Selective gene expression in failing human heart. Quantification of steady-state levels of messenger RNA in endomyocardial biopsies using the polymerase chain reaction

Rapid and sensitive method of quantitation of bone gla protein mRNA using competitive polymerase chain reaction

A method for sensitive quantitation of bone gla protein (BGP, osteocalcin) mRNA has been developed using competitive polymerase chain reaction after reverse transcription (competitive RT-PCR). The complementary DNA (cDNA) were transcribed from sample RNA was co-amplified in a PCR with a known amount of mutant BGP cDNA (competitor) using the identical oligonucleotide primers. The mutant cDNA with its unique restriction site allowed quantitation of sample and mutant PCR products after densitometric analysis of ethidium bromide-stained agarose gels. A linear relationship between initial sample BGP amount and the ratio of BGP to mutant BGP band intensity was obtained and used to make a standard curve to determine the initial BGP mRNA of unknown samples. These standard curves were made with known amounts of recombinant BGP cDNA. The competitive RT-PCR for BGP allows measurement of twofold differences in 1 and 2 micrograms total RNA and requires at least 10 times less sample RNA than usual Northern blotting. Moreover, heteroduplexes with one BGP strand and one mutant BGP strand formed as a result of high PCR cycles were quantifiable. This provided the advantages of rapid quantitation from ethidium bromide-stained gels without blotting, hybridization, or autoradiography. Multiple samples could be assayed for greater confidence in the results. The sensitivity, accuracy, and ease of the assay will facilitate analysis of BGP mRNA from a small amount of sample. The assay has been used to confirm the BGP mRNA changes with hormonal treatment in cultured cells and the age-related changes in whole tibia in vivo.

Alterations in sarcoplasmic reticulum gene expression in human heart failure. A possible mechanism for alterations in systolic and diastolic properties of the failing myocardium

Recent studies have shown that intracellular Ca2+ handling is abnormal in the myocardium of patients with end-stage heart failure. Muscles from the failing hearts showed a prolonged Ca2+ transient and a diminished capacity to restore a low resting Ca2+ level during diastole. Accordingly, we examined whether this defect in Ca2+ transport function is due to alterations in sarcoplasmic reticulum gene expression. We determined the messenger RNA (mRNA) levels of sarcoplasmic reticulum Ca2+ transport proteins in failing human hearts from 17 cardiac transplant recipients with a diagnosis of dilated cardiomyopathy, primary pulmonary hypertension, or ischemic heart disease. The expression levels of each mRNA were compared with each other and then correlated with that of atrial natriuretic factor (ANF) mRNA in the failing ventricle. The mRNA levels for the calcium release channel (ryanodine receptor, RYR2), Ca2+ uptake pump (Ca(2+)-ATPase, SERCA2 isoform), and phospholamban differed significantly between heart samples but showed an inverse relation with that of ventricular ANF mRNA. In contrast, calsequestrin mRNA levels remained unchanged in these failing hearts. In addition, beta-myosin and alpha-cardiac actin mRNA levels also showed an inverse relation with ANF mRNA levels. These changes were observed in both right and left ventricles of hearts with congestive heart failure due to dilated cardiomyopathy, primary pulmonary hypertension, or ischemic heart disease. The results are consistent with the hypothesis that abnormal calcium handling in the sarcoplasmic reticulum of failing hearts is due to the altered expression of the genes encoding sarcoplasmic reticulum proteins.

Altered expression of beta-adrenergic receptor kinase and beta 1-adrenergic receptors in the failing human heart

BACKGROUND

In chronic heart failure, the positive inotropic effects of beta-adrenergic receptor agonists are greatly reduced, in part as a result of two alterations of the cardiac beta-adrenergic receptors: loss of their function (receptor uncoupling) and reduction of their number (downregulation). In vitro studies have shown that a major mechanism leading to beta-adrenergic receptor uncoupling involves phosphorylation of the receptors by the specific beta-adrenergic receptor kinase (beta ARK).

METHODS AND RESULTS

We have therefore investigated expression of beta ARK and beta-adrenergic receptors in samples from the left ventricles of patients with dilated cardiomyopathy or ischemic cardiomyopathy and from nonfailing control ventricles. Contractile responses to beta-receptor stimulation were decreased in the failing hearts compared with control hearts, whereas those to forskolin and calcium remained unchanged. The messenger RNA (mRNA) levels of beta ARK, beta 1- and beta 2-receptors, and of glyceraldehyde phosphate dehydrogenase and beta-actin as controls were measured by quantitative polymerase chain reactions. In addition, beta ARK enzyme activity assays were performed, and the levels of beta 1- and beta 2-receptors were determined by radioligand binding. beta ARK mRNA levels were increased almost threefold in both forms of heart failure, and beta ARK activity was enhanced. beta 1-Receptor mRNA levels and beta 1-receptor numbers were decreased by approximately 50% in both failing groups, whereas these levels were unaltered for beta 2-receptors. There were no differences between dilated and ischemic cardiomyopathy for any of these parameters.

CONCLUSIONS

In addition to other alterations found in failing hearts, the diminished response to beta-receptor agonists appears to involve the combined effects of enhanced expression of beta ARK and reduced expression of beta 1-receptors.

