Nitric oxide synthase 2 is required for conversion of pro-fibrogenic inflammatory CD133 progenitors into F4/80 macrophages in experimental autoimmune myocarditis

Experimental autoimmune myocarditis (EAM) model mirrors important mechanisms of inflammatory dilated cardiomyopathy (iDCM). In EAM, inflammatory CD133 progenitors are a major cellular source of cardiac myofibroblasts in the post-inflammatory myocardium. We hypothesized that exogenous delivery of macrophage-colony-stimulating factor (M-CSF) can stimulate macrophage lineage differentiation of inflammatory progenitors and, therefore, prevent their naturally occurring myofibroblast fate in EAM. EAM was induced in wild-type (BALB/c) and nitric oxide synthase 2-deficient (Nos2(/)) mice and CD133 progenitors were isolated from inflamed hearts. In vitro, M-CSF converted inflammatory CD133 progenitors into nitric oxide-producing F4/80 macrophages and prevented transforming growth factor--mediated myofibroblast differentiation. Importantly, only a subset of heart-infiltrating CD133 progenitors expresses macrophage-specific antigen F4/80 in EAM. These CD133/F4/80(hi) cells show impaired myofibrogenic potential compared with CD133/F4/80 cells. M-CSF treatment of wild-type mice with EAM at the peak of disease markedly increased CD133/F4/80(hi) cells in the myocardium, and CD133 progenitors isolated from M-CSF-treated mice failed to differentiate into myofibroblasts. In contrast, M-CSF was not effective in converting CD133 progenitors from inflamed hearts of Nos2(/) mice into macrophages, and M-CSF treatment did not result in increased CD133/F4/80(hi) cell population in hearts of Nos2(/) mice. Accordingly, M-CSF prevented post-inflammatory fibrosis and left ventricular dysfunction in wild-type but not in Nos2(/) mice. Active and NOS2-dependent induction of macrophage lineage differentiation abrogates the myofibrogenic potential of heart-infiltrating CD133 progenitors. Modulating the in vivo differentiation fate of specific progenitors might become a novel approach for the treatment of inflammatory heart diseases.