Early increase in mRNA levels of pro-inflammatory cytokines and their interactions in the mouse hippocampus after transient global ischemia

There is convincing evidence that cytokines are involved in the inflammatory response following cerebral ischemia, but the interactions among the pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 in the early stage of ischemic reperfusion are not yet completely understood. In this study, we examined the early mRNA expressions of pro-inflammatory cytokines in the ischemic hippocampus after 30 min of bilateral common carotid artery occlusion in C57BL/6J wild-type (WT) and TNF-α, IL-1α/β or IL-6 gene knockout (KO) mice utilizing real-time polymerase chain reaction. The mRNA expressions of the pro-inflammatory cytokines TNF-α, IL-6 and IL-1β were significantly induced in ischemic WT mice compared with in the sham-operated mice. These increases peaked at 3 to 24 h for TNF-α, at 12 h for IL-1β, and at 6 to 24 h for IL-6 after ischemia. The pattern of temporal expression of the cytokine mRNAs in ischemic gene KO mice, however, differed from that in WT mice. The TNF-α mRNA expression showed a similar temporal expression pattern in IL-6 KO mice compared to in WT mice following ischemic reperfusion, and the levels at all time points were lower than in WT mice. The IL-1β mRNA level was very low in ischemic TNF-α KO mice and IL-6 KO mice in spite of a small peak observed in both at 24 h. The IL-6 mRNA level was significantly upregulated at all time points in both ischemic WT and TNF-α KO mice; however, the peak was delayed by 12-h in IL-1α/β KO mice. In conclusion, the present study indicates that the rapid increases in cytokine levels are interdependent, interactive, and possibly modulate each other in the mouse hippocampus after transient global ischemia.