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

Adrenergic Receptor Polymorphism and Maximal Exercise Capacity after Orthotopic Heart Transplantation

Background

Maximal exercise capacity after heart transplantion (HTx) is reduced to the 50–70% level of healthy controls when assessed by cardiopulmonary exercise testing (CPET) despite of normal left ventricular function of the donor heart. This study investigates the role of donor heart β₁ and β₂- adrenergic receptor (AR) polymorphisms for maximal exercise capacity after orthotopic HTx.

Methods

CPET measured peak VO₂ as outcome parameter for maximal exercise in HTx recipients ≥9 months and ≤4 years post-transplant (n = 41; mean peak VO₂: 57±15% of predicted value). Donor hearts were genotyped for polymorphisms of the β₁-AR (Ser49Gly, Arg389Gly) and the β₂-AR (Arg16Gly, Gln27Glu). Circumferential shortening of the left ventricle was measured using magnetic resonance based CSPAMM tagging.

Results

Peak VO₂ was higher in donor hearts expressing the β₁-Ser49Ser alleles when compared with β₁-Gly49 carriers (60±15% vs. 47±10% of the predicted value; p = 0.015), and by trend in cardiac allografts with the β₁-AR Gly389Gly vs. β₁-Arg389 (61±15% vs. 54±14%, p = 0.093). Peak VO2 was highest for the haplotype Ser49Ser-Gly389, and decreased progressively for Ser49Ser-Arg389Arg > 49Gly-389Gly > 49Gly-Arg389Arg (adjusted R² = 0.56, p = 0.003). Peak VO₂ was not different for the tested β₂-AR polymorphisms. Independent predictors of peak VO₂ (adjusted R² = 0.55) were β₁-AR Ser49Gly SNP (p = 0.005), heart rate increase (p = 0.016), and peak systolic blood pressure (p = 0.031). Left ventricular (LV) motion kinetics as measured by cardiac MRI CSPAMM tagging at rest was not different between carriers and non-carriers of the β₁-AR Gly49allele.

Conclusion

Similar LV cardiac motion kinetics at rest in donor hearts carrying either β₁-AR Gly49 or β₁-Ser49Ser variant suggests exercise-induced desensitization and down-regulation of the β₁-AR Gly49 variant as relevant pathomechanism for reduced peak VO₂ in β₁-AR Gly49 carriers.

Diastolic dysfunction in human cardiac allografts is related with reduced SERCA2a gene expression

Previous studies demonstrated that impaired left ventricular (LV) relaxation in cardiac allografts limits exercise tolerance post-transplant despite preserved systolic ejection fraction (EF). This study tested in human cardiac allografts whether the isovolumic relaxation time (IVRT), which provides the basis for most of diastolic LV filling, relates with gene expression of regulatory proteins of calcium homeostasis or cardiac matrix proteins. Gene expression was studied in 31 heart transplant recipients (25 male, 6 female) 13-83 months post-transplant with LVEF >50%, LV end-diastolic pressure <20 mmHg, normal LV mass index and without allograft rejection or significant cardiac pathology. IVRT related with the other diastolic parameters e-wave velocity (r = -0.46; p = 0.01), e/a-wave ratio (r = -0.5; p < 0.01) but not with heart frequency (r = -0.16; p = 0.4). No relation of IVRT was observed for immunosuppression, mean rejection grade or other medication. IVRT was not related with gene expression of desmin, collagen I, phospholamban, the Na+-Ca2+ exchanger, the ryanodine receptor or interstitial fibrosis but correlated inversely with SERCA2a (r = -0.48; p = 0.02). Prolonged IVRT is associated with decreased SERCA2a expression in cardiac allografts without significant other pathology. Similar observations in non-transplanted patients with diastolic failure suggest that decreased SERCA2a expression is an important common pathomechanism.

