What a study of pterygia teaches us about the cornea? Molecular mechanisms of formation

[Transplantation of the Bowman's layer in combined treatment of recurrent pterygium]

Pterygium is among the most frequent indications for extraocular ophthalmic surgery. The main method of pterygium treatment - its excision - is often combined with transplantation, non-transplantation, medication and other methods. However, the frequency of pterygium recurrence can exceed 35%, and the cosmetic and refraction outcomes satisfy neither the patient, nor the surgeon.

PURPOSE

The study analyses the technical capability and feasibility for transplantation of the Bowman's layer in the treatment of recurrent pterygium.

MATERIAL AND METHODS

The transplantation of the Bowmen's layer was performed according to the developed technique on 7 eyes with recurrent pterygium (7 patients aged 34 to 63 years). The combined surgery technique consisted of pterygium resection, laser ablation, autoconjunctival plasty, exposure to a cytostatic drug, non-suture transplantation of the Bowman's layer. Maximum length of the follow-up was 36 months. Analysis involved data from refractometry, visometry (without correction and with spectacle correction), and optical coherence tomography of the retina.

RESULTS

There were no complications in any of the studied cases. The cornea and the transplant retained transparency throughout the entire follow-up duration. 36 months after surgery mean spectacle-corrected visual acuity amounted to 0.86±0.2, topographic astigmatism - 1.48±1.4 diopters. Recurrence of pterygium was not observed. All patients were satisfied with the cosmetic outcomes of the treatment.

CONCLUSION

Non-suture transplantation of the Bowmen's layer recovers normal anatomy, physiology and transparency of the cornea after repeat surgical intervention for pterygium. No pterygium recurrences were observed throughout the entire follow-up after treatment with the proposed combined technique.

[Correction of refractive disorders after surgical treatment of recurrent pterygium (case study)]

Lamellar keratoplasty is the most effective and safe method of surgical treatment of recurrent pterygium, providing restoration of the corneal frame and optical properties and a high anti-relapse effect due to the barrier properties of the lamellar graft. However, potential postoperative changes in the regularity of the anterior and posterior surfaces of the cornea (especially in case of advanced stage of fibrovascular tissue growth) do not always allow achieving high functional results of treatment. The article presents a clinical case that demonstrates the effectiveness and safety of excimer laser correction of refractive disorders after surgical treatment of pterygium.

Evaluation of the Effects of Pterygium and Aging on Limbal Structure Using Optical Coherence Tomography

Previous studies suggest that regions of corneal limbus may possess structural differences. We aimed to investigate the limbal changes associated with pterygium and aging via optical coherence tomography (OCT). Palisades of Vogt epithelial thickness (POV-ET) and Bowman’s membrane epithelial thickness (BM-ET) were measured at the nasal, temporal, superior, and inferior quadrants of patients with pterygium and healthy subjects of different ages. Values were expressed as a ratio that functioned as an index used to evaluate the change of limbus. Ratio values determined for quadrants of the corneal limbus were correlated highly in young healthy subjects. Further, parameter values were significantly greater than those of elder healthy subjects. In young subjects, the temporal and superior quadrants of patients with pterygium were significantly lower than those of healthy subjects. Temporal and superior quadrants of elder pterygium patients affected by both pterygium and age were significantly lower than those of healthy subjects; however, the inferior quadrant of elderly pterygium patients was significantly higher than that of age-matched healthy subjects. Our findings revealed that the thickness of limbal epithelium was negatively correlated with age, while pterygium led to the thinning of the temporal and superior limbal epithelium and inferior limbal epithelial thickening.

Fibroblast Growth Factor-2 (FGF-2) Expression in Pterygia Using Cell Spot Arrays

Fibroblast growth factor (FGF) is a main regulator of cell differentiation, cell migration and angiogenesis in normal and abnormal conjunctiva epithelia, but specific mechanisms of its aberrant expression are yet to be investigated. In the present study, we investigated FGF-2 protein expression within several pterygia. Using a liquid-based cytology assay, we obtained cell specimens from pterygia and healthy tissues directly from patients. A combination of immunocytochemistry followed by digital image analysis showed significant overexpression of FGF-2 in all the examined pterygia. In 30/60 (50%) cases there were high levels of staining intensity, whereas in the remaining 30/60 (50%) cases there were moderate levels of expression. FGF-2 levels of the control group were significantly lower in comparison with the pterygia group. There was no significant correlation between FGF-2 levels and either sex or location of the pterygium. FGF-2 levels had a significant correlation with morphological characteristics of the pterygia. More specifically, FGF-2 levels were significantly higher in the pterygia with a fleshy morphology. Interestingly, recurrent lesions demonstrated high expression levels. An overexpression of FGF-2 has been observed frequently in pterygia, where it may play a crucial role in determining the lesion’s progression. FGF-2 upregulation correlates with the morphology of pterygia and its tendency to recur. Cell spot analysis based on liquid-based cytology is a simple, yet effective, method for detecting a broad spectrum of protein markers and could be useful in analyzing potential pterygia patient samples.

