p62 expression and autophagy in αB-crystallin R120G mutant knock-in mouse model of hereditary cataract

Lens autophagy protein ATG16L1: a potential target for cataract treatment

Rationale: Cataract is the leading cause of blindness and low vision worldwide, yet its pathological mechanism is not fully understood. Although macroautophagy/autophagy is recognized as essential for lens homeostasis and has shown potential in alleviating cataracts, its precise mechanism remains unclear. Uncovering the molecular details of autophagy in the lens could provide targeted therapeutic interventions alongside surgery. Methods: We monitored autophagic activities in the lens and identified the key autophagy protein ATG16L1 by immunofluorescence staining, Western blotting, and transmission electron microscopy. The regulatory mechanism of ATG16L1 ubiquitination was analyzed by co-immunoprecipitation and Western blotting. We used the crystal structure of E3 ligase gigaxonin and conducted the docking screening of a chemical library. The effect of the identified compound riboflavin was tested in vitro in cells and in vivo animal models. Results: We used HLE cells and connexin 50 (cx50)-deficient cataract zebrafish model and confirmed that ATG16L1 was crucial for lens autophagy. Stabilizing ATG16L1 by attenuating its ubiquitination-dependent degradation could promote autophagy activity and relieve cataract phenotype in cx50-deficient zebrafish. Mechanistically, the interaction between E3 ligase gigaxonin and ATG16L1 was weakened during this process. Leveraging these mechanisms, we identified riboflavin, an E3 ubiquitin ligase-targeting drug, which suppressed ATG16L1 ubiquitination, promoted autophagy, and ultimately alleviated the cataract phenotype in autophagy-related models. Conclusions: Our study identified an unrecognized mechanism of cataractogenesis involving ATG16L1 ubiquitination in autophagy regulation, offering new insights for treating cataracts.

HO-1-Mediated Autophagic Restoration Protects Lens Epithelial Cells Against Oxidative Stress and Cellular Senescence

Purpose

Oxidative stress and cellular senescence are risk factors for age-related cataract. Heme oxygenase 1 (HO-1) is a critical antioxidant enzyme and related to autophagy. Here, we investigate the crosstalk among HO-1, oxidative stress, and cellular senescence in mouse lens epithelial cells (LECs).

Methods

The gene expression of HO-1, p21, LC3, and p62 was measured in human samples. The protective properties of HO-1 were examined in hydrogen peroxide (H2O2)-damaged LECs. Autophagic flux was examined by Western blot and mRFP-GFP-LC3 assay. Western blotting and lysotracker staining were used to analyze lysosomal function. Flow cytometry was used to detect intracellular reactive oxygen species and analyze cell cycle. Senescence-associated β-galactosidase assay was used to determine cellular senescence. The crosstalk between HO-1 and transcription factor EB (TFEB) was further observed in TFEB-knockdown cells. The TFEB binding site in the promoter region of Hmox1 was predicted by the Jasper website and was confirmed by chromatin immunoprecipitation assay.

Results

HO-1 gene expression decreased in LECs of patients with age-related nuclear cataract, whereas mRNA expression levels of p21, LC3, and p62 increased. Upon H2O2-induced oxidative stress, LECs showed the characteristics of autophagic flux blockade, lysosomal dysfunction, and premature senescence. Interestingly, HO-1 significantly restored the impaired autophagic flux and lysosomal function and delayed cellular senescence. TFEB gene silencing greatly reduced the HO-1-mediated autophagic restoration, leading to a failure to prevent LECs from oxidative stress and premature senescence.

Conclusions

We demonstrated HO-1 effects on restoring autophagic flux and delaying cellular senescence under oxidative stress in LECs, which are dependent on TFEB.

Congenital cataracts affect the retinal visual cycle and mitochondrial function: A multi-omics study of GJA8 knockout rabbits

Congenital cataracts are a threat to visual development in children, and the visual impairment persists after surgical treatment; however, the mechanisms involved remain unclear. Previous clinical studies have identified the effect of congenital cataracts on retinal morphology and function. To further understand the molecular mechanisms by which congenital cataracts affect retinal development, we analyzed retina samples from 7-week-old GJA8-knockout rabbits with congenital cataracts and controls by four-dimensional label-free quantification proteomics and untargeted metabolomics. Bioinformatics analysis of proteomic data showed that retinol metabolism, oxidative phosphorylation, and fatty acid degradation pathways were downregulated in the retinas of rabbits with congenital cataracts, indicating that their visual cycle and mitochondrial function were affected. Additional validation of differentially abundant proteins related to the visual cycle and mitochondrial function was performed using Parallel reaction monitoring and western blot experiments. Untargeted metabolome analysis showed significant upregulation of the antioxidant glutathione and ascorbic acid in the retinas of rabbits with congenital cataracts, indicating that their oxidative stress balance was not dysregulated. SIGNIFICANCE: Congenital cataracts in children can alter retinal structure and function, yet the mechanisms are uncertain. Here is the first study to use proteomics and metabolomics approaches to investigate the effects of congenital cataracts on retinal development in the early postnatal period. Our findings suggest that congenital cataracts have an impact on the retinal visual cycle and mitochondrial function. These findings give insight on the molecular pathways behind congenital cataract-induced visual function impairment in the early postnatal period.

Dynamics and composition of small heat shock protein condensates and aggregates

Small heat shock proteins (sHSPs) are essential ATP-independent chaperones that protect the cellular proteome. These proteins assemble into polydisperse oligomeric structures, the composition of which dramatically affects their chaperone activity. The biomolecular consequences of variations in sHSP ratios, especially inside living cells, remain elusive. Here, we study the consequences of altering the relative expression levels of HspB2 and HspB3 in HEK293T cells. These chaperones are partners in a hetero-oligomeric complex, and genetic mutations that abolish their mutual interaction are associated with myopathic disorders. HspB2 displays three distinct phenotypes when co-expressed with HspB3 at varying ratios. Expression of HspB2 alone leads to formation of liquid nuclear condensates, while shifting the stoichiometry towards HspB3 resulted in the formation of large solid-like aggregates. Only cells co-expressing HspB2 with a limited amount of HspB3 formed fully soluble complexes that were distributed homogeneously throughout the nucleus. Strikingly, both condensates and aggregates were reversible, as shifting the HspB2:HspB3 balance in situ resulted in dissolution of these structures. To uncover the molecular composition of HspB2 condensates and aggregates, we used APEX-mediated proximity labelling. Most proteins interact transiently with the condensates and were neither enriched nor depleted in these cells. In contrast, we found that HspB2:HspB3 aggregates sequestered several disordered proteins and autophagy factors, suggesting that the cell is actively attempting to clear these aggregates. This study presents a striking example of how changes in the relative expression levels of interacting proteins affects their phase behavior. Our approach could be applied to study the role of protein stoichiometry and the influence of client binding on phase behavior in other biomolecular condensates and aggregates.

