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

MicroRNA-204-5p Attenuates Oxidative Stress, Apoptosis and Inflammation by Targeting TXNIP in Diabetic Cataract

Diabetic cataract (DC) is a major cause of blindness in diabetic patients and it is characterized by early onset and rapid progression. MiR-204-5p was previously identified as one of the top five down-regulated miRNAs in human DC lens tissues. We aimed to determine the expression of miR-204-5p in human lens epithelial cells (HLECs) and explore its effects and mechanisms in regulating the progression of DC. The expression of miR-204-5p in the anterior capsules of DC patients and HLECs was examined by RT-qPCR. Bioinformatics tools were then used to identify the potential target of miR-204-5p. The relationship between miR-204-5p and the target gene was confirmed through a dual luciferase reporter assay. Additionally, the regulatory mechanism of oxidative stress, apoptosis, and inflammation in DC was investigated by overexpressing miR-204-5p using miR-204-5p agomir. The expression of miR-204-5p was downregulated in the anterior capsules of DC patients and HLECs. Overexpression of miR-204-5p reduced ROS levels, pro-apoptosis genes (Bid, Bax, caspase-3), and IL-1β production in HG-treated HLECs. TXNIP was the direct target of miR-204-5p by dual luciferase reporter assay. Therefore, this study demonstrated that miR-204-5p effectively reduced oxidative damage, apoptosis, and inflammation in HLECs under HG conditions by targeting TXNIP. Targeting miR-204-5p could be a promising therapeutic strategy for the potential treatment of DC.

Metformin protects human lens epithelial cells from high glucose-induced senescence and autophagy inhibition by upregulating SIRT1

PURPOSE

The aim of this study is to explore whether metformin (MET) protects the human lens epithelial cells (HLECs) from high glucose-induced senescence and to identify the underlying mechanisms.

METHODS

A cellular senescence model was established by treating HLE-B3 cells with D-glucose and then intervened with MET. Concentrations of high glucose (HG) and MET were detected using CCK-8 and western blot. qRT-PCR, western blot, and senescence-associated β-galactosidase (SA-β-gal) were performed to verify the protective effect of MET on senescent HLE-B3 cells. Additionally, western blot and qRT-PCR were conducted to detect the effects of MET on autophagy-related markers p62 and LC3, as well as SIRT1.

RESULTS

In vitro, we observed apparent senescence in human lens epithelial cells (HLECs) under high glucose conditions. This was characterized by increased senescence-associated genes p21 and p53. However, the addition of MET significantly reduced the occurrence of HLECs senescence. We also observed that high glucose inhibited both autophagy and SIRT1, which could be restored by MET. Moreover, we verified that the anti-senescence effect of MET was mediated by SIRT1 using SIRT1 activators and inhibitors.

CONCLUSION

We have demonstrated that autophagy and SIRT1 activity are inhibited in HLE-B3 cells using the HG induced senescence model. Furthermore, our results showed that MET can delay senescence by activating SIRT1 and autophagy. These findings suggest that MET may be a promising candidate for alleviating cataract development and provide a direction for further investigation into the underlying molecular mechanisms.

Glucose dysregulation promotes oncogenesis in human bladder cancer by regulating autophagy and YAP1/TAZ expression

Glucose dysregulation is strongly correlated with cancer development, and cancer is prevalent in patients with Type 2 diabetes (T2D). We aimed to elucidate the mechanism underlying autophagy in response to glucose dysregulation in human bladder cancer (BC). 220 BC patients were included in this retrospective study. The expression of YAP1, TAZ and AMPK, EMT-associated markers, and autophagy marker proteins was analysed by immunohistochemistry, western blotting, and quantitative real-time PCR (qPCR). Further, T24 and UMUC-3 BC cells were cultured in media with different glucose concentrations, and the expression of YAP1, TAZ, AMPK and EMT-associated markers, and autophagy marker proteins was analysed by western blotting and qPCR. Autophagy was observed by immunofluorescence and electron microscopy. BC cell viability was tested using MTT assays. A xenograft nude mouse model of diabetes was used to evaluate tumour growth, metastasis and survival. A poorer pathologic grade and tumour-node-metastasis stage were observed in patients with BC with comorbid T2D than in others with BC. YAP1 and TAZ were upregulated in BC samples from patients with T2D. Mechanistically, high glucose (HG) promoted BC progression both in vitro and in vivo and inhibited autophagy. Specifically, various autophagy marker proteins and AMPK were negatively regulated under HG conditions and correlated with YAP1 and TAZ expression. These results demonstrate that HG inhibits autophagy and promotes cancer development in BC. YAP1/TAZ/AMPK signalling plays a crucial role in regulating glucose dysregulation during autophagy. Targeting these effectors exhibits therapeutic significance and can serve as prognostic markers in BC patients with T2D.

