High glucose: activating autophagy and affecting the biological behavior of human lens epithelial cells

Recent progress and research trend of anti-cataract pharmacology therapy: A bibliometric analysis and literature review

Cataract is the leading cause of blindness worldwide. Cataract phacoemulsification combined with intraocular lens implantation causes great burden to global healthcare, especially for low- and middle-income countries. Such burden would be significantly relieved if cataracts can effectively be treated or delayed by non-surgical means. Excitingly, novel drugs have been developed to treat cataracts in recent decades. For example, oxysterols are found to be able to innovatively reverse lens clouding, novel nanotechnology-loaded drugs improve anti-cataract pharmacological effect, and traditional Chinese medicine demonstrates promising therapeutic effects against cataracts. In the present review, we performed bibliometric analysis to provide an overview perspective regarding the research status, hot topics, and academic trends in the field of anti-cataract pharmacology therapy. We further reviewed the curative effects and molecular mechanisms of anti-cataract drugs such as lanosterol, metformin, resveratrol and curcumin, and prospected the possibility of their clinical application in future.

Apoptosis of Lens Epithelial Cells and Expression of NLRP3-related Proteins in Patients with Diabetes and Cataract

AIM

To compare the expression of apoptosis-related factors and Nlrp3-related proteins in the lens epithelial cells (LECs) of patients with diabetes and cataract and patients with age-related cataract (ARC) alone.

METHODS

All patients were divided into four groups according to the presence or absence of diabetes mellitus (DM) and the degree of diabetic retinopathy (DR). LECs were obtained during cataract surgery. The expression levels of cleaved caspase-3, caspase-7, ASC, caspase-1and Nlrp3 in LECs were determined. And analyzed by age, course of DM, and HbA1c levels.

RESULTS

The incidence of LEC apoptosis and positive rates of cleaved caspase-3 and caspase-7 expression were significantly higher in the groups with DM (P<0.05).The positive expression rates of ASC, caspase-1, and Nlrp3 increased with longer duration of DM, increased HbA1c level, or advanced DR (P<0.05).

CONCLUSION

In cataract patients with DM, the expression of apoptosis-related factors in LECs increased. Nlrp3-related protein expression levels, diabetes duration, HbA1c levels, and extent of DR may be potential risk factors for diabetic cataract formation.

Status of higher TGF-β1 and TGF-β2 levels in the aqueous humour of patients with diabetes and cataracts

BACKGROUND

Transforming growth factor (TGF) is a cytokine that acts on the proliferation, migration, differentiation, and apoptosis of cells and the accumulation of extracellular matrix components. Very few studies have precisely evaluated the concentration of TGF-β in the aqueous humour (AH) of diabetic and cataract (DMC) eyes due to the low expression of proteins in the AH or other reasons. The concentrations of TGF-β1, -β2, and -β3 in the AH of the DMC group were compared with those of the age-related cataract (ARC) group.

METHODS

We collected AH and lens epithelium samples from 33 DMC patients and 36 ARC patients. Luminex liquid suspension chip detection was applied to detect the concentration of TGF-β1, -β2, and -β3 in the AH samples. The expression of TGFB1/2/3 in lens epithelium samples was determined by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

The concentrations of TGF-β1 and TGF-β2 in AH samples of DMC eyes were higher than those of ARC eyes. The differences in TGF-β1 and TGF-β2 between the two groups were statistically significant (P value = 0.001 for TGF-β1, P value = 0.023 for TGF-β2). The difference of the correlation between TGF-β1 and glycosylated haemoglobin was significant (P value = 0.011, and Pearson correlation coefficient = 0.306). The difference of the correlation between TGF-β2 and glycosylated haemoglobin was significant (P value = 0.026, and Pearson correlation coefficient = 0.269). The mRNA expression levels of TGFB1 and TGFB2 were upregulated in DMC epithelium samples compared with ARC epithelium samples. The differences in TGFB1 and TGFB2 between the two groups were statistically significant (P value for TGFB1 = 0.041, P value for TGFB2 = 0.021).

