Preconditioning With Endoplasmic Reticulum Stress Ameliorates Ischemia-reperfusion Injury

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) represents a cellular stress induced by multiple stimuli and pathological conditions. These include hypoxia, oxidative injury, high-fat diet, hypoglycemia, protein inclusion bodies and viral infection. ER stress triggers an evolutionarily conserved series of signal transduction events, which constitutes the unfolded protein response. Resent reports showed that ER stress is associate with a lot of diseases. The initial intent of the UPR is to reestablish homeostasis and normal ER function, and adaptive mechanisms predominantly involve activation of transcriptional programs that induce expression of genes that are capable of enhancing the protein folding capacity of the ER and genes for ER-assisted degradation (ERAD). These adaptive mechanisms suggest the possibility of therapeutic approaches targeting ER stress in IR injury. In this study we established a rat IR injury model under preconditioning with ER stress and investigated the potential of therapeutic approaches targeting ER stress in IR injury in rats. 1. Establishing animal model with IR injury under ER stress preconditioning. SD rats were pretreated with the ER stress inducer tunicamycin (TM) before IR operation. For evaluating the protective effect of preconditioning with ER stress, animals were divided into a control group and five pretreated groups. Different dose of TM (50μg/kg body wt, 100μg/kg body wt, 300μg/kg body wt) and different inducing time (4d, 5d, 6d) were progressed in this study. Partial hepatic IR injury model (45 min of ischemia via vascular clamping and 24 h reperfusion) were established and the severity of liver damage was determined by measuring serum ALT and AST levels. At the dose of 100μg/kg body wt and 5d before operation, preconditioning ameliorated the IR injury significantly (serum ALT at 6h after reperfusion 1506.28±401.98 u/L versus 2671.33±565.53 u/L, serum AST at 6h after reperfusion 3139.71±989.31 versus 5949.83±1205.51 u/L, serum ALT at 12h after reperfusion 723.71±278.56u/L versus 1141.33±231.63u/L, serum AST 2562.00±1673.47 versus 2996.83±882.68u/L, p<0.05 respectively). But no protection occurred in other groups.2. Verifying the protective effect of ER stress preconditioning. Male wistar rats were divided into control-sham group (A), TM-sham group (B), control-IR group (C) and TM-IR group (D). TM preconditioning in rats showed significantly protection against IR injury evidenced by lack alteration of serum ALT (109.14±22.26 versus 513.72±304.90 u/L p<0.05) and normal liver histology. Immunohistochemistry and Western blotting showed over expression of the ER stress–inducible chaperones glucose-regulated protein 78 (GRP78) in IR treated rats. High expression of GRP78 in TM-sham group compared with control-sham group implied that ER stress was induced by TM administration. More abundant ER was observed in preconditioning group compared with control group under transmission electron microscope (TEM) when IR injury occurred.Conclusion: Preconditioning with ER stress ameliorates the severity of IR injury in certain condition. These findings suggest the possibility therapeutic approaches targeting ER stress in hepatic IR injury.