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Endogenous circulation of bone marrow-derived cells (BMCs) was observed in patients with dilated cardiomyopathy (DCM) who showed cardiac upregulation of Vascular Cell Adhesion Protein-1 (VCAM-1). However, the underlying pathophysiology is currently unknown. Thus, we aimed to analyze circulation, migration and G-CSF-based mobilization of BMCs in a murine model of virus-induced DCM. Mice with coxsackievirus B3 (CVB3) induced DCM and healthy controls were analyzed regarding their myocardial homing factors by PCR. To determine cardiac VCAM-1 expression ELISA and immunohistochemistry were applied. Flow cytometry was performed to analyze BMCs. Cardiac diameters and function were evaluated by echocardiography before and 4 weeks after G-CSF treatment. In murine CVB3-induced DCM an increase of BMCs in peripheral blood and a decrease of BMCs in bone marrow was observed. We found an enhanced migration of Very Late Antigen-4 (VLA-4⁺) BMCs to the diseased heart overexpressing VCAM-1 and higher numbers of CD45⁻CD34⁻Sca-1⁺ and CD45⁻CD34⁻c-kit⁺ cells. Mobilization of BMCs by G-CSF boosted migration along the VCAM-1/VLA-4 axis and reduced apoptosis of cardiomyocytes. Significant improvement of cardiac function was detected by echocardiography in G-CSF-treated mice. Blocking VCAM-1 by a neutralizing antibody reduced the G-CSF-dependent effects on stem cell migration and cardiac function. This is the first study showing that in virus-induced DCM VCAM-1/VLA-4 interaction is crucial for recruitment of circulating BMCs leading to beneficial anti-apoptotic effects resulting in improved cardiac function after G-CSF-induced mobilization.

Objective : Recently, it was shown that the physiologic repair mechanism of mobilization and homing of bone marrow-derived stem cells (BMCs) is impaired in dilated cardiomyopathy. In our study we aimed to analyze circulation and homing of CD34 + progenitor cell populations in a murine model of dilated cardiomyopathy due to coxsackie virus B3 (CVB3) induced myocarditis and the influence of G-CSF treatment on BMC homing and cardiac function. Methods and Results : First, SWR/J (H-2q)-mice were infected by intraperitoneal injection of 10 5 pfu CVB3. Healthy, age-matched SWR/J (H-2q)-mice served as controls. 12 weeks after infection, DCM was verified by MRI/Millar-tip-catheter and histology. In DCM mice, CD34 + BMC populations (CD34 + CD31 + , CD34 + Sca-1 + , CD34 + c-kit + and CD34 + CXCR-4 + ) measured by flow cytometry were significantly increased in peripheral blood, decreased in bone marrow and remained unchanged in the hearts in comparison to controls. Different from ischemic heart diseases, myocardial homing factors (SDF-1, SCF, HIF-1a, VCAM and HGF) assessed by real-time PCR were not upregulated in the CVB3-DCM group. Finally, 18 DCM-CVB3 mice were analyzed by MRI 8 weeks after CVB3 infection and randomized into G-CSF-or saline-treatment (100 μg/20μl s.c. daily for 2× 5 days). 12 weeks after infection, cardiac function was assessed using MRI: Change of ejection fraction was significantly better in the G-CSF-group compared to the controls (4.1±1.8 vs. −2.5±2.2%; p=0.03). The improvement of cardiac function was associated with enhanced homing of BMC subpopulations. Conclusions : We have shown that postmyocarditic cardiomyopathy is associated with a reduced migration of BMCs to the cardiomyopathic hearts due to a lack of increase of homing factors. This defect can partly be overcome by G-CSF-administration resulting in an increased number of stem cells in the myocardium and leading to a moderately improved cardiac function. Therefore our data provides new insights in the pathogenesis of dilated cariomyopathy and presents a promising non-invasive approach to ameliorate heart failure.