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

Sinonasal disease in polyostotic fibrous dysplasia and McCune-Albright Syndrome

OBJECTIVES/HYPOTHESIS

To characterize the spectrum, symptoms, progression, and effects of endocrine dysfunction on sinonasal disease in polyostotic fibrous dysplasia (PFD) and McCune-Albright Syndrome (MAS).

STUDY DESIGN

Retrospective review.

METHODS

A prospectively followed cohort of subjects with PFD/MAS underwent a comprehensive evaluation that included otolaryngologic and endocrine evaluation, and imaging studies. Head and facial computed tomography scans were analyzed, and the degree of fibrous dysplasia (FD) was graded using a modified Lund-MacKay scale. Those followed for >4 years were analyzed for progression.

RESULTS

A total of 106 patients meeting inclusion criteria were identified with craniofacial FD. A majority (92%) demonstrated sinonasal involvement. There were significant positive correlations between the sinonasal FD scale score and chronic congestion, hyposmia, growth hormone excess, and hyperthyroidism (P < .05 for all). Significant correlations were not found for headache/facial pain or recurrent/chronic sinusitis. Thirty-one subjects met the criteria for longitudinal analysis (follow-up mean, 6.3 years; range, 4.4-9 years). Those who demonstrated disease progression were significantly younger than those who did not (mean age, 11 vs. 25 years). Progression after age of 13 years was uncommon (n = 3) and minimal. Concomitant endocrinopathy or bisphosphonate use did not have any significant effect on progression of disease.

CONCLUSIONS

Sinonasal involvement of fibrous dysplasia in PFD/MAS is common. Symptoms are usually few and mild, and disease progression occurs primarily in young subjects. Concomitant endocrinopathy is associated with disease severity, but not progression.

Hypoplastic left heart syndrome myocytes are differentiated but possess a unique phenotype

INTRODUCTION

Hypoplastic left heart syndrome (HLHS) is the term used to describe a group of congenital malformations characterized by marked underdevelopment of the left side of the heart. HLHS accounts for nearly 25% of cardiac deaths in the first year of life. Although much has been reported regarding diagnosis, gross morphology and surgical treatment, no information on gene expression in HLHS myocytes is available.

METHODS

We examined heart tissue from patients with HLHS using routine histology, immunohistochemistry, quantitative polymerase chain reaction (PCR), two-dimensional (2-D) gel electrophoresis and protein identification by mass spectrometry.

RESULTS

Histologic examination of right and left ventricles from HLHS patients revealed characteristic features of myocyte differentiation, including striations and intercalated disc formation. Immunohistochemical staining using antibody to N-cadherin demonstrated clear development of intercalated discs between myocytes. However, many of the myocytes contained scant cytoplasm and were grouped in small, disorganized bundles separated by abundant connective tissue and dilated, thin-walled vessels. Quantitative PCR analysis demonstrated that both left and right ventricular tissue from HLHS hearts expressed the fetal or "heart failure" gene expression pattern. Two-dimensional gel electrophoresis and protein identification by mass spectrometry also confirmed that myocytes from HLHS ventricles were differentiated but expressed the fetal isoform of some cardiac specific proteins. However, HLHS myocytes in all of the heart samples (n=21) were inappropriately expressing platelet-endothelial cell adhesion molecule-1 (PECAM-1, CD31), a member of the cell adhesion molecule (CAM) family that has a primary role in the regulation of tissue morphogenesis. These findings indicate that myocytes from HLHS syndrome patients, while differentiated, have a unique gene expression pattern.

Modification of beta-adrenoceptor signal transduction pathway by genetic manipulation and heart failure

