Alpha crystallins in the retinal pigment epithelium and implications for the pathogenesis and treatment of age-related macular degeneration

Decrease of alpha-crystallin A by miR-325-3p in retinal cells under blue light exposure

Exposure to blue light can lead to retinal degeneration, causing adverse effects on eye health. Although the loss of retinal cells due to blue light exposure has been observed, the precise molecular mechanisms underlying this process remain poorly understood. In this study, we investigate the role of alpha-crystallin A (CRYAA) in neuro-retinal degeneration and their regulation by blue light. We observed significant apoptotic cell death in both the retina of rats and the cultured neuro-retinal cells. The expressions of Cryaa mRNA and protein were significantly downregulated in the retina exposed to blue light. We identified that miR-325-3p reduces Cryaa mRNA and protein by binding to its 3'-untranslated region. Upregulation of miR-325-3p destabilized Cryaa mRNA and suppresses CRYAA, whereas downregulation of miR-325-3p increased both expressions. Blue light-induced neuro-retinal cell death was alleviated by CRYAA overexpression. These results highlight the critical role of Cryaa mRNA and miR-325-3p molecular axis in blue light-induced retinal degeneration. Consequently, targeting CRYAA and miR-325-3p presents a potential strategy for protecting against blue light-induced retinal degeneration.

Proteostatic Remodeling of Small Heat Shock Chaperones─Crystallins by Ran-Binding Protein 2─and the Peptidyl-Prolyl cis-trans Isomerase and Chaperone Activities of Its Cyclophilin Domain

Disturbances in protein phase transitions promote protein aggregation─a neurodegeneration hallmark. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also regulate phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against phototoxicity by proteostatic regulations of neuroprotective substrates of Ranbp2 and by suppressing the buildup of polyubiquitylated substrates. Losses of peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 recapitulate molecular effects of Ranbp2 haploinsufficiency. These CY impairments also stimulate deubiquitylation activities and phase transitions of 19S cap subunits of the 26S proteasome that associates with Ranbp2. However, links between CY moonlighting activity, substrate ubiquitylation, and proteostasis remain incomplete. Here, we reveal the Ranbp2 regulation of small heat shock chaperones─crystallins in the chorioretina by proteomics of mice with total or selective modular deficits of Ranbp2. Specifically, loss of CY PPIase of Ranbp2 upregulates αA-Crystallin, which is repressed in adult nonlenticular tissues. Conversely, impairment of CY's chaperone activity opposite to the PPIase pocket downregulates a subset of αA-Crystallin's substrates, γ-crystallins. These CY-dependent effects cause age-dependent and chorioretinal-selective declines of ubiquitylated substrates without affecting the chorioretinal morphology. A model emerges whereby inhibition of Ranbp2's CY PPIase remodels crystallins' expressions, subdues molecular aging, and preordains the chorioretina to neuroprotection by augmenting the chaperone capacity and the degradation of polyubiquitylated substrates against proteostatic impairments. Further, the druggable Ranbp2 CY holds pan-therapeutic potential against proteotoxicity and neurodegeneration.

Proteostatic remodeling of small heat shock chaperones - crystallins by Ran-binding protein 2 and the peptidyl-prolyl cis-trans isomerase and chaperone activities of its cyclophilin domain

Disturbances in phase transitions and intracellular partitions of nucleocytoplasmic shuttling substrates promote protein aggregation - a hallmark of neurodegenerative diseases. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of disassembly and phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also play central roles in phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against photo-oxidative stress by proteostatic regulations of Ranbp2 substrates and by countering the build-up of poly-ubiquitylated substrates. Further, the peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 modulate the proteostasis of selective neuroprotective substrates, such as hnRNPA2B1, STAT3, HDAC4 or L/M-opsin, while promoting a decline of ubiquitylated substrates. However, links between CY PPIase activity on client substrates and its effect(s) on ubiquitylated substrates are unclear. Here, proteomics of genetically modified mice with deficits of Ranbp2 uncovered the regulation of the small heat shock chaperones - crystallins by Ranbp2 in the chorioretina. Loss of CY PPIase of Ranbp2 up-regulates αA-crystallin proteostasis, which is repressed in non-lenticular tissues. Conversely, the αA-crystallin's substrates, γ-crystallins, are down-regulated by impairment of CY's C-terminal chaperone activity. These CY-dependent effects cause the age-dependent decline of ubiquitylated substrates without overt chorioretinal morphological changes. A model emerges whereby the Ranbp2 CY-dependent remodeling of crystallins' proteostasis subdues molecular aging and preordains chorioretinal neuroprotection by augmenting the chaperone buffering capacity and the decline of ubiquitylated substrates against proteostatic impairments. Further, CY's moonlighting activity holds pan -therapeutic potential against neurodegeneration.

Small Extracellular Vesicles and Oxidative Pathophysiological Mechanisms in Retinal Degenerative Diseases

This review focuses on the role of small extracellular vesicles in the pathophysiological mechanisms of retinal degenerative diseases. Many of these mechanisms are related to or modulated by the oxidative burden of retinal cells. It has been recently demonstrated that cellular communication in the retina involves extracellular vesicles and that their rate of release and cargo features might be affected by the cellular environment, and in some instances, they might also be mediated by autophagy. The fate of these vesicles is diverse: they could end up in circulation being used as markers, or target neighbor cells modulating gene and protein expression, or eventually, in angiogenesis. Neovascularization in the retina promotes vision loss in diseases such as diabetic retinopathy and age-related macular degeneration. The importance of micro RNAs, either as small extracellular vesicles' cargo or free circulating, in the regulation of retinal angiogenesis is also discussed.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Extracellular vesicles: an emerging player in retinal homeostasis

Extracellular vesicles (EVs) encompass secreted membrane vesicles of varied sizes, including exosomes (-30-200 nm) and microvesicles (MVs) that are ∼100-1,000 nm in size. EVs play an important role in autocrine, paracrine, and endocrine signaling and are implicated in myriad human disorders including prominent retinal degenerative diseases, like age related macular degeneration (AMD) and diabetic retinopathy (DR). Studies of EVs in vitro using transformed cell lines, primary cultures, and more recently, induced pluripotent stem cell derived retinal cell type(s) (e.g., retinal pigment epithelium) have provided insights into the composition and function of EVs in the retina. Furthermore, consistent with a causal role of EVs in retinal degenerative diseases, altering EV composition has promoted pro-retinopathy cellular and molecular events in both in vitro and in vivo models. In this review, we summarize the current understanding of the role of EVs in retinal (patho)physiology. Specifically, we will focus on disease-associated EV alterations in specific retinal diseases. Furthermore, we discuss the potential utility of EVs in diagnostic and therapeutic strategies for targeting retinal diseases.

