ABSTRACT: Glaucoma is not only the second leading cause of blindness worldwide, but patient numbers will also increase significantly in the coming years due to aging societies. Glaucoma is a progressive optic neuropathy with changes at the optic nerve head, gradual retinal ganglion cell (RGC) death, and visual field loss [1]. Unfortunately, glaucoma can remain asymptomatic until it is rather far progressed, hence about 10-50 % of patients are unaware they suffer from this disease. High intraocular pressure (IOP) is the main risk factor; however, normal-tension glaucoma (NTG) occurs in patients with physiological IOP [2]. This form account for about 30 % of glaucoma patients [3]. Furthermore, sustained IOP lowering can slow down, but does not completely stop disease progression in patients. [4, 5]. Additionally, the administration of topical glaucoma medications can lead to side effects, such as ocular irritation, decreasing the compliance of patients. These facts emphasize the importance of discovering new treatment strategies. The exact pathogenesis for glaucoma is still unknown, but several factors are considered to be involved (fig.1). The most prominent factor is an elevated IOP, which can cause blockade of axonal protein transport at the lamina cribrosa, causing an initial axonal damage and RGC death by trophic insufficiency. In addition, ischemic/hypoxic damage [6], astrocyte and glia cell alterations, and excessive stimulation of the glutamatergic system [7] are discussed as possible pathomechanisms. Moreover, an involvement of the immune system is considered [8-10]. In glaucoma patients, up- and downregulations in the systemic and ocular antibody profile were detected [11-13]. Also, antibody deposits were observed in glaucomatous retinae [14]. It is likely that a combination of several pathogenic factors/mechanisms increases the possibility of developing glaucoma. For the investigation of pathomechanisms and novel therapies, it is necessary to have suitable models that allow such screening. To investigate whether antibodies detected in glaucoma patients are part of glaucoma pathogenesis or a result of disease progression, the experimental autoimmune glaucoma (EAG) animal model was established. This animal model is based on the fact that autoantibodies against S100B, a small calcium binding protein expressed in glia cells, were found to be increased in glaucoma patients [15]. In this model, an immunization with S100B led to a significant loss of RGCs after 28 days and a fast degeneration of optic nerves [20]. The IOP in this model was not altered. Therefore, we were able to mimic the effects seen in NTG patients, an IOP-independent glaucomatous degeneration, by immunizing rats with S100B. S100B is a calcium-binding protein. In the central nervous system (CNS), it is mainly expressed by glial cells such as oligodendrocytes, Schwann cells, ependymal cells, retinal Müller cells and astrocytes [16]. S100B regulates and maintains the homeostasis of the important second messenger calcium and is therefore involved in many cell activities, such as signal transduction, cell differentiation, regulation of cell motility, transcription and cell cycle processes [17, 18]. Extracellularly, S100B can act as a signal molecule and bind receptors such as the receptor for advanced glycation end products (RAGE). In high concentrations, S100B can have negative effects and lead to cell death. For example, the binding of RAGE can induce the activation of microglia cells leading to a release of proinflammatory cytokines to an excessive extent [19]. Furthermore, there seems to be a link between S100B and neuronal diseases. In glaucoma patients, high antibody titers against S100B were found [20]. To investigate the effect of S100B in glaucoma more precisely, the immunization with S100B leads to a loss of retinal ganglion cells (RGCs) without an elevation of the IOP after 28 days in the EAG model [21, 22]. The goal of the present study was to detect the retinal biomarkers in EAG animals 7 and 14 days after immunization with S100B. To detect these new markers in disease development, a label free quantitative mass spectrometry-based approach will be used.
Annika Guntermann 
