Risk factors for pterygium: Latest research progress on major pathogenesis

A pterygium is a wedge-shaped fibrovascular growth of the conjunctiva membrane that extends onto the cornea, which is the outer layer of the eye. It is also known as surfer's eye. Growth of a pterygium can also occur on the either side of the eye, attaching firmly to the sclera. Pterygia are one of the world's most common ocular diseases. However, the pathogenesis remains unsolved to date. As the pathogenesis of pterygium is closely related to finding the ideal treatment, a clear understanding of the pathogenesis will lead to better treatment and lower the recurrence rate, which is notably high and more difficult to treat than a primary pterygium. Massive studies have recently been conducted to determine the exact causes and mechanism of pterygia. We evaluated the pathogenetic factors ultraviolet radiation, viral infection, tumor suppressor genes p53, growth factors, oxidative stress, apoptosis and neuropeptides in the progression of the disease. The heightened expression of TRPV1 suggests its potential contribution in the occurrence of pterygium, promoting its inflammation and modulating sensory responses in ocular tissues. Subsequently, the developmental mechanism of pterygium, along with its correlation with dry eye disease is proposed to facilitate the identification of pathogenetic factors for pterygia, contributing to the advancement of understanding in this area and may lead to improved surgical outcomes.

Expression of CD44, PCNA and E-cadherin in pterygium tissues

PURPOSE

Pterygium is a common ocular surface disease defined by fibrovascular conjunctival growth extending onto the cornea. However, its pathogenesis remains unclear. This study aimed to determine the role of CD44, proliferating cell nuclear antigen (PCNA), and E-cadherin in pterygium formation and recurrence.

METHODS

Sixty patients with pterygium participated in the study, and we collected conjunctival samples from 30 patients to form a control group. CD44, PCNA, and E-cadherin expressions in surgically excised pterygium were compared with tissue samples from the control group.

RESULTS

We observed that the percentages of CD44 and PCNA were statistically higher in the primary pterygium group and recurrent pterygium group than in the control group (P < 0.001 and P < 0.001, respectively). Conversely, E-cadherin values were statistically higher in the control group than in the primary and recurrent pterygium groups (P = 0.013 and P < 0.001, respectively).

CONCLUSION

Cell proliferation and cell adhesion factors may play important roles in the pathogenesis of pterygium.

Multi-System-Level Analysis with RNA-Seq on Pterygium Inflammation Discovers Association between Inflammatory Responses, Oxidative Stress, and Oxidative Phosphorylation

A pterygium is a common conjunctival degeneration and inflammatory condition. It grows onto the corneal surface or limbus, causing blurred vision and cosmetic issues. Ultraviolet is a well-known risk factor for the development of a pterygium, although its pathogenesis remains unclear, with only limited understanding of its hereditary basis. In this study, we collected RNA-seq from both pterygial tissues and conjunctival tissues (as controls) from six patients (a total of twelve biological samples) and retrieved publicly available data, including eight pterygium samples and eight controls. We investigated the intrinsic gene regulatory mechanisms closely linked to the inflammatory reactions of pterygiums and compared Asian (Korea) and the European (Germany) pterygiums using multiple analysis approaches from different perspectives. The increased expression of antioxidant genes in response to oxidative stress and DNA damage implies an association between these factors and pterygium development. Also, our comparative analysis revealed both similarities and differences between Asian and European pterygiums. The decrease in gene expressions involved in the three primary inflammatory signaling pathways-JAK/STAT, MAPK, and NF-kappa B signaling-suggests a connection between pathway dysfunction and pterygium development. We also observed relatively higher activity of autophagy and antioxidants in the Asian group, while the European group exhibited more pronounced stress responses against oxidative stress. These differences could potentially be necessitated by energy-associated pathways, specifically oxidative phosphorylation.

Single-cell RNA sequencing reveals the complex cellular niche of pterygium

PURPOSE

Pterygium is a vision-threatening conjunctival fibrovascular degenerated disease with a high global prevalence up to 12 %, while no absolute pharmacotherapy has been applied in clinics. In virtue of single-cell RNA sequencing (scRNA-seq) technique, our study investigated underlying pathogeneses and potential therapeutic targets of pterygium from the cellular transcriptional level.

METHODS

A total of 45605 cells from pterygium of patients and conjunctiva of normal controls (NC) were conducted with scRNA-seq, and then analyzed via integrated analysis, pathway enrichment, pseudotime trajectory, and cell-cell communications. Besides, immunofluorescence and western blot were performed in vivo and in vitro to verify our findings.

RESULTS

In brief, 9 major cellular types were defined, according to canonical markers. Subsequently, we further determined the subgroups of each major cell lineages. Several newly identified cell sub-clusters could promote pterygium, including immuno-fibroblasts, epithelial mesenchymal transition (EMT)-epithelial cells, and activated vascular endothelial cells (activated-vEndo). Besides, we also probed the enrichment of immune cells in pterygium. Particularly, macrophages, recruited by ACKR1+activated-vEndo, might play an important role in the development of pterygium by promoting angiogenesis, immune suppression, and inflammation.

CONCLUSION

An intricate cellular niche was revealed in pterygium via scRNA-seq analysis and the interactions between macrophages and ACKR1+ activated-vEndo might be the key part in the development of pterygia.

Expression Analysis of the Small GTP-Binding Protein Rac in Pterygium

Objectives

To determine the roles of small GTP-binding proteins Rac1, Rac2, and Rac3 expression in pterygial tissue and to compare these expressions with normal conjunctival tissue.

Materials and Methods

Seventy-eight patients with primary pterygium were enrolled. Healthy conjunctival graft specimens obtained during pterygium surgery were used as control tissue. The real-time polymerase chain reaction method on the BioMark HD dynamic array system was utilized in genomic mRNA for the gene expression analysis. Protein expressions were analyzed using western blot and immunohistochemical methods.

Results

RAC1, RAC2, and RAC3 gene expressions in pterygial tissues were not markedly elevated when compared to the control specimens (p>0.05). As a very low level of RAC1 gene expression was observed, further protein expression analysis was performed for the Rac2 and Rac3 proteins. Western blot and immunohistochemical analysis of Rac2 and Rac3 protein expression revealed no significant differences between pterygial and healthy tissues (p>0.05).

Conclusion

This is the first study to identify the contribution of Rac proteins in pterygium. Our results indicate that the small GTP-binding protein Rac may not be involved in pterygium pathogenesis.

HIF1α and HIF2α immunoreactivity in epithelial tissue of primary and recurrent pterygium by immunohistochemical analysis

PURPOSE

Hypoxia-inducible factors (HIFs) are considered to play a significant role in the pathogenesis of pterygium. The aim of this study was to investigate the relative expression or immunoreactivity of HIF1α and HIF2α in the epithelium of primary pterygium, recurrences and healthy conjunctiva.

METHODS

Immunohistochemical staining was performed with antibodies against HIF1α and HIF2α, respectively, on 55/84 primary pterygium specimens, 6/28 recurrences and 20/20 control tissues (healthy conjunctiva).

RESULTS

Immunohistochemical staining revealed lower epithelial immunoreactivity of HIF1α and HIF2α in both primary pterygium (11% and 38%) and recurrences (18% and 21%) when compared to healthy conjunctival tissue (46% and 66%). Differences between immunoreactivity of HIF1α and of HIF2α in primary pterygium and controls were each highly significant (p < .001). Within the group of primary pterygium, epithelial immunoreactivity of HIF2α (38%) was significantly higher than that of HIF1α (11%). In recurrent pterygium and healthy conjunctiva, immunoreactivity levels of HIF2α were higher than those of HIF1α as well; however, differences between both isoforms were not significant.

CONCLUSION

Our study shows evidence that the higher expressed epithelial HIF2α, rather than HIF1α, and the balance between both HIF isoforms might be relevant factors associated with pathogenesis of primary pterygium. Modulation of HIF2α levels and activity may thus offer a new therapeutic approach to the treatment of advancing pterygium where the initial stage with its HIF1-peak has already passed.

Development and Characterization of Curcumin-Silver Nanoparticles as a Promising Formulation to Test on Human Pterygium-Derived Keratinocytes

Pterygium is a progressive disease of the human eye arising from sub-conjunctival tissue and extending onto the cornea. Due to its invasive growth, pterygium can reach the pupil compromising visual function. Currently available medical treatments have limited success in suppressing efficiently the disease. Previous studies have demonstrated that curcumin, polyphenol isolated from the rhizome of Curcuma longa, induces apoptosis of human pterygium fibroblasts in a dose- and time-dependent manner showing promising activity in the treatment of this ophthalmic disease. However, this molecule is not very soluble in water in either neutral or acidic pH and is only slightly more soluble in alkaline conditions, while its dissolving in organic solvents drastically reduces its potential use for biomedical applications. A nanoformulation of curcumin stabilized silver nanoparticles (Cur-AgNPs) seems an effective strategy to increase the bioavailability of curcumin without inducing toxic effects. In fact, silver nitrates have been used safely for the treatment of many ophthalmic conditions and diseases for a long time and the concentration of AgNPs in this formulation is quite low. The synthesis of this new compound was achieved through a modified Bettini's method adapted to improve the quality of the product intended for human use. Indeed, the pH of the reaction was changed to 9, the temperature of the reaction was increased from 90 °C to 100 °C and after the synthesis the Cur-AgNPs were dispersed in Borax buffer using a dialysis step to improve the biocompatibility of the formulation. This new compound will be able to deliver both components (curcumin and silver) at the same time to the affected tissue, representing an alternative and a more sophisticated strategy for the treatment of human pterygium. Further in vitro and in vivo assays will be required to validate this formulation.

