Dynamic and differential regulation in the microRNA expression in the developing and mature cataractous rat lens

Let-7c-3p suppresses lens epithelial-mesenchymal transition by inhibiting cadherin-11 expression in fibrotic cataract

Fibrotic cataract, including anterior subcapsular cataract (ASC) and posterior capsule opacification, always lead to visual impairment. Epithelial-mesenchymal transition (EMT) is a well-known event that causes phenotypic alterations in lens epithelial cells (LECs) during lens fibrosis. Accumulating studies have demonstrated that microRNAs are important regulators of EMT and fibrosis. However, the evidence explaining how microRNAs modulate the behavior and alter the cellular phenotypes of the lens epithelium in fibrotic cataract is insufficient. In this study, we found that hsa-let-7c-3p is downregulated in LECs in human ASC in vivo as well as in TGFβ2-induced EMT in vitro, indicating that hsa-let-7c-3p may participate in modulating the profibrotic processes in the lens. We then demonstrated that overexpression of hsa-let-7c-3p markedly suppressed human LEC proliferation and migration and attenuated TGFβ2-induced EMT and injury-induced ASC in a mouse model. In addition, hsa-let-7c-3p mediated lens fibrosis by directly targeting the CDH11 gene, which encodes cadherin-11 protein, an important mediator in the EMT signaling pathway. It decreased cadherin-11 protein expression at the posttranscriptional level but not at the transcriptional level by binding to a specific site in the 3-untranslated region (3'-UTR) of CDH11 mRNA. Moreover, blockade of cadherin-11 expression with a specific short hairpin RNA reversed TGFβ2-induced EMT in LECs in vitro. Collectively, these data demonstrated that hsa-let-7c-3p plays a clear role in attenuating ASC development and may be a novel candidate therapeutic for halting fibrosis and maintaining vision.

Transcriptome sequencing and microRNA-mRNA regulatory network construction in the lens from a Na2SeO3-induced Sprague Dawley rat cataract model

BACKGROUND

A sight-threatening, cataract is a common degenerative disease of the ocular lens. This study aimed to explore the regulatory mechanism of age-related cataract (ARC) formation and progression.

METHODS

Cataracts in Sprague Dawley rats were induced by adopting the method that injected selenite subcutaneously in the nape. We performed high-throughput RNA sequencing technology to identify the mRNA and microRNA(miRNA) expression profiles of the capsular membrane of the lens from Na2SeO3-induced and saline-injected Sprague Dawley rats. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were carried out to forecast the regulatory and functional role of mRNAs in cataracts by DAVID and Metascape. The protein-protein interaction(PPI) network of differentially expressed mRNA(DEmRNAs) was built via the STRING. Target miRNAs of hub genes were predicted by miRBD and TargetScan. Furthermore, differentially expressed miRNA(DEmiRNAs) were selected as hub genes' targets, validated by quantitative real-time polymerase chain reaction(qRT-PCR), and a DEmiRNA-DEmRNA regulatory network was constructed via Cytoscape.

RESULT

In total, 329 DEmRNAs including 40 upregulated and 289 downregulated genes were identified. Forty seven DEmiRNAs including 29 upregulated and 18 downregulated miRNAs were detected. The DEmRNAs are involved in lens development, visual perception, and aging-related biological processes. A protein-protein interaction network including 274 node genes was constructed to explore the interactions of DEmRNAs. Furthermore, a DEmiRNA-DEmRNA regulatory network related to cataracts was constructed, including 8 hub DEmRNAs, and 8 key DEmiRNAs which were confirmed by qRT-PCR analysis.

CONCLUSION

We identified several differentially expressed genes and established a miRNA-mRNA-regulated network in a Na2SeO3-induced Sprague Dawley rat cataract model. These results may provide novel insights into the clinical treatment of cataracts, and the hub DEmRNAs and key DEmiRNAs could be potential therapeutic targets for ARC.