Expression of dihydropyridine receptor (Ca2+ channel) and calsequestrin genes in the myocardium of patients with end-stage heart failure

Cytoplasmic free calcium ions (Ca2+) play a central role in excitation-contraction coupling of cardiac muscle. Abnormal Ca2+ handling has been implicated in systolic and diastolic dysfunction in patients with end-stage heart failure. The current study tests the hypothesis that expression of genes encoding proteins regulating myocardial Ca2+ homeostasis is altered in human heart failure. We analyzed RNA isolated from the left ventricular (LV) myocardium of 30 cardiac transplant recipients with end-stage heart failure (HF) and five organ donors (normal control), using cDNA probes specific for the cardiac dihydropyridine (DHP) receptor (the alpha 1 subunit of the DHP-sensitive Ca2+ channel) and cardiac calsequestrin of sarcoplasmic reticulum (SR). In addition, abundance of DHP binding sites was assessed by ligand binding techniques (n = 6 each for the patients and normal controls). There was no difference in the level of cardiac calsequestrin mRNA between the HF patients and normal controls. In contrast, the level of mRNA encoding the DHP receptor was decreased by 47% (P less than 0.001) in the LV myocardium from the patients with HF compared to the normal controls. The number of DHP binding sites was decreased by 35-48%. As reported previously, expression of the SR Ca(2+)-ATPase mRNA was also diminished by 50% (P less than 0.001) in the HF group. These data suggest that expression of the genes encoding the cardiac DHP receptor and SR Ca(2+)-ATPase is reduced in the LV myocardium from patients with HF. Altered expression of these genes may be related to abnormal Ca2+ handling in the failing myocardium, contributing to LV systolic and diastolic dysfunction in patients with end-stage heart failure.

Quantitative or semi-quantitative PCR: reality versus myth

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Expression of A-, B-, and C-type natriuretic peptide genes in failing and developing human ventricles. Correlation with expression of the Ca(2+)-ATPase gene

Brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are novel natriuretic peptides, originally isolated from porcine brain. Similar to atrial natriuretic peptide (ANP), BNP is also synthesized in and secreted from cardiocytes, but CNP is not expressed at significant levels in normal adult myocardium. Previous studies have indicated that the serum level and ventricular expression of the ANP gene were augmented in patients with heart failure. Recently, the serum level of BNP was also reported to increase in human heart failure. To examine whether or not the expression of these natriuretic peptides is regulated in ventricular myocardium in a concordant manner, we performed Northern blot analysis using total cellular RNA isolated from the diseased left ventricles of 30 cardiac transplant recipients with end-stage heart failure, seven ventricles from organ donors (control group), and two ventricles of artificially aborted 17- and 19-week-old fetuses. The levels of mRNAs encoding both BNP and ANP increased significantly (p less than 0.01) in the left ventricular myocardium from the patients with end-stage heart failure as compared with the control group. The levels of BNP mRNA correlated positively with those of ANP mRNA (r = 0.73, p less than 0.01) and negatively with those of sarcoplasmic reticulum Ca(2+)-ATPase mRNA (r = -0.66, p less than 0.01) in the left ventricular myocardium from the patients with heart failure. There was also a negative correlation between the levels of ANP and the sarcoplasmic reticulum Ca(2+)-ATPase mRNAs (r = -0.65, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible alterations in myocardial gene expression in a young man with dilated cardiomyopathy and hypothyroidism

Thyroid hormone effects on myocardial gene expression have been well defined in animal models, but their relationship to the pathogenesis of cardiac dysfunction in hypothyroid humans has been uncertain. We evaluated a profoundly hypothyroid young man with dilated cardiomyopathy. Before and during 9 months of thyroxine therapy, serial assessment of myocardial performance documented substantial improvements in the left ventricular ejection fraction (16-37%), left ventricular end-diastolic diameter (7.8-5.9 cm), and cardiac index (1.4-2.7 liters.min-1.m-2). Steady-state levels of mRNAs encoding selected cardiac proteins were measured in biopsy samples obtained before and after thyroxine replacement. In comparison with myocardium from nonfailing control hearts, this patient's pretreatment alpha-myosin heavy-chain mRNA level was substantially lower, the atrial natriuretic factor mRNA level was markedly elevated, and the phospholamban mRNA level was decreased. All of these derangements were reversed 9 months after restoration of euthyroidism. These observations in an unusual patient with profound myxedema and cardiac dilatation permit correlation between the reversible changes in myocardial function and steady-state mRNA levels in a cardiomyopathy. They suggest that alterations in gene expression in the dilated myopathic heart may be correctable when a treatable cause is identified.

Expression of alpha-subunits of G proteins in failing human heart: a reappraisal utilizing quantitative polymerase chain reaction

A decrease in the density of the beta 1-adrenergic receptor and an increase in the functional activity of the G inhibitory protein Gi accompany human heart failure; however, the molecular and biochemical mechanisms responsible for these changes are unclear. We previously reported that the steady-state levels of the mRNAs encoding both alpha Gi-3 and alpha Gs were significantly increased in failing human heart. However, these results are not consistent with recent studies demonstrating that immunodetectable levels of alpha G proteins are not different in failing human hearts when compared with non-failing controls. In addition, analysis of the 5' flanking regions of alpha Gi and alpha Gs suggests that these two genes are unlikely to be co-regulated as their regulatory domains are quite different. Therefore, we hypothesized that the disparity between the measurements of alpha G protein gene expression and assessment of the actual levels of alpha G proteins might be due to technical limitations of the Northern blot technique utilized in previous studies for assessment of the mRNA levels; (i) cytoskeletal beta-actin mRNA was used as a standard for normalization; and (ii) only relative levels of alpha G mRNAs were measured. The recent application of the polymerase chain reaction to quantification of mRNA levels in small quantities of human heart provided the tool with which to test this hypothesis. When expressed in molecules of mRNA per microgram of total RNA, there were no differences in the levels of alpha Gi and alpha Gs mRNAs in failing human heart when compared with non-failing controls.(ABSTRACT TRUNCATED AT 250 WORDS)