Minocycline mechanism of neuroprotection involves the Bcl-2 gene family in optic nerve transection

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.

Immunomodulatory and Antioxidant Drugs in Glaucoma Treatment

Glaucoma, a group of diseases characterized by progressive retinal ganglion cell loss, cupping of the optic disc, and a typical pattern of visual field defects, is a leading cause of severe visual impairment and blindness worldwide. Elevated intraocular pressure (IOP) is the leading risk factor for glaucoma development. However, glaucoma can also develop at normal pressure levels. An increased susceptibility of retinal ganglion cells to IOP, systemic vascular dysregulation, endothelial dysfunction, and autoimmune imbalances have been suggested as playing a role in the pathophysiology of normal-tension glaucoma. Since inflammation and oxidative stress play a role in all forms of glaucoma, the goal of this review article is to present an overview of the inflammatory and pro-oxidant mechanisms in the pathophysiology of glaucoma and to discuss immunomodulatory and antioxidant treatment approaches.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Animal Models of LED-Induced Phototoxicity. Short- and Long-Term In Vivo and Ex Vivo Retinal Alterations

Phototoxicity animal models have been largely studied due to their degenerative communalities with human pathologies, e.g., age-related macular degeneration (AMD). Studies have documented not only the effects of white light exposure, but also other wavelengths using LEDs, such as blue or green light. Recently, a blue LED-induced phototoxicity (LIP) model has been developed that causes focal damage in the outer layers of the superior-temporal region of the retina in rodents. In vivo studies described a progressive reduction in retinal thickness that affected the most extensively the photoreceptor layer. Functionally, a transient reduction in a- and b-wave amplitude of the ERG response was observed. Ex vivo studies showed a progressive reduction of cones and an involvement of retinal pigment epithelium cells in the area of the lesion and, in parallel, an activation of microglial cells that perfectly circumscribe the damage in the outer retinal layer. The use of neuroprotective strategies such as intravitreal administration of trophic factors, e.g., basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) or pigment epithelium-derived factor (PEDF) and topical administration of the selective alpha-2 agonist (Brimonidine) have demonstrated to increase the survival of the cone population after LIP.

Correlation of NUCB2/Nesfatin-1 with Cytokine Levels in Primary Open-Angle Glaucoma

Purpose

Nesfatin-1 is produced in various tissues of the body including the hypothalamus. Neuroprotective properties of the neuropeptide hormone Nesfatin-1 were recently described. The aim of the study was to analyze the molecule Nesfatin-1 as a possible biomarker in POAG with neuroprotective properties pointing out the retinal-hypothalamic axis as target site in POAG and to obtain a molecular signature of cytokines in POAG as neuroinflammatory processes are a key factor of glaucoma development.

Methods

In this study, n=35 patients with moderate and advanced POAG (mean age 65.0y, IOP 13.9±3.0mmHg) and n=35 healthy controls (mean age 51.6y, IOP 14.3±2.7mmHg) were included. Clinical parameters including IOP, cup to disc ratio (CDR), glaucoma medication and retinal nerve fiber layer thickness (RNFL) were recorded. Plasma was collected for NUCB2/nesfatin-1 measurement using a Nesfatin-1 ELISA and for detection of 13 inflammatory cytokines using a multiplex bead-based immunoassay (MagPix). Multiple linear regression analysis was performed to adjust for confounding factors.

Results

Sex-independent or sex-dependent variables showed no significant differences in the Nesfatin-1 level (p>0.05). As a trend, an increase in NUCB2/nesfatin-1 in male glaucoma patients was found. Increased concentrations of 11 cytokines (GM-CSF, Interferon-γ, Interleukin-1β, IL-2, 4, 5, 6, 7, 10, 12 and TNF-α) were detected in POAG. The female glaucoma patients demonstrated elevated cytokine concentrations compared to male patients. NUCB2/nesfatin-1 showed a significant correlation to IL-2 and IL-13 levels in POAG. Stepwise multiple regression analysis showed no difference in NUCB2/nesfatin-1 level between POAG and healthy controls after adjusting for sex and age (all p>0.05).

