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Tom A Gardiner, Paul Canning, Nuala Tipping, Alan W Stitt; Evidence of Increased Neuronal Glycogen Storage in Short-term Diabetes. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2718.
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© ARVO (1962-2015); The Authors (2016-present)
We have recently reported abnormal glycogen storage in retinal amacrine cells of 2 and 4 month diabetic rats, accompanied by alterations in the nuclear sequestration of phosphorylated glycogen synthase (pGS). In this study we examined if such changes were detectable after short-term diabetes.
Diabetes was induced in male Sprague-Dawley rats (240-280 gms) by an IP-injection of streptozotocin (STZ) at 65mg/kg of body weight. After 10 days, diabetic (n=7) and control rats (n=5) were culled and the eyes processed for wax embedding. Right eyes were fixed in Davidson's fixative (DF) and left eyes with 4% paraformaldehyde. Tissue sections were stained with periodic acid-Schiff (PAS) with amylase-digested negative controls for glycogen identification. The total number of glycogen positive amacrine cells was counted in 16 high-magnification (HM) fields/retina. Following antigen retrieval, parallel sections were stained for pGS using immunohistochemistry and by immunofluorescence for confocal microscopy. Glycogen synthase is inactivated by phosphorylation, and also by nuclear sequestration.
Following fixation in DF, glycogen was detectable in a small population of amacrine cells in control retina (mean 21.6 in 16 HM-fields/retinas SD±4.5). More glycogen positive amacrine cells were present in the diabetic retinas (mean 46.3 in 16 HM-fields/retinas SD±6.8); the difference was highly statistically significant (p<0.0001). The intensity of PAS staining, indicative of the amount of glycogen, was also greater in the diabetic retinas. No obvious difference in nuclear staining for pGS could be detected in IHC stained diabetic retina compared to controls, although confocal microscopy showed subtle reduction and complete loss in individual cells within the inner nuclear layer.
Several classes of retinal neurons utilize glycogen. Amacrine cells differ from other retinal neurons in that during diabetes they become congested with the carbohydrate and the present study shows that this process has commenced by 10 days of diabetes. No significant alteration in the status of pGS was noted at this early stage of the disease.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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