CONCLUSIONS

The concentrations of TGF-β1 and TGF-β2 in AH samples were significantly higher in DMC eyes than in ARC eyes. The higher the glycosylated haemoglobin was, the higher the concentrations of TGF-β1 and -β2 were. The mRNA expression of TGFB1 and TGFB2 was significantly upregulated in DMC epithelial samples compared with ARC epithelial samples, suggesting the proinflammatory status of the anterior chamber of DMC eyes.

Ghrelin Mitigates High-Glucose-Induced Oxidative Damage and Apoptosis in Lens Epithelial Cells

Oxidative stress induced by high glucose (HG) plays an important role in the mechanism of diabetic cataract. Evidence has shown that effects from oxidative stress induced damage of lens or human lens epithelial (HLE) cells. Antioxidant supplementation is a plausible strategy to avoid oxidative stress and maintain the function of lens. Ghrelin have been used in treatment of many diseases. In this study, we found that ghrelin attenuated HG-induced loss of cell viability, reduced oxidative damage, and cell apoptosis in HLE cells. Ghrelin inhibited apoptosis through the downregulation of Bax and the upregulation of Bcl-2. Our results suggest that ghrelin could be considered as a promising therapeutic intervention for diabetic cataract. We also observed rat lens transparent in cultured media and examined lens histopathological changes. The results showed that ghrelin could inhibit the histopathological injury of lenses and ultrastructural changes induced by HG. In conclusion, ghrelin may play a role in the treatment of ocular diseases involving diabetic cataract.

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.

Short-wavelength blue light contributes to the pyroptosis of human lens epithelial cells (hLECs)

PURPOSE

The purpose of this study is to examine the effect of short-wavelength blue light (SWBL) on cultured human lens epithelial cells (hLECs). The pathogenesis of cataracts after SWBL exposure is discussed.

METHODS

HLE-B3 hLECs were randomly divided into 3 groups: the NC group, which was grown in a dark incubator; the acetyl (Ac)-Tyr-Val-Ala-Asp-chloromethyl ketone (AC-YVAD-CMK) treatment group; and the SWBL exposure group. After SWBL (2500 lux) irradiation (for 8, 16, 24, and 32 h), caspase-1 and gasdermin D (GSDMD) expression levels in HLE-B3 hLECs were examined using ELISA, immunofluorescence staining, and Western blotting analyses. Double-positive staining of hLECs for activated and inhibited caspase-1 was used to determine pyroptosis in HLE-B3 hLECs.

RESULTS

SWBL led to hLEC death, but a caspase-1 inhibitor suppressed cell death. The flow cytometry results also confirmed the dose-dependent effect of SWBL irradiation on the pyroptotic death of hLECs. Caspase-1 and GSDMD expression levels in all hLEC groups changed with blue light exposure times (8, 16, 24, and 32 h) and were higher in the AC-YVAD-CMK and SWBL exposure groups than in the NC group. The immunofluorescence results revealed higher GSDMD-N expression in the cell membrane of both the AC-YVAD-CMK and SWBL exposure groups than in the NC group.

CONCLUSIONS

Based on the data, SWBL induces pyroptotic programmed cell death by activating the GSDMD signalling axis in HLE-B3 hLECs. These results provide new insights into the exploitation of new candidates for the prevention of cataracts.

Autophagy inhibition attenuates TGF-β2-induced epithelial-mesenchymal transition in lens epithelial cells

AIMS

Autophagy has been reported to play an essential role in fibrotic disorders. Known as fibrotic cataract, posterior capsular opacification (PCO) result from pathological epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs). This study aims to identify the role and potential mechanism of autophagy in TGF-β2-induced EMT in LECs.

MAIN METHODS

Primary rabbit LECs were treated with TGF-β2 to induce EMT as a model of fibrotic cataract in vitro. 3-methyladenine, chloroquine, bafilomycin A1, and gene silencing of autophagy-related protein 7 (ATG7) were treated in LECs for autophagy inhibition, while rapamycin was utilized for autophagy activation. The expression levels of EMT/autophagy-associated markers were analyzed by qRT-PCR, western blotting, immunofluorescence and transmission electron microscopy. We additionally examined cell migration ability with transwell migration assay and wound healing assay.

