The failing human heart expresses tumor necrosis factor-α (TNF-α). However, its pathophysiological significance is not clear. We previously reported that robust overexpression of TNF-α in the murine heart causes lethal myocarditis. In this study, we modified the transgene to reduce the production of TNF-α by preserving the destabilizing sequence in TNF-α cDNA. Expression was driven by the murine α-myosin heavy chain promoter. Use of this modified construct allowed us to establish a murine transgenic line (TG). TG offspring were examined at 6, 12, and 24 weeks. All showed a significantly higher heart weight–to–body weight ratio. Northern blot analysis confirmed the expression of transgene in the heart, and enzyme-linked immunosorbent assay demonstrated the presence of TNF-α protein. The TG heart demonstrated a mild, diffuse, lymphohistiocytic interstitial inflammatory infiltrate. Cardiomyocyte necrosis and apoptosis were present but not abundant. Magnetic resonance imaging showed that the TG heart...

Dilated Cardiomyopathy in Transgenic Mice With Cardiac-Specific Overexpression of Tumor Necrosis Factor-α

BACKGROUNDExperiments were performed in human ventricular myocytes to investigate properties of excitation-contraction coupling in patients with terminal heart failure. Myocytes were isolated from left ventricular myocardium of patients with cardiac failure caused by dilated or ischemic cardiomyopathy undergoing transplantation. These results were compared with those obtained from cells of healthy donor hearts that for technical reasons were not suitable for transplantation.METHODS AND RESULTS[Ca2+]i transients and Ca2+ currents were recorded from isolated cells under voltage clamp perfused internally with the Ca2+ indicator fura 2. In cells that were stimulated externally, the cell-permeant form of the indicator, fura 2-AM, was used. When action potentials were to be recorded, cells were stimulated in current clamp mode. Unstimulated Ca2+ current densities were not significantly different in myopathic and control cells. In diseased myocytes, resting [Ca2+]i levels were 165 +/- 61 nmol/l, compared with 95...

Intracellular calcium handling in isolated ventricular myocytes from patients with terminal heart failure.

Fat cell adrenergic receptors and the control of white and brown fat cell function.

Background—Tumor necrosis factor-α (TNF-α) is a multifunctional cytokine that has been detected in several human cardiac-related conditions, including congestive heart failure and septic cardiomyopathy. In these conditions, the origin of TNF-α secretion is, at least in part, cardiac myocytes. Methods and Results—To determine the consequences of TNF-α production by cardiac myocytes in vivo, we developed transgenic mice in which expression of a murine TNF-α coding sequence was driven by the murine α-myosin heavy chain promoter. Four transgenic founders developed an identical illness consisting of tachypnea, decreased activity, and hunched posture. In vivo, ECG-gated MRI of symptomatic transgenic mice documented a severe impairment of cardiac function evidenced by biventricular dilatation and depressed ejection fractions. All transgenic mice died prematurely. Pathological examination of affected animals revealed a globular dilated heart, bilateral pleural effusions, myocyte apoptosis, and transmural myocardi...

Cardiac Failure in Transgenic Mice With Myocardial Expression of Tumor Necrosis Factor-α

Serotonin uptake sites and serotonin receptors are altered in the limbic system of schizophrenics

Mechanism of noradrenaline-induced heterologous desensitization of adenylate cyclase stimulation in rat heart muscle cells: increase in the level of inhibitory G-protein α-subunits

Tumor necrosis factor α up-regulates Giα and Gß proteins and adenylyl cyclase responsiveness in rat cardiomyocytes

Exposure of rat heart muscle cells to noradrenaline (1 microM) for 48 hr led to a decrease in the number of beta 1-adrenoceptors of 50% and a concomitant decrease in adenylyl cyclase stimulation by isoprenaline and forskolin of about 60 and 30%, respectively. In addition, the levels of two inhibitory guanine nucleotide-binding protein (Gi protein) alpha-subunits (Gi alpha 40 and Gi alpha 41) were increased in membranes of noradrenaline-treated cells. Evidence is presented that noradrenaline induces this increase by activation of beta-adrenoceptors. First, the noradrenaline action was mimicked by the beta-adrenoceptor agonist isoprenaline. Second, beta-adrenoceptor blockade by timolol but not alpha-adrenoceptor blockade by prazosin prevented the noradrenaline-induced up-regulation of Gi alpha proteins. Furthermore, timolol but not prazosin abolished the noradrenaline-induced down-regulation of beta 1-adrenoceptors and the decreases in receptor-dependent (isoprenaline) and -independent (forskolin) adenylyl cyclase stimulation. The specific protein synthesis inhibitor Pseudomonas exotoxin A was used to study whether the noradrenaline-induced up-regulation of Gi alpha subunits depends on increased synthesis of these proteins. This toxin inhibits peptide chain elongation by ADP-ribosylating elongation factor 2. Treatment of rat heart muscle cells with Pseudomonas exotoxin A (1 ng/ml) completely prevented the noradrenaline-induced increase in Gi alpha proteins, measured by both pertussis toxin-catalyzed ADP-ribosylation and immunoblotting with anti-Gi alpha antibodies. Most importantly, Pseudomonas exotoxin A also completely prevented the noradrenaline-induced decrease in forskolin-stimulated adenylyl cyclase activity. Furthermore, the noradrenaline-induced decrease in isoprenaline-stimulated adenylyl cyclase activity was significantly attenuated by the toxin, although the down-regulation of beta 1-adrenoceptors caused by noradrenaline treatment was not affected. The data presented suggest that prolonged activation of beta-adrenoceptors in rat heart muscle cells, in addition to causing a receptor down-regulation, induces the synthesis of Gi alpha proteins, which then apparently mediate a decreased adenylyl cyclase responsiveness. The data, additionally, suggest that the synthesis of Gi alpha proteins is under control of the activity of the adenylyl cyclase system and that altered levels of these proteins may play a major role in long term regulation of signal transduction by this enzyme.

Pseudomonas exotoxin A prevents beta-adrenoceptor-induced upregulation of Gi protein alpha-subunits and adenylyl cyclase desensitization in rat heart muscle cells.

This text is about the molecular mechanisms underlying septic cardiomyopathy, a main feature of septic shock and multiple organ dysfunction syndrome, which are the leading causes of death in intensive care patients. Cytokines play an important pathogenetic role in this myocardial depression, with septic cardiomyopathy being the cardiac disease entity, where knowledge about cytokine action on the heart has most accumulated.

Cytokines and the heart : molecular mechanisms of septic cardiomyopathy

Prolonged exposure of cells to adenylyl cyclase stimulatory hormonal factors can cause an increase in the level of membrane inhibitory G protein (Gi) α-subunits, while inhibitory receptor agonists have been reported to induce the opposite response. As studied in cultured rat cardiomyocytes, the β-adrenoceptor-induced increase in the level of Giα proteins is protein synthesis-dependent, is apparently not accompanied by an increase in G protein β-subunits and results in a decreased adenylyl cyclase responsiveness. On the other hand, a decrease in Giα level apparently results in sensitization of adenylyl cyclase stimulation. These data suggest that the up- or down-regulation of the level and activity of Gi protein α-subunits is a rather general cellular response, providing an intracellular negative feedback control against prolonged receptor activation.

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C. Reithmann

Papers

Mechanism of noradrenaline-induced heterologous desensitization of adenylate cyclase stimulation in rat heart muscle cells: increase in the level of inhibitory G-protein α-subunits

Tumor necrosis factor α up-regulates Giα and Gß proteins and adenylyl cyclase responsiveness in rat cardiomyocytes

Pseudomonas exotoxin A prevents beta-adrenoceptor-induced upregulation of Gi protein alpha-subunits and adenylyl cyclase desensitization in rat heart muscle cells.

Cytokines and the heart : molecular mechanisms of septic cardiomyopathy

Hormonal regulation of Gi alpha level and adenylyl cyclase responsiveness.