Synapse and Receptor Alterations in Two Different S100B-Induced Glaucoma-Like Models

Abstract

Glaucoma is identified by an irreversible retinal ganglion cell (RGC) loss and optic nerve damage. Over the past few years, the immune system gained importance in its genesis. In a glaucoma-like animal model with intraocular S100B injection, RGC death occurs at 14 days. In an experimental autoimmune glaucoma model with systemic S100B immunization, a loss of RGCs is accompanied by a decreased synaptic signal at 28 days. Here, we aimed to study synaptic alterations in these two models. In one group, rats received a systemic S100B immunization (n = 7/group), while in the other group, S100B was injected intraocularly (n = 6–7/group). Both groups were compared to appropriate controls and investigated after 14 days. While inhibitory post-synapses remained unchanged in both models, excitatory post-synapses degenerated in animals with intraocular S100B injection (p = 0.03). Excitatory pre-synapses tendentially increased in animals with systemic S100B immunization (p = 0.08) and significantly decreased in intraocular ones (p = 0.04). Significantly more n-methyl-d-aspartate (NMDA) receptors (both p ≤ 0.04) as well as gamma-aminobutyric acid (GABA) receptors (both p < 0.03) were observed in S100B animals in both models. We assume that an upregulation of these receptors causes the interacting synapse types to degenerate. Heightened levels of excitatory pre-synapses could be explained by remodeling followed by degeneration.

Proteomic Analysis of Retinal Tissue in an S100B Autoimmune Glaucoma Model

“…Recently, a significantly lower inhibitory post-synapse signal was visualized by anti-gephyrin in a later stage of retinal degeneration. Here, the intensity remained unchanged in comparison to the control group, confirming a recent study result - that 14 days after immunization might be too early in the retinal degeneration process of systemically immunized S100B animals [ 35 ].…”

“…We could previously show, that 14 days after S100B immunization, more GABA-A receptor α3 and NMDA receptor 1 synapses could be detected, this is before a significant cell loss occurred. In contrast, gephyrin, as a marker for inhibitory post-synapses, was not altered [ 35 ]. As our analyses showed, gephyrin is also not affected after 28 days.…”

“…The number of RNA-binding proteins with multiple splicing (RBPMS) + cells in the ganglion cell layer and calretinin + cells in the inner nuclear layer were counted using ImageJ software (National Institute of Health, Bethesda, MD, USA). To measure the area of HSP60 and α2-macroglobulin, pictures were processed using an ImageJ macro (National Institute of Health), as described previously [ 35 , 36 ]. Briefly, pictures were converted into greyscale (32-bit), and a rolling ball radius of 40 pixels was subtracted to minimize background interference.…”

Heat Shock Protein Upregulation Supplemental to Complex mRNA Alterations in Autoimmune Glaucoma

“…The positive staining area of GFAP and HSP25 was measured using an ImageJ macro as described previously [ 29 , 30 ]. Briefly, images were transferred into grayscale (32-bit) and a defined rolling ball radius (GFAP and HSP25: 50 pixels) was subtracted to minimize background interference.…”

Towards an Understanding of Retinal Diseases and Novel Treatment

“…Furthermore, excitatory post-synapses and RGCs degenerated at once. The results suggest a relevant role of synapse alterations as early events in glaucomatous degeneration [ 3 ].…”