Polyinosinic-Polycytidylic Acid Has Therapeutic Effects against Cerebral Ischemia/Reperfusion Injury through the Downregulation of TLR4 Signaling via TLR3

Recent reports have shown that preconditioning with the TLR3 ligand polyinosinic-polycytidylic acid ( poly( I:C)) protects against cerebral ischemia/reperfusion ( I/R) injury. However, it is unclear whether poly( I:C) treatment after cerebral I/R injury is also effective. We used mouse/rat middle cerebral artery occlusion and cell oxygen-glucose deprivation models to evaluate the therapeutic effects and mechanisms of poly( I:C) treatment. Poly( I:C) was i. p. injected 3 h after ischemia ( treatment group). Cerebral infarct volumes and brain edemas were significantly reduced, and neurologic scores were significantly increased. TNF-a and IL-1b levels were markedly decreased, whereas IFN-b levels were greatly increased, in the ischemic brain tissues, cerebral spinal fluid, and serum. Injuries to hippocampal neurons and mitochondria were greatly reduced. The numbers of TUNEL-positive and Fluoro-Jade B+ cells also decreased significantly in the ischemic brain tissues. Poly( I:C) treatment increased the levels of Hsp27, Hsp70, and Bcl2 and decreased the level of Bax in the ischemic brain tissues. Moreover, poly( I:C) treatment attenuated the levels of TNF-a and IL-1b in serum and cerebral spinal fluid of mice stimulated by LPS. However, the protective effects of poly( I:C) against cerebral ischemia were abolished in TLR3 2/2 and TLR4 2/2 mice. Poly( I:C) downregulated TLR4 signaling via TLR3. Poly( I:C) treatment exhibited obvious protective effects 14 d after ischemia and was also effective in the rat permanent middle cerebral artery occlusion model. The results suggest that poly( I:C) exerts therapeutic effects against cerebral I/R injury through the downregulation of TLR4 signaling via TLR3. Poly( I:C) is a promising new drug candidate for the treatment of cerebral infarcts.