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Updated: May 26, 2026
An Assay to Detect Protection of the Retinal Vasculature from Diabetes-Related Death in Mice
Published on: January 12, 2024
Partial rescue of retinal function in chronically hypoglycemic mice
Yumiko Umino1, Nicolas Cuenca, Drew Everhart
1Center for Vision Research and SUNY Eye Institute, Department of Ophthalmology, SUNY Upstate Medical University, Syracuse, New York 13210, USA.
Purpose:
Mice rendered hypoglycemic by a null mutation in the glucagon receptor gene Gcgr display late-onset retinal degeneration and loss of retinal sensitivity. Acute hyperglycemia induced by dextrose ingestion does not restore their retinal function, which is consistent with irreversible loss of vision. The goal of this study was to establish whether long-term administration of high dietary glucose rescues retinal function and circuit connectivity in aged Gcgr-/- mice.
Methods:
Gcgr-/- mice were administered a carbohydrate-rich diet starting at 12 months of age. After 1 month of treatment, retinal function and structure were evaluated using electroretinographic (ERG) recordings and immunohistochemistry.
Results:
Treatment with a carbohydrate-rich diet raised blood glucose levels and improved retinal function in Gcgr-/- mice. Blood glucose increased from moderate hypoglycemia to euglycemic levels, whereas ERG b-wave sensitivity improved approximately 10-fold. Because the b-wave reflects the electrical activity of second-order cells, we examined for changes in rod-to-bipolar cell synapses. Gcgr-/- retinas have 20% fewer synaptic pairings than Gcgr+/- retinas. Remarkably, most of the lost synapses were located farthest from the bipolar cell body, near the distal boundary of the outer plexiform layer (OPL), suggesting that apical synapses are most vulnerable to chronic hypoglycemia. Although treatment with the carbohydrate-rich diet restored retinal function, it did not restore these synaptic contacts.
Conclusions:
Prolonged exposure to diet-induced euglycemia improves retinal function but does not reestablish synaptic contacts lost by chronic hypoglycemia. These results suggest that retinal neurons have a homeostatic mechanism that integrates energetic status over prolonged periods of time and allows them to recover functionality despite synaptic loss.
Insights
Dietary glucose improved retinal function in mice with glucagon receptor gene mutations, but did not restore lost synaptic connections. This suggests retinal neurons can recover function despite synaptic loss.
Area of Science:
- Neuroscience
- Ophthalmology
- Metabolic Research
Background:
- Glucagon receptor gene (Gcgr) null mutation in mice causes late-onset retinal degeneration and vision loss.
- Acute hyperglycemia does not restore vision, suggesting irreversible damage.
Purpose of the Study:
- To determine if long-term high dietary glucose can rescue retinal function and circuit connectivity in aged Gcgr-/- mice.
- Investigate the impact of chronic hypoglycemia on retinal structure and function.
Main Methods:
- Gcgr-/- mice received a carbohydrate-rich diet from 12 months of age for 1 month.
- Retinal function was assessed using electroretinographic (ERG) recordings.
- Retinal structure, including synaptic integrity, was evaluated via immunohistochemistry.
Main Results:
- Carbohydrate-rich diet normalized blood glucose levels in Gcgr-/- mice, improving ERG b-wave sensitivity approximately 10-fold.
- Retinal function recovery occurred despite a 20% reduction in rod-to-bipolar cell synapses.
- Lost synapses, primarily apical ones in the outer plexiform layer, were not reestablished by the diet.
Conclusions:
- Prolonged diet-induced euglycemia enhances retinal function but does not restore synaptic contacts lost due to chronic hypoglycemia.
- Retinal neurons may possess homeostatic mechanisms enabling functional recovery despite synaptic loss.
- This highlights a potential therapeutic window for managing vision impairment in metabolic disorders.