AUTOPHAGY IN THE EYE: FROM PHYSIOLOGY TO PATHOPHYSOLOGY

Autophagy is a catabolic self-degradative pathway that promotes the degradation and recycling of intracellular material through the lysosomal compartment. Although first believed to function in conditions of nutritional stress, autophagy is emerging as a critical cellular pathway, involved in a variety of physiological and pathophysiological processes. Autophagy dysregulation is associated with an increasing number of diseases, including ocular diseases. On one hand, mutations in autophagy-related genes have been linked to cataracts, glaucoma, and corneal dystrophy; on the other hand, alterations in autophagy and lysosomal pathways are a common finding in essentially all diseases of the eye. Moreover, LC3-associated phagocytosis, a form of non-canonical autophagy, is critical in promoting visual cycle function. This review collects the latest understanding of autophagy in the context of the eye. We will review and discuss the respective roles of autophagy in the physiology and/or pathophysiology of each of the ocular tissues, its diurnal/circadian variation, as well as its involvement in diseases of the eye.

Autophagy Requirements for Eye Lens Differentiation and Transparency

Recent evidence points to autophagy as an essential cellular requirement for achieving the mature structure, homeostasis, and transparency of the lens. Collective evidence from multiple laboratories using chick, mouse, primate, and human model systems provides evidence that classic autophagy structures, ranging from double-membrane autophagosomes to single-membrane autolysosomes, are found throughout the lens in both undifferentiated lens epithelial cells and maturing lens fiber cells. Recently, key autophagy signaling pathways have been identified to initiate critical steps in the lens differentiation program, including the elimination of organelles to form the core lens organelle-free zone. Other recent studies using ex vivo lens culture demonstrate that the low oxygen environment of the lens drives HIF1a-induced autophagy via upregulation of essential mitophagy components to direct the specific elimination of the mitochondria, endoplasmic reticulum, and Golgi apparatus during lens fiber cell differentiation. Pioneering studies on the structural requirements for the elimination of nuclei during lens differentiation reveal the presence of an entirely novel structure associated with degrading lens nuclei termed the nuclear excisosome. Considerable evidence also indicates that autophagy is a requirement for lens homeostasis, differentiation, and transparency, since the mutation of key autophagy proteins results in human cataract formation.

The interaction between autophagy and the epithelial-mesenchymal transition mediated by NICD/ULK1 is involved in the formation of diabetic cataracts

Background

Cataracts are the leading cause of blindness and a common ocular complication of diabetes. The epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) and altered autophagic activity occur during the development of diabetic cataracts. The disturbed interaction of autophagy with EMT in LECs stimulated by high glucose levels may participate in cataract formation.

Methods

A rat diabetic cataract model induced by streptozotocin (STZ) and human lens epithelial cells (HLE-B3) stimulated with a high glucose concentration were employed in the study. These models were treated with rapamycin (an inhibitor of mammalian target of rapamycin (mTOR)), and N-(N-[3,5-difluorophenacetyl]-1-alanyl)-S-phenylglycine t-butyl ester (DAPT, an inhibitor of γ-secretase) alone or in combination. Lens opacity was observed and photographed under a slit-lamp microscope. Histological changes in paraffin sections of lenses were detected under a light microscope after hematoxylin and eosin staining. Alterations of autophagosomes in LECs were counted and evaluated under a transmission electron microscope. The expression levels of proteins involved in the EMT, autophagy, and the signaling pathways in LECs were measured using Western blotting and immunofluorescence staining. Cell migration was determined by performing transwell and scratch wound assays. Coimmunoprecipitation (Co-IP) was performed to verify protein-protein interactions. Proteins were overexpressed in transfected cells to confirm their roles in the signaling pathways of interest.

Results

In LECs, a high glucose concentration induces the EMT by activating Jagged1/Notch1/Notch intracellular domain (NICD)/Snail signaling and inhibits autophagy through the AKT/mTOR/unc 51-like kinase 1 (ULK1) signaling pathway in vivo and in vitro, resulting in diabetic cataracts. Enhanced autophagic activity induced by rapamycin suppressed the EMT by inducing Notch1 degradation by SQSTM1/p62 and microtubule-associated protein light chain 3 (LC3) in LECs, while inhibition of the Notch signaling pathway with DAPT not only prevented the EMT but also activated autophagy by decreasing the levels of NICD, which bound to ULK1, phosphorylated it, and then inhibited the initiation of autophagy.

Conclusions

We describe a new interaction of autophagy and the EMT involving NICD/ULK1 signaling, which mediates crosstalk between these two important events in the formation of diabetic cataracts. Activating autophagy and suppressing the EMT mutually promote each other, revealing a potential target and strategy for the prevention of diabetic cataracts.

Blue light attenuates TGF-β2-induced epithelial-mesenchymal transition in human lens epithelial cells via autophagy impairment

Background

Pathogenesis of posterior capsular opacification (PCO) was related to pathological epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs). It has been reported that blue light could have an effect on EMT. This study aims to elucidate the role and potential mechanism of autophagy in EMT after blue light exposure in LECs.

Methods

HLE-B3 cells were treated with TGF-β2 with different concentration and time to induce EMT as a model of PCO in vitro. Cells were exposed to blue light with or without TGF-β2. The expression levels of EMT-associated markers were analyzed by qRT-PCR, western blotting and cell migration ability was determined by transwell migration assay and wound healing assay. The expressions of autophagy-related proteins were analyzed by western blotting, immunofluorescence and transmission electron microscopy. Rapamycin and chloroquine were utilized in cells for autophagy activation and inhibition.

Results

TGF-β2 induced autophagy activation during EMT progression in HLE-B3 cells in a dose- and time-dependent manner. Blue light exposure inhibited TGF-β2-induced EMT characterized by inhibited expression of EMT related markers and reduced migration capacity. Meanwhile, blue light exposure impaired autophagy activated by TGF-β2. Furthermore, Autophagy activation with rapamycin rescued EMT attenuated by blue light. Autophagy inhibition with chloroquine reduced TGF-β2-induced EMT in HLE-B3 cells.

Conclusion

Blue light exposure had inhibited effects on TGF-β2-induced EMT in LECs through autophagy impairment, which provides a new insight on prevention and treatment of PCO.

Recent Advances in KEAP1/NRF2-Targeting Strategies by Phytochemical Antioxidants, Nanoparticles, and Biocompatible Scaffolds for the Treatment of Diabetic Cardiovascular Complications

Significance: Modulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated antioxidant response is a key aspect in the onset of diabetes-related cardiovascular complications. With this review, we provide an overview of the recent advances made in the development of Nrf2-targeting strategies for the treatment of diabetes, with particular attention toward the activation of Nrf2 by natural antioxidant compounds, nanoparticles, and oxidative stress-modulating biocompatible scaffolds. Recent Advances: In the past 30 years, studies addressing the use of antioxidant therapies to treat diabetes have grown exponentially, showing promising but yet inconclusive results. Animal studies and clinical trials on the Nrf2 pathway have shown promising results, suggesting that its activation can delay or reverse some of the cardiovascular impairments in diabetes. Critical Issues: Hyperglycemia- and oscillating glucose levels-induced reactive oxygen species (ROS) accumulation is progressively emerging as a central factor in the onset and progression of diabetes-related cardiovascular complications, including endothelial dysfunction, retinopathy, heart failure, stroke, critical limb ischemia, ulcers, and delayed wound healing. In this context, accumulating evidence suggests a central role for Nrf2-mediated antioxidant response, one of the most studied cellular defensive mechanisms against ROS accumulation. Future Directions: Innovative approaches such as tissue engineering and nanotechnology are converging toward targeting oxidative stress in diabetes. Antioxid. Redox Signal. 36, 707-728.

