title: Β-adrenergic receptor stimulation induces endoplasmic reticulum stress in adult cardiac myocytes: role in apoptosis.
abstract: Accumulation of misfolded proteins and alterations in calcium homeostasis induces endoplasmic reticulum (ER) stress, leading to apoptosis. In this study, we tested the hypothesis that β-AR stimulation induces ER stress, and induction of ER stress plays a pro-apoptotic role in cardiac myocytes. Using thapsigargin and brefeldin A, we demonstrate that ER stress induces apoptosis in adult rat ventricular myocytes (ARVMs). β-AR-stimulation (isoproterenol; 3h) significantly increased expression of ER stress proteins, such as GRP-78, Gadd-153, and Gadd-34, while activating caspase-12 in ARVMs. In most parts, these effects were mimicked by thapsigargin. β-AR stimulation for 15 min increased PERK and eIF-2α phosphorylation. PERK phosphorylation remained higher, while eIF-2α phosphorylation declined thereafter, reaching to ~50% below basal levels at 3 h after β-AR stimulation. This decline in eIF-2α phosphorylation was prevented by β1-AR, not by β2-AR antagonist. Forskolin, adenylyl cyclase activator, simulated the effects of ISO on eIF-2α phosphorylation. Salubrinal (SAL), an ER stress inhibitor, maintained eIF-2α phosphorylation and inhibited β-AR-stimulated apoptosis. Furthermore, inhibition of caspase-12 using z-ATAD inhibited β-AR-stimulated and thapsigargin-induced apoptosis. In vivo, β-AR stimulation induced ER stress in the mouse heart as evidenced by increased expression of GRP-78 and Gadd-153, activation of caspase-12, and dephosphorylation of eIF-2α. SAL maintained phosphorylation of eIF-2α, inhibited activation of caspase-12, and decreased β-AR-stimulated apoptosis in the heart. Thus, β-AR stimulation induces ER stress in cardiac myocytes and in the heart, and induction of ER stress plays a pro-apoptotic role.
authors.affiliation: Department of Physiology, James H Quillen College of Medicine, James H Quillen Veterans Affairs Medical Center, East Tennessee State University, PO Box 70576, Johnson City, TN 37614, USA.
authors.forename: Suman
authors.initials: S
authors.lastname: Dalal
authors.forename: Cerrone R
authors.initials: CR
authors.lastname: Foster
authors.forename: Bhudev C
authors.initials: BC
authors.lastname: Das
authors.forename: Mahipal
authors.initials: M
authors.lastname: Singh
authors.forename: Krishna
authors.initials: K
authors.lastname: Singh
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D058671:Adrenergic beta-1 Receptor Antagonists / Q000494:pharmacology; D058672:Adrenergic beta-2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D020126:Brefeldin A / Q000008:administration & dosage; D053454:Caspase 12 / Q000378:metabolism; D061945:Caspase Inhibitors; D002478:Cells, Cultured; D002934:Cinnamates / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006360:Heat-Shock Proteins / Q000378:metabolism; D007545:Isoproterenol / Q000008:administration & dosage*; D008297:Male; D051379:Mice; D032383:Myocytes, Cardiac / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D019284:Thapsigargin / Q000008:administration & dosage; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D000262:Adenylyl Cyclases; D058671:Adrenergic beta-1 Receptor Antagonists; D058672:Adrenergic beta-2 Receptor Antagonists; D000943:Antigens, Differentiation; D020126:Brefeldin A; D053454:Caspase 12; D061945:Caspase Inhibitors; D002934:Cinnamates; D005576:Colforsin; D015852:Eukaryotic Initiation Factor-2; D006360:Heat-Shock Proteins; D007545:Isoproterenol; D011518:Proto-Oncogene Proteins; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D019284:Thapsigargin; D013890:Thiourea; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C497251:Ddit3 protein, rat; C489287:Ppp1r15a protein, rat; C496827:salubrinal