Nicotinamide-Rich Diet in DBA/2J Mice Preserves Retinal Ganglion Cell Metabolic Function as Assessed by PERG Adaptation to Flicker

Abstract

Flickering light increases metabolic demand in the inner retina. Flicker may exacerbate defective mitochondrial function in glaucoma, which will be reflected in the pattern electroretinogram (PERG), a sensitive test of retinal ganglion cell (RGC) function. We tested whether flicker altered the PERG of DBA/2J (D2) glaucomatous mice and whether vitamin B3-rich diet contributed to the flicker effect. D2 mice fed with either standard chow (control, n = 10) or chow/water enriched with nicotinamide (NAM, 2000 mg/kg per day) (treated, n = 10) were monitored from 3 to 12 months. The PERG was recorded with superimposed flicker (F-PERG) at either 101 Hz (baseline) or 11 Hz (test), and baseline-test amplitude difference (adaptation) evaluated. At endpoint, flat-mounted retinas were immunostained (RBPMS and mito-tracker). F-PERG adaptation was 41% in 3-month-old D2 and decreased with age more in control D2 than in NAM-fed D2 (GEE, p < 0.01). At the endpoint, F-PERG adaptation was 0% in control D2 and 17.5% in NAM-fed D2, together with higher RGC density (2.4×), larger RGC soma size (2×), and greater intensity of mitochondrial staining (3.75×). F-PERG adaptation may provide a non-invasive tool to assess RGC autoregulation in response to increased metabolic demand and test the effect of dietary/pharmacological treatments on optic nerve disorders.

Keywords: adaptation; mitochondria; nicotinamide; pattern electroretinogram; retinal ganglion cell.

Figure 1

Retinal ganglion cell (RGC) function measurements by pattern electroretinogram (PERG) superimposed with flicker light at 101 or 11 Hz. (A) Examples of baseline (blue) and test (red) PERG waveforms recorded D2 mouse at 3 months of age and at 12 months of age with either standard diet or vitamin B3-enriched diet. Note that B3-enriched diet has a protective effect of PERG amplitude; (B) Adaptation of F-PERG in D2 mice as a function of age. The amplitude difference between baseline F-PERG and test F-PERG diminished with age in the control group but not in B3-treated group (n = 10 for each group). Error bars represent the SEM.

Figure 2

NAM supplementation rescues retinal ganglion cell (RGC) and mitochondria, and preserves flicker-induced PERG adaptation. Examples of RBPMS-labeled RGCs (A), mitotracker (D), and merged labeling (G) in 3-month-old D2 mice. (B,E,H) corresponding examples for 13-month-old control mice. (C,F,I) corresponding examples for 13-month-old NAM-tread mice (Scale bar: 50 µm). (J) Mean (SE) RGC density (cells/mm²); (K) mean (SE) RGC soma size (µm²); (L) mean (SE) mitotracker intensity for the three groups of mice. (M) The Flicker-PERG adaptation index (test/baseline) decreases with increasing mitotracker intensity.