The beta-adrenoceptor (beta-AR) mediated signal transduction pathway in cardiomyocytes is known to involve beta1- and beta2-ARs, stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). The activation of beta1- and beta2-ARs has been shown to increase heart function by increasing Ca2+ -movements across the sarcolemmal membrane and sarcoplasmic reticulum through the stimulation of Gs-proteins, activation of AC and PKA enzymes and phosphorylation of the target sites. The activation of PKA has also been reported to increase phosphorylation of some myofibrillar proteins (for promoting cardiac relaxation) and nuclear proteins (for cardiac hypertrophy). The activation of beta2-AR has also been shown to affect Gi-proteins, stimulate mitogen activated protein kinase and increase protein synthesis by enhancing gene expression. Beta1- and beta2-ARs as well as AC are considered to be regulated by PKA- and protein kinase C (PKC)-mediated phosphorylations directly; both PKA and PKC also regulate beta-AR indirectly through the involvement of beta-AR kinase (betaARK), beta-arrestins and Gbeta gamma-protein subunits. Genetic manipulation of different components and regulators of beta-AR signal transduction pathway by employing transgenic and knockout mouse models has provided insight into their functional and regulatory characteristics in cardiomyocytes. The genetic studies have also helped in understanding the pathophysiological role of PARK in heart dysfunction and therapeutic role of betaARK inhibitors in the treatment of heart failure. Varying degrees of defects in the beta-AR signal transduction system have been identified in different types of heart failure to explain the attenuated response of the failing heart to sympathetic stimulation or catecholamine infusion. A decrease in beta1-AR density, an increase in the level of G1-proteins and overexpression of betaARK are usually associated with heart failure; however, these attenuations have been shown to be dependent upon the type and stage of heart failure as well as region of the heart. Both local and circulating renin-angiotensin systems, sympathetic nervous system and endothelial cell function appears to regulate the status of beta-AR signal transduction pathway in the failing heart. Thus different components and regulators of the beta-AR signal transduction pathway appears to represent important targets for the development of therapeutic interventions for the treatment of heart failure.

Heterotrimeric G proteins in heart disease

Guanine nucleotide binding proteins (G proteins) are largely grouped into three classes: heterotrimeric G proteins, ras-like or small molecular weight GTP binding proteins, and others like Gh. In the heart G proteins transduce signals from a variety of membrane receptors to generate diverse effects on contractility, heart rate, and myocyte growth. This central position of G proteins forming a switchboard between extracellular signals and intracellular effectors makes them candidates possibly involved in the pathogenesis of cardiac hypertrophy, heart failure, and arrhythmia. This review focuses primarily on discoveries of heterotrimeric G protein alterations in heart diseases that help us to understand the pathogenesis and pathophysiology. We also discuss the underlying molecular mechanisms of heterotrimeric G protein signalling.Key words: G proteins, signal transduction, adrenergic system, heart failure, hypertrophy.

Evidence of phenotypic alteration as a cause of systolic dysfunction in the failing heart

This article describes the phenotype of dilated cardiomyopathy in humans and describes parallel studies in experimental models that support or refute the relevance of these changes to the development of the heart failure phenotype.

Changes in gene expression in the intact human heart. Downregulation of alpha-myosin heavy chain in hypertrophied, failing ventricular myocardium

Using quantitative RT-PCR in RNA from right ventricular (RV) endomyocardial biopsies from intact nonfailing hearts, and subjects with moderate RV failure from primary pulmonary hypertension (PPH) or idiopathic dilated cardiomyopathy (IDC), we measured expression of genes involved in regulation of contractility or hypertrophy. Gene expression was also assessed in LV (left ventricular) and RV free wall and RV endomyocardium of hearts from end-stage IDC subjects undergoing heart transplantation or from nonfailing donors. In intact failing hearts, downregulation of beta1-receptor mRNA and protein, upregulation of atrial natriuretic peptide mRNA expression, and increased myocyte diameter indicated similar degrees of failure and hypertrophy in the IDC and PPH phenotypes. The only molecular phenotypic difference between PPH and IDC RVs was upregulation of beta2-receptor gene expression in PPH but not IDC. The major new findings were that (a) both nonfailing intact and explanted human ventricular myocardium expressed substantial amounts of alpha-myosin heavy chain mRNA (alpha-MHC, 23-34% of total), and (b) in heart failure alpha-MHC was downregulated (by 67-84%) and beta-MHC gene expression was upregulated. We conclude that at the mRNA level nonfailing human heart expresses substantial alpha-MHC. In myocardial failure this alteration in gene expression of MHC isoforms, if translated into protein expression, would decrease myosin ATPase enzyme velocity and slow speed of contraction.

