The Role Of Autophagy And Endoplasmic Reticulum Stress In Brain Ischemic Preconditioning And Drug Intervention

Aim: To investigate the role of autophagy and endoplasmic reticulum stress (ER stress) in cerebral ischemic preconditioning (IPC), and to explore if an autophagy inducer rapamycin can mimic IPC's neuroprotective effects.Methods: IPC model was induced by using intraluminal filament technique in rats. Activation of autophagy and endoplasmic reticulum stress in neurons in ischemic cortex was observed using electron microscopy. 3-MA (100-400 nmol) was injected intracerebroventricularly (icv.) before the onset of IPC. Rapamycin (8-32 ng) was injected intracerebroventricularly (icv.) before the onset of PFI. Ischemic injury was evaluated by 2,3,5- triphenyltetrazolium chloride (TTC) staining, brain water content and motor deficits. Western blot was employed to determine alternations in LC3/Beclin 1/caspase-12/HSP70 levels in ischemic cortex 6 h/24 h after ischemia.Results: IPC induced the robust formation of autophagosomes and endoplasmic reticulum stress. Neurological deficits, infract volume and brain water content were significantly increased in rats pre-treated with 3-MA (200-400 nmol). The expression of LC3/Beclin 1/ HSP70 was significantly increased after IPC and was attenuated by 3-MA treatment. However, 3-MA treatment increased the expression of caspase-12. A single i.c.v. injection of rapamycin 8-32 ng 24 h before the onset of PFI significantly reduced infarct volume, brain edema and motor deficits induced by PFI. Thus, IPC's neuroprotective effects can be mimicked by an autophagy inducer.Conclusions: 1. IPC increased the formation of autophagosomes and endoplasmic reticulum stress; 2. 3-MA completely suppressed the neuroproteciton induced by brain ischemic preconditioning and reduced the expression of LC3/Beclin 1, possiblly due to the inhibition of autophay pathway. 3. Ischemic preconditioning induced HSP70 upregulation and caspase-12 downregulation, offered a remarkable tolerance to a subsequent fatal ischemic insult. 4. Rapamycin can mimic IPC's neuroprotective effects.