The effect of simulated intraocular pressure (IOP) elevation on biomechanical properties and morphology of retinal ganglion cells (RGCs)

Abstract

<p><strong>Purpose </strong>: The mechanism by which elevated intraocular pressure (IOP) causes progressive loss of retinal ganglion cells (RGCs) remains obscure. We tested the hypothesis that durative elevated IOP would result in morphological and biomechanical degeneration of primary single RGCs using an experimental model of high IOP.</p><p><strong>Methods </strong>: Primary RGCs isolated from SD-rats were cultured for 4 days. Static pressure at 39.6±3.5 mmHg was then applied with mixed air (5% CO₂ and 21.4% O₂ in air) for 3 consecutive days. The control group was kept in the identical condition without pressure.<br>The stiffness of soma (S_s, n=11) and axon (S_a, n=14) of individual RGCs was measured using atomic force microscope at 0h, 24h, 48h and 72h. Axon length (L_a), total neurite length (L_n) and soma area (A_s) at four time points were monitored (n=11 in the controls; n = 28 in the pressure group). One-way ANOVA was used in statistical analysis (Mean±SD).</p><p><strong>Results </strong>: Under the elevated pressure, S_a significantly rose (2.09±0.27 kPa) compared to the controls (1.55±0.33 kPa, p=0.004) starting from 24h. In comparison, S_s significantly decreased at 48h (184.4±36.4 Pa) compared to those at 24h (262.9±51.4 Pa, p=0.007). At 48h, S_s was also significantly lower compared to the controls (254.1±27.7 Pa, p=0.025). No significant difference was found at four time points for both S_s and S_a in the controls.<br>The increase of L_a in the controls (1.35±0.19 times) was significantly larger than in the pressure group (1.05±0.13 times, p=0.002) at 24h. However, a significantly reduction in L_a was found at 72h (0.80±0.24 times) compared to 24h (1.05±0.13 times, p=0.004) under the pressure stimuli. Similar results were found for L_n. A_s significantly dropped at 48h (0.85±0.17 times) compared to 24h (0.97±0.09 times, p=0.004) in the pressure group. No significant difference of A_s was found at four time points in the controls.</p><p><strong>Conclusions </strong>: The results found that under the constant pressure stimuli for 48 h, the stiffness of RGC axon increased while the stiffness of RGC soma was lowered. IOP elevation not only significantly inhibited the neurite growth, but also reduced the soma area. Further investigation will be needed to discover the time point when RGCs begin to degenerate under different IOP levels, to shed light on the mechanism of RGC degeneration from the biomechanical perspective.</p>