Conclusion

As a trend, male POAG patients showed increased plasma NUCB2/nesfatin-1 levels. We further found inflammation as contributing factor to the pathogenesis of glaucoma, with a greater inflammatory response in women.

Inflammation in Glaucoma: From the back to the front of the eye, and beyond

The pathophysiology of glaucoma is complex, multifactorial and not completely understood. Elevated intraocular pressure (IOP) and/or impaired retinal blood flow may cause initial optic nerve damage. In addition, age-related oxidative stress in the retina concurrently with chronic mechanical and vascular stress is crucial for the initiation of retinal neurodegeneration. Oxidative stress is closely related to cell senescence, mitochondrial dysfunction, excitotoxicity, and neuroinflammation, which are involved in glaucoma progression. Accumulating evidence from animal glaucoma models and from human ocular samples suggests a dysfunction of the para-inflammation in the retinal ganglion cell layer and the optic nerve head. Moreover, quite similar mechanisms in the anterior chamber could explain the trabecular meshwork dysfunction and the elevated IOP in primary open-angle glaucoma. On the other hand, ocular surface disease due to topical interventions is the most prominent and visible consequence of inflammation in glaucoma, with a negative impact on filtering surgery failure, topical treatment efficacy, and possibly on inflammation in the anterior segment. Consequently, glaucoma appears as an outstanding eye disease where inflammatory changes may be present to various extents and consequences along the eye structure, from the ocular surface to the posterior segment, and the visual pathway. Here we reviewed the inflammatory processes in all ocular structures in glaucoma from the back to the front of the eye and beyond. Our approach was to explain how para-inflammation is necessary to maintain homoeostasis, and to describe abnormal inflammatory findings observed in glaucomatous patients or in animal glaucoma models, supporting the hypothesis of a dysregulation of the inflammatory balance toward a pro-inflammatory phenotype. Possible anti-inflammatory therapeutic approaches in glaucoma are also discussed.

Minocycline Increases in-vitro Cortical Neuronal Cell Survival after Laser Induced Axotomy

Background

Antibiotic therapies targeting multiple regenerative mechanisms have the potential for neuroprotective effects, but the diversity of experimental strategies and analyses of non-standardised therapeutic trials are challenging. In this respect, there are no cases of successful clinical application of such candidate molecules when it comes to human patients.

Methods

After 24 hours of culturing, three different minocycline (Sigma-Aldrich, M9511, Germany) concentrations (1 µM, 10 µM and 100 µM) were added to the primary cortical neurons 15 minutes before laser axotomy procedure in order to observe protective effect of minocycline in these dosages.

Results

Here, we have shown that minocycline exerted a significant neuroprotective effect at 1 and 100μM doses. Beyond confirming the neuroprotective effect of minocycline in a more standardised and advanced in-vitro trauma model, our findings could have important implications for future studies that concentrate on the translational block between animal and human studies.

Conclusion

Such sophisticated approaches might also help to conquer the influence of human-made variabilities in critical experimental injury models. To the best of our knowledge, this is the first study showing that minocycline increases in-vitro neuronal cell survival after laser-axotomy.

Microglia in the Retina: Roles in Development, Maturity, and Disease

Microglia, the primary resident immune cell type, constitute a key population of glia in the retina. Recent evidence indicates that microglia play significant functional roles in the retina at different life stages. During development, retinal microglia regulate neuronal survival by exerting trophic influences and influencing programmed cell death. During adulthood, ramified microglia in the plexiform layers interact closely with synapses to maintain synaptic structure and function that underlie the retina's electrophysiological response to light. Under pathological conditions, retinal microglia participate in potentiating neurodegeneration in diseases such as glaucoma, retinitis pigmentosa, and age-related neurodegeneration by producing proinflammatory neurotoxic cytokines and removing living neurons via phagocytosis. Modulation of pathogenic microglial activation states and effector mechanisms has been linked to neuroprotection in animal models of retinal diseases. These findings have led to the design of early proof-of-concept clinical trials with microglial modulation as a therapeutic strategy.

