Gender Differences In Cardiomyocyte Adhesion Cause Heart Failure

While several factors, including inflammatory cytokines, have been shown to be involved in the pathogenesis of ventricular dilatation, precisely how these events are interrelated has not been forthcoming. We recently reported that β1 integrin‐mediated adhesion of cardiac myocytes to extracellular matrix components in the heart is significantly reduced initially following imposition of a chronic volume overload. This disruption of cardiomyocyte adhesion preceded ventricular dilatation, however, the mechanism mediating the altered adhesion has not yet been established. One potential mechanism is significantly elevated levels of myocardial tumor necrosis factor‐α (TNF‐α) reported during the first week in male and ovariectomized female rats in the aortocaval (AV) fistula model of chronic volume overload. This study sought to test the hypothesis that pathophysiologic levels of TNF‐α produce ventricular dilatation by significantly reducing adhesion of cardiomyocytes to the extracellular matrix. Further, we sought to determine if this might be responsible for the gender related cardioprotection in this model of heart failure. Accordingly, adult male Sprague‐Dawley rats were continuously infused with TNF‐α for 3 days via subcutaneously implanted osmotic minipump (2.5 μg/kg/hr, Alzet model 2002, Alza Corp, Mountain View, CA). This rate of infusion resulted in systemic TNF‐α levels of 17 ± 6.3 pg/ml of serum comparable to that reported in patients with heart failure. Left ventricular cardiomyocytes were isolated and their adhesion to laminin were compared to an age matched, male control group. The infusion of TNF‐α for 3 days in male rats significantly decreased cardiomyocyte adhesion to laminin from 40.3 ± 3.0 to 27.1 ± 3.2% (p<0.05). In a subsequent study the acute effect of TNF‐α incubation (0 or 50 ng/ml for 30 min) on adhesion of isolated adult rat cardiomyocytes to laminin was determined at 3 days post‐fistula in intact female and ovariectomized rats and compared to sham‐operated control. Additional aliquots of cardiomyocytes were pretreated with the Src kinase inhibitor 4‐amino‐5‐(4‐chlorophenyl)‐7‐(t‐butyl)pyrazolo[3,4‐d]pyrimidine (PP2) or the p38 MAPK inhibitor, SB203580. Cardiomyocyte adhesion to laminin in the TNF‐α treated cells was significantly decreased relative to that of the untreated cells (P<0.001). The reduction in cardiomyocyte adhesion induced by TNF‐α was reversed by the Src kinase inhibitor, but not by the p38 MAPK pathway inhibitor. In addition to inhibiting cardiomyocyte adhesion, TNF‐α induced significant Src kinase activation, reflected by concurrent dephosphorylation of the inhibitory tyrosine, y529, and a 30% increase in Y418 phosphorylation. These observations demonstrate that TNF‐α produces a marked decrease in cardiomyocyte adhesion to the extracellular matrix component laminin, highlighting a novel mechanism contributing to the development of ventricular dilatation. Furthermore, this study implicates suppression of TNF‐α signal transduction as the mechanism by which estrogen prevents adverse myocardial remodeling. The findings also suggest that the effects of TNF‐α on cardiomyocyte adhesion are likely mediated via Src kinase activation. If this proves to be true, interventions directed at preserving cardiomyocyte adhesion represent a novel approach to prevent ventricular dilatation and the development of heart failure. Support or Funding Information This study was supported in part by NIH National Heart, Lung and Blood Institute grants HL73990 and HL62228.The effect of TNF‐α on adhesion of cardiomyocytes isolated from intact females (F) and ovariectomized (OX) rats post‐fistula and Sham‐operated groups. TNF‐α treatment significantly reduced the percentage of isolated cardiomyocytes adhering to laminin coated plates relative to the corresponding untreated control cells in the intact sham and fistula groups but not in the OX group (n = 5 hearts/group). ** = P<0.01; NS = non significant