Autophagy regulating kinases as potential therapeutic targets for age-related macular degeneration. Future Med Chem. 2012;4:2153-2161. [PMID: 23190104 DOI: 10.4155/fmc.12.169]

Antioxidative Role of Heterophagy, Autophagy, and Mitophagy in the Retina and Their Association with the Age-Related Macular Degeneration (AMD) Etiopathogenesis

Age-related macular degeneration (AMD), an oxidative stress-linked neurodegenerative disease, leads to irreversible damage of the central retina and severe visual impairment. Advanced age and the long-standing influence of oxidative stress and oxidative cellular damage play crucial roles in AMD etiopathogenesis. Many authors emphasize the role of heterophagy, autophagy, and mitophagy in maintaining homeostasis in the retina. Relevantly modifying the activity of both macroautophagy and mitophagy pathways represents one of the new therapeutic strategies in AMD. Our review provides an overview of the antioxidative roles of heterophagy, autophagy, and mitophagy and presents associations between dysregulations of these molecular mechanisms and AMD etiopathogenesis. The authors performed an extensive analysis of the literature, employing PubMed and Google Scholar, complying with the 2013-2023 period, and using the following keywords: age-related macular degeneration, RPE cells, reactive oxygen species, oxidative stress, heterophagy, autophagy, and mitophagy. Heterophagy, autophagy, and mitophagy play antioxidative roles in the retina; however, they become sluggish and dysregulated with age and contribute to AMD development and progression. In the retina, antioxidative roles also play in RPE cells, NFE2L2 and PGC-1α proteins, NFE2L2/PGC-1α/ARE signaling cascade, Nrf2 factor, p62/SQSTM1/Keap1-Nrf2/ARE pathway, circulating miRNAs, and Yttrium oxide nanoparticles performed experimentally in animal studies.

Association Between Oral Metformin Use and the Development of Age-Related Macular Degeneration in Diabetic Patients: A Systematic Review and Meta-Analysis

Purpose

Metformin is a biguanide derivative that is commonly used for the treatment of diabetes mellitus (DM). It demonstrates antioxidative, anti-inflammatory, and antiangiogenic activity within the ocular tissue and thus may be implicated in the treatment of age-related macular degeneration (AMD). However, epidemiological studies have shown conflicting results.

Methods

The Ovid MEDLINE/Embase, Cochrane Library, and Web of Science databases were systematically searched from inception through August 3, 2022. Studies reporting the association between metformin use and odds of AMD were enrolled. Adjusted odds ratios (ORs) of AMD were extracted and pooled with random-effects model meta-analysis. Subgroup analyses based on AMD subtypes, ethnicity, study design, sex, and confirmation of AMD diagnosis were conducted.

Results

A total of 9 observational studies with 1,446,284 participants were included in the analysis. The meta-analysis showed that metformin use was associated with a significant reduction in the odds of AMD (pooled ORs = 0.81, 95% confidence interval [CI] = 0.70-0.93). Subgroup analyses revealed that metformin use was not significantly associated with dry or wet AMD. Black (pooled ORs = 0.61, 95% CI = 0.58-0.64) and Hispanic populations (pooled ORs = 0.85, 95% CI = 0.81-0.89) demonstrated significantly lower odds of AMD.

Conclusions

This systematic review and meta-analysis found that patients with DM with metformin usage were at lower odds of developing AMD. Future prospective clinical trials are needed to confirm this association.

Age-Related Macular Degeneration (AMD) Transmitochondrial Cybrids Protected from Cellular Damage and Death by Human Retinal Progenitor Cells (hRPCs)

Purpose

One of the leading causes of irreversible blindness worldwide, age-related macular degeneration (AMD) is a progressive disorder leading to retinal degeneration. While several treatment options exist for the exudative form of AMD, there are currently no FDA-approved treatments for the more common nonexudative (atrophic) form. Mounting evidence suggests that mitochondrial damage and retinal pigment epithelium (RPE) cell death are linked to the pathogenesis of AMD. Human retinal progenitor cells (hRPCs) have been studied as a potential restorative therapy for degenerative conditions of the retina; however, the effects of hRPC treatment on retinal cell survival in AMD have not been elucidated.

