Transforming growth factor-beta-induced epithelial-mesenchymal transition in the lens: a model for cataract formation

Dual role of Par-4 in abrogation of EMT and switching on Mesenchymal to Epithelial Transition (MET) in metastatic pancreatic cancer cells

Epithelial-mesenchymal transition (EMT) is a critical event that occurs during the invasion and metastatic spread of cancer cells. Here, we conceive a dual mechanism of Par-4-mediated inhibition of EMT and induction of MET in metastatic pancreatic cancer cells. First, we demonstrate that 1,1'-β-D-glucopyranosyl-3,3'-bis(5-bromoindolyl)-octyl methane (NGD16), an N-glycosylated derivative of medicinally important phytochemical 3,3'-diindolylmethane (DIM) abrogates EMT by inducing pro-apoptotic protein Par-4. Induction of Par-4 (by NGD16 or ectopic overexpression) strongly impedes invasion with inhibition of major mesenchymal markers viz. Vimentin and Twist-1 epithelial marker- E-cadherin. Further, NGD16 triggers MET phenotypes in pancreatic cancer cells by augmenting ALK2/Smad4 signaling in a Par-4-dependent manner. Conversely, siRNA-mediated silencing of endogenous Par-4 unveil reversal of MET with diminished E-cadherin expression and invasive phenotypes. Additionally, we demonstrate that intact Smad4 is essential for Par-4-mediated maintenance of E-cadherin level in MET induced cells. Notably, we imply that Par-4 induction regulates E-cadherin levels in the pancreatic cancer cells via modulating Twist-1 promoter activity. Finally, in vivo studies with syngenic mouse metastatic pancreatic cancer model reveal that NGD16 strongly suppresses metastatic burden, ascites formation, and prolongs the overall survival of animals effectively.

Role of Smad3 signaling in the epithelial‑mesenchymal transition of the lens epithelium following injury

Transforming growth factor-β (TGF-β) is important in the development of posterior capsule opacification (PCO), and inhibition of the TGF-β pathway may represent a novel method of treating PCO. Drosophila protein, mothers against decapentaplegic homolog 3 (Smad3) is a phosphorylated receptor-activated Smad required for the transmission of TGF-β signals. Smad3 knockout (KO) disturbs the activation of TGF-β signaling, thus inhibiting the onset of PCO. In the present study, lens epithelial cell (LEC) damage induced by extracapsular cataract extraction was simulated by puncture of the anterior capsule using a 26-gauge hypodermic needle. The effect of Smad3 in the trauma-induced epithelial-mesenchymal transition (EMT) of the lens epithelium in Smad3-KO and wild-type (WT) mice was then observed. The expression levels of EMT markers and extracellular matrix components were measured in the two groups by reverse transcription-quantitative polymerase chain reaction analysis, western blot analysis and immunofluorescence staining. Apoptosis was also detected in the punctured anterior capsule. The Smad3-KO mice exhibited lower expression levels of α-smooth muscle actin, lumican, osteopontin, fibronectin and collagen, compared with the WT mice. Additionally, the Smad3-KO mice exhibited a higher percentage of apoptotic cells than the WT mice. Smad3 signaling was associated with the induction of trauma-induced EMT, and Smad3 KO interfered with TGF-β signaling pathway activation, but did not completely inhibit the trauma-induced EMT in LECs. Therefore, Smad3 may be a target in the treatment of PCO and other fibrosis-related diseases.

Long noncoding RNA KCNQ1OT1 promotes proliferation and epithelial‑mesenchymal transition by regulation of SMAD4 expression in lens epithelial cells

Long noncoding RNAs (lncRNAs) are associated with various diseases including cataracts. The role of lncRNA potassium voltage-gated channel subfamily Q member 1 opposite strand/antisense transcript 1 (KCNQ1OT1) on lens epithelial cell (LEC) proliferation and epithelial-mesenchymal transition (EMT) in cataracts disease remains unclear. In the present study, KCNQ1OT1 and mothers against decapentaplegic homolog (SMAD)4 expression levels were upregulated in human cataract lens posterior capsular samples and in transforming growth factor (TGF)-β2-treated SRA01/04 cells, as demonstrated by reverse transcription-quantitative polymerase chain reaction, immunohistochemical staining and western blot analyses. A further loss of function test revealed that suppression of KCNQ1OT1 inhibited the proliferation and EMT of TGF-β2-treated SRA01/04 cells. Additionally, the present study reported that increase and decrease of KCNQ1OT1 regulated SMAD4 expression, which indicated that SMAD4 may be a downstream gene of KCNQ1OT1. Finally, a constructed SMAD4 RNA interference experiment confirmed that the function of KCNQ1OT1 was to act on LEC proliferation and EMT, and this was achieved via the SMAD4 signaling pathway. The findings of the present study may provide a novel target for molecular therapy of cataracts disease.

Matrix-bound AGEs enhance TGFβ2-mediated mesenchymal transition of lens epithelial cells via the noncanonical pathway: implications for secondary cataract formation

Advanced glycation end products (AGEs) are post-translational modifications formed from the reaction of reactive carbonyl compounds with amino groups in proteins. Our laboratory has previously shown that AGEs in extracellular matrix (ECM) proteins promote TGFβ2 (transforming growth factor-beta 2)-mediated epithelial-to-mesenchymal transition (EMT) of lens epithelial cells (LECs), which could play a role in fibrosis associated with posterior capsule opacification. We have also shown that αB-crystallin plays an important role in TGFβ2-mediated EMT of LECs. Here, we investigated the signaling mechanisms by which ECM-AGEs enhance TGFβ2-mediated EMT in LECs. We found that in LECs cultured on AGE-modified basement protein extract (AGE-BME), TGFβ2 treatment up-regulated the mesenchymal markers α-SMA (α-smooth muscle actin) and αB-crystallin and down-regulated the epithelial marker E-cadherin more than LECs cultured on unmodified BME and treated with TGFβ2. Using a Multiplex Assay, we found that AGE-BME significantly up-regulated the noncanonical pathway by promoting phosphorylation of ERK (extracellular signal-regulated kinases), AKT, and p38 MAPK (mitogen-activated protein kinases) during TGFβ2-mediated EMT. This EMT response was strongly suppressed by inhibition of AKT and p38 MAPK phosphorylation. The AKT inhibitor LY294002 also suppressed TGFβ2-induced up-regulation of nuclear Snail and reduced phosphorylation of GSK3β. Inhibition of Snail expression suppressed TGFβ2-mediated α-SMA expression. αB-Crystallin was up-regulated in an AKT-dependent manner during AGE-BME/TGFβ2-mediated EMT in LECs. The absence of αB-crystallin in LECs suppressed TGFβ2-induced GSK3β phosphorylation, resulting in lower Snail levels. Taken together, these results show that ECM-AGEs enhance the TGFβ2-mediated EMT response through activation of the AKT/Snail pathway, in which αB-crystallin plays an important role as a linker between the TGFβ2 and AGE-mediated signaling pathways.

ERK1/2-Dependent Gene Expression Contributing to TGFβ-Induced Lens EMT

PURPOSE

This study aims to highlight some of the genes that are differentially regulated by ERK1/2 signaling in TGFβ-induced EMT in lens, and their potential contribution to this pathological process.

MATERIALS AND METHODS

Rat lens epithelial explants were cultured with or without TGFβ over a 3-day-culture period to induce EMT, in the presence or absence of UO126 (ERK1/2 signaling inhibitor), both prior to TGFβ-treatment, or 24 or 48 hours after TGFβ treatment. Smad2/3-nuclear immunolabeling was used to indicate active TGFβ signaling, and quantitative RT-PCR was used to analyze changes in the different treatment groups in expression of the following representative genes: TGFβ signaling (Smad7, Smurf1, and Rnf111), epithelial markers (Pax6, Cdh1, Zeb1, and Zeb2), cell survival/death regulators (Bcl2, Bax, and Bad) and lens mesenchymal markers (Mmp9, Fn1, and Col1a1), over the 3 days of culture.

