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

Transcriptome exploration of ferroptosis-related genes in TGFβ- induced lens epithelial to mesenchymal transition during posterior capsular opacification development

BACKGROUND

Posterior capsular opacification (PCO) is the main reason affecting the long-term postoperative result of cataract patient, and it is well accepted that fibrotic PCO is driven by transforming growth factor beta (TGFβ) signaling. Ferroptosis, closely related to various ocular diseases, but has not been explored in PCO.

METHODS

RNA sequencing (RNA-seq) was performed on both TGF-β2 treated and untreated primary lens epithelial cells (pLECs). Differentially expressed genes (DEGs) associated with ferroptosis were analyzed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to investigate their biological function. Additionally, protein-to-protein interactions among selected ferroptosis-related genes by PPI network and the top 10 genes with the highest score (MCC algorithm) were selected as the hub genes. The top 20 genes with significant fold change values were validated using quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Our analysis revealed 1253 DEGs between TGF-β2 treated and untreated pLECs, uncovering 38 ferroptosis-related genes between two groups. Among these 38 ferroptosis-related genes,the most prominent GO enrichment analysis process involved in the response to oxidative stress (BPs), apical part of cell (CCs),antioxidant activity (MFs). KEGG were mainly concentrated in fluid shear stress and atherosclerosis, IL-17 and TNF signaling pathways, and validation of top 20 genes with significant fold change value were consistent with RNA-seq.

CONCLUSIONS

Our RNA-Seq data identified 38 ferroptosis-related genes in TGF-β2 treated and untreated pLECs, which is the first observation of ferroptosis related genes in primary human lens epithelial cells under TGF-β2 stimulation.

Modeling Cataract Surgery in Mice

Cataract surgery (CS) is an effective treatment for cataracts, a major cause of visual disability worldwide. However, CS leads to ocular inflammation, and in the long term, it can result in posterior capsular opacification (PCO) and/or lens dislocation driven by the post-surgical overgrowth of lens epithelial cells (LECs) and their conversion to myofibroblasts and/or aberrant fiber cells. However, the molecular mechanisms by which CS results in inflammation and PCO are still obscure because most in vitro models do not recapitulate the wound healing response of LECs seen in vivo, while traditional animal models of cataract surgery, such as rabbits, do not allow the genetic manipulation of gene expression to test mechanisms. Recently, our laboratory and others have successfully used genetically modified mice to study the molecular mechanisms that drive the induction of proinflammatory signaling and LEC epithelial to mesenchymal transition, leading to new insight into PCO pathogenesis. Here, we report the established protocol for modeling cataract surgery in mice, which allows for robust transcriptional profiling of the response of LECs to lens fiber cell removal via RNAseq, the evaluation of protein expression by semi-quantitative immunofluorescence, and the use of modern mouse genetics tools to test the function of genes that are hypothesized to participate in the pathogenesis of acute sequelae like inflammation as well as the later conversion of LECs to myofibroblasts and/or aberrant lens fiber cells.

First Case Report of Developmental Bilateral Cataract with a Novel Mutation in the ZEB2 Gene Observed in Mowat-Wilson Syndrome

Background: Mowat-Wilson syndrome (MWS) is extremely rare multisystemic autosomal dominant disorder caused by mutations in the Zinc Finger E-Box Binding Homeobox 2 (ZEB2) gene. Ocular pathologies are one of the symptoms that appear in the clinical picture of MWS individuals, but not many have been described so far. Pathologies such as optic nerve or retinal epithelium atrophy, iris or optic disc coloboma as well as congenital cataracts have been most frequently described until now. Therefore, we would like to report the first case of bilateral developmental cataract in a 9-year-old girl with MWS who underwent successful cataract surgery with intraocular lens implantation. Case Presentation: A 9-year-old girl, diagnosed with p.Gln694Ter mutation in ZEB2 gene and suspicion of MWS was referred to the Children's Outpatient Ophthalmology Clinic for ophthalmological evaluation. Her previous assessments revealed abnormalities of the optic nerve discs. The patient was diagnosed with atrophy of the optic nerves, convergent strabismus, and with-the-rule astigmatism. One year later, during the follow-up visit, the patient was presented with decreased visual acuity (VA), developmental total cataract in the right eye and a developmental partial cataract in the left eye. This resulted in decreased VA confirmed by deteriorated responses in visual evoked potential (VEP) test. The girl underwent a two-stage procedure of cataract removal, first of one eye and then of the other eye with artificial lens implants. In the 2 years following the operation, no complications were observed and, most remarkably, VA improved significantly. Conclusions: The ZEB2 gene is primarily responsible for encoding the Smad interaction protein 1 (SIP1), which is involved in the proper development of various eye components. When mutated, it results in multilevel abnormalities, also in the proper lens formation, that prevent the child from normal vision development. This typically results in the formation of congenital cataracts in children with MWS syndrome, however, our case shows that it also leads to the formation of developmental cataracts. This is presumably due to the effect of the lack of SIP1 on other genes, altering their downstream expression and is a novel insight into the importance of the SIP1 in the occurrence of ocular pathologies. To the best of our knowledge, this is the first case of bilateral developmental cataract in the context of MWS. Moreover, a novel mutation (p.Gln694Ter) in the ZEB2 gene was found corresponding to this syndrome entity. This report allows us to gain a more comprehensive insight into the genetic spectrum and the corresponding phenotypic features in MWS syndrome patients.

