Autophagy dysregulation and the fate of retinal ganglion cells in glaucomatous optic neuropathy

Modeling of Retina and Optic Nerve Ischemia-Reperfusion Injury through Hypoxia-Reoxygenation in Human Induced Pluripotent Stem Cell-Derived Retinal Ganglion Cells

Retinal ganglion cells (RGCs) are specialized projection neurons that constitute part of the retina, and the death of RGCs causes various eye diseases, but the mechanism of RGC death is still unclear. Here, we induced cell death in human induced pluripotent stem cell (hiPSC)-derived RGC-rich retinal tissues using hypoxia-reoxygenation in vitro. Flow cytometry, immunochemistry, and Western blotting showed the apoptosis and necrosis of RGCs under hypoxia-reoxygenation, and they were rescued by an apoptosis inhibitor but not by a necrosis inhibitor. This revealed that the cell death induced in our model was mainly due to apoptosis. To our knowledge, this is the first model to reproduce ischemia-reperfusion in hiPSC-derived RGCs. Thus, the efficacy of apoptosis inhibitors and neuroprotective agents can be evaluated using this model, bringing us closer to clinical applications.

Lysosomes in retinal health and disease

Lysosomes play crucial roles in various cellular processes - including endocytosis, phagocytosis, and autophagy - which are vital for maintaining retinal health. Moreover, these organelles serve as environmental sensors and act as central hubs for multiple signaling pathways. Through communication with other cellular components, such as mitochondria, lysosomes orchestrate the cytoprotective response essential for preserving cellular homeostasis. This coordination is particularly critical in the retina, given its high metabolic rate and susceptibility to photo-oxidative stress. Consequently, impaired lysosomal function and dysregulated communication between lysosomes and other organelles contribute significantly to the pathobiology of major retinal degenerative diseases. This review explores the pivotal role of lysosomes in retinal cells and their involvement in retinal degenerative diseases.

Neuroprotective Effect of a Nutritional Supplement Containing Spearmint Extract, Forskolin, Homotaurine and Group B Vitamins in a Mouse Model of Transient Ocular Hypertension

Glaucoma is one of the most common sight-threatening eye disorders and one of the main causes of irreversible blindness worldwide. The current therapies focusing on reducing intraocular pressure (IOP) are often insufficient to prevent the progression of the disease, so the therapeutic management of glaucoma remains a challenge. The aim of this study was to evaluate the neuroprotective, IOP-lowering independent effects of a nutritional supplement containing forskolin, homotaurine, spearmint extract and vitamins of the B group in a model of acute glaucoma developed in mice. Glaucoma was induced in adult wild-type C57BL/6J mice by transient elevation of IOP. The dietary supplement, branded as Gangliomix^® (125 mg/kg/day), was administered by oral gavage for 17 days and ocular hypertension was induced on the 10th day of treatment. A histological analysis of the retinas was performed and RGC survival was evaluated with fluorogold labeling and Brn3a immunostaining on wholemount and retinal sections. Expression of alpha-spectrin, caspase-3, PARP-1 and GFAP was studied with western blotting or immunofluorescence. A significant increase in RGC survival was reported in the retina of mice treated with the dietary supplement as compared to vehicle-treated animals. The observed neuroprotection was associated with a calpain activity decrease, reduction in caspase-3 and PARP-1 activation, and prevention of GFAP upregulation. These effects were independent from the hypotensive effects of the supplement. Altogether, our data suggest that the dietary supplementation with forskolin, homotaurine, spearmint extract and vitamins of the B group supports RGC survival and may offer beneficial effects in glaucoma patients in combination with the currently used IOP-lowering therapy.

Geranylgeranylacetone-induced heat shock protein70 expression reduces retinal ischemia-reperfusion injury through PI3K/AKT/mTOR signaling

Retinal ischemia-reperfusion (I/R) injury is a common pathophysiological stress state connected to various diseases, including acute glaucoma, retinal vascular obstruction, and diabetic retinopathy. Recent studies have suggested that geranylgeranylacetone (GGA) could increase heat shock protein70 (HSP70) level and reduce retinal ganglion cells (RGCs) apoptosis in a rat retinal I/R model. However, the underlying mechanism remains unclear. Moreover, the injury caused by retinal I/R includes not only apoptosis but also autophagy and gliosis, and the effects of GGA on autophagy and gliosis have not been reported. Our study established a retinal I/R model by anterior chamber perfusion pressuring to 110 mmHg for 60 min, followed by 4 h of reperfusion. The levels of HSP70, apoptosis-related proteins, GFAP, LC3-II, and PI3K/AKT/mTOR signaling proteins were determined by western blotting and qPCR after treatment with GGA, HSP70 inhibitor quercetin (Q), PI3K inhibitor LY294002, and mTOR inhibitor rapamycin. Apoptosis was evaluated by TUNEL staining, meanwhile, HSP70 and LC3 were detected by immunofluorescence. Our results demonstrated that GGA-induced HSP70 expression significantly reduced gliosis, autophagosome accumulation, and apoptosis in retinal I/R injury, indicating that GGA exerted protective effects on retinal I/R injury. Moreover, the protective effects of GGA mechanistically relied on the activation of PI3K/AKT/mTOR signaling. In conclusion, GGA-induced HSP70 overexpression has protective effects on retinal I/R injury by activating PI3K/AKT/mTOR signaling.