Methods

In this study, we used a cell coculture system consisting of hRPCs and AMD or age-matched normal cybrid cells to characterize the effects of hRPCs in protecting AMD cybrids from cellular and mitochondrial damage and death.

Results

AMD cybrids cocultured with hRPCs showed (1) increased cell viability; (2) decreased gene expression related to apoptosis, autophagy, endoplasmic reticulum (ER) stress, and antioxidant pathways; and (3) downregulation of mitochondrial replication genes compared to AMD cybrids without hRPC treatment. Furthermore, hRPCs cocultured with AMD cybrids showed upregulation of (1) neuronal and glial markers, as well as (2) putative neuroprotective factors, responses not found when hRPCs were cocultured with age-matched normal cybrids.

Conclusion

The current study provides the first evidence that therapeutic benefits may be obtainable using a progenitor cell-based approach for atrophic AMD. Our results suggest that bidirectional interactions exist between hRPCs and AMD cybrids such that hRPCs release trophic factors that protect the cybrids against the cellular and mitochondrial changes involved in AMD pathogenesis while, conversely, AMD cybrids upregulate the release of these neuroprotective factors by hRPCs while promoting hRPC differentiation. These in vitro data provide evidence that hRPCs may have therapeutic potential in atrophic AMD.

Interplay between reactive oxygen species and autophagy in the course of age-related macular degeneration

Pathological biomolecules such as lipofuscin, methylglyoxal-modified proteins (the major precursors of advanced glycationend products), misfolding protein deposits and dysfunctional mitochondria are source of oxidative stress and act as strong autophagic stimulators in age-related macular degeneration. Disturbed autophagy accelerates progression of the disease, since it leads to retinal cells' death and activates inflammation by the interplay with the NLRP3 inflammasome complex. Vascular dysfunction and hypoxia, as well as circulating autoantibodies against autophagy regulators (anti-S100A9, anti-ANXA5, and anti-HSPA8, A9 and B4) compromise an autophagy-mediated mechanism as well. Metformin, the autophagic stimulator, may act as a senostatic drug to inhibit the senescent phenotype in the age-related macular degeneration. PGC-1α , Sirt1 and AMPK represent new therapeutic targets for interventions in this disease.

Translocator protein (18 kDa) (TSPO) ligands activate Nrf2 signaling and attenuate inflammatory responses and oxidative stress in human retinal pigment epithelial cells

Degeneration of the retinal pigment epithelium (RPE) is a hallmark of atrophic age-related macular degeneration (AMD). Microglia mediated inflammatory responses and oxidative stress are critical pathophysiological processes in the onset and progression of RPE degeneration. Given the central role of the RPE, strategies to protect these cells from damage caused by oxidative stress and inflammation present a promising therapeutic approach to mitigate AMD. Ligands for the translocator protein (18 kDa) (TSPO) have been shown to confer protection against retinal inflammatory responses and neurodegeneration by acting primarily through retinal glia. However, despite RPE cells demonstrating strong TSPO expression, it remains unclear whether TSPO ligands could also inhibit inflammatory responses of RPE cells. Here, we investigated the influence of three different TSPO ligands XBD173, PK11195 and Ro5-4864 on inflammatory responses in human ARPE-19 cells triggered by supernatants from reactive human microglial cells and the lysosomal destabilizer, LLOMe. Our findings revealed that TSPO ligands significantly inhibited proinflammatory gene expression, inflammasome-mediated caspase-1 activation, lipid accumulation and intracellular ROS levels in stressed ARPE-19 cells. Notably, TSPO ligands induced activation of Nrf2 pathway and its downstream regulated genes in ARPE-19 cells, with Hmox-1 being the most strongly upregulated gene. Collectively, our study indicates that TSPO ligands can enhance the Nrf2 antioxidant pathway in RPE cells and protect them from cellular damage resulting from inflammation and oxidative stress.