RNA-binding proteins and post-transcriptional regulation in lens biology and cataract: Mediating spatiotemporal expression of key factors that control the cell cycle, transcription, cytoskeleton and transparency

Development of the ocular lens - a transparent tissue capable of sustaining frequent shape changes for optimal focusing power - pushes the boundaries of what cells can achieve using the molecular toolkit encoded by their genomes. The mammalian lens contains broadly two types of cells, the anteriorly located monolayer of epithelial cells which, at the equatorial region of the lens, initiate differentiation into fiber cells that contribute to the bulk of the tissue. This differentiation program involves massive upregulation of select fiber cell-expressed RNAs and their subsequent translation into high amounts of proteins, such as crystallins. But intriguingly, fiber cells achieve this while also simultaneously undergoing significant morphological changes such as elongation - involving about 1000-fold length-wise increase - and migration, which requires modulation of cytoskeletal and cell adhesion factors. Adding further to the challenges, these molecular and cellular events have to be coordinated as fiber cells progress toward loss of their nuclei and organelles, which irreversibly compromises their potential for harnessing genetically hardwired information. A long-standing question is how processes downstream of signaling and transcription, which may also participate in feedback regulation, contribute toward orchestrating these cellular differentiation events in the lens. It is now becoming clear from findings over the past decade that post-transcriptional gene expression regulatory mechanisms are critical in controlling cellular proteomes and coordinating key processes in lens development and fiber cell differentiation. Indeed, RNA-binding proteins (RBPs) such as Caprin2, Celf1, Rbm24 and Tdrd7 have now been described in mediating post-transcriptional control over key factors (e.g. Actn2, Cdkn1a (p21Cip1), Cdkn1b (p27Kip1), various crystallins, Dnase2b, Hspb1, Pax6, Prox1, Sox2) that are variously involved in cell cycle, transcription, cytoskeleton maintenance and differentiation in the lens. Furthermore, deficiencies of these RBPs have been shown to result in various eye and lens defects and/or cataract. Because fiber cell differentiation in the lens occurs throughout life, the underlying regulatory mechanisms operational in development are expected to also be recruited for the maintenance of transparency in aged lenses. Indeed, in support of this, TDRD7 and CAPRIN2 loci have been linked to age-related cataract in humans. Here, I will review the role of key RBPs in the lens and their importance in understanding the pathology of lens defects. I will discuss advances in RBP-based gene expression control, in general, and the important challenges that need to be addressed in the lens to define the mechanisms that determine the epithelial and fiber cell proteome. Finally, I will also discuss in detail several key future directions including the application of bioinformatics approaches such as iSyTE to study RBP-based post-transcriptional gene expression control in the aging lens and in the context of age-related cataract.

Role of Decorin in Posterior Capsule Opacification and Eye Lens Development

Decorin (DCN) is involved in a variety of physiological and pathological processes. Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) has been proposed as a major cause for the development of posterior capsule opacification (PCO) after cataract surgery. We investigated the plausible target gene(s) that suppress PCO. The expression of Dcn was significantly upregulated in rat PCO tissues compared to that observed in the control using a microarray-based approach. LECs treated with fibroblast growth factor (FGF) 2 displayed an enhanced level of DCN expression, while LECs treated with transforming growth factor (TGF)β-2 showed a decrease in DCN expression. The expression of tropomyosin 1 (Tpm1), a marker of lens EMT increased after the addition of TGFβ-2 in human LEC; however, upregulation of Tpm1 mRNA or protein expression was reduced in human LECs overexpressing human DCN (hDCN). No phenotypic changes were observed in the lenses of 8- and 48-week-old transgenic mice for lens-specific hDCN (hDCN-Tg). Injury-induced EMT of the mouse lens, and the expression patterns of α smooth muscle actin, were attenuated in hDCN-Tg mice lenses. Overexpression of DCN inhibited the TGFβ-2-induced upregulation of Tpm1 and EMT observed during wound healing of the lens, but it did not affect mouse lens morphology until 48 weeks of age. Our findings demonstrate that DCN plays a significant role in regulating EMT formation of LECs and PCO, and suggest that for therapeutic intervention, maintenance of physiological expression of DCN is essential to attenuate EMT progression and PCO formation.

