Dilated cardiomyopathy (DCM) as a consequence of viral
myocarditis is a worldwide cause of morbidity and death. The deposition of matrix
proteins, such as
collagen, in the course of ongoing viral
myocarditis results in cardiac remodeling and finally in cardiac
fibrosis, the hallmark of DCM. To identify mediators of virus-induced cardiac
fibrosis, microarray analysis was conducted in a murine model of chronic coxsackievirus B3 (CVB3)
myocarditis. By this attempt, we identified
connective tissue growth factor (CTGF) as a novel factor highly expressed in infected hearts. Further investigations by quantitative reverse transcription polymerase chain reaction and Western blot analysis confirmed a strong induction of cardiac CTGF expression in the course of CVB3
myocarditis. By in situ hybridization and immunohistochemistry, basal CTGF messenger
ribonucleic acid (
mRNA) and
protein expression were confined in noninfected control hearts mainly to endothelial cells, whereas in CVB3-infected hearts, also numerous fibroblasts were found to express CTGF. Regulation of CTGF is known to be basically mediated by
transforming growth factor (
TGF)-beta. In the course of CVB3
myocarditis, CTGF upregulation coincided with increased cardiac
TGF-beta and
procollagen type I mRNA expression, preceding the formation of fibrotic lesions. In in vitro experiments, we found that downregulation of CVB3 replication by means of small interfering RNAs (siRNAs) reverses the upregulation of CTGF
mRNA expression. In contrast, downregulation of CTGF by
siRNA molecules did not significantly reduce viral load, indicating that CTGF is not essential for CVB3 life cycle. The significantly enhanced transcript levels of
TGF-beta, CTGF, and
procollagen type I in cultivated CVB3-infected primary cardiac fibroblasts substantiate the role of fibroblasts as a relevant cell population in cardiac remodeling processes. We conclude that CTGF is a crucial molecule in the development of
fibrosis in ongoing enteroviral
myocarditis. Thus, downregulation of cardiac CTGF expression may open novel therapeutic approaches counteracting the development of cardiac
fibrosis and subsequent heart muscle dysfunction.