Berberine Protects Human Retinal Pigment Epithelial Cells from Hydrogen Peroxide-Induced Oxidative Damage through Activation of AMPK

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly with less effective treatment, especially for dry AMD (90% of AMD). Although the etiology of this disease is not well elucidated, increasing evidences indicate that excessive reactive oxygen species (ROS) impairing the physiological functions of retinal pigment epithelium (RPE) cells may be one of the main causes. Therefore, it could be a great strategy to find some drugs that can effectively protect RPE cells from oxidative damage which is desired to treat and slow the process of AMD. In the present study, a well-known traditional Chinese medicine berberine (BBR) was found to suppress hydrogen peroxide (H₂O₂)-induced oxidative damage in D407 cells, a human RPE cell line. Pre-treatment of D407 cells with BBR significantly suppressed H₂O₂-induced cell apoptosis by restoring abnormal changes in nuclear morphology, preventing the decline of mitochondrial membrane potential, reducing lactate dehydrogenase release and inhibiting caspase 3/7 activities induced by H₂O₂. Western blot analysis showed that BBR was able to stimulate the phosphorylation/activation of AMPK in a time- and dose-dependent manner in D407 cells, while treatment of cells with AMPK pathway inhibitor Compound C, or knockdown of the AMPK by specific siRNA blocked the effect of BBR. Similar results were obtained in primary cultured human RPE cells. Taken together, these results demonstrated that BBR was able to protect RPE cells against oxidative stress via the activation of AMPK pathway. Our findings also indicate the potential application of BBR in AMD treatment.

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.

Autophagy Stimulus Promotes Early HuR Protein Activation and p62/SQSTM1 Protein Synthesis in ARPE-19 Cells by Triggering Erk1/2, p38MAPK, and JNK Kinase Pathways

RNA-binding protein dysregulation and altered expression of proteins involved in the autophagy/proteasome pathway play a role in many neurodegenerative disease onset/progression, including age-related macular degeneration (AMD). HuR/ELAVL1 is a master regulator of gene expression in human physiopathology. In ARPE-19 cells exposed to the proteasomal inhibitor MG132, HuR positively affects at posttranscriptional level p62 expression, a stress response gene involved in protein aggregate clearance with a role in AMD. Here, we studied the early effects of the proautophagy AICAR + MG132 cotreatment on the HuR-p62 pathway. We treated ARPE-19 cells with Erk1/2, AMPK, p38^MAPK, PKC, and JNK kinase inhibitors in the presence of AICAR + MG132 and evaluated HuR localization/phosphorylation and p62 expression. Two-hour AICAR + MG132 induces both HuR cytoplasmic translocation and threonine phosphorylation via the Erk1/2 pathway. In these conditions, p62 mRNA is loaded on polysomes and its translation in de novo protein is favored. Additionally, for the first time, we report that JNK can phosphorylate HuR, however, without modulating its localization. Our study supports HuR's role as an upstream regulator of p62 expression in ARPE-19 cells, helps to understand better the early events in response to a proautophagy stimulus, and suggests that modulation of the autophagy-regulating kinases as potential therapeutic targets for AMD may be relevant.

Into the eyes of bone marrow-derived mesenchymal stem cells therapy for myocardial infarction and other diseases

Applications of bone marrow-derived mesenchymal stem cells (BM-MSCs) have been documented for diseases occur in the sports system, the central nervous system, the cardiovascular system etc. However, poor viability of donor stem cells after transplantation limits their therapeutic efficiency. Although the autophagy theory has been reported, the underlying mechanisms are still poorly understood. Isolation and culture methods of mesenchymal stem cells are currently concentrate on four ways. Overall, BM-MSCs have both important research significance and clinical application value in cell replacement therapy, gene therapy and reconstruction of tissues as well as organs especially for myocardial infarction (MI). In this article, we review the biological characteristics of BM-MSCs and its research progress especially in MI.

Advances in Age-related Macular Degeneration Understanding and Therapy

While the development of anti-vascular endothelial growth factor (anti-VEGF) as a therapy for neovascular age-related macular degeneration (AMD) was a great success, the pathologic processes underlying dry AMD that eventually leads to photoreceptor dysfunction, death, and vision loss remain elusive to date, with a lack of effective therapies and increasing prevalence of the disease. There is an overwhelming need to improve the classification system of AMD, to increase our understanding of cell death mechanisms involved in both neovascular and non-neovascular AMD, and to develop better biomarkers and clinical endpoints to eventually be able to identify better therapeutic targets—especially early in the disease process. There is no doubt that it is a matter of time before progress will be made and better therapies will be developed for non-neovascular AMD.

