Abstract 185: Role of Lymphangiogenic Factors in a Murine Model of Viral Myocarditis
Background Recent reports have emphasized the important role of inflammation in the pathophysiology of cardiovascular diseases. Lymphatic system is important in immune responses. The vascular endothelial growth factor (VEGF)-C/VEGF-D/VEGF receptor (VEGFR)-3 signaling pathway is crucial for lymphangiogenesis. However, the roles of lymphatic vessels in myocardium remain unclear. This study was designed to examine the role of myocardial lymphangiogenesis in a murine model of viral myocarditis.
Methods and Results Four-week-old DBA/2 mice were inoculated with encephalomyocarditis virus (day 0). The hearts were fixed in 10% formalin, embedded in paraffin, sectioned, and analyzed, performing immunohisto-chemical staining on day 1, 3, 4, 5, 7, 9, 12, 14, 90. We used the antibodies against VEGFR-3 or podopranin, which is specific for lymphatic vessels. In addition, we examined the effects of VEGF-C156S, lymphangiogenesis inducer, or VEGFR3-Fc, lymphangiogenesis blocker, on myocardial injuries and hemodynamics in the same model, using adenoviruses gene transfer. Immunohistochemical staining for VEGFR-3 and podopranin resulted in successful labeling of lymphatic capillaries in myocardium. Lympahatic vessels appeared 3 days after viral inoculation. Lymphatic vessels were enlarged, and pericardium was strongly stained on day 7. In the subacute phase and chronic phase, lymphatic vessels were diffusely distributed in the fibrotic area. Lymphatic density and area increased from day 3 to chronic phase. The number of lymphatic vessels was about fourteen times (142 ± 12.3 on day 90 vs. 10.4 ± 1.9 vessels/mm2 on day3, p < 0.05) and lymphatic area was about fifteen times (9.1 ± 1.6 on day 90 vs. 0.6 ± 0.2 % on day3, p < 0.05) than those on day 3. VEGF-C156S and VEGFR3-Fc proteins were successfully expressed in myocardium. VEGFR3-Fc attenuated myocardial injuries, and improved hemodynamic parameters on day 14.
Conclusions Lymphatics related to the myocardial edema. These findings provide new insights into the role of myocardial lymphangiogenesis in the pathophysiology of viral myocarditis, and suggest therapeutic benefits by modulating lymphangiogenesis in viral myocarditis.