title: Microarray analysis provides new insights into the function of apolipoprotein O in HepG2 cell line.
abstract: BACKGROUND
  Apolipoprotein O (apoO) is a new member of the apolipoprotein family. However, data on its physiological functions are limited and inconsistent. Using a microarray expression analysis, this study explored the function of apoO in liver cells.
  
  
  METHODS
  HepG2 cells were treated either with oleic acid or tumor necrosis factor-α for 24 h. mRNA and protein expression of apoO were assessed by quantitative real-time PCR (qRT-PCR) and Western blot respectively. An efficient lentiviral siRNA vector targeting the human apoO gene was designed and constructed. The gene expression profile of HepG2 human hepatocellular carcinoma cells transfected with the apoO silencing vector was investigated using a whole-genome oligonucleotide microarray. The expression levels of some altered genes were validated using qRT-PCR.
  
  
  RESULTS
  ApoO expression in HepG2 cells was dramatically affected by lipid and inflammatory stimuli. A total of 282 differentially expressed genes in apoO-silenced HepG2 cells were identified by microarray analysis. These genes included those participating in fatty acid metabolism, such as ACSL4, RGS16, CROT and CYP4F11, and genes participating in the inflammatory response, such as NFKBIZ, TNFSF15, USP2, IL-17, CCL23, NOTCH2, APH-1B and N2N. The gene Uncoupling protein 2 (UCP2), which is involved in both these metabolic pathways, demonstrated significant changes in mRNA level after transfection.
  
  
  CONCLUSIONS
  It is likely that apoO participates in fatty acid metabolism and the inflammatory response in HepG2 cells, and UCP2 may act as a mediator between lipid metabolism and inflammation in apoO-silenced HepG2 cells.
authors.forename: Chen-Lu
authors.initials: CL
authors.lastname: Wu
authors.affiliation: Department of Cardiology, the Second Xiangya Hospital of Central South University, Middle Ren-Min Road No,139, Changsha, Hunan, 410011, PR China. zhaosp@medmail.com.
authors.forename: Shui-Ping
authors.initials: SP
authors.lastname: Zhao
authors.forename: Bi-Lian
authors.initials: BL
authors.lastname: Yu
mesh_terms: D001053:Apolipoproteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D056945:Hep G2 Cells; D006801:Humans; D007249:Inflammation / Q000235:genetics; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism; D050356:Lipid Metabolism / Q000235:genetics; D046228:Microarray Analysis; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D058977:Molecular Sequence Annotation; D019301:Oleic Acid / Q000494:pharmacology*; D020411:Oligonucleotide Array Sequence Analysis; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000071246:Uncoupling Protein 2
chemical_list: C000589295:APOO protein, human; D001053:Apolipoproteins; D005227:Fatty Acids; D007473:Ion Channels; D024101:Mitochondrial Proteins; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; C000604389:UCP2 protein, human; D000071246:Uncoupling Protein 2; D019301:Oleic Acid