Enhanced glaucomatous damage accompanied by glial response in a new multifactorial mouse model

Increased inflammation in older high-pressure glaucoma mice

Besides an elevated intraocular pressure (IOP), advanced age is one of the most crucial risk factors for developing glaucoma. βB1-Connective Tissue Growth Factor (βB1-CTGF) high-pressure glaucoma mice were used in this study to assess whether glaucoma mice display more inflammatory and aging processes than age-matched controls. Therefore, 20-month-old βB1-CTGF and corresponding wildtype (WT) controls were examined. After IOP measurements, retinas were processed for (immuno-)histological and quantitative real-time PCR analyses. A significantly higher IOP and diminished retinal ganglion cell numbers were noted in βB1-CTGF mice compared to WT. An enhanced macrogliosis as well as an increased number of microglia/macrophages and microglia was detected in retinas of old glaucoma mice. Interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and transforming growth factor-β2 were upregulated, suggesting an ongoing inflammation. Moreover, βB1-CTGF retinas displayed an increased senescence-associated β-galactosidase staining accompanied by a downregulation of Lmnb1 (laminin-B1) mRNA levels. Our results provide a deeper insight into the association between inflammation and high-pressure glaucoma and thus might help to develop new therapy strategies.

Glaucoma, More than Meets the Eye: Patterns of Demyelination Revealed in Human Postmortem Glaucomatous Optic Nerve

Glaucoma is a neurodegenerative disease affecting millions worldwide, characterised by retinal ganglion cell (RGC) degeneration which leads to blindness in more advanced cases. Although the pathogenesis and underlying mechanisms of glaucoma are not fully understood, there are theories that hint at demyelination playing a role in the disease process. Demyelination, or the degeneration of the myelin sheath surrounding axons, has been found in previous studies using animal models of glaucoma and clinical assessments of glaucoma patients. However, this has not been fully realised or quantified in glaucoma patients. Utilising postmortem optic nerve samples from glaucoma and healthy subjects, various immunohistochemical and morphological assessments were performed to determine the extent, if any, of demyelination in glaucomatous optic nerves. Our findings revealed that alongside nerve shrinkage and degeneration of nerve tissue fascicles, there were significantly less myelin proteins, specifically myelin basic protein (MBP), in glaucoma optic nerves. Additionally, the loss of MBP was correlated with decreased oligodendrocyte (OLG) precursors and increasing glial activity. This further supports previous evidence that demyelination may be a secondary degenerative process associated with glaucoma disease progression. Not only do these results provide evidence for potential disease mechanisms, but this is also the first study to quantify optic nerve demyelination in glaucoma postmortem tissue.

In a novel autoimmune and high-pressure glaucoma model a complex immune response is induced

Background

The neurodegenerative processes leading to glaucoma are complex. In addition to elevated intraocular pressure (IOP), an involvement of immunological mechanisms is most likely. In the new multifactorial glaucoma model, a combination of high IOP and optic nerve antigen (ONA) immunization leads to an enhanced loss of retinal ganglion cells accompanied by a higher number of microglia/macrophages in the inner retina. Here, we aimed to evaluate the immune response in this new model, especially the complement activation and the number of T-cells, for the first time. Further, the microglia/macrophage response was examined in more detail.

Methods

Six-week-old wildtype (WT+ONA) and βB1-connective tissue growth factor high-pressure mice (CTGF+ONA) were immunized with 1 mg ONA. A wildtype control (WT) and a CTGF group (CTGF) received NaCl instead. Six weeks after immunization, retinae from all four groups were processed for immunohistology, RT-qPCR, and flow cytometry, while serum was used for microarray analyses.

Results

We noticed elevated numbers of C1q+ cells (classical complement pathway) in CTGF and CTGF+ONA retinae as well as an upregulation of C1qa, C1qb, and C1qc mRNA levels in these groups. While the complement C3 was only increased in CTGF and CTGF+ONA retinae, enhanced numbers of the terminal membrane attack complex were noted in all three glaucoma groups. Flow cytometry and RT-qPCR analyses revealed an enhancement of different microglia/macrophages markers, including CD11b, especially in CTGF and CTGF+ONA retinae. Interestingly, increased retinal mRNA as well as serum levels of the tumor necrosis factor α were found throughout the different glaucoma groups. Lastly, more T-cells could be observed in the ganglion cell layer of the new CTGF+ONA model.

Conclusion

These results emphasize an involvement of the complement system, microglia/macrophages, and T-cells in glaucomatous disease. Moreover, in the new multifactorial glaucoma model, increased IOP in combination with autoimmune processes seem to enforce an additional T-cell response, leading to a more persistent pathology. Hence, this new model mimics the pathomechanisms occurring in human glaucoma more accurately and could therefore be a helpful tool to find new therapeutic approaches for patients in the future.

Glaucoma Animal Models beyond Chronic IOP Increase

Glaucoma is a complex and multifactorial disease defined as the loss of retinal ganglion cells (RGCs) and their axons. Besides an elevated intraocular pressure (IOP), other mechanisms play a pivotal role in glaucoma onset and progression. For example, it is known that excitotoxicity, immunological alterations, ischemia, and oxidative stress contribute to the neurodegeneration in glaucoma disease. To study these effects and to discover novel therapeutic approaches, appropriate animal models are needed. In this review, we focus on various glaucoma animal models beyond an elevated IOP. We introduce genetically modified mice, e.g., the optineurin E50K knock-in or the glutamate aspartate transporter (GLAST)-deficient mouse. Excitotoxicity can be mimicked by injecting the glutamate analogue N-methyl-D-aspartate intravitreally, which leads to rapid RGC degeneration. To explore the contribution of the immune system, the experimental autoimmune glaucoma model can serve as a useful tool. Here, immunization with antigens led to glaucoma-like damage. The ischemic mechanism can be mimicked by inducing a high IOP for a certain amount of time in rodents, followed by reperfusion. Thereby, damage to the retina and the optic nerve occurs rapidly after ischemia/reperfusion. Lastly, we discuss the importance of optic nerve crush models as model systems for normal-tension glaucoma. In summary, various glaucoma models beyond IOP increase can be utilized.