Upregulation of miR-630 Induced by Oxidative Damage Resists Cell Migration Through Targeting ALCAM in Human Lens Epithelium Cells

Cataractogenesis and molecular pathways, with reactive free oxygen species as a common pathway

Slowing down or stopping the natural process of cataractogenesis is certainly a challenge for those who today propose an option other than surgery. Addressing the same problem in different ways constitutes a new approach to solving what is today the number one cause of reversible blindness worldwide. The technological revolution, as well as the advances in the biological sciences, allows us to conceive mechanisms never thought of before to stop the process that, as a common pathway, constitutes opacification of the crystalline lens. A new dawn for cataracts is coming through molecular, newly-discovered mechanisms. Cataractogenesis and molecular pathways have reactive free oxygen species as a common pathway. Surgical removal is today's gold standard, but perhaps not for much longer.

CircMED12L Protects Against Hydrogen Peroxide-induced Apoptotic and Oxidative Injury in Human Lens Epithelial Cells by miR-34a-5p/ALCAM axis

PURPOSE

Cataract is the leading cause of visual impairment and reversible blindness. Despite advances in surgical removal of cataracts, cataract continues to be a leading public-health issue due to the complications after surgery. Circular RNAs (circRNAs) have been showed to be implicated in the pathophysiology of age-related cataract (ARC). Herein, this work elucidated the role and mechanism of circMED12L in the process of ARC.

METHODS

Human lens epithelial cells (HLECs) were exposed to hydrogen peroxide (H₂O₂) in experimental groups. Levels of genes and proteins were measured by qRT-PCR and western blotting. Cell growth was evaluated by Cell Counting Kit-8 (CCK-8) assay and flow cytometry, respectively. The oxidative stress was assessed by detecting the activity of malondialdehyde, catalase, and superoxide dismutase. The interaction between miR-34a-5p and circMED12L or ALCAM (activated leukocyte cell adhesion molecule) was validated using dual-luciferase reporter and RNA immunoprecipitation assays.

RESULTS

CircMED12L expression was lower in the lens epithelium of ARC patients and H₂O₂-induced HLECs compared with the normal individuals and untreated cells. Functionally, forced expression of circMED12L could alleviate H₂O₂-induced viability inhibition, as well as apoptotic and oxidative injury in HLECs. Mechanistically, circMED12L/miR-34a-5p/ALCAM constituted a feedback loop in HLECs. MiR-34a-5p was increased, while ALCAM was decreased in ARC patients and H₂O₂-induced HLECs. High expression of miR-34a-5p reversed the protective effects of circMED12L on HLECs under H₂O₂ treatment. Besides, inhibition of miR-34a-5p could repress H₂O₂-induced apoptotic and oxidative injury in HLECs, which were abolished by subsequent ALCAM knockdown.

CONCLUSION

Overexpression of circMED12L could protect against H₂O₂-induced apoptosis and oxidative stress in HLECs by miR-34a-5p/ALCAM axis.

Noncoding RNAs in cataract formation: star molecules emerge in an endless stream

For decades, research on the pathological mechanism of cataracts has usually focused on the abnormal protein changes caused by a series of risk factors. However, an entire class of molecules, termed non-coding RNA (ncRNA), was discovered in recent years and proven to be heavily involved in cataract formation. Recent studies have recognized the key regulatory roles of ncRNAs in cataracts by shaping cellular activities such as proliferation, apoptosis, migration and epithelial-mesenchymal transition (EMT). This review summarizes our current insight into the biogenesis, properties and functions of ncRNAs and then discusses the development of research on ncRNAs in cataracts. Considering the significant role of ncRNA in cataract formation, research on novel associated regulatory mechanisms is urgently needed, and the development of therapeutic alternatives for the treatment of cataracts seems promising.

