Myocarditis is an important cause of heart failure and sudden cardiac death especially in young adults. In the majority of cases myocarditis causes mild symptoms, while in 10-20% of cases myocarditis may lead to dilatative cardiomyopathy. As there are currently no specific therapies for these conditions, profound understanding of underlying pathomechanisms of myocarditis leading to dilatative cardiomyopathy is essential. Autoimmune reactions may cause myocarditis leading to heart failure and can be reproduced in the experimental autoimmune myocarditis (EAM) mouse model. Whereas A/J wt mice are susceptible for EAM, C57BL/6 wt mice however have a strain specific resistance towards developing an EAM after immunization with cardiac troponin I (TnI). Our preliminary work indicates that cardiac overexpression of murine lactate dehydrogenase subunit B (mLDHB) may protect susceptible A/J mice from developing of EAM. Therefore, we decided to study the effect of mLDHB knockout in C57BL/6 mice which are resistant in developing EAM.

Methods

C57BL/6 wt and mLDHBko male and female mice were immunized with cardiac troponin I peptide (TnI) or Complete Freuds Adjuvants (CFA) as control. Mice were immunized on days 0, 7, 14 and sacrificed on day 28. In order to characterize effects of immunization, heart sections of mice were examined using HE and Afog staining. To determine potential myocardial damage hsTnT levels (pg/ml) in mouse sera were analyzed and echocardiography as well as heart-to-body weight ratio were determined to characterize effects of subsequent heart failure. Successful knockout of mLDHB was demonstrated using western blot analysis. 

Results

Histopathological staining did not show any signs of myocardial inflammation or fibrosis in mLDHBko male and female mice after immunization with cardiac troponin I peptide. Congruously, no signs of impaired cardiac function were seen in echocardiography and hsTnT levels were not elevated. In summary, systemic knockout of mLDHB gene was not sufficient in overcoming the EAM resistance of both male and female C57BL/6 mice.