RESULTS

ERK1/2 was found to regulate the expression of Smurf1, Smad7, Rnf11, Cdh1, Pax6, Zeb1, Bcl2, Bax, and Bad genes in lens cells. TGFβ signaling was evident by nuclear localization of Smad2/3 and this was effectively blocked by pre-treatment with UO126, but not by post-treatment with this ERK1/2 signaling inhibitor. TGFβ induced the expression of its signaling partners (Smad7, Smurf1, and Rnf111), as well as lens mesenchymal genes (Mmp9, Fn1, and Col1a1), consistent with its role in inducing an EMT. These TGFβ-responsive signaling genes, as well as the mesenchymal markers, were all positively regulated by ERK1/2-activity. The expression levels of the lens epithelial genes we examined, and genes that were associated with cell death/survival, were not directly impacted by TGFβ.

CONCLUSIONS

TGFβ-mediated ERK1/2 signaling positively modulates the expression of mesenchymal genes in lens epithelial explants undergoing EMT, in addition to regulating TGFβ-mediated regulatory genes. Independent of TGFβ, ERK1/2 activity can also regulate the expression of endogenous lens epithelial genes, highlighting its potential key role in regulation of both normal and pathological lens cellular processes.

CTGF Contributes to the Development of Posterior Capsule Opacification: an in vitro and in vivo study

Connective tissue growth factor (CTGF) is a crucial factor that plays a major role in the process of posterior capsule opacification (PCO). However, the effects of CTGF on the proliferation and migration of lens epithelial cells (LECs) and on the mechanism of the epithelial mesenchymal transition (EMT) and extracellular matrix (ECM) in human lens epithelial cells (HLECs) as well as the effects of shRNA-mediated CTGF knockdown on the development of PCO in rats remain unclear. In the present study, we found that CTGF promoted EMT, proliferation, migration and the expression of p-ERK1/2 protein in HLECs but exerted little effect on the expression of p-p38 and p-JNK1/2 proteins. MEK inhibitor U0126 effectively restrained the CTGF-induced expression of α-smooth muscle actin (α-SMA), fibronectin (Fn) and type I collagen (COL-1) in HLECs. CTGF knockdown effectively postponed the onset of PCO in the rats and significantly reduced the expression of α-SMA in the capsule. In conclusion, CTGF contributed to the development of PCO presumably by promoting proliferation, migration of LECs, EMT specific protein expression and ECM synthesis in HLECs, which is dependent on ERK signalling. Furthermore, blocking CTGF effectively inhibited PCO in the rats and the EMT specific protein expression in the lens capsule.

Tropomyosin 2 heterozygous knockout in mice using CRISPR-Cas9 system displays the inhibition of injury-induced epithelial-mesenchymal transition, and lens opacity

The process of epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) after cataract surgery contributes to tissue fibrosis, wound healing and lens regeneration via a mechanism not yet fully understood. Here, we show that tropomyosin 2 (Tpm2) plays a critical role in wound healing and lens aging. Posterior capsular opacification (PCO) after lens extraction surgery was accompanied by elevated expression of Tpm2. Tpm2 heterozygous knockout mice, generated via the clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9) system showed promoted progression of cataract with age. Further, injury-induced EMT of the mouse lens epithelium, as evaluated histologically and by the expression patterns of Tpm1 and Tpm2, was attenuated in the absence of Tpm2. In conclusion, Tpm2 may be important in maintaining lens physiology and morphology. However, Tpm2 is involved in the progression of EMT during the wound healing process of mouse LECs, suggesting that inhibition of Tpm2 may suppress PCO.

Investigation of the anti-cataractogenic mechanisms of curcumin through in vivo and in vitro studies

BACKGROUND

Cataract is the leading cause of blindness in elderly people worldwide, especially in developing countries. Studies to identify strategies that can prevent or retard cataract formation are urgently required. This study aimed to investigate the potential mechanism of the cytoprotective effects of curcumin in in vivo and in vitro experiments.

METHODS

Male Wistar rats were randomly divided into three groups: the control group, the model group (administered 20 μmol/kg sodium selenite), and the curcumin group (pretreated with 75 mg/kg body weight curcumin 24 h prior to the administration of sodium selenite). The expression levels of heat shock protein 70 (HSP70), the activities of 8-hydroxy-2-deoxyguanosine (8-OHdG), catalase (CAT), malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) were assessed by using RT-PCR assay and ELISA. In addition, the cell viability, cell apoptosis, and cell cycle were assessed using a CCK-8 assay and flow cytometry in in vitro studies, followed by RT-PCR analysis to identify the mRNA expression levels of caspase 3, Bcl-2 associated X (Bax), B-cell lymphoma 2 (Bcl-2), cyclooxygenase (Cox-2), c-met, and Slug.

RESULTS

Cataract was successfully established in rats of the model group and the curcumin group through intraperitoneal injection of sodium selenite. The expression levels of HSP70 and the activities of 8-OHdG and MDA in the curcumin group were decreased compared with those in the model group, whereas the activities of CAT, SOD, and GSH-Px were significantly higher than those in the model group (P < 0.05). In the in vitro studies, the cell viability and cell apoptosis significantly increased and decreased, respectively, in the curcumin group compared with the model group. Correspondingly, the mRNA expression of caspase-3, Bax, and Cox-2 was lower in the curcumin group than in the model group (P < 0.05).

CONCLUSIONS

This study suggested that curcumin attenuated selenite-induced cataract through the reduction of the intracellular production of reactive oxygen species and the protection of cells from oxidative damage.

Laminins in an in vitro anterior lens capsule model established using HLE B-3 cells

Cataracts are the most common eye disease to cause blindness in patients. The abnormal deposition of laminins (LMs) in the lens capsule and the disruption of capsular epithelium contribute to cataract development, although the mechanism by which this occurs is currently unclear. The present study aimed to reproduce HLE B-3 basement membranes (BMs) using HLE B-3 cells and to analyze the similarities of LM expression between HLE B-3 BMs and human anterior lens capsule (ALC). Immunohistochemistry (IHC), ELISA, western blot analysis and immunoprecipitation (IP)-western blot analysis were used to detect total LMs, LM trimers and 11 LM subunits in HLE B-3 cells, HLE B-3 BMs and human ALCs. In IHC staining, HLE B-3 cells and human ALCs were positive for LMs. In LM ELISA, all samples analyzed were positive for LMs. Western blot analysis detected all LM subunits except for LMγ3 in HLE B-3 cell lysate, 4 subunits (LMα4, LMα2, LMα1 and LMγ1) in HLE B-3 cell culture supernatant, 5 subunits (LMα4, LMα2, LMα1, LMβ3 and LMγ1) in HLE B-3 BMs, and 3 subunits (LMα4, LMγ2 and LMγ1) in human ALCs. The results of IP-western blot analysis revealed that the LM411 trimer was detected in HLE B-3 cell culture supernatant. These results indicated that HLE B-3 BMs were similar to human ALCs in terms of LM expression. Therefore, HLE B-3 BMs could be used as an in vitro ALC model to determine the role of LMs in ALC in the pathogenesis of cataracts and to select potential anti-cataract drugs.

Aldo-Keto Reductases: Multifunctional Proteins as Therapeutic Targets in Diabetes and Inflammatory Disease

Aldose reductase (AR) is an NADPH-dependent aldo-keto reductase that has been shown to be involved in the pathogenesis of several blinding diseases such as uveitis, diabetic retinopathy (DR) and cataract. However, possible mechanisms linking the action of AR to these diseases are not well understood. As DR and cataract are among the leading causes of blindness in the world, there is an urgent need to explore therapeutic strategies to prevent or delay their onset. Studies with AR inhibitors and gene-targeted mice have demonstrated that the action of AR is also linked to cancer onset and progression. In this review we examine possible mechanisms that relate AR to molecular signaling cascades and thus explain why AR inhibition is an effective strategy against colon cancer as well as diseases of the eye such as uveitis, cataract, and retinopathy.

Trichostatin A Restores Expression of Adherens and Tight Junction Proteins during Transforming Growth Factor β-Mediated Epithelial-to-Mesenchymal Transition

Purpose:

Adherens junctions and polarity markers play an important role in maintaining epithelial phenotype but get altered during the epithelial-mesenchymal transition (EMT). Alterations of these markers during EMT of lens epithelial cell (LEC) can lead to vision compromising conditions. The aim of this study was to examine if Trichostatin-A (TSA), a histone deacetylase inhibitor, can prevent EMT by restoring the adherens junction complex in LEC.

