title: Acid Sphingomyelinase Mediates Oxidized-LDL Induced Apoptosis in Macrophage via Endoplasmic Reticulum Stress.
abstract: OBJECTIVE
  Macrophage apoptosis is a vital event in advanced atherosclerosis, and oxidized low-density lipoprotein (ox-LDL) is a major contributor to this process. Acid sphingomyelinase (ASM) and ceramide are also involved in the induction of apoptosis, particularly in macrophages. Our current study focuses on ASM and investigates its role in ox-LDL-induced macrophage apoptosis.
  
  
  METHODS
  Human THP-1 and mouse peritoneal macrophages were cultured in vitro and treated with ox-LDL. ASM activity and ceramide levels were quantified using ultra performance liquid chromatography. Protein and mRNA levels were analyzed using Western blot analysis and quantitative real-time PCR, respectively. Cell apoptosis was determined using Hoechst staining and flow cytometry.
  
  
  RESULTS
  Ox-LDL-induced macrophage apoptosis was triggered by profound endoplasmic reticulum (ER) stress, leading to an upregulation of ASM activity and ceramide levels at an early stage. ASM was inhibited by siRNA or desipramine (DES), and/or ceramide was degraded by recombinant acid ceramidase (AC). These events attenuated the effect of ox-LDL on ER stress. In contrast, recombinant ASM upregulated ceramide and ER stress. ASM siRNA, DES, recombinant AC, and ER stress inhibitor 4-phenylbutyric acid were blocked by elevated levels of C/EBP homologous protein (CHOP); ox-LDL induced elevated levels of CHOP. These events attenuated macrophage apoptosis.
  
  
  CONCLUSIONS
  These results indicate that ASM/ceramide signaling pathway is involved in ox-LDL-induced macrophage apoptosis via ER stress pathway.
authors.affiliation: Departments of Nuclear Medicine, Xiangya Hospital, Central South University.
authors.forename: Min
authors.initials: M
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Pan
authors.forename: Rui-Zheng
authors.initials: RZ
authors.lastname: Shi
authors.forename: Yong-Ping
authors.initials: YP
authors.lastname: Bai
authors.forename: Bo-Yang
authors.initials: BY
authors.lastname: You
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang
authors.forename: Qiong-Mei
authors.initials: QM
authors.lastname: Fu
authors.forename: Edward H
authors.initials: EH
authors.lastname: Schuchman
authors.forename: Xing-Xuan
authors.initials: XX
authors.lastname: He
authors.forename: Guo-Gang
authors.initials: GG
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000473:pathology*; D051379:Mice; D009000:Monocytes / Q000187:drug effects / Q000473:pathology*; D060888:Real-Time Polymerase Chain Reaction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*
chemical_list: D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase