Carole S. Frye

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

The failing human heart expresses tumor necrosis factor-alpha (TNF-alpha). However, its pathophysiological significance is not clear. We previously reported that robust overexpression of TNF-alpha in the murine heart causes lethal myocarditis. In this study, we modified the transgene to reduce the production of TNF-alpha by preserving the destabilizing sequence in TNF-alpha cDNA. Expression was driven by the murine alpha-myosin heavy chain promoter. Use of this modified construct allowed to the establish a mutine 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-alpha 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 was significantly dilated with reduced ejection fraction. Although the left ventricular dP/dtmax was not different at baseline, its responsiveness to isoproterenol was significantly blunted in TG. Atrial natriuretic factor was expressed in the TG ventricle. A group of TG died spontaneously, and subsequent autopsies revealed exceptional dilation of the heart, increased lung weight, and pleural effusion, suggesting that they died of congestive heart failure. The cumulative mortality rate at 6 months was 23%. In conclusion, the mouse overexpressing TNF-alpha recapitulated the phenotype of congestive heart failure. This provides a novel model to elucidate the role of this cytokine in the development of congestive heart failure.

Cardiac-specific overexpression of tumor necrosis factor-alpha causes lethal myocarditis in transgenic mice

BACKGROUND Tumor necrosis factor (TNF)-alpha, a proinflammatory cytokine with negative inotropic effects, can be detected in myocardium with end-stage heart failure, after endotoxin administration, and during transplant rejection. Various studies suggest that TNF-alpha participates in the pathogenesis of cardiac dysfunction. To test this hypothesis, transgenic mice were made that selectively overexpress TNF-alpha in cardiomyocytes. METHODS AND RESULTS A transgene construct was made containing the murine alpha-myosin heavy chain promoter and the coding sequence of murine TNF-alpha, followed by the simian virus 40 T-antigen intron and polyadenylation signals. Injection of this construct into fertilized eggs yielded three transgenic mice, all of which died spontaneously before the completion of weaning. Gross pathologic analysis of these mice demonstrated a decrease in body weight with markedly increased heart weight. Histologic examination of the heart revealed a substantial, diffuse lymphohistiocytic inflammatory infiltrate, associated with interstitial edema. Reverse transcriptase polymerase chain reaction showed that the transgene was expressed in the heart. Enzyme-linked immunosorbent assay demonstrated a substantial amount of TNF-alpha protein in the transgenic heart. CONCLUSION Overexpression of TNF-alpha in the heart leads to severe myocarditis and cardiomegaly. These results support the hypothesis that myocardial expression of TNF-alpha can contribute to the pathogenesis of cardiac dysfunction.

Sex-related survival differences in murine cardiomyopathy are associated with differences in TNF-receptor expression.

Epidemiological evidence suggests that the prognosis of heart failure in women is better than in men. In our murine model of dilated cardiomyopathy arising from cardiac-specific overexpression of TNF-alpha, the 6-month survival rate was significantly better in females than in males. Young female transgenic mice exhibited left ventricular wall thickening without dilatation, whereas age-matched male transgenic hearts were markedly dilated. Basal and isoproterenol-stimulated fractional shortening was preserved in female transgenic mice, but not in male transgenic mice. Myocardial expression of proinflammatory cytokines and the extent of myocardial infiltrates were similar in male and female transgenic mice. Myocardial expression of TNF-receptor mRNAs (type I and type II) was significantly higher in male mice in both transgenic and wild-type littermates, whereas sex-specific differences were not observed in either peripheral white blood cells or liver tissue. After TNF-alpha challenge, myocardial but not liver production of ceramide was significantly higher in male than in female mice. Thus, differential expression of myocardial TNF receptors may contribute to sex differences in the severity of congestive heart failure and mortality consequent to cardiac-specific overexpression of TNF-alpha.

Interleukin-1β Inhibits Phospholamban Gene Expression in Cultured Cardiomyocytes

Phospholamban is a key regulatory protein that defines diastolic function. Proinflammatory cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) can depress contractility and intracellular Ca2+ currents and transients. An alteration in phospholamban expression is a possible pathway by which these cytokines modulate cardiac function. To test this hypothesis, primary cultures of neonatal rat cardiomyocytes were incubated with IL-1 beta, TNF-alpha, or both, and the level of phospholamban transcripts was examined by Northern blot analyses. Phospholamban transcript levels were decreased approximately equal to 50% (P < .0001) in cells exposed to 2 ng/mL IL-1 beta (20 hours), whereas TNF-alpha had no effect. Western blot analyses showed that IL-1 beta also reduced phospholamban protein levels (60% of control, P < .0001). The effects on transcript levels were gene specific; IL-1 beta induced transcripts for inducible NO synthase (iNOS), did not alter GAPDH transcripts, and reduced sarcoplasmic reticulum Ca(2+)-ATPase (65% of control, P < .001) transcripts. Cardiomyocytes treated with IL-1 beta showed no alterations in basal contractile parameters (maximum velocity of contraction and relaxation and maximal amplitude of contraction) but were unresponsive to beta-adrenergic stimulation. Studies performed in the presence of second-messenger inhibitors showed that the effect of IL-1 beta on phospholamban transcript levels was blocked by dexamethasone, was insensitive to inhibitors of iNOS, cyclooxygenase, or tyrosine kinases, but was enhanced by the addition of the protein kinase inhibitor staurosporine. These data demonstrate that IL-1 beta alters the expression of phospholamban, a key regulator of cardiac contractility, at both the transcript and protein levels. The results suggest novel mechanisms by which IL-1 beta may modify cardiac function.