Methods:

Fetal human lens epithelial cell line (FHL124) was used. Cells were treated with 10 ng/ml TGF-β2 in the presence or absence of TSA. Real time-PCR and western blotting were carried out for HDAC1, HDAC2, CDH1 (E-cad), TJP1 (ZO-1) and CTNNB1 (β-cat). Level of histone acetylation was analyzed by western blotting. Chromatin Immunoprecipitation was carried out to study the level of acetylated histone H4 and HDAC2 at the promoter regions of CDH1, TJP1, and CTNNB1. E-cad, ZO-1, and β-cat were localized using immunofluorescence. Kruskal-Wallis test was used for statistical analysis.

Results:

TSA down-regulated HDAC1 and HDAC2 and led to an increase in global acetylation. The mRNA and protein levels of E-cad, ZO-1, and β-cat decreased during EMT but were up-regulated by TSA treatment. TSA also helped in stabilizing these proteins at cell-cell junctions during EMT. TSA decreases association of HDAC2 at the promoter regions of adherens junction genes while increasing histone H4 acetylation status.

Conclusion:

TSA increases histone acetylation and restores the adherens junction complex in LECs. TSA helps in preventing EMT and thus shows potential against lens fibrosis and vision compromising conditions.

Induction of Immune Surveillance of the Dysmorphogenic Lens

The lens has been considered to be an immune privileged site not susceptible to the immune processes normally associated with tissue injury and wound repair. However, as greater insight into the immune surveillance process is gained, we have reevaluated the concept of immune privilege. Our studies using an N-cadherin lens-specific conditional knockout mouse, N-cad^Δlens, show that loss of this cell-cell junctional protein leads to lens degeneration, necrosis and fibrotic change, postnatally. The degeneration of this tissue induces an immune response resulting in immune cells populating the lens that contribute to the development of fibrosis. Additionally, we demonstrate that the lens is connected to the lymphatic system, with LYVE(+) labeling reaching the lens along the suspensory ligaments that connect the lens to the ciliary body, providing a potential mechanism for the immune circulation. Importantly, we observe that degeneration of the lens activates an immune response throughout the eye, including cornea, vitreous humor, and retina, suggesting a coordinated protective response in the visual system to defects of a component tissue. These studies demonstrate that lens degeneration induces an immune response that can contribute to the fibrosis that often accompanies lens dysgenesis, a consideration for understanding organ system response to injury.

Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis

Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.

Roles of TGFβ and FGF signals during growth and differentiation of mouse lens epithelial cell in vitro

Transforming growth factor β (TGFβ) and fibroblast growth factor (FGF) signaling pathways play important roles in the proliferation and differentiation of lens epithelial cells (LECs) during development. Low dosage bFGF promotes cell proliferation while high dosage induces differentiation. TGFβ signaling regulates LEC proliferation and differentiation as well, but also promotes epithelial-mesenchymal transitions that lead to cataracts. Thus far, it has been difficult to recapitulate the features of germinative LECs in vitro. Here, we have established a LEC culture protocol that uses SB431542 (SB) compound to inhibit TGFβ/Smad activation, and found that SB treatment promoted mouse LEC proliferation, maintained LECs’ morphology and distinct markers including N-cadherin, c-Maf, Prox1, and αA-, αB-, and β-crystallins. In contrast, low-dosage bFGF was unable to sustain those markers and, combined with SB, altered LECs’ morphology and β-crystallin expression. We further found that Matrigel substrate coatings greatly increased cell proliferation and uniquely affected β-crystallin expression. Cultured LECs retained the ability to differentiate into γ-crystallin-positive lentoids by high-dosage bFGF treatment. Thus, a suppression of TGFβ/Smad signaling in vitro is critical to maintaining characteristic features of mouse LECs, especially expression of the key transcription factors c-Maf and Prox1.

β1-Integrin Deletion From the Lens Activates Cellular Stress Responses Leading to Apoptosis and Fibrosis

Purpose

Previous research showed that the absence of β1-integrin from the mouse lens after embryonic day (E) 13.5 (β1MLR10) leads to the perinatal apoptosis of lens epithelial cells (LECs) resulting in severe microphthalmia. This study focuses on elucidating the molecular connections between β1-integrin deletion and this phenotype.

Methods

RNA sequencing was performed to identify differentially regulated genes (DRGs) in β1MLR10 lenses at E15.5. By using bioinformatics analysis and literature searching, Egr1 (early growth response 1) was selected for further study. The activation status of certain signaling pathways (focal adhesion kinase [FAK]/Erk, TGF-β, and Akt signaling) was studied via Western blot and immunohistochemistry. Mice lacking both β1-integrin and Egr1 genes from the lenses were created (β1MLR10/Egr1-/-) to study their relationship.

Results

RNA sequencing identified 120 DRGs that include candidates involved in the cellular stress response, fibrosis, and/or apoptosis. Egr1 was investigated in detail, as it mediates cellular stress responses in various cell types, and is recognized as an upstream regulator of numerous other β1MLR10 lens DRGs. In β1MLR10 mice, Egr1 levels are elevated shortly after β1-integrin loss from the lens. Further, pErk1/2 and pAkt are elevated in β1MLR10 LECs, thus providing the potential signaling mechanism that causes Egr1 upregulation in the mutant. Indeed, deletion of Egr1 from β1MLR10 lenses partially rescues the microphthalmia phenotype.

Conclusions

β1-integrin regulates the appropriate levels of Erk1/2 and Akt phosphorylation in LECs, whereas its deficiency results in the overexpression of Egr1, culminating in reduced cell survival. These findings provide insight into the molecular mechanism underlying the microphthalmia observed in β1MLR10 mice.

Bone Morphogenetic Protein-7 Suppresses TGFβ2-Induced Epithelial-Mesenchymal Transition in the Lens: Implications for Cataract Prevention

Purpose

Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) is a key pathologic mechanism underlying cataract. Two members of the transforming growth factor-β (TGFβ) superfamily, TGFβ and bone morphogenetic protein-7 (BMP-7) have functionally distinct roles in EMT. While TGFβ is a potent inducer of EMT, BMP-7 counteracts the fibrogenic activity of TGFβ. We examine the modulating effect of BMP-7 on TGFβ-induced EMT in LECs.

Methods

Rat lens epithelial explants were treated exogenously with TGFβ2 alone or in combination with BMP-7 for up to 5 days. Expression levels of E-cadherin, β-catenin, α-smooth muscle actin (α-SMA), and phosphorylated downstream Smads were determined using immunofluorescence and Western blotting. Reverse transcriptase quantitative PCR (RT-qPCR) was used to study gene expression levels of EMT markers and downstream BMP target genes, including the Inhibitors of differentiation (Id).

Results

Transforming growth factor-β2 induced LECs to transdifferentiate into myofibroblastic cells. Addition of BMP-7 suppressed TGFβ2-induced α-SMA protein levels and mesenchymal gene expression, with retention of E-cadherin and β-catenin expression to the cell membrane. Addition of BMP-7 prevented lens capsular wrinkling and cellular loss associated with TGFβ2-induced EMT over the 5-day treatment period. The inhibitory effect of BMP-7 was accompanied by an early induction of pSmad1/5 and suppression of TGFβ2-induced pSmad2/3. Treatment with TGFβ2 alone suppressed gene expression of Id2/3 and addition of BMP-7 restored Id2/3 expression.

Conclusions

Exogenous administration of BMP-7 abrogated TGFβ2-induced EMT in rat lens epithelial explants. Understanding the complex interplay between the TGFβ- and BMP-7–associated Smad signaling pathways and their downstream target genes holds therapeutic promise in cataract prevention.

