title: Multiple programmed cell death pathways are involved in N-methyl-N-nitrosourea-induced photoreceptor degeneration.
abstract: OBJECTIVE
  To identify programmed cell death (PCD) pathways involved in N-methyl-N-nitrosourea (MNU)-induced photoreceptor (PR) degeneration.
  
  
  METHODS
  Adult C57BL/6 mice received a single MNU i.p. injection (60 mg/kg bodyweight), and were observed over a period of 7 days. Degeneration was visualized by H&E overview staining and electron microscopy. PR cell death was measured by quantifying TUNEL-positive cells in the outer nuclear layer (ONL). Activity measurements of key PCD enzymes (calpain, caspases) were used to identify the involved cell death pathways. Furthermore, the expression level of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78), key players in endoplasmic reticulum (ER) stress-induced apoptosis, was analyzed using quantitative real-time PCR.
  
  
  RESULTS
  A decrease in ONL thickness and the appearance of apoptotic PR nuclei could be detected beginning 3 days post-injection (PI). This was accompanied by an increase of TUNEL-positive cells. Significant upregulation of activated caspases (3, 9, 12) was found at different time periods after MNU injection. Additionally, several other players of nonconventional PCD pathways were also upregulated. Consequently, calpain activity increased in the ONL, with a maximum on day 7 PI and an upregulation of CHOP and GRP78 expression beginning on day 1 PI was found.
  
  
  CONCLUSIONS
  The data indicate that regular apoptosis is the major cause of MNU-induced PR cell death. However, alternative PCD pathways, including ER stress and calpain activation, are also involved. Knowledge about the mechanisms involved in this mouse model of PR degeneration could facilitate the design of putative combinatory therapeutic approaches.
authors: Department of Ophthalmology, Inselspital, University of Bern, Freiburgstrasse 14, 3010, Bern, Switzerland.
authors: Miriam
authors: M
authors: Reisenhofer
authors: Jasmin
authors: J
authors: Balmer
authors: Rahel
authors: R
authors: Zulliger
authors: Volker
authors: V
authors: Enzmann
mesh_terms: D000477:Alkylating Agents; D000818:Animals; D017209:Apoptosis; D002154:Calpain / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D004195:Disease Models, Animal; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000235:genetics; D006801:Humans; D020287:In Situ Nick-End Labeling; D007274:Injections, Intraperitoneal; D008770:Methylnitrosourea; D051379:Mice; D008810:Mice, Inbred C57BL; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012162:Retinal Degeneration / Q000139:chemically induced / Q000235:genetics / Q000473:pathology*; D051742:Transcription Factor CHOP / Q000235:genetics
chemical_list: D000477:Alkylating Agents; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D012333:RNA, Messenger; D051742:Transcription Factor CHOP; D008770:Methylnitrosourea; D002154:Calpain; D020169:Caspases