Expression of SARS-CoV-2 receptor ACE2 and TMPRSS2 in human primary conjunctival and pterygium cell lines and in mouse cornea

PURPOSE

To determine the expressions of SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) and type II transmembrane serine protease (TMPRSS2) genes in human and mouse ocular cells and comparison to other tissue cells.

METHODS

Human conjunctiva and primary pterygium tissues were collected from pterygium patients who underwent surgery. The expression of ACE2 and TMPRSS2 genes was determined in human primary conjunctival and pterygium cells, human ocular and other tissue cell lines, mesenchymal stem cells as well as mouse ocular and other tissues by reverse transcription-polymerase chain reaction (RT-PCR) and SYBR green PCR.

RESULTS

RT-PCR analysis showed consistent expression by 2 ACE2 gene primers in 2 out of 3 human conjunctival cells and pterygium cell lines. Expression by 2 TMPRSS2 gene primers could only be found in 1 out of 3 pterygium cell lines, but not in any conjunctival cells. Compared with the lung A549 cells, similar expression was noted in conjunctival and pterygium cells. In addition, mouse cornea had comparable expression of Tmprss2 gene and lower but prominent Ace2 gene expression compared with the lung tissue.

CONCLUSION

Considering the necessity of both ACE2 and TMPRSS2 for SARS-CoV-2 infection, our results suggest that conjunctiva would be less likely to be infected by SARS-CoV-2, whereas pterygium possesses some possibility of SARS-CoV-2 infection. With high and consistent expression of Ace2 and Tmprss2 in cornea, cornea rather than conjunctiva has higher potential to be infected by SARS-CoV-2. Precaution is necessary to prevent possible SARS-CoV-2 infection through ocular surface in clinical practice.

Activation of the Sphingosine 1 Phosphate-Rho Pathway in Pterygium and in Ultraviolet-Irradiated Normal Conjunctiva

Sphingosine 1 phosphate (S1P) is a bioactive lipid that regulates cellular activity, including proliferation, cytoskeletal organization, migration, and fibrosis. In this study, the potential relevance of S1P–Rho signaling in pterygium formation and the effects of ultraviolet (UV) irradiation on activation of the S1P/S1P receptor axis and fibrotic responses were investigated in vitro. Expressions of the S1P2, S1P4, and S1P5 receptors were significantly higher in pterygium tissue than in normal conjunctiva, and the concentration of S1P was significantly elevated in the lysate of normal conjunctival fibroblast cell (NCFC) irradiated with UV (UV-NCFCs). RhoA activity was significantly upregulated in pterygium fibroblast cells (PFCs) and UV-NCFCs, and myosin phosphatase–Rho interacting protein (MRIP) was upregulated, and myosin phosphatase target subunit 1 (MYPT1) was downregulated in PFCs. Fibrogenic changes were significantly upregulated in both PFCs and UV-NCFCs compared to NCFCs. We found that the activation of the S1P receptor–Rho cascade was observed in pterygium tissue. Additionally, in vitro examination showed S1P–rho activation and fibrogenic changes in PFCs and UV-NCFCs. S1P elevation and the resulting upregulation of the downstream Rho signaling pathway may be important in pterygium formation; this pathway offers a potential therapeutic target for suppressing pterygium generation.

Identification and Interaction Analysis of Significant Genes and MicroRNAs in Pterygium

PURPOSE

MiRNAs have been widely analyzed in the occurrence and development of many diseases, including pterygium. This study aimed to identify the key genes and miRNAs in pterygium and to explore the underlying molecular mechanisms.

METHODS

MiRNA expression was initially extracted and pooled by published literature. Microarray data about differentially expressed genes was downloaded from Gene Expression Omnibus (GEO) database and analyzed with the R programming language. Functional and pathway enrichment analyses were performed using the database for Annotation, Visualization and Integrated Discovery (DAVID). The protein-protein interaction network was constructed with the STRING database. The associations between chemicals, differentially expressed miRNAs, and differentially expressed genes were predicted using the online resource. All the networks were constructed using Cytoscape.

RESULTS

We found that 35 miRNAs and 301 genes were significantly differentially expressed. Functional enrichment analysis showed that upregulated genes were significantly enriched in extracellular matrix (ECM) organization, while downregulated genes were mainly involved in cell death and apoptotic process. Finally, we concluded the chemical-gene affected network, miRNA-mRNA interacted networks, and significant pathway network.

CONCLUSION

We identified lists of differentially expressed miRNAs and genes and their possible interaction in pterygium. The networks indicated that ECM breakdown and EMT might be two major pathophysiological mechanisms and showed the potential significance of PI3K-Akt signalling pathway. MiR-29b-3p and collagen family (COL4A1 and COL3A1) might be new treatment target in pterygium.

Bromfenac Inhibits TGF-β1-Induced Fibrotic Effects in Human Pterygium and Conjunctival Fibroblasts

Purpose

Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown antifibrotic effects on several diseases. The aims of the present in vitro study were to investigate the antifibrotic effects of bromfenac (a kind of NSAID) on primary human pterygium fibroblasts (HPFs) and primary human conjunctival fibroblasts (HConFs), as well as to explore the possible mechanisms of these effects.

Methods

The cells used in this study were primary HPFs and HConFs, and profibrotic activation was induced by transforming growth factor-beta1 (TGF-β1). Western blot, quantitative real-time PCR, and immunofluorescence (IF) assays were used to detect the effects of TGF-β1 and bromfenac on the synthesis of fibronectin (FN), type III collagen (COL3), and alpha-smooth muscle actin (α-SMA) in HPFs and HConFs; the changes of signaling pathways were detected by Western blot; cell migration ability was detected by wound healing assay; cell proliferation ability was detected by CCK-8 assay; and pharmaceutical inhibitions of the downstream signaling pathways of TGF-β1 were used to assess their possible associations with the effects of bromfenac.

Results

Bromfenac suppressed the TGF-β1-induced protein expression of FN (0.59 ± 0.07 folds, P = 0.008), COL3 (0.48 ± 0.08 folds, P = 0.001), and α-SMA (0.61 ± 0.03 folds, P = 0.008) in HPFs. Bromfenac also attenuated TGF-β1-induced cell migration (0.30 ± 0.07 folds, P < 0.001), cell proliferation (0.64 ± 0.03 folds, P = 0.002) and the expression levels of p-AKT (0.66 ± 0.08 folds, P = 0.032), p-ERK1/2 (0.69 ± 0.11 folds, P = 0.003), and p-GSK-3β-S9 (0.65 ± 0.10 folds, P = 0.002) in HPFs. PI3K/AKT inhibitor (wortmannin) and MEK/ERK inhibitor (U0126) reduced the TGF-β1-induced synthesis of FN, COL3, and α-SMA in HPFs. All the results were similar in HConFs.

Conclusions

Bromfenac protects against TGF-β1-induced synthesis of FN, α-SMA, and COL3 in HPFs and HConFs at least in part by inactivating the AKT and ERK pathways.

Continuous exposure of nicotine and cotinine retards human primary pterygium cell proliferation and migration

Pterygium is a triangular-shaped hyperplastic growth, characterized by conjunctivalization, inflammation, and connective tissue remodeling. Our previous meta-analysis found that cigarette smoking is associated with a reduced risk of pterygium. Yet, the biological effect of cigarette smoke components on pterygium has not been studied. Here we reported the proliferation and migration properties of human primary pterygium cells with continuous exposure to nicotine and cotinine. Human primary pterygium cells predominantly expressed the α5, β1, and γ subunits of the nicotinic acetylcholine receptor. Continuous exposure to the mixture of 0.15 μM nicotine and 2 μM cotinine retarded pterygium cell proliferation by 16.04% (P = 0.009) and hindered their migration by 11.93% ( P = 0.039), without affecting cell apoptosis. SNAIL and α-smooth muscle actin protein expression was significantly downregulated in pterygium cells treated with 0.15 μM nicotine-2 μM cotinine mixture by 1.33- ( P = 0.036) and 1.31-fold ( P = 0.001), respectively. Besides, the 0.15 μM nicotine-2 μM cotinine mixture also reduced matrix metalloproteinase (MMP)-1 and MMP-9 expressions in pterygium cells by 1.56- ( P = 0.043) and 1.27-fold ( P = 0.012), respectively. In summary, this study revealed that continuous exposure of nicotine and cotinine inhibited human primary pterygium cell proliferation and migration in vitro by reducing epithelial-to-mesenchymal transition and MMP protein expression, partially explaining the lower incidence of pterygium in cigarette smokers.

A novel role for CRIM1 in the corneal response to UV and pterygium development

Pterygium is a pathological proliferative condition of the ocular surface, characterised by formation of a highly vascularised, fibrous tissue arising from the limbus that invades the central cornea leading to visual disturbance and, if untreated, blindness. Whilst chronic ultraviolet (UV) light exposure plays a major role in its pathogenesis, higher susceptibility to pterygium is observed in some families, suggesting a genetic component. In this study, a Northern Irish family affected by pterygium but reporting little direct exposure to UV was identified carrying a missense variant in CRIM1 NM_016441.2: c.1235 A > C (H412P) through whole-exome sequencing and subsequent analysis. CRIM1 is expressed in the developing eye, adult cornea and conjunctiva, having a role in cell differentiation and migration but also in angiogenesis, all processes involved in pterygium formation. We demonstrate elevated CRIM1 expression in pterygium tissue from additional individual Northern Irish patients compared to unaffected conjunctival controls. UV irradiation of HCE-S cells resulted in an increase in ERK phosphorylation and CRIM1 expression, the latter further elevated by the addition of the MEK1/2 inhibitor, U0126. Conversely, siRNA knockdown of CRIM1 led to decreased UV-induced ERK phosphorylation and increased BCL2 expression. Transient expression of the mutant H412P CRIM1 in corneal epithelial HCE-S cells showed that, unlike wild-type CRIM1, it was unable to reduce the cell proliferation, increased ERK phosphorylation and apoptosis induced through a decrease of BCL2 expression levels. We propose here a series of intracellular events where CRIM1 regulation of the ERK pathway prevents UV-induced cell proliferation and may play an important role in the in the pathogenesis of pterygium.

Deregulation of p53/survivin apoptotic markers correlated to PTEN expression in pterygium neoplastic cells

PURPOSE

Pterygium is a distinct clinicopathological entity characterized by degenerated and neoplastic-like features. Concerning its rise on normal conjunctiva epithelia, the role of specific gene deregulations including apoptotic/anti-apoptotic factors and significant suppressor genes in signaling transduction pathways is under investigation. In the current study, we co-analyzed p53, survivin and PTEN proteins in pterygia and normal conjunctiva.

METHODS

Using a liquid-based cytology assay, 50 cell specimens were obtained by a smooth scraping on conjunctiva epithelia and fixed accordingly. Among them, 38 were pterygia and the remaining (n=12) normal epithelia (control group). Immunocytochemistry assays were implemented on the corresponding slides by applying ani-p53, survivin, and PTEN antibodies. Digital image analysis was performed for evaluating objectively the corresponding immunostaining intensity levels.

RESULTS

The majority of the examined pterygia cases overexpressed the markers p53:22/38-57.9%, survivin:30/38-78.9%, and PTEN:25/38-65.7%. Interestingly, overall p53/PTEN co-expression was found to be statistically significant (p=0.022).

CONCLUSIONS

Survivin overexpression leads to an increased anti-apoptotic activity playing a central molecular role in the pathogenesis and progression of pterygia. Furthermore, although p53 expression is observed in these lesions, its impact seems to be low compared to survivin's influence on them. Additionally, the role of PTEN in the process is potentially significant providing a suppressor balance to the p53/ survivin complex.

Expression of p53 Protein in Pterygium

Purpose

The pathogenesis of pterygium is still not completely understood and many environmental factors, including ultraviolet (UV) radiation, play an important role in its etiology. Chronic exposure to UV radiation causes mutations in the p53 tumor suppressor gene, eventually leading to tumor formation. We analyzed the immunohistochemical expression of p53 proteins in pterygial tissues to determine the role of the p53 tumor suppressor gene in the development of pterygium.

Methods

Pterygial specimens were studied immunohistochemically using antibodies against p53 protein.

Results

Out of 38 specimens studied, 35 (92.1%) had conjunctival epithelial cells without p53 specific nuclear staining. Only three specimens (7.9%) had a few p53 stained cells. The role of UV radiation in the pathogenesis of pterygium is supported by epidemiological, geographical and microscopic findings. However, our results are not consistent with these data on a genetic basis.

Conclusions

We conclude that defective p53 tumor suppressor gene function seems to have no role in the pathogenesis of pterygium.

Evaluation of Interleukin-17 and Interleukin-23 in Pterygium: Immunohistochemistry Study

PURPOSE

To compare the interleukin-17 (IL-17) and interleukin-23 (IL-23) positive cell counts between pterygium and normal conjunctiva.

DESIGN

A case-control study.

METHODS

This study received ethical approval (NMRR Research ID 23957) and informed consent was obtained from all participants. It involved 20 participants with 20 samples of pterygium and 20 samples of normal conjunctiva that were obtained from the same eye of each participant. All the participants underwent history taking, slit lamp examination, and pterygium excision surgery. Both samples underwent immunohistochemistry procedure. Pretreatment procedure was conducted using heat-induced epitope retrieval with PT link, subsequently followed by EnVision FLEX staining procedure and incubation with anti‒IL-17 antibody and anti‒IL-23 antibody. Slides were examined in high-power fields (400x) for both samples in 3 different fields. Total positive stained cell counts in all 3 fields with IL-17 and IL-23 between pterygium and normal conjunctiva were analyzed by using Wilcoxon signed rank test.

RESULTS

IL-17 positive cell counts for normal conjunctiva showed mean 196.10 ± 80.487 but for pterygium was 331.10 ± 108.416. As for IL-23, the mean for positive cell counts for normal conjunctiva was 62.10 ± 33.462 and IL-23 positive cell counts for pterygium showed mean 102.95 ± 41.378. Both IL-17 and IL-23 were significantly increased in pterygium compared with normal conjunctiva (P < 0.001).

CONCLUSIONS

Both IL-17 and IL-23 were found to be significantly higher in the pterygium group than in the normal conjunctiva group with P < 0.001 by Wilcoxon signed rank test.

Inhibitory effects of rosmarinic acid on pterygium epithelial cells through redox imbalance and induction of extrinsic and intrinsic apoptosis

Pterygium is a common tumor-like ocular disease, which may be related to exposure to chronic ultraviolet (UV) radiation. Although the standard treatment for pterygium is surgical intervention, the recurrence rate of pterygium is high when no effective inhibitory drug is used after surgery. Rosmarinic acid (RA) is a polyphenol antioxidant with many biological activities, including anti-UV and anti-tumor properties. This study aimed to examine the inhibitory effects of RA on pterygium epithelial cells (PECs). Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was used to examine the cell cytotoxicity of PECs after RA treatment. A fluorescent probe, DCFH-DA (2',7'-dichlorofluorescin diacetate), was stained with PECs to measure intracellular reactive oxygen species (ROS) levels. Antioxidant activity assays were used to measure the levels of superoxide dismutase (SOD) and catalase (CAT) in PECs. Western blot analysis was used to determine the protein expression of nuclear factor E2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1), quinone acceptor oxidoreductase 1 (NQO1), and apoptosis-associated proteins. RA significantly reduced the cell viability of the PECs. Treatment with RA remarkably increased the Nrf2 protein expression levels in the nucleus, HO-1 and NQO1 protein expression levels, and the activities of SOD and CAT. As a result, intracellular ROS levels in PECs were decreased. Additionally, the induction of extrinsic apoptosis on PECs by RA was associated with increasing expressions levels of Fas, Fas-associated protein with death domain (FADD), tumor necrosis factor-alpha (TNF-α), and caspase 8 protein. Moreover, the induction of intrinsic apoptotic cell death in PECs was confirmed through upregulation of cytochrome c, Bax, caspase 9, and caspase 3 and downregulation of Bcl-2 and pro-caspase 3. Our study demonstrated that RA could inhibit the viability of PECs through regulation of extrinsic and intrinsic apoptosis pathways. Therefore, RA may have potential as a therapeutic medication for pterygium.

Inhibition of Pterygium Fibroblast Migration and Outgrowth by Bevacizumab and Cyclosporine A Involves Down-Regulation of Matrix Metalloproteinases-3 and -13

We examined the connection between matrix metalloproteinase (MMP) expression/activity and pterygium fibroblast migration, and how these were affected by bevacizumab and/or cyclosporine A (CsA). Fibroblasts were obtained from 20 pterygia and 6 normal conjunctival specimens. Expression levels of MMP-3 and MMP-13 were examined after bevacizumab administration. Immunofluorescence staining was used to examine expression of both MMPs in fibroblasts migrating out from explanted pterygium tissues. Rates of cell migration from explant-cultured pterygia tissues and scratch-wounded confluent pterygium fibroblasts were examined in the presence of MMP-3 or MMP-13 inhibitors, as well as bevacizumab and/or CsA. A scratch wound healing migration assay was performed to determine the effects of bevacizumab and/or CsA. Protein expression of both MMPs in pterygium tissues and in cells migrating from organ-cultured pterygium tissues was greater than that observed in normal cells. Inhibition of the activities of both MMPs decreased their expression levels; these were also significantly reduced in bevacizumab-injected pterygium tissues. Bevacizumab significantly reduced the expression of both MMPs and cell migration. Pretreatment with CsA prior to bevacizumab exposure markedly inhibited cell migration and the expression of both MMPs. CsA enhanced the inhibitory effects of bevacizumab on pterygium fibroblast migration in vitro, possibly by inhibiting expression of both MMPs. These findings suggest that combined CsA and bevacizumab treatment may provide a potential therapeutic strategy for reducing the rate of pterygium recurrence.

