Proteomic and gene expression patterns of keratoconus

Outcomes after corneal crosslinking treatment in paediatric patients with keratoconus

PURPOSE

This study aims to determine the efficacy and safety of accelerated corneal crosslinking in children with keratoconus.

METHODS

The study enrolled 64 patients aged 16 years or younger, each contributing one eye for a total of 64 eyes for analysis. Participants underwent an accelerated form of corneal cross-linking with 15 min of ultraviolet A irradiation at a rate of 7 mW/cm2, resulting in a cumulative energy dose of 5.4 J/cm2. The primary outcome measures were best corrected visual acuity (BCVA) and corneal tomography at 6 and 12 months post-intervention. Parameters assessed included BCVA, spherical and cylindrical refraction, keratometry (K1 and K2), maximum keratometry (Kmax) and thinnest corneal thickness (TCT). These metrics were documented preoperatively and then again at 6 and 12 months postoperatively. In addition, any ocular or systemic conditions related to keratoconus were recorded for each participant.

RESULTS

The results showed an improvement in BCVA at 12 months after surgery. K1 showed a decrease at both post-operative follow-ups while K2 remained constant throughout the observation period. Kmax showed a notable decrease at the 12 month postoperative follow-up. Although the TCT showed an initial decrease, it reached a stable state after 12 months of crosslinking. Refractive values remained stable at all subsequent examinations. Notably, no complications such as corneal opacity, non-healing epithelial defects or corneal infections occurred during the follow-up period. The most common ocular comorbidity was allergic conjunctivitis (34.4%).

CONCLUSION

The findings suggest that accelerated corneal crosslinking treatment is effective in slowing or halting the progression of keratoconus. Furthermore, there were no persistent overt complications observed at 12 months after the procedure.

Inflammatory profile of keratoconic corneal epithelium

BACKGROUND

Recent studies have presented inflammatory features on keratoconus (KC) and many inflammatory markers are described in the tears of patients with this disease. The KC pathogenesis is still unknown just like the correlation with inflammatory patterns. However, environmental and genetic issues may be part of the progress of KC. In addition, some systemic features, such as allergy and obesity, seem to be related to the progression of KC. Our purpose was to evaluate the neuropeptides vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), chemokines ligand 2 (CCL-2) and 5 (CCL-5), and interleukins 6 (IL-6) and 8 (IL-8) on corneal epithelial cells and blood of patients with KC and in healthy controls. In addition, the neutrophil-to-lymphocyte ratio (NLR) was evaluated to predict inflammation.

METHODS

This including prospective observational study included 32 KC patients who underwent corneal crosslinking (CXL) and 32 control patients who underwent photorefractive keratectomy (PRK). Patients' corneal epithelial cells were removed surgically, and blood (buffy coat) was analyzed. Samples in triplicate were evaluated on rt-PCR for neuropeptides (VIP e NPY), interleukins (IL-6 e IL-8), and chemokines (CCL-2 and CCL-5).

RESULTS

Our study showed statistically higher CCL-5 and IL-8 on corneal epithelial cells in patients with KC. Blood cells were statistically higher in VIP and NPY in the KC group. Interleukin-8 on blood cells was statistically significant in KC'S group; for CCL-2 and CCL-5 they were statistically lower in patients with KC compared with controls. NLR showed no difference between the groups.

CONCLUSIONS

Our data support the findings of other studies that suggested altering KC status, such as inflammatory corneal disease. The presence of IL-8 in the cornea and blood samples of KC's group suggested systemic disease with a possible local or repercussion action. Further studies are warranted to elucidate KC pathogenesis and its correlation to systemic disease.

