Immune phenomena in glaucoma and conformational disorders: why is the second eye not involved?

Detection of plasma complement and immune globulin in different sorts of glaucoma

PURPOSE

To compare the plasma immune globulin and complement levels in different sorts of glaucoma to assess its association.

METHODS

Cohort study. Plasma samples were collected from 226 normal controls and 236 glaucoma patients included 92 with acute primary angle-closure glaucoma (APACG), 76 with chronic primary angle-closure glaucoma (CPACG), 68 with primary open-angle glaucoma (POAG). 163 glaucoma patients with high intraocular pressure(IOP) was classified as a subgroup. Six indexes were analyzed: C3, C4, CH₅₀, IgA, IgG, and IgM.

RESULTS

There was a significant difference in C4, IgA, IgG, and IgM between patients with high IOP and normal controls groups(P < 0.01). TheC4 (0.27 ± 0.69 g/L), IgA (3.11 ± 1.04 g/L), IgG (12.07 ± 1.92 g/L) and IgM (1.17 ± 0.49 g/L) were higher(P < 0.05) in the high IOP groups compared with the normal controls (C4:0.25 ± 0.07 g/L, IgA: 2.54 ± 1.07 g/L, IgG: 11.21 ± 2.22 g/L, IgM:0.99 ± 0.41 g/L). There was a significant difference in age, C3, IgA, IgG, and IgM among the normal control, APACG, CPACG, and POAG. The C3 level in the APACG group (1.14 ± 0.16 g/L) was higher than normal group (1.06 ± 0.18 g/L). The IgA level was lower(P < 0.05) in the normal group (2.54 ± 1.07 g/L) compared with APACG (3.16 ± 0.97 g/L) and POAG group (2.91 ± 1.11 g/L). The IgG level of normal controls (11.21 ± 2.22 g/L) was lower (P < 0.05) than APACG group (12.15 ± 2.02 g/L) and CPACG group (11.95 ± 2.28 g/L). The IgM level was lower(P < 0.05) in the normal group (0.99 ± 0.41 g/L) compared with the APACG (1.24 ± 0.66 g/L) and CPACG group (1.17 ± 0.45 g/L).

CONCLUSIONS

The levels of the plasma expression of C3, IgA, IgG, IgM may be useful for discriminating the glaucoma patients and for assessing the progress of glaucoma in different sorts.

In Vivo Small Molecule Delivery to the Optic Nerve in a Rodent Model

Small molecule delivery to the optic nerve would allow for exploration of molecular and cellular pathways involved in normal physiology and optic neuropathies such as glaucoma, and provide a tool for screening therapeutics in animal models. We report a novel surgical method for small molecule drug delivery to the optic nerve head (ONH) in a rodent model. In proof-of-principle experiments, we delivered cytochalasin D (Cyt D; a filamentous actin inhibitor) to the junction of the superior optic nerve and globe in rats to target the actin-rich astrocytic cytoskeleton of the ONH. Cyt D delivery was quantified by liquid chromatography and mass spectrometry of isolated optic nerve tissue. One day after Cyt D delivery, anterior ONH filamentous actin bundle content was significantly reduced as assessed by fluorescent-tagged phalloidin labeling, relative to sham delivery. Anterior ONH nuclear counts and axon-specific beta-3 tubulin levels, as well as peripapillary retinal ganglion cell layer nuclear counts were not significantly altered after Cyt D delivery relative to sham delivery. Lastly, the surgical delivery technique caused minimal observable axon degeneration up to 10 days post-surgery. This small molecule delivery technique provides a new approach to studying optic neuropathies in in vivo rodent models.

Neuroinflammation in glaucoma: A new opportunity

Mounting evidence suggests neuroinflammation is a key process in glaucoma, yet the precise roles are not known. Understanding these complex processes, which may also be a key in other common neurodegenerations such as Alzheimer's disease, will lead to targeted therapeutics for a disease that affects as many as 80 million people worldwide. Here, we define neuroinflammation as any immune-relevant response by a variety of cell types including astrocytes, microglia, and peripherally derived cells occurring in the optic nerve head and/or retina. In this review article, we first discuss clinical evidence for neuroinflammation in glaucoma and define neuroinflammation in glaucoma. We then review the inflammatory pathways that have been associated with glaucoma. Finally, we set out key research directions that we believe will greatly advance our understanding of the role of neuroinflammation in glaucoma. This review arose from a discussion of neuroinflammation in glaucoma at the 2015 meeting of The Lasker/IRRF Initiative for Innovation in Vision Science. This manuscript sets out to summarize one of these sessions; "Inflammation and Glaucomatous Neurodegeneration", as well as to review the current state of the literature surrounding neuroinflammation in glaucoma.

