5952The involvement and interplay of HMGB1 with soluble MD-2 in dilated cardiomyopathy and its impact in immune cell recruitment

Objective Dilated cardiomyopathy (DCM) is characterized by systolic dysfunction and simultaneous dilatation of the left or both ventricles. Besides other causes, the innate immune system plays a major role in the development and progression of the disease. To uncover links between molecular mechanisms and disease progression our group has focused on the toll like receptor 4 / myeloid differentiation factor-2 (MD-2) system. Purpose We already reported that soluble MD-2 (sMD-2) is a risk factor for survival in patients with DCM. High mobility group box protein 1 (HMGB1) is a potent intrinsic interaction partner of MD-2. In the current study, we quantified HMGB-1 in plasma from patients with DCM at baseline, upon first hospital admission. Furthermore, we studied the impact of different HMGB-1 isoforms on monocyte adhesion in vitro. Methods We included 77 DCM patients divided by median time point of death after first hospital admission into “early death”, “late death” and “alive” group. MD-2 was quantified by means of ELISA. MD-2 and HMGB1 was quantified by means of ELISA. Statistical analysis was performed using a linear regression model. Human umbilical vein endothelial cells (HUVEC; n=6) were treated for 48h with two isoforms of HMGB1 (disulfide (ds) and fully reduced (fr)) alone and in combination with MD-2. Subsequently, those activated HUVEC were incubated with fresh isolated peripheral blood mononuclear cells (PBMCs) for 20 min. Finally, monocyte adhesion was quantified using multicolour FACS. Results At baseline, we found significantly increased sMD-2 level in the “early death” group (591.3±75.5 ng/ml) compared to the “later death” group (369.2±46.5 ng/ml; p=0.015) and the “alive” group (303.2±18.1 ng/ml; p<0.001). Likewise, we could demonstrate significantly increased levels of HMGB1 in the “early death” group (0.93±0.14 ng/ml) compared to the “later death” (0.57±0.17 ng/ml; p=0.04) and the “alive” group (0.49±0.06 ng/ml; p<0.001). In all patients who died during the observation period, sMD-2 and HMGB1 plasma levels showed a positive correlation. In vitro, we could demonstrate a significantly increased monocyte adhesion on HUVECs in the dsHMGB1 and the frHMGB1 group compared to controls (p=0.001; p=0.004). In contrast, the dsHMGB1 MD-2 group showed a significantly decreased monocyte adhesion on HUVECs compared to dsHMGB1 treatment alone (p=0.049). In the frHMGB1 MD-2 group, however, the reduction of the monocyte adhesion was less pronounced and did not reach significance (Fig. 1). Conclusion Our findings give a first hint that the interplay between HMGB1 and MD-2 is particularly involved in the development and progression of DCM. Furthermore, the data suggest that soluble MD-2 is capable of reducing the pro-inflammatory effects of dsHMGB1 but not of frHMGB1