Novel RNA extraction method from human tears

Human tears can be used as a noninvasive source of genetic materials and biomarkers in the prognosis and diagnosis of ocular and non-ocular diseases. The present protocol is a novel direct RNA extraction method from tears. This study aims to provide a suitable method for direct extraction of RNA from tears with high quality and quantity. In this study, we develop a TRIzol base protocol for direct RNA extraction from human tears. quality and quantity of extracted RNA measured by calculation of 260/280 UV absorption ratio using Nanodrop and real-time PCR. RNA was extracted with this modified method and a purified (260/280 UV absorption ratio between 1.8 to 2 and a high yield of total RNA, on average 95 μg, from tears was extracted. In conclusion, we developed an easy and suitable method for direct extraction of total RNA from tears with high quality and quantity.

Keratocyte biology

The study of corneal stromal keratocytes is motivated by its strong association with corneal health and visual function. They play a dominant role in the maintenance of corneal homeostasis and transparency through the production of collagens, proteoglycans and corneal crystallins. Trauma-induced apoptosis of keratocytes and replacement by fibroblasts and myofibroblasts disrupt the stromal matrix organization, resulting in corneal haze formation and vision loss. It is, therefore, important to understand the biology and behaviours of keratocytes and the associated stromal cell types (like fibroblasts, myofibroblasts, stromal stem cells) in wound healing, corneal pathologies (including keratoconus, keratitis, endothelial disorders) as well as different ophthalmic situations (such as collagen crosslinking/photodynamic treatment, keratoplasty and refractive surgery, and topical medications). The recent development of ex vivo propagation of keratocytes and stromal stem cells, and their translational applications, either via stromal injection or incorporated in bioscaffold, have been shown to restore the corneal transparency and regenerate native stromal tissue in animal models of corneal haze and other disorders.

Combined Protocols for Corneal Collagen Cross-Linking with Photorefractive Surgery for Refractive Management of Keratoconus: Update on Techniques and Review of Literature

With the development and gradual dissemination of corneal collagen cross-linking (CXL) in the twenty-first century as an early treatment for keratoconus, the management paradigm has shifted to include a greater focus on complete refractive correction for these patients. Though supplemental hard contact lens therapy remains a mainstay of visual rehabilitation in keratoconus, there has been increasing appeal in a completely surgical approach by combining CXL with adjuvant refractive procedures to both halt the ectatic process and enhance functional visual outcomes. Collectively termed "CXL plus" procedures, several combined protocols have been studied to various degrees in conjunction with CXL, involving photorefractive keratectomy (PRK), transepithelial phototherapeutic keratectomy (PTK), conductive keratoplasty (CK), intrastromal corneal ring segments (ICRS) implantation, phakic intraocular lens (PIOL) implantation, or multiple of these techniques together. The scope of this review aims to encompass a summary of current CXL protocols and present the current status of studies involving adjunctive keratorefractive procedures combined with CXL. By discussing the results to date of these CXL plus protocols, we can assess what further areas of investigation are necessary within this field as the next step to optimizing treatment modalities and outcomes for our keratoconus patients, regardless of disease severity.

The Proteins of Keratoconus: a Literature Review Exploring Their Contribution to the Pathophysiology of the Disease

INTRODUCTION

Keratoconus (KC) is a complex, genetically heterogeneous multifactorial degenerative disorder characterized by corneal ectasia and thinning. Its incidence is approximately 1/2000-1/50,000 in the general population. KC is associated with moderate to high myopia and irregular astigmatism, resulting in severe visual impairment. KC structural abnormalities primarily relate to the weakening of the corneal collagen. Their understanding is crucial and could contribute to effective management of the disease, such as with the aid of corneal cross-linking (CXL). The present article critically reviews the proteins involved in the pathophysiology of KC, with particular emphasis on the characteristics of collagen that pertain to CXL.

METHODS

PubMed, MEDLINE, Google Scholar and GeneCards databases were screened for relevant articles published in English between January 2006 and June 2018. Keyword combinations of the words "keratoconus," "risk factor(s)," "genetics," "genes," "genetic association(s)," "proteins", "collagen" and "cornea'' were used. In total, 272 articles were retrieved, reviewed and selected, with greater weight placed on more recently published evidence. Based on the reviewed literature, an attempt was made to tabulate the up- and down-regulation of genes involved in KC and their protein products and to delineate the mechanisms involved in CXL.