Alteration of the MEK1/2–ERK1/2 Signaling Pathway in the Retina Associated with Age and Development of AMD-Like Retinopathy

Age-related macular degeneration (AMD) is a complex neurodegenerative disease and a major cause of irreversible visual impairment in patients in developed countries. Although age is the greatest risk factor in AMD, molecular mechanisms involved in AMD remain unknown. Growing evidence shows that dysregulation of MAPK signaling contributes to aging and neurodegenerative diseases; however, the information on the role of MAPK upregulation in these processes is controversial. ERK1 and ERK2 participate in the maintenance of proteostasis through the regulation of protein aggregation induced by the endoplasmic reticulum stress and other stress-mediated cell responses. To assess the contribution of alterations in the ERK1/2 signaling to the AMD development, we compared age-associated changes in the activity of ERK1/2 signaling pathway in the retina of Wistar rats (control) and OXYS rats that develop AMD-like retinopathy spontaneously. The activity of the ERK1/2 signaling increased during physiological aging in the retina of Wistar rats. The manifestation and progression of the AMD-like pathology in the retina of OXYS rats was accompanied by hyperphosphorylation of ERK1/2 and MEK1/2, the key kinases of the ERK1/2 signaling pathway. The progression of the AMD-like pathology was also associated with the ERK1/2-dependent tau protein hyperphosphorylation and increase in the ERK1/2-dependent phosphorylation of alpha B crystallin at Ser45 in the retina.

An increase in mitochondrial TOM activates apoptosis to drive retinal neurodegeneration

Intronic polymorphic TOMM40 variants increasing TOMM40 mRNA expression are strongly correlated to late onset Alzheimer's Disease. The gene product, hTomm40, encoded in the APOE gene cluster, is a core component of TOM, the translocase that imports nascent proteins across the mitochondrial outer membrane. We used Drosophila melanogaster eyes as an in vivo model to investigate the relationship between elevated Tom40 (the Drosophila homologue of hTomm40) expression and neurodegeneration. Here we provide evidence that an overabundance of Tom40 in mitochondria invokes caspase-dependent cell death in a dose-dependent manner, leading to degeneration of the primarily neuronal eye tissue. Degeneration is contingent on the availability of co-assembling TOM components, indicating that an increase in assembled TOM is the factor that triggers apoptosis and degeneration in a neural setting. Eye death is not contingent on inner membrane translocase components, suggesting it is unlikely to be a direct consequence of impaired import. Another effect of heightened Tom40 expression is upregulation and co-association of a mitochondrial oxidative stress biomarker, DmHsp22, implicated in extension of lifespan, providing new insight into the balance between cell survival and death. Activation of regulated death pathways, culminating in eye degeneration, suggests a possible causal route from TOMM40 polymorphisms to neurodegenerative disease.

Retinal pigment epithelium extracellular vesicles are potent inducers of age-related macular degeneration disease phenotype in the outer retina

Age-related macular degeneration (AMD) is a leading cause of blindness. Vision loss is caused by the retinal pigment epithelium (RPE) and photoreceptors atrophy and/or retinal and choroidal angiogenesis. Here we use AMD patient-specific RPE cells with the Complement Factor H Y402H high-risk polymorphism to perform a comprehensive analysis of extracellular vesicles (EVs), their cargo and role in disease pathology. We show that AMD RPE is characterised by enhanced polarised EV secretion. Multi-omics analyses demonstrate that AMD RPE EVs carry RNA, proteins and lipids, which mediate key AMD features including oxidative stress, cytoskeletal dysfunction, angiogenesis and drusen accumulation. Moreover, AMD RPE EVs induce amyloid fibril formation, revealing their role in drusen formation. We demonstrate that exposure of control RPE to AMD RPE apical EVs leads to the acquisition of AMD features such as stress vacuoles, cytoskeletal destabilization and abnormalities in the morphology of the nucleus. Retinal organoid treatment with apical AMD RPE EVs leads to disrupted neuroepithelium and the appearance of cytoprotective alpha B crystallin immunopositive cells, with some co-expressing retinal progenitor cell markers Pax6/Vsx2, suggesting injury-induced regenerative pathways activation. These findings indicate that AMD RPE EVs are potent inducers of AMD phenotype in the neighbouring RPE and retinal cells.

A Review on the Application of Stem Cell Secretome in the Protection and Regeneration of Retinal Ganglion Cells; a Clinical Prospect in the Treatment of Optic Neuropathies

PURPOSE

Retinal ganglion cells (RGCs) are one the most specialized neural tissues in the body. They transmit (and further process) chemoelectrical information originating in outer retinal layers to the central nervous system. In fact, the optic nerve is composed of RGC axons. Like other neural cells, RGCs will not completely heal after the injury, leading to irreversible vision loss from disorders such as glaucoma that primarily affect these cells. Several methods have been developed to protect or regenerate RGCs during or after the insult has occurred. This study aims to review the most recent clinical, animal and laboratory experiments designed for the regeneration of RGC that apply the stem cell-derived secretome.

METHODS

We extracted the studies from Web of Science (ISI), Medline (PubMed), Scopus, Embase, and Google scholar from the first record to the last report registered in 2022, using the following keywords; "secretome" OR "conditioned medium" OR "exosome" OR "extracellular vesicle" AND "stem cell" AND "RGC" OR "optic neuropathy". Any registered clinical trials related to the subject were also extracted from clinicaltrial.gov. All published original studies that express the effect of stem cell secretome on RGC cells in optic neuropathy, whether in vitro, in animal studies, or in clinical trials were included in this survey.

RESULTS

In this review, we provided an update on the existing reports, and a brief description of the details applied in the procedure. Compared to cell transplant, applying stem cell-derived secretome has the advantage of minimized immunogenicity yet preserving efficacy via its rich content of growth factors.

CONCLUSIONS

Different sources of stem cell secretomes have distinct implications in the management of RGC injury, which is the main subject of the present article.

Mechanisms of Epithelial-Mesenchymal Transition and Prevention of Dispase-Induced PVR by Delivery of an Antioxidant αB Crystallin Peptide

Proliferative Vitreoretinopathy (PVR) is a refractory retinal disease whose primary pathogenesis involves the epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells. At present, there is no effective treatment other than surgery for PVR. The purpose of this study was to investigate the effect of αB crystallin peptide (αBC-P) on EMT in PVR. We have previously shown that this peptide is antiapoptotic and regulates RPE redox status. Subconfluent primary human RPE (hRPE) cells were stimulated by TGFβ2 (10 ng/mL) with or without αBC-P (50 or 75 μg/mL) for 48 h and expression of EMT/mesenchymal to epithelial transition (MET) markers was determined. Mitochondrial ROS (mtROS) generation in hRPE cells treated with TGFβ2 was analyzed. The effect of TGFβ2 and αBC-P on oxidative phosphorylation (OXPHOS) and glycolysis in hRPE was studied. RPE cell migration was also assessed. A PVR-like phenotype was induced by intravitreal dispase injection in C57BL/6J mice. PVR progression and potential therapeutic efficiency of αBC-Elastin-like polypeptides (ELP) was studied using fundus photography, OCT imaging, ERG, and histologic analysis of the retina. αSMA, E-cadherin, Vimentin, Fibronectin and, RPE65, and CTGF were analyzed on Day 28. Additionally, the amount of VEGF-A in retinal cell lysates was measured. The EMT-associated αSMA, Vimentin, SNAIL and SLUG showed a significant upregulation with TGFβ2, and their expression was significantly suppressed by cotreatment with αBC-P. The MET-associated markers, E-cadherin and Sirt1, were significantly downregulated by TGFβ2 and were restored by αBC-P. Incubation of hRPE with TGFβ2 for 24 h showed a marked increase in mitochondrial ROS which was noticeably inhibited by αBC-ELP. We also showed that after TGFβ2 treatment, SMAD4 translocated to mitochondria which was blocked by αBC-ELP. Mitochondrial oxygen consumption rate increased with TGFβ2 treatment for 48 h, and αBC-P co-treatment caused a further increase in OCR. Glycolytic functions of RPE were significantly suppressed with αBC-P (75 μg/mL). In addition, αBC-P significantly inhibited the migration from TGFβ2 treatment in hRPE cells. The formation of proliferative membranes was suppressed in the αBC-ELP-treated group, as evidenced by fundus, OCT, and H&E staining in dispase-induced PVR in mice. Furthermore, ERG showed an improvement in c-wave amplitude. In addition, immunostaining showed significant suppression of αSMA and RPE65 expression. It was also observed that αBC-ELP significantly reduced the expression level of vimentin, fibronectin, and CTGF. Our findings suggest that the antioxidant αBC-P may have therapeutic potential in preventing PVR by reversing the phenotype of EMT/MET and improving the mitochondrial function in RPE cells.

