Cardiac remodeling and inflammation are hallmarks of cardiac failure and correlate with outcome in patients. However, the basis for the development of both remains unclear. We have previously reported that cardiac inflammation triggers transdifferentiation of fibroblasts to myofibroblasts and therefore increase accumulation of cardiac collagen, one key pathology in cardiac remodeling. Hence, identifying key pathways for inflammation would be beneficial for patients suffering from heart failure also. Besides their well-characterized function in matrix regulation, we here investigate the role of fibroblasts in the inflammatory process. We address for the first time the role of fibroblasts as inflammatory supporter cells in heart failure. Using endomyocardial biopsies from patients with heart failure and dilated cardiomyopathy, we created a primary human cardiac fibroblast cell culture system. We found that mechanical stretch mimicking cardiac dilation in heart failure induces activation of fibroblasts and not only stimulates production of extracellular matrix but more interestingly up-regulates chemokine production and triggers typical inflammatory pathways in vitro. Moreover, the cell culture supernatant of stretched fibroblasts activates inflammatory cells and induces further recruitment of monocytes by allowing transendothelial migration into the cardiac tissue. Our findings reveal that cardiac fibroblasts provide pro-inflammatory mediators and may act as sentinel cells activated by mechanical stress. Those cells are able to recruit inflammatory cells into the cardiac tissue, a process known to aggravate outcome of patients. This might be important in different forms of heart failure and therefore may be one general mechanism specific for fibroblasts.

Fibroblasts are widely distributed cells and are responsible for the deposition of extracellular matrix (ECM) components but also secrete ECM-degrading matrix metalloproteases. A finely balanced equilibrium between deposition and degradation of ECM is essential for structural integrity of tissues. In the past, fibroblasts have typically been understood as a uniform cell population with comparable functions regardless of their origin. Here, we determined growth curves of fibroblasts derived from heart, skin, and lung and clearly show the lowest proliferation rate for cardiac fibroblasts. Furthermore, we examined basal expression levels of collagen and different MMPs in these three types of fibroblasts and compared these concerning their site of origin. Interestingly, we found major differences in basal mRNA expression especially for MMP1 and MMP3. Moreover, we treated fibroblasts with TNF-α and observed different alterations under these proinflammatory conditions. In conclusion, fibroblasts show different properties in proliferation and MMP expression regarding their originated tissue.

TRIF is a member of the innate immune system known to be involved in viral recognition and type I IFN activation. Because IFNs are thought to play an important role in viral myocarditis, we investigated the role of TRIF in induced myocarditis in mice. Whereas C57BL/6 (wild-type) mice showed only mild myocarditis, including normal survival postinfection with coxsackievirus group B serotype 3 (CVB3), infection of TRIF−/− mice led to the induction of cardiac remodeling, severe heart failure, and 100% mortality (p < 0.0001). These mice showed markedly reduced virus control in cardiac tissues and cardiomyocytes. This was accompained with dynamic cardiac cytokine activation in the heart, including a suppression of the antiviral cytokine IFN-β in the early viremic phase. TRIF−/− myocytes displayed a TLR4-dependent suppression of IFN-β, and pharmacological treatment of CVB3-infected TRIF−/− mice with murine IFN-β led to improved virus control and reduced cardiac inflammation. Additionally, this treatment within the viremic phase of myocarditis showed a significant long-term outcome indexed by reduced mortality (20 versus 100%; p < 0.001). TRIF is essential toward a cardioprotection against CVB3 infection.

Background-Myocarditis is an important cause for cardiac failure, especially in younger patients, followed by the development of cardiac dysfunction and death. The present study investigated whether gene deletion of matrix metalloproteinase-2 influences cardiac inflammation and function in murine coxsackievirus B3 (CVB3)-induced myocarditis. Methods and Results-Matrix metalloproteinase-2 knockout mice (MMP-2