Retinal Mueller Glial Cells Trigger the Hallmark Inflammatory Process in Autoimmune Uveitis

Abstract

Spontaneous equine recurrent uveitis (ERU) is an incurable autoimmune disease affecting the eye. Although retinal-autoantigen specific T-helper 1 cells have been demonstrated to trigger disease progression and relapses, the molecular processes leading to retinal degeneration and consequent blindness remain unknown. To elucidate such processes, we studied changes in the total retinal proteome of ERU-diseased horses compared to healthy controls. Severe changes in the retinal proteome were found for several markers for blood-retinal barrier breakdown and whose emergence depended upon disease severity. Additionally, uveitic changes in the retina were accompanied by upregulation of aldose 1-epimerase, selenium-binding protein 1, alpha crystallin A chain, phosphatase 2A inhibitor (SET), and glial fibrillary acidic protein (GFAP), the latter indicating an involvement of retinal Mueller glial cells (RMG) in disease process. To confirm this, we screened for additional RMG-specific markers and could demonstrate that, in uveitic retinas, RMG concomitantly upregulate vimentin and GFAP and downregulate glutamine synthetase. These expression patterns suggest for an activated state of RMG, which further downregulate the expression of pigment epithelium-derived factor (PEDF) and begin expressing interferon-gamma, a pro-inflammatory cytokine typical for T-helper 1 cells. We thus propose that RMG may play a fatal role in uveitic disease progression by directly triggering inflammatory processes through the expression and secretion of interferon-gamma.

Deciphering Membrane-Associated Molecular Processes in Target Tissue of Autoimmune Uveitis by Label-Free Quantitative Mass Spectrometry

“…Taken together, we conclude that the presented method is suitable to compare membrane-protein enriched fractions from retinas and results in a much increased analysis depth compared with conventional 2D gel-based proteomics comparisons (5,22).…”

“…The spontaneous animal model equine recurrent uveitis (ERU) 1 (3) enabled us to undertake several studies comparing diseased versus healthy condition by proteomic analyses utilizing retina, vitreous and serum samples from horses (4). As a result, we have shown that retinal Mueller cells are players in the pathogenesis of the disease as they transform into a gliotic phenotype-decreasing expression of glutamine synthetase and pigment epitheliumderived factor (PEDF) and simultaneously start expressing interferon gamma (5). This observation is complemented by a quantitative comparison of serum samples with twodimensional-DIGE, where PEDF was also significantly downregulated in ERU cases (6).…”

Pigment epithelium-derived factor mitigates inflammation and oxidative stress in retinal pericytes exposed to oxidized low-density lipoprotein

“…We reported recently that PEDF is a potent endogenous anti-inflammatory factor (Zhang et al 2006). Decreased intraocular PEDF levels have been observed in patients with diabetic retinopathy and in animal models of type 1 diabetes and spontaneous uveitis (Boehm et al 2003, Zhang et al 2006, Hauck et al 2007. Administration of PEDF into the vitreous significantly inhibits leukostasis and reduces vascular permeability in the retina in STZ-induced diabetic rats, suggesting a potential role of PEDF on leukocyte/ monocyte activation and infiltration in diabetic retinopathy (Yamagishi et al 2006, Zhang et al 2006.…”

The Retinal Proteome in Experimental Diabetic Retinopathy

“…Up-regulation of ␣A-crystallin during diabetes occurs early in the course of the disease at the same time as vimentin and GFAP, two markers of Mü ller glial cells, the latter indicating an involvement of Mü ller cells in the disease process (39). This finding, correlated with the presence of antibodies against ␣B-crystallins in serum from multiple sclerosis patients and mice with experimental autoimmune encephalomyelitis (40), suggests that the up-regulation of crystallins could be involved in the inflammatory component of diabetic retinopathy.…”