718-2 Functional Effects of TNFα Gene Expression in the Heart

Abstract

TNFα, a proinflammatory cytokine, has been implicated in the pathogenesis of septic shock, viral myocarditis, and congestive heart failure. While the activated macrophage is thought to be the 1° source for TNFα production, a recent report showed that TNFα mRNA was expressed in the heart. However, the significance of this finding is not known. Accordingly, the purpose of this study was to determine: (1) which cell types in the heart produce TNFα mRNA and protein; and (2) whether the TNFα which is produced is active biologically. we stimulated isolated, buffer perfused cat hearts (n = 8) with lipopolysaccharide (LPS) — a classical stimulus for TNFα production; control hearts (n = 5) were stimulated with diluent. Northern blot analysis showed that mRNA for TNFα was detected within 30 min and peaked at 90 min after LPS stimulation; mRNA forTNFα was not detectable in control hearts. TNFα protein (> 500 U/ml) was detectable by bioassay 60 min after LPS treatment and peaked by 120 min; TNFα protein was not detectable in control hearts. TNFα contained in the effluent (1:2 dilution) from the LPS treated hearts produced negative inotropic effects in isolated contracting feline cardiac myocytes. Immunohistochemical studies of LPS treated hearts localized TNFα to the cardiac myocytes, endothelial cells and to vascular smooth muscle cells; control hearts were negative for TNFα immunostaining. Subsequent studies employing myocytes and non-myocyte cell types isolated from LPS stimulated hearts showed that TNFα mRNA and protein were produced by myocytes and non-myocytes. these data show for the first time that myocyte and non-myocyte cell types in the heart can rapidly produce biologically active TNFα which is capable of causing negative inotropic effects.