Osteopontin and Fibronectin Levels Are Decreased in Vitreous of Autoimmune Uveitis and Retinal Expression of Both Proteins Indicates ECM Re-Modeling

Abstract

Autoimmune uveitis is an intraocular inflammation that arises through autoreactive T-cells attacking the inner eye, eventually leading to blindness. However, the contributing molecular pathomechanisms within the affected tissues remain as yet elusive. The extracellular matrix (ECM) is a highly dynamic structure that varies tremendously and influences the encompassing tissue. In order to assess ECM re-modeling in autoimmune uveitis, we investigated the expression of ECM molecules fibronectin and osteopontin in vitreous and retina samples. This was carried out in the only spontaneous animal model for human autoimmue uveitis, namely equine recurrent uveitis (ERU) that resembles the human disease in clinical as well as in immunopathological aspects. ERU is a naturally occurring autoimmune disease in horses that develops frequently and has already proved its value to study disease-related pathomechanisms. Western blot analysis of fibronectin and osteopontin in healthy and uveitic vitreous revealed significant reduction of both proteins in uveitis. Immunohistochemical expression of fibronectin in healthy retinas was restricted to the inner limiting membrane abutting vimentin positive Müller cell endfeet, while in uveitic sections, a disintegration of the ILM was observed changing the fibronectin expression to a dispersed pattern extending toward the vitreous. Retinal expression of osteopontin in control tissue was found in a characteristic Müller cell pattern illustrated by co-localization with vimentin. In uveitic retinas, the immunoreactivity of osteopontin in gliotic Müller cells was almost absent. The ability of Müller cells to express fibronectin and osteopontin was additionally shown by immunocytochemistry of primary cultured equine Müller cells and the equine Müller cell line eqMC-7. In conclusion, severe ECM re-modeling in autoimmune uveitis reported here, might affect the adhesive function of fibronectin and thus the anchoring of Müller cell endfeet to the ILM. Furthermore, the absence of osteopontin in gliotic Müller cells might represent reduced neuroprotection, an osteopontin attribute that is intensively discussed.

Label-free LC-MSMS analysis of vitreous from autoimmune uveitis reveals a significant decrease in secreted Wnt signalling inhibitors DKK3 and SFRP2

“…Several of these proteins have already been detected as relevant for ERU and further characterized through earlier candidate specific analyses, e.g. osteopontin (SPP1), fibronectin 1 (FN1) [21] or PEDF [5,8,25]. A very interesting finding was the strong decrease in expression of SFRP2 and DKK3 in ERU vitreous ( Fig.…”

“…The highest ranking pathway was 'ECM-receptor interaction and focal adhesion,' with 6 overlap members ( Table 2). Two members of ECMreceptor interaction network were recently verified and characterized in ERU [21], namely osteopontin (SPP1), which is additionally associated with pathways 'integrins in angiogenesis, beta1 integrin cell surface interactions,' 'integrin cell surface interactions,' 'osteopontin-mediated events' and 'signaling by PDGF' ( Table 2). The second previously reported protein is fibronectin 1 [20] (FN1; also associated with five additional downregulated pathways, see Table 2).…”

“…The second previously reported protein is fibronectin 1 [20] (FN1; also associated with five additional downregulated pathways, see Table 2). Both proteins are produced by retinal Müller glial cells (RMG), which lose neuroprotective abilities and develop an inflammatory phenotype in ERU [21,22]. Since the target organ plays an important role in pathophysiology of ERU and the retina consists of many different cell types organised into six main classes [23], the identification of cellular players is key to understanding pathomechanisms of disease.…”

Glia–neuron interactions in the mammalian retina

“…Fibronectin was also shown to be produced by cultured adult mouse retinal astrocytes (Scheef et al, 2005), although there are inconsistent reports regarding fibronectin expression in the adult retina and it remains unclear whether or not it is found in the ILM of adult retina of different mammalian species (Chen et al, 2009b;Deeg et al, 2011;Hiscott et al, 1992;Kohno et al, 1987;Ljubimov et al, 1996). Fibronectin has an important developmental role in vascularisation (Jiang et al, 1994), yet its function in the adult retina requires further study.…”

Matricellular Proteins in the Trabecular Meshwork: Review and Update

“…[230][231][232][233][234][235] Within the eye, osteopontin is involved in corneal and choroidal wound healing, lens epithelial injury, autoimmune uveitis, and proliferative diabetic retinopathy. [236][237][238][239][240][241][242] Using cDNA microarrays, TM cells have been shown to express osteopontin. 243 Given that TM cells have phagocytic activity that may alter outflow facility, osteopontin may be involved in this process.…”