| Objective:To investigate the effect of hypoxic preconditioning on the immuno-modulatory properties of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and the effect of cotransplantation of hUC-MSCs and human umbilical cord blood (hUCB) derived-CD34+cells in a rabbit model of myocardial infarction.Methods:hUC-MSCs with or without hypoxic preconditioning by cobalt chloride were plated in a24-well plate, and then cocultured with hUCB-CD34+cells and PBMCs for96h at37℃in a5%CO2incubator. For the negative control. hUC-MSCs were omitted. The groups were divided as follows:Al=HP-MSCs+hUCB-CD34+cells+PBMC, A2=hUC-MSCs+hUCB-CD34+cells+PBMC, Negative Control=hUCB-CD34+cells+PBMC. Culture supernatants of each group were collected, and the IL-10and IFN-y levels were measured by ELISA. A rabbit model of MI was established using a modified Fujita method. The animals were then randomized into three groups and received intramyocardial injections of0.4ml of PBS alone (n=8, PBS group), hUC-MSCs in PBS (n=8. hUC-MSCs group), or hUC-MSCs+CD34+cells in PBS (n=8, Cotrans group), at four points in the infarct border zone. Echocardiography was performed at baseline, four weeks after MI induction, and four weeks after cell transplantation, respectively. Stem cell differentiation and neovascularization in the infracted area were characterized for the presence of cardiac Troponin I (cTnI) and CD31by immunohistochemical staining, and the extent of myocardial fibrosis was evaluated by hematoxylin and eosin (H&E) and Masson s tri chrome.Results:IFN-γ was27.00±1.11pg/ml.14.20±0.81pg/ml. and7.22±0.14pg/ml. and IL-10was31.68±3.08pg/ml.61.42±1.08pg/ml. and85.85±1.80pg/ml for the Control. Al and A2groups, respectively, which indicated that hUCB-CD34+cells induced immune reaction of peripheral blood mononuclear cells, whereas both hUC-MSCs and HP-MSCs showed an immunosuppressive effect. which however was attenuated by hypoxic preconditioning. The Cotrans group had less collagen deposition in the infarcted myocardium and better heart function than the hUC-MSCs or PBS group. The presence of cTnl-positive cells and CD31-positive tubular structures indicated the differentiation of stem cells into cardiomyocytes and neovascularization. The microvessel density was12.19±3.05/HP for the hUC-MSCs group and31.63±2.45/HP for the Cotrans group, respectively (P<0.01).Conclusions:Both hUC-MSCs and HP-MSCs have an immunosuppressive effect on lymphocytes, which however can be attenuated by hypoxic preconditioning. Cotransplantation of hUC-MSCs and hUCB-CD34+cells can improve heart function and decrease collagen deposition in post-MI rabbits. Thus a combined regimen of hUC-MSCs and hUCB-CD34+cells would be more desirable than either cells administered alone. This is most likely due to the increase of cardiomyocytes and enhanced angiogenesis in the infarcted myocardium. |
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