The Enantiomer of Allopregnanolone Prevents Pressure-Mediated Retinal Degeneration Via Autophagy

In an ex vivo rat ocular hypertension (OHT) model, the neurosteroid allopregnanolone (AlloP) exerts neuroprotective effects via enhancement of both GABA_A receptors and autophagy. We now examine whether its enantiomer (ent-AlloP), which is largely inactive at GABA receptors, offers similar neuroprotection in ex vivo and in vivo rat OHT models. Ex vivo rat retinal preparations were incubated in a hyperbaric condition (10 and 75 mmHg) for 24 h. An in vivo ocular hypertension (OHT) model was induced by intracameral injection of polystyrene microbeads. We examined pharmacological effects of AlloP, ent-AlloP, picrotoxin (a GABA_A receptor antagonist), and 3-MA (an autophagy inhibitor) histologically and biochemically. We found that both AlloP and ent-AlloP have marked neuroprotective effects in the retina, but effects of the unnatural enantiomer are independent of GABA_A receptors. Electron microscopic analyses show that pressure elevation significantly increased autophagosomes (APs) in the nerve fiber layer and addition of AlloP also increased APs and degenerative autophagic vacuoles (AVds). ent-AlloP markedly increased APs and AVds compared to AlloP. Examination of LC3B-II and SQSTM1 protein levels using immunoblotting revealed that AlloP increased LC3B-II, and ent-AlloP further enhanced LC3B-II and suppressed SQSTM1, indicating that autophagy is a major mechanism underlying neuroprotection by ent-AlloP. In an rat in vivo OHT model, single intravitreal ent-AlloP injection prevented apoptotic cell death of retinal ganglion cells similar to AlloP. However, even in this model, ent-AlloP was more effective in activating autophagy than AlloP. We conclude that ent-AlloP may be a prototype of potential therapeutic for treatment of glaucoma as an autophagy enhancer without affecting GABA receptors.

CD82 protects against glaucomatous axonal transport deficits via mTORC1 activation in mice

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive optic nerve degeneration and retinal ganglion cell loss. Axonal transport deficits have been demonstrated to be the earliest crucial pathophysiological changes underlying axonal degeneration in glaucoma. Here, we explored the role of the tetraspanin superfamily member CD82 in an acute ocular hypertension model. We found a transient downregulation of CD82 after acute IOP elevation, with parallel emergence of axonal transport deficits. The overexpression of CD82 with an AAV2/9 vector in the mouse retina improved optic nerve axonal transport and ameliorated subsequent axon degeneration. Moreover, the CD82 overexpression stimulated optic nerve regeneration and restored vision in a mouse optic nerve crush model. CD82 exerted a protective effect through the upregulation of TRAF2, which is an E3 ubiquitin ligase, and activated mTORC1 through K63-linked ubiquitylation and intracellular repositioning of Raptor. Therefore, our study offers deeper insight into the tetraspanin superfamily and demonstrates a potential neuroprotective strategy in glaucoma treatment.

Protective effect of ultrasound microbubble combined with gross saponins of tribulus terrestris on glaucomatous optic nerve damage

Background

To investigate the protective effect of ultrasound microbubble combined with gross saponins of tribulus terrestris (GSTT) (a Chinese herb) on glaucomatous optic nerve damage.

Methods

Rabbits were randomly divided into five groups. Normal (Group A), high intraocular pressure (IOP, Group B), GSTT (Group C), GSTT + ultrasound (Group D), and GSTT + ultrasound + microbubble destruction (Group E). The high intraocular pressure eye (model eye) was compared to the normal eye (control eye) at 1, 2, and 4 weeks after model establishment. Rabbits were sacrificed 4 weeks later to measure the retina thickness using Cirrus OCT, slit lamp photograph, and fundus photography. The retina and optic nerve of rabbits in each group were collected and the stretched retina were prepared for retinal ganglion cell (RGC) counting, the optic nerve axon was measured, and a transmission electron microscopy was used.

