Differential modulation of photoreceptors and Müller glial cell function between acute hyperglycemia and long-term diabetes

Abstract

Purpose : Before the appearance of retinal vascular histopathology, diabetes has metabolic and functional effects on multiple other targets within the retina including photoreceptors, bipolar cells and Müller glia. How non-vascular cells of the retina adapt to chronic high glucose remains unclear, therefore we compared effects of acute glucose elevation and chronic diabetes on light-induced activity of photoreceptors, Müller glia and bipolar cells using ex vivo and in vivo electroretinography (ERG).

Methods : Scotopic ex vivo ERG was performed using retinas isolated from C57BL/6J mice (normoglycemic, 1.5-3 months) or diabetic db/db mice (6 months). Retinal tissue was superfused with Ames’ medium (containing 6 mM glucose, 95% O₂/5% CO₂), supplemented with 0.25 mM glutamate and either 30 mM mannitol or glucose. Responses from photoreceptors and ON bipolar cells were recorded in the presence of 40 μM DL-AP4 and 100 μM Ba²⁺ or Ba²⁺ alone, respectively. Müller glia components were isolated by subtracting waveforms in the presence of DL-AP4 and Ba²⁺ from those with DL-AP4 alone. Scotopic in vivo ERG was recorded in db/db and db/+ control mice (6 months) under isoflurane anesthesia.

Results : Photoreceptor light responses increased by acute glucose elevation ex vivo in C57B/6J mice (n=5, p=0.001), while ON bipolar cell responses did not change (n=4-5). We found a linear relationship between Müller cell response amplitude (R_M) and the area under the corresponding photoreceptor response (A_Rp). The slope of the A_Rp-R_M plot was increased by 48% in elevated glucose compared to mannitol (n=10, p=0.004). In db/db mice (n=9 eyes from 5 animals), scotopic a- and b-wave amplitudes were reduced compared to db/+ control mice in vivo (n=10 eyes from 5 animals, p=0.008 and p=0.001, respectively). The slope of the A_Rp-R_M plot were not changed in db/db mice by high-glucose exposure (n=3).

Conclusions : Acutely elevated glucose and long-term diabetes have opposite effects on light-induced activity of photoreceptors and Müller glia and the Müller cells become insensitive to an acute hyperglycemic insult in the retinas isolated from diabetic mice. These results suggest adaptational changes in the photoreceptor and Müller glia cells induced by prolonged hyperglycemia during diabetes.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.