Data-independent acquisition-based quantitative proteomic analysis of m.3243A>G MELAS reveals novel potential pathogenesis and therapeutic targets

The pathogenesis of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke like episodes (MELAS) syndrome has not been fully elucidated. The m.3243A > G mutation which is responsible for 80% MELAS patients affects proteins with undetermined functions. Therefore, we performed quantitative proteomic analysis on skeletal muscle specimens from MELAS patients. We recruited 10 patients with definitive MELAS and 10 age- and gender- matched controls. Proteomic analysis based on nanospray liquid chromatography-mass spectrometry (LC-MS) was performed using data-independent acquisition (DIA) method and differentially expressed proteins were revealed by bioinformatics analysis. We identified 128 differential proteins between MELAS and controls, including 68 down-regulated proteins and 60 up-regulated proteins. The differential proteins involved in oxidative stress were identified, including heat shock protein beta-1 (HSPB1), alpha-crystallin B chain (CRYAB), heme oxygenase 1 (HMOX1), glucose-6-phosphate dehydrogenase (G6PD) and selenoprotein P. Gene ontology and kyoto encyclopedia of genes and genomes pathway analysis showed significant enrichment in phagosome, ribosome and peroxisome proliferator-activated receptors (PPAR) signaling pathway. The imbalance between oxidative stress and antioxidant defense, the activation of autophagosomes, and the abnormal metabolism of mitochondrial ribosome proteins (MRPs) might play an important role in m.3243A > G MELAS. The combination of proteomic and bioinformatics analysis could contribute potential molecular networks to the pathogenesis of MELAS in a comprehensive manner.

Proteome profiling of Extracellular Vesicles in Pseudomonas aeruginosa endophthalmitis: Prognostic and therapeutic significance in a mouse model

Endophthalmitis is a sight-threatening infection and a serious consequence of complications during intraocular surgery or penetrating injury of which Pseudomonas aeruginosa is an important etiology. Extracellular vesicles (EVs) have evolved as a promising entity for developing diagnostic and therapeutic biomarkers due to their involvement in intracellular communication and pathogenesis of diseases. We aimed to characterise the protein cargo of extracellular vesicles, isolated from a murine (C57BL/6) model of P. aeruginosa endophthalmitis by LC-MS/MS at 24 h post infection (p.i). EVs were extracted by ultracentrifugation, characterized by Dynamic Light Scattering (DLS) and western blotting with tetraspannin markers, CD9 and CD81 and quantified by the ExoCet quantification kit. Multiplex ELISA was performed to estimate the levels of TNF-α, IL-6, IFN-γ and IL-1β. Proteomic analysis identified 2010 proteins (FDR ≤0.01) in EVs from infected mice eyes, of which 137 were differentially expressed (P-value ≤ 0.05). A total of 101 proteins were upregulated and 36 were downregulated. Additionally, 43 proteins were exclusive to infection set. KEGG and Gene Ontology revealed, Focal adhesion, Phagosome pathway, Complement cascade and IL-17 signalling pathway are crucial upregulated pathways involving proteins such as Tenascin, caveolin 1, caveolin 2, glutamine synthetase, microtubule-associated protein, C1, C8 and IL-17. Tenascin and caveolins are known to suppress anti-inflammatory cytokines further exacerbating the disease. The result of this study provides insight into the global extracellular vesicle proteome of P. aeruginosa endophthalmitis with their functional correlation and distinctive pattern of expression and tenascin, caveolin 1 and caveolin 2 are attractive biomarkers for P. aeruginosa endophthalmitis.

Cellular and molecular alterations in neurons and glial cells in inherited retinal degeneration

Multiple gene mutations have been associated with inherited retinal dystrophies (IRDs). Despite the spectrum of phenotypes caused by the distinct mutations, IRDs display common physiopathology features. Cell death is accompanied by inflammation and oxidative stress. The vertebrate retina has several attributes that make this tissue vulnerable to oxidative and nitrosative imbalance. The high energy demands and active metabolism in retinal cells, as well as their continuous exposure to high oxygen levels and light-induced stress, reveal the importance of tightly regulated homeostatic processes to maintain retinal function, which are compromised in pathological conditions. In addition, the subsequent microglial activation and gliosis, which triggers the secretion of pro-inflammatory cytokines, chemokines, trophic factors, and other molecules, further worsen the degenerative process. As the disease evolves, retinal cells change their morphology and function. In disease stages where photoreceptors are lost, the remaining neurons of the retina to preserve their function seek out for new synaptic partners, which leads to a cascade of morphological alterations in retinal cells that results in a complete remodeling of the tissue. In this review, we describe important molecular and morphological changes in retinal cells that occur in response to oxidative stress and the inflammatory processes underlying IRDs.

Small Heat Shock Proteins in Retinal Diseases

This review summarizes the latest findings on small heat shock proteins (sHsps) in three major retinal diseases: glaucoma, diabetic retinopathy, and age-related macular degeneration. A general description of the structure and major cellular functions of sHsps is provided in the introductory remarks. Their role in specific retinal diseases, highlighting their regulation, role in pathogenesis, and possible use as therapeutics, is discussed.

Evidence for Paracrine Protective Role of Exogenous αA-Crystallin in Retinal Ganglion Cells

Expression and secretion of neurotrophic factors have long been known as a key mechanism of neuroglial interaction in the central nervous system. In addition, several other intrinsic neuroprotective pathways have been described, including those involving small heat shock proteins such as α-crystallins. While initially considered as a purely intracellular mechanism, both αA-crystallins and αB-crystallins have been recently reported to be secreted by glial cells. While an anti-apoptotic effect of such secreted αA-crystallin has been suggested, its regulation and protective potential remain unclear. We recently identified residue threonine 148 (T148) and its phosphorylation as a critical regulator of αA-crystallin intrinsic neuroprotective function. In the current study, we explored how mutation of this residue affected αA-crystallin chaperone function, secretion, and paracrine protective function using primary glial and neuronal cells. After demonstrating the paracrine protective effect of αA-crystallins secreted by primary Müller glial cells (MGCs), we purified and characterized recombinant αA-crystallin proteins mutated on the T148 regulatory residue. Characterization of the biochemical properties of these mutants revealed an increased chaperone activity of the phosphomimetic T148D mutant. Consistent with this observation, we also show that exogeneous supplementation of the phosphomimetic T148D mutant protein protected primary retinal neurons from metabolic stress despite similar cellular uptake. In contrast, the nonphosphorylatable mutant was completely ineffective. Altogether, our study demonstrates the paracrine role of αA-crystallin in the central nervous system as well as the therapeutic potential of functionally enhanced αA-crystallin recombinant proteins to prevent metabolic-stress induced neurodegeneration.

