Myeloid differentiation factor-2 activates monocytes in patients with dilated cardiomyopathy.

Plasma levels of myeloid differentiation factor-2 (MD-2), a co-receptor of toll-like-receptor 4 (TLR4), independently predict mortality in patients with dilated cardiomyopathy (DCM). We tested whether monocyte activation by MD-2 contributes to immune activation and inflammatory status in DCM patients. We found increased MD-2 plasma levels in 25 patients with recent-onset DCM (1250 ± 80.7 ng/ml) compared to 25 age- and gender-matched healthy controls (793.4 ± 52.0 ng/ml; p < 0.001). Monocytes isolated from DCM patients showed a higher expression (141.7 ± 12.4%; p = 0.006 vs. controls) of the MD-2 encoding gene, LY96 and an increased NF-κB-activation. Further, the TLR4-activator lipopolysaccharide (LPS) caused a higher increase in interleukin (IL)-6 in monocytes from DCM patients compared to controls (mean fluorescence intensity: 938.7 ± 151.0 vs. 466.9 ± 51.1; p = 0.005). MD-2 increased IL-6 secretion in a TLR4/NF-κB-dependent manner in monocyte-like THP-1-cells as demonstrated by TLR4-siRNA and NF-κB-inhibition. Since endothelial cells (ECs) are responsible for recruiting monocytes to the site of inflammation, ECs were treated with MD-2 leading to an activation of Akt and increased secretion of monocyte-chemoattractant-protein-1 (MCP-1). Activation of ECs by MD-2 was accompanied by an increased expression of the adhesion molecules CD54, CD106 and CD62E, resulting in an increased monocyte recruitment, which was attenuated by CD54 inhibition. In addition, in murine WT but not LY96-KO bone marrow-derived macrophages LPS increased the amount of CD54 and CD49d/CD29. MD-2 facilitates a pro-inflammatory status of monocytes and EC-mediated monocyte recruitment via TLR4/NF-κB. Elevated MD-2 plasma levels are possibly involved in monocyte-related inflammation-promoting disease progression in DCM. Our results suggest that MD-2 contributes to increasing monocytic inflammatory activity and triggers the recruitment of monocytes to ECs in DCM.

High-Mobility Group Box Protein 1 Is an Independent Prognostic Marker for All-Cause Mortality in Patients With Dilated Cardiomyopathy.

High-mobility group box protein 1 (HMGB1) is released during tissue damage and activates the innate immune system through toll-like receptor 4. Because mortality in dilated cardiomyopathy (DCM) is associated with activation of the innate immune system, we hypothesized that HMGB1 possesses a prognostic value in estimating mortality in patients with DCM. We determined HMGB1 and N-terminal B-type natriuretic peptide (NT-proBNP) levels in 67 patients with DCM (12 women, mean age 53.6 ± 1.5 years). Kaplan-Meier analyzes revealed that higher levels of HMGB1 and NT-proBNP are related to increased all-cause mortality. Multivariable Cox regression confirmed HMGB1 as a risk factor for mortality in patients with DCM, independent of NT-proBNP, age, and gender (hazard ratio per 1 SD 1.920, 95% confidence interval 1.401 to 2.631, p <0.001). HMGB1 is a promising candidate to estimate the prognosis of patients with DCM.