Gene expression profiling reveals multiple protective influences of the peptide alpha-melanocyte-stimulating hormone in experimental heart transplantation

Novel therapies are sought to increase efficiency and survival of transplanted organs. Previous research on experimental heart transplantation showed that treatment with the anti-inflammatory peptide alpha-melanocyte-stimulating hormone (alpha-MSH) prolongs allograft survival. The aim of the present research was to determine the molecular mechanism of this protective activity. Gene expression profile was examined in heart grafts removed on postoperative days 1 and 4 from rats treated with saline or the synthetic alpha-MSH analog Nle4DPhe7 (NDP)-alpha-MSH. On postoperative day 1, the peptide induced expression of cytoskeleton proteins, intracellular kinases, transcription regulators, metallopeptidases, and protease inhibitors. Conversely, NDP-alpha-MSH repressed immune, inflammatory, cell cycle, and protein turnover mediators. Later effects of alpha-MSH treatment included down-regulation of oxidative stress response and up-regulation of ion channels, calcium regulation proteins, phosphatidylinositol signaling system, and glycolipidic metabolism. NDP-alpha-MSH exerted its effects on both Ag-dependent and -independent injury. The results indicate that NDP-alpha-MSH preserves heart function through a broad effect on multiple pathways and suggest that the peptide could improve the outcome of organ transplantation in combination with immunosuppressive treatments.

Measurement of adenylate cyclase activity in the right ventricular endomyocardial biopsy samples from patients with chronic congestive heart failure

A highly sensitive fluorometric assay technique was adopted in order to examine the adenylate cyclase activity in the minute right ventricular endomyocardial biopsy samples from patients with chronic congestive heart failure (n = 10). Norepinephrine (10(-4) M) and adenosine (10(-3) M) were incubated for 30 min with 10 microl of membrane preparation (1-2 mg protein/mg) to analyze the extent of the receptor-coupled adenylate cyclase activity. Forskolin (10(-4) M) stimulation was used to estimate the maximum adenylate cyclase activity (pmol/mg protein/min, mean +/- SE). The new microanalytical cyclic AMP assay involves four steps: enzymatic destruction of noncyclic adenine nucleotides and phosphorylated metabolites, conversion of cyclic AMP to ATP, amplification of ATP by enzymatic cycling, and fluorometric measurement of NADPH, which is generated in proportion to initial cyclic AMP levels. Basal and forskolin-stimulated maximum adenylate cyclase activities were 75 +/- 8 and 123 +/- 15, respectively. Norepinephrine increased the adenylate cyclase activity to 107 +/- 14, while adenosine tended to decrease it to 65 +/- 7. In addition, elimination of adenosine by adenosine deaminase (10 U/ml) slightly increased the adenylate cyclase activity to 82 +/- 9. These results indicate that the adenylate cyclase activity can be measured in minute endomyocardial biopsy samples. Use of this new approach shows promise of becoming a new and potentially important way to predict the efficacy of pharmacological treatment.

Myocardial sympathetic denervation prevents chamber-specific alteration of beta-adrenergic transmembrane signaling in rabbits with heart failure

OBJECTIVES

The purpose of this study was to assess the effect of myocardial sympathetic denervation on the chamber-specific alteration of beta-adrenergic signaling in left ventricular failure in rabbits.

BACKGROUND

Local abnormalities in sympathetic nerve terminals, including the neuronal reuptake of norepinephrine, are thought to be responsible for the chamber-specific regulation of beta-adrenergic signaling in heart failure.

METHODS

Sixteen rabbits were given 6-hydroxydopamine, 25 mg/kg body weight intravenously on days 1 and 2 and 50 mg/kg intravenously on days 7 and 8. Another 16 rabbits received vehicle. Aortic regurgitation was induced in eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits on day 14. Another eight of the 6-hydroxydopamine-treated and eight of the vehicle-treated rabbits underwent a sham operation. The hearts were excised for biochemical analysis on day 21.

RESULTS

Hemodynamic characteristics on day 21 showed left ventricular failure in both the aortic regurgitation groups. The plasma norepinephrine concentration on day 21 was higher in both the aortic regurgitation groups than in the sham groups. The beta-adrenoceptor densities and isoproterenol plus 5'-guanylylimidodiphosphate-, 5'-guanylylimidodiphosphate- and sodium fluoride-stimulated adenylyl cyclase activities were decreased only in the failing left ventricle of the vehicle-pretreated aortic regurgitation group, but in both ventricles of the 6-hydroxydopamine-pretreated aortic regurgitation group. The basal and forskolin-stimulated adenylyl cyclase activities were similar in both the aortic regurgitation groups and in the sham groups.

CONCLUSIONS

Sympathetic denervation prevented chamber-specific alterations in beta-adrenergic signaling in acute left ventricular failure. Local loss of sympathetic nerve endings, and especially the defective neuronal norepinephrine reuptake, are likely to be responsible for the chamber-specific alteration of the beta-adrenoceptor-G protein-adenylyl cyclase system in heart failure in rabbits.