The effect of sex on the mouse lens transcriptome

The transcriptome of mammalian tissues differs between males and females, and these differences can change across the lifespan, likely regulating known sexual dimorphisms in disease prevalence and severity. Cataract, the most prevalent disease of the ocular lens, occurs at similar rates in young individuals, but its incidence is elevated in older women compared to men of the same age. However, the influence of sex on the lens transcriptome was unknown. RNAseq based transcriptomic profiling of young adult C57BL/6J mouse lens epithelial and fiber cells revealed that few genes are differentially expressed between the sexes. In contrast, lens cells from aged (24 month old) male and female C57BL/6J mice differentially expressed many genes, including several whose expression is lens preferred. Like cataracts, posterior capsular opacification (PCO), a major sequela of cataract surgery, may also be more prevalent in women. Lens epithelial cells isolated from mouse eyes 24 h after lens fiber cell removal exhibited numerous transcriptomic differences between the sexes, including genes implicated in complement cascades and extracellular matrix regulation, and these differences are much more pronounced in aged mice than in young mice. These results provide an unbiased basis for future studies on how sex affects the lens response to aging, cataract development, and cataract surgery.

The aging mouse lens transcriptome

Age is a major risk factor for cataract (ARC). However, the influence of aging on the lens transcriptome is under studied. Lens epithelial (LEC) and fiber cells (LFC) were isolated from young (3 month old) and aged (24 month old) C57BL/6J mice, and the transcriptome elucidated via RNAseq. EdgeR estimated differential gene expression in pairwise contrasts, and Advaita's Ipathway guide and custom R scripts were used to evaluate the potential biological significance of differentially expressed genes (DEGs). This analysis revealed age-dependent decreases in lens differentiation marker expression in both LECs and LFCs, with gamma crystallin transcripts downregulating nearly 50 fold in aged LFCs. The expression of the transcription factors Hsf4 and Maf, which are known to activate lens fiber cell preferred genes, are downregulated, while FoxE3, which represses gamma crystallin expression, is upregulated in aged fibers. Aged LECs upregulate genes controlling the immune response, complement pathways, and cellular stress responses, including glutathione peroxidase 3 (Gpx3). Aged LFCs exhibit broad changes in the expression of genes regulating cell communication, and upregulate genes involved in antigen processing/presentation and cholesterol metabolism, while changes in the expression of mitochondrial respiratory chain genes are consistent with mitochondrial stress, including upregulation of NDufa4l2, which encodes an alternate electron transport chain protein. However, age did not profoundly affect the response of LECs to injury as both young and aged LECs upregulate inflammatory gene signatures at 24 h post injury to similar extents. These RNAseq profiles provide a rich data set that can be mined to understand the genetic regulation of lens aging and how this impinges on the pathophysiology of age related cataract.

Lens Epithelial Cells Initiate an Inflammatory Response Following Cataract Surgery

Purpose

Lens epithelial cell (LEC) conversion to myofibroblast is responsible for fibrotic cataract surgery complications including posterior capsular opacification. While transforming growth factor beta (TGFβ) signaling is important, the mechanisms by which the TGFβ pathway is activated post cataract surgery (PCS) are not well understood.

Methods

RNA-seq was performed on LECs obtained from a mouse cataract surgery model at the time of surgery and 24 hours later. Bioinformatic analysis was performed with iPathwayGuide. Expression dynamics were determined by immunofluorescence.

