[Effect of endoplasmic reticulum stress in brain injury following chronic intermittent hypoxia in weanling rat]

Abstract

Objective: To explore the role of endoplasmic reticulum stress in brain injury following chronic intermittent hypoxia (CIH) in weanling rats.

Methods: A total of 48 male healthy Sprague-Dawley rats (3-4-week-old, 80-100 g) were randomly divided into 4 groups: 2-week-CIH (2IH) group, 4-week-CIH (4IH) group, 2-week-control (2C) group and 4-week-control (4C) group. The morphologic changes were observed by hematoxylin-eosin (HE) staining and cell apoptosis detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay. Then hippocampus and prefrontal cortices were collected for transcription and expression analysis of glucose regulated protein 78 (GRP78) by reverse transcription (RT)-PCR and Western blotting respectively. And the expressions of Caspase-12 mRNA and Caspase-12 protein in prefrontal cortex were analyzed by RT-PCR and immunohistochemistry.

Results: The neuronal apoptosis in hippocampus and prefrontal cortices in CIH exposed groups were more pronounced than those of the control groups (all P < 0.01), especially in the 4IH group (hippocampus: 8.78% ± 0.71% vs 3.26% ± 0.45%, cortices: 6.02% ± 0.32% vs 2.91% ± 0.29%). The expression levels of GRP78 mRNA (hippocampus: 0.424 ± 0.033 vs 0.326 ± 0.013 and 0.444 ± 0.028 vs 0.310 ± 0.015, cortices: 0.514 ± 0.038 vs 0.430 ± 0.017 and 0.524 ± 0.038 vs 0.439 ± 0.033) and GRP78 protein in hippocampus and prefrontal cortices (hippocampus: 0.221 ± 0.032 vs 0.178 ± 0.014 and 0.241 ± 0.019 vs 0.170 ± 0.013, cortices: 0.307 ± 0.012 vs 0.226 ± 0.022 and 0.311 ± 0.023 vs 0.225 ± 0.025), and the expression levels of Caspase-12 mRNA (0.396 ± 0.004 vs 0.323 ± 0.014, 0.417 ± 0.011 vs 0.313 ± 0.011) and Caspase-12 protein (0.334 ± 0.035 vs 0.197 ± 0.023, 0.368 ± 0.079 vs 0.215 ± 0.024) in prefrontal cortex in the IH groups all were more than those in the 2C and 4C groups (all P < 0.05).

Conclusions: Chronic intermittent hypoxia can up-regulate the GRP78 transcription and expression in brain regions associated with learning and memory. This may induce the endoplasmic reticulum stress and activate the Caspase-12 mediated apoptosis signaling pathway. In the end, neuronal apoptosis occurs. All these factors may play an important role in the impairment of learning memory during the exposure of growing rats to chronic intermittent hypoxia.