MicroRNA miR-29c-3p modulates FOS expression to repress EMT and cell proliferation while induces apoptosis in TGF-β2-treated lens epithelial cells regulated by lncRNA KCNQ1OT1

Age-related cataract (ARC) is a main cause of blindness for elderly people. MicroRNA hsa_miR-29c-3p (miR-29c-3p) was implicated in many biological processes in complicated diseases. However, the biological mechanism of miR-29c-3p in ARC is still undefined. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that miR-29c-3p was lowly expressed, while FBJ murine osteosarcoma viral oncogene homolog (FOS) and KCNQ1 overlapping transcript 1 (KCNQ1OT1) were highly expressed in cataract tissues and in TGF-β2-treated SRA01/04 cells. Western blot assay indicated that TGF-β2 could promote epithelial-mesenchymal transition (EMT). Moreover, our data suggested that miR-29c-3p overexpression suppressed EMT, cell proliferation and promoted apoptosis in TGF-β2-treated SRA01/04 cells. The dual-luciferase reporter assay verified that FOS was a target of miR-29c-3p and miR-29c-3p was directly targeted by KCNQ1OT1. Furthermore, KCNQ1OT1 could regulate FOS expression by sponging miR-29c-3p. Functional assays revealed that miR-29c-3p regulated FOS to repress EMT, cell proliferation and facilitate apoptosis in TGF-β2-treated SRA01/04 cells mediated by KCNQ1OT1. In conclusion, KCNQ1OT1/miR-29c-3p/FOS axis played a vital role in the progression of ARC.

TGF-β regulation of microRNA miR-497-5p and ocular lens epithelial cell mesenchymal transition

The purpose of this study was to investigate the role of a human lens microRNA (miR-497-5p) in regulating epithelialmesenchymal transition (EMT) under the control of transforming growth factor beta (TGF-β). A microRNA array was used to evaluate the microRNA profiles of untreated and TGF-β-treated human lens epithelial cells in culture. This showed that TGF-β treatment led to the upregulation of 96 microRNAs and downregulation of 39 microRNAs. Thirteen microRNAs were predicted to be involved in the pathogenesis of posterior capsule opacification (PCO). Meanwhile, overexpression of miR-497-5p suppressed cell proliferation and EMT 48 h post-transfection, and inhibition of miR-497-5p accelerated cell proliferation and EMT. Treatment with TGF-β inhibited the expression of miR-497-5p, but not cell proliferation. miR-497-5p was also found to regulate the level of CCNE1 and FGF7, which are reported to be actively involved in EMT. CCNE1 and FGF7 were bona fide targets of miR-497-5p. The results suggest that miR-497-5p participates in the direct regulation of lens epithelial cell EMT and is regulated by TGF-β. miR-497-5p may be a novel target for PCO therapy.

MicroRNA-23b-3p promotes the proliferation, migration, and epithelial-mesenchymal transition of lens epithelial cells by targeting Sprouty2

Cataract, opacification of the lens, is one of the most important reasons of visual impairment and blindness. Though microRNAs (miRNAs) have been demonstrated to play important roles in cataractogenesis, the underlying molecular mechanisms in this progress remain obscure. In the present study, microRNA-23b-3p (miR-23b) overexpression promoted the proliferation, migration and epithelial-mesenchymal transition (EMT), whereas miR-23b knockdown markedly inhibited the proliferation, migration and TGF-β-induced EMT of lens epithelial cells (LECs). In TGF-β-induced LECs, the expression of miR-23b was markedly upregulated and the expression of Sprouty2 (SPRY2) was markedly downregulated, furthermore the mRNA and protein levels of SPRY2 were markedly decreased in miR-23b inhibitor-transfected LECs. We then performed a Dual-luciferase reporter assay to confirm that miR-23b directly targeted SPRY2. The promoted migration and EMT of LECs by enforced expression of miR-23b were suppressed by SPRY2 overexpression. The findings present the first evidence indicating that miR-23b can promote the proliferation, migration, and EMT of LECs by targeting SPRY2 and the inhibition of miR-23b may possess the therapeutic potential for cataract.

lncRNA H19 contributes to oxidative damage repair in the early age-related cataract by regulating miR-29a/TDG axis