[Pterygium: etiology, pathogenesis, treatment]

Pterygium is a degenerative condition characterized by fibrovascular outgrowth of conjunctiva over the cornea. Many theories exist that try to explain its pathogenesis. The current belief is that this disease is multifactorial with ultraviolet radiation being the most important trigger. Attention is also paid to such factors as tear film changes, cytokines and growth factors disbalance, immunologic disturbances, genetic mutations, and viral infections. Modern classifications consider the rate of fibrovascular growth, its progressive potential, and histological features. In the beginning pterygium is usually asymptomatic, however, dry eye manifestations may be present, such as burning, itching, and/or tearing. As the lesion grows toward the optical zone, visual acuity gets compromised, and thus, surgical treatment is required. Because of recurrences and repeated surgeries, the growth of the lesion may become more aggressive and cause irregular astigmatism. Comprehensive surgery of pterygium is aimed at not only removing the lesion, but also preventing recurrences. Advisable are modified bare sclera techniques with subsequent transposition of the conjunctival flap, conjunctival autotransplantation, amniotic membrane transplantation, and peripheral lamellar keratoplasty (in cases of significant ingrowth). In some cases, antirecurrent adjuvant therapy may be considered that involves the use of mitomycin C, 5-fluoruracil, and VEGF inhibitors. However, the search for the best treatment for pterygium, i.e. an easy to perform, cosmetically-friendly method associated with minimal risk of recurrences and/or complications, remains an interest of modern ophthalmology.

Evaluation of transforming growth factor-beta1 gene expression in pterygium tissue of atopic patients

BACKGROUND

The exact pathogenesis of pterygium is still not fully understood. Growth factors are considered to play an important role in the formation of pterygium. Transforming growth factor (TGF)-β1 is considered to be one of the main mediators of fibroblast stimulation and tissue remodeling in allergic conditions. The objective of the present study was to investigate the association between TGF-β1 gene expression and pterygium in atopic and nonatopic participants.

METHODS

We used questionnaires to record demographic and clinical information from patients who underwent pterygium excision surgery. Skin prick examination was done to confirm or rule out atopy in 30 patients with atopy (Case Group) and 30 individuals without atopy (Control Group). Additionally, measurement of serum immunoglobulin E, cytokines, including interleukin-4 and interferon-γ, and peripheral blood eosinophil count was performed to confirm atopy in 30 consecutive patients (Case Group). A semiquantitative reverse transcription polymerase chain reaction was performed to determine TGF-β1 gene expression in all individuals.

RESULTS

TGF-β1 mRNA gene expression was significantly higher (p = 0.0001) in atopic patients 2.50 ± 1.11 compared to nonatopic individuals 1.40 ± 0.46. Eosinophil count and serum immunoglobulin E were significantly higher (p = 0.031 and p = 0.001, respectively) in atopic patients compared to the Control Group. Serum interleukin-4 was also significantly higher (p = 0.01) in atopic patients compared with nonatopic individuals.

CONCLUSION

Excess expression of TGF-β1 gene in pterygium tissue of atopic individuals suggests that growth factors play a role in the pathogenesis of pterygium.

Evaluation of global differential gene and protein expression in primary Pterygium: S100A8 and S100A9 as possible drivers of a signaling network

Purpose

Pterygium is a wing shaped fibrovascular growth on the ocular surface, characterized by fibrosis, angiogenesis, extracellular matrix remodeling, and inflammatory infiltrates. Epidemiologic studies have linked pterygium formation to various chronic inflammatory conditions, such as ultraviolet radiation, sawdust exposure, and dry eye disease. The purpose of this study is to identify proteins that are differentially expressed in primary pterygium by using a combination of gene microarray and proteomic platforms.

Methods

Paired pterygium and uninvolved conjunctiva tissues of four patients were evaluated for differences in global gene transcript levels using a genechip microarray. Proteins extracted from another four pairs of tissues were quantified by iTRAQ approach. Western blot and immunofluorescent staining on additional patients were used to validate dysregulated protein expression obtained from microarray and proteomics data. In addition, primary conjunctival fibroblasts were treated with recombinant S100A8, S100A9 or both. Transcript level changes of a panel of potential target genes were evaluated by real time-PCR.

Results

The following were up-regulated at both protein and transcript levels S100 A8 and A9, aldehyde dehydrogenase 3 family, member1 (ALDH3A1) and vimentin (VIM). Conversely, serpin peptidase inhibitor clade A member 1 (SERPINA1) and transferrin (TF) were down-regulated. Upon adding S100A8, S100A9 or both, the inflammatory chemokine CXCL1, matrix proteins vimentin, biglycan, and gelsolin, as well as annexin-A2, thymosin-β4, chymase (CMA1), member of Ras oncogene family RAB10 and SERPINA1 were found to be up-regulated.

Conclusions

We identified 3 up-regulated and 2 down-regulated proteins by using a stringent approach comparing microarray and proteomic data. On stimulating cells with S100A8/9, a repertoire of key genes found to be up-regulated in pterygium tissue, were induced in these cells. S100A8/9 may be an upstream trigger for inflammation and other disease pathways in pterygium.

Concomitant examination of inflammation and angiogenesis in the pathogenesis of primary moderate pterygium in a well-designed case-control study

Pterygium is a common ocular lesion whose exact etiology is a point of contention. Chronic inflammation and angiogenesis are two major proposed mechanisms of the disease in the current literature. The objective of this study is to examine these two mechanisms in a very well-designed setting. In a case-control study, 24 tissue specimens from the patients with primary moderate pterygium (cases) and 15 specimens excised from the nasal bulbar region in healthy counterparts (controls) were compared in terms of the count of mast cells (inflammation), as well as the status of Cd31/vascular Endothelial Growth Factor (VEGF) expression (angiogenesis) in Tabriz Nikookari and Sina Teaching Hospitals. The case (mean age: 58.08 +/- 10.03 years, 84% males) and control (Mean age: 62.33 +/- 9.19 years, 80% males) groups were age-and sex-matched (p = 0.19, 0.75, respectively). The mean mast cell count was significantly higher in the case group (27.72 +/- 15.19 versus 12.00 +/- 7.09 cells mm(-2), p = 0.001). The study of immunoreactivity revealed that the positive expression (moderate-severe) of CD31 was significantly more frequent in the case group (88 versus 26.7%; p<0.001; Odds ratio = 20, 95% confidence interval 3.85-100). There was also higher rate of VEGF-positive (moderate-severe) cells in the group with pterygium (88 versus 20%; p<0.001; Odds ratio= 33.3, 95% confidence interval 5.00-100). This study indicates that both inflammation and angiogenesis play pivotal role, in parallel, in pathogenesis of pterygium.

Over-expression of human cystatin C in pterygium versus healthy conjunctiva

BACKGROUND

A prospective, non-randomised, transversal and comparative study, carried out in INOVA Vision Institute and Autonomous University of Aguascalientes. Pterygium is an important illness that affects 22% people from tropic and equatorial zones. Is an inflammatory process caused by UV rays, and it has a behavior similar to a neoplasm. For this study was taken into consideration 191 samples from the INOVA Vision Institute, Aguascalientes, Mexico. Include 73 pterygia samples, which were obtained during resection under sterile conditions. 44 normal conjunctiva samples were obtained from the same patients when harvesting the conjunctival autograft, or from other patients undergoing extracapsular cataract extraction from the superior bulbar region. Tears from patients with pterygium (n = 50) and normal volunteers (n = 24) were obtained using a calibrated glass micro capillary tube. The surgical conjunctiva and pterygia samples were subjected to reverse-transcription polymerase chain reaction (RT-PCR), western blot, and immunohistochemistry. Tears were analyzed by enzyme-linked immunosorbent assays.

METHODS

This was a prospective, non-randomised study involving 191 biological samples taken from patients with pterygium and normal volunteers, whom were operated under local anaesthesia by either complete resection of the lesion with primary closure, or resection with conjunctival autograft. Tissue samples were fixed in 10% formaldehyde. Sections were routinely stained with hematoxylin and eosin. HCC expression was evaluated by reverse-transcription polymerase chain reaction (RT-PCR), immunohistochemistry, and by western blotting. All tears samples were analyzed by enzyme-linked immunosorbent assays (ELISA).

RESULTS

Expression levels and distribution patterns of HCC in normal conjunctiva and pterygium. Higher levels of HCC mRNAs and proteins were detected in pterygium compared with a normal conjunctiva. Immunohistochemistry revealed that HCC was localized in the apical cells of the epithelium in the normal conjunctiva. In contrast, HCC was detected in all extension of epithelial tissue, from apical to basal cells in pterygia. The concentration of HCC protein in tears was higher in patients with pterygium versus controls.

