ABSTRACT
Preconditioning with lipopolysaccharide (LPS), a toll-like receptor 4 (TLR4) ligand, provides neuroprotection against subsequent cerebral ischemic brain injury, through a tumor necrosis factor (TNF)alpha-dependent process. Here, we report the first evidence that another TLR, TLR9, can induce neuroprotection. We show that the TLR9 ligand CpG oligodeoxynucleotide (ODN) can serve as a potent preconditioning stimulus and provide protection against ischemic brain injury. Our studies show that systemic administration of CpG ODN 1826 in advance of brain ischemia (middle cerebral artery occlusion (MCAO)) reduces ischemic damage up to 60% in a dose- and time-dependent manner. We also offer evidence that CpG ODN preconditioning can provide direct protection to cells of the central nervous system, as we have found marked neuroprotection in modeled ischemia in vitro. Finally, we show that CpG preconditioning significantly increases serum TNFalpha levels before MCAO and that TNFalpha is required for subsequent reduction in damage, as mice lacking TNFalpha are not protected against ischemic injury by CpG preconditioning. Our studies show that preconditioning with a TLR9 ligand induces neuroprotection against ischemic injury through a mechanism that shares common elements with LPS preconditioning via TLR4.
Subject(s)
Brain Ischemia/drug therapy , Brain Ischemia/metabolism , Ischemic Preconditioning/methods , Lipopolysaccharides/pharmacology , Neuroprotective Agents/pharmacology , Toll-Like Receptor 9/metabolism , Animals , Brain Ischemia/pathology , Cell Death/drug effects , Disease Models, Animal , Infarction, Middle Cerebral Artery/drug therapy , Infarction, Middle Cerebral Artery/metabolism , Infarction, Middle Cerebral Artery/pathology , Ligands , Male , Mice , Mice, Inbred C57BL , Neurons/pathology , Oligodeoxyribonucleotides/pharmacology , Tumor Necrosis Factor-alpha/metabolismABSTRACT
BACKGROUND AND PURPOSE: Mild hypothermia confers profound neuroprotection in ischemia. We recently discovered 2 natural derivatives of thyroxine, 3-iodothyronamine (T(1)AM) and thyronamine (T(0)AM), that when administered to rodents lower body temperature for several hours without induction of a compensatory homeostatic response. We tested whether T(1)AM- and T(0)AM-induced hypothermia protects against brain injury from experimental stroke. METHODS: We tested T(1)AM and T(0)AM 1 hour after and 2 days before stroke in a mouse model of focal ischemia. To determine whether T(1)AM and T(0)AM require hypothermia to protect against stroke injury, the induction of hypothermia was prevented. RESULTS: T(1)AM and T(0)AM administration reduced body temperature from 37 degrees C to 31 degrees C. Mice given T(1)AM or T(0)AM after the ischemic period had significantly smaller infarcts compared with controls. Mice preconditioned with T(1)AM before ischemia displayed significantly smaller infarcts compared with controls. Pre- and postischemia treatments required the induction of hypothermia. T(1)AM and T(0)AM treatment in vitro failed to confer neuroprotection against ischemia. CONCLUSIONS: T(1)AM and T(0)AM, are potent neuroprotectants in acute stroke and T(1)AM can be used as antecedent treatment to induce neuroprotection against subsequent ischemia. Hypothermia induced by T(1)AM and T(0)AM may underlie neuroprotection. T(1)AM and T(0)AM offer promise as treatments for brain injury.