Oxidative stress, epigenetic regulation and pathological processes of lens epithelial cells underlying diabetic cataract

Background

Cataract is a blinding disease worldwide. It is an age-related disease that mainly occurs in people over 65 years old. Cataract is also prevalent in patients with diabetes mellites (DM). The pathological mechanisms underlying diabetic cataract (DC) are more complex than that of age-related cataract. Studies have identified that polyol pathway, advanced glycation end products (AGEs) and oxidative stress are the primary pathogenesis of DC. In recent years, molecular-level regulations and pathological processes of lens epithelial cells (LECs) have been confirmed to play roles in the initiation and progression of DC. A comprehensive understanding and elucidation of how chronic hyperglycemia drives molecular-level regulations and cytopathological processes in the lens will shed lights on the prevention, delay and treatment of DC.

Main text

Excessive glucose in the lens enhances polyol pathway and AGEs formation. Polyol pathway causes imbalance in the ratio of NADPH/NADP+ and NADH/NAD+. Decrease in NADPH/NADP+ ratio compromises antioxidant enzymes, while increase in NADH/NAD+ ratio promotes reactive oxygen species (ROS) overproduction in mitochondria, resulting in oxidative stress. Oxidative stress in the lens causes oxidation of DNA, proteins and lipids, leading to abnormalities in their structure and functions. Glycation of proteins by AGEs decreases solubility of proteins. High glucose triggered epigenetic regulations directly or indirectly affect expressions of genes and proteins in LECs. Changes in autophagic activity, increases in fibrosis and apoptosis of LECs destroy the morphological structure and physiological functions of the lens epithelium, disrupting lens homeostasis.

Conclusions

In both diabetic animal models and diabetics, oxidative stress plays crucial roles in the formation of cataract. Epigenetic regulations, include lncRNA, circRNA, microRNA, methylation of RNA and DNA, histone acetylation and pathological processes, include autophagy, fibrosis and apoptosis of LECs also involved in DC.

Differentially expressed gene profiles and associated ceRNA network in ATG7-Deficient lens epithelial cells under oxidative stress

Oxidation is an essential factor during cataract development. Autophagy, usually a cytoprotective process, is always found elevated in lens epithelial cells under oxidation, yet its roles and associated molecular mechanisms under such circumstances are rarely elucidated. Herein, we extracted and re-analyzed the RNA sequencing data of the GSE161701 dataset from the Gene Expression Omnibus database to identify the differentially expressed mRNAs and lncRNAs by using the R package "DESeq2". Further analyses of gene ontology and KEGG enrichment were implemented via the packages "clusterProfiler" and "enrichplot". We found that after the knockout of ATG7, differentially expressed genes were more associated with hemopoiesis, vasculature development, axonogenesis, and hypoxia regulation. When stimulated with H₂O₂, LECs displayed a gene expression profile correlating with apoptotic and proliferative pathways, such as the MAPK signaling pathway and FoxO signaling pathway. The differentially expressed gene profiles of the two types of LECs (wild type and ATG7 deficient) under oxidation were distinct to a large extent. Furthermore, 1,341 up-regulated and 1912 down-regulated differential mRNAs and 263 up-regulated and 336 down-regulated differential lncRNAs between these two types of LECs subjected to H₂O₂ were detected, among which 292 mRNAs and 24 lncRNAs possibly interacted with ten cataract-related miRNAs. A competing endogenous lncRNA-miRNA-mRNA network based on such interactions was finally constructed.