Age‐related cataract (ARC) is caused by the exposure of the lens to UVB which promotes oxidative damage and cell death. This study aimed to explore the role of lncRNA H19 in oxidative damage repair in early ARC. lncRNAs sequencing technique was used to identify different lncRNAs in the lens of early ARC patients. Human lens epithelial cells (HLECs) were exposed to ultraviolet irradiation; and 8‐OHdG ELISA, Cell counting kit 8 (CCK8), EDU, flow cytometry and TUNEL assays were used to detect DNA damage, cell viability, proliferation and apoptosis. Luciferase assay was used to examine the interaction among H19, miR‐29a and thymine DNA glycosylase (TDG) 3'UTR. We found that lncRNA H19 and TDG were highly expressed while miR‐29a was down‐regulated in the three types of early ARC and HLECs exposed to ultraviolet irradiation, compared to respective controls. lncRNA H19 knockdown aggravated oxidative damage, reduced cell viability and proliferation, and promoted apoptosis in HLECs, while lncRNA H19 overexpression led to opposite effects in HLECs. Mechanistically, miR‐29a bound TDG 3'UTR to repress TDG expression. lncRNA H19 up‐regulated the expression of TDG by repressing miR‐29a because it acted as ceRNA through sponging miR‐29a. In conclusion, the interaction among lncRNA H19, miR‐29a and TDG is involved in early ARC. lncRNA H19 could be a useful marker of early ARC and oxidative damage repair pathway of lncRNA H19/miR‐29a/TDG may be a promising target for the treatment of ARC.

microRNA-378a Regulates the Reactive Oxygen Species (ROS)/Phosphatidylinositol 3-Kinases (PI3K)/AKT Signaling Pathway in Human Lens Epithelial Cells and Cataract

BACKGROUND Cataract is associated with increased apoptosis of the epithelial cells of the ocular lens. Previous studies have shown that microRNA-378a (miR-378a) has a role in the development of cataract, but the molecular mechanisms remain unclear. This study aimed to investigate the effects of miR-378a in human lens epithelial cells (HLECs) in vitro and normal lens tissues and cataract tissues. MATERIAL AND METHODS HLECs were grown in culture. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blot were used to examine gene expression levels. The MTT and TUNEL assay measured cell growth and apoptosis. Changes in the fluorescence ratio of ethidium to dihydroethidium (E: DHE) and in 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (C-H₂DCFDA) were used to detect superoxide (O₂⁻) and hydrogen peroxide (H₂O₂). The expression levels of miR-378a and the superoxide dismutase 1 gene (SOD1) were measured in normal human lens tissues and cataract tissues. RESULTS Upregulation of miR-378a reduced the expression of SOD1. Levels of O₂⁻ were upregulated and H₂O₂ was slightly down-regulated by miR-378a. The use of a miR-378a mimic suppressed cell growth and enhanced apoptosis of HLECs, which were reversed by the use of a miR-378a inhibitor. SOD1 overexpression rescued the miR-378a-induced phenotypes of HLEC cells. Treatment with the PI3K inhibitor, LY294002, reversed miR-378a and ROS-regulated proliferation and apoptosis of HLEC cells. Also, miR-378a was upregulated, and SOD1 was down-regulated in human cataract tissues. CONCLUSIONS In HLECs, expression of miR-378a regulated ROS and PI3K/AKT signaling, and miR-378a was upregulated, and SOD1 was down-regulated in human cataract tissue.

MicroRNAs: new players in cataract

Cataract is the most common cause of blindness worldwide. Multiple factors such as aging, eye injury, diabetes mellitus, ultraviolet exposure, drug use and other ocular diseases are etiologically linked to cataractogenesis. Due to a rapid increase in aging population, age-related cataract has become the leading cause of blindness. Therefore, it is urgent to understand the molecular mechanism underlying cataractogenesis. MicroRNAs (miRNAs) are a group of endogenous, small noncoding RNAs that regulate gene expression at the post-translational level through binding with the 3'-untranslated regions of target mRNAs. Studies have shown that miRNAs play important roles in multiple cellular functions, including apoptosis, cell proliferation, senescence and stress response. Deregulated expression of miRNAs is also linked to the pathogenesis of many diseases, including ocular diseases. In our review, we focus on miRNAs that are involved in cataract development and discuss their potential applications as novel diagnostic markers and therapeutic targets.

