Estrogen may contribute to ischemic tolerance through modulation of cellular stress-related proteins.
Ischemic tolerance describes a phenomenon whereby subcritical stimuli evoke cellular protective mechanisms resulting in increased tolerance to subsequent ischemia. In the present study we propose that the cytoprotective effects attributed to 17beta-estradiol and tunicamycin in an in vivo rodent model of ischemia are reflected by changes in neuronal tissue levels of m-calpain, HSP70, GRP94 and GRP78. Rats pretreated with 17beta-estradiol, tunicamycin or both demonstrated dose-dependent reductions in infarct area following 4 h of permanent middle cerebral artery occlusion (MCAO). Western blot analysis revealed that 4 h of MCAO was associated with decreased cortical expression of HSP70 and m-calpain and increased expression of GRP78. Pretreatment with 12.5 microg/kg 17beta-estradiol did not change this pattern of protein expression following MCAO. While GRP94 expression was elevated in sham-operated rats pretreated with 17beta-estradiol, the ensuing ischemic tolerance did not appear to be mediated by changes in cellular stress proteins. Pretreatment with 50 microg/kg tunicamycin significantly reduced HSP70 in cortical tissue samples taken from sham-operated rats and appeared to attenuate the threshold for activation of m-calpain in rats undergoing 4 h of MCAO. Lastly, a combined treatment in which rats undergoing MCAO were pretreated with both tunicamycin (24 h prior) and 17beta-estradiol (30 min prior) was associated with an attenuated stress response as indicated by reduced expression of GRP78 and GRP94 when compared to saline-treated controls. The results of this study suggest that the ischemic tolerance observed following MCAO in rats pretreated with either 17beta-estradiol or tunicamycin is likely mediated in part through differential effects on cellular stress proteins.
Dept. of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PEI, Canada.
Monique C
MC
Saleh
Barry J
BJ
Connell
Tarek M
TM
Saleh
D000818:Animals; D002154:Calpain / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D020244:Infarction, Middle Cerebral Artery / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014415:Tunicamycin / Q000494:pharmacology; D000091342:Endoplasmic Reticulum Chaperone BiP
D002154:Calpain; D004958:Estradiol; D004967:Estrogens; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D014415:Tunicamycin; C051684:GRP78 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP; C018551:glucose-regulated proteins; C449000:m-calpain