Mechanisms of RPE senescence and potential role of αB crystallin peptide as a senolytic agent in experimental AMD

Oxidative stress in the retinal pigment epithelium (RPE) can cause mitochondrial dysfunction and is likely a causative factor in the pathogenesis of age-related macular degeneration (AMD). Under oxidative stress conditions, some of the RPE cells become senescent and a contributory role for RPE senescence in AMD pathology has been proposed. The purpose of this study is to 1) characterize senescence in human RPE; 2) investigate the effect of an αB Crystallin chaperone peptide (mini Cry) in controlling senescence, in particular by regulating mitochondrial function and senescence-associated secretory phenotype (SASP) production and 3) develop mouse models for studying the role of RPE senescence in dry and nAMD. Senescence was induced in human RPE cells in two ways. First, subconfluent cells were treated with 0.2 μg/ml doxorubicin (DOX); second, subconfluent cells were treated with 500 μM H₂O₂. Senescence biomarkers (senescence-associated beta-galactosidase (SA-βgal), p21, p16) and mitochondrial proteins (Fis1, DRP1, MFN2, PGC1-α, mtTFA) were analyzed in control and experimental groups. The effect of mini Cry on mitochondrial bioenergetics, glycolysis and SASP was determined. In vivo, retinal degeneration was induced by intravenous injection of NaIO3 (20 mg/kg) and subretinal fibrosis by laser-induced choroidal neovascularization. Increased SA-βgal staining and p16 and p21 expression was observed after DOX- or H₂O₂-induced senescence and mini Cry significantly decreased senescence-positive cells. The expression of mitochondrial biogenesis proteins PGC-1 and mTFA increased with senescence, and mini Cry reduced expression significantly. Senescent RPE cells were metabolically active, as evidenced by significantly enhanced oxidative phosphorylation and anaerobic glycolysis, mini Cry markedly reduced rates of respiration and glycolysis. Senescent RPE cells maintain a proinflammatory phenotype characterized by significantly increased production of cytokines (IFN-ˠ, TNF-α, IL1-α IL1-β, IL-6, IL-8, IL-10), and VEGF-A; mini Cry significantly inhibited their secretion. We identified and localized senescent RPE cells for the first time in NaIO3-induced retinal degeneration and laser-induced subretinal fibrosis mouse models. We conclude that mini Cry significantly impairs stress-induced senescence by modulating mitochondrial biogenesis and fission proteins in RPE cells. Characterization of senescence could provide further understanding of the metabolic changes that accompany the senescent phenotype in ocular disease. Future studies in vivo may better define the role of senescence in AMD and the therapeutic potential of mini Cry as a senotherapeutic.

Novel Possible Protein Targets in Neovascular Age-Related Macular Degeneration: A Pilot Study Experiment

Age-related macular degeneration (AMD) is among the world's leading causes of blindness. In its neovascular form (nAMD), around 25% of patients present further anatomical and visual deterioration due to persistence of neovascular activity, despite gold-standard treatment protocols using intravitreal anti-VEGF medications. Thus, to comprehend, the molecular pathways that drive choroidal neoangiogenesis, associated with the vascular endothelial growth factor (VEGF), are important steps to elucidate the mechanistic events underneath the disease development. This is a pilot study, a prospective, translational experiment, in a real-life context aiming to evaluate the protein profiles of the aqueous humor of 15 patients divided into three groups: group 1, composed of patients with nAMD, who demonstrated a good response to anti-VEGF intravitreal injections during follow-up (good responsive); group 2, composed of patients with anti-VEGF-resistant nAMD, who demonstrated choroidal neovascularization activity during follow-up (poor/non-responsive); and group 3, composed of control patients without systemic diseases or signs of retinopathy. For proteomic characterization of the groups, mass spectrometry (label-free LC-MS/MS) was used. A total of 2,336 proteins were identified, of which 185 were distinctly regulated and allowed the differentiation of the clinical conditions analyzed. Among those, 39 proteins, including some novel ones, were analyzed as potential disease effectors through their pathophysiological implications in lipid metabolism, oxidative stress, complement system, inflammatory pathways, and angiogenesis. So, this study suggests the participation of other promising biomarkers in neovascular AMD, in addition to the known VEGF.

Exosomes, extracellular vesicles and the eye

Exosomes are a subset of extracellular vesicles which accommodate a cargo of bioactive biomolecules that generally includes proteins, nucleic acids, lipids, sugars, and related conjugates depicting the cellular environment and are known to mediate a wide array of biological functions, like cellular communication, cellular differentiation, immunomodulation, neovascularization, and cellular waste management. The exponential implication of exosomes in the pathological development and progression of various disorders including neurodegenerative diseases, cardiovascular diseases, and cancer has offered a tremendous opportunity for exploring their role in ocular conditions. Ocular diseases such as age-related macular disease, glaucoma, infectious endophthalmitis, diabetic retinopathy, autoimmune uveitis etc face various challenges in their early diagnosis and treatments due to contributing factors such as delay in the onset of symptoms, microbial identification, difficulty in obtaining samples for biopsy or being diagnosed as masquerade syndromes. Studies have reported unique exosomal cargos that are involved in successful delivery of miRNA or proteins to recipient cells to express desired expression or exploited as a diagnostic marker for various diseases. Furthermore, engineered exosomes can be used for targeted delivery of therapeutics and exosomes being natural nanoparticles found in all types of cells, host may not elicit an immune response against it. With the rapid advancement of opting personalized therapeutics, extending exosomal research to sight-threatening ocular infections can possibly advance the current diagnostic and therapeutic approaches. This review briefs about the current knowledge of exosomes in visual systems, advancements in exosomal and ophthalmic research, participation of exosomes in the pathogenesis of common ocular diseases, the challenges for exosomal therapies along with the future of this promising domain of research for diseases that fatally threaten billions of people worldwide.

Molecular Mechanisms of Retinal Pigment Epithelium Dysfunction in Age-Related Macular Degeneration

The retinal pigment epithelium (RPE), situated upon Bruch’s membrane, plays multiple roles in the ocular system by interacting with photoreceptors and. Therefore, dysfunction of the RPE causes diseases related to vision loss, such as age-related macular degeneration (AMD). Despite AMD being a global cause of blindness, the pathogenesis remains unclear. Understanding the pathogenesis of AMD is the first step for its prevention and treatment. This review summarizes the common pathways of RPE dysfunction and their effect in AMD. Potential treatment strategies for AMD based on targeting the RPE have also been discussed.

