Bone marrow mesenchymal stem cell transplantation downregulates plasma level and the microglia expression of transforming growth factor β1 in the acute phase of cerebral cortex ischemia

Background:Both bone marrow mesenchymal stem cell(BM-MSC)and transforming growth factor-β1(TGF-β1)have a strong anti-inflammatory capacity in stroke.But their relationship has not been well addressed.In this study,we investigated how intravenous BM-MSC transplantation in rats effected the expression of TGF-β148 h post cerebral ischemia,and we analyzed the main cells that produce TGF-β1.Methods:We used a distal middle cerebral artery occlusion(dMCAO)model in twenty Sprague-Dawley(SD)rats.The rats were randomly divided into two groups:the ischemic control group and the postischemic BM-MSC transplantation group.One hour after the dMCAO model was established,the rats were injected in the tail vein with either 1 ml saline or 1×106 BM-MSCs suspended in 1 ml saline.ELISAs were used to detect TGF-β1 content in the brain infarct core area,striatum and the plasma at 48 h after cerebral infarction.Immunofluorescent staining of brain tissue sections for TGF-β1,Iba-1,CD68 and NeuN was performed to determine the number and the proportion of double stained cells and to detect possible TGF-β1 producing cells in the brain tissue.Results:Forty-eight hours after ischemia,the TGF-β1 content in the infarcted area of the BM-MSC transplantation group(23.94±4.48 pg/ml)was significantly lower than it was in the ischemic control group(34.18±4.32 pg/ml)(F=13.534,P=0.006).The TGF-β1 content in the rat plasma in the BM-MSC transplantation group(75.91±12.53 pg/ml)was significantly lower than it was in the ischemic control group(131.18±16.07 pg/ml)(F=36.779,P=0.0002),suggesting that after transplantation of BM-MSCs,TGF-β1 levels in the plasma decreased,but there was no significant change in the striatum area.Immunofluorescence staining showed that the total number of nucleated cells(1037.67±222.16 cells/mm2)in the infarcted area after transplantation was significantly higher than that in the ischemic control group(391.67±69.50 cells/mm2)(F=92.421,P<0.01);the number of TGF-β1+cells after transplantation(35.00±13.66 cells/mm2)was significantly reduced in comparison to that in the ischemic control group(72.33±32.08 cells/mm2)(F=37.680,P<0.01).The number of TGF-β1+/Iba-1+microglia cells in the transplantation group(3.67±3.17 cells/mm2)was significantly reduced in comparison to that of the ischemic control group(13.67±5.52 cells/mm2)(F=29.641,P<0.01).The proportion of TGF-β1+/Iba-1+microglia cells out of all Iba-1+microglia cells after transplantation(4.38±3.18%)was significantly decreased compared with that in the ischemic control group(12.81±4.86%)(F=28.125,P<0.01).Conclusions:Iba-1+microglia is one of the main cell types that express TGF-β1.Intravenous transplantation of BM-MSCs does not cooperate with TGF-β1+cells in immune-regulation,but reduces the TGF-β1 content in the infarcted area and in the plasma at 48 h after cerebral infarction.