RESULTS

A total of 117 proteins and protein classes have been implicated in the pathogenesis and pathophysiology of KC. These have been tabulated in seven distinct tables according to their gene coding, their biochemistry and their metabolic control.

CONCLUSION

The pathogenesis and pathophysiology of KC remain enigmatic. Emerging evidence has improved our understanding of the molecular characteristics of KC and could further improve the success rate of CXL therapies.

Differential epithelial and stromal protein profiles in cone and non-cone regions of keratoconus corneas

Keratoconus (KC) is an ectatic corneal disease characterized by progressive thinning and irregular astigmatism, and a leading indication for corneal transplantation. KC-associated changes have been demonstrated for the entire cornea, but the pathological thinning and mechanical weakening is usually localized. We performed quantitative proteomics using Sequential Windowed Acquisition of All Theoretical Fragment Ion Mass Spectrometry (SWATH-MS) to analyze epithelial and stromal changes between the topographically-abnormal cone and topographically-normal non-cone regions of advanced KC corneas, compared to age-matched normal corneas. Expression of 20 epithelial and 14 stromal proteins was significantly altered (≥2 or ≤0.5-fold) between cone and non-cone in all 4 KC samples. Ingenuity pathway analysis illustrated developmental and metabolic disorders for the altered epithelial proteome with mitochondrion as the significant gene ontology (GO) term. The differential stromal proteome was related to cellular assembly, tissue organization and connective tissue disorders with endoplasmic reticulum protein folding as the significant GO term. Validation of selected protein expression was performed on archived KC, non-KC and normal corneal specimens by immunohistochemistry. This is the first time to show that KC-associated proteome changes were not limited to the topographically-thinner and mechanically-weakened cone but also non-cone region with normal topography, indicating a peripheral involvement in KC development.

Interplay between hereditary and environmental factors to establish an in vitro disease model of keratoconus

Keratoconus (KC) is a bilateral corneal dystrophy and a multifactorial, multigenic disorder with an etiology involving a strong environmental component and complex inheritance patterns. The underlying pathophysiology of KC is poorly understood because of potential crosstalk between genetic-epigenetic variants possibly triggered by the environmental factors. Here, we decode the etiopathological basis of KC using genomic, transcriptomic, proteomic and metabolic approaches. The lack of relevant models that accurately imitate this condition has been particularly limiting in terms of the effective management of KC. Tissue-engineered in vitro models of KC could address this need and generate valuable insights into its etiopathology for the establishment of disease models to accelerate drug discovery.

Outcomes of Corneal Cross-Linking Correlate With Cone-Specific Lysyl Oxidase Expression in Patients With Keratoconus

PURPOSE

To evaluate the correlation of visual and keratometry outcomes after corneal cross-linking (CXL) in patients with keratoconus with cone epithelium-specific gene expression levels.

METHODS

Corneal epithelium was obtained from 35 eyes that underwent accelerated CXL (KXLII, 9 mW/cm for 10 min). Using corneal topography, epithelium over the cone and periphery was obtained separately from each subject. The ratio of gene expression for lysyl oxidase (LOX), matrix metalloproteinase 9 (MMP9), bone morphogenic protein 7, tissue inhibitor of metalloproteinase 1, collagen, type I, alpha 1, and collagen, type IV, alpha 1 (COL IVA1) from the cone and peripheral cornea was correlated with the outcome of cross-linking surgery. Patients were assessed for visual acuity, keratometry, refraction, and corneal densitometry before and 6 months after surgery. Based on the change in corneal flattening indicated by ΔKmax, the outcomes were classified as a higher response or lower response.