MicroRNA-26a and -26b inhibit lens fibrosis and cataract by negatively regulating Jagged-1/Notch signaling pathway

Fibrosis is a chronic process involving development and progression of multiple diseases in various organs and is responsible for almost half of all known deaths. Epithelial–mesenchymal transition (EMT) is the vital process in organ fibrosis. Lens is an elegant biological tool to investigate the fibrosis process because of its unique biological properties. Using gain- and loss-of-function assays, and different lens fibrosis models, here we demonstrated that microRNA (miR)-26a and miR-26b, members of the miR-26 family have key roles in EMT and fibrosis. They can significantly inhibit proliferation, migration, EMT of lens epithelial cells and lens fibrosis in vitro and in vivo. Interestingly, we revealed that the mechanisms of anti-EMT effects of miR-26a and -26b are via directly targeting Jagged-1 and suppressing Jagged-1/Notch signaling. Furthermore, we provided in vitro and in vivo evidence that Jagged-1/Notch signaling is activated in TGFβ2-stimulated EMT, and blockade of Notch signaling can reverse lens epithelial cells (LECs) EMT and lens fibrosis. Given the general involvement of EMT in most fibrotic diseases, cancer metastasis and recurrence, miR-26 family and Notch pathway may have therapeutic uses in treating fibrotic diseases and cancers.

The murine lens: A model to investigate in vivo epithelial-mesenchymal transition

Epithelial–mesenchymal transition (EMT) produces myofibroblasts that contribute to the formation of fibrotic tissue with an impairment of tissue homeostasis and functionality. The crystalline lens of the eye is a unique transparent and isolated tissue. The lens vesicle becomes isolated from the surface ectoderm, its cells are all contained as they line the inner surface of the lens capsule. Clinically the formation of fibrotic tissue by the lens epithelial cells causes a type of cataract or opacification and contraction of the lens capsule postcataract surgery. Production of EMT in the intact animal lens by using specific gene transfer to the lens or experimental lens injury has been shown to be a powerful tool to investigate EMT processes. It is not easy to uncover whether the origin of the myofibroblast is epithelial cell‐derived or from other cell lineages in fibrotic tissues. However, myofibroblasts that appear in the crystalline lens pathology are totally derived from the lens epithelial cells for the reasons mentioned above. Here, we report on different animal models of lens EMT, using either transgenic approaches or injury to study the biological aspects of EMT. Developmental Dynamics 247:340–345, 2018. © 2017 The Authors Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists

Lens, Epithelial‐mesenchymal transition, mice.

Long noncoding RNA expression profile in HLE B-3 cells during TGF-β2-induced epithelial-mesenchymal transition

Background

Recent evidence has shown that long noncoding RNAs (lncRNAs) are involved in the process of epithelial-mesenchymal transition (EMT). However, little research has focused on the expression profile of lncRNAs during EMT in human lens epithelial cells (LECs) and their functions have not yet been described.

Methods

Dysregulated lncRNAs and mRNAs in normal human lens epithelial B-3(HLE B-3) cells and during transforming growth factor β₂(TGF-β₂)-induced EMT were analyzed via lncRNA microarray. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway analyses of differentially expressed mRNAs were performed to identify their functions and pathologic pathways. Six candidate lncRNAs were validated via quantitative real-time reverse transcription polymerase chain reaction(qRT-PCR) to confirm the microarray data.

Results

A total of 775 lncRNAs (325 up-regulated and 450 down-regulated) and 935 mRNAs (329 up-regulated and 606 down-regulated) were differentially expressed in HLE B-3 cells during TGF-β2-induced EMT compared to normal HLE B-3 cells. GO and KEGG Pathway analyses indicated the functions of differentially expressed mRNAs in the TGF-β₂-induced EMT in HLE B-3 cells. qRT-PCR confirmed the trends indicated in microarray analysis for all 6 candidate lncRNAs.

Conclusion

Our study lays the foundation for future research in lncRNAs related to EMT in HLE B-3 cells and could provide new avenues for the prevention and treatment of posterior capsule opacification (PCO).

Dual function of TGFβ in lens epithelial cell fate: implications for secondary cataract

The most common vision-disrupting complication of cataract surgery is posterior capsule opacification (PCO; secondary cataract). PCO is caused by residual lens cells undergoing one of two very different cell fates: either transdifferentiating into myofibroblasts or maturing into lens fiber cells. Although TGFβ has been strongly implicated in lens cell fibrosis, the factors responsible for the latter process have not been identified. We show here for the first time that TGFβ can induce purified primary lens epithelial cells within the same culture to undergo differentiation into either lens fiber cells or myofibroblasts. Marker analysis confirmed that the two cell phenotypes were mutually exclusive. Blocking the p38 kinase pathway, either with direct inhibitors of the p38 MAP kinase or a small-molecule therapeutic that also inhibits the activation of p38, prevented TGFβ from inducing epithelial-myofibroblast transition and cell migration but did not prevent fiber cell differentiation. Rapamycin had the converse effect, linking MTOR signaling to induction of fiber cell differentiation by TGFβ. In addition to providing novel potential therapeutic strategies for PCO, our findings extend the so-called TGFβ paradox, in which TGFβ can induce two disparate cell fates, to a new epithelial disease state.

ERK1/2 signaling is required for the initiation but not progression of TGFβ-induced lens epithelial to mesenchymal transition (EMT)

Transforming Growth Factor Beta (TGFβ) potently induces lens epithelial to mesenchymal transition (EMT). The resultant mesenchymal cells resemble those found in plaques of human forms of subcapsular cataract. Smad signaling has long been implicated as the sole driving force of TGFβ-mediated activity. Rat lens epithelial explants were used to examine the role of the Smad-independent signaling, namely the MAPK/ERK1/2 signaling pathway, in the initiation and progression of TGFβ-induced EMT. Phase contrast microscopy was used to observe the morphological changes associated with TGFβ-induced EMT in this model, including cell elongation, cell membrane blebbing, cell loss as indicated by the area of bare capsule and capsular wrinkling. The levels of Smad2, Smad2/3 and ERK1/2 phosphorylation measured using western blotting confirmed that the addition of UO126 was sufficient in blocking all TGFβ-induced ERK1/2 activation, as well as reducing Smad signaling at 18 h. Immunofluorescent labeling and further western blotting confirmed that TGFβ-induced EMT was associated with an increase in α-smooth muscle actin (α-SMA) and a reduction of E-cadherin at cell borders. Pre-treatment with UO126 was effective at blocking the TGFβ-induced EMT, as evidenced by a reduction of α-SMA expression and protein labeling, E-cadherin labeling at cell borders, and a reduction of cell loss, cell elongation and capsular wrinkling. Post-treatment with UO126 at 2 and 6 h after TGFβ addition was also effective at blocking EMT while post-treatment with UO126 at 24 and 48 h was not sufficient in hampering TGFβ-induced EMT. Our data implicates ERK1/2 signaling in the initiation but not the progression of TGFβ-induced EMT in rat lens epithelial cells. The tight regulation of intracellular signaling pathways such as ERK1/2 are required for the maintenance of lens epithelial cell integrity and hence tissue transparency. A greater understanding of the molecular mechanisms that drive the induction and progression of EMT in the lens will provide the basis for potential therapeutics for human cataract.

Effect of an MG132-Sustained Drug Delivery Capsular Ring on the Inhibition of Posterior Capsule Opacification in a Rabbit Model

PURPOSE

To design an MG132-sustained drug delivery capsular ring (SDDCR) and investigate its effect on the inhibition of posterior capsule opacification (PCO) in a rabbit model.

METHODS

The SDDCRs were prepared by forming a slice of film made by the mixture of poly lactic-co-glycolic acid (PLGA) and MG132 on the surface of capsular tension rings (CTRs). The drug-loading capacity, entrapment efficiency, and in vitro release of the drug-containing film were detected. Eighteen New Zealand white rabbits were operated with phacoemulsification and MG132-SDDCRs/PLGA-CTRs/CTRs implantation in the single eye. The images of the anterior segments were acquired at certain days, and the epithelial-mesenchymal transition (EMT) markers were detected by western blot and immunofluorescence.

RESULTS

The drug-loading capacity and entrapment efficiency of MG132-SDDCRs were 1.15% ± 0.04% and 66.16% ± 0.027%, respectively, and the drug released well within a month. The PCO degree of the MG132-SDDCR group was significantly lower than the other groups. The expression of alpha-smooth muscle actin, fibronectin, vimentin, and collagen-I was lower, and the expression of E-cadherin (E-cad) was higher in the MG132-SDDCR group than the other groups.