Automatic quantitative analysis of experimental primary and secondary retinal neurodegeneration: implications for optic neuropathies

Secondary neurodegeneration is thought to play an important role in the pathology of neurodegenerative disease, which potential therapies may target. However, the quantitative assessment of the degree of secondary neurodegeneration is difficult. The present study describes a novel algorithm from which estimates of primary and secondary degeneration are computed using well-established rodent models of partial optic nerve transection (pONT) and ocular hypertension (OHT). Brn3-labelled retinal ganglion cells (RGCs) were identified in whole-retinal mounts from which RGC density, nearest neighbour distances and regularity indices were determined. The spatial distribution and rate of RGC loss were assessed and the percentage of primary and secondary degeneration in each non-overlapping segment was calculated. Mean RGC number (82 592±681) and RGC density (1695±23.3 RGC/mm²) in naïve eyes were comparable with previous studies, with an average decline in RGC density of 71±17 and 23±5% over the time course of pONT and OHT models, respectively. Spatial analysis revealed greatest RGC loss in the superior and central retina in pONT, but significant RGC loss in the inferior retina from 3 days post model induction. In comparison, there was no significant difference between superior and inferior retina after OHT induction, and RGC loss occurred mainly along the superior/inferior axis (~30%) versus the nasal–temporal axis (~15%). Intriguingly, a significant loss of RGCs was also observed in contralateral eyes in experimental OHT. In conclusion, a novel algorithm to automatically segment Brn3a-labelled retinal whole-mounts into non-overlapping segments is described, which enables automated spatial and temporal segmentation of RGCs, revealing heterogeneity in the spatial distribution of primary and secondary degenerative processes. This method provides an attractive means to rapidly determine the efficacy of neuroprotective therapies with implications for any neurodegenerative disorder affecting the retina.

Immune response after intermittent minimally invasive intraocular pressure elevations in an experimental animal model of glaucoma

BACKGROUND

Elevated intraocular pressure (IOP), as well as fluctuations in IOP, is a main risk factor for glaucoma, but its pathogenic effect has not yet been clarified. Beyond the multifactorial pathology of the disease, autoimmune mechanisms seem to be linked to retinal ganglion cell (RGC) death. This study aimed to identify if intermittent IOP elevations in vivo (i) elicit neurodegeneration, (ii) provokes an immune response and (iii) whether progression of RGC loss can be attenuated by the B lymphocyte inhibitor Belimumab.

METHODS

Using an intermittent ocular hypertension model (iOHT), Long Evans rats (n = 21) underwent 27 unilateral simulations of a fluctuating pressure profile. Nine of these animals received Belimumab, and additional seven rats served as normotensive controls. Axonal density was analyzed in PPD-stained optic nerve cross-sections. Retinal cross-sections were immunostained against Brn3a, Iba1, and IgG autoantibody depositions. Serum IgG concentration and IgG reactivities were determined using ELISA and protein microarrays. Data was analyzed using ANOVA and Tukey HSD test (unequal N) or student's independent t test by groups.

RESULTS

A wavelike IOP profile led to a significant neurodegeneration of optic nerve axons (-10.6 %, p < 0.001) and RGC (-19.5 %, p = 0.02) in iOHT eyes compared with fellow eyes. Belimumab-treated animals only showed slightly higher axonal survival and reduced serum IgG concentration (-29 %) after iOHT. Neuroinflammatory events, indicated by significantly upregulated microglia activation and IgG autoantibody depositions, were shown in all injured retinas. Significantly elevated serum autoantibody immunoreactivities against glutathione-S-transferase, spectrin, and transferrin were observed after iOHT and were negatively correlated to the axon density.

CONCLUSIONS

Intermittent IOP elevations are sufficient to provoke neurodegeneration in the optic nerve and the retina and elicit changes of IgG autoantibody reactivities. Although the inhibition of B lymphocyte activation failed to ameliorate axonal survival, the correlation between damage and changes in the autoantibody reactivity suggests that autoantibody profiling could be useful as a biomarker for glaucoma.

The Role of the IL-20 Subfamily in Glaucoma

Glaucoma is a common disease that leads to loss of peripheral vision and, if left untreated, ultimately to blindness. While the exact cause(s) of glaucoma is still unknown, two leading risk factors are age and elevated intraocular pressure. Several studies suggest a possible link between glaucoma and inflammation in humans and animal models. In particular, our lab recently identified a T104M mutation in IL-20 receptor-B (IL-20RB) in primary open angle glaucoma patients from a large pedigree. Several of the interleukin- (IL-) 20 family of cytokines and receptors are expressed in ocular tissues including the trabecular meshwork, optic nerve head, and retinal ganglion cells. The DBA/2J mouse develops high intraocular pressures with age and has characteristic optic nerve defects that make it a useful glaucoma model. IL-24 expression is significantly upregulated in the retina of these mice, while IL-20RA expression in the optic nerve is downregulated following pressure-induced damage. The identification of a mutation in the IL-20RB gene in a glaucoma pedigree and changes in expression levels of IL-20 family members in the DBA/2J mouse suggest that disruption of normal IL-20 signaling in the eye may contribute to degenerative processes associated with glaucoma.

Macro- and microglial responses in the fellow eyes contralateral to glaucomatous eyes

Most studies employing experimental models of unilateral glaucoma have used the normotensive contralateral eye as the normal control. However, some studies have recently reported the activation of the retinal macroglia and microglia in the uninjured eye, suggesting that the eye contralateral to experimental glaucoma should not be used as a control. This review analyzes the studies describing the contralateral findings and discusses some of the routes through which the signals can reach the contralateral eye to initiate the glial reactivation.