Abstract 3816: Endothelial Nitric Oxide Synthase of the Bone Marrow Regulates Cardiac Angiogenesis in Pressure Overload
Introduction: Cardiac pressure overload induces the release of bone marrow derived vascular progenitor cells. The endothelial nitric oxide synthase (eNOS) regulates the mobilisation and function of endothelial progenitor cells (EPC).
Hypothesis: ENOS in the bone marrow regulates myocardial repair processes in the setting of cardiac pressure overload.
Methods and Results: After lethal irradiation, C57Bl/6 mice received eNOS−/− (BM−) bone marrow and eNOS−/− mice received wildtype bone marrow (BM+). 4 weeks after transplantation, pressure overload was induced by transaortic constriction (TAC, 360 μm for 35 days; n=10 –15 per group). Compared to sham surgery (S), elevated left ventricular pressure by TAC was diminished in mice receiving eNOS−/− bone marrow. Transplantation of eNOS−/− bone marrow enhanced cardiac hypertrophy but not cardiomyocyte size. While TAC did not change cardiac capillary density (ratio of CD31+ cells per cardiomyocytes), animals with eNOS−/− bone marrow showed significantly reduced capillarization (S-BM− 0.9±0.1, TAC-BM− 1±0.1, S-BM+ 1.3±0.1, TAC-BM+ 1.3±0.1; TAC vs S n.s., BM+ vs BM− p<0.01). Mice receiving eNOS−/− bone marrow showed less EPC in the peripheral blood independent of pressure overload ([EPC per 10 000 cells] S-BM− 204±19, TAC-BM− 205±21, S-BM+309±25, TAC-BM+312±16; TAC vs S n.s., BM+ vs BM-p<0.001). The migratory capacity of DiLDL+/Lectin+ EPC in the Boyden chamber was reduced after TAC and was further downregulated in mice with eNOS−/− bone marrow ([cells per 0.3 cm2] S-BM− 127±7, TAC-BM− 107±7, S-BM+ 202±22, TAC-BM+ 128±9; TAC vs S p<0.001, BM+ vs BM− p<0.001). Following transplantation of green fluorescent protein positive (GFP) bone marrow in wildtype (WT-GFP) and in eNOS−/− mice (eNOS−/− GFP), TAC increased the number of bone marrow derived endothelial cells in the myocardium, but there was no difference between wildtype and eNOS−/− mice ([%] S-WT-GFP 2.4±0.4, S-eNOS−/−GFP 1.7±0.6, TAC-WT-GFP 7.7±1.4, TAC-eNOS−/− GFP 4.4±0.9; TAC vs S p<0.01, WT vs eNOS−/− n.s.).
Conclusions: eNOS of the bone marrow but not of the extramedullar tissue plays a key role for amelioration of cardiac capillarization by bone marrow derived endothelial cells.