Results

The LEC transcriptome is massively altered by 24 hours PCS. The differentially expressed genes included those important for lens biology, and fibrotic markers. However, the most dramatic changes were in the expression of genes regulating the innate immune response, with the top three altered genes exhibiting greater than 1000-fold upregulation. Immunolocalization revealed that CXCL1, S100a9, CSF3, COX-2, CCL2, LCN2, and HMOX1 protein levels upregulate in LECs between 1 hour and 6 hours PCS and peak at 24 hours PCS, while their levels sharply attenuate by 3 days PCS. This massive upregulation of known inflammatory mediators precedes the infiltration of neutrophils into the eye at 18 hours PCS, the upregulation of canonical TGFβ signaling at 48 hours PCS, and the infiltration of macrophages at 3 days PCS.

Conclusions

These data demonstrate that LECs produce proinflammatory cytokines immediately following lens injury that could drive postsurgical flare, and suggest that inflammation may be a major player in the onset of lens-associated fibrotic disease PCS.

Spatiotemporal dynamics of canonical Wnt signaling during embryonic eye development and posterior capsular opacification (PCO)

The appropriate spatial and temporal regulation of canonical Wnt signaling is vital for eye development. However, the literature often conflicts on the distribution of canonical Wnt signaling in the eye. Here, using a sensitive mouse transgenic reporter line, we report a detailed re-evaluation of the spatiotemporal dynamics of canonical Wnt signaling in the developing eye. Canonical Wnt activity was dynamic in the optic vesicle and later in the retina, while it was absent from the ectodermal precursors of the lens and corneal epithelium. However, later in corneal development, canonical Wnt reporter activity was detected in corneal stroma and endothelium precursors as they form from the neural crest, although this was lost around birth. Interestingly, while no canonical Wnt signaling was detected in the corneal limbus or basal cells at any developmental stage, it was robust in adult corneal wing and squamous epithelial cells. While canonical Wnt reporter activity was also absent from the postnatal lens, upon lens injury intended to model cataract surgery, it upregulated within 12 h in remnant lens epithelial cells, and co-localized with alpha smooth muscle actin in fibrotic lens epithelial cells from 48 h post-surgery onward. This pattern correlated with downregulation of the inhibitor of canonical Wnt signaling, Dkk3. These data demonstrate that canonical Wnt signaling is dynamic within the developing eye and upregulates in lens epithelial cells in response to lens injury. As canonical Wnt signaling can collaborate with TGFβ to drive fibrosis in other systems, these data offer the first evidence in a lens-injury model that canonical Wnt may synergize with TGFβ signaling to drive fibrotic posterior capsular opacification (PCO).

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.

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.

Development of novel filtering criteria to analyze RNA-sequencing data obtained from the murine ocular lens during embryogenesis

Next-generation sequencing of the transcriptome (RNA-Seq) is a powerful method that allows for the quantitative determination of absolute gene expression, and can be used to investigate how these levels change in response to an experimental manipulation or disease condition. The sensitivity of this method allows one to analyze transcript levels of all expressed genes, including low abundance transcripts that encode important regulatory molecules, providing valuable insights into the global effects of experimental manipulations. However, this increased sensitivity can also make it challenging to ascertain which expression changes are biologically significant. Here, we describe a novel set of filtering criteria - based on biological insights and computational approaches - that were applied to prioritize genes for further study from an extensive number of differentially expressed transcripts in lenses lacking Smad interacting protein 1 (Sip1) obtained via RNA-Seq by Manthey and colleagues in Mechanisms of Development (Manthey et al., 2014). Notably, this workflow allowed an original list of over 7,100 statistically significant differentially expressed genes (DEGs) to be winnowed down to 190 DEGs that likely play a biologically significant role in Sip1 function during lens development. Focusing on genes whose expression was upregulated or downregulated in a manner opposite to what normally occurs during lens development, we identified 78 genes that appear to be strongly dependent on Sip1 function. From these data (GEO accession number GSE49949), it appears that Sip1 regulates multiple genes in the lens that are generally distinct from those regulated by Sip1 in other cellular contexts, including genes whose expression is prominent in the early head ectoderm, from which the lens differentiates. Further, the analysis criteria outlined here represent a filtering scheme that can be used to prioritize genes in future RNA-Seq investigations performed at this stage of ocular lens development.