Abstract
Background
Retinal degeneration is followed by significant changes in the structure and function of photoreceptors in humans and several genetic animal models. However, it is not clear whether similar changes occur when the degeneration is induced pharmacologically. Therefore, our aim was to investigate the influence of retinotoxic N-methyl-N-nitrosourea (MNU) on the function, morphology and underlying molecular pathways of programmed cell death.
Methods
C57/BL6 mice were injected with different doses of MNU, and function was determined by analysing optokinetic reflex measurements and cued water maze results at several time points post-injection. Morphometric measurements were also taken from H&E-stained paraffin eye sections. TUNEL-positive cells and caspase-3 and -6 were detected by immunohistochemistry. To assess the molecular changes leading to cell death, qRT-PCR from neurosensory retina mRNA was performed.
Results
The application of MNU led to an instant decrease in function and a delayed decrease in the thickness of the retinal outer nuclear layer. These responses were observed in the absence of any structural changes in the retinal pigment epithelium. The degeneration of the photoreceptor cell layer was highest with 60 mg/kg MNU. The assessment of TUNEL-positive cells visualised cell death after treatment, but no detectable caspase-3 activity was observed concomitant with these changes. qRT-PCR revealed the possible involvement of the inflammatory mediator caspase-1 and endoplasmic reticulum stress-mediated apoptosis by caspase-12.
Conclusion
MNU leads to the dose-dependent degeneration of photoreceptor cells in mice by caspase-3-independent pathways and is, therefore, a suitable model to study retinal degeneration in an animal model.
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Acknowledgements
The authors thank Monika Kilchenmann for her excellent technical assistance and Richard L. Benton for critically reading the manuscript. This work was partly supported by grants from the Fritz Tobler-Foundation (RZ) and the Berne University Research Foundation (VE).
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Zulliger, R., Lecaudé, S., Eigeldinger-Berthou, S. et al. Caspase-3-independent photoreceptor degeneration by N-methyl-N-nitrosourea (MNU) induces morphological and functional changes in the mouse retina. Graefes Arch Clin Exp Ophthalmol 249, 859–869 (2011). https://doi.org/10.1007/s00417-010-1584-6
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DOI: https://doi.org/10.1007/s00417-010-1584-6