Introduction
Several studies1, 2, including ours (to be published), have demonstrated that administration of hematopoietic cytokines enhanced the availability of circulating hematopoietic stem cells to the brain, as well as their capacity for neurogenesis and angiogenesis in rats with cerebral ischemia. However, the mechanisms involved in this process are not fully understood. In this study, we investigated whether administration of hematopoietic cytokines influences the microenvironment, such as mRNA expression of tissue cytokines, within ischemic brain.
Methods
Focal ischemia was produced by occluding the left middle cerebral artery in male C57 Black/6 mice under halothane anesthesia. Mice were injected subcutaneously with human recombinant granulocyte colony-stimulating factor (G-CSF) + stem cell factor (SCF) from day1 to 3 (cytokines-treated group; n=5), or non-injected (control group; n=7). Mice were sacrificed at 4 days after occlusion, and the parts of brain tissues corresponding to the core of infarct, peri-infarct, and non-infarct regions were sampled. In each sampled brain region, we checked mRNA expressions of IL-6 and TNF as pro-inflammatory cytokines, IL-10, TGF-β1, TGF-β2 and TGF-β3 as anti-inflammatory cytokines, G-CSF and SCF as hematopoietic cytokines, and iNOS, using RT-PCR.
Results
In both control and cytokines-treated groups, the expression of TGF-β1 in the core of infarct and peri-infarct regions, and the expression of TNF in the core of infarct region were significantly higher than those in non-infarct region. However, mRNA expression of TNF in peri-infarct region was suppressed in cytokines-treated group, compared with that in control group. mRNA expressions of IL-6, IL-10, TGF-β2, TGF-β3, G-CSF, SCF and iNOS in any regions did not differ between the two groups.
Conclusions
Our results showed that mRNA expression of tissue cytokines within ischemic brain rapidly increased, at least, by 4 days after stroke, and that administration of hematopoietic cytokines suppressed the rise of pro-inflammatory cytokine, TNF in peri-infarct region. Therefore, it is concluded that administration of hematopoietic cytokines may provide a more favorable environment for neurogenesis, especially in peri-infarct region, in addition to its direct effects on bone marrow-derived cells and intrinsic neural stem cells.