Decreased adenylate cyclase activity and expression of Gs alpha in human myocardium after orthotopic cardiac transplantation

We studied several aspects of guanine nucleotide-stimulated adenylate cyclase function in patients after orthotopic cardiac transplantation. In 28 patients, adenylate cyclase activity was measured in endomyocardial biopsy samples obtained just before and at monthly intervals after cardiac transplantation. In biopsies obtained > or = 6 months after transplantation, basal adenylate cyclase activity was decreased by 67% (n = 12; P < .05), GTP gamma S-stimulated adenylate cyclase activity was decreased by 78% (n = 12; P < .05), Mn+2+forskolin-stimulated adenylate cyclase activity was decreased by 80% (n = 8; P < .05), and Mn+2-stimulated adenylate cyclase activity (a measure of activity of the catalytic subunit of adenylate cyclase) was decreased by 83% (n = 8, P < .05). Western blot analysis demonstrated that 6 months after cardiac transplantation, the level of Gs alpha protein was decreased by 61 +/- 12% (n = 8; P < .001). There was no change in the level of Gi alpha as assessed by pertussis toxin-catalyzed ADP-ribosylation (n = 4; P = NS). With the use of the quantitative polymerase chain reaction, a 50 +/- 10% (n = 6; P < .001) reduction in the steady-state level of Gs alpha mRNA was observed. There was no change in the level of mRNA for Gi-3 alpha. Thus, after orthotopic cardiac transplantation in humans, guanine nucleotide-stimulated adenylate cyclase activity is decreased in parallel with decreased levels of Gs alpha protein and mRNA.

Endomyocardial gene expression during development of pacing tachycardia-induced heart failure in the dog

Selective and specific changes in gene expression characterize the end-stage failing heart. However, the pattern and relation of these changes to evolving systolic and diastolic dysfunction during development of heart failure remains undefined. In the present study, we assessed steady-state levels of mRNAs encoding a group of cardiac proteins during the early development of left ventricular dysfunction in dogs with pacing-induced cardiomyopathy. Corresponding hemodynamic assessments were made in the conscious state in the same animals and at the same time points at baseline, after 1 week of ventricular pacing, and at the onset of clinical heart failure. Systolic dysfunction dominated after 1 week of pacing, whereas diastolic dysfunction was far more pronounced with the onset of heart failure. Atrial natriuretic factor mRNA was undetectable in 7 of 12 hearts at baseline but was expressed in all hearts at 1 week (P < .01 by chi 2 test), and it increased markedly with progression to failure (P = .05). Creatine kinase-B mRNA also rose markedly with heart failure (P < .01). Levels of mRNA encoding beta-myosin heavy chain, mitochondrial creatine kinase, phospholamban, and sarcoplasmic reticulum Ca(2+)-ATPase did not significantly change from baseline, despite development of heart failure. Additional analysis to determine if these mRNA changes were related to the severity of diastolic or systolic dysfunction revealed that phospholamban mRNA decreased in hearts with larger net increases in end-diastolic pressure (+19.2 +/- 1.9 mm Hg) compared with those hearts in which it did not change (+4.0 +/- 4.9, P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)

CD4-positive cells from patients with IgA nephropathy demonstrate increased mRNA of cytokines that induce the IgA switch and differentiation

IgA nephropathy (IgAN) is characterized by raised serum IgA1 and mesangial IgA1 deposits. We have previously shown increased T-cell activation in IgAN. Recently, transforming growth factor-beta (TGF-beta) has been shown to induce IgA isotype switch at a clonal level and interleukin 5 (IL5) promotes differentiation into IgA-bearing B cells. In the present study we have examined the TGF-beta and IL5 mRNA expression by mitogen-activated CD4-positive T cells from patients with IgAN (n = 25), patients with other primary nephritides (CGN) (n = 24), and healthy control subjects (n = 25). The cytokine genes were analysed by reverse transcription (RT)-polymerase chain reaction (PCR) and were semi-quantitated by normalizing the differences occurring during RT and PCR using a housekeeping gene, beta-actin. CD4-positive T cells from IgA nephritic patients expressed a higher level of IL5 mRNA than healthy controls (P < 0.01) and patients with CGN (P < 0.005). CD4-positive T cells from IgA nephritic patients expressed a higher level of TGF-beta mRNA than healthy controls (P < 0.01) but no difference was demonstrated on comparison with CGN patients. Elevated TGF-beta mRNA expression in patients with CGN probably reflects its other important function as a 'sclerogenic' factor involved in the glomerulosclerosis found in these nephritides. Our data suggest that there is increased expression of cytokine genes which induce the IgA isotype switch and differentiation; these immunological abnormalities may be important in the pathogenesis of IgAN.

