Disruptions of Autophagy in the Rat Retina with Age During the Development of Age-Related-Macular-Degeneration-like Retinopathy

Mitochondrial quality control in non-exudative age-related macular degeneration: From molecular mechanisms to structural and functional recovery

Non-exudative age-related macular degeneration (NE-AMD) is the leading blindness cause in the elderly. Clinical and experimental evidence supports that early alterations in macular retinal pigment epithelium (RPE) mitochondria play a key role in NE-AMD-induced damage. Mitochondrial dynamics (biogenesis, fusion, fission, and mitophagy), which is under the central control of AMP-activated kinase (AMPK), in turn, determines mitochondrial quality. We have developed a NE-AMD model in C57BL/6J mice induced by unilateral superior cervical ganglionectomy (SCGx), which progressively reproduces the disease hallmarks circumscribed to the temporal region of the RPE/outer retina that exhibits several characteristics of the human macula. In this work we have studied RPE mitochondrial structure, dynamics, function, and AMPK role on these parameters' regulation at the nasal and temporal RPE from control eyes and at an early stage of experimental NE-AMD (i.e., 4 weeks post-SCGx). Although RPE mitochondrial mass was preserved, their function, which was higher at the temporal than at the nasal RPE in control eyes, was significantly decreased at 4 weeks post-SCGx at the same region. Mitochondria were bigger, more elongated, and with denser cristae at the temporal RPE from control eyes. Exclusively at the temporal RPE, SCGx severely affected mitochondrial morphology and dynamics, together with the levels of phosphorylated AMPK (p-AMPK). AMPK activation with metformin restored RPE p-AMPK levels, and mitochondrial dynamics, structure, and function at 4 weeks post-SCGx, as well as visual function and RPE/outer retina structure at 10 weeks post-SCGx. These results demonstrate a key role of the temporal RPE mitochondrial homeostasis as an early target for NE-AMD-induced damage, and that pharmacological AMPK activation could preserve mitochondrial morphology, dynamics, and function, and, consequently, avoid the functional and structural damage induced by NE-AMD.

Advanced Research in Age-Related Macular Degeneration: Special Issue

Age-related macular degeneration (AMD) is an eye disease that is the leading cause of irreversible vision loss in people over 55 years of age [...].

Retinoprotective Effect of SkQ1, Visomitin Eye Drops, Is Associated with Suppression of P38 MAPK and ERK1/2 Signaling Pathways Activity

Visomitin eye drops are the first and, so far, the only drug based on SkQ1 - the mitochondria-targeted antioxidant 10-(6'-plastoquinonyl) decyltriphenylphosphonium, developed in the laboratories of Moscow State University under the leadership of Academician V. P. Skulachev. SkQ1 is considered as a potential tool to combat the aging program. We have previously shown that it is able to prevent and/or suppress development of all manifestations of accelerated senescence in OXYS rats, including retinopathy, similar to the age-related macular degeneration (AMD). Here, we assessed the effect of Visomitin instillations on progression of the AMD-like pathology and p38 MAPK and ERK1/2 activity in the OXYS rat retina (from the age of 9 to 12 months). Wistar and OXYS rats treated with placebo (composition identical to Visomitin with the exception of SkQ1) were used as controls. Ophthalmological examination showed that in the OXYS rats receiving placebo, retinopathy progressed and severity of clinical manifestations did not differ from the intact OXYS rats. Visomitin suppressed progression of the AMD-like pathology in the OXYS rats and significantly improved structural and functional parameters of the retinal pigment epithelium cells and state of microcirculation in the choroid, which, presumably, contributed to preservation of photoreceptors, associative and ganglion neurons. It was found that the activity of p38 MAPK and ERK1/2 in the retina of 12-month-old OXYS rats is higher than that of the Wistar rats of the same age, as indicated by the increased content of phosphorylated forms of p38 MAPK and ERK1/2 and their target protein tau (at position T181 and S396). Visomitin decreased phosphorylation of p38 MAPK, ERK1/2, and tau indicating suppression of activity of these MAPK signaling cascades. Thus, Visomitin eye drops are able to suppress progression of the AMD-like pathology in the OXYS rats and their effect is associated with the decrease in activity of the MAPK signaling cascades.