CONCLUSION

HCC may play an important role in protecting normal conjunctiva, and regulating inflammatory conditions of the anterior ocular surface.

Immunohistochemical detection of Hsp90 and Ki-67 in pterygium

BACKGROUND

To examine the immunohistochemical expression of heat shock protein 90 (Hsp90) and Ki-67 protein in human pterygium.

MATERIALS AND METHODS

Tissues obtained during pterygium surgery of 15 patients who underwent the bare-sclera procedure and 10 normal conjunctivae were studied. All of these pterygia were primary ones. Recurrent pterygia were excluded. Normal bulbar conjunctivas (2 x 2 mm) were obtained from the nasal region close to the limbus from patients during their cataract and retina surgeries. Immunohistochemical detection of Hsp90 and Ki67 was done using the streptavidin-biotin method in paraffin embedded tissue sections.

RESULTS

The percentage of cells stained for Hsp90 was greater for pterygium epithelium (76 ± 10.8) than for normal conjunctiva (1.4 ± 0.8). In each pterygium sample more than 60% of cells were positive. The differences in positive cells between normal and pterygium epithelium were highly significant for Hsp90 (P < 0,001).Pterygium epithelium also showed a higher percentage of cells that stained for Ki67 (10.1 ± 9.5) than for normal conjunctiva (2.1 ± 1.9). The differences in positive cells were also statistically significant for Ki67 (P < 0.01). Although there were significant differences in the majority of samples observed. It was noted that in some samples there was no difference between normal and pterygium epithelium for Ki67.

CONCLUSION

Our results indicate an abnormal expression of Hsp90 and ki-67 in pterygium samples when compared to normal conjunctiva.The finding of abnormal expression of levels of Hsp90 in pterygium samples can stimulate new research into pterygium and its recurrence.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1128478792898812.

Expression of vascular endothelial growth factor C in human pterygium

Vascular endothelial growth factor C (VEGF-C) and its receptor VEGFR-3 mediate lymphangiogenesis. In this study, we analyzed the expression of VEGF-C and VEGFR-3 as well as lymphatic vessels in the pterygium and normal conjunctiva of humans. Fifteen primary nasal pterygia and three normal bulbar conjunctivas, surgically removed, were examined in this study. The lymphatic vessel density (LVD) and blood vessel density were determined by the immunolabeling of D2-40 and CD31, markers for lymphatic and blood vessels, respectively. VEGF-C and VEGFR-3 expression in pterygial and conjunctival tissue proteins was detected by Western blotting and were evaluated using immunohistochemistry. The LVD was significantly higher in the pterygium than normal conjunctiva (p < 0.05). Western blot demonstrated high-level expression of VEGF-C and VEGFR-3 in the pterygium compared with normal conjunctiva. VEGF-C immunoreactivity was detected in the cytoplasm of pterygial and normal conjunctival epithelial cells. The number of VEGF-C-immunopositive cells in pterygial epithelial cells was significantly higher than in normal conjunctival cells (p < 0.05). VEGFR-3 immunoreactivity was localized in the D2-40-positive lymphatic endothelial cells. The present findings suggest the potential role of VEGF-C in the pathogenesis and development of a pterygium through lymphangiogenesis and the VEGF-C/VEGFR-3 pathway as a novel therapeutic target for the human pterygium.

Study of alkaline phosphatase activity and DNA content of pterygium tissue showing its degenerative character

A prospective, non-randomised, interventional case series study was designed among 127 specimens obtained from 100 consecutive patients presenting with primary pterygium attending the outpatient department of a teaching hospital in Kolkata, West Bengal between September 2009 and August 2010. After harvesting the pterygium it was transported in 10% formol saline for staining, fixing and embedding prior to evaluation of tissue alkaline phosphatase level and estimation of DNA content in nucleus of cells in pterygium tissue. The main outcome was to measure alkaline phosphatase activity and DNA content in pterygium tissue and normal bulbar conjunctiva along with histopathological staining and to see if any correlation exists between alkaline phosphatase activity and DNA content of pterygium tissue in different stages of evolution as suggested by histological staining. The elastic proliferation and hyaline degeneration are prominent in well developed pterygium. The alkaline phosphatase activity in all cases of pterygium is maximum and the DNA content of the cells of the pterygium tissue is diminished as compared to normal bulbar conjunctiva. Histopathological changes as evident from epithelial cell changes from cylindrical to flat cells with cyst formation in basal layers, the disappearance of nuclei in the submucosa coupled with increase in hyaline content of the tissue all point towards degenerative changes. Biochemically too there is a decrease in DNA content in the nuclei of the cells in pterygium, histochemically there is an increase in the alkaline phosphatase activity, all these changes point to pterygium being a degenerative tissue.

Aberrant DNA methylation of matrix remodeling and cell adhesion related genes in pterygium

Background

Pterygium is a common ocular surface disease characterized by abnormal epithelial and fibrovascular proliferation, invasion, and matrix remodeling. This lesion, which migrates from the periphery to the center of the cornea, impairs vision and causes considerable irritation. The mechanism of pterygium formation remains ambiguous, and current treatment is solely surgical excision, with a significant risk of recurrence after surgery. Here, we investigate the role of methylation in DNA sequences that regulate matrix remodeling and cell adhesion in pterygium formation.

Methodology/Principal Findings

Pterygium and uninvolved conjunctiva samples were obtained from the same eye of patients undergoing surgery. The EpiTYPER Sequenom technology, based on differential base cleavage and bisulfite sequencing was used to evaluate the extent of methylation of 29 matrix and adhesion related genes. In pterygium, three CpG sites at −268, −32 and −29 bp upstream of transglutaminase 2 (TGM-2) transcription initiation were significantly hypermethylated (p<0.05), whereas hypomethylation was detected at CpGs +484 and +602 bp downstream of matrix metalloproteinase 2 (MMP-2) transcription start site, and −809, −762, −631 and −629 bp upstream of the CD24 transcription start site. RT-qPCR, western blot and immunofluorescent staining showed that transcript and protein expression were reduced for TGM-2 and increased for MMP-2 and CD24. Inhibition of methylation in cultured conjunctival epithelial cells increased these transcripts.

Conclusions/Significance

We found regions of aberrant DNA methylation which were consistent with alteration of TGM-2, MMP-2, and CD24 transcript and protein expression, and that inhibition of methylation in cultured cells can increase the expression of these genes. Since these genes were related to cell adhesion and matrix remodeling, dysregulation may lead to fibroblastic and neovascular changes and pterygium formation. These results have implications for the prognostication of pterygium in clinical practice, for example, detection of epigenetic changes may have a role in predicting post surgical recurrence of aggressive lesions.

Angiogenesis in the pathogenesis of pterygium

Pterygium represents an epithelial hyperplasia associated with fibro-vascular growth. It is an active process, associate with cellular proliferation, remodeling of the connective tissue, angiogenesis and inflammation. The aim of this study consists of emphasizing angiogenesis involvement in the pterygium pathogeny. The material used for this study consisted of 21 pterygion fragments surgically removed in the Ophthalmology Clinic of the Emergency County Hospital, Craiova. Nine patients were men, 22 were women, and they were aged between 58 and 81 years. Ten fragments of epibulbar conjunctiva from the vicinity of the sclero-corneal limbus were used as control tissue. They were initially histological processed by paraffin inclusion. The immunohistochemical processing was made in the Histological, Histopathological and Immunohistochemical Techniques Laboratory of the University of Medicine and Pharmacy of Craiova. The working technique used was ABC÷HRP (Avidin complexed with biotinylated peroxidase). Angiogenesis in the pterygion was investigated with CD31 marker that allows the identification of the vascular endothelium and the establishment of the vascular microdensity and with VEGF, which allowed the identification of the main source of proangiogenic factors in pterygium. Our study emphasized the existence of a much richer vascularization at the level of the pterygium, compared with the one of the normal conjunctiva. The respective blood vessels were best represented in the subepithelial conjunctive, due to the increased necessities of the proliferating pterygium epithelium. The morphology of the blood vessels is specific for the neoformation vessels, which have a small caliber, are branched and have a rarely visible lumen. The investigation of the vascular microdensity has shown the existence of an intense angiogenesis process at the level of the pterygium and the overexpression of the VEGF, mainly in the proliferating structures of the pterygium, plead for the pathogenic involvement of this growth factor in the development of the pterygium.

[Expression of embryonic markers in pterygium derived mesenchymal cells]

BACKGROUND

Destruction of the limbal epithelium barrier is the most important mechanism of pterygium formation (conjunctiva proliferation, encroaching onto the cornea). It is thought to arise from activated and proliferating limbal epithelial stem cells. The objective of this study is to evaluate the presence of undifferentiated mesenchymal cells (stem cells) in cultured cells extracted from human pterygium.

MATERIAL AND METHODS

Cells from 6 human pterygium were isolated by explantation and placed in cultures with amniomax medium. Once the monolayer was reached the cells were seeded onto 24 well microplates. The cells were studied in the second sub-culture. The immunohistochemical expression of different embryonic stem cell markers, OCT3/4 and CD9, was analysed. The differentiated phenotypes were characterised with the monoclonal antibodies anti-CD31, α-actin and vimentin.

