Abstract
Purpose :
Intraocular pressure (IOP) fluctuation is suggested as a risk factor of glaucoma. The association between progressive degeneration of retinal ganglion cells (RGCs) and pulsatile IOP remains obscure. Using an adjustable pressure platform, we tested the hypothesis that responses of primary RGCs to pressure fluctuation associated with cardiac cycle might reflect the progressive degeneration of RGCs.
Methods :
Primary RGCs derived from SD-rats were cultured for 4 days. Static pressures 14 mmHg (normal pressure, NP) and 40 mmHg (abnormal high pressure, AHP), and one dynamic pressure 14±2.5 mmHg (fluctuation at normal pressure, FNP) were then applied with mixed gas (5% CO2 and 21.4% O2 in the air) for 3 consecutive days. Pressure and O2 level were monitored continuously. Axon length, total neurite length, and soma area (La, Ln, and As, n=18) for identical single RGCs at 0h, 24h, 48h and 72h were measured using ImageJ, respectively. Immunocytochemistry (ICC) staining on beta-tubulin III was conducted at each time point. One-way ANOVA followed by Bonferroni post-hoc tests was used in statistical analysis (Mean±S.D.).
Results :
Under NP, both La and Ln were significantly increased at 72h (p<0.01), while no significant difference of As could be found. Under AHP for 48h, the increase of La was significantly lower (1.0±0.1 times, p=0.02) than under NP (1.4±0.5 times), and As also dropped significantly (0.8±0.2 times, p<0.001).
Under FNP, the significant increase of La emerged more slowly (72h, p=0.02) than in NP (48h, p=0.003). Interestingly, no significant changes could be found over 72hrs for Ln, which was similar to AHP. However, Ln has already increased significantly under NP at 48h (1.5±0.5 times, p=0.001). Sa showed no significant difference in or between NP and FNP. Additionally, microtubule aggregation into segments in neurites was observed in both FNP at 72h and EP at 48h, followed by neurite beading in EP at 72h.
Conclusions :
The pressure fluctuation (±2.5 mmHg) with a normal baseline IOP (i.e. 14 mmHg) range would contribute to inhibition of the neurite growth, which is comparable with the RGC responses to constant AHP. This finding indicates that the pulsatile IOP potentially triggers degeneration of RGCs. Further investigation will be needed to better understand the relationship between pressure fluctuation range and RGC degeneration.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.