Pharmacogenetic Association between Allelic Variants of the Autophagy-Related Genes and Anti-Vascular Endothelial Growth Factor Treatment Response in Neovascular Age-Related Macular Degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of late-onset blindness in elderly. The occurrence and development of AMD is a multifactorial complex process where autophagy plays an important role. The first-line drugs for neovascular AMD (nAMD) are inhibitors of VEGF, with up to 30% of patients having an incomplete response to treatment. Genetic factors may influence the response to anti-VEGF therapy and explain treatment outcome variability. We aimed to estimate the role of polymorphic markers of the MTOR (rs1064261, rs1057079, rs11121704, rs2295080), SQSTM1 (rs10277), ULK1 (rs11246867, rs3088051), MAP1LC3A (rs73105013) and ATG5 (rs573775) genes in the development of nAMD and the efficacy of anti-VEGF therapy response.

METHODS

Genotyping by allele-specific PCR was performed in 317 controls and 315 nAMD patients in the Russian population. Of them, 196 treatment-naive nAMD patients underwent three monthly intravitreal injections (IVIs) of aflibercept. Genotypic frequencies were compared with OCT markers of therapy effectiveness and best-corrected visual acuity (BCVA) measures. The main outcomes were the BCVA gain and decrease in central retinal thickness (CRT).

RESULTS

MTOR-rs1057079-C, MTOR-rs11121704-C and MTOR-rs2295080-G alleles were associated with an increased risk of nAMD. The BCVA was increased in 117 (59.7%) patients by 10 [5-20] letters, did not changed in 59 (30.1%), and was decreased in 20 (10.2%) patients. ULK1-rs3088051 was associated with BCVA change. Among patients with the TT and CT genotypes for ULK1-rs3088051, an improvement in visual acuity was noted in 67.6% and 53.8% of cases, while in patients with the CC genotype, an increase in BCVA was recorded in 37.5% of cases (p = 0.01). The decrease in CRT was associated with SQSTM1-rs10277 (p = 0.001): it was significantly higher in TT (93 [58-122] mkm) and CT (66 [30-105] mkm) carriers compared to the CC genotype (47 [24-68] mkm). Other SNPs did not show significant associations with the outcome of anti-VEGF treatment.

CONCLUSIONS

MTOR gene polymorphisms are moderately associated with the risk of nAMD. SQSTM1-rs10277 and ULK1-rs3088051 may influence short-term response to intravitreal anti-VEGF treatment. The results suggest that autophagy could be a target for future drugs to overcome resistance to anti-VEGF therapy.

Age-related deficits in retinal autophagy following intraocular pressure elevation in autophagy reporter mouse model

This study quantified age-related changes to retinal autophagy using the CAG-RFP-EGFP-LC3 autophagy reporter mice and considered how aging impacts autophagic responses to acute intraocular pressure (IOP) stress. IOP was elevated to 50 mm Hg for 30 minutes in 3-month-old and 12-month-old CAG-RFP-EGFP-LC3 (n = 7 per age group) and Thy1-YFPh transgenic mice (n = 3 per age group). Compared with younger eyes, older eyes showed diminished basal autophagy in the outer retina, while the inner retina was unaffected. Autophagic flux (red:yellow puncta ratio) was elevated in the inner plexiform layer. Three days following IOP elevation, older eyes showed poorer functional recovery, most notably in ganglion cell responses compared to younger eyes (12 months old: -33.4 ± 5.3% vs. 3 months mice: -13.4 ± 4.5%). This paralleled a reduced capacity to upregulate autophagic puncta volume in the inner retina in older eyes, a response that was seen in younger eyes. Age-related decline in basal and stress-induced autophagy in the retina is associated with greater retinal ganglion cells' susceptibility to IOP elevation.

SkQ1 as a Tool for Controlling Accelerated Senescence Program: Experiments with OXYS Rats

According to the concept suggested by V. P. Skulachev and co-authors, aging of living organisms can be considered as a special case of programmed death of an organism - phenoptosis, and mitochondrial antioxidant SkQ1 is capable of inhibiting both acute and chronic phenoptosis (aging). The authors of the concept associate effects of SkQ1 with suppression of the enhanced generation of ROS in mitochondria. Numerous studies have confirmed the ability of SkQ1 to inhibit manifestations of the "healthy", or physiological, aging. According to the results of our studies, SkQ1 is especially effective in suppressing the program of genetically determined accelerated senescence in OXYS rats, which appears as an early development of a complex of age-related diseases: cataracts, retinopathy (similar to the age-related macular degeneration in humans), osteoporosis, and signs of Alzheimer's disease. Accelerated senescence in OXYS rats is associated with mitochondrial dysfunction, but no direct associations with oxidative stress have been identified. Nevertheless, SkQ1 is able to prevent and/or suppress development of all manifestations of accelerated senescence in OXYS rats. Its effects are due to impact on the activity of many signaling pathways and processes, but first of all they are associated with restoration of the structural and functional parameters of mitochondria. It could be suggested that the use of SkQ1 could represent a promising strategy in prevention of accelerated phenoptosis - early development of a complex of age-related diseases (multimorbidity) in people predisposed to it.

