Attenuation of virus-induced myocardial injury by inhibition of the angiotensin II type 1 receptor signal and decreased nuclear factor-kappa B activation in knockout mice

Objectives This study examined the role of angiotensin II (Ang-II) in a murine model of viral myocarditis. Background Ang-II plays an important role in the pathophysiology of various cardiovascular disorders. However, the role of Ang-II in inflammatory heart diseases is not known. Methods Four-week-old wild-type (WT) and Ang-II type 1 receptor (AT1R) knockout (KO) mice were inoculated with the encephalomyocarditis virus (EMCV). Survival, histopathology, expression of proinflammatory cytokines, and activity of nuclear factor-kappa B (NF-kB) in the heart were examined. Results The 14-day survival was significantly increased in KO compared with WT mice. Histopathologic scores for myocardial necrosis (0.86 ± 0.69 vs. 2.44 ± 0.88, p < 0.01) and cellular infiltration (0.86 ± 0.38 vs. 2.33 ± 0.50, p < 0.01) were lower in KO than in WT mice. The expression of tumor necrosis factor-alpha (TNF-alpha) was increased 43.2-fold, that of interleukin-1-beta (IL-1-beta) 45.8-fold, and the activity of NF-kB 2.24-fold by EMCV inoculation in WT mice (each p < 0.01), but not in KO mice (5.9-fold, 6.3-fold, and 1.12-fold, respectively, each p = NS). The AT1R blocker also significantly attenuated the expression of proinflammatory cytokines and the activation of NF-kB in virus-inoculated WT mice. Intravenous Ang-II injection enhanced the activation of NF-kB (2.28-fold, p < 0.01) and increased the expression of TNF-alpha (2.31-fold, p < 0.01) and IL-1-beta (2.45-fold, p < 0.01) in heart tissue of WT but not KO mice. Conclusions These results indicate that the AT1R signal is obligatory for the development of virus-induced myocardial injury through the proinflammatory action of Ang-II via the NF-kB/cytokine pathway.