TLR2 has a detrimental role in mouse transient focal cerebral ischemia

A significant up-regulation of Toll-like-receptor (TLR) mRNAs between 3 and 48 h reperfusion time after induction of transient focal cerebral ischemia for 1 h was revealed by applying global gene expression profiling in postischemic mouse brains. Compared to TLR4 and TLR9, TLR2 proved to be the most significantly up-regulated TLR in the ipsilateral brain hemisphere. TLR2-protein was found to be expressed mainly in microglia in the postischemic brain tissue, but also in selected endothelial cells, neurons, and astrocytes. Additionally, TLR2-related genes with pro-inflammatory and pro-apoptotic capabilities were induced. Therefore we hypothesized that TLR2-signaling could exacerbate the primary brain damage after ischemia. Two days after induction of transient focal cerebral ischemia (1 h), we found a significant decrease of the infarct volume in TLR2 deficient mice compared to wild type mice (75 ± 5 vs. 42 ± 7 mm3). We conclude that TLR2 up-regulation and TLR2-signaling are important events in focal cerebral ischemia and contribute to the deterioration of ischemic damage.