Abstract

DO.14.02

Eye involvement in a murine model of NPC1 disease

Marine Hovakimyan1, Karen Falke1, Maria Kröger1, Oliver Stachs1, Arndt Rolfs2, Moriz Frech2, Andreas Wree3, Rudolf F. Guthoff1
1Universitäts-Augenklinik Rostock, 2Albrecht-Kossel-Institut für Neurodegeneration, Universität Rostock, Rostock, 3Institut für Anatomie, Universität Rostock, Rostock

Objective
Niemann-Pick Type C (NPC) disease is a lysosomal lipid storage disorder of autosomal recessive inheritance. In most cases (95%) the disease is caused by mutations in NPC1 gene, and the remainder 5 % of cases are caused by mutations in NPC2 gene. Proteins, coded by both genes are directly involved in cholesterol metabolism and trafficking.
The pathological hallmark is the massive accumulation of cholesterol in late endosomes and lysosomes. The lipid accumulation occurs primarily in neurons of cerebellum and hippocampus and non neuronal tissues such as liver, spleen, intestine.
In the present study, ophthalmoscopic features of NPC1 disease were investigated, using a knock out mouse model.
Methods
Nine inbred homozygous NPC1-/- knock out mice aged 5 to 11 weeks and 9 age matched NPC1+/+ siblings were used in the study. At first, in vivo laser scanning confocal microscopy was performed bilaterally on corneae. Secondary, the animals were killed, and the eyes were excised and used for the histological examination.
Results
In confocal imaging, there were no changes in the morphology of corneal superficial epithelial cell layer between NPC1+/+ and NPC1-/- mice: the cells had characteristic appearance with dark cytoplasm and bright nuclei. The pathological changes in form of hyperreflective intracellular deposits were limited to the corneal basal epithelial cell layer of NPC1-/- mice. No pathological changes were revealed in the morphology of subbasal nerve plexus. The stromal region had also the similar appearance in wild and homozygous mice. The endothelium exhibited normal cell morphology, density and reflectivity. The central corneal thickness obtained with confocal microscopy was 150-180 µm, and did not differ between both groups.
H.E. staining showed no differences between wild and homozygous mice. The staining for filipin (for detection of unesterified cholesterol) was negative in the corneal epithelium in both groups. Interestingly, intense accumulation of cholesterol was detected in the retinal ganglion cells as shown by filipin staining.
Conclusions
Our findings show, that the accumulation of cholesterol in NPC1-/- mice eye does not occur in the cornea, but in the retina. Further studies are needed to clarify the nature of intracellular inclusions in the corneal epithelium.

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