Proteostasis in aging-associated ocular disease

Vision impairment has devastating consequences for the quality of human life. The cells and tissues associated with the visual process must function throughout one's life span and maintain homeostasis despite exposure to a variety of insults. Maintenance of the proteome is termed proteostasis, and is vital for normal cellular functions, especially at an advanced age. Here we describe basic aspects of proteostasis, from protein synthesis and folding to degradation, and discuss the current status of the field with a particular focus on major age-related eye diseases: age-related macular degeneration, cataract, and glaucoma. Our intent is to allow vision scientists to determine where and how to harness the proteostatic machinery for extending functional homeostasis in the aging retina, lens, and trabecular meshwork. Several common themes have emerged despite these tissues having vastly different metabolisms. Continued exposure to insults, including chronic stress with advancing age, increases proteostatic burden and reduces the fidelity of the degradation machineries including the ubiquitin-proteasome and the autophagy-lysosome systems that recognize and remove damaged proteins. This "double jeopardy" results in an exponential accumulation of cytotoxic proteins with advancing age. We conclude with a discussion of the challenges in maintaining an appropriate balance of protein synthesis and degradation pathways, and suggest that harnessing proteostatic capacities should provide new opportunities to design interventions for attenuating age-related eye diseases before they limit sight.

Quantitative Metabolomic Analysis of Changes in the Rat Blood Serum during Autophagy Modulation: A Focus on Accelerated Senescence

Autophagy is involved in the maintenance of cellular homeostasis and the removal of damaged proteins and organelles and is necessary to maintain cell metabolism in conditions of energy and nutrient deficiency. A decrease in autophagic activity plays an important role in age-related diseases. However, the metabolic response to autophagy modulation remains poorly understood. Here, we for the first time explored the effects of (1) autophagy activation by 48 h fasting, (2) inhibition by chloroquine (CQ) treatment, and (3) combined effects of fasting and CQ on the quantitative composition of metabolites in the blood serum of senescent-accelerated OXYS and control Wistar rats at the age of 4 months. By means of high-resolution ¹H NMR spectroscopy, we identified the quantitative content of 55 serum metabolites, including amino acids, organic acids, antioxidants, osmolytes, glycosides, purine, and pyrimidine derivatives. Groups of 48 h fasting (induction of autophagy), CQ treatment (inhibition of autophagy), and combined effects (CQ + fasting) are clearly separated from control groups by principal component analysis. Fasting for 48 h led to significant changes in the serum metabolomic profile, primarily affecting metabolic pathways related to fatty acid metabolism, and led to metabolism of several amino acids. Under CQ treatment, the most affected metabolites were citrate, betaine, cytidine, proline, tryptophan, glutamate, and mannose. As shown by two-way ANOVA, for many metabolites the effects of autophagy modulation depend on the animal genotype, indicating a dysregulation of metabolome reactivity in OXYS rats. Thus, the metabolic responses to modulation of autophagy in OXYS rats and Wistar rats are different. Altered metabolites in OXYS rats may serve as potential biomarkers of the manifestation of the signs of accelerated aging. Metabolic signatures characteristic to fasting and CQ treatment revealed in this work might provide a better understanding of the connections between metabolism and autophagy.

Role of the AMPK signalling pathway in the aetiopathogenesis of ocular diseases

BACKGROUND

AMP-activated protein kinase (AMPK) plays a precise role as a master regulator of cellular energy homeostasis. AMPK is activated in response to the signalling cues that exhaust cellular ATP levels such as hypoxia, ischaemia, glucose depletion and heat shock. As a central regulator of both lipid and glucose metabolism, AMPK is considered to be a potential therapeutic target for the treatment of various diseases, including eye disorders.

OBJECTIVE

To review all the shreds of evidence concerning the role of the AMPK signalling pathway in the pathogenesis of ocular diseases.

