Left ventricular dilation in toll-like receptor 2 deficient mice after myocardial ischemia/reperfusion through defective scar formation

Restoration of myocardial blood flow after ischemia triggers an inflammatory response involving toll-like receptors (TLRs). TLR2−/−-mice show short-term advantages upon reperfusion injury as compared with WT controls. Accordingly, it has been shown that transient TLR2-blockade prior to reperfusion is associated with improved left-ventricular performance after myocardial scar formation. We present here adverse myocardial remodeling due to a chronic lack of TLR2 expression. Myocardial ischemia/reperfusion (MI/R) was surgically induced in C3HeN-mice by ligation of the left anterior descending coronary artery for 20 min, followed by 24 h or 28 days of reperfusion. TLR2−/−-mice and TLR2-Ab treated (T2.5) WT-mice displayed a reduction of infarct size, plasma troponin T concentrations, and leukocyte infiltration as compared with untreated controls after 24 h of reperfusion. After 28 days, however, magnetic resonance imaging revealed a marked left ventricular dilation in TLR2−/−-animals, which was associated with pronounced matrix remodeling characterized by reduced collagen and decorin density in the infarct scar. Our data show adverse effects on myocardial remodeling in TLR2−/−-mice. Although interception with TLR2 signaling is a promising concept for the prevention of reperfusion injury after myocardial ischemia, these data give cause for serious concern with respect to the time-point and duration of the potential treatment.