ERP72 EXPRESSION ACTIVATED BY TRANSIENT CEREBRAL-ISCHEMIA OR DISTURBANCE OF NEURONAL ENDOPLASMIC-RETICULUM CALCIUM STORES

Stress-induced activation of the expression of the endoplasmic reticul um (ER)-resident chaperon and member of the protein disulfide isomeras e family erp72 was studied after transient cerebral ischemia in vivo u sing the four-vessel occlusion method and experimental depletion of ER calcium stores in primary neuronal cell cultures. After 8 days in vit ro, neurons were exposed to thapsigargin (Tg), an irreversible inhibit or of ER Ca2+-ATPase, or the Tg solvent DMSO. In separate experiments neurons were pre-loaded with the cell-permeant calcium chelator BAPTA- AM before Tg exposure. Stress-induced changes in erp72 expression were analysed by quantitative PCR. Transient cerebral ischemia produced a significant increase in erp72 mRNA levels which rose to about 200% of control (hippocampus) or 300% of control (cortex). After depletion of ER calcium stores neuronal erp72 mRNA levels rose markedly, peaking at 12 h of recovery. Counteracting the Tg-induced rise in cytoplasmic ca lcium activity by preloading cells with the chelator BAPTA-AM did not influence erp72 expression significantly, suggesting that the activati on of erp72 expression resulted from the depletion of ER calcium store s and not from the corresponding increase in cytoplasmic calcium activ ity. An activation of erp72 expression is indicative of a disturbance of ER function. The results of the present study therefore provide evi dence to support the notion that transient cerebral ischemia induces d isturbances of neuronal ER function, probably through a depletion of E R calcium stores.