Abstract 3739: Aggravated Myocardial Damage in Lectin-like Domain Deficient Thrombomodulin Mice is Mediated by HMGB1
Background: Cardiac failure due to adverse myocardial remodelling is a frequent cause of cardiovascular morbidity and mortality. We demonstrated that thrombomodulin (TM), through its anti-inflammatory lectin-like domain (LLD) is a powerful cardioprotective molecule, possibly by scavenging the pro-inflammatory cytokine HMGB1. HMGB1’s role in cardiac inflammation and remodelling is controversial. Using a knock-in mouse lacking the LLD of TM (TMLeD/LeD) and an in vitro model of cardiomyocyte hypoxia, we examined the role of HMGB1 in ischemia with reperfusion and apoptosis.
Methods: Wildtype (WT)-, TMLeD/LeD- and WT-mice with systemic over expression of LLD by hydrodynamic transfection (HDTF) were subjected to transient (30 min; MI/R) LAD-ligation. Infarct size, HMGB1 expression and apoptosis were analyzed. Neonatal rat cardiomyocytes were transfected with siRNA to TLR-2 and TLR-4 and exposed to hypoxia (0,8 % 02). Apoptosis was quantitated on TUNEL-stainings. Non-parametric tests detected differences at p<0.05.
Results: Infarctions (24h) were 30% larger in TMLeD/LeD- compared to WT-mice (n=8, p<0.01) accompanied by increased levels of HMGB1 protein (173±18% vs. 92±20%, TMLeD/LeD vs WT, n=9, p<0.05). In contrast, circulating LLD reduced infarcts by 60% (n=6, p<0.01) and HMGB1 to 36% (p<0.05). Significantly more apoptosis was detected in post-ischemic areas of TMLeD/LeD- vs. WT (120±25 vs, 28±7 TUNEL-positive cells/mm2, n=5, p<0.01). In vitro, HMGB1 increased hypoxia-induced cardiomyocyte apoptosis by 28% (n=15, p<0.01) whereas this effect was not detectable in TLR-2 siRNA treated cells. (n=5, p<0.05)
Conclusions: HMGB1 expression and cardiomyocyte apoptosis are increased in TMLeD/LeD-mice. In vitro HMGB1 shows a pro-apoptotic effect on hypoxia-induced apoptosis, which is mediated by TLR-2. HMGB-1-antagonistic or LLD-agonistic strategies are therefore promising therapeutic strategies to prevent cardiomyocyte death.