Increased mRNA encoding for transforming factor-beta in CD4+ cells from patients with IgA nephropathy

IgA nephropathy (IgAN) is a mesangial proliferative glomerulonephritis characterized by predominant mesangial IgA deposits. Recently, transforming growth factor-beta (TGF-beta) is shown to exert widespread effects on extracellular matrix by enhancing its accumulation. In an experimental model of acute mesangial glomerulonephritis TGF-beta appeared to be involved in the process of glomerulosclerosis, and treatment with antagonists of TGF-beta prevented the development of glomerulosclerosis. We examined the TGF-beta mRNA expression by mitogen activated CD4+ T cells from 31 patients with IgAN, 25 healthy controls and 10 patients with minimal change nephropathy (MCN) or focal glomerulonephritis (FGN) who were comparable in age and sex. The cytokine gene was analyzed with reverse transcription followed by polymerase chain reaction and was semiquantitated by normalizing the differences occurring during reverse transcription and polymerase chain reaction using a housekeeping gene, beta-actin. CD4+ T cells from IgA nephritic patients expressed a higher level of TGF-beta mRNA than that of healthy controls or that of MCN/FGN [TGF-beta/actin ratio 1.11 (median), range 0.24 to 3.87 vs. 0.88, range 0.2 to 3.83, P = 0.0157 and 0.36 range 0.09 to 1.6, P = 0.006]. When the biopsies were classified into three grades according to the severity of glomerular and interstitial pathology, there were highly significant differences between the TGF-beta mRNA in CD4+ T cells from the three groups of IgA nephritic patients (grade 1, 0.52, range 0.24 to 0.79; grade 2, 1.2, range 0.5 to 3.33; grade 3, 2.17, range 1.45 to 3.87].(ABSTRACT TRUNCATED AT 250 WORDS)

Intraglomerular expression of transforming growth factor-beta 1 (TGF-beta 1) mRNA in patients with glomerulonephritis: quantitative analysis by competitive polymerase chain reaction

TGF-beta 1 is involved in the pathogenesis of glomerular sclerosis. We studied the intraglomerular expression of TGF-beta 1 mRNA in patients with glomerulonephritis using competitive polymerase chain reaction (PCR). This method is sensitive enough to quantify cDNA copies of mRNA present in small amounts of samples. Renal biopsy specimens were obtained from 42 patients with various kinds of glomerulonephritis. Ten glomeruli were dissected from renal biopsy specimens. Normal glomeruli were also obtained from the resected kidneys of eight patients with renal cell cancer. Total RNA was extracted from the glomeruli and reverse transcribed into cDNA with reverse transcriptase. To prepare samples containing identical amounts of beta-actin cDNA (8 pg), we performed competitive PCR by co-amplifying mutant templates of beta-actin with a unique EcoRI site. Next, to measure TGF-beta 1 cDNA, we performed competitive PCR by co-amplifying mutant templates of TGF-beta 1. We observed a higher glomerular expression of TGF-beta 1 mRNA in cases of mesangial proliferative glomerulonephritis having a moderate increase in mesangial matrix, diabetic nephropathy and diffuse proliferative lupus nephritis, compared with normal glomeruli. Results suggest that the intraglomerular synthesis of TGF-beta 1 may be involved in the progression of glomerulonephritis in humans.

Downregulation of adenylylcyclase types V and VI mRNA levels in pacing-induced heart failure in dogs

We have shown that the heart expresses two distinct forms of adenylylcyclase mRNA, types V and VI. In this study we have characterized the expression of these two mRNA species in heart failure generated by overdrive pacing at a rate of 240 beats/min. After 4 wk, left ventricular end-diastolic pressure and heart rate increased significantly with the appearance of signs of heart failure, i.e., edema, ascites, and exercise intolerance. Basal as well as forskolin-stimulated adenylylcyclase activities decreased significantly, which was accompanied by a reduction in the steady state mRNA levels of adenylylcyclase types V and VI. These data suggest that in this model of cardiomyopathy, the downregulation of adenylylcyclase catalytic activity results, at least in part, from a reduction in the steady state levels of types V and VI adenylylcyclase mRNA levels.

