Apoptosis and Glial Reactivity in a Model of Acute Serous Retinal Detachment in the Rat

Abstract

Purpose: : Serous Retinal Detachments (SRDs) involving the macula can cause significant visual loss and have limited therapeutic options. To understand the pathophysiology of SRD, we developed an acute model in the rat. We asked if early cellular processes observed in rhegmatogenous RD - photoreceptor apoptosis and glial reactivity - also occurred in SRD. We also developed quantifiable measures of the glial filamentary response and a sensitive ratio of pro- versus anti-apoptotic gene expression. We also asked if nestin, an intermediate filament associated with neuroglial progenitor cell phenotype, could be detected.

Methods: : Under direct visualization, acute SRDs were induced through transcleral injection of Provisc©, with the goal of detaching 25% or 50% of the retina. At 24, 48 and 72 hours, whole eyes were fixed in formalin, and paraffin-embedded for H&E, TUNEL and immunohistochemical (IHC) analysis. Same-species antibody controls were used. Other eyes were dissected, and the detached and non-detached segments of retina prepared for SybrGreen quantitative polymerase chain reaction (qPCR) or protein analyses. SHAM eyes served as controls. Cell culture was used to confirm the utility of Bcl-2/Bax ratios in determining the pro-survival versus pro-apoptotic response.

Results: : TUNEL-positive photoreceptor apoptosis was observed in all SRDs. By H&E, large SRDs demonstrated near full-thickness loss of the outer nuclear layer. Similar to RRDs, IHC confirmed opsin redistribution in photoreceptor cells, and GFAP and vimentin upregulation in Mueller cells. Quantitative PCR of GFAP mRNA showed 5, 8 and 18-fold upregulation at the three time-points. Uniquely, we also noted upregulation of nestin within Mueller glia. Bcl-2/Bax qPCR ratios increased to 17-fold in cell culture, and are currently under evaluation in the detached retina.

Conclusions: : This study demonstrates that under acute conditions, SRDs, like RRDs, demonstrate protein redistribution in the photoreceptors, photoreceptor apoptosis, and glial reactivity. Uniquely we have developed a qPCR-based method to measure both the pro-survival/pro-apoptotic ratio, and the extent of glial cell reactivity. Both these measures will have utility in determining the relative effects of different drugs or dosing regimens for tissue protection in RD. The demonstration of nestin in SRD may also suggest de-differentiation or cellular plasticity that could be a potential target for novel therapies.

Keywords: retinal detachment • apoptosis/cell death • glia