MiR-34a-5p negatively regulates oxidative stress on lens epithelial cells by silencing GPX3 - a novel target

Purpose MiR-34a-5p is reported to be related with age-related nuclear cataract. This study investigated the mechanism of miR-34a-5p in the regulation of oxidative stress on lens epithelial cells.Methods The three candidate miRNAs were screened by CCK-8 assays after transfection of mimics or inhibitor in H₂O₂-treated HLE-B3 cells. The apoptosis, ROS level and GPX activity of HLE-B3 cells transfected with miR-34a-5p mimics or inhibitor were analysed by flow cytometry, cellular ROS and GPX activity test. The target genes of miR-34a-5p were predicted by proteomic and bioinformatic analysis. The relationship between miR-34a-5p and GPX3 were internally validated by qRT-PCR and Western blot and externally verified by dual-luciferase reporter assay. The effect of miR-34a-5p-GPX3 axis on regulation of oxidative stress in HLE-B3 cells were conducted by overexpression of GPX3 and tested by flow cytometry analysis, cellular ROS and GPX detection.Results The viability of H₂O₂-treated HLE-B3 cells were weakened by up-regulated miR-34a-5p. Cell apoptosis and oxidative damage were also induced by overexpression of miR-34a-5p. GPX3 and SRC were identified as target genes of miR-34a-5p by combined analysis of proteomic and bioinformatics, while GPX3 was selected for further research for its connection with anti-oxidation. Western blot and qRT-PCR tests proved that GPX3 is negatively regulated by miR-34a-5p. Dual-luciferase reporter assay verified that GPX3 is the direct target of miR-34a-5p. The increased oxidative stress induced by transfection of miR-34a-5p mimics in H₂O₂-treated HLE-B3 cells was attenuated by overexpression of GPX3.Conclusions MiR-34a-5p is a negative regulator of oxidative stress on lens epithelial cells and the mechanism is by silencing the expression of GPX3. These data suggests that miR-34a-5p may be a potential novel therapeutic target for the prevention and treatment of age-related cataract.

MicroRNA Alterations Induced in Human Skin by Diesel Fumes, Ozone, and UV Radiation

Epigenetic alterations are a driving force of the carcinogenesis process. MicroRNAs play a role in silencing mutated oncogenes, thus defending the cell against the adverse consequences of genotoxic damages induced by environmental pollutants. These processes have been well investigated in lungs; however, although skin is directly exposed to a great variety of environmental pollutants, more research is needed to better understand the effect on cutaneous tissue. Therefore, we investigated microRNA alteration in human skin biopsies exposed to diesel fumes, ozone, and UV light for over 24 h of exposure. UV and ozone-induced microRNA alteration right after exposure, while the peak of their deregulations induced by diesel fumes was reached only at the end of the 24 h. Diesel fumes mainly altered microRNAs involved in the carcinogenesis process, ozone in apoptosis, and UV in DNA repair. Accordingly, each tested pollutant induced a specific pattern of microRNA alteration in skin related to the intrinsic mechanisms activated by the specific pollutant. These alterations, over a short time basis, reflect adaptive events aimed at defending the tissue against damages. Conversely, whenever environmental exposure lasts for a long time, the irreversible alteration of the microRNA machinery results in epigenetic damage contributing to the pathogenesis of inflammation, dysplasia, and cancer induced by environmental pollutants.

TGF-β2-induced circ-PRDM5 regulates migration, invasion, and EMT through the miR-92b-3p/COL1A2 pathway in human lens epithelial cells

CircRNA circ-PRDM5 (PR/SET domain 5) (circ-PRDM5) is overexpressed in age-related cataracts. Nevertheless, the biological role of circ-PRDM5 in posterior capsule opacities (PCO) (a common complication after cataract surgery) is unclear. Human lens epithelial cells SRA01/04 (LECs) were stimulated with TGF-β2 (transforming growth factor beta-2) to mimic the PCO model in vitro. Cell viability, migration, and invasion were determined by MTT, transwell, or wound-healing assays. Protein levels of EMT (epithelial-to-mesenchymal transition) markers and COL1A2 (collagen type I alpha 2 chain) were analyzed by western blotting (WB). Relative expression of circ-PRDM5, miR-92b-3p, and COL1A2 mRNA was analyzed by qRT-PCR. The targeting relationship was confirmed by dual-luciferase reporter and RIP assays. We observed that circ-PRDM5 and COL1A2 were upregulated in PCO tissues and TGF-β2-treated LECs, while miR-92b-3p was downregulated. Both circ-PRDM5 and COL1A2 knockdown impaired TGF-β2-induced LEC migration, invasion, and EMT. Also, circ-PRDM5 could adsorb miR-92b-3p to regulate COL1A2 expression. Furthermore, miR-92b-3p inhibitor offset circ-PRDM5 knockdown-mediated influence on migration, invasion, and EMT of LECs under TGF-β2 stimulation. Also, COL1A2 overexpression overturned the repressive influence of miR-92b-3p mimic on TGF-β2-induced LEC migration, invasion, and EMT. In summary, TGF-β2-induced circ-PRDM5 facilitated LEC migration, invasion, and EMT by adsorbing miR-92b-3p and increasing COL1A2 expression, offering new insights into the development of PCO.