Reduced beta 1 receptor messenger RNA abundance in the failing human heart

Heart failure in humans is characterized by alterations in myocardial adrenergic signal transduction, the most prominent of which is down-regulation of beta 1-adrenergic receptors. We tested the hypothesis that down-regulation of beta 1-adrenergic receptors in the failing human heart is related to decreased steady-state levels of beta 1 receptor mRNA. Due to the extremely low abundance of beta 1 receptor mRNA, measurements were possible only by quantitative polymerase chain reaction (QPCR) or by RNase protection methods. Because the beta 1 receptor gene is intronless and beta 1 receptor mRNA abundance is low, QPCR yielded genomic amplification in total RNA, and mRNA measurements had to be performed in poly (A)(+)-enriched RNA. By QPCR the concentration of beta 1 receptor mRNA varied from 0.34 to 7.8 x 10(7) molecules/microgram poly(A)(+)-enriched RNA, and the assay was sensitive to 16.7 zeptomol. Using 100-mg aliquots of left ventricular myocardium obtained from organ donors (nonfailing ventricles, n = 12) or heart transplant recipients (failing ventricles, n = 13), the respective beta 1 mRNA levels measured by QPCR were 4.2 +/- 0.7 x 10(7)/micrograms vs. 2.10 +/- 0.3 x 10(7)/micrograms (P = 0.006). In these same nonfailing and failing left ventricles the respective beta 1-adrenergic receptor densities were 67.9 +/- 6.9 fmol/mg vs. 29.6 +/- 3.5 fmol/mg (P = 0.0001). Decreased mRNA abundance in the failing ventricles was confirmed by RNase protection assays in total RNA, which also demonstrated a 50% reduction in beta 1 message abundance. We conclude that down-regulation of beta 1 receptor mRNA contributes to down-regulation of beta 1 adrenergic receptors in the failing human heart.

Changes in myocardial and vascular receptors in heart failure

Heart failure results in dramatic changes in certain neurotransmitter and hormone receptors. The majority of the changes occur in the heart and generally can be classified as regulatory phenomena that withdraw the failing heart from adrenergic stimulation. Of these, the most prominent is beta 1-receptor downregulation. Changes in vascular receptors are much less prominent and there is no direct evidence that any vascular receptor changes in heart failure. The changes that occur in myocardial receptors suggest that antiadrenergic therapy would be effective in the treatment of heart failure by removing adrenergic signaling transduced by the remaining components of the receptor pathways. Taken together, the receptor desensitization changes present in the failing heart provide a rationale for beta 1- plus beta 2-adrenergic blockade or even combined beta 1-, beta 2-alpha 1-adrenergic receptor blockade in heart failure.

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.

The contribution of increased collagen synthesis to human glomerulosclerosis: a quantitative analysis of alpha 2IV collagen mRNA expression by competitive polymerase chain reaction

We previously reported that one of the main components of the sclerotic material in human glomerular diseases was type IV collagen. In this study we examined the contribution of increased synthesis to this process at the gene expression level. Sufficient material has not been available to study type IV collagen synthesis by normal or sclerotic glomeruli in humans. We took advantage of the availability of nephrectomy specimens from patients with renal carcinoma, and of the observation that approximately 50% of these patients develop varying degrees of glomerulosclerosis. We microdissected glomeruli from 10 patients and analyzed them using in situ reverse transcription coupled with polymerase chain reaction (PCR) analyses (in situ RT-PCR). alpha 2IV collagen mRNA, after reverse transcription into cDNA, was detected in all patients and appeared to be increased in those with glomerulosclerosis (n = 5). A competitive PCR assay was developed to quantitate this change. There was an average 3.7-fold increase in glomerular type IV collagen cDNA in patients with significant sclerosis. This change was not due to an increased number of glomerular cells. Thus, glomerulosclerosis in humans is associated with an elevation of glomerular type IV collagen gene expression, suggesting that increased synthesis of type IV collagen may represent one component of this process.

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.