Left Ventricular Remodeling in Transgenic Mice With Cardiac Restricted Overexpression of Tumor Necrosis Factor

Abstract

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.

Transforming growth factor-β receptor antagonism attenuates myocardial fibrosis in mice with cardiac-restricted overexpression of tumor necrosis factor

“…The characterization of the MHCsTNF mice used in these studies has been reported previously. 1,11 Briefly, MHCsTNF mice develop progressive myocardial fibrosis from 8-12 weeks of age that is characterized by increased levels of TGFβ1 and TGFβ2 mRNA and protein. 1 All mice housed under standard environmental conditions and maintained on commercial chow and tap water ad libitum.…”

“…1,11 Briefly, MHCsTNF mice develop progressive myocardial fibrosis from 8-12 weeks of age that is characterized by increased levels of TGFβ1 and TGFβ2 mRNA and protein. 1 All mice housed under standard environmental conditions and maintained on commercial chow and tap water ad libitum. All studies conformed with the principles of the National Institutes of Health "Guide for the Care and Use of Laboratory Animals," and were approved by the Baylor College of Medicine Animal Care and Use Committee.…”

“…1 Myocardial collagen content was determined using the picrosirius red technique, as described. 1 Briefly, after completing the ex vivo studies described below, hearts were perfusion-fixed, embedded in paraffin and stained.…”

“…1 Myocardial collagen content was determined using the picrosirius red technique, as described. 1 Briefly, after completing the ex vivo studies described below, hearts were perfusion-fixed, embedded in paraffin and stained. The percent area of extracellular picrosirius red staining was computed from 3 random fields within the mid-myocardium in order to exclude large epicardial arteries and/ or veins, as well as any cutting and/or compression artifacts.…”

“…[1][2][3] Although the progressive LV dilation in these mice has been attributed to TNFinduced activation of matrix metalloproteinases (MMPs) with subsequent degradation of fibrillar collagen, the mechanisms that are responsible for the progressive myocardial fibrosis that accrues in these mice is not all understood. Given that TNF inhibits collagen gene expression and/or collagen synthesis in cardiac fibroblasts, 4,5 the increased myocardial fibrosis observed in the transgenic models with cardiac restricted overexpression of TNF is unlikely to be a direct effect of TNF-mediated signaling.…”