RPE-derived exosomes rescue the photoreceptors during retina degeneration: an intraocular approach to deliver exosomes into the subretinal space

Retinal degeneration (RD) refers to a group of blinding retinopathies leading to the progressive photoreceptor demise and vision loss. Treatments against this debilitating disease are urgently needed. Intraocular delivery of exosomes represents an innovative therapeutic strategy against RD. In this study, we aimed to determine whether the subretinal delivery of RPE-derived exosomes (RPE-Exos) can prevent the photoreceptor death in RD. RD was induced in C57BL6 mice by MNU administration. These MNU administered mice received a single subretinal injection of RPE-Exos. Two weeks later, the RPE-Exos induced effects were evaluated via functional, morphological, and behavior examinations. Subretinal delivery of RPE-Exos efficiently ameliorates the visual function impairments, and alleviated the structural damages in the retina of MNU administered mice. Moreover, RPE-Exos exert beneficial effects on the electrical response of the inner retinal circuits. Treatment with RPE-Exos suppressed the expression levels of inflammatory factors, and mitigated the oxidative damage, indicating that subretinal delivery of RPE-Exos constructed a cytoprotective microenvironment in the retina of MNU administered mice. Our data suggest that RPE-Exos have therapeutic effects against the visual impairments and photoreceptor death. These findings will enrich our knowledge of RPE-Exos, and highlight the discovery of a promising medication for RD.

Mesenchymal Stem Cell-Derived Exosomes as an Emerging Paradigm for Regenerative Therapy and Nano-Medicine: A Comprehensive Review

Mesenchymal Stem Cells are potent therapeutic candidates in the field of regenerative medicine, owing to their immunomodulatory and differentiation potential. However, several complications come with their translational application like viability, duration, and degree of expansion, long-term storage, and high maintenance cost. Therefore, drawbacks of cell-based therapy can be overcome by a novel therapeutic modality emerging in translational research and application, i.e., exosomes. These small vesicles derived from mesenchymal stem cells are emerging as new avenues in the field of nano-medicine. These nano-vesicles have caught the attention of researchers with their potency as regenerative medicine both in nanotherapeutics and drug delivery systems. In this review, we discuss the current knowledge in the biology and handling of exosomes, with their limitations and future applications. Additionally, we highlight current perspectives that primarily focus on their effect on various diseases and their potential as a drug delivery vehicle.

Therapeutic Potential of α-Crystallins in Retinal Neurodegenerative Diseases

The chaperone and anti-apoptotic activity of α-crystallins (αA- and αB-) and their derivatives has received increasing attention due to their tremendous potential in preventing cell death. While originally known and described for their role in the lens, the upregulation of these proteins in cells and animal models of neurodegenerative diseases highlighted their involvement in adaptive protective responses to neurodegeneration associated stress. However, several studies also suggest that chronic neurodegenerative conditions are associated with progressive loss of function of these proteins. Thus, while external supplementation of α-crystallin shows promise, their potential as a protein-based therapeutic for the treatment of chronic neurodegenerative diseases remains ambiguous. The current review aims at assessing the current literature supporting the anti-apoptotic potential of αA- and αB-crystallins and its potential involvement in retinal neurodegenerative diseases. The review further extends into potentially modulating the chaperone and the anti-apoptotic function of α-crystallins and the use of such functionally enhanced proteins for promoting neuronal viability in retinal neurodegenerative disease.

The engineered expression of secreted HSPB5-Fc in CHO cells exhibits cytoprotection in vitro

Background

HSPB5 is an ATP-independent molecular chaperone that is induced by heat shock or other proteotoxic stresses. HSPB5 is cytoprotective against stress both intracellularly and extracellularly. It acts as a potential therapeutic candidate in ischemia-reperfusion and neurodegenerative diseases.

Results

In this paper, we constructed a recombinant plasmid that expresses and extracellularly secrets a HSPB5-Fc fusion protein (sHSPB5-Fc) at 0.42 μg/ml in CHO-K1 cells. This sHSPB5-Fc protein contains a Fc-tag at the C-terminal extension of HSPB5, facilitating protein-affinity purification. Our study shows that sHSPB5-Fc inhibits heat-induced aggregation of citrate synthase in a time and dose dependent manner in vitro. Administration of sHSPB5-Fc protects lens epithelial cells against cisplatin- or UVB-induced cell apoptosis. It also decreases GFP-Htt^ex1-Q74 insolubility, and reduces the size and cytotoxicity of GFP-Htt^ex1-Q74 aggregates in PC-12 cells.

Conclusion

This recombinant sHSPB5-Fc exhibits chaperone activity to protect cells against proteotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00700-y.

Exosomes in the pathogenesis and treatment of ocular diseases

Exosomes have diverse functions and rich content and are involved in intercellular communication, immune regulation, viral infection, tissue regeneration, and the occurrence, development and metastasis of tumours. Notably, various stem cell-derived exosomes are expected to become new therapeutic approaches for inflammatory diseases and tumours and have good clinical application prospects. However, few studies have examined exosomes in ophthalmic diseases. Therefore, based on the functions of exosomes, this paper summarizes progress in the possible use of exosomes as treatment for specific ophthalmic diseases, aiming to determine the pathogenesis of exosomes to achieve more effective clinical diagnosis and treatment of these diseases.

Emerging Role of Exosomes in Retinal Diseases

Retinal diseases, the leading causes of vison loss and blindness, are associated with complicated pathogeneses such as angiogenesis, inflammation, immune regulation, fibrous proliferation, and neurodegeneration. The retina is a complex tissue, where the various resident cell types communicate between themselves and with cells from the blood and immune systems. Exosomes, which are bilayer membrane vesicles with diameters of 30–150 nm, carry a variety of proteins, lipids, and nucleic acids, and participate in cell-to-cell communication. Recently, the roles of exosomes in pathophysiological process and their therapeutic potential have been emerging. Here, we critically review the roles of exosomes as possible intracellular mediators and discuss the possibility of using exosomes as therapeutic agents in retinal diseases.

Antioxidant Defenses in the Human Eye: A Focus on Metallothioneins

The human eye, the highly specialized organ of vision, is greatly influenced by oxidants of endogenous and exogenous origin. Oxidative stress affects all structures of the human eye with special emphasis on the ocular surface, the lens, the retina and its retinal pigment epithelium, which are considered natural barriers of antioxidant protection, contributing to the onset and/or progression of eye diseases. These ocular structures contain a complex antioxidant defense system slightly different along the eye depending on cell tissue. In addition to widely studied enzymatic antioxidants, including superoxide dismutase, glutathione peroxidase, catalase, peroxiredoxins and selenoproteins, inter alia, metallothioneins (MTs) are considered antioxidant proteins of growing interest with further cell-mediated functions. This family of cysteine rich and low molecular mass proteins captures and neutralizes free radicals in a redox-dependent mechanism involving zinc binding and release. The state of the art of MTs, including the isoforms classification, the main functions described to date, the Zn-MT redox cycle as antioxidant defense system, and the antioxidant activity of Zn-MTs in the ocular surface, lens, retina and its retinal pigment epithelium, dependent on the number of occupied zinc-binding sites, will be comprehensively reviewed.

Slowed Progression of Age-Related Geographic Atrophy Following Subthreshold Laser

Purpose

To determine the effect of panmacular low-intensity/high-density subthreshold diode micropulse laser (SDM) on age-related geographic atrophy (ARGA) progression.