Rapamycin relieves the cataract caused by ablation of Gja8b through stimulating autophagy in zebrafish

Macroautophagy/autophagy is known to be important for intracellular quality control in the lens. GJA8 is a major gap junction protein in vertebrate lenses. Mutations in GJA8 cause cataracts in humans. The well-known cataractogenesis mechanism is that mutated GJA8 leads to abnormal assembly of gap junctions, resulting in defects in intercellular communication among lens cells. In this study, we observed that ablation of Gja8b (a homolog of mammalian GJA8) in zebrafish led to severe defects in organelle degradation, an important cause of cataractogenesis in developing lens. The role of autophagy in organelle degradation in lens remains disputable. Intriguingly, we also observed that ablation of Gja8b induced deficient autophagy in the lens. More importantly, in vivo treatment of zebrafish with rapamycin, an autophagy activator that inhibits MAPK/JNK and MTORC1 signaling, stimulated autophagy in the lens and relieved the defects in organelle degradation, resulting in the mitigation of cataracts in gja8b mutant zebrafish. Conversely, inhibition of autophagy by treatment with the chemical reagent 3-MA blocked these recovery effects, suggesting the important roles of autophagy in organelle degradation in the lens in gja8b mutant zebrafish. Further studies in HLE cells revealed that GJA8 interacted with ATG proteins. Overexpression of GJA8 stimulated autophagy in HLE cells. These data suggest an unrecognized cataractogenesis mechanism caused by ablation of Gja8b and a potential treatment for cataracts by stimulating autophagy in the lens.Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; AV: autophagic vacuoles; Dpf: days post fertilization; GJA1: gap junction protein alpha 1; GJA3: gap junction protein alpha 3; GJA8: gap junction protein alpha 8; Hpf: hours post fertilization; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PtdIns3K: class III phosphatidylinositol 3-kinase; WT: wild type.

EphA2 inhibits SRA01/04 cells apoptosis by suppressing autophagy via activating PI3K/Akt/mTOR pathway

This study attempted to determine the effect of EphA2 on H₂O₂-treated lens epithelial cells (SRA01/04) and the underlying mechanisms. MTT assay and flow cytometry were performed to assess cell viability and cell apoptosis. Western blot was carried out to examine the levels of proteins associated with apoptosis and autophagy. Our results revealed that EphA2 significantly elevated the reduced cell viability, and inhibited the increased cell apoptosis in H₂O₂-treated SRA01/04 cells, along with the significant up-regulated Bcl-2 and down-regulated Cleaved-caspase-3 and Bax protein levels, but which were all abolished by Rapa (autophagy activator). We also found that EphA2 significantly suppressed cell autophagy in H₂O₂-treated SRA01/04 cells. Additionally, EphA2 significantly up-regulated the protein levels of p-Akt and p-mTOR in H₂O₂-treated SRA01/04 cells, and the inhibition of Akt by MK-2206 and inhibition of mTOR by Rapa both obviously reversed EphA2-mediated the inhibition of autophagy in H₂O₂-treated SRA01/04 cells. In summary, these data demonstrated that EphA2 inhibited the apoptosis of SRA01/04 cells by inhibiting autophagy via activating PI3K/Akt/mTOR pathway.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Autophagy attenuates high glucose-induced oxidative injury to lens epithelial cells

Purpose: Autophagic dysfunction and abnormal oxidative stress are associated with cataract. The purpose of the present study was to investigate the changes of cellular autophagy and oxidative stress and their association in lens epithelial cells (LECs) upon exposure to high glucose.

Methods: Autophagy and oxidative stress-related changes were detected in streptozotocin-induced Type 1 diabetic mice and normal mouse LECs incubated in high glucose conditions. Rapamycin at a concentration of 100 nm/l or 50 μM chloroquine was combined for analysis of the relationship between autophagy and oxidative stress. The morphology of LECs during autophagy was observed by transmission electron microscopy. The expressions of autophagy markers (LC3B and p62) were identified, as well as the key factors of oxidative stress (SOD2 and CAT) and mitochondrial reactive oxygen species (ROS) generation.

Results: Transmission electron microscopy indicated an altered autophagy activity in diabetic mouse lens tissues with larger autophagosomes and multiple mitochondria. Regarding the expressions, LC3B was elevated, p62 was decreased first and then increased, and SOD2 and CAT were increased before a decrease during 4 months of follow-up in diabetic mice and 72 h of culture under high glucose for mouse LECs. Furthermore, rapamycin promoted the expressions of autophagy markers but alleviated those of oxidative stress markers, whereas chloroquine antagonized autophagy but enhanced oxidative stress by elevating ROS generation in LECs exposed to high glucose.

Conclusions: The changes in autophagy and oxidative stress were fluctuating in the mouse LECs under constant high glucose conditions. Autophagy might attenuate high glucose-induced oxidative injury to LECs.

MicroRNA Let-7c-5p-Mediated Regulation of ERCC6 Disrupts Autophagic Flux in Age-Related Cataract via the Binding to VCP

Purpose: DNA damage contributes to the pathogenesis of age-related cataract (ARC) and is repaired through the nucleotide excision repair (NER) pathway, which includes ERCC6. Evidence has demonstrated that defective autophagy leads to lens organelle degradation and cataract. This study aimed to investigate the effects of ERCC6 on autophagy and determine its mechanisms in ARC.Methods: The clinical case-control study comprised 30 patients with ARC and 30 age-matched controls who received transparent lens extraction. Transmission electron microscopy was used to assess the ultrastructure of autophagic vesicles in lens anterior capsule tissues and lens epithelial cell line (SRA01/04). Real-time polymerase chain reaction and western blot analyses were performed to measure relative gene expression levels. Gene expression levels and localization were assessed by immunofluorescence. A coimmunoprecipitation assay was used to investigate the relationship between CSB which encoded by ERCC6 and VCP. ERCC6-siRNA and let-7 c-5p mimic were used to alter the expression of ERCC6 and let-7 c-5p.Results: Autophagy induction occurred in lens anterior capsule tissues of patients with ARC and in UVB-induced SRA01/04 cells, where the number of LC3B puncta was increased. Consistent with this result, the expression of beclin1 (BECN1) and LC3B, in addition to that of p62, was increased. Additionally, ERCC6 expression decreased, and silencing ERCC6 induced increases in the expression of BECN1, LC3B and p62. Moreover, CSB interacted with VCP, and let-7 c-5p induced dysregulation of autophagy by targeting ERCC6.Conclusion: In ARC, Let-7 c-5p-mediated downregulation of ERCC6 might prevent the degradation of autophagic vacuoles. CSB binds to VCP, inducing autophagosomes to combine with lysosomes and be degraded.

