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RATIONALE: The myeloid differentiation factor (MyD)88/interleukin (IL)-1 axis activates self-antigen-presenting cells and promotes autoreactive CD4(+) T-cell expansion in experimental autoimmune myocarditis, a mouse model of inflammatory heart disease. OBJECTIVE: The aim of this study was to determine the role of MyD88 and IL-1 in the progression of acute myocarditis to an end-stage heart failure. METHODS AND RESULTS: Using alpha-myosin heavy chain peptide (MyHC-alpha)-loaded, activated dendritic cells, we induced myocarditis in wild-type and MyD88(-/-) mice with similar distributions of heart-infiltrating cell subsets and comparable CD4(+) T-cell responses. Injection of complete Freund's adjuvant (CFA) or MyHC-alpha/CFA into diseased mice promoted cardiac fibrosis, induced ventricular dilation, and impaired heart function in wild-type but not in MyD88(-/-) mice. Experiments with chimeric mice confirmed the bone marrow origin of the fibroblasts replacing inflammatory infiltrates and showed that MyD88 and IL-1 receptor type I signaling on bone marrow-derived cells was critical for development of cardiac fibrosis during progression to heart failure. CONCLUSIONS: Our findings indicate a critical role of MyD88/IL-1 signaling in the bone marrow compartment in postinflammatory cardiac fibrosis and heart failure and point to novel therapeutic strategies against inflammatory cardiomyopathy.

BACKGROUND: Hypercholesterolemia-induced endothelial dysfunction due to excessive production of reactive oxygen species is a major trigger of atherogenesis. The c-Jun-N-terminal kinases (JNKs) are activated by oxidative stress and play a key role in atherogenesis and inflammation. We investigated whether JNK2 deletion protects from hypercholesterolemia-induced endothelial dysfunction and oxidative stress. METHODS AND RESULTS: Male JNK2 knockout (JNK2(-/-)) and wild-type (WT) mice (8 weeks old) were fed either a high-cholesterol diet (HCD; 1.25% total cholesterol) or a normal diet for 14 weeks. Aortic lysates of WT mice fed a HCD showed an increase in JNK phosphorylation compared with WT mice fed a normal diet (P<0.05). Endothelium-dependent relaxations to acetylcholine were impaired in WT HCD mice (P<0.05 versus WT normal diet). In contrast, JNK2(-/-) HCD mice did not exhibit endothelial dysfunction (96+/-5% maximal relaxation in response to acetylcholine; P<0.05 versus WT HCD). Endothelium-independent relaxations were identical in all groups. A hypercholesterolemia-induced decrease in nitric oxide (NO) release of endothelial cells was found in WT but not in JNK2(-/-) mice. In parallel, endothelial NO synthase expression was upregulated only in JNK2(-/-) HCD animals, whereas the expression of antioxidant defense systems such as extracellular superoxide dismutase and manganese superoxide dismutase was decreased in WT but not in JNK2(-/-) HCD mice. In contrast to JNK2(-/-) mice, WT HCD displayed an increase in O(2)(-) and ONOO(-) concentrations as well as nitrotyrosine staining and peroxidation. CONCLUSIONS: JNK2 plays a critical role as a mediator of hypercholesterolemia-induced endothelial dysfunction and oxidative stress. Thus, JNK2 may provide a novel target for prevention of vascular disease and atherosclerosis.