title: Role of endoplasmic reticulum calcium disequilibria in the mechanism of homocysteine-induced ER stress.
abstract: Our laboratory demonstrated that hyperhomocysteinemia accelerates atherosclerosis in mouse models through ER stress and activation of the unfolded protein response (UPR). In this study, we tested the hypothesis that homocysteine-induced ER stress may arise from ER-Ca(2+) disequilibria. We found that homocysteine-induced cytosolic Ca(2+) transients in T24/83 cells and human aortic smooth muscle cells (HASMCs). These calcium effects occurred at concentrations of homocysteine in the external medium (1-5 mM) that increase intracellular homocysteine in these cell types. Prolonged homocysteine treatment (5 h) at these exogenous concentrations reduced ER-Ca(2+) emptying evoked by thapsigargin. However, these homocysteine-induced effects on ER-Ca(2+) emptying were of a much smaller magnitude than those evoked by A23187 or thapsigargin (ER stressors known to induce ER stress through ER-Ca(2+) depletion). T24/83 cells stably overexpressing the Ca(2+)-binding ER chaperone GRP78 showed diminished cytosolic Ca(2+) transients induced by homocysteine and reduced ER-Ca(2+) emptying evoked by thapsigargin. Prevention of the homocysteine-induced UPR by cycloheximide pretreatment normalized GRP78 expression and ER-Ca(2+) emptying evoked by thapsigargin. These results are inconsistent with a mechanism of ER stress induction by homocysteine through ER-Ca(2+) depletion.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University, and the Henderson Research Centre, Hamilton, Ontario, Canada.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Dickhout
authors.forename: Sudesh K
authors.initials: SK
authors.lastname: Sood
authors.forename: Richard C
authors.initials: RC
authors.lastname: Austin
mesh_terms: D001011:Aorta / Q000166:cytology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000172:deficiency* / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D016257:Fura-2; D006360:Heat-Shock Proteins / Q000378:metabolism; D006710:Homocysteine / Q000494:pharmacology*; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D018832:Molecular Chaperones / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D001749:Urinary Bladder Neoplasms / Q000473:pathology
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D005456:Fluorescent Dyes; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D007476:Ionophores; D018832:Molecular Chaperones; D006710:Homocysteine; D000001:Calcimycin; D019284:Thapsigargin; D002118:Calcium; D016257:Fura-2