Methods

The retinal images of all eyes with ARGA in a previously reported database, consisting of all eyes with dry age-related macular degeneration (AMD) active in a vitreoretinal practice electronic medical record (EMR), were identified and analyzed to determine the velocity of radial linear ARGA progression during observation and after panmacular SDM.

Results

Sixty-seven eyes of 49 patients with ARGA, mean age of 86 years were identified as having follow-up both before and after initiation of SDM treatment. All were included in the study. These eyes were followed a mean 910 days (2.5 years) prior to SDM treatment and a mean 805 days (2.2 years) after. Measurement masked to treatment vs observation found the radius of ARGA lesions progressed 1 to 540 µm per year (mean 137µm, SD 107) prior to treatment (controls); and −44 to 303 µm per year (mean 73µm, SD 59) after initiation of periodic panmacular SDM laser. Thus, the velocity of radial linear progression decreased 47% per year following panmacular SDM (p<0.0001). There were no adverse treatment effects.

Conclusion

In cohort of eyes with high-risk dry AMD, panmacular SDM slowed linear radial ARGA progression velocity 47% per year (p<0.0001) without adverse treatment effects. Validated, these findings would constitute an important advance in the prevention of age-related visual loss and a benchmark for future therapies.

Retinal pigment epithelium and age-related macular degeneration: A review of major disease mechanisms

Age‐related macular degeneration (AMD) is a progressive degenerative disease that is the leading cause of vision loss in the elderly population. Degeneration/dysregulation of the retinal pigment epithelium (RPE), a supportive monolayer of cells underlying the photoreceptors, is commonly seen in patients with AMD. While treatment exists for the neovascular/wet form of AMD, there is currently no cure for the non‐exudative/dry form of AMD, making it imperative to understand the pathogenesis of this disease. Although our understanding of the aetiology of AMD has increased over the years, the underlying disease mechanism has not yet been identified, mainly due to the multifactorial nature of this disease. Herein, we review some of the commonly proposed degeneration pathways of RPE cells and their role in the pathogenesis of AMD; including activation of the complement cascade, oxidative stress‐induced cell death mechanisms, dysfunctional mitochondria and the role of crystallins in AMD disease progression.

Autophagy in Age-Related Macular Degeneration: A Regulatory Mechanism of Oxidative Stress

Age-related macular degeneration (AMD) is a leading cause of severe visual loss and irreversible blindness in the elderly population worldwide. Retinal pigment epithelial (RPE) cells are the major site of pathological alterations in AMD. They are responsible for the phagocytosis of shed photoreceptor outer segments (POSs) and clearance of cellular waste under physiological conditions. Age-related, cumulative oxidative stimuli contribute to the pathogenesis of AMD. Excessive oxidative stress induces RPE cell degeneration and incomplete digestion of POSs, leading to the continuous accumulation of cellular waste (such as lipofuscin). Autophagy is a major system of degradation of damaged or unnecessary proteins. However, degenerative RPE cells in AMD patients cannot perform autophagy sufficiently to resist oxidative damage. Increasing evidence supports the idea that enhancing the autophagic process can properly alleviate oxidative injury in AMD and protect RPE and photoreceptor cells from degeneration and death, although overactivated autophagy may lead to cell death at early stages of retinal degenerative diseases. The crosstalk among the NFE2L2, PGC-1, p62, AMPK, and PI3K/Akt/mTOR pathways may play a crucial role in improving disturbed autophagy and mitigating the progression of AMD. In this review, we discuss how autophagy prevents oxidative damage in AMD, summarize potential neuroprotective strategies for therapeutic interventions, and provide an overview of these neuroprotective mechanisms.

Exploration of Oxygen-Induced Retinopathy Model to Discover New Therapeutic Drug Targets in Retinopathies

Oxygen-induced retinopathy (OIR) is a pure hypoxia-driven angiogenesis model and the most widely used model for ischemic retinopathies, such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy (PDR), and retinal vein occlusion (RVO). OIR model has been used to test new potential anti-angiogenic factors for human diseases. We have recently performed the most comprehensive characterization of OIR by a relatively novel mass spectrometry (MS) technique, sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS) proteomics and used genetically modified mice strains to identify novel molecular drug targets in angiogenic retinal diseases. We have confirmed the relevance of the identified molecular targets to human diseases by determining their expression pattern in neovascular membranes obtained from PDR and RVO patients. Based on our results, crystallins were the most prominent proteins induced by early hypoxic environment during the OIR, while actomyosin complex and Filamin A-R-Ras axis, that regulates vascular permeability of the angiogenic blood vessels, stood out at the peak of angiogenesis. Our results have revealed potential new therapeutic targets to address hypoxia-induced pathological angiogenesis and the associated vascular permeability in number of retinal diseases.

Transporter-Mediated Mitochondrial GSH Depletion Leading to Mitochondrial Dysfunction and Rescue with αB Crystallin Peptide in RPE Cells

Mitochondrial glutathione (mGSH) is critical for cell survival. We recently reported the localization of OGC (SLC25A11) and DIC (SLC25A10) in hRPE. Herein, we investigated the suppression of OGC and DIC and the effect of αB crystallin chaperone peptide co-treatment on RPE cell death and mitochondrial function. Non-polarized and polarized human RPE were co-treated for 24 h with phenyl succinic acid (PS, 5 mM) or butyl malonic acid (BM, 5 mM) with or without αB cry peptide (75 µg/mL). mGSH levels, mitochondrial bioenergetics, and ETC proteins were analyzed. The effect of mGSH depletion on cell death and barrier function was determined in polarized RPE co-treated with PS, OGC siRNA or BM and αB cry peptide. Inhibition of OGC and DIC resulted in a significant decrease in mGSH and increased apoptosis. mGSH depletion significantly decreased mitochondrial respiration, ATP production, and altered ETC protein expression. αB cry peptide restored mGSH, attenuated apoptosis, upregulated ETC proteins, and improved mitochondrial bioenergetics and biogenesis. mGSH transporters exhibited differential polarized localization: DIC (apical) and OGC (apical and basal). Inhibition of mGSH transport compromised barrier function which was partially restored by αB cry peptide. Our findings suggest mGSH augmentation by its transporters may be a valuable approach in AMD therapy.

Stem cell-derived retinal pigment epithelium from patients with age-related macular degeneration exhibit reduced metabolism and matrix interactions

Modeling age‐related macular degeneration (AMD) is challenging, because it is a multifactorial disease. To focus on interactions between the retinal pigment epithelium (RPE) and Bruch's membrane, we generated RPE from AMD patients and used an altered extracellular matrix (ECM) that models aged Bruch's membrane. Induced pluripotent stem cells (iPSCs) were generated from fibroblasts isolated from AMD patients or age‐matched (normal) controls. RPE derived from iPSCs were analyzed by morphology, marker expression, transepithelial electrical resistance (TER), and phagocytosis of rod photoreceptor outer segments. Cell attachment and viability was tested on nitrite‐modified ECM, a typical modification of aged Bruch's membrane. DNA microarrays with hierarchical clustering and analysis of mitochondrial function were used to elucidate possible mechanisms for the observed phenotypes. Differentiated RPE displayed cell‐specific morphology and markers. The TER and phagocytic capacity were similar among iPSC‐derived RPE cultures. However, distinct clusters were found for the transcriptomes of AMD and control iPSC‐derived RPE. AMD‐derived iPSC‐RPE downregulated genes responsible for metabolic‐related pathways and cell attachment. AMD‐derived iPSC‐RPE exhibited reduced mitochondrial respiration and ability to attach and survive on nitrite‐modified ECM. Cells that did attach induced the expression of complement genes. Despite reprogramming, iPSC derived from AMD patients yielded RPE with a transcriptome that is distinct from that of age‐matched controls. When challenged with an AMD‐like modification of Bruch's membrane, AMD‐derived iPSC‐RPE activated the complement immune system.