METHOD

Scientific data search and review of available information evaluating the influence of AMPK signalling on ocular diseases.

RESULTS

Review highlights the significance of AMPK signalling in the aetiopathogenesis of ocular diseases, including cataract, glaucoma, diabetic retinopathy, retinoblastoma, age-related macular degeneration, corneal diseases, etc. The review also provides the information on the AMPK-associated pathways with reference to ocular disease, which includes mitochondrial biogenesis, autophagy and regulation of inflammatory response.

CONCLUSION

The study concludes the role of AMPK in ocular diseases. There is growing interest in the therapeutic utilization of the AMPK pathway for ocular disease treatment. Furthermore, inhibition of AMPK signalling might represent more pertinent strategy than AMPK activation for ocular disease treatment. Such information will guide the development of more effective AMPK modulators for ocular diseases.[Formula: see text].

Autophagy as a Target for the Retinoprotective Effects of the Mitochondria-Targeted Antioxidant SkQ1

Age-related macular degeneration (AMD) is a complex neurodegenerative disease, a main cause of vision loss in elderly people. The pathogenesis of dry AMD, the most common form of AMD (~ 80% cases), involves degenerative changes in the retinal pigment epithelium (RPE), which are closely associated with the age-associated impairments in autophagy. Reversion of these degenerative changes is considered as a promising approach for the treatment of this incurable disease. The purpose of our study was to assess the relationship between previously identified retinoprotective effects of the mitochondrial antioxidant plastoquinonyl-decyl-triphenylphosphonium (SkQ1) and its influence on the autophagy process in senescence-accelerated OXYS rats characterized by the development of AMD-like retinopathy (Wistar rats were used as a control). The treatment with SkQ1 (250 nmol/kg body weight) during the period of active disease progression (from 12 to 18 months of age) completely prevented progression of clinical manifestations of retinopathy in the OXYS rats, suppressed atrophic changes in the RPE cells and activated autophagy in the retina, which was evidenced by a significant decrease in the content of the multifunctional adapter protein p62/Sqstm1 and increase in the level of the Beclin1 gene mRNA. In general, the results obtained earlier and in the present study have shown that SkQ1 is a promising agent for prevention and suppression of AMD.

Solanum melongena L. Extract Protects Retinal Pigment Epithelial Cells from Blue Light-Induced Phototoxicity in In Vitro and In Vivo Models

N-retinylidene-N-retinylethanolamine (A2E) accumulation in the retina is a prominent marker of retinal degenerative diseases. Blue light exposure is considered as an important factor contributing to dry age-related macular degeneration (AMD). Eggplant and its constituents have been shown to confer health benefits, but their therapeutic effects on dry AMD remain incompletely understood. In this study, we showed that an extract of Solanum melongena L. (EPX) protected A2E-laden ARPE-19 cells against blue light-induced cell death via attenuating reactive oxygen species. Transcriptomic analysis demonstrated that blue light modulated the expression of genes associated with stress response, inflammation, and cell death, and EPX suppressed the inflammatory pathway induced by blue light in A2E-laden ARPE-19 cells by inhibiting the nuclear translocation of nuclear factor kappa B and transcription of pro-inflammatory genes (CXCL8 and IL1B). The degradation of intracellular A2E was considered the major mechanism underlying the protective effect of EPX. Moreover, chlorogenic acid isolated from EPX exerted protective effects against blue light-induced cell damage in A2E-laden ARPE-19 cells. In vivo, EPX administration in BALB/c mice reduced the fundus damage and degeneration of the retinal layer in a blue light-induced retinal damage model. Collectively, our findings suggest the potential role of Solanum melongena L. extract for AMD treatment.

An In-Vitro Cell Model of Intracellular Protein Aggregation Provides Insights into RPE Stress Associated with Retinopathy

