Abstract
BACKGROUND AND AIMS: The therapeutic efficacy of single-dose mesenchymal stromal cell (MSC) therapy for heart failure (HF) remains inconsistent. This study aimed to investigate whether infusion with two-dose human umbilical cord MSC (hUCMSCs) could be therapeutically superior to single-dose therapy in a rat model of dilated cardiomyopathy (DCM) and explored the underlying mechanisms. METHODS: Male Sprague-Dawley rats were intraperitoneally injected with doxorubicin (DOX) to establish a DCM model and randomized to intravenously receive single-dose or two-dose hUCMSCs at an interval of 14 days. Their left ventricular (LV) systolic and diastolic functions were analyzed by echocardiography. The percentages of Th1, Th2, Th17, and Treg cells in the heart, spleen, lymph nodes, and peripheral blood and the levels of serum cytokines in individual rats were analyzed by flow cytometry and cytometric bead assay, respectively. The degrees of cardiac fibrosis and cardiomyocyte apoptosis were examined by histology. The importance of indoleamine 2,3-dioxygenase (IDO), an activator of Treg differentiation, in the therapeutic effect of hUCMSCs on inflammation and heart function of rats was determined after induction of IDO over-expression (IDO-OE) using IFN-γ (1 ng/ml) and TNF-α (10 ng/ml) stimulation or silencing (IDO-KD) using small interfering RNA (siRNA) technology. RESULTS: Compared with the single dose, two-dose hUCMSCs were more effective in improving LV performance, attenuating cardiac dilation, reducing cardiomyocyte apoptosis and cardiac fibrosis. Two-dose hUCMSC therapy significantly increased Treg number in the heart and peripheral blood, accompanied by increased cardiac IDO expression. Compared with the control hUCMSCs, IDO-OE hUCMSCs significantly enhanced Treg and Th2 cell responses and decreased systemic Th17 cell responses and Th1 cell numbers in the mediastinal lymph nodes. Treatment with IDO-OE hUCMSCs significantly improved LV remodeling and dysfunction. However, treatment with IDO-KD hUCMSCs had opposite effects in rats. CONCLUSIONS: Administration of two-dose hUCMSCs has better therapeutic effects than single-dose therapy for inhibiting myocardial inflammation to improve LV function in DCM rats. These effects are associated with upregulating IDO expression and its systemic anti-inflammatory activities.