Comparative Transcriptomic Analysis to Identify the Important Coding and Non-coding RNAs Involved in the Pathogenesis of Pterygium

Pterygium is a common ocular surface disease characterized by abnormal fibrovascular proliferation and invasion, similar to tumorigenesis. The formation of tumors is related to a change in the expression of various RNAs; however, whether they are involved in the formation and development of pterygium remains unclear. In this study, transcriptome analysis of messenger RNAs (mRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) of paired pterygium and normal conjunctiva was performed to explore key genes regulating the development of pterygium. In total, 579 mRNAs, 275 lncRNAs, and 21 circRNAs were differentially expressed (DE) in pterygium compared with paired conjunctival tissues. Functional enrichment analysis indicated that DE RNAs were associated with extracellular matrix organization, blood vessel morphogenesis, and focal adhesion. Furthermore, through protein-protein interaction network and mRNA-lncRNA co-expression network analysis, key mRNAs including FN1, VCAM1, and MMP2, and key lncRNAs including MIR4435-2HG and LINC00968 were screened and might be involved in the pathogenesis of pterygium. In addition, several circRNAs including hsa_circ_0007482 and hsa_circ_001730 were considered to be involved in the pterygium development. This study provides a scientific basis for elucidating the pathogenesis of pterygium and will be beneficial for the development of preventive and therapeutic strategies.

Effects of excimer laser phototherapeutic keratectomy in limbal-conjunctival autograft transplantation for recurrent pterygium: a retrospective case control study

BACKGROUND

Repeated surgery excisions could induce obvious irregular astigmatism in patients with recurrent pterygium. Our study is aimed to illustrate the effect of adjunct excimer laser phototherapeutic keratectomy (PTK) in limbal-conjunctival autograft transplantation on visual quality for patients with recurrent pterygium.

METHODS

Retrospective case-control study. Eyes that underwent pterygium excision with (PTK group) or without (control group) PTK from 2006 to 2017 were retrospectively included. Recurrence rate, preoperative and postoperative surface regularity index (SRI), surface asymmetry index (SAI), cylinder and LogMAR vision were collected. Postoperative anterior segment optical coherence topography and in vivo confocal microscopy were performed to monitor the cornea epithelium healing and cellular recovery process respectively.

RESULTS

A total of 99 eyes of 99 patients were collected, of which 39 were treated with PTK and 60 without PTK. The mean follow-up time was 50.4 ± 38.1 months. The recurrence rate was 10.3% (4 eyes) in the PTK group and 13.3% (8 eyes) in the control group (p = 0.759). The SRI decreased 0.53 (range: - 0.88, 2.81), SAI decreased 0.53 (range: - 0.64, 2.94), and the cylinder decreased 2.08 (range:-0.16, 9.40) D in the PTK group, and the corresponding values were 0.48 (range:-0.45, 2.27), 0.27 (range:-1.06, 2.21) and 0.71 (range:-1.75, 3.55) D in the control group, respectively (Z = 1.76, 2.15, and 3.97, p = 0.005, 0.016, and 0.000 respectively). LogMAR vision improved in both groups after surgery, with an improvement of 0.18 (range: 0.00, 0.70) in the PTK group and 0.06 (range: - 0.12, 0.50) in the control group (Z = 4.08, p = 0.000). Besides, the eyes treated with PTK showed faster re-epithelization and better cellular recovery.

CONCLUSIONS

For recurrent pterygium, surgical excision with adjunct PTK might be a better option with improved corneal surface and vision outcomes.

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.

Association between pterygium, sun exposure, and serum 25-hydroxyvitamin in a nationally representative sample of Korean adults

Purpose

Ultraviolet-B (UVB) light exposure is the major risk factor for developing a pterygium, and serum 25-hydroxyvitamin D (25(OH)D) level is an objective measure of UVB light exposure. In this study, we investigated the association between pterygium, sun exposure, and serum 25(OH)D.