RESULTS

Reduction in keratometric indices correlated with improved spherical equivalent after CXL. Preoperative levels of cone-specific LOX expression in cases with a higher response were significant (P = 0.001). COL IVA1, bone morphogenic protein 7, and tissue inhibitor of metalloproteinase 1 gene expressions were reduced in the cones of the subjects with a lower response. MMP9 levels were relatively lower in cases with a higher response compared with those with a lower response.

CONCLUSIONS

Our study demonstrates that preoperative levels of molecular factors such as LOX, MMP9, and COL IVA1 aid in understanding CXL outcomes at the tissue level.

Characterization of Corneal Epithelial Cells in Keratoconus

Purpose

We studied the cellular characteristics of epithelial cells in the cone and extraconal periphery of corneas in keratoconus eyes.

Methods

This prospective observational study was conducted at Narayana Nethralaya Eye Institute. A total of 83 and 42 eyes with keratoconus and normal topography, respectively, were included in the study. Corneal epithelial cells were collected and analyzed for apoptosis, proliferation, epithelial-mesenchymal transition, and differentiation status using molecular and biochemical tools. Statistical analysis was performed using the Student's t-test.

Results

Corneal epithelial cells from the cone showed significantly higher expression of proapoptotic marker BAX (P < 0.005) compared to controls. Significantly elevated expression of cell cycle markers CYCLIN D1 (P < 0.005) and Ki67 (P < 0.005) were noted in the extraconal region compared to controls. Cells of the cone showed significantly higher ZO-1 (P < 0.005) and lower vimentin (P < 0.005) compared to controls. Significantly lower expression of the differentiation marker CK3/12 (P < 0.05) was observed in cones compared to controls.

Conclusions

Cones of keratoconic corneas show enhanced cell death, poor differentiation, proliferation and epithelial-mesenchymal transition. The cellular changes of the corneal epithelial cells in the cone and extraconal region differ significantly in a keratoconus corneas.

Translational Relevance

Characterization of patient-specific corneal epithelial cellular status in keratoconus has the potential to determine the optimal treatment and therapeutic outcomes paving the way towards personalized treatment in the future.

Pediatric Corneal Cross-linking: Comparison of Visual and Topographic Outcomes Between Conventional and Accelerated Treatment

PURPOSE

To compare visual and topographic outcomes 1 year after conventional (C-CXL) vs accelerated corneal cross-linking (A-CXL) in pediatric keratoconus (KC).

DESIGN

Comparative, retrospective, consecutive case series.

METHODS

Patients with topography-confirmed, progressive KC and a corneal thickness of ≥400 μm at the time of surgery were enrolled. Uncorrected (UCVA) and best phoropter-corrected visual acuity (BCVA) and normal maximum keratometry reading (Kmax) were measured at study entry and at the 12-month follow-up. Treatment failure rate was defined as the percentage of eyes with an increase in Kmax of more than 1.0 diopter during follow-up. The adverse event rate was the percentage of eyes with a loss of ≥2 Snellen lines of BCVA from baseline. This was a single-center analysis of 78 eyes of 58 patients that underwent C-CXL (39 eyes) and A-CXL (39 eyes). No eyes were lost to follow-up after 12 months.

RESULTS

No significant difference between changes in 12 months after as compared to the time before CXL for UCVA (0.01 log MAR; 95% confidence interval -0.14 to 0.15, P = .944), BCVA (0.05 log MAR; 95% confidence interval -0.05 to 0.15, P = .310), and Kmax (-0.77 diopters; 95% confidence interval -2.20 to 0.65, P = .282) between the C-CXL and A-CXL group were observed. Treatment failure rate was observed in 9 of 39 eyes (23.1%) in C-CXL and in 6 of 39 eyes (15.4%) in A-CXL (P = .389). Adverse events were seen only in 1 eye in the C-CXL group.

CONCLUSIONS

In this retrospective comparison, the accelerated approach was equally as effective as the conventional protocol to treat pediatric keratoconus.