The mechanism of the interaction of α-crystallin and UV-damaged βL-crystallin

α-Crystallin maintains the transparency of the lens by preventing the aggregation of damaged proteins. The aim of our work was to study the chaperone-like activity of native α-crystallin in near physiological conditions (temperature, ionic power, pH) using UV-damaged β_L-crystallin as the target protein. α-Crystallin in concentration depended manner inhibits the aggregation of UV-damaged β_L-crystallin. DSC investigation has shown that refolding of denatured UV-damaged β_L-crystallin was not observed under incubation with α-crystallin. α-Crystallin and UV-damaged β_L-crystallin form dynamic complexes with masses from 75 to several thousand kDa. The content of UV-damaged β_L-crystallin in such complexes increases with the mass of the complex. Complexes containing >10% of UV-damaged β_L-crystallin are prone to precipitation whereas those containing <10% of the target protein are relatively stable. Formation of a stable 75 kDa complex is indicative of α-crystallin dissociation. We suppose that α-crystallin dissociation is the result of an interaction of comparable amounts of the chaperone-like protein and the target protein. In the lens simultaneous damage of such amounts of protein, mainly β and gamma-crystallins, is impossible. The authors suggest that in the lens rare molecules of the damaged protein interact with undissociated oligomers of α-crystallin, and thus preventing aggregation.

Autoimmune-Mediated Retinopathy in CXCR5-Deficient Mice as the Result of Age-Related Macular Degeneration Associated Proteins Accumulation

Previous research has shown that CXCR5^−/− mice develop retinal degeneration (RD) with age, a characteristic related to age macular degeneration (AMD). RD in these mice is not well-understood, and in this study, we sought to characterize further the RD phenotype and to gain mechanistic insights into the function of CXCR5 in the retina. CXCR5^−/− and WT control mice were used. Fundus images demonstrated a significant (p < 0.001) increase of hypo-pigmented spots in the retina of aged CXCR5^−/− mice compared with WT control mice. PAS staining indicated localization of deposits in the sub-retinal pigment epithelia (RPE) layer. AMD-associated proteins Cryab, amyloid beta, and C3d were detected within the RPE/sub-RPE tissues by immunofluorescence (IF). In addition, western blot analysis of COX-2, Arg1, and VEGF-a revealed an increase in the signaling of these molecules within the RPE/choroid complex. Transmission electron microscopy (TEM) indicated a drusen-like structure of sub-RPE deposits with an accumulation of vacuolated cellular debris. Loss of photoreceptors was detected by peanut lectin staining and was corroborated by a reduction in MAP2 signaling. Loss of blood-retinal barrier integrity was demonstrated by a reduction of ZO-1 expression. Inflammatory cells were detected in the sub-RPE space, with an increase in IBA-1 positive microglia cells on the surface of the RPE. Mass spectrometry analysis of CXCR5^−/− mouse RPE/choroid proteins extracts, separated by SDS-page and incubated with autologous serum, identified autoantibodies against AMD-associated proteins: Cryaa, Cryab, and Anxa2. In vitro evaluations in BV-2 cell culture indicated a significant increase in production of Arg-1 (p < 0.001) and COX-2 (p < 0.01) in the presence of anti-CXCR5 antibody when compared with Igg-treated control BV-2 cells stimulated with IL-4 and TNFα/IFNγ, respectively. Anti-CXCR5 antibody treatment without stimulating agents did not affect Arg-1 and COX-2 expression; this suggests that CXCR5 may have a regulatory role in microglia cells activation. These results indicate that with age, CXCR5^−/− mice develop RD characterized by microglia dysfunction, increased production of CXCL13 in the RPE progressive photoreceptor, neuronal loss, and sub-RPE deposition of cellular debris, resulting in the production of immunogenic proteins and autoimmune-mediated RD.

SWATH-MS Proteomic Analysis of Oxygen-Induced Retinopathy Reveals Novel Potential Therapeutic Targets

Purpose

Oxygen-induced retinopathy (OIR) is the most widely used model for ischemic retinopathies such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy (PDR), and retinal vein occlusion (RVO). The purpose of this study was to perform the most comprehensive characterization of OIR by a recently developed technique, sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics.

Methods

Control and OIR retina samples collected from various time points were subjected to SWATH-MS and detailed data analysis. Immunohistochemistry from mouse retinas as well as neovascular membranes from human PDR and RVO patients were used for the detection of the localization of the proteins showing altered expression in the retina and to address their relevance to human ischemic retinopathies.

Results

We report the most extensive proteomic profiling of OIR to date by quantifying almost 3000 unique proteins and their expression differences between control and OIR retinas. Crystallins were the most prominent proteins induced by hypoxia in the retina, while angiogenesis related proteins such as Filamin A and nonmuscle myosin IIA stand out at the peak of angiogenesis. Majority of the changes in protein expression return to normal at P42, but there is evidence to suggest that proteins involved in neurotransmission remain at reduced level.

Conclusions

The results reveal new potential therapeutic targets to address hypoxia-induced pathological angiogenesis taking place in number of retinal diseases. The extensive proteomic profiling combined with pathway analysis also identifies novel molecular networks that could contribute to the pathogenesis of retinal diseases.

On the origin of proteins in human drusen: The meet, greet and stick hypothesis

Retinal drusen formation is not only a clinical hallmark for the development of age-related macular degeneration (AMD) but also for other disorders, such as Alzheimer's disease and renal diseases. The initiation and growth of drusen is poorly understood. Attention has focused on lipids and minerals, but relatively little is known about the origin of drusen-associated proteins and how they are retained in the space between the basal lamina of the retinal pigment epithelium and the inner collagenous layer space (sub-RPE-BL space). While some authors suggested that drusen proteins are mainly derived from cellular debris from processed photoreceptor outer segments and the RPE, others suggest a choroidal cell or blood origin. Here, we reviewed and supplemented the existing literature on the molecular composition of the retina/choroid complex, to gain a more complete understanding of the sources of proteins in drusen. These "drusenomics" studies showed that a considerable proportion of currently identified drusen proteins is uniquely originating from the blood. A smaller, but still large fraction of drusen proteins comes from both blood and/or RPE. Only a small proportion of drusen proteins is uniquely derived from the photoreceptors or choroid. We next evaluated how drusen components may "meet, greet and stick" to each other and/or to structures like hydroxyapatite spherules to form macroscopic deposits in the sub-RPE-BL space. Finally, we discuss implications of our findings with respect to the previously proposed homology between drusenogenesis in AMD and plaque formation in atherosclerosis.