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.

Proteostasis in aging-associated ocular disease

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

Diabetic Nephropathy: Pathogenesis to Cure

Diabetic nephropathy (DN) is a leading cause of end-stage renal disorder (ESRD). It is defined as the increase in urinary albumin excretion (UAE) when no other renal disease is present. DN is categorized into microalbuminuria and macroalbuminuria. Factors like high blood pressure, high blood sugar levels, genetics, oxidative stress, hemodynamic and metabolic changes affect DN. Hyperglycemia causes renal damage through activating protein kinase C (PKC), producing advanced end glycation products (AGEs) and reactive oxygen species (ROS). Growth factors, chemokines, cell adhesion molecules, inflammatory cytokines are found to be elevated in the renal tissues of the diabetic patient. Many different and new diagnostic methods and treatment options are available due to the increase in research efforts and progression in medical science. However, until now, no permanent cure is available. This article aims to explore the mechanism, diagnosis, and therapeutic strategies in current use for increasing the understanding of DN.

High glucose induces an early and transient cytoprotective autophagy in retinal Müller cells

PURPOSE

We investigated the autophagic response of rat Müller rMC-1 cells during a short-term high glucose challenge.

METHODS

rMC-1 cells were maintained in 5 mM glucose (LG) or exposed to 25 mM glucose (HG). Western blot analysis was used to evaluate the expression levels of markers of autophagy (LC3-II, p62) and glial activation (AQP4), as well as the activation of TRAF2/JNK, ERK and AKT pathways. Autophagic flux assessment was performed using the autophagy inhibitor chloroquine. ROS levels were measured by flow cytometry using dichlorofluorescein diacetate. ERK involvement in autophagy induction was addressed using the ERK inhibitor FR180204. The effect of autophagy inhibition on cell viability was evaluated by SRB assay.

RESULTS

Activation of autophagy was observed in the first 2-6 h of HG exposure. This early autophagic response was transient, not accompanied by an increase in AQP4 or in the phospho-activation of JNK, a key mediator of cellular response to oxidative stress, and required ERK activity. Cells exposed to HG had a lower viability upon autophagy inhibition by chloroquine, as compared to those maintained in LG.

CONCLUSION

A short-term HG challenge triggers in rMC-1 cells a process improving the ability to cope with stressful conditions, which involves ERK and an early and transient autophagy activation.

Downregulation of AMPK dependent FOXO3 and TFEB involves in the inhibition of autophagy in diabetic cataract

PURPOSE

Autophagy plays a crucial role in intracellular quality control of crystalline lens and AMPK has regulatory effect on autophagy. However, whether AMPK regulated autophagy is involved in diabetic cataract (DC) progression remains unknown. This study aims to investigate the AMPK-FOXO3 and AMPK-TFEB induced autophagy activity in DC patients.

MATERIALS AND METHODS

First, anterior capsule specimens from DC and age-related cataract (ARC) patients were obtained to compare the expression difference of autophagy-related genes. The phosphorylation levels of AMPK, AKT, and mTOR and the expression of FOXO3 and TFEB were measured. Then, human lens epithelial cells (LECs, SRA 01/04) were cultured with 30 mM or 5.5 mM glucose, and AMPK activator (AICAR) and inhibitor (Compound C) were applied to further investigate the regulatory role of AMPK on autophagy.

RESULTS

Compared with ARC patients, the expression of autophagy-related genes ATG5, FYCO1, ATG8, ATG12, Beclin1, and ULK1 in anterior capsules LECs of DC patients were significantly down-regulated. Meanwhile, AMPK and AMPK-dependent transcription factors, FOXO3 and TFEB were also inhibited. Similar results were found in high glucose (HG) treated SRA 01/04 model. Notably, this down-regulation of autophagy activity was rescued by AICAR in vitro, which was manifested by inhibition of AKT and mTOR phosphorylation and up-regulation of FOXO3, TFEB, Beclin1 and LC3B-II expression.