Results

Retina thickness based on Cirrus OCT: mean retinal thickness in Group E was significantly greater than that in Group B, but still thinner than that in Group A. RGCs counts: RGCs counts in Group E were significantly higher than those in Groups B, C, and D but still lower than those in Group A. Quantitative analysis of optic nerve axons: In Group E, the number of optic nerves was increased, diameters of optic nerve axons were decreased, the percentage of optic nerve area occupied by axons was increased, and there were statistically significant differences compared to Groups B, C, and D. Content of GSTT in retina: The content of GSTT in Group E was significantly higher than that in other groups. Observation of the rabbit optic nerves: In Group E, the structure of the myelin sheath of the optic nerve was still intact but less ordered, and the microtubule and microfilament structures in the axons were clear.

Conclusions

Combination of the ultrasound microbubble and GSTT can improve the protective effect of GSTT on optic nerve damage in rabbits with ocular hypertension.

The neurosteroid allopregnanolone protects retinal neurons by effects on autophagy and GABRs/GABAA receptors in rat glaucoma models

In an ex vivo rat glaucoma model using dissected retinas, the neurosteroid allopregnanolone (AlloP) protects retinal ganglion cells (RGCs) via GABR/GABAA receptors. To determine the involvement of macroautophagy/autophagy in neuroprotection by AlloP, we examined the effects of autophagy activators, rapamycin and torin 2, and autophagy inhibitors, bafilomycin A1 and SAR405, on retinal retinal morphology and expression of MAP1 LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) and SQSTM1 (sequestosome 1). Administration of rapamycin or torin 2 exerted partial histological neuroprotection, while combined administration of AlloP with bafilomycin A1 or SAR405 induced severe degeneration in a hyperbaric condition. Electron microscopic analyses showed that the addition of AlloP significantly increased autophagosomes and degenerative autophagic vacuoles in the retinal nerve fiber layer. Immunoblotting showed that the addition of AlloP or autophagic activators increased the lipidated form of LC3B (LC3B-II) and suppressed SQSTM1. Moreover, bafilomycin A1 increased LC3B-II and SQSTM1 protein levels in the presence of AlloP without changes in corresponding mRNAs compared to AlloP-treated retinas in a hyperbaric condition. These data indicate that AlloP likely induces a protective form of autophagy in this model. In an in vivo rat model of glaucoma, we also observed neuroprotective effects of AlloP. Injection of polystyrene microbeads into the anterior chamber increased intraocular pressure about 3-fold and induced RGC apoptosis. A single intravitreal injection of AlloP or autophagy activators prevented apoptosis and protected RGCs with autophagy activation. We conclude that AlloP may serve as a potential therapeutic agent for the treatment of glaucoma via diverse mechanisms.Abbreviations: 2HBCD: 2-Hydroxypropyl)-β-cyclodextrin; 3-MA: 3-methyladenine; AlloP: allopregnanolone; AP: autophagosome; AVd: degradative autophagic vacuoles; GCL: ganglion cell layer; INL: inner nuclear layer; IOP: intraocular pressure; IPL: inner plexiform layer; LC3B-I: cytosolic form of LC3B; LCB-II: lipidated form of LC3B; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mPTP: mitochondrial permeability transition pore; NDS: neuronal damage score; NFL: nerve fiber layer; OH: ocular hypertension; ON: optic nerve; ONL: outer nuclear layer; OPL: outer plexiform layer; p-STR: scotopic threshold response; RGC: retinal ganglion cells; RT-PCR: real-time reverse transcription polymerase chain reaction; SQSTM1: sequestosome 1; TUNEL: TdT-mediated dUTP Nick End Labeling.

The Role of Autophagy in Eye Diseases

Autophagy is a catabolic process that ensures homeostasis in the cells of our organism. It plays a crucial role in protecting eye cells against oxidative damage and external stress factors. Ocular pathologies of high incidence, such as age-related macular degeneration, cataracts, glaucoma, and diabetic retinopathy are of multifactorial origin and are associated with genetic, environmental factors, age, and oxidative stress, among others; the latter factor is one of the most influential in ocular diseases, directly affecting the processes of autophagy activity. Alteration of the normal functioning of autophagy processes can interrupt organelle turnover, leading to the accumulation of cellular debris and causing physiological dysfunction of the eye. The aim of this study is to review research on the role of autophagy processes in the main ocular pathologies, which have a high incidence and result in high costs for the health system. Considering the role of autophagy processes in cell homeostasis and cell viability, the control and modulation of autophagy processes in ocular pathologies could constitute a new therapeutic approach.