CONCLUSIONS

MG132-SDDCRs could be established successfully. The PCO process was prevented, and the expression of EMT markers was inhibited by the implantation of MG132-SDDCRs, indicating that this could be a potential treatment against PCO.

FGF2 antagonizes aberrant TGFβ regulation of tropomyosin: role for posterior capsule opacity

Transforming growth factor (TGF) β2 and fibroblast growth factor (FGF) 2 are involved in regulation of posterior capsule opacification (PCO) and other processes of epithelial–mesenchymal transition (EMT) such as cancer progression, wound healing and tissue fibrosis as well as normal embryonic development. We previously used an in vivo rodent PCO model to show the expression of tropomyosin (Tpm) 1/2 was aberrantly up‐regulated in remodelling the actin cytoskeleton during EMT. In this in vitro study, we show the Tpms family of cytoskeleton proteins are involved in regulating and stabilizing actin microfilaments (F‐actin) and are induced by TGFβ2 during EMT in lens epithelial cells (LECs). Importantly, we found TGFβ2 and FGF2 played contrasting roles. Stress fibre formation and up‐regulation of α‐smooth muscle actin (αSMA) induced by TGFβ2 could be reversed by Tpm1/2 knock‐down by siRNA. Expression of Tpm1/2 and stress fibre formation induced by TGFβ2 could be reversed by FGF2. Furthermore, FGF2 delivery to TGFβ‐treated LECs perturbed EMT by reactivating the mitogen‐activated protein kinase (MAPK)/ extracellular signal‐regulated kinase (ERK) pathway and subsequently enhanced EMT. Conversely, MEK inhibitor (PD98059) abated the FGF2‐mediated Tpm1/2 and αSMA suppression. However, we found that normal LECs which underwent EMT showed enhanced migration in response to combined TGFβ and FGF2 stimulation. These findings may help clarify the mechanism reprogramming the actin cytoskeleton during morphogenetic EMT cell proliferation and fibre regeneration in PCO. We propose that understanding the physiological link between levels of FGF2, Tpm1/2 expression and TGFβs‐driven EMT orchestration may provide clue(s) to develop therapeutic strategies to treat PCO based on Tpm1/2.

De-ubiquitinating enzyme, USP11, promotes transforming growth factor β-1 signaling through stabilization of transforming growth factor β receptor II

The transforming growth factor β-1 (TGFβ-1) signaling pathway plays a central role in the pathogenesis of pulmonary fibrosis. Two TGFβ-1 receptors, TβRI and TβRII, mediate this pathway. TβRI protein stability, as mediated by the ubiquitin/de-ubiquitination system, has been well studied; however, the molecular regulation of TβRII still remains unclear. Here we reveal that a de-ubiquitinating enzyme, USP11, promotes TGFβ-1 signaling through de-ubiquitination and stabilization of TβRII. We elucidate the role that mitoxantrone (MTX), an USP11 inhibitor, has in the attenuation of TGFβ-1 signaling. Inhibition or downregulation of USP11 results in increases in TβRII ubiquitination and reduction of TβRII stability. Subsequently, TGFβ-1 signaling is greatly attenuated, as shown by the decreases in phosphorylation of SMAD2/3 levels as well as that of fibronectin (FN) and smooth muscle actin (SMA). Overexpression of USP11 reduces TβRII ubiquitination and increases TβRII stabilization, thereby elevating phosphorylation of SMAD2/3 and the ultimate expression of FN and SMA. Further, elevated expression of USP11 and TβRII were detected in lung tissues from bleomycin-challenged mice and IPF patients. Therefore, USP11 may contribute to the pathogenesis of pulmonary fibrosis by stabilization of TβRII and promotion of TGFβ-1 signaling. This study provides mechanistic evidence for development of USP11 inhibitors as potential antifibrotic drugs for pulmonary fibrosis.

Effects of peptide ratios in nanofibre-based hydrogels for the prevention of capsular opacification

PURPOSE

To moderate the capsular opacification (CO) response after lens surgery, an experimental study was performed in which nanofibre-based hydrogels (nanogels) with different ratios of attached peptides were applied to provide extracellular matrix-related cues for lens epithelial cells (LECs) in a porcine eye model.

METHODS

The lens content was removed, and the capsules were refilled with nanogel. Lenses were divided into two groups, the first group (n = 34) was refilled with nanogels containing different ratios of two laminin-derived peptides (IKVAV + YIGSR), and the latter group (n = 26) was refilled with nanogel combinations of a fibronectin-derived and a type IV collagen-derived peptide (RGDS + DGEA). Two lenses were refilled with culture medium to investigate the effect of the medium on LECs. After refilling, lenses were extracted and cultured for 3 weeks. Lens epithelial cells (LECs) were assessed for morphology and alpha-smooth muscle actin (αSMA) expression using confocal laser scanning microscopy.

RESULTS

Differences were seen in cell morphology between lenses refilled with nanogels with IKVAV + YIGSR and RGDS + DGEA peptides. In nanogels with IKVAV + YIGSR peptides, differences in LEC morphology were largest when ratios between the peptides were unequal, whereas LEC responses from the RGDS + DGEA refilled groups showed variation in LEC morphology dependent on the total quantity of mixed-in peptides. The culture medium did not induce proliferation or transformation of LECs.

CONCLUSIONS

Ratios and concentrations of cell adhesion-mediating peptides both can direct the LEC response, depending on the adhesion molecules of origin, by influencing LEC proliferation and transformation. Nanogels with incorporated peptides may be tuned towards CO prevention.

β1-integrin controls cell fate specification in early lens development

Integrins are heterodimeric cell surface molecules that mediate cell-extracellular matrix (ECM) adhesion, ECM assembly, and regulation of both ECM and growth factor induced signaling. However, the developmental context of these diverse functions is not clear. Loss of β1-integrin from the lens vesicle (mouse E10.5) results in abnormal exit of anterior lens epithelial cells (LECs) from the cell cycle and their aberrant elongation toward the presumptive cornea by E12.5. These cells lose expression of LEC markers and initiate expression of the Maf (also known as c-Maf) and Prox1 transcription factors as well as other lens fiber cell markers. β1-integrin null LECs also upregulate the ERK, AKT and Smad1/5/8 phosphorylation indicative of BMP and FGF signaling. By E14.5, β1-integrin null lenses have undergone a complete conversion of all lens epithelial cells into fiber cells. These data suggest that shortly after lens vesicle closure, β1-integrin blocks inappropriate differentiation of the lens epithelium into fibers, potentially by inhibiting BMP and/or FGF receptor activation. Thus, β1-integrin has an important role in fine-tuning the response of the early lens to the gradient of growth factors that regulate lens fiber cell differentiation.

RhoA/ROCK signaling regulates TGFβ-induced epithelial-mesenchymal transition of lens epithelial cells through MRTF-A

Transforming growth factor (TGF)-β-induced epithelial-mesenchymal transition (EMT) leads to the formation of ocular fibrotic pathologies, such as anterior subcapsular cataract and posterior capsule opacification. Remodeling of the actin cytoskeleton, mediated by the Rho family of GTPases, plays a key role in EMT, however, how actin dynamics affect downstream markers of EMT has not been fully determined. Our previous work suggests that myocardin related transcription factor A (MRTF-A), an actin-binding protein, might be an important mediator of TGFβ-induced EMT in lens epithelial cells. The aim of the current study was to determine the requirement of RhoA/ROCK signaling in mediating TGFβ-induced nuclear accumulation of MRTF-A, and ultimate expression of α-smooth muscle actin (αSMA), a marker of a contractile, myofibroblast phenotype. Using rat lens epithelial explants, we demonstrate that ROCK inhibition using Y-27632 prevents TGFβ-induced nuclear accumulation of MRTF-A, E-cadherin/β-catenin complex disassembly, and αSMA expression. Using a novel inhibitor specifically targeting MRTF-A signaling, CCG-203971, we further demonstrate the requirement of MRTF-A nuclear localization and activity in the induction of αSMA expression. Overall, our findings suggest that TGFβ-induced cytoskeletal reorganization through RhoA/ROCK/MRTF-A signaling is critical to EMT of lens epithelial cells.