RESULTS

All the cell populations obtained from pterygium showed vimentin expression. Less than 1% of the cells were positive for CD31 and α-actin markers. The majority of the cell population was positive for OCT3/4 and CD9.

CONCLUSIONS

The cell population obtained from pterygium expressed mesenchymal cell phenotype and embryonic markers, such us OCT3/4 and CD9. This undifferentiated population could be involved in the large recurrence rate of this type of tissue after surgery.

Antivascular endothelial growth factors in anterior segment diseases

Proangiogenic growth factors, mainly VEGF (vascular endothelial growth factor) play a significant role in anterior segment diseases, characterized by neovascularization. Newly grown vessels in the cornea can lead to an impairment of transparency and visual acuity. Neovascularization of the iris (rubeosis iridis) and the anterior chamber angle are caused by ischemic retinopathies, usually leading to neovascular glaucoma with serious loss of vision. A pterygium is characterized, amongst others, by fibrovascular proliferation and may have vision threatening consequences if left untreated. Several antiangiogenic drugs have evolved in the last decade, mainly used for the treatment of choroidal neovascularization in age-related macular degeneration. Bevacizumab though, is also widely used off-label, in topic form or as an intracameral injection, to treat anterior segment neovascularization with encouraging results.

[Expression of p53 and flow cytometric analysis of DNA index and S-phase fraction in pterygium]

OBJECTIVE

To study the expression of p53 and DNA index (DI) and S-phase fraction (SPF) in pterygium, and explore their contribution of pathogenesis of pterygium.

METHODS

Surgically excised pterygia of 84 cases (96 eyes) with newly developed pterygium and 30 samples of normal conjunctiva as control were collected for immunohistochemistry to detected the expression of p53. The DI value and the SPF value were detected in all specimens with FCM.

RESULTS

The expression of p53 in pterygium was significantly higher than that of normal conjunctiva (P < 0.001). The DI value and the SPF value in pterygium were higher than that of normal conjunctiva but without statistical significance (P > 0.05).

CONCLUSIONS

The high expression of p53 and high level of DI value and SPF value suggest the pathogenesis of pterygium may be out of balance of cell apoptosis and cell proliferation.

Occurrence of human papillomavirus in pterygia

PURPOSE

The aim of the study was to assess the occurrence of human papillomavirus (HPV) DNA in pterygium.

METHODS

The study involved 89 patients undergoing surgical procedures at the Department of Ophthalmology, Medical University of Lublin, Poland. Group 1 included 58 patients with clinically diagnosed pterygium. Group 2 consisted of 31 individuals with normal conjunctiva. The material was collected during elective surgical procedures. The presence of HPV genome was determined using polymerase chain reaction (PCR). Once the presence of HPV DNA was confirmed, 28 HPV genotypes were determined using reverse hybridization.

RESULTS

The determinations confirmed the presence of HPV DNA in pterygium. In the material collected from 58 cases of pterygium (group 1), HPV DNA was identified in 16 patients (27.6%). In the material from 31 diagnostic specimens of normal conjunctiva (group 2), the presence of HPV was demonstrated in three cases (9.7%). A statistically significant difference was found in the presence of HPV DNA between the patients from groups 1 and 2 (p = 0.041). HPV type 16 was most common and was demonstrated in 56% of HPV-positive cases of pterygium. HPV 16 and HPV 6 co-infections were found in 19% of cases, while HPV 18 and HPV 6 co-infections were observed in 13%. In group 2, all three patients with HPV showed HPV 18.

CONCLUSION

It seems that HPV is not necessary to induce pterygium; however, it might play a synergistic role in the multi-stage process of its development.

The role of substance P in the pathogenesis of pterygia

PURPOSE

Pterygium is a prevalent ocular surface disorder thought to be triggered by chronic ultraviolet damage to the limbus. One of the enigmatic features of pterygium is its wing-like shape, and the mechanism(s) supporting its centripetal growth remain to be elucidated. Because the growth pattern of pterygia mirrors the radial arrangement of corneal nerves, the authors propose that neuropeptides may facilitate its directional growth. This hypothesis prompted an investigation of the role of the sensory neuropeptide substance P (SP) and its receptor (NK(1) receptor) in directing cell migration in pterygia that may explain the characteristic growth pattern.

METHODS

Immunohistochemical analysis for SP and the NK(1) receptor was performed on five pterygium specimens with corresponding autologous conjunctiva and limbus. Migration of pterygium epithelium, fibroblasts, and vascular endothelial cells toward SP was assessed by using a modified Boyden chamber.

RESULTS

SP and NK(1) receptors were localized to infiltrating fibroblasts, mononuclear cells and the epithelia of pterygium, conjunctiva, and limbus, with elevated NK(1) receptor staining observed in pterygia. SP at nanomolar concentrations induced cell migration in pterygium fibroblasts and vascular endothelium in a dose-dependent fashion, which was inhibited by an NK(1) receptor antagonist. Pterygium epithelial cells were not migratory in these experiments.

CONCLUSIONS

For the first time, this study showed the presence of NK(1) receptor in pterygia and that SP is a potent chemoattractant for pterygium fibroblasts and vascular endothelial cells, implying that SP may contribute to the shape of pterygia through its profibrogenic and angiogenic action.

Increased expression of erythropoietin receptor in human pterygial tissues

Erythropoietin (Epo) induces physiological activities such as cell proliferation, migration, and angiogenesis in Epo receptor (EpoR)-expressing vascular endothelial and tumor cells. Recently, it has been demonstrated that growth factor-independent proliferation is frequently observed during the cell transformation process. Pterygium is a fibrovascular proliferating tissue that includes transformed cells. The aim of this study was to examine the localization of Epo and EpoR proteins in human pterygial tissues. Eleven samples including nine pterygia and two normal bulbar conjunctivas, which were surgically excised, were studied. Formalin-fixed, paraffin-embedded tissue sections were constructed and then were examined by immunohistochemistry with anti-Epo and EpoR antibodies. Cytoplasmic immunoreactivity for EpoR was heterogeneously detected in basal and suprabasal cells of the pterygium epithelium. In the pterygium stroma, a variety of endothelial cells forming vascular cavities showed cytolasmic immunoreactivity for EpoR. In normal conjunctival epithelium, a few basal cells showed a weak homogeneous immunoreactivity for EpoR in the cytoplasm. The number of EpoR-expressing epithelial cells was much higher in the pterygium compared to the normal conjunctiva. EpoR expression was marginally detected in stromal microvessels of the normal conjunctiva. Immunoreactivity for Epo was not noted in pterygium epithelium and stroma, and in normal conjunctiva. These results suggest that the Epo-independent EpoR-signaling pathway plays a potential role in cell proliferation and angiogenesis in human pterygium.

[Expression of cyclooxygenase-2 in pterygium and effects of selective cyclooxygenase-2 inhibitor on human pterygium fibroblasts]

OBJECTIVE

To investigate the expression of cyclooxygenase-2 (COX-2) in pterygium and the effect of selective COX-2 inhibitor (Nimesulide) on proliferation of human pterygium fibroblasts (HPF) in culture.

METHODS

Samples of pterygium and conjunctiva were obtained from patients in the Department of Ophthalmology in Union Hospital of Wuhan. The expression of COX-2 in pterygium was determined by immunohistochemistry. The HPF cells were isolated, cultured and identified. Expression of cyclooxygenase-2 was detected by Western blot in HPF following basic fibroblast growth factor (bFGF) treatment at different concentrations (1, 10, 100 ng/ml). The MTT method was used to assay the biologic activities of Nimesulide in different doses (0, 25, 50, 100, 200 micromol/L) and different time (24, 48, 72, 96 h).

RESULTS

The positive rate of expression of COX-2 was 70%. The expression of COX-2 became more significantly as dose increased with the stimulation of bFGF. Administration of 50 micromol/L Nimesulide for 24 h could significantly inhibit HPF proliferation in a dose- and time-dependent manner (P < 0.05).

CONCLUSIONS

bFGF can induce the expression of COX-2 in HPF, COX-2 may be one of factors involved in the formation of pterygium. Nimesulide can significantly inhibit HPF proliferation.

Endothelial progenitor cells in pterygium pathogenesis

PURPOSE

The pathogenesis of pterygium is not well known, and controversy exists about the cell origins and the nature of initial trigger required for its development. We investigated whether endothelial progenitor cells (EPCs) are involved in pathogenesis of pterygium and the mechanism underlying the selective recruitment of EPCs during this process.

METHODS

We studied 13 normal controls and 28 pterygium patients (primary (n=15), recurrent (n=13)). Substance-P, vascular endothelial growth factor (VEGF), and stem cell factor (SCF) were measured in plasma and tears using ELISA, and circulating CD34(+) and c-kit(+) mononuclear cells (MNCs) by flow cytometry. Anterior segment fluorescein angiography (FAG) was performed to evaluate hypoxic conditions in the early stage of pterygium. Surgically removed pterygial tissues were analyzed immunohistochemically using the progenitor cell markers, CD34, c-kit, VEGFR-1, and VEGFR-2.