Detection of Autophagy-Related Gene Expression by Conjunctival Impression Cytology in Age-Related Macular Degeneration

Purpose: To investigate the association of autophagy-related gene expression with age-related macular degeneration (AMD). Methods: Patients with AMD were recruited for analysis by conjunctival impression cytology. mRNA was assessed by real-time polymerase chain reaction (RT-PCR) to evaluate whether the expression of 26 autophagy-related genes (ATGs) was correlated with AMD. Further studies on cell viability and autophagic flux in response to oxidative stress by H2O2 were performed in human retinal pigment epithelial (RPE) cell lines based on the results of impression cytology. Results: Both the neovascular AMD (nAMD) and polypoidal choroidal vasculopathy (PCV) groups had significantly higher mRNA levels of gamma-aminobutyric acid receptor-associated protein-like 1 (GABARAPL1) and microtubule-associated proteins 1A/1B light chain 3B (MAP1LC3B) than the control group, but there was no significant difference between these two groups. Age difference existed only in the AMD group. GABARAPL1 and MAP1LC3B mRNA expression increased significantly after acute oxidative stress in adult retinal pigment epithelial (ARPE-19) cells. Cell viability significantly increased and decreased in the cells harboring GABARAPL1 expression vector and silenced with siRNA against GABARAPL1, respectively, during short-term oxidative stress, whereas viability increased in the GABARAPL1-silenced cells after long-term oxidative stress. Silencing GABARAPL1 itself caused a reduction in autophagic flux under both short and long-term oxidative stress. Conclusion: Our study showed the possibility of assessing autophagy-related gene expression by conjunctival impression cytology. GABARAPL1 was significantly higher in AMD. Although an in vitro study showed an initial protective effect of autophagy, a cell viability study revealed the possibility of a harmful effect after long-term oxidative injury. The underlying mechanism or critical factors require further investigation.

Glaucoma and neuroinflammation: An overview

Glaucoma is an optic neuropathy characterized by well-defined optic disc morphological changes (i.e., cup enlargement, neuroretinal border thinning, and notching, papillary vessel modifications) consequent to retinal ganglion cell loss, axonal degeneration, and lamina cribrosa remodeling. These modifications tend to be progressive and are the main cause of functional damage in glaucoma. Despite the latest findings about the pathophysiology of the disease, the exact trigger mechanisms and the mechanism of degeneration of retinal ganglion cells and their axons have not been completely elucidated. Neuroinflammation may play a role in both the development and the progression of the disease as a result of its effects on retinal environment and retinal ganglion cells. We summarize the latest findings about neuroinflammation in glaucoma and examine the connection between risk factors, neuroinflammation, and retinal ganglion cell degeneration.

Autophagy in the Aging and Experimental Ocular Hypertensive Mouse Model

Purpose

To investigate autophagy in the outflow pathway and ganglion cell layer in the aging and ocular hypertensive mouse.

Methods

Both 4-month-old and 18-month-old C57BL/6J and GFP-LC3 mice were subjected to unilateral injection of hypertonic saline into a limbal vein, causing sclerosis of the outflow pathway and subsequent elevation of intraocular pressure (IOP). IOP was measured on a weekly basis using a rebound tonometer. Protein expression levels of LC3B, Lamp1, and p62 were evaluated by western blot and/or immunofluorescence. Retinal ganglion cell (RGC) count was performed in whole retinal flat mounts using an anti-Brn3a antibody. Optic nerves were fixed with 4% paraformaldehyde and resin-embedded for axon counts and electron microscopy.

Results

In contrast to 18-month-old mice, which developed sustained elevated IOP with a single injection, 4-month-old mice were refractory to high elevations of IOP. Interestingly, both the percentage of animals that developed elevated IOP and the mean ∆IOP were significantly higher in the transgenic mice compared to C57BL/6J. Immunofluorescence and western blot analysis showed dysregulated autophagy in the iridocorneal and retina tissues from 18-month-old mice compared to 4-month-old ones. Moreover, the LC3-II/LC3-I ratio correlated with IOP. As expected, injected hypertensive eyes displayed axonal degeneration and RGC death. RGC and axon loss were significantly exacerbated with aging, especially when combined with GFP-LC3 expression. Autophagic structures were observed in the degenerating axons.

Conclusions

Our results indicate dysregulation of autophagy in the trabecular meshwork and retinal tissues with aging and suggest that such dysregulation of autophagy contributes to neurodegeneration in glaucoma.

Impact of neurotrophic factors combination therapy on retinitis pigmentosa

Objective

We aimed to determine the location of neurotrophic receptors tropomyosin receptor kinase (Trk)B, TrkC, and ciliary neurotrophic factor receptor (CNTFR)α in the retina of retinal degeneration (rd) mice and to explore the dynamic changes of B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X-protein (Bax), and microtubule-associated protein light chain 3 (LC3) expression and ultrastructure in the retina of rd mice intravitreally injected with neurotrophic factors.

Methods

Rd mice aged 2 and 3 weeks post-natally (PN) received intravitreal injections of neurotrophic factors. Two weeks later, their retinas were harvested for the detection of Bax, Bcl-2, and LC3 mRNA and protein expression.

