Loss of the Extracellular Matrix Molecule Tenascin-C Leads to Absence of Reactive Gliosis and Promotes Anti-inflammatory Cytokine Expression in an Autoimmune Glaucoma Mouse Model

Abstract

Previous studies demonstrated that retinal damage correlates with a massive remodeling of extracellular matrix (ECM) molecules and reactive gliosis. However, the functional significance of the ECM in retinal neurodegeneration is still unknown. In the present study, we used an intraocular pressure (IOP) independent experimental autoimmune glaucoma (EAG) mouse model to examine the role of the ECM glycoprotein tenascin-C (Tnc). Wild type (WT ONA) and Tnc knockout (KO ONA) mice were immunized with an optic nerve antigen (ONA) homogenate and control groups (CO) obtained sodium chloride (WT CO, KO CO). IOP was measured weekly and electroretinographies were recorded at the end of the study. Ten weeks after immunization, we analyzed retinal ganglion cells (RGCs), glial cells, and the expression of different cytokines in retina and optic nerve tissue in all four groups. IOP and retinal function were comparable in all groups. Although RGC loss was less severe in KO ONA, WT as well as KO mice displayed a significant cell loss after immunization. Compared to KO ONA, less βIII-tubulin + axons, and downregulated oligodendrocyte markers were noted in WT ONA optic nerves. In retina and optic nerve, we found an enhanced GFAP + staining area of astrocytes in immunized WT. A significantly higher number of retinal Iba1 + microglia was found in WT ONA, while a lower number of Iba1 + cells was observed in KO ONA. Furthermore, an increased expression of the glial markers Gfap, Iba1, Nos2 , and Cd68 was detected in retinal and optic nerve tissue of WT ONA, whereas comparable levels were observed in KO ONA. In addition, pro-inflammatory Tnfa expression was upregulated in WT ONA, but downregulated in KO ONA. Vice versa, a significantly increased anti-inflammatory Tgfb1 expression was measured in KO ONA animals. We conclude that Tnc plays an important role in glial and inflammatory response during retinal neurodegeneration. Our results provide evidence that Tnc is involved in glaucomatous damage by regulating retinal glial activation and cytokine release. Thus, this transgenic EAG mouse model for the first time offers the possibility to investigate IOP-independent glaucomatous damage in direct relation to ECM remodeling.

Extracellular Matrix Remodeling in the Retina and Optic Nerve of a Novel Glaucoma Mouse Model

“…It is therefore tempting to speculate that tenascin-C-mediated signaling plays an important role in the activation and migration of astrocytes and microglia, which has a harmful effect on RGC survival in our glaucoma mouse model. Consistent with this assumption, we recently demonstrated that Tnc knock-out mice exhibit less severe IOP-independent glaucomatous damage of RGCs and optic nerve fibers, decreased micro-and macroglial reactivity, and increased anti-inflammatory cytokine expression [70].…”

Evaluation of the Effectiveness of a Chronic Ocular Hypertension Mouse Model Induced by Intracameral Injection of Cross-Linking Hydrogel

“…The fluorescence images were scanned and captured with a confocal laser-scanning microscope (LSM 510 META; Zeiss, Jena, Germany). Quantitative analysis of fluorescence density was performed according to a previous study ( 14 , 15 ). Briefly, for retinal slices, three randomly selected nonoverlapping subranges of 300 μm within a 1-mm distance from the optic disc margin of each unilateral side were outlined for a total of six subranges for each slice.…”

The Interaction Between Microglia and Macroglia in Glaucoma

“…In a study of IOP-independent experimental autoimmune glaucoma (EAG) mice models, the mice were immunized with an optic nerve antigen (ONA). Compared with the control group, the EAG mice displayed fewer Brna+ RGCs and SMI-31+ optic nerve neurofilaments, with a significantly higher number of retinal Iba1 + microglia and GFAP + astrocytes (Wiemann et al, 2020).…”