTS: Myocardial mRNA levels were determined by real-time quantitative polymerase chain reaction in 12 recovery patients (at LVAD implantation, explantation, and 1 year after explantation). IGF-I mRNA was elevated at the time of LVAD explantation relative to donors, with 2 groups distinguishable: Those with low IGF-I mRNA at implantation who showed significant increase during recovery and those with high IGF-I mRNA at implantation who remained high. Levels returned to normal by 1 year after explantation. Microarray analysis of implantation and explantation samples of recovery patients further revealed elevated IGF-II and IGF binding proteins IGFBP4 and IGFBP6. IGF-I levels correlated with stromal cell-derived factor mRNA measured both in LVAD patients and in a wider cohort of heart failure patients. CONCLUSIONS: The data suggest involvement of elevated myocardial IGF-I mRNA in recovery. IGF-I may act to limit atrophy and apoptosis during reverse remodeling and to promote repair and regeneration in concert with stromal cell derived factor.

Increased expression of extracellular matrix regulators TIMP1 and MMP1 in deteriorating heart failure.

BACKGROUND: The authors previously identified and compared alterations in gene expression in the myocardia of patients with deteriorating heart failure who underwent left ventricular assist device (LVAD) implantation with those of patients with stable end-stage failure (ESF). We hypothesized that matrix metalloproteinases (MMPs) and their endogenous inhibitors, the tissue inhibitors of MMPs (TIMPs), would be implicated in the mechanisms that underlie deteriorating heart failure. METHODS: Gridded macro-array filters were used to provide a broad overview of MMP and TIMP mRNA expression in heart failure. Precise mRNA levels of TIMP1, MMP1, and beta-spectrin were determined using quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) of myocardial samples from 27 patients with deteriorating heart failure who underwent LVAD implantation, from 17 patients with stable ESF who underwent elective heart transplantation, and from 28 donor organs with good hemodynamic function. RESULTS: Gridded macro-arrays analysis of pooled failing heart samples determined that TIMP1 mRNA was the most readily detectable TIMP in failing myocardium. Quantitative RT-PCR showed that expression levels in individual patients were similar in patients with stable ESF (1.00 +/- 0.24, n = 17) and in donor organ samples (1.49 +/- 0.22, n = 28) but were significantly increased in the deteriorating heart failure group (5.38 +/- 0.32, n = 26, p < 0.0001 compared with patients with ESF). Similarly, MMP1 levels did not differ between donor and ESF groups but increased in the deteriorating failure group (6.04 +/- 0.50, n = 27, p < 0.001 compared with the ESF group). Levels of beta-II spectrin were the same in all 3 groups. Both TIMP1 and MMP1 showed positive correlation with each other and with previously determined levels of mRNA for both interleukin-1beta (IL-1beta) and IL-6 in this patient series when considering all patients individually, but neither correlated with tumor necrosis factor alpha. CONCLUSIONS: Patients with deteriorating heart failure have increased expression of TIMP1 and MMP1 mRNA. Correlation with pro-inflammatory cytokines suggests common pathways of regulation and potential activation by IL-6 and IL1-beta.

Clenbuterol induces cardiac myocyte hypertrophy via paracrine signalling and fibroblast-derived IGF-1.

The ß(2)-selective adrenoreceptor agonist clenbuterol promotes both skeletal and cardiac muscle hypertrophy and is undergoing clinical trials in the treatment of muscle wasting and heart failure. We have previously demonstrated that clenbuterol induces a mild physiological ventricular hypertrophy in vivo with normal contractile function and without induction of α-skeletal muscle actin (αSkA), a marker of pathological hypertrophy. The mechanisms of this response remain poorly defined. In this study, we examine the direct action of clenbuterol on cardiocyte cultures in vitro. Clenbuterol treatment resulted in increased cell size of cardiac myocytes with increased protein accumulation and myofibrillar organisation characteristic of hypertrophic growth. Real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed elevated mRNA expression of ANP and brain natriuretic peptide (BNP) but without change in αSkA, consistent with physiological hypertrophic growth. Clenbuterol-treated cultures also showed elevated insulin-like growth factor I (IGF-1) mRNA and activation of the protein kinase Akt. Addition of either IGF-1 receptor-blocking antibodies or LY294002 in order to inhibit phosphatidylinositol 3-kinase, a downstream effector of the IGF-1 receptor, inhibited the hypertrophic response indicating that IGF-1 signalling is required. IGF-1 expression localised primarily to the minor population of cardiac fibroblasts present in the cardiocyte cultures. Together these data show that clenbuterol acts to induce mild cardiac hypertrophy in cardiac myocytes via paracrine signalling involving fibroblast-derived IGF-1.

Molecular signature of recovery following combination left ventricular assist device (LVAD) support and pharmacologic therapy.

