Deletion of Atf6α enhances kainate-induced neuronal death in mice

• The unfolded protein response was activated both in neurons and in glial cells after injection of kainate into the mouse hippocampus.
• Kainate caused a more profound neuronal death in the CA3 region of Atf6α−/− mice than in that of wild type mice.
• Enhanced neuronal death in Atf6α−/− mice was associated with impaired Ca2+ homeostasis and hyperactivity in neurons.

Excessive amount of l-glutamate in the brain causes neuronal damage in various pathological conditions including epilepsy and stroke. We previously reported that the 150-kDa oxygen-regulated protein (ORP150), a molecular chaperone in the endoplasmic reticulum (ER), inhibited the l-glutamate-induced neuronal death, at least partly, by improving Ca2+ homeostasis in the ER. In the present study, we analyzed the role of activating transcription factor 6α (ATF6α), an upstream transcriptional factor critical for the operation of the ER, using mouse intrahippocampal kainate (KA) injection model. Expression of Hspa5, which encodes the molecular chaperone 78 kDa glucose-regulated protein (GRP78), increased after KA injection in the wild type (WT) mice. Comparative analysis using WT and Atf6α−/− mice revealed that KA induced pronounced neuronal death in the CA3 region of Atf6α−/− mice. The enhanced neuronal death in Atf6α−/− mice was associated with reduced expression of molecular chaperones in the ER and significant induction of c-fos in the hippocampal neurons. Furthermore, an injection of dantrolene, an inhibitor of ryanodine receptor, partially rescued these effects in Atf6α−/− mice after KA injection. Our results suggest that ATF6α plays an important role in neuronal survival after KA-induced excitotoxicity through the regulation of Ca2+ response and neuronal activity.

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