The Role of Autophagy in Eye Diseases

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

Changes in relative histone abundance and heterochromatin in αA-crystallin and αB-crystallin knock-in mutant mouse lenses

Objective

Understanding the mechanisms of cataract formation is important for age-related and hereditary cataracts caused by mutations in lens protein genes. Lens proteins of the crystallin gene families α-, β-, and γ-crystallin are the most abundant proteins in the lens. Single point mutations in crystallin genes cause autosomal dominant cataracts in multigenerational families. Our previous proteomic and RNAseq studies identified genes and proteins altered in the early stages of cataract formation in mouse models. Histones H2A, H2B, and H4 increase in abundance in αA- and αB-crystallin mutant mouse lenses and in cultured cells expressing the mutant form of αA-crystallin linked with hereditary cataracts.

Results

In this study of histones in mutant lenses, we extracted histones from adult mouse lenses from cryaa-R49C and cryab-R120G mutant knock-in mice. We characterized the histones using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF)-mass spectrometric analysis and gel electrophoresis and characterized the lens nucleus morphology using electron microscopy (EM). The relative abundance of histone H3 protein decreased in lenses from cryaa-R49C mutant mice and the relative abundance of histone H2 increased in these lenses. Electron microscopy of nuclei from cryaa-R49C-homozygous mutant mouse lenses revealed a pronounced alteration in the distribution of heterochromatin.

p62/Sequestosome 1 levels increase and phosphorylation is altered in Cx50D47A lenses, but deletion of p62/sequestosome 1 does not improve transparency

Purpose

p62/Sequestosome 1 (p62) is a stress-induced protein that is involved in several different intracellular pathways, including regulation of aspects of protein degradation. p62 levels are elevated in several types of cataracts. We investigated whether levels of p62 and its phosphorylation were altered in the lenses of Cx50D47A mice, which express a mutant of connexin50 (Cx50) that leads to cataracts and impaired lens differentiation. To evaluate the importance of p62 in the lens defects caused by a connexin50 mutant, we also examined the effect of deleting p62 in homozygous Cx50D47A mice.

Methods

Protein levels were determined with immunoblotting. Mouse lenses were examined with dark-field illumination microscopy. Intensities of the opacities and lens equatorial diameters were quantified using ImageJ. Nuclei and nuclear remnants were detected with fluorescence microscopy of lens sections stained with 4',6-diamino-2-phenylindole dihydrochloride (DAPI).

Results

Levels of total p62 were increased in the lenses of homozygous Cx50D47A mice compared to those of the wild-type animals. The ratio of p62 phosphorylated at threonine-269/serine-272 (T269/S272) to total p62 was significantly decreased, whereas the ratio of p62 phosphorylated at serine-349 (S349) to total p62 was significantly increased in lenses of homozygous Cx50D47A mice. However, deletion of p62 did not affect the sizes of the lenses or the severity of their cataracts in homozygous Cx50D47A mice. Deletion of p62 did not improve connexin50 or connexin46 levels. Moreover, deletion of p62 did not change the levels of crystallins, histone H3, the mitochondrial import receptor subunit TOM20 homolog, or the abundance of nuclei and nuclear fragments in the lenses of homozygous Cx50D47A mice. Homozygous deletion of p62 led to an 84% increase in the levels of ubiquilin 2, but did not significantly affect the levels of ubiquilin 1 or ubiquilin 4.

Conclusions

Although homozygous Cx50D47A lenses have increased levels of p62, a specific reduction in p62 phosphorylation at T269/S272, and a specific increase in p62 phosphorylation at S349, this protein is not a critical determinant of the severity of the abnormalities of these lenses (reduced growth or differentiation and cataracts). The lens may utilize redundant or compensatory systems (such as changes in levels of ubiquilin 2) to compensate for the lack of p62 in homozygous Cx50D47A lenses.

Let-7c-3p Regulates Autophagy under Oxidative Stress by Targeting ATG3 in Lens Epithelial Cells

Background

Oxidative stress is an important factor during age-related cataract formation. Apoptosis and autophagy induced by oxidative stress have been reported as key factors in age-related cataract. In our research, we investigated the role of let-7c-3p in the regulation of autophagy and apoptosis during the formation of age-related cataract. Material and Methods. Real-time PCR and western blot were employed to detect the expression of let-7c-3p in the tissues of age-related cataract. Human lens epithelial cells (LECs) were treated with H₂O₂ as an age-related cataract model. The extent of apoptosis was measured by flow cytometry and western blot. To detect autophagy, immunofluorescence was used to analyze the spot number of LC3, and western blot was used to detect the expression of LC3-II/I and ATG3. The molecular mechanisms of let-7c-3p regulating autophagy via ATG3 under oxidative stress were performed by a luciferase report gene assay and rescue experiment.

Results

Downregulation of let-7c-3p was found in the age-related cataract group aged >65 years relative to the age-related cataract group aged ≤65 years. Consistently, the expression of let-7c-3p was also lower under oxidative stress. The activities of LEC apoptosis and autophagy induced by oxidative stress were inhibited by let-7c-3p. By the bioinformatics database and the luciferase reporter assay, ATG3 was found to be a direct target of let-7c-3p. Let-7c-3p reduced the ATG3-mediated autophagy level, which was induced by oxidative stress in LECs.

Conclusion

Let-7c-3p inhibits autophagy by targeting ATG3 in LECs in age-related cataract.

Heat shock factor 4 regulates lysosome activity by modulating the αB-crystallin-ATP6V1A-mTOR complex in ocular lens

BACKGROUND

Germline mutations in heat shock factor 4 (HSF4) cause congenital cataracts. Previously, we have shown that HSF4 is involved in regulating lysosomal pH in mouse lens epithelial cell in vitro. However, the underlying mechanism remains unclear.

METHODS

HSF4-deficient mouse lens epithelial cell lines and zebrafish were used in this study. Immunoblotting and quantitative RT-PCR were used for expression analysis. The protein-protein interactions were tested with GST-pull downs. The lysosomes were fractioned by ultracentrifugation.

RESULTS

HSF4 deficiency or knock down of αB-crystallin elevates lysosomal pH and increases the ubiquitination and degradation of ATP6V1A by the proteasome. αB-crystallin localizes partially in the lysosome and interacts solely with the ATP6V1A protein of the V1 complex of V-ATPase. Furthermore, αB-crystallin can co-precipitate with mTORC1 and ATP6V1A in GST pull down assays. Inhibition of mTORC1 by rapamycin or siRNA can lead to dissociation of αB-crystallin from the ATP6V1A and mTORC1complex, shortening the half-life of ATP6V1A and increasing the lysosomal pH. Mutation of ATP6V1A/S441A (the predicted mTOR phosphorylation site) reduces its association with αB-crystallin. In the zebrafish model, HSF4 deficiency reduces αB-crystallin expression and elevates the lysosomal pH in lens tissues.

CONCLUSION

HSF4 regulates lysosomal acidification by controlling the association of αB-crystallin with ATP6V1A and mTOR and regulating ATP6V1A protein stabilization.