Methods

This population-based, cross-sectional study comprised 12,258 adults (aged ≥19 years) participating in the fifth annual Korea National Health and Nutrition Examination Survey from 2010 to 2012. The enrolled subjects underwent interviews, clinical examinations, and laboratory investigations. The serum 25(OH)D levels were measured, and pterygium was examined by using a slit lamp. We used three adjusted logistic regression models and selected covariates as potential confounders.

Results

The overall prevalence of pterygium was 7.09, and 53.1% of these subjects were women. The prevalence of pterygium was higher in elderly subjects and those who lived at low latitudes. In multivariate analysis with adjustment for confounding factors, subjects with a serum 25(OH)D level > 30 ng/mL, 25–30 ng/mL, and 15–20 ng/mL had an odds ratio (OR) (95% confidence interval [CI]) of 1.565 (1.035–2.366), 1.545 (1.086–2.198), 1.8 (1.358–2.386), and 1.535 (1.216–1.938), respectively, compared to those with a serum 25(OH)D level < 15 ng/mL. Subjects with a daily sun exposure > 5 h had an OR (95% CI) of 1.761 (1.395–2.223) compared to subjects with a daily sun exposure < 2 h.

Conclusion

The present study provides epidemiological evidence of an association of daily sun exposure and serum 25(OH)D levels with pterygium in a representative Korean population.

Aberrant expression of genes and proteins in pterygium and their implications in the pathogenesis

Pterygium is a common ocular surface disease induced by a variety of factors. The exact pathogenesis of pterygium remains unclear. Numbers of genes and proteins are discovered in pterygium and they function differently in the occurrence and development of this disease. We searched the Web of Science and PubMed throughout history for literatures about the subject. The keywords we used contain pterygium, gene, protein, angiogenesis, fibrosis, proliferation, inflammation, pathogenesis and therapy. In this review, we summarize the aberrant expression of a range of genes and proteins in pterygium compared with normal conjunctiva or cornea, including growth factors, matrix metalloproteinases and tissue inhibitors of metalloproteinases, interleukins, tumor suppressor genes, proliferation related proteins, apoptosis related proteins, cell adhesion molecules, extracellular matrix proteins, heat shock proteins and tight junction proteins. We illustrate their possible mechanisms in the pathogenesis of pterygium as well as the related intervention based on them for pterygium therapy.

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.

Removal of Tenon fortified by conjunctival-limbal autograft in treatment of pterygium

PURPOSE

To describe a simple and effective technique for the prevention of pterygium recurrence.

METHODS

This is a retrospective consecutive single-center case series with recurrence rate as the main outcome measure. Dissection of the conjunctiva, the Tenon's layer, and the sclera was continued up to the insertion of medial rectus. The exposed Tenon's layer was excised for 2 to 3 mm. The entire free edges of the conjunctiva was tacked firmly to the sclera. The conjunctival-limbal graft was sutured firmly to the sclera, recipient limbus, and to the conjunctiva incorporating the reciprocal edges.

RESULTS

We report findings in a total of 36 patients, with 20 (%55.5) males and 16 (%44.4) females. Median age of the patients was 44.5 years (range 16-80). The mean follow-up period was 23.1 ± 6.5 months. The mean size of pterygium in mm length was 3.8 ± 0.7. Recurrence did not occur in any patient. Diplopia was not reported by any patients.

CONCLUSIONS

Conjunctival-limbal autograft combining with selective exicison of Tenon's layer but without damage to any essential tissue such as the semilunar fold or Tenon's capsule pulley is a relatively simple and effective procedure.

The role of ultraviolet radiation in the pathogenesis of pterygia (Review)

Pterygium is a common ophthalmic disease affecting humans only. Extensive epidemiological data have demonstrated a causative effect of chronic ultraviolet (UV) radiation on pterygia. Progress has been made in determining the origin of pterygia, their nasal predilection and wing‑shaped appearance, and the roles of UV radiation in the initiation and the development of pterygia. In the present review, the current understanding of the involvement of UV radiation in the pathogenesis of pterygia is summarized. This involvement includes the alteration of limbal stem cells and fibroblasts that contribute to the initiation of pterygia and the induction of various pro‑inflammatory cytokines, growth factors and matrix metalloproteinases that promote the progression of pterygia. Further elucidation of the roles of UV radiation in the pathogenesis of pterygia may help to encourage individuals at risk of developing pterygia to take preventive measures and aid researchers in the development of novel targeted therapeutic agents to treat pterygia.