Osteogenic differentiation of human lens epithelial cells might contribute to lens calcification

Calcification of the human lens has been described in senile cataracts and in young patients with congenital cataract or chronic uveitis. Lens calcification is also a major complication of cataract surgery and plays a role in the opacification of intraocular lenses. A cell-mediated process has been suggested in the background of lens calcification, but so far the exact mechanism remained unexplored. Lens calcification shares remarkable similarities with vascular calcification; in both pathological processes hydroxyapatite accumulates in the soft tissue. Vascular calcification is a regulated, cell-mediated process in which vascular cells undergo osteogenic differentiation. Our objective was to investigate whether human lens epithelial cells (HuLECs) can undergo osteogenic transition in vitro, and whether this process contributes to lens calcification. We used inorganic phosphate (Pi) and Ca to stimulate osteogenic differentiation of HuLECs. Osteogenic stimuli (2.5mmol/L Pi and 1.2mmol/L Ca) induced extracellular matrix mineralization and Ca deposition in HuLECs with the critical involvement of active Pi uptake. Osteogenic stimuli almost doubled mRNA expressions of osteo-/chondrogenic transcription factors Runx2 and Sox9, which was accompanied by a 1.9-fold increase in Runx2 and a 5.5-fold increase in Sox9 protein expressions. Osteogenic stimuli induced mRNA and protein expressions of alkaline phosphatase and osteocalcin in HuLEC. Ca content was higher in human cataractous lenses, compared to non-cataractous controls (n=10). Osteocalcin, an osteoblast-specific protein, was expressed in 2 out of 10 cataractous lenses. We conclude that osteogenic stimuli induce osteogenic differentiation of HuLECs and propose that this mechanism might play a role in lens calcification.

AGE-RAGE interaction in the TGFβ2-mediated epithelial to mesenchymal transition of human lens epithelial cells

Basement membrane (BM) proteins accumulate chemical modifications with age. One such modification is glycation, which results in the formation of advanced glycation endproducts (AGEs). In a previous study, we reported that AGEs in the human lens capsule (BM) promote the TGFβ2-mediated epithelial-to-mesenchymal transition (EMT) of lens epithelial cells, which we proposed as a mechanism for posterior capsule opacification (PCO) or secondary cataract formation. In this study, we investigated the role of a receptor for AGEs (RAGE) in the TGFβ2-mediated EMT in a human lens epithelial cell line (FHL124). RAGE was present in FHL124 cells, and its levels were unaltered in cells cultured on either native or AGE-modified BM or upon treatment with TGFβ2. RAGE overexpression significantly enhanced the TGFβ2-mediated EMT responses in cells cultured on AGE-modified BM compared with the unmodified matrix. In contrast, treatment of cells with a RAGE antibody or EN-RAGE (an endogenous ligand for RAGE) resulted in a significant reduction in the TGFβ2-mediated EMT response. This was accompanied by a reduction in TGFβ2-mediated Smad signaling and ROS generation. These results imply that the interaction of matrix AGEs with RAGE plays a role in the TGFβ2-mediated EMT of lens epithelial cells and suggest that the blockade of RAGE could be a strategy to prevent PCO and other age-associated fibrosis.

Growth factor restriction impedes progression of wound healing following cataract surgery: identification of VEGF as a putative therapeutic target

Secondary visual loss occurs in millions of patients due to a wound-healing response, known as posterior capsule opacification (PCO), following cataract surgery. An intraocular lens (IOL) is implanted into residual lens tissue, known as the capsular bag, following cataract removal. Standard IOLs allow the anterior and posterior capsules to become physically connected. This places pressure on the IOL and improves contact with the underlying posterior capsule. New open bag IOL designs separate the anterior capsule and posterior capsules and further reduce PCO incidence. It is hypothesised that this results from reduced cytokine availability due to greater irrigation of the bag. We therefore explored the role of growth factor restriction on PCO using human lens cell and tissue culture models. We demonstrate that cytokine dilution, by increasing medium volume, significantly reduced cell coverage in both closed and open capsular bag models. This coincided with reduced cell density and myofibroblast formation. A screen of 27 cytokines identified nine candidates whose expression profile correlated with growth. In particular, VEGF was found to regulate cell survival, growth and myofibroblast formation. VEGF provides a therapeutic target to further manage PCO development and will yield best results when used in conjunction with open bag IOL designs.

αB-crystallin is essential for the TGF-β2-mediated epithelial to mesenchymal transition of lens epithelial cells

Transforming growth factor (TGF)-β2-mediated pathways play a major role in the epithelial to mesenchymal transition (EMT) of lens epithelial cells (LECs) during secondary cataract formation, which is also known as posterior capsule opacification (PCO). Although αB-crystallin is a major protein in LEC, its role in the EMT remains unknown. In a human LEC line (FHL124), TGF-β2 treatment resulted in changes in the EMT-associated proteins at the mRNA and protein levels. This was associated with nuclear localization of αB-crystallin, phosphorylated Smad2 (pSmad2) (S245/250/255), pSmad3 (S423/425), Smad4 and Snail and the binding of αB-crystallin to these transcription factors, all of which were reduced by the down-regulation of αB-crystallin. Expression of the functionally defective R120G mutant of αB-crystallin reduced TGF-β2-induced EMT in LECs of αB-crystallin knockout (KO) mice. Treatment of bovine lens epithelial explants and mouse LEC with TGF-β2 resulted in changes in the EMT-associated proteins at the mRNA and protein levels. This was accompanied by increase in phosphorylation of p44/42 mitogen-activated protein kinases (MAPK) (T202/Y204), p38 MAPK (T180/Y182), protein kinase B (Akt) (S473) and Smad2 when compared with untreated cells. These changes were significantly reduced in αB-crystallin depleted or knocked out LEC. The removal of the fibre cell mass from the lens of wild-type (WT) mice resulted in the up-regulation of EMT-associated genes in the capsule-adherent epithelial cells, which was reduced in the αB-crystallin KO mice. Together, our data show that αB-crystallin plays a central role in the TGF-β2-induced EMT of LEC. αB-Crystallin could be targeted to prevent PCO and pathological fibrosis in other tissues.

CtBP2 Regulates TGFβ2-Induced Epithelial-Mesenchymal Transition Through Notch Signaling Pathway in Lens Epithelial Cells

BACKGROUND

Epithelial-mesenchymal transition (EMT) of human lens epithelial cells (LECs) contributes to posterior capsule opacification (PCO). C-terminal binding protein 2 (CtBP2) has been reported to be essential in EMT and embryonic development. However, the function of CtBP2 in EMT of LECs is unknown. The goal of this study was to investigate the role of CtBP2 through Notch signaling in transforming growth factor β2 (TGFβ2)-induced EMT in LECs.

METHODS

The human LEC line SRA01/04 was cultured in the presence of TGFβ2 for different periods of time or with γ-Secretase Inhibitor IX (DAPT), a specific inhibitor of Notch receptor cleavage, for 24 h, utilizing plasmid-based method. The levels of protein expression of CtBP2, EMT markers, and Notch signaling molecules were measured by Western bolts.

RESULTS

Treatment of SRA01/04 cells with TGFβ2 induced typical molecular changes of EMT and increased the expression of CtBP2 in a time-dependent manner. Similarly, the expressions of Jagged1 and Notch1 were increased after TGFβ2 treatment. Knockdown of CtBP2 by specific siRNA inhibited TGFβ2-induced changes of Connexin 43 (CX43), α-smooth muscle actin (α-SMA), Notch1, and Notch intracellular domain (NICD). In addition, treatment of LECs with ectopic expression of CtBP2 changed the expressions of CX43, α-SMA, Notch1, and NICD, but blockade of Notch pathway with DAPT inhibited CtBP2-induced changes of α-SMA and CX43.

CONCLUSION

Our data suggest that CtBP2 plays a critical role in TGFβ2-induced EMT via the Jagged/Notch signaling pathway in human LECs and may contribute to the development of PCO.