Results

TrkB and TrkC expression levels were lower at 3 weeks PN compared with 0, 1, and 2 weeks PN, but CNTFRα expression was still detected in certain layers. The three receptors were expressed in different retinal layers at the same timepoint. Bax expression was downregulated in, rhBDNF + rhCNTF, rhBDNF + rhNT-3, groups 2 weeks after intravitreal injection; Bcl-2 expression was upregulated in the rhBDNF + rhCNTF + rhNT-3 group at PN-4w; and LC3 expression was upregulated in rhBDNF + rhCNTF + rhNT-3 groups.

Conclusions

The combined use of neurotrophic factors had a more significant effect on Bax, Bcl-2, and LC3 expression than the same factors used alone.

Natural Products: Evidence for Neuroprotection to Be Exploited in Glaucoma

Glaucoma, a leading cause of irreversible blindness worldwide, is an optic neuropathy characterized by the progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is recognized as the main risk factor. Despite effective IOP-lowering therapies, the disease progresses in a significant number of patients. Therefore, alternative IOP-independent strategies aiming at halting or delaying RGC degeneration is the current therapeutic challenge for glaucoma management. Here, we review the literature on the neuroprotective activities, and the underlying mechanisms, of natural compounds and dietary supplements in experimental and clinical glaucoma.

Axonal Protection by Nicotinamide Riboside via SIRT1-Autophagy Pathway in TNF-Induced Optic Nerve Degeneration

Nicotinamide adenine dinucleotide (NAD⁺) synthesis pathway has been involved in many biological functions. Nicotinamide riboside (NR) is widely used as an NAD⁺ precursor and known to increase NAD⁺ level in several tissues. The present study aimed to examine the effect of NR on tumor necrosis factor (TNF)-induced optic nerve degeneration and to investigate whether it alters SIRT1 expression and autophagic status in optic nerve. We also examined the localization of nicotinamide riboside kinase 1 (NRK1), which is a downstream enzyme for NR biosynthesis pathway in retina and optic nerve. Intravitreal injection of TNF or TNF plus NR was performed on rats. The p62 and LC3-II protein levels were examined to evaluate autophagic flux in optic nerve. Immunohistochemical analysis was performed to localize NRK1 expression. Morphometric analysis showed substantial axonal protection by NR against TNF-induced axon loss. TNF-induced increment of p62 protein level was significantly inhibited by NR administration. NR administration alone significantly increased the LC3-II levels and reduced p62 levels compared with the basal levels, and upregulated SIRT1 levels in optic nerve. Immunohistochemical analysis showed that NRK1 exists in retinal ganglion cells (RGCs) and nerve fibers in retina and optic nerve. NR administration apparently upregulated NRK1 levels in the TNF-treated eyes as well as the control eyes. Pre-injection of an SIRT1 inhibitor resulted in a significant increase of p62 levels in the NR plus TNF treatment group, implicating that SIRT1 regulates autophagy status. In conclusion, NRK1 exists in RGCs and optic nerve axons. NR exerted protection against axon loss induced by TNF with possible involvement of upregulated NRK1 and SIRT1-autophagy pathway.

Effects of caloric restriction on retinal aging and neurodegeneration

Glaucoma is the most common neurodegenerative cause of irreversible blindness worldwide. Restricted caloric regimens are an attractive approach for delaying the progression of neurodegenerative diseases. Here we review the current literature on the effects of caloric restriction on retinal neurons, under physiological and pathological conditions. We focused on autophagy as one of the mechanisms modulated by restricted caloric regimens and involved in the death of retinal ganglion cells (RGCs) over the course of glaucoma.

Biologically active pigment and ShlA cytolysin of Serratia marcescens induce autophagy in a human ocular surface cell line

BACKGROUND

The cellular process of autophagy is essential for maintaining the health of ocular tissue. Dysregulation of autophagy is associated with several ocular diseases including keratoconus and macular degeneration. It is known that autophagy can be used to respond to microbial infections and that certain microbes can exploit the autophagic process to their benefit. In this study, a genetic approach was used to identify surface-associated and secreted products generated by the opportunistic pathogen Serratia marcescens involved in activation of autophagy.

METHODS

A recombinant human corneal limbal epithelial cell line expressing a LC3-GFP fusion protein was challenged with normalized secretomes from wild-type and mutant S. marcescens derivatives. LC3-GFP fluorescence patterns were used to assess the ability of wild-type and mutant bacteria to influence autophagy. Purified prodigiosin was obtained from stationary phase bacteria and used to challenge ocular cells.

RESULTS

Mutations in the global regulators eepR and gumB genes highly reduced the ability of the bacteria to activate autophagy in corneal cells. This effect was further narrowed down to the secreted cytolysin ShlA and the biologically active pigment prodigiosin. Purified prodigiosin and ShlA from Escherichia coli further supported the role of these factors in activating autophagy in human corneal cells. Additional genetic data indicate a role for flagellin and type I pili, but not the nuclease, S-layer protein, or serratamolide biosurfactant in activation of autophagy.

