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Symantas Ragauskas, Lucia Podracka, Seppo Ronkko, Jooseppi Puranen, AnneMari Haapaniemi, Taneli Heikkinen, Outi Kontkanen, Jukka Puolivali, Juha Yrjanheikki, Giedrius Kalesnykas; Insoluble Aggregates Of Mutant Huntingtin Protein Do Not Cause Degeneration Of Retinal Ganglion Cells In R6/2 Mice. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2449.
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To study mutant Huntingtin protein (mHtt) accumulation and its clearance in retinal ganglion cells (RGCs) of R6/2 mice during the disease progression.
Four to 19-week-old R6/2 mice and their wild-type (WT) littermates were used. Retinal wholemounts, paraffin-embedded retinal and frozen optic nerve sections were processed for histology, immunohistochemistry and TUNEL-based staining. The total number of RGC layer (RGCL) cells, glial fibrillary acidic protein (GFAP)-positive retinal astrocytes and RGCL cells containing mHtt were counted using stereology. The protein levels of heat shock protein 70 kDa (HSP70), p62 and LC3 were compared using Western blotting. Metabolic state of retinal cells, optic nerve and superior colliculus were assessed by measuring NAD+, NADH and total NAD levels using resazurin-based assay.
At young age (4 weeks) mainly soluble form of mHtt was present in neurons of RGCL, whereas at the age of 8, 12 and 16 weeks the vast majority of neurons had aggregated form of mHtt. R6/2 and WT mice did not differ in TUNEL labeling of RGCL or the total number of RGCL neurons and GFAP-positive astrocytes. Soluble mHtt was found in GFAP-positive astrocytes and Iba-1-positive macrophages of optic nerves, but not in GFAP-positive retinal astrocytes. Western blotting of retinas showed an increased protein level of p62, but decreased HSP70 and a single 16 kDa band of LC3.
Cellular accumulation of the aggregated form of mHtt increases with age, but does not induce autophagy or cause degeneration of retinal astrocytes and RGCL neurons. Metabolic state of retinal cells, optic nerve and cells from superior colliculus is unaltered even at the late stage of the disease.
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