Involvement of endoplasmic reticulum stress in homocysteine-induced apoptosis of osteoblastic cells.
Hyperhomocysteinemia has been shown to increase the incidence of osteoporosis and osteoporotic fractures. Endoplasmic reticulum (ER) stress was recently shown to be associated with apoptosis in several types of cells. In this study, we determined the effect of homocysteine (Hcy) on the apoptosis of osteoblastic cells and investigated whether ER stress participates in Hcy-induced osteoblast apoptosis. Human osteoblastic cells were incubated with Hcy. Hcy dose-dependently decreased cell viability and increased apoptosis in osteoblastic cells. Osteoblastic cells are more susceptible to Hcy-mediated cell death than other cell types. Expression of cleaved caspase-3 was significantly increased by Hcy, and pretreatment with caspase-3 inhibitor rescued the cell viability by Hcy. Hcy treatment led to an increase in release of mitochondrial cytochrome c. It also triggered ER stress by increased expression of glucose-regulated protein 78, inositol-requiring transmembrane kinase and endonuclease 1α (IRE-1α), spliced X-box binding protein, activating transcription factor 4, and C/EBP homologous protein. Silencing IRE-1α expression by small interfering RNA effectively suppressed Hcy-induced apoptosis of osteoblastic cells. Our results suggest that hyperhomocysteinemia induces apoptotic cell death in osteoblasts via ER stress.
Division of Rheumatology, Department of Internal Medicine, College of Medicine, Yeouido St. Mary's Hospital, The Catholic University of Korea, #62 Yeouido-dong, Yeongdeungpo-ku, Seoul, South Korea.
Su-Jung
SJ
Park
Ki-Jo
KJ
Kim
Wan-Uk
WU
Kim
Il-Hoan
IH
Oh
Chul-Soo
CS
Cho
D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000737:chemistry / Q000378:metabolism; D061945:Caspase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D004722:Endoribonucleases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D006710:Homocysteine / Q000378:metabolism; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D020138:Hyperhomocysteinemia / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D058990:Molecular Targeted Therapy; D009928:Organ Specificity; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010024:Osteoporosis / Q000209:etiology* / Q000517:prevention & control; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
D061945:Caspase Inhibitors; D034741:RNA, Small Interfering; D006710:Homocysteine; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases; C505407:CASP3 protein, human; D053148:Caspase 3