title: Role of C/EBP homologous protein in retinal ganglion cell death after ischemia/reperfusion injury.
abstract: OBJECTIVE
  To investigate the role of C/EBP homologous protein (CHOP), a proapoptotic protein, and the unfolded protein response (UPR) marker that is involved in endoplasmic reticulum (ER) stress-mediated apoptosis in mouse retinal ganglion cell (RGC) death following ischemia/reperfusion (I/R) injury.
  
  
  METHODS
  Retinal I/R injury was induced in adult C57BL/6J wild-type (WT) and CHOP knockout (Chop(-/-)) mice by raising IOP to 120 mm Hg for 60 minutes. Expression of CHOP and other UPR markers was studied by Western blot and immunohistochemistry. Retinal ganglion cell counts were performed in retinal flat mounts stained with an RGC marker. Retinal ganglion cell function was evaluated by scotopic threshold response (STR) electroretinography.
  
  
  RESULTS
  In WT mice, retinal CHOP was upregulated by 30% in I/R-injured eyes compared to uninjured eyes 3 days after injury (P < 0.05). Immunohistochemistry confirmed CHOP upregulation specifically in RGCs. CHOP knockout did not affect baseline RGC density or STR amplitude. Ischemia/reperfusion injury decreased RGC densities and STR amplitudes in both WT and Chop(-/-) mice. However, survival of RGCs in I/R-injured Chop(-/-) mouse was 48% higher (P < 0.05) than that in I/R-injured WT mouse 3 days after I/R injury. Similarly, RGC density was significantly higher in Chop(-/-) eyes at 7, 14, and 28 days after I/R injury. Scotopic threshold response amplitudes of Chop(-/-) mice were significantly higher at 3 and 7 days after I/R than those of WT mice.
  
  
  CONCLUSIONS
  Absence of CHOP partially protects against RGC loss and reduction in retinal function after I/R injury, indicating that CHOP and, thus, ER stress play an important role in RGC apoptosis in retinal I/R injury.
authors.affiliation: North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States Department of Cell Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas, United States.
authors.forename: Sonali
authors.initials: S
authors.lastname: Nashine
authors.affiliation: North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States.
authors.forename: Byung-Jin
authors.initials: BJ
authors.lastname: Kim
authors.affiliation: North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States Department of Cell Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas, United States.
authors.forename: Abbot F
authors.initials: AF
authors.lastname: Clark
authors.affiliation: North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States Department of Pharmaceutical Sciences, University of North Texas Health Science Center, Fort Worth, Texas, United States.
authors.forename: Iok-Hou
authors.initials: IH
authors.lastname: Pang
mesh_terms: D000818:Animals; D015153:Blotting, Western; D016923:Cell Death; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004596:Electroretinography; D059865:Endoplasmic Reticulum Stress; D005786:Gene Expression Regulation; D005838:Genotype; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D012313:RNA / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D015427:Reperfusion Injury / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D051742:Transcription Factor CHOP / Q000096:biosynthesis / Q000235:genetics*
chemical_list: C497249:DDIT3 protein, human; D051742:Transcription Factor CHOP; D012313:RNA
keywords: CHOP; apoptosis; retinal ganglion cell; retinal ischemia