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Multiple programmed cell death pathways are involved in N-methyl-N-nitrosourea-induced photoreceptor degeneration

Reisenhofer, Miriam ; Balmer, Jasmin ; Zulliger, Rahel ; Enzmann, Volker

In: Graefe's Archive for Clinical and Experimental Ophthalmology, 2015, vol. 253, no. 5, p. 721-731

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    Title
    • Multiple programmed cell death pathways are involved in N-methyl-N-nitrosourea-induced photoreceptor degeneration
    Author
    • Reisenhofer, Miriam. Department of Ophthalmology, Inselspital, University of Bern, Freiburgstrasse 14, 3010, Bern, Switzerland
    • Balmer, Jasmin. Department of Ophthalmology, Inselspital, University of Bern, Freiburgstrasse 14, 3010, Bern, Switzerland
    • Zulliger, Rahel. Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
    • Enzmann, Volker. Department of Ophthalmology, Inselspital, University of Bern, Freiburgstrasse 14, 3010, Bern, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Graefe's Archive for Clinical and Experimental Ophthalmology, 2015, vol. 253, no. 5, p. 721-731. Springer Berlin Heidelberg
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:331782
    Summary
    Purpose: 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 (60mg/kg bodyweight), and were observed over a period of 7days. 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 3days 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.