TGF-β2 induces epithelial-mesenchymal transition in cultured human lens epithelial cells through activation of the PI3K/Akt/mTOR signaling pathway

The present study aimed to investigate whether the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway is involved in the transforming growth factor β₂ (TGF-β₂)-induced epithelial-mesenchymal transition (EMT) in human lens epithelial (HLE) cells. HLEB-3 cells were cultured and stimulated with 10 ng/ml TGF-β₂ for 24 h. Western blotting was then performed to analyze the expression levels of connexin 43 and fibronectin, and the activities of Akt and mTOR. Confocal cell immunofluorescence was used to observe the expression of phosphorylated (p)-Akt. The toxicity of 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) was assessed using a Cell Counting Kit-8 assay, and inhibition investigations were performed using a PI3K inhibitor. The expression of connexin 43 was suppressed and the expression of fibronectin was increased when the cells were stimulated with 10 ng/ml TGF-β₂ for 24 h. In addition, Akt and mTOR were activated during TGF-β₂-induced EMT. Treatment of with LY294002 (20 µM) inhibited the activation of Akt and mTOR and effectively prevented TGF-β₂-induced EMT in the HLECs. Therefore, the results of the present study indicated that TGF-β₂ induces EMT by activating the PI3K/Akt/mTOR signaling pathway in cultured HLECs.

Nanofiber-based hydrogels with extracellular matrix-based synthetic peptides for the prevention of capsular opacification

Nanofiber-based hydrogels (nanogels) with different, covalently bound peptides were used as an extracellular environment for lens epithelial cells (LECs) in order to modulate the capsular opacification (CO) response after lens surgery in a porcine eye model. Lenses were divided into 15 groups (n = 4 per group), the lens content was removed and the empty capsules were refilled with nanogel without peptides and nanogels with 13 combinations of 5 different peptides: two laminin-derived, two fibronectin-derived, and one collagen IV-derived peptide representing cell adhesion motifs. A control group of 4 lenses was refilled with hyaluronan. After refilling, lenses were extracted from the porcine eye and cultured for three weeks. LECs were assessed for morphology and alpha smooth muscle actin (αSMA) expression using confocal laser scanning microscopy. Compared to hyaluronan controls, lenses filled with nanogel had less CO formation, indicated by a lower αSMA expression (P = 0.004). Microscopy showed differences in morphological cell response within the nanogel refilled groups. αSMA expression in these groups was highest in lenses refilled with nanogel without peptides (9.54 ± 11.29%). Overall, LEC transformation is reduced by the presence of nanogels and the response is improved even further by incorporation of extracellular matrix peptides representing adhesion motifs. Thus, nanomaterials targeting biological pathways, in our case interactions with integrin signaling, are a promising avenue toward reduction of CO. Further research is needed to optimize nanogel-peptide combinations that fully prevent CO.

Expression of transcription factors Slug in the lens epithelial cells undergoing epithelial-mesenchymal transition induced by connective tissue growth factor

AIM

To investigate the expression of transcription factors Slug in human lens epithelial cells (HLECs) undergoing epithelial-mesenchymal transition (EMT) induced by connective tissue growth factor (CTGF).

METHODS

HLECs were treated with CTGF of different concentrations (20, 50 and 100 ng/mL) or without CTGF (control) for 24h. The morphological changes of HLECs were analysed by microscopy. The expression and cellular localization of Slug was evaluated by immumo-fluorescence. Expressions of Slug, E-cadherin and alpha smooth muscle actin (α-SMA) were further determined by Western blot analysis.

RESULTS

HLECs showed spidle fibrolasts-like characteristics and loosely connected each other after CTGF treatment. The immuno-fluorescence staining indicated that Slug was localized in the nuclei and its expression was induced by CTGF. The relative expressions of Slug protein were 1.64±0.11, 1.96 ±0.03, 3.12 ±0.10, and 4.08±0.14, respectively, in response to control group and treatment with CTGF of 20, 50 and 100 ng/mL (F=443.86, P<0.01). The increased Slug protein levels were correlated well with up-expression of α-SMA (0.78±0.05, 0.85±0.06, 2.17±0.15, 2.86±0.10; F=449.85, P<0.01) and down-expression of E-cadherin (2.50±0.11, 1.79±0.26, 1.05±0.14, 0.63±0.08; F=101.55, P<0.01).

CONCLUSION

Transcription factor Slug may be involved in EMT of HLECs induced by CTGF in vitro.

Aldose Reductase Mediates Transforming Growth Factor β2 (TGF-β2)-Induced Migration and Epithelial-To-Mesenchymal Transition of Lens-Derived Epithelial Cells

PURPOSE

Cataract surgery involves removal of lens tissue, but is associated with a high complication rate due to regrowth of residual lens epithelial cells to produce posterior capsule opacification (PCO) and diminished visual acuity. As inhibitors of aldose reductase (AR) have been shown to suppress markers of PCO, our studies were designed to identify a role for AR in the pathogenesis of PCO.

METHODS

Sorbinil-mediated AR inhibition was determined by measuring sorbitol accumulation. Cell migration was measured using both transwell and scratch assays. Proteins in the SMAD signaling pathway were measured by Western blotting. The interactions of AR and SMADs were demonstrated by co-immunoprecipitation (Co-IP) and proximity ligation assay (PLA). Epithelial-to-mesenchymal transition (EMT) expression was measured by Western blot and quantitative PCR (q-PCR). Matrix metalloproteinase (MMP)-2 and MMP-9 activities were measured in conditioned medium by zymography.

RESULTS

We observed that either Sorbinil-mediated AR inhibition or siRNA-mediated AR gene knockdown prevented migration of lens epithelial cells following exposure to TGF-β2. AR inhibition or AR knockdown reduced SMAD and MMP activation triggered by TGF-β2. In addition, we demonstrated AR inhibition or AR knockdown decreased TGF-β2-induced expression of EMT markers. Co-IP studies and PLA were used to demonstrate that AR and SMAD2 interact either directly or in close concert with additional factor(s) in a nonenzymatic manner.

CONCLUSIONS

This study demonstrates that AR participates in the response of lens epithelial cells to TGF-β2. Our studies raise the possibility that AR inhibition may be effective in preventing development of PCO by disrupting the TGF-β2/SMAD pathway.

The Association Between Aqueous Connective Tissue Growth Factor and the Severity of Age-related Cataracts as Graded by the Lens Opacities Classification System III

PURPOSE

To evaluate the relationship between aqueous humor concentrations of connective tissue growth factor (CTGF) and the severity of age-related cataracts.

MATERIALS AND METHODS

We conducted a prospective clinical study on 43 eyes of 43 patients with senile cataracts scheduled to undergo routine phacoemulsification surgery. Before surgery, all patients were graded for cataract severity using the Lens Opacities Classification System III in terms of four features: nuclear opalescence (NO), nuclear color (NC), cortical cataracts (C), and posterior sub-capsular cataracts (P). During surgery, aqueous humor samples were obtained from all patients, and sandwich enzyme-linked immunosorbent assays (ELISAs) were used to determine CTGF concentrations. To assess any relationship between cataract severity and CTGF levels of the aqueous humor, various correlation analyses and multiple linear regression were used.

RESULTS

We found a positive correlation between the overall cataract grade and aqueous CTGF level (p < 0.05). In addition, four features of the cataract grade (nuclear opalescence, nuclear color, cortical cataract and posterior sub-capsular cataract) were positively correlated with the aqueous CTGF concentration (p < 0.05). The final regression model identified overall cataract grade as an independent predictor of increased CTGF levels in the aqueous humor (p < 0.05).

CONCLUSIONS

CTGF tends to increase in the aqueous humor as the severity of age-related cataracts increases. Therefore, this cytokine may play an important role in the pathogenesis of age-related cataracts. Additional studies are required for clarification of this finding.

