Circulating NOS3 modulates left ventricular remodeling following reperfused myocardial infarction.

Purpose: Nitric oxide (NO) is constitutively produced and released from the endothelium and several blood cell types by the isoform 3 of the NO synthase (NOS3). We have shown that NO protects against myocardial ischemia/reperfusion (I/R) injury and that depletion of circulating NOS3 increases within 24 h of ischemia/reperfusion the size of myocardial infarction (MI) in chimeric mice devoid of circulating NOS3. In the current study we hypothesized that circulating NOS3 also affects remodeling of the left ventricle following reperfused MI.

Methods: To analyze the role of circulating NOS3 we transplanted bone marrow of NOS3-/- and wild type (WT) mice into WT mice, producing chimerae expressing NOS3 only in vascular endothelium (BC-/EC+) or in both, blood cells and vascular endothelium (BC+/EC+). Both groups underwent 60 min of coronary occlusion in a closed-chest model of reperfused MI. During the 3 weeks post MI, structural and functional LV remodeling was serially assessed (24 h, 4 d, 1 w, 2 w and 3 w) by echocardiography. At 72 hours post MI, gene expression of several extracellular matrix (ECM) modifying molecules was determined by quantitative RT-PCR analysis. At 3 weeks post MI, hemodynamics were obtained by pressure catheter, scar size and collagen content were quantified post mortem by Gomori's One-step trichrome staining.

Results: Three weeks post MI, LV end-systolic (53.2±5.9 μl; ***p≤0.001; n = 5) and end-diastolic volumes (82.7±5.6 μl; *p<0.05; n = 5) were significantly increased in BC-/EC+, along with decreased LV developed pressure (67.5±1.8 mm Hg; n = 18; ***p≤0.001) and increased scar size/left ventricle (19.5±1.5%; n = 13; **p≤0.01) compared to BC+/EC+ (ESV: 35.6±2.2 μl; EDV: 69.1±2.6 μl n = 8; LVDP: 83.2±3.2 mm Hg; n = 24; scar size/LV13.8±0.7%; n = 16). Myocardial scar of BC-/EC+ was characterized by increased total collagen content (20.2±0.8%; n = 13; ***p≤0.001) compared to BC+/EC+ (15.9±0.5; n = 16), and increased collagen type I and III subtypes.

Conclusion: Circulating NOS3 ameliorates maladaptive left ventricular remodeling following reperfused myocardial infarction.