Preconditioning with a TLR2 specific ligand increases resistance to cerebral ischemia/reperfusion injury

The brain's resistance to ischemic injury can be transiently augmented by prior exposure to a sub-lethal stress stimulus, i.e. preconditioning. It has been reported that Toll-like receptors (TLRs) are involved in the preconditioning-induced protective effect against ischemic brain injury. In this study, we investigated the effect of preconditioning with a TLR2 specific ligand, Pam3CSK4, on focal cerebral ischemia/reperfusion (I/R) injury in mice. Pam3CSK4 was administered systemically 24 h before the mice were subjected to focal cerebral ischemia (1 h) followed by reperfusion. Cerebral infarct size was determined, blood brain barrier (BBB) permeability was evaluated, and expression of tight-junction proteins were examined after focal cerebral I/R. Results showed that pre-treatment with Pam3CSK significantly reduced brain infarct size (1.9 ± 0.5% vs 9.4 ± 2.2%) compared with the untreated I/R group. Pam3CSK4 pre-treatment also significantly reduced acute mortality (4.3% vs 24.2%), preserved neurological function (8.22 ± 0.64 vs 3.91 ± 0.57), and attenuated brain edema (84.61 ± 0.08% vs 85.29 ± 0.09%) after cerebral I/R. In addition, Pam3CSK4 pre-treatment preserved BBB function as evidenced by decreased leakage of serum albumin (0.528 ± 0.026 vs 0.771 ± 0.059) and Evans Blue (9.23 ± 0.72 μg/mg vs 12.56 ± 0.65 μg/mg) into brain tissue. Pam3CSK4 pre-treatment also attenuated the loss of the tight junction protein occludin in response to brain I/R injury. These results suggest that TLR2 is a new target of ischemic preconditioning in the brain and preconditioning with a TLR2 specific ligand will protect the brain from I/R injury.