ACTIVATION OF GADD153 EXPRESSION THROUGH TRANSIENT CEREBRAL-ISCHEMIA - EVIDENCE THAT ISCHEMIA CAUSES ENDOPLASMIC-RETICULUM DYSFUNCTION

The expression of the gene encoding the C/EBP-homologous protein (CHOP ), which is also known as growth arrest and DNA-damage-inducible gene 153 (gadd153), has been shown to be specifically activated under condi tions that disturb the functioning of the endoplasmic reticulum (ER). To investigate a possible role of ER dysfunction in the pathological p rocess of ischemic cell damage, we studied ischemia-induced changes in gadd153 expression using quantitative PCR. Transient cerebral ischemi a was produced in rats by four-vessel occlusion. In the hippocampus, i schemia induced a pronounced increase in gadd153 mRNA levels, peaking at 8 h of recovery (6.4-fold increase, p < 0.01), whereas changes in t he cortex were less marked (non-significant increase). To elucidate th e possible mechanism underlying this activation process, gadd153 mRNA levels were also evaluated in primary neuronal cell cultures under two different conditions, both leading to a depletion of ER calcium pools in the presence or absence of an increase in cytoplasmic calcium acti vity. The first procedure, exposure to thapsigargin, an irreversible i nhibitor of ER Ca2+-ATPase, caused a marked increase in gadd153 mRNA l evels both in cortical and hippocampal neurons, peaking at 12-18 h aft er treatment. The second procedure, immersion of cells in calcium free medium supplemented with EGTA, caused only a transient increase in ga dd153 mRNA levels, peaking at 6 h of recovery, indicating that a deple tion of ER calcium stores in the absence of an increase in cytoplasmic calcium activity is sufficient to activate neuronal gadd153 expressio n. The results imply that transient cerebral ischemia disturbs the fun ctioning of the ER and that these pathological changes are more pronou nced in the hippocampus compared to the cortex. (C) 1998 Elsevier Scie nce B.V. All rights reserved.