CONCLUSIONS

This work identifies specific bacterial components that activate autophagy and give insight into potential host-pathogen interactions or compounds that can be used to therapeutically manipulate autophagy.

Axonal protection by a small molecule SIRT1 activator, SRT2104, with alteration of autophagy in TNF-induced optic nerve degeneration

PURPOSE

To examine the effects of SRT2104, an SIRT1 activator, in optic nerve degeneration induced by TNF and to investigate whether it affects the autophagic status after induction of axonal degeneration.

STUDY DESIGN

Experimental.

METHODS

Adult male Wistar rats received intravitreal injection of TNF alone, concomitant injection of SRT2104 and TNF, or injection of SRT2104 alone. The autophagic status in the optic nerve was evaluated to examine p62 and LC3-II expression by immunoblot analysis. The effect of SRT2104 on TNF-induced axon loss was determined by counting the number of axons.

RESULTS

Intravitreal injection of SRT2104 showed a modest protective tendency in the 2-pmol-treated groups against TNF-induced axon loss, although the tendency was not significant on quantitative analysis. However, significant protective effects were found in the 20- or 200-pmol-treated groups. Injection of SRT2104 alone significantly decreased the p62 levels and increased the LC3-II levels as compared with the basal levels. Similarly, concomitant injection of SRT2104 and TNF significantly decreased the p62 levels and increased the LC3-II levels as compared with the TNF-treated group. Upregulation of SIRT1 expression was observed in the optic nerve after SRT2104 treatment.

CONCLUSION

The SIRT1 activator SRT2104 exerts axonal protection in TNF-induced optic nerve degeneration. This effect may be associated with upregulated autophagic status in the optic nerve.

Optic Nerve Lipidomics Reveal Impaired Glucosylsphingosine Lipids Pathway in Glaucoma

Purpose

To determine major differences in lipid profile between human control and glaucomatous optic nerve. To assess major enzymes in lipid pathway if aberration is revealed for a lipid class by profiling.

Methods

Optic nerve (ON) samples were obtained from human cadaveric donors [control (n = 11) and primary open-angle glaucoma (POAG; n = 12)]; the lipids were extracted using Bligh and Dyer methods. Control and glaucoma donors were all Caucasians age 72.3 ± 5.9 and 70.3 ± 10.5 (inclusive of both sexes), respectively. Lipids were extracted after weighing the tissue; the protein amounts in the corresponding aqueous phase of organic solvent extraction were recorded. High-resolution mass spectrometry was performed using a Q-exactive mass spectrometer coupled with an EASY-nLC 1000 liquid chromatograph instrument. Bioinformatics and statistical analysis were performed using LipidSearch v.4.1 and MetaboAnalyst 4.0/STATA 14.2. Protein amounts were determined using Bradford's method. Western blot, ELISA, and immunohistochemistry utilized established protocols and were performed for protein quantification and localization, respectively. Additional donor tissues were utilized for Western blot, ELISA, and immunohistochemistry.

Results

Principal component analysis (PCA) placed control and glaucomatous ONs in two distinct groups based on analysis of lipid profiles. Total lipid, total phospholipids, total ceramide, and total sphingolipids were similar (without significant difference) between control and glaucoma. However, we found a significant increase in glucosylsphingosine in glaucoma compared to control samples. We found similar levels of glucocerebrosidase (GBA), ceramide glucosyltransferase (UGCG), decreased nonlysosomal glucocerebrosidase (GBA2), and increased lysosomal and nonlysosomal acylsphingosine amidohydrolase (ASAH1 and ASAH2) levels in glaucomatous ON compared to control.

Conclusions

We found significant differences in glucosylsphingosine lipids, consistent with decreased GBA and GBA2 and increased ASAH1 and ASAH2 immunoreactivity in glaucoma, suggesting the potential impairment of sphingolipid enzymatic pathways in lysosomal and nonlysosomal cellular compartments.

The Relationship Between Autophagy and Brain Plasticity in Neurological Diseases

Autophagy, a catabolic degradation system, is utilized for destroying and recycling the damaged or unnecessary cellular components. Brain plasticity refers to the remarkable characteristics of brain neurons that change their structure and function according to previous experience. This review was performed by searching the relevant articles in databases of SCIENCEDIRECT, PUBMED, and Web of Science, from respective inception to January 2019. Here, we review the neuroprotective effect of autophagy in neurological diseases and the mechanism of autophagy in brain plasticity. Moreover, the mechanism of autophagy in the process of brain plasticity can provide the possibility for the development of new treatment methods in the future, thus benefiting patients with neurological diseases. In summary, autophagy and brain plasticity play important roles in neurological diseases.