IGF-1, Inflammation and Retinal Degeneration: A Close Network

Retinal degenerative diseases are a group of heterogeneous diseases that include age-related macular degeneration (AMD), retinitis pigmentosa (RP), and diabetic retinopathy (DR). The progressive degeneration of the retinal neurons results in a severe deterioration of the visual function. Neuroinflammation is an early hallmark of many neurodegenerative disorders of the retina including AMD, RP and DR. Microglial cells, key components of the retinal immune defense system, are activated in retinal degenerative diseases. In the microglia the interplay between the proinflammatory/classically activated or antiinflammatory/alternatively activated phenotypes is a complex dynamic process that occurs during the course of disease due to the different environmental signals related to pathophysiological conditions. In this regard, an adequate transition from the proinflammatory to the anti-inflammatory response is necessary to counteract retinal neurodegeneration and its subsequent damage that leads to the loss of visual function. Insulin like-growth factor-1 (IGF-1) has been considered as a pleiotropic factor in the retina under health or disease conditions and several effects of IGF-1 in retinal immune modulation have been described. In this review, we provide recent insights of inflammation as a common feature of retinal diseases (AMD, RP and RD) highlighting the role of microglia, exosomes and IGF-1 in this process.

The Small Heat Shock Protein α-Crystallin B Shows Neuroprotective Properties in a Glaucoma Animal Model

Glaucoma is a neurodegenerative disease that leads to irreversible retinal ganglion cell (RGC) loss and is one of the main causes of blindness worldwide. The pathogenesis of glaucoma remains unclear, and novel approaches for neuroprotective treatments are urgently needed. Previous studies have revealed significant down-regulation of α-crystallin B as an initial reaction to elevated intraocular pressure (IOP), followed by a clear but delayed up-regulation, suggesting that this small heat-shock protein plays a pathophysiological role in the disease. This study analyzed the neuroprotective effect of α-crystallin B in an experimental animal model of glaucoma. Significant IOP elevation induced by episcleral vein cauterization resulted in a considerable impairment of the RGCs and the retinal nerve fiber layer. An intravitreal injection of α-crystallin B at the time of the IOP increase was able to rescue the RGCs, as measured in a functional photopic electroretinogram, retinal nerve fiber layer thickness, and RGC counts. Mass-spectrometry-based proteomics and antibody-microarray measurements indicated that a α-crystallin injection distinctly up-regulated all of the subclasses (α, β, and γ) of the crystallin protein family. The creation of an interactive protein network revealed clear correlations between individual proteins, which showed a regulatory shift resulting from the crystallin injection. The neuroprotective properties of α-crystallin B further demonstrate the potential importance of crystallin proteins in developing therapeutic options for glaucoma.

Autophagy in the eye: Development, degeneration, and aging

Autophagy is a catabolic pathway that promotes the degradation and recycling of cellular components. Proteins, lipids, and even whole organelles are engulfed in autophagosomes and delivered to the lysosome for elimination. In response to stress, autophagy mediates the degradation of cell components, which are recycled to generate the nutrients and building blocks required to sustain cellular homeostasis. Moreover, it plays an important role in cellular quality control, particularly in neurons, in which the total burden of altered proteins and damaged organelles cannot be reduced by redistribution to daughter cells through cell division. Research has only begun to examine the role of autophagy in the visual system. The retina, a light-sensitive tissue, detects and transmits electrical impulses through the optic nerve to the visual cortex in the brain. Both the retina and the eye are exposed to a variety of environmental insults and stressors, including genetic mutations and age-associated alterations that impair their function. Here, we review the main studies that have sought to explain autophagy's importance in visual function. We describe the role of autophagy in retinal development and cell differentiation, and discuss the implications of autophagy dysregulation both in physiological aging and in important diseases such as age-associated macular degeneration and glaucoma. We also address the putative role of autophagy in promoting photoreceptor survival and discuss how selective autophagy could provide alternative means of protecting retinal cells. The findings reviewed here underscore the important role of autophagy in maintaining proper retinal function and highlight novel therapeutic approaches for blindness and other diseases of the eye.

Methods for culturing retinal pigment epithelial cells: a review of current protocols and future recommendations

The retinal pigment epithelium is an important part of the vertebrate eye, particularly in studying the causes and possible treatment of age-related macular degeneration. The retinal pigment epithelium is difficult to access in vivo due to its location at the back of the eye, making experimentation with age-related macular degeneration treatments problematic. An alternative to in vivo experimentation is cultivating the retinal pigment epithelium in vitro, a practice that has been going on since the 1970s, providing a wide range of retinal pigment epithelial culture protocols, each producing cells and tissue of varying degrees of similarity to natural retinal pigment epithelium. The purpose of this review is to provide researchers with a ready list of retinal pigment epithelial protocols, their effects on cultured tissue, and their specific possible applications. Protocols using human and animal retinal pigment epithelium cells, derived from tissue or cell lines, are discussed, and recommendations for future researchers included.

Circulating Autoantibodies in Age-Related Macular Degeneration Recognize Human Macular Tissue Antigens Implicated in Autophagy, Immunomodulation, and Protection from Oxidative Stress and Apoptosis

BACKGROUND

We investigated sera from elderly subjects with and without age-related macular degeneration (AMD) for presence of autoantibodies (AAbs) against human macular antigens and characterized their identity.

METHODS

Sera were collected from participants in the Age-Related Maculopathy Ancillary (ARMA) Study, a cross-sectional investigation ancillary to the Health ABC Study, enriched with participants from the general population. The resulting sample (mean age: 79.2±3.9 years old) included subjects with early to advanced AMD (n = 131) and controls (n = 231). Sera were tested by Western blots for immunoreactive bands against human donor macular tissue homogenates. Immunoreactive bands were identified and graded, and odds ratios (OR) calculated. Based on these findings, sera were immunoprecipitated, and subjected to 2D gel electrophoresis (GE). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify the targets recognized by circulating AAbs seen on 2D-GE, followed by ELISAs with recombinant proteins to confirm LC-MS/MS results, and quantify autoreactivities.

RESULTS

In AMD, 11 immunoreactive bands were significantly more frequent and 13 were significantly stronger than in controls. Nine of the more frequent bands also showed stronger reactivity. OR estimates ranged between 4.06 and 1.93, and all clearly excluded the null value. Following immunoprecipitation, 2D-GE and LC-MS/MS, five of the possible autoreactivity targets were conclusively identified: two members of the heat shock protein 70 (HSP70) family, HSPA8 and HSPA9; another member of the HSP family, HSPB4, also known as alpha-crystallin A chain (CRYAA); Annexin A5 (ANXA5); and Protein S100-A9, also known as calgranulin B that, when complexed with S100A8, forms calprotectin. ELISA testing with recombinant proteins confirmed, on average, significantly higher reactivities against all targets in AMD samples compared to controls.

CONCLUSIONS

Consistent with other evidence supporting the role of inflammation and the immune system in AMD pathogenesis, AAbs were identified in AMD sera, including early-stage disease. Identified targets may be mechanistically linked to AMD pathogenesis because the identified proteins are implicated in autophagy, immunomodulation, and protection from oxidative stress and apoptosis. In particular, a role in autophagy activation is shared by all five autoantigens, raising the possibility that the detected AAbs may play a role in AMD via autophagy compromise and downstream activation of the inflammasome. Thus, we propose that the detected AAbs provide further insight into AMD pathogenesis and have the potential to contribute to disease biogenesis and progression.