Circ-MKLN1/miR-377-3p/CTGF Axis Regulates the TGF-β2-induced Posterior Capsular Opacification in SRA01/04 Cells

OBJECTIVE

Posterior capsular opacification (PCO) is a common postoperative ocular complication after cataract surgery. Little research focused on the regulation of circular RNAs (circRNAs) in PCO. This study was designed to investigate the function of circRNA-muskelin (circ-MKLN1) in PCO.

METHODS

SRA01/04 cells were treated with transforming growth factor (TGF)-β2. Cell viability was analyzed by Cell Counting Kit-8 (CCK-8) assay. Transwell assay was used for cell migration and invasion detection. Cell migration was also measured by wound healing assay. Epithelial-mesenchymal transition (EMT)-related proteins and connective tissue growth factor (CTGF) were quantified using western blot.

RESULTS

Cell viability, migration, invasion and EMT process in SRA01/04 cells were facilitated by TGF-β2. Circ-MKLN1 expression was enhanced in 17 PCO lens samples relative to 19 normal lens samples and TGF-β2-treated SRA01/04 cells contrasted to control cells. Downregulation of circ-MKLN1 inhibited the effects of TGF-β2 on SRA01/04 cells. Circ-MKLN1 targeted miR-377-3p and the regulation of si-circ-MKLN1 for the TGF-β2-induced influences was related to the upregulation of miR-377-3p. CTGF was the target gene for miR-377-3p. CTGF knockdown also abolished the TGF-β2-mediated cell growth, migration and invasion of SRA01/04 cells. The function of miR-377-3p was achieved by reducing the CTGF level. TGF-β2-induced CTGF expression promotion was alleviated by si-circ-MKLN1 through upregulating the expression of miR-377-3p.

CONCLUSION

These results showed that circ-MKLN1 contributed to the progression of PCO in vitro by increasing the CTGF expression via sponging miR-377-3p. Circ-MKLN1 might be important for improving the molecular target therapy in PCO.

CircPAG1 Inhibits the High Glucose-Induced Lens Epithelial Cell Injury by Sponging miR-630 and Upregulating EPHA2

Background: Circular RNAs (circRNAs) have been considered as vital regulators in the progression of human ocular diseases, including diabetic cataract (DC). This report was designed to research the biological role of circRNA phosphoprotein associated with glycosphingolipid-enriched microdomains 1 (circPAG1) in high glucose (HG)-induced lens epithelial damages.Methods: Lens epithelial damage in DC was investigated by the effects of 25 mM glucose (HG) on human lens epithelial cells (HLE-B3). CircPAG1, microRNA-630 (miR-630), and ephrin type-A receptor 2 (EPHA2) levels were examined by the quantitative real-time polymerase chain reaction (qRT-PCR). Cell proliferation analysis was performed by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) assay and colony formation assay. Cell apoptosis was measured through flow cytometry. Protein levels were detected using western blot. Oxidative stress was determined by malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-PX) levels via the corresponding kits. Dual-luciferase reporter and RNA immunoprecipitation (RIP) and RNA pull-down assays were used for target binding analysis.Results: CircPAG1 expression was downregulated in lens samples of DC patients and HG-treated lens epithelial cells. HG inhibited cell growth but promoted apoptosis and oxidative stress in HLE-B3 cells, while circPAG1 overexpression relieved these damages. Moreover, circPAG1 was identified as a molecular sponge for miR-630. HG-induced cell injury was also attenuated by the inhibition of miR-630, and the function of circPAG1 was related to its sponge effect on miR-630. In addition, miR-630 directly targeted EPHA2 and circPAG1 could regulate the EPHA2 expression via sponging miR-630. Furthermore, we found that the protective role of circPAG1 against the HG-induced cell injury was ascribed to the upregulation of EPHA2.Conclusion: Our evidence suggested that circPAG1 alleviated cell damages in HG-treated human lens epithelial cells by regulating the miR-630/EPHA2 axis.