The Complement Regulatory Protein CD46 Deficient Mouse Spontaneously Develops Dry-Type Age-Related Macular Degeneration-Like Phenotype

In the mouse, membrane cofactor protein (CD46), a key regulator of the alternative pathway of the complement system, is only expressed in the eye and on the inner acrosomal membrane of spermatozoa. We noted that although Cd46(-/-) mice have normal systemic alternative pathway activating ability, lack of CD46 leads to dysregulated complement activation in the eye, as evidenced by increased deposition of C5b-9 in the retinal pigment epithelium (RPE) and choroid. A knockout of CD46 induced the following cardinal features of human dry age-related macular degeneration (AMD) in 12-month-old male and female mice: accumulation of autofluorescent material in and hypertrophy of the RPE, dense deposits in and thickening of Bruch's membrane, loss of photoreceptors, cells in subretinal space, and a reduction of choroidal vessels. Collectively, our results demonstrate spontaneous age-related degenerative changes in the retina, RPE, and choroid of Cd46(-/-) mice that are consistent with human dry AMD. These findings provide the exciting possibility of using Cd46(-/-) mice as a convenient and reliable animal model for dry AMD. Having such a relatively straight-forward model for dry AMD should provide valuable insights into pathogenesis and a test model system for novel drug targets. More important, tissue-specific expression of CD46 gives the Cd46(-/-) mouse model of dry AMD a unique advantage over other mouse models using knockout strains.

Inflammation and its role in age-related macular degeneration

Inflammation is a cellular response to factors that challenge the homeostasis of cells and tissues. Cell-associated and soluble pattern-recognition receptors, e.g. Toll-like receptors, inflammasome receptors, and complement components initiate complex cellular cascades by recognizing or sensing different pathogen and damage-associated molecular patterns, respectively. Cytokines and chemokines represent alarm messages for leukocytes and once activated, these cells travel long distances to targeted inflamed tissues. Although it is a crucial survival mechanism, prolonged inflammation is detrimental and participates in numerous chronic age-related diseases. This article will review the onset of inflammation and link its functions to the pathogenesis of age-related macular degeneration (AMD), which is the leading cause of severe vision loss in aged individuals in the developed countries. In this progressive disease, degeneration of the retinal pigment epithelium (RPE) results in the death of photoreceptors, leading to a loss of central vision. The RPE is prone to oxidative stress, a factor that together with deteriorating functionality, e.g. decreased intracellular recycling and degradation due to attenuated heterophagy/autophagy, induces inflammation. In the early phases, accumulation of intracellular lipofuscin in the RPE and extracellular drusen between RPE cells and Bruch's membrane can be clinically detected. Subsequently, in dry (atrophic) AMD there is geographic atrophy with discrete areas of RPE loss whereas in the wet (exudative) form there is neovascularization penetrating from the choroid to retinal layers. Elevations in levels of local and systemic biomarkers indicate that chronic inflammation is involved in the pathogenesis of both disease forms.

TAK1 is involved in the autophagy process in retinal pigment epithelial cells

Autophagy is an evolutionarily conserved mechanism for degrading long-lived or malfunctioning proteins and organelles, such as those resulting from oxidative stress. Several publications have demonstrated the importance of the autophagy process in the pathophysiology of dry age-related macular degeneration (AMD). Still, the mechanism underlying this process and its involvement in dry AMD are not fully characterized. Investigating the autophagy process in retinal pigment epithelial (RPE) cells, we identified transforming growth factor β activated kinase 1 (TAK1) as a key player in the process. We found increased TAK1 phosphorylation in ARPE-19 and D407 cells treated with different inducers of autophagy, such as oxidative stress and rapamycin. Moreover, utilizing TAK1 specific inhibitor prior to oxidative stress or rapamycin treatment, we found significant reduction in LC3A/B-II expression. These results point at the involvement of TAK1 in the regulation of autophagy in RPE cells. This study suggests that aberrant activity of this kinase impairs autophagy and subsequently leads to alterations in the vitality of RPE cells. Proper activity of TAK1 may be essential for efficient autophagy, and crucial for the ability of RPE cells to respond to stress and dispose of damaged organelles, thus preventing or delaying retinal pathologies.