Effect of porcine chondrocyte-derived extracellular matrix on the pterygium in mouse model

PURPOSE

To investigate the effect of porcine chondrocyte-derived extracellular matrix (PCDECM) on an experimental mouse model of human pterygial epithelial cells.

METHODS

Cultured human pterygial epithelial cells (hPECs) were stained with pan-cytokeratin (CK), CK3/2p, vimentin, and CK13 antibodies to characterize the cells. A pterygium mouse model was developed by injecting 1X10⁴ hPECs into the nasal subconjunctival space in athymic nude mice. PCDECM (25 mg/mL, 10 μL) was injected into the nasal subconjunctival space in the right eye 7, 10 and 14 days after the epithelial cell injection (PCDECM group). Image analysis was performed using ImageJ® to compare the lesion size. A histopathological analysis of the cornea was conducted to evaluate the state of the epithelium and the expression of pterygial epithelial cell markers.

RESULTS

The isolated pterygial cells were positive for pan-CK, CK3/2p and vimentin, and they were negative for CK13 under immunofluorescence microscopy. On day 17 after epithelial cell injection, the size of the lesion compared to the entire cornea was increased to 37.1 % in the control group. However, in the PCDECM group, the lesion covered only 26.3 % of the entire cornea. The corneas of the pterygium mice showed an epithelium of irregular thickness, proliferation of the stroma, extracellular matrix breakdown and overexpression of pterygium-positive markers. However, these changes were significantly suppressed by the application of PCDEDM.

CONCLUSIONS

Our findings suggest that PCDECM seems to suppress pterygial epithelial cell growth and it could be used as a promising biomaterial for the noninvasive treatment of pterygium.

Expression of CREB in primary pterygium and correlation with cyclin D1, ki-67, MMP7, p53, p63, Survivin and Vimentin

AIM

Ultraviolet (UV) B irradiation induces gene expression that leads to skin cancer. Among the transcription factors induced by UVB radiation exposure, the cyclic AMP response element-binding protein (CREB) is significant. Since several factors downstream of CREB signaling are known to be involved in pterygium pathogenesis, we investigated CREB expression in pterygial and human conjunctival tissues to evaluate if a similar expression pattern is present. Moreover, we analyzed the correlation with CREB expression and other known pterygium markers.

METHODS

Primary pterygium samples and normal bulbar conjunctivas surgically removed were analyzed. Formalin-fixed, paraffin-embedded tissues were stained by immunohistochemistry with anti-CREB, anti-vimentin, anti-ki-67, anti-survivin, anti-MMP7, anti-p63, anti-cyclin D1, or anti-p53 antibodies.

RESULTS

94.4% of pterygium samples were positive for CREB with a significant difference compared to the control group (p = 0.002). The staining was localized in the epithelium and absent in the stroma. An increased expression was found for cyclin D1 (p = 0.019), ki-67 (p = 0.005), vimentin (p = 0.003), survivin (p < 0.001), p63 (p = 0.003), and MMP7 (p = 0.002). CREB expression showed a significant correlation with cyclin D1 (ρ = 0.49; p = 0.035), ki-67 (ρ = 0.61; p = 0.007), and p53 (ρ = 0.57; p = 0.013) in pterygium.

CONCLUSIONS

These results permit to hypothesize that CREB is involved in pterygium pathogenesis. Since various molecules have been discovered to inhibit CREB, these data could be of interest for pterygium treatment.

The mechanisms and consequences of ultraviolet-induced immunosuppression in the skin and eye

Ultraviolet radiation (UVR) of the skin results in immune suppression to antigens encountered shortly after the exposure. The pathways leading to the downregulation in immunity are complex, initiated by chromophores located at the surface of the skin and ending with the generation of immunosuppressive mediators and regulatory cells. Ultraviolet-induced immunosuppression can be considered not only as beneficial, such as in preventing chronic inflammatory responses and allergic and automimmune reactions, but it can also be detrimental, such as in the lack of control of skin tumors and infectious diseases. The eye is an immune privileged site through a wide variety of mechanisms that allow selected immune responses without causing inflammation. The role of UVR in altering immune responses in the eye is not clear and is discussed in relation to photokeratitis, herpetic stromal keratitis, and pterygium.