RESULTS

Anterior segment FAG findings showed an increase in non-perfusion areas and attenuated vessels in the nasal limbus during early-stage pterygium. Circulating CD34(+) MNCs and c-kit(+) MNCs were increased in pterygium groups compared with normal controls. Systemic and local cytokines including SP, VEGF, and SCF in pterygium groups were also elevated and showed positive correlations with CD34(+) and c-kit(+) MNC numbers. Immunohistochemical analysis of pterygium showed strong progenitor cell marker immunoreactivities.

CONCLUSIONS

EPCs might be involved in pterygium development, and ocular hypoxia triggers this neovascularization by recruiting EPCs derived from the bone marrow via the production of systemic and local cytokines.

Modulation of Cholesterol Homeostasis by Antiproliferative Drugs in Human Pterygium Fibroblasts

PURPOSE

The authors have previously shown that the growth of cultured fibroblasts obtained from primary pterygia was associated with an increase in cholesterol esterification, suggesting that alterations of cholesterol homeostasis may be involved in the development and progression of this disorder. This investigation was conducted to determine whether antiproliferative agents such as pioglitazone (PIO) and everolimus (EVE) may inhibit proteins involved in the cholesterol ester cycle and the proliferation of pterygium fibroblasts (PF).

METHODS

Quiescent normal conjunctival fibroblasts and PFs were treated with or without inhibitors of cell proliferation (PIO and EVE) or with inhibitors of cholesterol esterification-progesterone (Pg) and Sandoz compound (SaH)-and then were stimulated to growth by 10% fetal calf serum (FCS). Cell proliferation was assessed by counting cells. Trypan blue uptake was used to determine cell viability. mRNA and protein levels were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively.

RESULTS

PIO and EVE significantly abolished the increase in cholesterol esters, acyl-coenzyme A cholesterol acyltransferase (ACAT1), and multidrug resistance protein (MDR1) mRNA observed in growing cells. Each inhibitor upregulated ATP-binding cassette-A1 (ABCA1), neutral cholesterol ester hydrolase (NCEH) mRNA, and caveolin-1 expression in a manner similar to that of specific inhibitors of cholesterol esterification such as Pg and SaH.

CONCLUSIONS

Intracellular modifications of cholesterol homeostasis may be relevant to pterygium development. Moreover, antiproliferative agents such as PIO and EVE may represent a potential topical medication in the prevention and inhibition of pterygium growth at an early stage, probably by modulation of cholesterol ester metabolism.

The Ets-1 transcription factor is involved in pterygial angiogenesis

Pterygial pathology is characterized by abnormal corneal epithelial proliferation, stromal modulation, matrix degradation and a strong tendency for otherwise absent corneal vascularization. As the proto-oncogene Ets-1 is known to play a key role in angiogenesis and matrix degradation in other tissues, its involvement in corneal vascularization was investigated. Fifteen pterygia representing two groups were studied. Group 1 consisted of five clinically active pterygia, and group 2 consisted of 10 samples of clinically non-active pterygia. (35)S-labelled ets-1 antisense and sense riboprobes were used for in-situ hybridization of Ets-1 transcription factor in all pterygia. The cytoplasm of blood vessel endothelial cells showed strong expression of ets-1 mRNA in all group 1 pterygia. In contrast, no expression of ets-1 was found in group 2 pterygia. Proto-oncogene ets-1 expression has been shown for the first time in the metaplastic pterygium, an eye tissue of unknown pathogenesis.

MLH1 and MSH2 Expression in Pterygia

PURPOSE

Pterygia have been reported to share some of the genetic defects seen in cancers, including microsatellite instability (MSI). We examined pterygia for the presence of proteins typically missing or defective in adenocarcinomas with MSI. We also performed microsatellite analysis on DNA from pterygia to test for instability in the size of the microsatellites, using markers conventionally used to characterize MSI in tumors (Bethesda convention markers).

METHODS

We examined 13 pterygia by immunohistochemistry for MLH1 and MSH2, 2 proteins involved in DNA mismatch repair. In addition, we amplified the pterygial DNA with primers specific for 5 Bethesda markers (BAT25, BAT26, D2S123, D5S346, and D17S250).

RESULTS

MLH1 staining was present at low levels in the basal cells of the cornea and migrating limbal cells of the pterygia. MSH2 staining was present in basal and in maturing epithelial cells of the cornea and migrating limbal cells of pterygia. We observed no reproducible examples of MSI or loss of heterozygosity (LOH).

CONCLUSIONS

We were unable to confirm the presence of MSI and LOH by using the markers we examined. MSH2 staining appeared to be normal in pterygia. MLH1 staining was present but in reduced amounts compared with that seen in the conjunctiva.

β-Catenin Activation and Epithelial-Mesenchymal Transition in the Pathogenesis of Pterygium

PURPOSE

To investigate whether beta-catenin activation and epithelial-mesenchymal transition (EMT) is involved in the pathogenesis of pterygium.

METHODS

beta-Catenin and E-cadherin expression were examined in surgically excised tissue and eye bank corneas with intact pterygium. Snail and Slug, the transcriptional repressors of E-cadherin, and matrix metalloproteinase (MMP)-7, a down-stream gene regulated by beta-catenin were also investigated. Epithelial cells undergoing EMT-like changes were identified by double immunostaining for alpha-smooth muscle actin (SMA)/vimentin and cytokeratin 14. Transmission electron microscopy was used to examine the ultrastructure of the pterygial head.

RESULTS

Histopathology showed aberrant fibrotic proliferation beneath the pterygium epithelium, with epithelial processes extending into the stroma. Transmission electron microscopy revealed the dissociation of epithelial cells, which were surrounded by activated fibroblast-like cells. Characteristic downregulation of E-cadherin and intranuclear accumulation of beta-catenin and lymphoid-enhancer-factor-1 in pterygial epithelium were also observed by immunohistochemistry. Of note, epithelial cells extending into the stroma were positive for both alpha-SMA/vimentin and cytokeratin 14. Snail and Slug were immunopositive in the nuclei of pterygial epithelial cells, but not in normal corneal epithelial cells.

CONCLUSIONS

EMT of basal epithelial cells may play a key role in the pathogenesis of pterygium.

Immunolocalisation of E-cadherin and beta-catenin in human pterygium

AIM

The pterygium represents an invasion of a wing of altered ocular surface tissue into the normal cornea. The head itself is slightly elevated and white, which is the only site of firm adhesion to the globe. The mechanisms of cell proliferation and adhesion in pterygium epithelium, however, are unknown. The aim of this study was to analyse the expression of cell adhesion molecules in pterygium tissues.

METHODS

Six pterygia were surgically removed using the bare-sclera procedure, and two normal corneas and a normal bulbar conjunctiva were also obtained. Formalin-fixed, paraffin-embedded tissues were analysed by immunohistochemistry with anti-E-cadherin and beta-catenin antibodies.

RESULTS

Immunoreactivity for E-cadherin was not detected in the normal cornea and conjunctiva. In contrast, all corneal and conjunctival epithelial cells showed a weak homogeneous immunoreaction for beta-catenin on the cell membrane. In the pterygium head, the thickness was relatively marked compared with the body, and normal conjunctival and corneal epithelia. E-cadherin as well as beta-catenin was heterogeneously expressed in the cell membrane and cytoplasm of a variety of epithelial cells, whereas the expression was less marked in the body. Several epithelial cells showed intense nuclear immunoreactivity for beta-catenin. Immunoreactivity of beta-catenin, but not E-cadherin, was detected in only a few stromal cells, which were less marked than in epithelial cells.

CONCLUSION

It is suggested that E-cadherin and beta-catenin are concentrated in pterygium tissue, and are possibly involved with epithelial proliferation and adhesion.

[Blood vessel multiply and significance of expression of Cox-2, VEGF in pterygium]

OBJECTIVE

To investigate the role of cyclooxygenases-2 (Cox-2) and vascular endothelial growth factor (VEGF) in the occurrence and development of human pterygium.

METHODS

The immunohistochemical elivision method was used to examine the expressions of Cox-2 and VEGF in 30 cases of pterygium and 15 cases with normal conjunctiva.

RESULTS

The positive rate of Cox-2 was 42.8% in resting stage, 84.6% in active stage, 90.0% in recurrent pterygium and 6.6% in normal conjunctiva. The positive rate of VEGF was 57.1% in resting stage, 69.2% in active stage, 100.0% in recurrent pterygium and 13.3% in the normal conjunctiva. There was significant difference in the expressions of Cox-2 and VEGF between the pterygium and normal conjunctiva (P < 0.05, P < 0.001).

CONCLUSIONS

There are high Cox-2 and VEGF expressions in pterygium, which suggests that there is abnormal blood vessel multiply in pterygium, and the Cox-2 and VEGF plays an important role in the incidence and development of pterygium. Specific Cox-2 and VEGF inhibitor become a new target for the therapy of pterygium. Specific Cox-2 and VEGF inhibitor become a new target for the therapy of pterygium.