Protective effect of autophagy on human retinal pigment epithelial cells against lipofuscin fluorophore A2E: implications for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly. Degeneration of retinal pigment epithelial (RPE) cells is a crucial causative factor responsible for the onset and progression of AMD. A2E, a major component of toxic lipofuscin implicated in AMD, is deposited in RPE cells with age. However, the mechanism whereby A2E may contribute to the pathogenesis of AMD remains unclear. We demonstrated that A2E was a danger signal of RPE cells, which induced autophagy and decreased cell viability in a concentration- and time-dependent manner. Within 15 min after the treatment of RPE with 25 μM A2E, the induction of autophagosome was detected by transmission electron microscopy. After continuous incubating RPE cells with A2E, intense punctate staining of LC3 and increased expression of LC3-II and Beclin-1 were identified. Meanwhile, the levels of intercellular adhesion molecule (ICAM), interleukin (IL)1β, IL2, IL-6, IL-8, IL-17A, IL-22, macrophage cationic peptide (MCP)-1, stromal cell-derived factor (SDF)-1, and vascular endothelial growth factor A (VEGFA) were elevated. The autophagic inhibitor 3-methyladenine (3-MA) and activator rapamycin were also used to verify the effect of autophagy on RPE cells against A2E. Our results revealed that 3-MA decreased the autophagosomes and LC3 puncta induced by A2E, increased inflammation-associated protein expression including ICAM, IL1β, IL2, IL-6, IL-8, IL-17A, IL-22, and SDF-1, and upregulated VEGFA expression. Whereas rapamycin augmented the A2E-mediated autophagy, attenuated protein expression of inflammation-associated and angiogenic factors, and blocked the Akt/mTOR pathway. Taken together, A2E induces autophagy in RPE cells at the early stage of incubation, and this autophagic response can be inhibited by 3-MA or augmented by rapamycin via the mTOR pathway. The enhancement of autophagy has a protective role in RPE cells against the adverse effects of A2E by reducing the secretion of inflammatory cytokines and VEGFA.

Stress involvement as trigger factor in different skin conditions

Dermatological conditions are intimately related to stress. There was a great interest in this field in the last years. Stress could be involved as a trigger factor for a lot of cutaneous diseases: alopecia areata, psoriasis, vitiligo, lichen planus, acne, atopic dermatitis, urticaria. For other conditions: seborrheic dermatitis, hyperhydrosis, herpes, pemphigus, a.s.o, there are anecdotal notices. On the other hand, the skin disease itself could induce a secondary stress for the patient, influencing his quality of life. The stress per se is less important than the “perceived stress”, the patient’s perception of the stressful situation. This perception could be influenced by the psychological state of the patient. Anxiety, depression could change the perception of the event. It is important to take care of these aspects during the consultation. A good cooperation with psychiatrist or/and psychologist could improve the results, besides the specific therapy.

Autophagy and heterophagy dysregulation leads to retinal pigment epithelium dysfunction and development of age-related macular degeneration

Age-related macular degeneration (AMD) is a complex, degenerative and progressive eye disease that usually does not lead to complete blindness, but can result in severe loss of central vision. Risk factors for AMD include age, genetics, diet, smoking, oxidative stress and many cardiovascular-associated risk factors. Autophagy is a cellular housekeeping process that removes damaged organelles and protein aggregates, whereas heterophagy, in the case of the retinal pigment epithelium (RPE), is the phagocytosis of exogenous photoreceptor outer segments. Numerous studies have demonstrated that both autophagy and heterophagy are highly active in the RPE. To date, there is increasing evidence that constant oxidative stress impairs autophagy and heterophagy, as well as increases protein aggregation and causes inflammasome activation leading to the pathological phenotype of AMD. This review ties together these crucial pathological topics and reflects upon autophagy as a potential therapeutic target in AMD.