Background-Activation of both type 1 and type 2 tumor necrosis factor (TNF) receptors (TNFR1 and TNFR2) confers cytoprotection in cardiac myocytes. Noting that the scaffolding protein TNF receptor-associated factor 2 (TRAF2) is common to both TNF receptors, we hypothesized that the cytoprotective responses of TNF were mediated through TRAF2. Methods and Results-Mice with cardiac-restricted overexpression of low levels of TNF (MHCsTNF 3 ) and TRAF2(MHC-TRAF2 LC ) and mice lacking TNFR1, TNFR2, and TNFR1/TNFR2 were subjected to ischemia (30 minutes) reperfusion (30 minutes) injury ex vivo using a Langendorff apparatus. MHCsTNF 3 mice were protected against ischemia-reperfusion injury as shown by a significant Ϸ30% greater left ventricular developed pressure, Ϸ80% lower creatine kinase release, and Evans blue dye uptake compared with littermates. The extent of ischemia-reperfusion induced injury was similar in wild-type, TNFR1, and TNFR2 deficient mice; however, mice lacking TNFR1/TNFR2 had a significant Ϸ40% lower left ventricular developed pressure, a Ϸ65% greater creatine kinase release, and Ϸ40% greater Evans blue dye uptake compared with littermates. Interestingly, MHC-TRAF2 LC mice had a significant Ϸ50% lower left ventricular developed pressure, a Ϸ70% lower creatine kinase release, and Ϸ80% lower Evans blue dye uptake compared with littermate controls after ischemia-reperfusion injury. Biochemical analysis of the MHC-TRAF2 LC hearts showed that there was activation of nuclear factor-kappaB but not c-Jun N-terminal kinase activation. Conclusion-Taken together, these results suggest that TNF confers cytoprotection in the heart through TRAF2-mediated activation of nuclear factor-B. (Circ Heart Fail. 2010;3:157-164.)
Background Transgenic mice with cardiac restricted overexpression of tumor necrosis factor (MHCsTNF mice) develop progressive myocardial fibrosis, diastolic dysfunction and adverse cardiac remodeling. Insofar as tumor necrosis factor (TNF) does not directly stimulate fibroblast collagen synthesis, we asked whether TNF-induced fibrosis was mediated indirectly through interactions between mast cells and cardiac fibroblasts. Methods and Results Cardiac mast cell number increased 2–3-fold (p < 0.001) in MHCsTNF mice compared to littermate (LM) controls. Outcrossing MHCsTNF mice with mast cell deficient (c-kit−/−) mice showed that the 11-fold increase (p < 0.001) in collagen volume fraction in MHCsTNF/c-kit+/− mice was abrogated in MHCsTNF/c-kit−/− mice, and that the leftward shifted LV pressure-volume curve in the MHCsTNF/c-kit+/− mice was normalized in the MHCsTNF/c-kit−/− hearts. Furthermore, the increase in TGF-β1 and type I TGF-β receptor (TβR I) mRNA levels was significantly (p = 0.03, p = 0.01 respectively) attenuated in MHCsTNF/c-kit−/− when compared to MHCsTNF/c-kit+/− mice. Co-culture of fibroblasts with mast cells resulted in enhanced α-smooth muscle actin expression, increased proliferation and collagen mRNA expression, and increased contraction of 3-D collagen gels in MHCsTNF fibroblasts compared to LM fibroblasts. The effects of mast cells were abrogated by TβR I antagonist NP-40208. Conclusions These results suggest that increased mast cell density with resultant mast cell-cardiac fibroblast cross-talk is required for the development of myocardial fibrosis in inflammatory cardiomyopathy. Cardiac fibroblasts exposed to sustained inflammatory signaling exhibit an increased repertoire of pro-fibrotic phenotypic responses in response to mast cell mediators.
