Minocycline reduces inflammatory response and cell death in a S100B retina degeneration model.

BACKGROUND: Previous studies noted that intravitreal injection of S100B triggered a glaucoma-like degeneration of retina and optic nerve as well as microglia activation after 14 days. The precise role of microglia in our intravitreal S100B model is still unclear. Hence, microglia were inhibited through minocycline. The aim is to investigate whether microglia have a significant influence on the degeneration process or whether they are only a side effect in the model studied here. METHODS: Minocycline was applied daily in rats by intraperitoneal injection using two different concentrations (13.5 mg/kg body weight, 25 mg/kg body weight). One day after treatment start, S100B or PBS was intravitreally injected in one eye per rat. The naïve groups received no injections. This resulted in a total of five groups (naïve n = 14, PBS n = 14, S100B n = 13, 13.5 mg/kg mino n = 15, 25 mg/kg mino n = 15). At day 14, electroretinogram measurements were performed, followed by immunofluorescence and label-free quantitative proteomics analysis. The focus of these investigations was on the survival of RGCs as well as their axons, the response of the microglia, and the identification of further pathological modes of action of S100B. RESULTS: The best signal transmission was detected via ERG in the 13.5 mg/kg mino group. The inhibition of the microglia protected optic nerve neurofilaments and decreased the negative impact of S100B on RGCs. However, the minocycline treatment could not trigger complete protection of RGCs. Furthermore, in retina and optic nerve, the minocycline treatment reduced the number and activity of S100B-triggered microglia in a concentration-dependent manner. Proteomics analysis showed that S100B application led to numerous metabolic functions and cellular stress, mainly an increased inflammatory response, glycolysis, and mitochondrial dysfunction, which caused oxidative stress in the retina. Importantly, the protective capability of lower dose of minocycline was unraveled by suppressing the apoptotic, inflammatory, and the altered metabolic processes caused by S100B insult in the retina. CONCLUSION: Intravitreally injected S100B not only led to a pro-inflammatory microglial reaction, but also a mitochondrial and metabolic dysfunction. Also, these results suggest that an excessive microglial response may be a significant degenerative factor, but not the only trigger for increased cell death.

Synapse and Receptor Alterations in Two Different S100B-Induced Glaucoma-Like Models.

Glaucoma is identified by an irreversible retinal ganglion cell (RGC) loss and optic nerve damage. Over the past few years, the immune system gained importance in its genesis. In a glaucoma-like animal model with intraocular S100B injection, RGC death occurs at 14 days. In an experimental autoimmune glaucoma model with systemic S100B immunization, a loss of RGCs is accompanied by a decreased synaptic signal at 28 days. Here, we aimed to study synaptic alterations in these two models. In one group, rats received a systemic S100B immunization (n = 7/group), while in the other group, S100B was injected intraocularly (n = 6-7/group). Both groups were compared to appropriate controls and investigated after 14 days. While inhibitory post-synapses remained unchanged in both models, excitatory post-synapses degenerated in animals with intraocular S100B injection (p = 0.03). Excitatory pre-synapses tendentially increased in animals with systemic S100B immunization (p = 0.08) and significantly decreased in intraocular ones (p = 0.04). Significantly more n-methyl-d-aspartate (NMDA) receptors (both p ≤ 0.04) as well as gamma-aminobutyric acid (GABA) receptors (both p < 0.03) were observed in S100B animals in both models. We assume that an upregulation of these receptors causes the interacting synapse types to degenerate. Heightened levels of excitatory pre-synapses could be explained by remodeling followed by degeneration.

Impaired oligodendrogenesis and myelination by elevated S100B levels during neurodevelopment.

High levels of the inflammatory molecule S100B protein have been identified in sera from several perinatal inflammatory conditions involving myelin damage and associated with an adverse prognosis or the emergence of sequelea. S100B is essential for oligodendrocyte (OL) differentiation and maturation, but it remains to be established if excessive levels of released S100B upon early brain injury are deleterious in the neurodevelopmental period. Here, we investigated this possibility by evaluating how elevated S100B affects oligodendrogenesis during this period. First, using primary cultures of OL we observed that damage-induced micromolar levels of S100B impair OL differentiation process. S100B elevated concentrations reduced both transition from immature NG2+ oligodendrocyte precursor cells (OPC) to mature MBP+ OL, and morphological maturation of differentiated OL. Interestingly, these effects were abolished by the use of receptor for advanced glycation end-products (RAGE) antagonist FPS-ZM1, suggesting an involvement of the S100B-RAGE axis on oligodendrogenesis impairment. Next, we used organotypic cerebellar slice cultures to explore the role of S100B in a more complex multicellular environment. Also in this model excessive S100B levels impaired oligodendrogenesis resulting in a reduced myelination. Further, elevated S100B levels compromised neuronal and synaptic integrity, while inducing astrogliosis, nuclear factor (NF)-kB activation and inflammation. Again, the FPS-ZM1 co-treatment prevented S100B-induced damaging effects. Overall, our results indicate that persistently elevated S100B levels have deleterious effects during the neurodevelopmental period through RAGE-dependent processes. Thus, targeting high S100B levels and/or S100B-RAGE interaction may constitute good therapeutic strategies to reduce brain injury, including deficits in neuronal architecture, synaptogenesis and myelination associated with perinatal inflammatory conditions.