Abstract
Purpose :
RhoB is a small GTPase with a role in apoptosis, intracellular transport and angiogenesis as studied in cancer, diabetes, and retinopathy of prematurity. The lack of RhoB GTPase and how it affects the normal and stressed retina has not been extensively studied. Previous studies on the critical period have shown that supplemental oxygen during the critical period decreased photoreceptor death in the retina while hypoxic conditions increased photoreceptor death. Therefore, we investigated how RhoB -/- mice’s retina neurons would react to oxygen changes during the critical period of retinal development and how aging affects these retinas.
Methods :
RhoB null mice (C57Bl/6JRhoB-/- or RhoB -/-) and control C57bl/6J (C57) mice were used in this study. Mice were placed into a chamber that allowed for different oxygen concentrations at 16% O2 (hypoxia), 21% O2 (normoxia), or 75% O2 (hyperoxia) from Post-natal day 7 (P7) to P20. Immunofluorescence was conducted at P12, P16, P28 and 1 year to quantify the number of apoptotic cells. Retinal thickness was assessed in three layers of the retina, outer nuclear layer (ONL), inner nuclear layer (INL), and ganglion cell layer (GCL) at P28 and 1 year. Electroretinography (ERG) were conducted at P27 and 1 year. Lastly, intraocular pressure (IOP) was measured using a tonopen in aging animals.
Results :
Young RhoB -/- exhibited significantly increased cell death in the ONL, INL and GCL at 21% O2 when compared to control mice in the early critical period (P12). At 4 weeks, RhoB -/- mice displayed significantly more GCL death compared to C57 in all varying oxygen conditions (p<0.05). While normoxic and hypoxic RhoB-/- animals showed decreased visual function compared to C57, this difference was normalized by hyperoxic treatment. In aging retina, RhoB -/- showed 4 times more death than C57 mice in its photoreceptors and thinner retinal layers in the ONL, INL and GCL. Aging RhoB -/- showed higher IOP measurements at 18.3mm Hg vs 11.9mm Hg in controls and worse visual function as showed by the A and B waves.
Conclusions :
RhoB-/- mice showed reduced visual function accompanied by higher apoptotic cell death and thinner retinal layers. Hyperoxia partially mitigated these changes. Moreover, RhoB-/- mice showed increased IOP at 1 year of age. In depth histological analysis will be required to find out the specific effects of the mutation in the retina and what leads to ocular hypertension.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.