Moderate oxidative stress promotes epithelial-mesenchymal transition in the lens epithelial cells via the TGF-β/Smad and Wnt/β-catenin pathways

The epithelial-mesenchymal transition (EMT) plays a significant role in fibrosis and migration of lens epithelial cells (LECs), and eventually induces posterior capsule opacification (PCO). In the past, it was generally believed that the TGF-β/Smad pathway regulates lens EMT. A recent study found that attenuated glutathione level promotes LECs EMT via the Wnt/β-catenin pathway, which suggests a more complex pathogenesis of PCO. To test the hypothesis, we used the mouse cataract surgery PCO model and tested both canonical Wnt/β-catenin and TGF-β/Smad signaling pathways. The results showed that both TGF-β/Smad and Wnt/β-catenin pathways were activated during the lens capsule fibrosis. Compared with the freshly isolated posterior capsule, the expression level of phosphorylated Smad2 was highest at day3 and then slightly decreased, but the expression level of Wnt10a gradually increased from day0 to day7. It shows that these two pathways are involved in the lens epithelium's fibrotic process and may play different roles in different periods. Subsequently, we established oxidative stress-induced EMT model in primary porcine lens epithelial cells and found that both the TGF-β/Smad and Wnt/β-catenin pathways were activated. Further study suggests that block Wnt/β-catenin pathway using XAV939 alone or block TGF-β/Smad pathway using LY2109761 could partially block pLECs fibrosis, but blocking Wnt/β-catenin and TGF-β/Smad pathway using combined XAV939 and LY2109761 could completely block pLECs fibrosis. In conclusion, this study demonstrates that both TGF-β/Smad and canonical Wnt/β-catenin pathways play a significant role in regulating epithelial-mesenchymal transformation of lens epithelial cells but might be in a different stage.

Protective Effects of Nicotinamide Riboside on H2O2-induced Oxidative Damage in Lens Epithelial Cells

Purpose: To investigate the protective effects of nicotinamide riboside (NR) on oxidative damage in hydrogen peroxide (H₂O₂)-exposed human lens epithelial cell lines (SRA01/04) and the possible mechanisms underlying its protective effects.Materials and methods: SRA01/04 cells were divided into three groups: the control (CON) group, model (H₂O₂) group and treatment (NR+H₂O₂) group. Superoxide dismutase (SOD), catalase (CAT) and total glutathione (GSH) levels were detected to evaluate oxidative damage induced by different concentrations of H₂O₂ in SRA01/04 cells. After SRA01/04 cells were treated with NR and/or H₂O₂, cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and Hoechst staining, cell apoptosis was analysed using flow cytometry, reactive oxygen species (ROS) were measured with the DCFH-DA probe, and mitochondria were stained with MitoTracker to measure the mitochondrial membrane potential (MMP). In addition, western blotting was performed to detect the levels of proteins associated with apoptosis and related signalling pathways.Results: H₂O₂ induced oxidative damage in SRA01/04 cells by inhibiting the activity of SOD and CAT and reducing total GSH levels. Treatment of SRA01/04 cells with NR significantly increased cell viability and reduced cell apoptosis and ROS generation, whereas SOD and CAT activities and total GSH and MMP levels were improved by the NR treatment in an H₂O₂-exposed cell model. Furthermore, NR significantly inhibited the activation of the MAPK pathway but promoted activation of the JAK2/Stat3 pathway compared with the model group.Conclusions: NR may alleviate oxidative damage by targeting the MAPK and JAK2/Stat3 pathways in H₂O₂-treated SRA01/04 cells. NR may represent anovel drug for preventing or treating cataracts.