Visual Defects and Ageing

Many diseases are related to age, among these neurodegeneration is particularly important. Alzheimer's disease Parkinson's and Glaucoma have many common pathogenic events including oxidative damage, Mitochondrial dysfunction, endothelial alterations and changes in the visual field. These are well known in the case of glaucoma, less in the case of neurodegeneration of the brain. Many other molecular aspects are common, such as the role of endoplasmic reticulum autophagy and neuronal apoptosis while others have been neglected due to lack of space such as inflammatory cytokine or miRNA. Moreover, the loss of specific neuronal populations, the induction of similar mechanisms of cell injury and the deposition of protein aggregates in specific anatomical areas are very similar events between these diseases. Intracellular and/or extracellular accumulation of protein aggregates is a key feature of many neurodegenerative disorders. The existence of abnormal protein aggregates has been documented in the RGCs of glaucomatous patients such as the anomalous Tau protein or the β-amyloid accumulations. Intra-cell catabolic processes also appear to be common in both glaucoma and neurodegeneration. They also help us to understand how the basis between these diseases is common and how the visual aspects can be a serious problem for those who are affected.

Rapamycin and fasting sustain autophagy response activated by ischemia/reperfusion injury and promote retinal ganglion cell survival

Autophagy, the cellular process responsible for degradation and recycling of cytoplasmic components through the autophagosomal–lysosomal pathway, is fundamental for neuronal homeostasis and its deregulation has been identified as a hallmark of neurodegeneration. Retinal hypoxic–ischemic events occur in several sight-treating disorders, such as central retinal artery occlusion, diabetic retinopathy, and glaucoma, leading to degeneration and loss of retinal ganglion cells. Here we analyzed the autophagic response in the retinas of mice subjected to ischemia induced by transient elevation of intraocular pressure, reporting a biphasic and reperfusion time-dependent modulation of the process. Ischemic insult triggered in the retina an acute induction of autophagy that lasted during the first hours of reperfusion. This early upregulation of the autophagic flux limited RGC death, as demonstrated by the increased neuronal loss observed in mice with genetic impairment of basal autophagy owing to heterozygous ablation of the autophagy-positive modulator Ambra1 (Ambra1^+/gt). Upregulation of autophagy was exhausted 24 h after the ischemic event and reduced autophagosomal turnover was associated with build up of the autophagic substrate SQSTM-1/p62, decreased ATG12-ATG5 conjugate, ATG4 and BECN1/Beclin1 expression. Animal fasting or subchronic systemic treatment with rapamycin sustained and prolonged autophagy activation and improved RGC survival, providing proof of principle for autophagy induction as a potential therapeutic strategy in retinal neurodegenerative conditions associated with hypoxic/ischemic stresses.

Contribution of autophagy to ocular hypertension and neurodegeneration in the DBA/2J spontaneous glaucoma mouse model

Glaucoma is a progressive optic neuropathy characterized by axonal degeneration and retinal ganglion cells loss. Several factors have been postulated to play a role in glaucoma, elevated intraocular pressure (IOP) being the best well-known causative factor. The mechanisms leading to ocular hypertension and glaucoma are still not fully understood. An increasing number of evidence indicates a role of autophagy in the pathophysiological process of ocular hypertension and glaucoma. However, while all of the studies agree that autophagy is induced in RGCs in response to injury, autophagy was found to either protect or promote cell death depending on the experimental model used. In order to gain more insight into both, the role of autophagy in the pathogenesis of glaucoma and the effect of chronic IOP elevation in the autophagy pathway, we have investigated here for the first time autophagy in the iridocorneal angle region, retinal ganglion cell bodies, and ON axons in the spontaneous ocular hypertensive DBA/2J mouse glaucoma model and in the transgenic DBA/2J::GFP-LC3 mice, generated in our laboratory. Our results indicate decreased autophagic flux in the outflow pathway cells in the DBA/2J mice, characterized by increased levels of LC3-II and p62 together with a decrease in the lysosomal marker LAMP1, evaluated by western blot and immunofluorescence. Elevated presence of autophagic vacuoles in the DBA/2J and, in particular, in the DBA/2J::GFP-LC3 mice was also observed. Expression of the GFP-LC3 transgene was associated to higher cumulative IOP in the DBA/2J background. In addition to higher elevation in IOP, DBA/2J::GFP-LC3 were characterized by further RGCs and exacerbated axonal degeneration compared to DBA/2J. This was accompanied by the notable high presence of autophagic figures within degenerating axons. These results strongly suggest overactivation of autophagy as a potential cellular mechanism leading to ON degeneration in the chronic hypertensive DBA/2J mice.

Mechanistical retinal drug targets and challenges

The retina is constantly exposed to light that increases reactive oxygen species in retina. Oxidative stress, inflammation and neurodegeneration are the major contributors in the most common retinal diseases, such as age-related macular degeneration (AMD), glaucoma and diabetic retinopathy (DR). Emerging developments and research for novel therapy targets and drug delivery to the posterior segment offer a promising future for the treatment of retinal diseases including rare hereditary diseases. In this review we discuss about promising mechanistical retinal drug targets. Vascular endothelial growth factor (VEGF) signaling and anti-VEGF treatments are excluded.

