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-β1 48 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 × 10 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,  = 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,  = 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/mm) in the infarcted area after transplantation was significantly higher than that in the ischemic control group (391.67 ± 69.50 cells/mm) (F = 92.421,  < 0.01); the number of TGF-β1 cells after transplantation (35.00 ± 13.66 cells/mm) was significantly reduced in comparison to that in the ischemic control group (72.33 ± 32.08 cells/mm) (F = 37.680,  < 0.01). The number of TGF-β1/Iba-1 microglia cells in the transplantation group (3.67 ± 3.17 cells/mm) was significantly reduced in comparison to that of the ischemic control group (13.67 ± 5.52 cells/mm) (F = 29.641,  < 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,  < 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.