Glaucoma Pathogenesis and Neurotrophins: Focus on the Molecular and Genetic Basis for Therapeutic Prospects

BACKGROUND

Retinal ganglion cell (RGC) degeneration is a major feature of glaucoma pathology. Neuroprotective approaches that delay or halt the progression of RGC loss are needed to prevent vision loss which can occur even after conventional medical or surgical treatments to lower intraocular pressure.

OBJECTIVE

The aim of this review was to examine the progress in genetics and cellular mechanisms associated with endoplasmic reticulum (ER) stress, RGC dysfunction and cell death pathways in glaucoma.

MATERIALS AND METHODS

Here, we review the involvement of neurotrophins like brain derived neurotrophic factor (BDNF) and its high affinity receptor tropomyosin receptor kinase (TrkB) in glaucoma. The role of ER stress markers in human and animal retinas in health and disease conditions is also discussed. Further, we analysed the literature highlighting genetic linkage in the context of primary open angle glaucoma and suggested mechanistic insights into potential therapeutic options relevant to glaucoma management.

RESULTS

The literature review of the neurobiology underlying neurotrophin pathways, ER stress and gene associations provide critical insights into association of RGCs death in glaucoma. Alteration in signalling pathway is associated with increased risk of misfolded protein aggregation in ER promoting RGC apoptosis. Several genes that are linked with neurotrophin signalling pathways have been reported to be associated with glaucoma pathology.

CONCLUSION

Understanding genetic heterogeneity and involvement of neurotrophin biology in glaucoma could help to understand the complex pathophysiology of glaucoma. Identification of novel molecular targets will be critical for drug development and provide neuroprotection to the RGCs and optic nerve.

Caspases in retinal ganglion cell death and axon regeneration

Retinal ganglion cells (RGC) are terminally differentiated CNS neurons that possess limited endogenous regenerative capacity after injury and thus RGC death causes permanent visual loss. RGC die by caspase-dependent mechanisms, including apoptosis, during development, after ocular injury and in progressive degenerative diseases of the eye and optic nerve, such as glaucoma, anterior ischemic optic neuropathy, diabetic retinopathy and multiple sclerosis. Inhibition of caspases through genetic or pharmacological approaches can arrest the apoptotic cascade and protect a proportion of RGC. Novel findings have also highlighted a pyroptotic role of inflammatory caspases in RGC death. In this review, we discuss the molecular signalling mechanisms of apoptotic and inflammatory caspase responses in RGC specifically, their involvement in RGC degeneration and explore their potential as therapeutic targets.

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.

Epigenetics and Signaling Pathways in Glaucoma

Glaucoma is the most common cause of irreversible blindness worldwide. This neurodegenerative disease becomes more prevalent with aging, but predisposing genetic and environmental factors also contribute to increased risk. Emerging evidence now suggests that epigenetics may also be involved, which provides potential new therapeutic targets. These three factors work through several pathways, including TGF-β, MAP kinase, Rho kinase, BDNF, JNK, PI-3/Akt, PTEN, Bcl-2, Caspase, and Calcium-Calpain signaling. Together, these pathways result in the upregulation of proapoptotic gene expression, the downregulation of neuroprotective and prosurvival factors, and the generation of fibrosis at the trabecular meshwork, which may block aqueous humor drainage. Novel therapeutic agents targeting these pathway members have shown preliminary success in animal models and even human trials, demonstrating that they may eventually be used to preserve retinal neurons and vision.

Retinal ganglion cell apoptotic pathway in glaucoma: Initiating and downstream mechanisms

Apoptosis of retinal ganglion cells (RGCs) in glaucoma causes progressive visual field loss, making it the primary cause of irreversible blindness worldwide. Elevated intraocular pressure and aging, the main risk factors for glaucoma, accelerate RGC apoptosis. Numerous pathways and mechanisms were found to be involved in RGC death in glaucoma. Neurotrophic factors deprivation is an early event. Oxidative stress, mitochondrial dysfunction, inflammation, glial cell dysfunction, and activation of apoptotic pathways and prosurvival pathways play a significant role in RGC death in glaucoma. The most important among the involved pathways are the MAP-kinase pathway, PI-3 kinase/Akt pathway, Bcl-2 family, caspase family, and IAP family.