GENERAL SIGNIFICANCE

This study uncovers a novel function of αB-crystallin, demonstrating that αB-crystallin can regulate lysosomal ATP6V1A protein stabilization by complexing to ATP6V1A and mTOR. This highlights a novel mechanism by which HSF4 regulates the proteolytic process of organelles during lens development.

Opacification of lentoid bodies derived from human induced pluripotent stem cells is accelerated by hydrogen peroxide and involves protein aggregation

Despite the recent breakthrough in cataract drug development, further improvements have been limited by the lack of human in vitro cataract disease models. This study, therefore, aims to generate a qualified cataract disease model. Mature lentoid bodies (LBs) on Day 25 (D25), which were differentiated from human induced pluripotent stem cells (iPSCs) using the "fried egg" method, were continually culturing (control) or extra treated with either ultraviolet (UV) radiation or hydrogen peroxide (H₂ O₂ ). The LBs' shape alteration and opacity were examined using light microscopy and mean gray value evaluation. Their structure and crystallin expression were examined using immunofluorescence and transmission electron microscopy (TEM). Real-time polymerase chain reaction and western blot were used to investigate the potential role of autophagy in cloudy LBs. Mature LBs became cloudy with time which was accelerated by H₂ O₂ . Immunofluorescence examinations and TEM showed that the H₂ O₂ -treated and control LBs had similar shapes, lens capsule, and monolayer lens epithelial cell (LEC) structures. However, we were unable to do further assessment of the UV-treated LBs as the structures of LBs were easily damaged when treated with UV radiation. Cells containing aggregated protein (αA-crystallin and αB-crystallin) puncta were more abundant in the H₂ O₂ -treated LBs as compared with control LBs. Moreover, LC3B expression decreased with age in anterior lens capsules obtained from age-related cataracts (ARCs) patients as compared with LC3B levels in primary LECs, which is consistent with that LC3B expression in LBs was lower on D45 than on D25. Our study found that human iPSCs-derived LBs became cloudy with time which was accompanied by protein aggregation, and this phenomenon was accelerated by H₂ O₂ , suggesting that LBs with extending culture may serve as a human model for in vitro ARCs.

MicroRNA-29 enhances autophagy and cleanses exogenous mutant αB-crystallin in retinal pigment epithelial cells

Retinal pigment epithelial cells (RPEs), a pigmented cell layer in the outer retina, are constantly exposed to photo-oxidative stress. Autophagy relieves the stress by removing oxidative protein adducts, protein aggregates, and damaged mitochondria. We previously found that miR-29 is downregulated in choroid/RPE tissue in a model of exudative age-related macular degeneration (AMD), suggesting that miR-29 deficiency may contribute to autophagy inhibition and AMD progression. Here we wanted to test whether overexpression of miR-29 in RPEs could enhance autophagy, thereby facilitating removal of drusen components. Indeed, overexpression of miR-29 in the RPEs increased autophagy, assessed by decreased protein levels of p62, increased lipid form of microtubule-associated protein light chain (LC3-II), and elevated autophagy flux. Furthermore, overexpression of miR-29 mitigated the formation of mutant αB-crystallin (R120G) protein aggregates. In probing the mechanism, we demonstrated that miR-29 post-transcriptionally repressed LAMPTOR1/p18 via targeting its 3'-UTRs of messenger RNA. MiR-29 overexpression and knockdown of LAMPTOR1/p18 led to limited mTORC1 recruitment to lysosomes and inhibition of mTORC1 activity. Altogether, miR-29 enhances autophagy which aids in removal of protein aggregates. These findings reveal a novel role of miR-29, which has the potential of being a therapeutic strategy for rescuing RPE degeneration in ocular disorders.

Fluorescent magnetic PEI-PLGA nanoparticles loaded with paclitaxel for concurrent cell imaging, enhanced apoptosis and autophagy in human brain cancer

Magnetic nanoparticles are regarded as a promising drug delivery vehicle with the improved efficacy and lowered side effects for antitumor therapy. Herein, the poly lactic-co-glycolic acid (PLGA) modified magnetic nanoplatform was synthesized using superparamagnetic γ-Fe₂O₃ nanoparticles (MNPs) as a core, and then labelled with polyethylenimine (PEI)-conjugated fluorescein isothiocyanate (FITC), and simultaneously loaded with antitumor drug paclitaxel (PTX) for theranostic analysis of antitumor effects investigated in human brain glioblastoma U251 cells. As a result, the prepared PEI-PLGA-MNPs showed a relatively round sphere with an average size of 80 nm approximately, and the FITC-labeling PEI-PLGA-MNPs were efficiently endocytosed by the U251 cells for cellular imaging. Moreover, the fabricated PEI-PLGA-PTX-MNPs also demonstrated an inhibition of the targeted cell proliferation and migration, and a programmed cell death, via both apoptosis modulating by a burst of reactive oxygen species (ROS) and autophagy with accumulation of autophagosomes and LC3-II signals detected in the treated glioblastoma U251 cells after uptaking. Therefore, the constructed nanoplatform could be effectively applied for simultaneous cellular imaging and drug delivery in human brain glioblastoma treatment in future.

MiR-30a inhibits BECN1-mediated autophagy in diabetic cataract

Purpose

To investigate the role of microRNAs in the regulation of autophagy and apoptosis in lens epithelial cells (LECs) during diabetic cataract formation.

Methods

A miRNA microarray study and quantitative real-time PCR were performed to identify the expression of miRNAs in LECs of diabetic cataract. Human LECs were cultured in high glucose conditions as a diabetic cataract model. BECN1 and LC3B were detected by Western blotting and quantitative real-time PCR. The extent of apoptosis was measured using FACSCalibur flow cytometry.

Results

Downregulation of miR-30a was identified in LECs attached to diabetic cataract tissues. By the bioinformatic assay and the luciferase activity assay, BECN1 was found to be a direct target of miR-30a. MiR-30a reduced the BECN1-mediated autophagy activity induced by high glucose in LECs in vitro. The ratio of LECs apoptosis was also decreased.

Conclusion

MiR-30a was involved in the inhibition of autophagy by targeting BECN1 in LECs in human diabetic cataract.

Small heat shock proteins in ageing and age-related diseases

Small heat shock proteins (sHSPs) are gatekeepers of cellular homeostasis across species, preserving proteome integrity under stressful conditions. Nonetheless, recent evidence suggests that sHSPs are more than molecular chaperones with merely auxiliary role. In contrast, sHSPs have emerged as central lifespan determinants, and their malfunction has been associated with the manifestation of neurological disorders, cardiovascular disease and cancer malignancies. In this review, we focus on the role of sHSPs in ageing and age-associated diseases and highlight the most prominent paradigms, where impairment of sHSP function has been implicated in human pathology.

The Evolving Functions of Autophagy in Ocular Health: A Double-edged Sword

Autophagy plays an adaptive role in cell survival, development, differentiation and intracellular homeostasis. Autophagy is recognized as a 'self-cannibalizing' process that is active during stresses such as starvation, chemotherapy, infection, ageing, and oxygen shortage to protect organisms from various irritants and to regenerate materials and energy. However, autophagy can also lead to a form of programmed cell death distinct from apoptosis.