CONCLUSIONS

Down-regulation of AMPK-FOXO3 and AMPK-TFEB induced autophagy activity was found in both LECs of anterior capsule from DC patients and SRA 01/04 cells under HG condition, which may be the underlying mechanism of DC formation. Thus, targeting AMPK-induced autophagy may be a potential therapeutic approach for diabetic cataract.

Aged Nrf2-Null Mice Develop All Major Types of Age-Related Cataracts

Purpose

Age-related cataracts affect the majority of older adults and are a leading cause of blindness worldwide. Treatments that delay cataract onset or severity have the potential to delay cataract surgery, but require relevant animal models that recapitulate the major types of cataracts for their development. Unfortunately, few such models are available. Here, we report the lens phenotypes of aged mice lacking the critical antioxidant transcription factor Nfe2l2 (designated as Nrf2 −/−).

Methods

Three independent cohorts of Nrf2 −/− and wild-type C57BL/6J mice were evaluated for cataracts using combinations of slit lamp imaging, photography of freshly dissected lenses, and histology. Mice were fed high glycemic diets, low glycemic diets, regular chow ad libitum, or regular chow with 30% caloric restriction.

Results

Nrf2 −/− mice developed significant opacities between 11 and 15 months and developed advanced cortical, posterior subcapsular, anterior subcapsular, and nuclear cataracts. Cataracts occurred similarly in male mice fed high or low glycemic diets, and were also observed in 21-month male and female Nrf2 −/− mice fed ad libitum or 30% caloric restriction. Histological observation of 18-month cataractous lenses revealed significant disruption to fiber cell architecture and the retention of nuclei throughout the cortical region of the lens. However, fiber cell denucleation and initiation of lens differentiation was normal at birth, with the first abnormalities observed at 3 months.

Conclusions

Nrf2 −/− mice offer a tool to understand how defective antioxidant signaling causes multiple forms of cataract and may be useful for screening drugs to prevent or delay cataractogenesis in susceptible adults.

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.

Application of natural killer cells in pancreatic cancer

Pancreatic cancer, a highly malignant disease, is characterized by rapid progression and early metastasis. Although the integrative treatment of pancreatic cancer has made great progress, the prognosis of patients with advanced pancreatic cancer remains extremely poor. In recent years, with the advancements in tumor immunology, immunotherapy has become a promising remedy for pancreatic cancer. Natural killer (NK) cells are the key lymphocytes in the innate immune system. NK cell function does not require antigen pre-sensitization and is not major histocompatibility complex restricted. By targeting tumors or virus-infected cells, the cells play a key role in immune surveillance. Although several questions about NK cells in pancreatic cancer still need to be further studied, there are extensive theories supporting the clinical application prospects of NK cell immunotherapy in pancreatic cancer. Since very few studies have evaluated the role of NK cells in pancreatic cancer, this review provides a comprehensive update of the role of NK cells in pancreatic cancer immunotherapy.

Protective effect of syringic acid via restoring cells biomechanics and organelle structure in human lens epithelial cells

We have previously reported that syringic acid (SA) extracted from D. aurantiacum var. denneanum (kerr) may be used to prevent diabetic cataract (DC). However, the underlying mechanisms through which SA prevents DC in human lens epithelial cells (HLECs) remained unclear. In the present study, we employed single-molecule optics technologies, including transmission electron microscopy (TEM), atomic force microscopy (AFM), laser scanning confocal microscopy (LSCM) and Raman spectroscopy, to monitor the effect of SA on HLECs biomechanics and organelle structure in real-time. TEM suggested that SA improved the ultrastructure of HLECs with regard to nuclear chromatin condensation and reducing mitochondrial swelling and degeneration, which may aid in the maintenance of HLECs integrity in the presence of glucose. AFM revealed a reduced surface roughness and stiffness following SA treatment, suggesting an improved viscoelasticity of HELCs. Raman spectrometry and LSCM further revealed that these changes were related to a modification of cell liquidity and cytoskeletal structure by SA. Taken together, these results provide insights into the effects of SA on the biomechanics of HLECs and further strengthen the evidence for its potential use as a novel therapeutic strategy for DC prevention.