Fibrosis in the lens. Sprouty regulation of TGFβ-signaling prevents lens EMT leading to cataract

Cataract is a common age-related condition that is caused by progressive clouding of the normally clear lens. Cataract can be effectively treated by surgery; however, like any surgery, there can be complications and the development of a secondary cataract, known as posterior capsule opacification (PCO), is the most common. PCO is caused by aberrant growth of lens epithelial cells that are left behind in the capsular bag after surgical removal of the fiber mass. An epithelial-to-mesenchymal transition (EMT) is central to fibrotic PCO and forms of fibrotic cataract, including anterior/posterior polar cataracts. Transforming growth factor β (TGFβ) has been shown to induce lens EMT and consequently research has focused on identifying ways of blocking its action. Intriguingly, recent studies in animal models have shown that EMT and cataract developed when a class of negative-feedback regulators, Sprouty (Spry)1 and Spry2, were conditionally deleted from the lens. Members of the Spry family act as general antagonists of the receptor tyrosine kinase (RTK)-mediated MAPK signaling pathway that is involved in many physiological and developmental processes. As the ERK/MAPK signaling pathway is a well established target of Spry proteins, and overexpression of Spry can block aberrant TGFβ-Smad signaling responsible for EMT and anterior subcapsular cataract, this indicates a role for the ERK/MAPK pathway in TGFβ-induced EMT. Given this and other supporting evidence, a case is made for focusing on RTK antagonists, such as Spry, for cataract prevention. In addition, and looking to the future, this review also looks at possibilities for supplanting EMT with normal fiber differentiation and thereby promoting lens regenerative processes after cataract surgery. Whilst it is now known that the epithelial to fiber differentiation process is driven by FGF, little is known about factors that coordinate the precise assembly of fibers into a functional lens. However, recent research provides key insights into an FGF-activated mechanism intrinsic to the lens that involves interactions between the Wnt-Frizzled and Jagged/Notch signaling pathways. This reciprocal epithelial-fiber cell interaction appears to be critical for the assembly and maintenance of the highly ordered three-dimensional architecture that is central to lens function. This information is fundamental to defining the specific conditions and stimuli needed to recapitulate developmental programs and promote regeneration of lens structure and function after cataract surgery.

Prevention of posterior capsular opacification

Posterior capsular opacification (PCO) is a common complication of cataract surgery. The development of PCO is due to a combination of the processes of proliferation, migration, and transdifferentiation of residual lens epithelial cells (LECs) on the lens capsule. In the past decades, various forms of PCO prevention have been examined, including adjustments of techniques and intraocular lens materials, pharmacological treatments, and prevention by interfering with biological processes in LECs. The only method so far that seems effective is the implantation of an intraocular lens with sharp edged optics to mechanically prevent PCO formation. In this review, current knowledge of the prevention of PCO will be described. We illustrate the biological pathways underlying PCO formation and the various approaches to interfere with the biological processes to prevent PCO. In this type of prevention, the use of nanotechnological advances can play a role.

Quantitative analysis of injury-induced anterior subcapsular cataract in the mouse: a model of lens epithelial cells proliferation and epithelial-mesenchymal transition

The mouse lens capsular injury model has been widely used in investigating the mechanisms of anterior subcapsular cataract (ASC) and posterior capsule opacification (PCO), and evaluating the efficacy of antifibrotic compounds. Nevertheless, there is no available protocol to quantitatively assess the treatment outcomes. Our aim is to describe a new method that can successfully quantify the wound and epithelial-mesenchymal transition (EMT) markers expression in vivo. In this model, lens anterior capsule was punctured with a hypodermic needle, which triggered lens epithelial cells (LECs) proliferation and EMT rapidly. Immunofluorescent staining of injured lens anterior capsule whole-mounts revealed the formation of ASC and high expression of EMT markers in the subcapsular plaques. A series of sectional images of lens capsule were acquired from laser scanning confocal microscopy (LSCM) three-dimensional (3D) scanning. Using LSCM Image Browser software, we can not only obtain high resolution stereo images to present the spatial structures of ASC, but also quantify the subcapsular plaques and EMT markers distribution sucessfully. Moreover, we also demonstrated that histone deacetylases (HDACs) inhibitor TSA significantly prevented injury-induced ASC using this method. Therefore, the present research provides a useful tool to study ASC and PCO biology as well as the efficacy of new therapies.

The Patched 1 tumor-suppressor gene protects the mouse lens from spontaneous and radiation-induced cataract

Age-related cataract is the most common cause of visual impairment. Moreover, traumatic cataracts form after injury to the eye, including radiation damage. We report herein that sonic hedgehog (Shh) signaling plays a key role in cataract development and in normal lens response to radiation injury. Mice heterozygous for Patched 1 (Ptch1), the Shh receptor and negative regulator of the pathway, develop spontaneous cataract and are highly susceptible to cataract induction by exposure to ionizing radiation in early postnatal age, when lens epithelial cells undergo rapid expansion in the lens epithelium. Neonatally irradiated and control Ptch1(+/-) mice were compared for markers of progenitors, Shh pathway activation, and epithelial-to-mesenchymal transition (EMT). Molecular analyses showed increased expression of the EMT-related transforming growth factor β/Smad signaling pathway in the neonatally irradiated lens, and up-regulation of mesenchymal markers Zeb1 and Vim. We further show a link between proliferation and the stemness property of lens epithelial cells, controlled by Shh. Our results suggest that Shh and transforming growth factor β signaling cooperate to promote Ptch1-associated cataract development by activating EMT, and that the Nanog marker of pluripotent cells may act as the primary transcription factor on which both signaling pathways converge after damage. These findings highlight a novel function of Shh signaling unrelated to cancer and provide a new animal model to investigate the molecular pathogenesis of cataract formation.

The Zeb proteins δEF1 and Sip1 may have distinct functions in lens cells following cataract surgery

PURPOSE

Posterior capsular opacification (PCO), the most prevalent side effect of cataract surgery, occurs when residual lens epithelial cells (LECs) undergo fiber cell differentiation or epithelial-to-mesenchymal transition (EMT). Here, we used a murine cataract surgery model to investigate the role of the Zeb proteins, Smad interacting protein 1 (Sip1) and δ-crystallin enhancer-binding factor 1 (δEF1), during PCO.

METHODS

Extracapsular extraction of lens fiber cells was performed on wild-type and Sip1 knockout mice. Protein expression patterns were assessed at multiple time points after surgery using confocal immunofluorescence. βB1-Crystallin mRNA levels were measured using quantitative RT-PCR. We used Transfac searches to identify δEF1 binding sites in the βB1-crystallin promoter and transfection analysis to test the ability of δEF1 to regulate βB1-crystallin expression.

RESULTS

δEF1, which, in other systems, can activate fibrotic genes (e.g., α-smooth muscle actin) and repress epithelial genes, upregulates by 48 hours after fiber cell removal. In culture, δEF1 repressed βB1-crystallin promoter activity, suggesting that it may also turn off lens gene expression following surgery, contributing to "fibrotic PCO" development. Sip1 also upregulates in LECs by 48 hours, but analysis of Sip1 knockout lenses demonstrated that Sip1 does not play a major role in EMT or fiber cell differentiation after surgery. However, Sip1 knockout LECs do express the ectodermal marker keratin 8, suggesting that Sip1 may limit the reprogramming of residual LECs to an embryonic state.

CONCLUSIONS

Zeb transcription factors likely play important, but distinct roles in PCO development after cataract surgery.

Expression of transforming growth factor β and fibroblast growth factor 2 in the lens epithelium of Morioka cataract mice

In the Morioka cataract (MCT) mice, lens opacity appears at 6 to 8 weeks of age, and swollen lens fiber is electron-microscopically observed at 3 weeks after birth. The present study was designed to characterize the expression of transforming growth factor β (TGFβ) and fibroblast growth factor 2 (FGF2) in the lens epithelium of the MCT mice. Immunohistochemical analysis showed that the expression of TGFβ in the lens epithelium of the MCT mice was stronger than that of the wild-type ddY mice at 2 and 4 weeks after birth. The expression of TGFβ receptors (TGFβRI and TGFβRII) and FGF2 in the lens epithelium of the MCT mice was stronger than that of the wild-type ddY mice at 4 weeks and weaker than that of the wild-type ddY mice at 15 weeks after birth. Using real time polymerase chain reaction (PCR), quantitative RT-PCR analysis showed that expression of TGFβ1 and TGFβ2 mRNA in the lens of 2-week-old MCT mice was significantly higher compared to age-matched wild-type ddY mice. These findings indicate that the lens epithelium of MCT mice has increased expression of TGFβ before cataract affection and that changes in the expression of FGF2 as well as TGFβ may contribute to the progression of the cataract in the mice.