Components of the autophagic pathway are constitutively expressed at a high level in the eye, including in the cornea, lens, retina, and orbit. In addition, the activation of autophagy is directly linked to the development of eye diseases such as age-related macular degeneration (ARMD), cataracts, diabetic retinopathy (DR), glaucoma, photoreceptor degeneration, ocular tumours, ocular infections and thyroid-associated ophthalmopathy (TAO). A high level of autophagy defends against external stress; however, excessive autophagy can result in deterioration, as observed in ocular diseases such as ARMD and DR.

This review summarizes recent developments elucidating the relationship between autophagy and ocular diseases and the potential roles of autophagy in the pathogenesis and treatment of these diseases.

Identification and Ultrastructural Characterization of a Novel Nuclear Degradation Complex in Differentiating Lens Fiber Cells

An unresolved issue in structural biology is how the encapsulated lens removes membranous organelles to carry out its role as a transparent optical element. In this ultrastructural study, we establish a mechanism for nuclear elimination in the developing chick lens during the formation of the organelle-free zone. Day 12-15 chick embryo lenses were examined by high-resolution confocal light microscopy and thin section transmission electron microscopy (TEM) following fixation in 10% formalin and 4% paraformaldehyde, and then processing for confocal or TEM as described previously. Examination of developing fiber cells revealed normal nuclei with dispersed chromatin and clear nucleoli typical of cells in active ribosome production to support protein synthesis. Early signs of nuclear degradation were observed about 300 μm from the lens capsule in Day 15 lenses where the nuclei display irregular nuclear stain and prominent indentations that sometimes contained a previously undescribed macromolecular aggregate attached to the nuclear envelope. We have termed this novel structure the nuclear excisosome. This complex by confocal is closely adherent to the nuclear envelope and by TEM appears to degrade the outer leaflet of the nuclear envelope, then the inner leaflet up to 500 μm depth. The images suggest that the nuclear excisosome separates nuclear membrane proteins from lipids, which then form multilamellar assemblies that stain intensely in confocal and in TEM have 5 nm spacing consistent with pure lipid bilayers. The denuded nucleoplasm then degrades by condensation and loss of structure in the range 600 to 700 μm depth producing pyknotic nuclear remnants. None of these stages display any classic autophagic vesicles or lysosomes associated with nuclei. Uniquely, the origin of the nuclear excisosome is from filopodial-like projections of adjacent lens fiber cells that initially contact, and then appear to fuse with the outer nuclear membrane. These filopodial-like projections appear to be initiated with a clathrin-like coat and driven by an internal actin network. In summary, a specialized cellular organelle, the nuclear excisosome, generated in part by adjacent fiber cells degrades nuclei during fiber cell differentiation and maturation.

Congenital microcornea-cataract syndrome-causing mutation X253R increases βB1-crystallin hydrophobicity to promote aggregate formation

The high solubility and lifelong stability of crystallins are crucial to the maintenance of lens transparency and optical properties. Numerous crystallin mutations have been linked to congenital cataract, which is one of the leading causes of newborn blindness. Besides cataract, several crystallin mutations have also been linked to syndromes such as congenital microcornea-cataract syndrome (CMCC). However, the molecular mechanism of CMCC caused by crystallin mutations remains elusive. In the present study, we investigated the mechanism of CMCC caused by the X253R mutation in βB1-crystallin. The exogenously expressed X253R proteins were prone to form p62-negative aggregates in HeLa cells, strongly inhibited cell proliferation and induced cell apoptosis. The intracellular X253R aggregates could be successfully redissolved by lanosterol but not cholesterol. The extra 26 residues at the C-terminus of βB1-crystallin introduced by the X253R mutation had little impact on βB1-crystallin structure and stability, but increased βB1-crystallin hydrophobicity and decreased its solubility. Interestingly, the X253R mutant fully abolished the aggregatory propensity of βB1- and βA3/βB1-crystallins at high temperatures, suggesting that X253R was an aggregation-inhibition mutation of β-crystallin homomers and heteromers in dilute solutions. Our results suggest that an increase in hydrophobicity and a decrease in solubility might be responsible for cataractogenesis induced by the X253R mutation, while the cytotoxic effect of X253R aggregates might contribute to the defects in ocular development. Our results also highlight that, at least in some cases, the aggregatory propensity in dilute solutions could not fully mimic the behaviours of mutated proteins in the crowded cytoplasm of the cells.

Lens ER-stress response during cataract development in Mip-mutant mice

Major intrinsic protein (MIP) is a functional water-channel (AQP0) that also plays a key role in establishing lens fiber cell architecture. Genetic variants of MIP have been associated with inherited and age-related forms of cataract; however, the underlying pathogenic mechanisms are unclear. Here we have used lens transcriptome profiling by microarray-hybridization and qPCR to identify pathogenic changes during cataract development in Mip-mutant (Lop/+) mice. In postnatal Lop/+ lenses (P7) 99 genes were up-regulated and 75 were down-regulated (>2-fold, p=<0.05) when compared with wild-type. A pathway analysis of up-regulated genes in the Lop/+ lens (P7) was consistent with endoplasmic reticulum (ER)-stress and activation of the unfolded protein response (UPR). The most up-regulated UPR genes (>4-fold) in the Lop/+ lens included Chac1>Ddit3>Atf3>Trib3>Xbp1 and the most down-regulated genes (>5-fold) included two anti-oxidant genes, Hspb1 and Hmox1. Lop/+ lenses were further characterized by abundant TUNEL-positive nuclei within central degenerating fiber cells, glutathione depletion, free-radical overproduction, and calpain hyper-activation. These data suggest that Lop/+ lenses undergo proteotoxic ER-stress induced cell-death resulting from prolonged activation of the Eif2ak3/Perk-Atf4-Ddit3-Chac1 branch of the UPR coupled with severe oxidative-stress.

NFκB is a central regulator of protein quality control in response to protein aggregation stresses via autophagy modulation

NFκB is a master regulator of protein quality control. It helps the cells to survive proteotoxicity by modulating autophagy via up-regulation of BAG3 and HspB8 expression, a molecular mechanism relevant to protein conformational diseases.

During cell life, proteins often misfold, depending on particular mutations or environmental changes, which may lead to protein aggregates that are toxic for the cell. Such protein aggregates are the root cause of numerous diseases called “protein conformational diseases,” such as myofibrillar myopathy and familial amyotrophic lateral sclerosis. To fight against aggregates, cells are equipped with protein quality control mechanisms. Here we report that NFκB transcription factor is activated by misincorporation of amino acid analogues into proteins, inhibition of proteasomal activity, expression of the R120G mutated form of HspB5 (associated with myofibrillar myopathy), or expression of the G985R and G93A mutated forms of superoxide dismutase 1 (linked to familial amyotrophic lateral sclerosis). This noncanonical stimulation of NFκB triggers the up-regulation of BAG3 and HspB8 expression, two activators of selective autophagy, which relocalize to protein aggregates. Then NFκB-dependent autophagy allows the clearance of protein aggregates. Thus NFκB appears as a central and major regulator of protein aggregate clearance by modulating autophagic activity. In this context, the pharmacological stimulation of this quality control pathway might represent a valuable strategy for therapies against protein conformational diseases.