Survival Improvement in Human Retinal Pigment Epithelial Cells via Fas Receptor Targeting by miR-374a

Oxidative conditions of the eye could contribute to retinal cells loss through activating the Fas-L/Fas pathway. This phenomenon is one of the leading causes of some ocular diseases like age-related macular degeneration (AMD). By targeting proteins at their mRNA level, microRNAs (miRNAs) can regulate gene expression and cell function. The aim of the present study is to investigate Fas targeting by miR-374a and find whether it can inhibit Fas-mediated apoptosis in primary human retinal pigment epithelial (RPE) cells under oxidative stress. So, the primary human RPE cells were transfected with pre-miR-374a pLEX construct using polymeric carrier and were exposed to H₂ O₂ (200 μM) as an oxidant agent for induction of Fas expression. Fas expression at mRNA and protein level was evaluated by quantitative real-time PCR and Western blot analysis, respectively. These results revealed that miR-374a could prevent Fas upregulation under oxidative conditions. Moreover, Luciferase activity assay confirmed that Fas could be a direct target of miR-374a. The cell viability studies demonstrated that caspase-3 activity was negligible in miR-374a treated cells compared to the controls. Our data suggest miR-374a is a negative regulator of Fas death receptor which is able to enhance the cell survival and protect RPE cells against oxidative conditions. J. Cell. Biochem. 118: 4854-4861, 2017. © 2017 Wiley Periodicals, Inc.

MicroRNA-29b Overexpression Decreases Extracellular Matrix mRNA and Protein Production in Human Corneal Endothelial Cells

PURPOSE

MicroRNAs are small noncoding RNAs that regulate gene expression at the posttranscriptional level. We reported that levels of microRNA (miR)-29 family are decreased in corneas of patients with Fuchs endothelial corneal dystrophy (FECD). The miR-29 family regulates the production of extracellular matrix (ECM) proteins. Accumulation of ECM proteins in Descemet membrane is an important pathologic change in FECD. In this study, we transfected miR-29b into human corneal endothelial cells and tissues and evaluated ECM protein expression levels.

METHODS

An immortalized Fuchs human corneal endothelial cell line (iFECD) was established by infection of corneal endothelial cells from patients with FECD with hTERT lentivirus. MiR-29b was transfected into iFECD, and the expression levels of ECMs collagen type 1 alpha 1 (COL1A1), collagen type 4 alpha 1 (COL4A1), and laminin gamma 1 (LAMC1) were evaluated with quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blot. Expression level of LAMC1 protein in miR-29b-transfected donor corneal endothelium was also evaluated by Western blot.

RESULTS

Compared with control, miR-29b expression level after transfection of iFECD was increased to 335.6% (±91.0%), and ECM expression levels were significantly decreased. Compared with control, qRT-PCR demonstrated reduction of ECM to the following levels: COL1A1: 1.9% (±0.4%); COL4A1: 7.1% (±1.7%); and LAMC1: 21.5% (±2.7%). Western blot showed reduced protein expression: COL1A1: 4.8% (±3.2%); COL4A1: 42.5% (±25.0%); and LAMC1: 44.8% (±3.1%). In miR-29b-transfected corneal tissue, LAMC1 protein expression level was decreased to 14.4% (±20.5%).

CONCLUSIONS

Overexpression of miR-29b decreased ECM protein production in human corneal endothelial cells. Thus, miR-29 replacement therapy might be a new treatment strategy for FECD aimed at reducing pathologic production of ECM proteins in Descemet membrane.

Expression and regulation of microRNA-29a and microRNA-29c in early diabetic rat cataract formation

AIM

To determine the role of microRNA (miRNA)-29a and miRNA-29c in the regulation of apoptosis in early rat diabetic cataract formation.

METHODS

Streptozotocin (STZ)-induced diabetic Sprague-Dawley (SD) rats were used in the study. The expression level of miRNA-29a, miRNA-29c, and BCL2-modifying factor (BMF) in lens epithelial cells (LECs) samples were measured using quantitative real-time polymerase chain reaction. Prediction algorithms of miRanda, TargetScan 6.2, and mirRDB to perform a miRNA gene network analysis were used for the potential miRNA-29a and miRNA-29c targets.

RESULTS

The miRNA-29a and miRNA-29c expression levels were all significantly lower in the control group compared to the 2 and 4wk diabetic samples (P<0.01). The network analysis indicated that one miRNA-29a and miRNA-29c targets was BMF. There was significantly higher expression of BMF mRNA compared to the normal controls (P<0.01).

