Background-The mechanisms responsible for tumor necrosis factor (TNF)-induced LV structural remodeling in the adult heart are not known. Methods and Results-We generated a line of transgenic mice (MHCsTNF) with cardiac restricted overexpression of TNF that develop progressive LV dilation/remodeling from 4 to 12 weeks of age. During the early phases of LV structural remodeling, there was a significant increase in total matrix metalloproteinase (MMP) activity that corresponded to a decrease in total myocardial fibrillar collagen content. As the MHCsTNF mice aged, there was a significant decrease in total MMP zymographic activity that was accompanied by an increase in total fibrillar collagen content. The changes in total MMP activity and myocardial fibrillar collagen content were related to a time-dependent increase in myocardial tissue inhibitor of metalloproteinases (TIMP)-1 levels, resulting in a significant time-dependent decrease in the MMP activity/TIMP level ratio in the MHCsTNF mice. To determine a possible mechanism for the increase in myocardial fibrosis, we also measured levels of TGF-␤ 1 and TGF-␤ 2 protein levels, which were shown to be significantly elevated in the hearts of the MHCsTNF mice. Conclusions-Our results suggest that progressive time-dependent changes in the balance between MMP activity and TIMP activity are responsible, at least in part, for the spectrum of TNF-induced changes in the myofibrillar collagen content that occur during LV structural remodeling in the MHCsTNF mice.

Previous studies have shown that proinflammatory cytokines, such as tumor necrosis factor (TNF), are expressed after acute hemodynamic overloading and myocardial ischemia͞infarction. To define the role of TNF in the setting of ischemia͞infarction, we performed a series of acute coronary artery occlusions in mice lacking one or both TNF receptors. Left ventricular infarct size was assessed at 24 h after acute coronary occlusion by triphenyltetrazolium chloride (TTC) staining in wild-type (both TNF receptors present) and mice lacking either the type 1 (TNFR1), type 2 (TNFR2), or both TNF receptors (TNFR1͞TNFR2). Left ventricular infarct size as assessed by TTC staining was significantly greater (P < 0.005) in the TNFR1͞ TNFR2-deficient mice (77.2% ؎ 15.3%) when compared with either wild-type mice (46.8% ؎ 19.4%) or TNFR1-deficient (47.9% ؎ 10.6%) or TNFR2-deficient (41.6% ؎ 16.5%) mice. Examination of the extent of necrosis in wild-type and TNFR1͞TNFR2-deficient mice by anti-myosin Ab staining demonstrated no significant difference between groups; however, the peak frequency and extent of apoptosis were accelerated in the TNFR1͞TNFR2-deficient mice when compared with the wild-type mice. The increase in apoptosis in the TNFR1͞TNFR2-deficient mice did not appear to be secondary to a selective up-regulation of the Fas ligand͞receptor system in these mice. These data suggest that TNF signaling gives rise to one or more cytoprotective signals that prevent and͞or delay the development of cardiac myocyte apoptosis after acute ischemic injury.

Background-Proinflammatory cytokines play key roles in atherogenesis and disease progression. Because hyperhomocysteinemia is an independent risk factor for cardiovascular disease, we hypothesized that homocysteine could be atherogenic by altering the expression of specific cytokines in vascular endothelial cells. Methods and Results-Northern blot and RNase protection assays showed that DL-homocysteine induced mRNA expression of the proinflammatory cytokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) in cultured human aortic endothelial cells (HAECs). Homocysteine had no effect on expression of other cytokines, namely tumor necrosis factor-␣, granulocyte-macrophage colony-stimulating factor, interleukin-1␤, and transforming growth factor-␤. MCP-1 mRNA expression increased 1 hour after homocysteine treatment, reached a maximum within 2 to 4 hours, and declined to basal levels over the next 24 hours. Induction of mRNA expression for both chemokines was observed with as little as 10 mol/L DL-homocysteine, and maximal expression was achieved with 50 mol/L DL-homocysteine. Homocysteine also triggered the release of MCP-1 and IL-8 protein from HAECs into the culture medium. The induction was specific for homocysteine, because equimolar concentrations of L-homocystine, L-cysteine, and L-methionine had no effect on mRNA levels and protein release. Furthermore, L-homocysteine induced chemokine expression, but D-homocysteine did not, thus demonstrating enantiomeric specificity. The culture medium from homocysteine-treated HAECs promoted chemotaxis in human peripheral blood monocytes and U937 cells. Anti-human recombinant MCP-1 antibody blocked the migration. Conclusions-Pathophysiological levels of L-homocysteine alter endothelial cell function by upregulating MCP-1 and IL-8 expression and secretion. This suggests that L-homocysteine may contribute to the initiation and progression of vascular disease by promoting leukocyte recruitment.