Integrin αVβ5-mediated Removal of Apoptotic Cell Debris by the Eye Lens and Its Inhibition by UV Light Exposure

Accumulation of apoptotic material is toxic and associated with cataract and other disease states. Identification of mechanisms that prevent accumulation of apoptotic debris is important for establishing the etiology of these diseases. The ocular lens is routinely assaulted by UV light that causes lens cell apoptosis and is associated with cataract formation. To date, no molecular mechanism for removal of toxic apoptotic debris has been identified in the lens. Vesicular debris within lens cells exposed to UV light has been observed raising speculation that lens cells themselves could act as phagocytes to remove toxic apoptotic debris. However, phagocytosis has not been confirmed as a function of the intact eye lens, and no mechanism for lens phagocytosis has been established. Here, we demonstrate that the eye lens is capable of phagocytizing extracellular lens cell debris. Using high throughput RNA sequencing and bioinformatics analysis, we establish that lens epithelial cells express members of the integrin αVβ5-mediated phagocytosis pathway and that internalized cell debris co-localizes with αVβ5 and with RAB7 and Rab-interacting lysosomal protein that are required for phagosome maturation and fusion with lysosomes. We demonstrate that the αVβ5 receptor is required for lens epithelial cell phagocytosis and that UV light treatment of lens epithelial cells results in damage to the αVβ5 receptor with concomitant loss of phagocytosis. These data suggest that loss of αVβ5-mediated phagocytosis by the eye lens could result in accumulation of toxic cell debris that could contribute to UV light-induced cataract formation.

Autophagy in the lens

The lens of the eye is a transparent tissue composed of lens fiber cells that differentiate from lens epithelial cells and degrade all cytoplasmic organelles during terminal differentiation. Autophagy is a major intracellular degradation system in which cytoplasmic proteins and organelles are degraded in the lysosome. Although autophagy is constitutively activated in the lens and has been proposed to be involved in lens organelle degradation, its precise role is not well understood. Recent genetic studies in mice have demonstrated that autophagy is critically important for intracellular quality control in the lens but can be dispensable for lens organelle degradation. Here, we review recent findings on the roles of autophagy and lysosomes in organelle degradation and intracellular quality control in the lens, and discuss their possible involvement in the development of human cataract.

Autophagy and UPR in alpha-crystallin mutant knock-in mouse models of hereditary cataracts

BACKGROUND

Knock-in mice provide useful models of congenital and age-related cataracts caused by α-crystallin mutations. R49C αA-crystallin and R120G αB-crystallin mutations are linked with hereditary cataracts. Knock-in αA-R49C+/- heterozygotes develop cataracts by 1-2months, whereas homozygote mice have cataracts at birth. The R49C mutation drastically reduces lens protein water solubility and causes cell death in knock-in mouse lenses. Mutant crystallin cannot function as a chaperone, which leads to protein aggregation and lens opacity. Protein aggregation disrupts the lens fiber cell structure and normal development and causes cell death in epithelial and fiber cells. We determined what aspects of the wild-type phenotype are age-dependently altered in the mutant lens.

METHODS

Wild-type, heterozygote (αA-R49C+/-), and homozygote (αA-R49C+/+) mouse lenses were assessed pre- and postnatally for lens morphology (electron microscopy, immunohistochemistry), and autophagy or unfolded protein response markers (immunoblotting).

RESULTS

Morphology was altered by embryonic day 17 in R49C+/+ lenses; R49C+/- lens morphology was unaffected at this stage. Active autophagy in the lens epithelium of mutant lenses was indicated by the presence of autophagosomes using electron microscopy. Protein p62 levels, which are degraded specifically by autophagy, increased in αA-R49C mutant versus wild-type lenses, suggesting autophagy inhibition in the mutant lenses. The unfolded protein response marker XBP-1 was upregulated in adult lenses of αB-R120G+/+ mice, suggesting its role in lens opacification.

CONCLUSIONS

Mutated crystallins alter lens morphology, autophagy, and stress responses.

GENERAL SIGNIFICANCE

Therapeutic modulation of autophagic pathways may improve protein degradation in cataractous lenses and reduce lens opacity. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Lens Biology and Biochemistry

The primary function of the lens resides in its transparency and ability to focus light on the retina. These require both that the lens cells contain high concentrations of densely packed lens crystallins to maintain a refractive index constant over distances approximating the wavelength of the light to be transmitted, and a specific arrangement of anterior epithelial cells and arcuate fiber cells lacking organelles in the nucleus to avoid blocking transmission of light. Because cells in the lens nucleus have shed their organelles, lens crystallins have to last for the lifetime of the organism, and are specifically adapted to this function. The lens crystallins comprise two major families: the βγ-crystallins are among the most stable proteins known and the α-crystallins, which have a chaperone-like function. Other proteins and metabolic activities of the lens are primarily organized to protect the crystallins from damage over time and to maintain homeostasis of the lens cells. Membrane protein channels maintain osmotic and ionic balance across the lens, while the lens cytoskeleton provides for the specific shape of the lens cells, especially the fiber cells of the nucleus. Perhaps most importantly, a large part of the metabolic activity in the lens is directed toward maintaining a reduced state, which shelters the lens crystallins and other cellular components from damage from UV light and oxidative stress. Finally, the energy requirements of the lens are met largely by glycolysis and the pentose phosphate pathway, perhaps in response to the avascular nature of the lens. Together, all these systems cooperate to maintain lens transparency over time.

Role of crystallins in diabetic complications

BACKGROUND

Crystallins are the major structural proteins of vertebrate eye lens responsible for maintaining the refractive index of the lens. However, recent studies suggest that they also have a functional significance in non-lenticular tissues. Prolonged uncontrolled diabetes results in the development of macro and microvascular complications that are the leading causes of morbidity and mortality in diabetic patients all over the world.

SCOPE OF REVIEW

Recent studies have shown that crystallins play an instrumental role in diabetes and its complications. Therefore, this review highlights the current data on the impact of chronic hyperglycemia on expression, distribution, glycation, phosphorylation, chaperone-like function and, anti-apoptotic activity of crystallins. Furthermore, we discussed the insights for developing therapeutic strategies for diabetic complications including natural agents, peptides, and pharmacological chaperones that modulate or mimic chaperone activity of α-crystallins.

MAJOR CONCLUSIONS

Upregulation of crystallins appears to be a common feature of chronic diabetes. Further, chronic hyperglycemia induces the glycation and phosphorylation of crystallins, mainly α-crystallins and thereby alters their properties. The disturbed interaction of αB-crystallin with various apoptotic mediators including Bax and caspases is also an important factor for increased cell death in diabetes. Numerous dietary agents, peptides, and chemical chaperones prevent apoptosis and the loss of chaperone activity in diabetes.

