Abstract
Retinal Müller glial cells (RMG) are involved in virtually every retinal disease; however, the role of these glial cells in neuroinflammation is still poorly understood. Since cell surface proteins play a decisive role in immune system signaling pathways, this study aimed at characterizing the changes of the cell surface proteome of RMG after incubation with prototype immune system stimulant lipopolysaccharide (LPS). While mass spectrometric analysis of the human Müller glia cell line MIO-M1 revealed 507 cell surface proteins in total, with 18 proteins significantly more abundant after stimulation (ratio ≥ 2), the surfaceome of primary RMG comprised 1425 proteins, among them 79 proteins with significantly higher abundance in the stimulated state. Pathway analysis revealed notable association with immune system pathways such as “antigen presentation”, “immunoregulatory interactions between a lymphoid and a non-lymphoid cell” and “cell migration”. We could demonstrate a higher abundance of proteins that are usually ascribed to antigen-presenting cells (APCs) and function to interact with T-cells, suggesting that activated RMG might act as atypical APCs in the course of ocular neuroinflammation. Our data provide a detailed description of the unstimulated and stimulated RMG surfaceome and offer fundamental insights regarding the capacity of RMG to actively participate in neuroinflammation in the retina.
Highlights
In recent years, retinal Müller glial cells (RMG) have gained increasing attention, as they are involved in virtually every retinal disease and represent valuable therapeutic targets
We identified 507 cell surface proteins in cells of the human retinal Müller glia cell line Moorfields/Institute of Ophthalmology- Müller 1 (MIO-M1) (Supplementary Table S1) and 1425 proteins in the surfaceome of primary equine RMG (Supplementary Table S2)
To assess the capacity of RMG to respond to immune stimuli, MIO-M1 cells as well as primary RMG were stimulated with LPS for 24 h
Summary
Retinal Müller glial cells (RMG) have gained increasing attention, as they are involved in virtually every retinal disease and represent valuable therapeutic targets (reviewed in [1,2,3,4]). RMG are involved in maintaining retinal water-, pH- and ion- homeostasis [7,8], and they contribute to the blood–retinal barrier (BRB) with their endfeet [9]. They support retinal neurons by recycling neurotransmitters [5,10] and supplying them with nutrients [1,11,12]. In order to gain further insight into the capacity of RMG to transform into an activated phenotype upon a danger signal, we carried out an in-depth analysis of the RMG surfaceome after stimulation with prototype immune system stimulant lipopolysaccharide (LPS). Our results demonstrate that the RMG surfaceome changes considerably in response to immune stimulation and provide fundamental knowledge about the contribution of RMG to immune system signaling
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