CONCLUSION

Apoptosis occurs in rat LECs following high blood glucose exposure. It is likely that apoptosis during diabetic cataract formation involves the decreased expression of miRNA-29a and miRNA-29c and the increased expression of BMF.

Systems biology of lens development: A paradigm for disease gene discovery in the eye

Over the past several decades, the biology of the developing lens has been investigated using molecular genetics-based approaches in various vertebrate model systems. These efforts, involving target gene knockouts or knockdowns, have led to major advances in our understanding of lens morphogenesis and the pathological basis of cataracts, as well as of other lens related eye defects. In particular, we now have a functional understanding of regulators such as Pax6, Six3, Sox2, Oct1 (Pou2f1), Meis1, Pnox1, Zeb2 (Sip1), Mab21l1, Foxe3, Tfap2a (Ap2-alpha), Pitx3, Sox11, Prox1, Sox1, c-Maf, Mafg, Mafk, Hsf4, Fgfrs, Bmp7, and Tdrd7 in this tissue. However, whether these individual regulators interact or their targets overlap, and the significance of such interactions during lens morphogenesis, is not well defined. The arrival of high-throughput approaches for gene expression profiling (microarrays, RNA-sequencing (RNA-seq), etc.), which can be coupled with chromatin immunoprecipitation (ChIP) or RNA immunoprecipitation (RIP) assays, along with improved computational resources and publically available datasets (e.g. those containing comprehensive protein-protein, protein-DNA information), presents new opportunities to advance our understanding of the lens tissue on a global systems level. Such systems-level knowledge will lead to the derivation of the underlying lens gene regulatory network (GRN), defined as a circuit map of the regulator-target interactions functional in lens development, which can be applied to expedite cataract gene discovery. In this review, we cover the various systems-level approaches such as microarrays, RNA-seq, and ChIP that are already being applied to lens studies and discuss strategies for assembling and interpreting these vast amounts of high-throughput information for effective dispersion to the scientific community. In particular, we discuss strategies for effective interpretation of this new information in the context of the rich knowledge obtained through the application of traditional single-gene focused experiments on the lens. Finally, we discuss our vision for integrating these diverse high-throughput datasets in a single web-based user-friendly tool iSyTE (integrated Systems Tool for Eye gene discovery) - a resource that is already proving effective in the identification and characterization of genes linked to lens development and cataract. We anticipate that application of a similar approach to other ocular tissues such as the retina and the cornea, and even other organ systems, will significantly impact disease gene discovery.

Transcriptome Profiling of Developing Murine Lens Through RNA Sequencing

PURPOSE

Transcriptome is the entire repertoire of transcripts present in a cell at any particular time. We undertook a next-generation whole transcriptome sequencing approach to gain insight into the transcriptional landscape of the developing mouse lens.

METHODS

We ascertained mouse lenses at six developmental time points including two embryonic (E15 and E18) and four postnatal stages (P0, P3, P6, and P9). The ocular tissue at each time point was maintained as two distinct pools serving as biological replicates for each developmental stage. The mRNA and small RNA libraries were paired-end sequenced on Illumina HiSeq 2000 and subsequently analyzed using bioinformatics tools.

RESULTS

Mapping of mRNA and small RNA libraries generated 187.56 and 154.22 million paired-end reads, respectively. We detected a total of 14,465 genes in the mouse ocular lens at the above-mentioned six developmental stages. Of these, 46 genes exhibited a 40-fold differential (higher or lower) expression at one the five developmental stages (E18, P0, P3, P6, and P9) compared with their expression level at E15. Likewise, small RNA profiling identified 379 microRNAs (miRNAs) expressed in mouse lens at six developmental time points. Of these, 49 miRNAs manifested an 8-fold differential (higher or lower) expression at one the five developmental stages, as mentioned above compared with their expression level at E15.

CONCLUSIONS

We report a comprehensive profile of developing murine lens transcriptome including both mRNA and miRNA through next-generation RNA sequencing. A complete repository of the lens transcriptome of six developmental time points will be monumental in elucidating processes essential for the development of the ocular lens and maintenance of its transparency.