GENERAL SIGNIFICANCE

Understanding the role of crystallins will aid in developing therapeutic strategies for alleviating pathophysiological conditions such as protein aggregation, inflammation, oxidative stress and apoptosis associated with chronic complications of diabetes including cataract, retinopathy, and cardiomyopathy. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Cyclosporine A prevents ex vivo PCO formation through induction of autophagy-mediated cell death

The purpose of this study was to determine the Cyclosporine A (CsA) dose and minimum drug delivery time needed to prevent posterior capsule opacification (PCO) in an ex vivo canine model and evaluate the mechanism of CsA-induced cell death. Canine lens epithelial cells (LEC) were treated with CsA and changes in cell migration, proliferation, and density were monitored over time. CsA-treated LEC underwent transmission electron microscopy (TEM), immunofluorescence, and immunoblotting in the presence or absence of autophagy inhibitors to evaluate the mechanism of cell death. Lens capsules were harvested from canine cadaver eyes for an ex vivo model of PCO. Lens capsules were treated with CsA for 1, 2, 3, 4, 5, 6, or 7 days, and subsequently maintained in culture for a total of 28 days in the absence of drug. CsA reduced LEC viability in a dose dependent manner. Morphologically, CsA-treated LEC were swollen, had intact nuclei, lacked peripheral chromatin condensation, and demonstrated prominent vacuolization; TEM revealed autophagosomes. LC3-II protein expression and acridine orange fluorescence increased in CsA-treated cells. A small non-significant induction of cleaved caspase-3 was observed in CsA-treated LEC. Lens capsules treated with 5, 6, or 7 days of 10 μg/mL CsA showed a significant decrease in ex vivo PCO formation; 6 days of drug delivery prevented PCO. This study finds that morphologic changes, formation of acidic vesicles, and increased expression of LC3-II supports the hypothesis that CsA mediates LEC death via autophagy; this is a novel finding in the lens. Induction of CsA-induced apoptosis was minimal. Six days of intracapsular CsA drug delivery prevented ex vivo PCO formation.

Differentiation state-specific mitochondrial dynamic regulatory networks are revealed by global transcriptional analysis of the developing chicken lens

The mature eye lens contains a surface layer of epithelial cells called the lens epithelium that requires a functional mitochondrial population to maintain the homeostasis and transparency of the entire lens. The lens epithelium overlies a core of terminally differentiated fiber cells that must degrade their mitochondria to achieve lens transparency. These distinct mitochondrial populations make the lens a useful model system to identify those genes that regulate the balance between mitochondrial homeostasis and elimination. Here we used an RNA sequencing and bioinformatics approach to identify the transcript levels of all genes expressed by distinct regions of the lens epithelium and maturing fiber cells of the embryonic Gallus gallus (chicken) lens. Our analysis detected more than 15,000 unique transcripts expressed by the embryonic chicken lens. Of these, more than 3000 transcripts exhibited significant differences in expression between lens epithelial cells and fiber cells. Multiple transcripts coding for separate mitochondrial homeostatic and degradation mechanisms were identified to exhibit preferred patterns of expression in lens epithelial cells that require mitochondria relative to lens fiber cells that require mitochondrial elimination. These included differences in the expression levels of metabolic (DUT, PDK1, SNPH), autophagy (ATG3, ATG4B, BECN1, FYCO1, WIPI1), and mitophagy (BNIP3L/NIX, BNIP3, PARK2, p62/SQSTM1) transcripts between lens epithelial cells and lens fiber cells. These data provide a comprehensive window into all genes transcribed by the lens and those mitochondrial regulatory and degradation pathways that function to maintain mitochondrial populations in the lens epithelium and to eliminate mitochondria in maturing lens fiber cells.

Pinosylvin-mediated protection against oxidative stress in human retinal pigment epithelial cells

PURPOSE

In this work, we investigated the ability of pinosylvin (PS), 3,5-dihydroxy-trans-stilbene, to modulate oxidative stress in human RPE cells. PS, a stilbenoid polyphenol, occurs in high concentrations in bark byproducts and therefore represents an attractive bioactive compound for health-promoting applications.

METHODS

First, we evaluated the toxicity range of PS by exposing ARPE-19 cells to 0.1-200 µM concentrations of PS for 24 h followed by the cell viability test. In the next stage, the ARPE-19 cells were preincubated in PS for 24 h followed by hydroquinone (HQ) exposure without PS for another 24 h. The cell viability test was conducted after HQ exposure. To elucidate the potential mechanisms behind PS-mediated protection against oxidative stress, the ARPE-19 cells were treated with 5 µM PS for 6 h, and mRNA was extracted at four time points (2 h, 6 h, 12 h, 24 h) to determine changes in the expression of nuclear factor-erythroid 2-related factor-2 (Nrf2), sequestosome 1 (p62/SQSTM1), heme oxygenase-1 (HO-1), and glutathione S-transferase pi 1 (GSTP1) genes. To clarify the molecular mechanism behind PS-mediated protection further, the ARPE-19 cells were transfected with p62 and Nrf2 siRNAs for 24 h, and the roles of p62, Nrf2, and its target gene HO-1 in conferring protection against oxidative stress were studied with quantitative real-time PCR (qRT-PCR) and the cell viability test.

RESULTS

PS treatment at concentrations of 5 and 10 µM significantly enhanced cell survival from oxidative stress. The expression levels of an enzyme with antioxidative, anti-inflammatory, and immunomodulatory properties, HO-1, were increased by PS treatment and correlated strongly with cell survival. PS treatment did not elevate the expression levels of Nrf2 or its target genes, p62 or GSTP1, even though it had a clear effect on the expression of HO-1, another gene controlled by Nrf2. RNA interference analysis further confirmed the important role of Nrf2 and HO-1 in PS-mediated protection against oxidative stress whereas the role of p62 seemed to be insignificant at the gene expression and cell viability levels.

CONCLUSIONS

Our results suggest that PS treatment conferred protection against oxidative stress through the induction of HO-1 in human RPE cells. Consequently, PS-stilbene compounds, which can be isolated in significant amounts from bark waste, may possess health-promoting properties against aging-related diseases associated with oxidative stress such as age-related macular degeneration (AMD) and Alzheimer's disease. These natural compounds may offer opportunities for high-value use of bark waste in diverse health-related applications.

Suppression of MAPK/JNK-MTORC1 signaling leads to premature loss of organelles and nuclei by autophagy during terminal differentiation of lens fiber cells

Although autophagic pathways are essential to developmental processes, many questions still remain regarding the initiation signals that regulate autophagy in the context of differentiation. To address these questions we studied the ocular lens, as the programmed elimination of nuclei and organelles occurs in a precisely regulated spatiotemporal manner to form the organelle-free zone (OFZ), a characteristic essential for vision acuity. Here, we report our discovery that inactivation of MAPK/JNK induces autophagy for formation of the OFZ through its regulation of MTORC1, where MAPK/JNK signaling is required for both MTOR activation and RPTOR/RAPTOR phosphorylation. Autophagy pathway proteins including ULK1, BECN1/Beclin 1, and MAP1LC3B2/LC3B-II were upregulated in the presence of inhibitors to either MAPK/JNK or MTOR, inducing autophagic loss of organelles to form the OFZ. These results reveal that MAPK/JNK is a positive regulator of MTORC1 signaling and its developmentally regulated inactivation provides an inducing signal for the coordinated autophagic removal of nuclei and organelles required for lens function.