Morphological and functional evaluation of retinal ganglion cells in R6/2 mice

Abstract

Purpose: To study mutated Huntigtin (mHtt) protein deposition and its effect on retinal ganglion cell (RGC) survival and function in R6/2 mice.

Methods: R6/2 mice and their wild-type littermates (WT) were used at the age of 4 to 19 weeks. Immunohistochemistry and stereology were employed to quantify the total number of RGC layer (RGCL) cells, the total number of retinal astrocytes, and RGCL cells that contained soluble and aggregates forms of mHtt. The deposition of mHtt was studied in retinas and optic nerves using immunohistochemistry and confocal microscopy. Optic nerve axons from R6/2 and WT mice were quantified. Electroretinography (ERG) recordings were used to assess the functional status of retinal cells.

Results: The total number of RGCL cells, the total number of GFAP-positive retinal astrocytes, and the total number of RGC axons in the optic nerve did not differ between 18-week old R6/2 mice and their littermate controls. Mutant Htt deposits were localized in nuclear layers of retina. At the age of 4 weeks R6/2 mice had predominantly soluble mHtt in the RGCL cells, whereas the aggregated form of mHtt was found in the majority of cells from the 12-week old R6/2 mice onwards. Retinal astrocytes did not contain mHtt deposits. However, mHtt deposits were found to localize in the GFAP-ir astrocytes of the optic nerve. The ERG recordings showed a deficit in the cone-related function already at the 4-week of age in R6/2 mice with a complete loss of pattern ERG signal at the 8 week of age as compared to the WT controls. The rod-related measurements showed significant deficit at the age of 8 week.

Conclusions: Deposition of mHtt does not cause RGC degeneration or retinal astrocyte loss in R6/2 mice even at the late stage of HD-related pathology. However, the R6/2 mice experience visual functional deficits already at the age of 8 weeks.

Keywords: 688 retina • 554 immunohistochemistry • 508 electrophysiology: non-clinical