Impaired cargo trafficking and the aggregation of intracellular macromolecules are key features of neurodegeneration, and a hallmark of aged as well as diseased retinal pigment epithelial (RPE) cells in the eye. Here, photoreceptor outer segments (POS), which are internalized daily by RPE cells, were modified by UV-irradiation to create oxidatively modified POS (OxPOS). Oxidative modification was quantified by a protein carbonyl content assay. Human ARPE-19 cells were synchronously pulsed with POS or OxPOS to study whether oxidatively modified cargos can recapitulate features of RPE pathology associated with blinding diseases. Confocal immunofluorescence microscopy analysis showed that OxPOS was trafficked to LAMP1, LAMP2 lysosomes and to LC3b autophagy vacuoles. Whilst POS were eventually degraded, OxPOS cargos were sequestered in late compartments. Co-localization of OxPOS was also associated with swollen autolysosomes. Ultrastructural analysis revealed the presence of electron-dense OxPOS aggregates in RPE cells, which appeared to be largely resistant to degradation. Measurement of cellular autofluorescence, using parameters used to assess fundus autofluorescence (FAF) in age-related macular disease (AMD) patients, revealed that OxPOS contributed significantly to a key feature of aged and diseased RPE. This in vitro cell model therefore represents a versatile tool to study disease pathways linked with RPE damage and sight-loss.

A Re-Appraisal of Pathogenic Mechanisms Bridging Wet and Dry Age-Related Macular Degeneration Leads to Reconsider a Role for Phytochemicals

Which pathogenic mechanisms underlie age-related macular degeneration (AMD)? Are they different for dry and wet variants, or do they stem from common metabolic alterations? Where shall we look for altered metabolism? Is it the inner choroid, or is it rather the choroid–retinal border? Again, since cell-clearing pathways are crucial to degrade altered proteins, which metabolic system is likely to be the most implicated, and in which cell type? Here we describe the unique clearing activity of the retinal pigment epithelium (RPE) and the relevant role of its autophagy machinery in removing altered debris, thus centering the RPE in the pathogenesis of AMD. The cell-clearing systems within the RPE may act as a kernel to regulate the redox homeostasis and the traffic of multiple proteins and organelles toward either the choroid border or the outer segments of photoreceptors. This is expected to cope with the polarity of various domains within RPE cells, with each one owning a specific metabolic activity. A defective clearance machinery may trigger unconventional solutions to avoid intracellular substrates’ accumulation through unconventional secretions. These components may be deposited between the RPE and Bruch’s membrane, thus generating the drusen, which remains the classic hallmark of AMD. These deposits may rather represent a witness of an abnormal RPE metabolism than a real pathogenic component. The empowerment of cell clearance, antioxidant, anti-inflammatory, and anti-angiogenic activity of the RPE by specific phytochemicals is here discussed.

Alterations of STEP46 and STEP61 Expression in the Rat Retina with Age and AMD-Like Retinopathy Development

Tyrosine phosphatase STEP (striatal-enriched tyrosine protein phosphatase) is a brain-specific protein phosphatase and is involved in the pathogenesis of many neurodegenerative diseases. Here, we examined the impact of STEP on the development of age-related macular degeneration (AMD)-like pathology in senescence-accelerated OXYS rats. Using OXYS and Wistar rats (control), we for the first time demonstrated age-dependent changes in Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the retina. The increases in STEP protein levels and the decrease of total and STEP phosphatase activities in the retina (as compared with Wistar rats) preceded the manifestation of clinical signs of AMD in OXYS rats (age 20 days). There were no differences in these retinal parameters between 13-month-old Wistar rats and OXYS rats with pronounced signs of AMD. Inhibition of STEP with TC-2153 during progressive AMD-like retinopathy (from 9 to 13 months of age) reduced the thickness of the retinal inner nuclear layer, as evidenced by a decreased amount of parvalbumin-positive amacrine neurons. Prolonged treatment with TC-2153 had no effect on Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the OXYS retina. Thus, TC-2153 may negatively affect the retina through mechanisms unrelated to STEP.

Mechanisms of Neuronal Death in the Cerebral Cortex during Aging and Development of Alzheimer's Disease-Like Pathology in Rats

Alzheimer's disease (AD) is the commonest type of late-life dementia and damages the cerebral cortex, a vulnerable brain region implicated in memory, emotion, cognition, and decision-making behavior. AD is characterized by progressive neuronal loss, but the mechanisms of cell death at different stages of the disease remain unknown. Here, by means of OXYS rats as an appropriate model of the most common (sporadic) AD form, we studied the main pathways of cell death during development of AD-like pathology, including the preclinical stage. We found that apoptosis is activated at the pre-symptomatic stage (age 20 days) correlating with the retardation of brain development in the OXYS strain early in life. Progression of the AD-like pathology was accompanied by activation of apoptosis and necroptosis resulting from a decline of autophagy-mediated proteostasis. Our results are consistent with the idea that the nature of changes in the pathways of apoptosis, autophagy, and necrosis depends on the stage of AD.