KEY FINDINGS

TGF-β2 promoted autophagy flux during EMT progression of LECs in a time-dependent manner. Autophagy activation by rapamycin enhanced TGF-β2-triggered fibrogenic responses and cell migration in LECs, whereas pharmacological inhibition of autophagy alleviated TGF-β2-induced increases of EMT markers and cell migration of LECs. In addition, the phosphorylation of Smad2/3 induced by TGF-β2 was suppressed through autophagy inhibition, while it was promoted upon autophagy activation, indicating that TGF-β2/Smad signaling was involved in the modulation of autophagy on EMT in LECs. Furthermore, ATG7-silenced LECs exerted anti-fibrosis effect induced by TGF-β2 through downregulation of autophagy.

SIGNIFICANCE

Intervention/inhibition of autophagy could attenuate TGF-β2-induced EMT in LECs, which provides autophagy-related insights on preventing and treating the fibrotic cataract or other fibrotic diseases.

LncRNA KCNQ1OT1 knockdown inhibits viability, migration and epithelial-mesenchymal transition in human lens epithelial cells via miR-26a-5p/ITGAV/TGF-beta/Smad3 axis

BACKGROUND

Long noncoding RNA potassium voltage-gated channel subfamily Q member 1 opposite strand/antisense transcript 1 (KCNQ1OT1) takes part in diabetic cataract progression. This research aims to analyze the function and mechanism of KCNQ1OT1 on viability, migration and epithelial-mesenchymal transition (EMT) in lens epithelial cells.

METHODS

20 diabetic cataract posterior lens capsule tissues and normal samples were collected. Lens epithelial cells (SRA01/04) were stimulated via high glucose (HG). The levels of KCNQ1OT1, miR-26a-5p, integrin αV (ITGAV), TGF-β, Smad3 and phosphorylated (p)-Smad3 were measured via quantitative real-time polymerase chain reaction or Western blot. Cell viability, migration and EMT were analyzed via MTT, wound healing, transwell and Western blot assays. The target relationship between miR-26a-5p and KCNQ1OT1 or ITGAV was determined via luciferase reporter assay.

RESULTS

KCNQ1OT1 was up-regulated and miR-26a-5p level was reduced in diabetic cataract tissues and HG-treated SRA01/04 cells. Silence of KCNQ1OT1 or miR-26a-5p up-regulation repressed cell viability, migration and EMT in SRA01/04 cells stimulated via HG. KCNQ1OT1 could target miR-26a-5p and controlled cell viability, migration and EMT via regulating miR-26a-5p. ITGAV was targeted via miR-26a-5p and positively regulated via KCNQ1OT1. ITGAV overexpression promoted cell viability, migration and EMT in HG-treated SRA01/04 cells, which were mitigated by KCNQ1OT1 silence. KCNQ1OT1 knockdown mitigated HG-induced the activation of TGF-β/Smad3 signaling by regulating miR-26a-5p.

CONCLUSION

KCNQ1OT1 knockdown represses cell viability, migration and EMT through miR-26a-5p/ITGAV/TGF-β/Smad3 axis in SRA01/04 cells under HG condition, providing a new target for the treatment of diabetic cataract.

Novel biomarkers for the evaluation of aging-induced proteinopathies

Proteinopathies are characterized by aging related accumulation of misfolded protein aggregates. Irreversible covalent modifications of aging proteins may significantly affect the native three dimentional conformation of proteins, alter their function and lead to accumulation of misfolded protein as dysfunctional aggregates. Protein misfolding and accumulation of aberrant proteins are known to be associated with aging-induced proteinopathies such as amyloid ß and tau proteins in Alzheimer's disease, α-synuclein in Parkinson's disease and islet amyloid polypeptides in Type 2 diabetes mellitus. Protein oxidation processes such as S-nitrosylation, dityrosine formation and some of the newly elucidated processes such as carbamylation and citrullination recently drew the attention of researchers in the field of Gerontology. Studying over these processes and illuminating their relations between proteinopathies may help to diagnose early and even to treat age related disorders. Therefore, we have chosen to concentrate on aging-induced proteinopathic nature of these novel protein modifications in this review.