Expression of p27(KIP1) and cyclin D1, and cell proliferation in human pterygium

BACKGROUND

The pterygium is a growth onto the cornea of fibrovascular tissue that is continuous with the conjunctiva, whereas the mechanisms of cell proliferation in pterygium epithelium are unknown.

AIM

To analyse the histopathology and the expression of cell cycle-related molecules in pterygium tissues.

METHODS

Seven pterygia were surgically removed using the bare-sclera procedure, and three normal bulbar conjunctivas were also obtained. Formalin-fixed, paraffin-wax-embedded tissues were analysed by immunohistochemistry with anti-p27(KIP1), cyclin D1 and Ki-67 antibodies.

RESULTS

Conjunctival epithelium consisted of several layers of round cells with a few goblet cells. Nuclear immunoreactivity for p27(KIP1) was noted in many normal epithelial cells, where cyclin D1 and Ki-67-positive nuclei were intermingled. A variety of goblet cells were located in the superficial layer of the pterygium head as well as those of the body epithelia. Several pterygium epithelial cells were p27(KIP1) positive, whereas nuclear immunoreactivity for cyclin D1 and Ki-67 was detected in many epithelial cells. By contrast, immunoreactivity for p27(KIP1), cyclin D1 and Ki-67 was hardly detected in the pterygium stroma.

CONCLUSION

It is suggested that pterygium growth and development are associated with the proliferation of epithelium, which is possibly involved in the expression of cell cycle-related molecules.

Oxidative stress in pterygium: relationship between p53 and 8-hydroxydeoxyguanosine

PURPOSE

Ultraviolet (UV) radiation is known to cause oxidative DNA damage and is thought to be a major factor implicated in the pathogenesis of pterygium, a benign invasive lesion of the bulbar conjunctiva. Among all the photooxidative DNA products, 8-hydroxydeoxyguanosine (8-OHdG) is regarded as a sensitive and stable biomarker for evaluating the degree of DNA damage. The protein p53 is a major cell stress regulator that acts to integrate signals from a wide range of cellular stresses. UV radiation can cause mutations in the p53 tumor suppressor gene that, when inactivated through mutation and loss of heterozygosity, can lead to cell proliferation and genomic instability. In many types of UV-radiation damaged cells, p53 is overexpressed and immunohistochemically detectable. Recent data on tissues exposed to factors inducing oxidative stress have provided evidence of the concomitant presence of increased levels of 8-OHdG and protein p53. To verify a possible significant association between p53 and 8-OHdG, we examined a series of 31 Ecuadorian pterygia for the expression of the two markers. Moreover, we evaluated if clinical variables such as patient's age, gender, geographic location, and disease stage, might play a role affecting the 8-OHdG and p53 immunohistochemical staining results.

METHODS

Primary pterygium samples were treated for immunohistochemical evaluations of 8-OHdG and p53 protein. Mouse monoclonal antibodies to 8-OHdG and p53 were used. Statistical analyses were performed using the SPSS 12 statistical software package.

RESULTS

In our study, 21 (67.74%) pterygial samples were positive for 8-OHdG staining, 11 (35.48%) specimens were positive for p53 expression, and all negative control samples showed no staining. The staining for 8-OHdG was limited to the nuclei of the epithelial layer. No substantial staining was visible in the subepithelial fibrovascular layers. No differences in the pattern of staining between 8-OHdG and p53 were observed. All samples positive for p53 (11/31, 35.48%) were also positive for 8-OHdG immunostaining, and all specimens negative for 8-OHdG (10/31, 32.26%) were also negative for p53. When analyzed by Fisher's exact test, 8-OHdG expression was significantly associated with p53 positivity (p=0.0049). Student's t-test demonstrated statistically significant association between the expression of p53 and age (p=0.02). The correlation between the two markers and the other clinical variables revealed no statistically significant association.

CONCLUSIONS

Although pterygium is a lesion with limited local invasion and an inability to metastasize, the concomitant presence of altered p53 in 8-OHdG-immunoreactive cells could provide evidence of apparent genetic instability, which is in contrast to its benign clinical course.

Fibroblasts isolated from human pterygia exhibit altered lipid metabolism characteristics

To determine whether the fibrovascular proliferation observed in pterygium, may be, at least in part, mediated by an increased activity of cholesterol metabolism. The correlation between lipid metabolism and rate of growth was studied in human normal conjunctival (NCF) and primary pterygium fibroblasts (PFs) in primary culture. The expression of two proliferation markers (Ki-67 and p53) was evaluated by immunohistochemical staining techniques. Proliferation was evaluated by [(3)H]thymidine incorporation and by immunohistochemical assays. Lipid metabolism was evaluated by (14)C-oleate incorporated into cholesterol esters as well as by oil red O staining. Moreover, the cultures of pterygium fibroblasts were supplemented with two antiproliferative drugs in order to confirm the effective alterations in cholesterol metabolism related to proliferation. Immunohistochemistry of frozen sections from primary pterygium demonstrated an increased staining in Ki-67 and p53 compared with staining observed in normal conjunctiva. A dramatically increased activity of intracellular cholesterol metabolism was demonstrated in pterygium fibroblasts obtained from four different patients. This finding was confirmed by the reduction of cholesterol metabolism in pterygium fibroblasts treated with antiproliferative drugs. Collectively, these data support the hypothesis that alterations of cholesterol metabolism are involved in the development of pterygia. This finding may represent a target of new therapeutic approaches for treatment and prevention of pterygium.

Angiogenesis in pterygium: study of microvessel density, vascular endothelial growth factor, and thrombospondin-1

PURPOSE

This retrospective study aims to elucidate the role of angiogenesis in the pathogenesis of pterygium. We evaluated microvessel density (MVD), and expression of vascular endothelial growth factor (VEGF) and thrombospondin-1 (TSP-1).

METHODS

Fifty-two surgically excised pterygia and seven normal conjunctivae were immunohistochemically studied applying the streptavidin-biotin method in paraffin-embedded tissue sections. Monoclonal antibodies were targeted against CD31, VEGF, and TSP-1 proteins.

RESULTS

Pterygium presented with statistically significant higher average count of microvessels compared to normal conjunctivae (17.97+/-8.5 vs5.72+/-5 per high power field, P=0.001). In 24/52 (46.2%) cases of pterygium, high expression levels for VEGF were demonstrated, whereas the mean percentage of VEGF-positive epithelial cells was 58.03%. Furthermore, normal conjunctival presented statistically significant higher expression levels for VEGF in epithelial cells (83.14+/-36.08 vs58.03+/-31.23%, P=0.007). On the contrary, the presence of VEGF immunoreactivity in vascular endothelial and stromal cells was significantly higher in pterygium tissues (P<0.0001). Stromal staining for TSP-1 was detected in only 29/52 (55.8%) of the cases and no correlation with normal conjunctivae was found. Finally, statistically significant positive correlation between MVD values and stromal VEGF expression was found (P=0.049).

CONCLUSION

The angiogenesis-related factors that were studied proved to be highly expressed in pterygium tissue. On the contrary, TSP expression level was low, allowing inducers of angiogenesis to act uninhibited. This phenomenon could provide the pathogenic basis of pterygium formation.

UVB-Mediated Induction of Cytokines and Growth Factors in Pterygium Epithelial Cells Involves Cell Surface Receptors and Intracellular Signaling

PURPOSE

Pterygium is a proliferative, inflammatory, and invasive ocular surface disease associated with excessive ultraviolet (UV) exposure. This investigation was conducted to identify UV activated signaling pathways in pterygium epithelial cells (PECs) that mediate cytokine and growth factor production and to determine whether these pathways are sensitive to blockade by anti-inflammatory agents such as retinoic acid (RA) and interferon (IFN)-alpha.

METHODS

PECs were pretreated with or without inhibitors of the ERK1/2, JNK, and p38 (PD98059, SB202190, and SB203580, respectively) mitogen-activated protein kinases (MAPK) or with inhibitors of the tyrosine kinase activity of epidermal growth factor receptor (EGFR; PD153035) and platelet-derived growth factor (PDGF; AG1295); exposed to UVB (20 mJ/cm2); and then further treated with the same inhibitors. Media were harvested and analyzed by ELISA for interleukin (IL)-6, IL-8, and vascular endothelial growth factor (VEGF). Cytokine mRNA was assessed by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Inhibitors of ERK1/2, JNK, and p38 MAPKs significantly abolished the UVB-mediated increase in IL-6, IL-8, and VEGF. PD153035 reduced IL-8, AG1295 repressed IL-6, and both inhibitors partially downregulated VEGF production in UV-exposed PECs. RA and IFN-alpha dose dependently abrogated IL-6 and IL-8 but had no effect on VEGF expression after UV exposure.

CONCLUSIONS

The results have identified a stress-induced intracellular pathway and potential cell-surface transmitters that may be relevant to pterygium development. Moreover, two anti-inflammatory/antiangiogenic agents were identified that reduced cytokine production in the study model. Topical application of these drugs may benefit patients with pterygia, potentially reducing the necessity for surgical intervention.