AIMS: A novel combination therapy consisting of a left ventricular assist device (LVAD) combined with pharmacologic therapy including the selective beta(2)-agonist, clenbuterol, has shown promise in restoring ventricular function in patients with heart failure. The aim of this study was to identify common genes and signalling pathways whose expression was associated with reversal of heart failure and restoration of ventricular function. METHODS AND RESULTS: Microarray analysis was performed on six paired human heart samples harvested at the time of LVAD implant and at the time of LVAD explant for recovery of ventricular function (post). Follow-up data shows that the improvements in ventricular function have been maintained for an average of 3.8 years post-explant. Analysis of the gene expression data revealed: (i) a significant association of integrin pathway signalling with recovery and (ii) the identification of several novel targets including, EPAC2, in the well-described cAMP pathway whose expression was down-regulated with recovery, and was associated with improvements in cardiac contractility, metabolism, and function. CONCLUSION: This data set represents the first description of signalling pathways associated with the functional recovery of end-stage human heart failure and the identification of new targets in the human heart that are modified by this combination therapy.

Structure and regulation of human troponin genes.

The recent completion of a first draft of the human genome has allowed "in silico" genome browsing to become routine. Such computer-based research is now a useful adjunct to experiments based at the bench, and is accelerating gene discovery and the analysis and understanding of genes in their genomic contexts. This review summarises recent findings on genes encoding proteins of the troponin complex. We describe the organization of the three pairs of genes which encode isoforms of troponins I and T, and discuss how this relates to their evolution and regulation. Detailed analysis of the chromosomal context of the cardiac troponin I and slow skeletal troponin T genes reveals a region of densely packed differentially expressed genes, including new genes identified by automatic genome annotation. This information is discussed within the context of detailed analysis of the best-studied gene in this region, cardiac troponin I. In this way, we illustrate the uses to which a combination of conventional bench experiments and "in silico" analyses may be put in understanding the relationship between structure and function within the genome.

Structure and regulation of human troponin genes.

The recent completion of a first draft of the human genome has allowed "in silico" genome browsing to become routine. Such computer-based research is now a useful adjunct to experiments based at the bench, and is accelerating gene discovery and the analysis and understanding of genes in their genomic contexts. This review summarises recent findings on genes encoding proteins of the troponin complex. We describe the organization of the three pairs of genes which encode isoforms of troponins I and T, and discuss how this relates to their evolution and regulation. Detailed analysis of the chromosomal context of the cardiac troponin I and slow skeletal troponin T genes reveals a region of densely packed differentially expressed genes, including new genes identified by automatic genome annotation. This information is discussed within the context of detailed analysis of the best-studied gene in this region, cardiac troponin I. In this way, we illustrate the uses to which a combination of conventional bench experiments and "in silico" analyses may be put in understanding the relationship between structure and function within the genome. (Mol Cell Biochem 263: 81-90, 2004).

The slow skeletal muscle troponin T gene is expressed in developing and diseased human heart.

Cardiac muscle development is characterised by the activation of contractile protein genes and subsequent modulation of expression resulting, ultimately, in the formation of a mature four-chambered organ. Myocardial gene expression is also altered in the adult in response to pathological stimuli and this is thought to contribute to the altered contractile characteristics of the diseased heart. We have examined the expression of the slow skeletal troponin T (TnT) gene in the human heart during development and in disease using whole mount in situ hybridisation and real-time quantitative (TaqMan) polymerase chain reaction (PCR). Slow skeletal TnT mRNA shows transitory and regional expression in the early foetal heart, which occurs at different times in atria and ventricles. In ventricular myocardium, expression is seen in the outer epicardial layer at a time when the coronary circulation is being established. Expression was detected at low levels in the adult human heart and was significantly increased in end-stage heart failure. Similarly, expression was readily detectable during early rat heart development and was up-regulated in pressure overload hypertrophy in adult. Together these data show for the first time that slow skeletal TnT mRNA is readily detectable during early human heart development. They further suggest that slow skeletal TnT may be responsive to myocardial stress and that elevated levels may contribute to myocardial dysfunction in adult disease.

The slow skeletal muscle troponin T gene is expressed in developing and diseased human heart.

Cardiac muscle development is characterised by the activation of contractile protein genes and subsequent modulation of expression resulting, ultimately, in the formation of a mature four-chambered organ. Myocardial gene expression is also altered in the adult in response to pathological stimuli and this is thought to contribute to the altered contractile characteristics of the diseased heart. We have examined the expression of the slow skeletal troponin T (TnT) gene in the human heart during development and in disease using whole mount in situ hybridisation and real-time quantitative (TaqMan) polymerase chain reaction (PCR). Slow skeletal TnT mRNA shows transitory and regional expression in the early foetal heart, which occurs at different times in atria and ventricles. In ventricular myocardium, expression is seen in the outer epicardial layer at a time when the coronary circulation is being established. Expression was detected at low levels in the adult human heart and was significantly increased in end-stage heart failure. Similarly, expression was readily detectable during early rat heart development and was up-regulated in pressure overload hypertrophy in adult. Together these data show for the first time that slow skeletal TnT mRNA is readily detectable during early human heart development. They further suggest that slow skeletal TnT may be responsive to myocardial stress and that elevated levels may contribute to myocardial dysfunction in adult disease. (Mol Cell Biochem 263: 91-97, 2004).