Early LC3 lipidation induced by d-limonene does not rely on mTOR inhibition, ERK activation and ROS production and it is associated with reduced clonogenic capacity of SH-SY5Y neuroblastoma cells

BACKGROUND

d-Limonene is a natural monoterpene abundant in Citrus essential oils. It is endowed with several biological activities, including inhibition of carcinogenesis and promotion of tumour regression. Recently, d-limonene has been shown to modulate autophagic markers in vitro at concentrations found in vivo, in clinical pharmacokinetic studies. Autophagy is an intracellular catabolic process serving as both an adaptive metabolic response and a quality control mechanism. Because autophagy defects have been linked to a wide range of human pathologies, including neurodegeneration and cancer, there is a need for new pharmacological tools to control deregulated autophagy.

PURPOSE

To better understand the effects of d-limonene on autophagy, to identify the molecular mechanisms through which this monoterpene rapidly triggers LC3 lipidation and to evaluate the role for autophagy in long-term effects of d-limonene.

METHODS

Human SH-SY5Y neuroblastoma, HepG2 hepatocellular carcinoma and MCF7 breast cancer cells were used. Endogenous LC3-II levels were evaluated by western blotting. Autophagic flux assay was performed using bafilomycin A1 and chloroquine. Intracellular distribution of LC3 protein was studied by confocal microscopy analysis of LC3B-GFP transduced cells. Expression of lysosomal-membrane protein LAMP-1 was assessed by immunofluorescence analysis. Phosphorylated levels of downstream substrates of mTOR kinase (p70S6 kinase, 4E-BP1, and ULK1) and ERK were analyzed by western blotting. Production of reactive oxygen species (ROS) was assessed by live confocal microscopy of cells loaded with CellROX^® Green Reagent. Clonogenic assay was used to evaluate the ability of treated cells to proliferate and form colonies.

RESULTS

LC3 lipidation promoted by d-limonene correlates with autophagosome formation and stimulation of basal autophagy. LC3 lipidation does not rely on inhibition of mTOR kinase, which instead appears to be transiently activated. In addition, d-limonene rapidly activates ERK and stimulates ROS generation, yet none of these events is implicated in lipidation of LC3, which was only partly reduced by chelation of intracellular calcium. The early LC3 lipidation induced by d-limonene is associated with inhibition of clonogenic capacity which is reverted by the autophagy inhibitor chloroquine.

CONCLUSIONS

d-Limonene rapidly stimulates the autophagic flux in cultured cancer cells, which could be usefully exploited for therapeutic purposes.

Effect of Microtubule Disruption on Dynamics of Acidic Organelles in the Axons of Primary Cultured Retinal Ganglion Cells

PURPOSE

Axonal transport is fundamental to autophagy in neuronal cells. To understand its biological significance in various conditions, it is necessary to monitor the process of autophagy. However, monitoring methods are often limited to static analyses, such as protein expression and histological observations. Autophagy has multistep process and is highly dynamic; therefore, additional techniques are necessary to study autophagy. In this study, we quantified the dynamics of autophagy-related organelle transport under conditions of dynamic instability and catastrophic disruption of microtubules using in vitro live imaging.

MATERIALS AND METHODS

Retinal ganglion cells (RGCs) were isolated from postnatal day 3 Sprague-Dawley rats by immunopanning. After 7 days of culture, acidic organelles were stained by LysoTracker. Dynamics of acidic organelles was quantified using kymographs. Colchicine was used to induce microtubule disruption. Movement of acidic organelles was observed at five time points: before, and at 6, 24, 72, and 120 h after colchicine stimulation. Ethidium homodimer-1 (EthD-1) was used to determine cell viability.

RESULTS

The status of axonal transport of acidic organelles (n = 363) from 27 RGCs was classified into four categories: anterograde (1.4%), retrograde (90%), stationary (8.0%), and fluttering (0.28%). Six hours after the induction of microtubule disruption in 14 of 27 RGCs, almost all acidic organelles (n = 236) were stationary. All acidic components had completely stopped moving 24 h later. At 72 h after stimulation, axonal fragmentation, and shrinking and disappearance of soma were observed in 71% of RGCs. Finally, the remaining RGCs became positive for EthD-1. In the control (13 of 27 RGCs), axonal transport was maintained for 120 h and EthD-1-positive RGCs were not observed.

CONCLUSION

Almost all acidic organelles were transported retrogradely along the axon, which was inhibited by colchicine. Understanding the dynamics of acidic organelles may provide useful parameters for characterizing autophagy of neuronal cells in pathophysiological conditions.