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-β-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.