The endothelial nitric oxide synthase (eNOS) contributes to cardiac remodelling. We studied the role of eNOS in the development of myocardial fibrosis during cardiac overload.

Ten-week-old male C57/Bl6 wildtype (WT) and eNOS mice (eNOS^−/−) were subjected to transverse aortic constriction (TAC, 360 μm) and WT were treated with l-N^G-nitroarginine methyl ester (l-NAME, 100 mg/kg/day) for 35 days. Inhibition of eNOS by l-NAME induced interstitial fibrosis, augmented replacement fibrosis, and induced apoptosis of cardiac fibroblasts and cardiomyocytes. l-NAME and eNOS^−/− markedly increased the fibrosis induced by TAC and enhanced the myocardial prevalence of CXCR4^pos fibroblasts. Myocardial stromal-derived factor-1 (SDF-1) expression was up-regulated by l-NAME and down-regulated after TAC. Blood pressure lowering by co-treatment with hydralazine (250 mg/L/day) did not reverse the l-NAME effects.

In mice transplanted with green fluorescent protein (GFP)^pos bone marrow, l-NAME increased the percentage of GFP^pos fibroblasts in the myocardium to 45–70%. Strain-mismatched BMT of eNOS^−/−-BM increased and of WT-BM decreased the percentage of CXCR4^pos fibroblasts in all groups. The number of fibrocytes (CD45^pos collagen I^pos cells) in the peripheral blood and in the bone marrow was increased both by TAC and l-NAME. l-NAME but not the inhibitor of inducible NOS 1400 W and of neuronal NOS 7-nitroindazole increased hydroxyproline and collagen Iα1. l-NAME up-regulated SDF-1 mRNA in cultured neonatal rat cardiac fibroblasts as well as their migratory capacity.

eNOS inhibition induces and enhances cardiac fibrosis independently of blood pressure by activating SDF-1/CXCR4, extracellular matrix production in cardiac fibroblasts and by increasing recruitment of fibrocytes from the bone marrow.