High-mobility group box 1 (HMGB1) released from necrotic cells or macrophages functions as a late inflammatory mediator and has been shown to induce cardiovascular collapse during sepsis. Thus far, however, the effect(s) of HMGB1 in the heart are not known. We determined the effects of HMGB1 on isolated feline cardiac myocytes by measuring sarcomere shortening in contracting cardiac myocytes, intracellular Ca2+ transients by using fluo-3, and L-type calcium currents by using whole cell perforate configuration of the patch-clamp technique. Treatment of isolated myocytes with HMGB1 (100 ng/ml) resulted in a 70% decrease in sarcomere shortening and a 50% decrease in the height of the peak Ca2+ transient within 5 min (P < 0.01). The immediate negative inotropic effects of HMGB1 on cell contractility and calcium homeostasis were partially reversible upon washout of HMGB1. A significant inhibition of the inward l-type calcium currents was also documented by the patch-clamp technique. HMGB1 induced the PKC-epsilon translocation, and a PKC inhibitor significantly attenuated the negative inotropic effects of HMGB1. These studies show for the first time that HMGB1 impairs sarcomere shortening by decreasing calcium availability in cardiac myocytes through modulating membrane calcium influx and suggest that HMGB1 maybe acts as a novel myocardial depressant factor during cardiac injury.
BackgroundWe have demonstrated that tumor necrosis factor (TNF) receptor‐associated factor 2 (TRAF2), a scaffolding protein common to TNF receptors 1 and 2, confers cytoprotection in the heart. However, the mechanisms for the cytoprotective effects of TRAF2 are not known.Methods/ResultsMice with cardiac‐restricted overexpression of low levels of TRAF2 (MHC‐TRAF2LC) and a dominant negative TRAF2 (MHC‐TRAF2DN) were subjected to ischemia (30‐minute) reperfusion (60‐minute) injury (I/R), using a Langendorff apparatus. MHC‐TRAF2LC mice were protected against I/R injury as shown by a significant ≈27% greater left ventricular (LV) developed pressure after I/R, whereas mice with impaired TRAF2 signaling had a significantly ≈38% lower LV developed pressure, a ≈41% greater creatine kinase (CK) release, and ≈52% greater Evans blue dye uptake after I/R, compared to LM. Transcriptional profiling of MHC‐TRAF2LC and MHC‐TRAF2DN mice identified a calcium‐triggered exocytotic membrane repair protein, dysferlin, as a potential cytoprotective gene responsible for the cytoprotective effects of TRAF2. Mice lacking dysferlin had a significant ≈39% lower LV developed pressure, a ≈20% greater CK release, and ≈29% greater Evans blue dye uptake after I/R, compared to wild‐type mice, thus phenocopying the response to tissue injury in the MHC‐TRAF2DN mice. Moreover, breeding MHC‐TRAF2LC onto a dysferlin‐null background significantly attenuated the cytoprotective effects of TRAF2 after I/R injury.ConclusionThe study shows that dysferlin, a calcium‐triggered exocytotic membrane repair protein, is required for the cytoprotective effects of TRAF2‐mediated signaling after I/R injury.
Background Tumor necrosis factor (TNF) superfamily ligands that provoke a dilated cardiac phenotype signal through a common scaffolding protein termed TNF receptor associated factor 2 (TRAF2); however, virtually nothing is known with regard to TRAF2 signaling in the adult mammalian heart. Methods and Results We generated multiple founder lines of mice with cardiac restricted overexpression of TRAF2 and characterized the phenotype of mice with higher expression levels of TRAF2 (MHC-TRAF2HC). MHC-TRAF2HC transgenic mice developed a time-dependent increase in cardiac hypertrophy, LV dilation and adverse LV remodeling, and a significant decrease in LV +dP/dt and −dP/dt when compared to littermate (LM) controls (p < 0.05 compared to LM). During the early phases of LV remodeling there was a significant increase in total matrix metalloproteinase (MMP) activity that corresponded with a decrease in total myocardial fibrillar collagen content. As the MHC-TRAF2HC mice aged, there was a significant decrease in total MMP activity accompanied by an increase in total fibrillar collagen content and an increase in myocardial tissue inhibitor of metalloproteinase-1 levels. There was a significant increase in NF-κB activation at 4 – 12 weeks and JNK activation at 4 weeks in the MHCs TRAF2HC mice. Transciptional profiling revealed that > 95% of the hypertrophic/dilated cardiomyopathy-related genes that were significantly upregulated genes in the MHC-TRAF2HC hearts contained κB elements in their promoters. Conclusions These results show for the first time that targeted overexpression of TRAF2 is sufficient to mediate adverse cardiac remodeling in the heart.
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