Tear biomarkers for keratoconus

Keratoconus is a progressive corneal thinning, ectatic condition, which affects vision. Recent advances in corneal topography measurements has helped advance proper diagnosis of this condition and increased research and clinical interests in the disease etiopathogenesis. Considerable progress has been achieved in understanding the progression of the disease and tear fluid has played a major role in the progress. This review discusses the importance of tear fluid as a source of biomarker for keratoconus and how advances in technology have helped map the complexity of tears and thereby molecular readouts of the disease. Expanding knowledge of the tear proteome, lipidome and metabolome opened up new avenues to study keratoconus and to identify probable prognostic or diagnostic biomarkers for the disease. A multidimensional approach of analyzing tear fluid of patients layering on proteomics, lipidomics and metabolomics is necessary in effectively decoding keratoconus and thereby identifying targets for its treatment.

Attenuation of lysyl oxidase and collagen gene expression in keratoconus patient corneal epithelium corresponds to disease severity

PURPOSE

Keratoconus (KC) is characterized by progressive vision loss due to corneal thinning and structural abnormalities. It is hypothesized that KC is caused by deregulated collagen levels and collagen fibril-maturating enzyme lysyl oxidase (LOX). Further, it is currently not understood whether the gene expression deregulated by the corneal epithelium influences KC pathogenesis. We studied (i) the expressions of the LOX, collagen I (COL IA1), collagen IV (COL IVA1), MMP9, and IL6 genes in KC corneal epithelia, (ii) validated their expression levels in patient tissues, and (iii) correlated expression levels with KC disease severity. The primary goal of this study was to evaluate the importance of these genes in the progression of KC.

METHODS

We analyzed the gene expression levels of the key proteins LOX, collagens (COL IA1 and COL IVA1), MMP9, and IL6 in debrided corneal epithelia from a large cohort of KC patients (90 eyes) and compared them to control patients (52 eyes) without KC. We measured the total LOX activity in the tears of KC patients compared to controls. We also correlated the protein expression levels of LOX and collagens by immunohistochemistry (IHC) in primary tissues from KC patients (27 eyes) undergoing keratoplasty compared to healthy donor corneas (15 eyes).

RESULTS

We observed a significant reduction in LOX transcript levels in KC corneal epithelia, and LOX activity in KC tears correlated with disease severity. Collagen transcripts were also reduced in KC while MMP9 transcript levels were upregulated and correlated with disease severity. IL6 was moderately increased in KC patients. IHC demonstrated a reduction in the protein expression levels of LOX in the epithelium and collagen IV in the basement membrane of KC patients compared to healthy donor corneas.

CONCLUSIONS

The data demonstrates that the structural deformity of the KC cornea may be dependent on reduced expressions of collagens and LOX, as well as on MMP9 elevated by the corneal epithelium.

Accelerated corneal collagen cross-linking in pediatric patients: two-year follow-up results

Purpose. To evaluate the effectiveness and safety of accelerated corneal collagen cross-linking (ACXL) in patients below 14 years of age with progressive keratoconus. Materials and Methods. Thirty eyes of 18 patients with established progressive keratoconus underwent preoperative and postoperative visual acuity assessment, topography, and specular microscopy prior to ACXL and were followed up for 24 months. Results. Mean age of the patients was 12.7 years with ten males and eight females. There was an improvement in the mean postoperative uncorrected distant visual acuity (from 0.76 ± 0.26 to 0.61 ± 0.25; P = 0.005), mean corrected distant visual acuity (from 0.24 ± 0.19 to 0.12 ± 0.12; P < 0.001), mean spherical refraction (from −3.04 DS ± 3.60 to −2.38 DS ± 3.37; P = 0.28), mean cylinder (from −3.63 DC ± 1.82 to −2.80 DC ± 1.48; P = 0.008), and spherical equivalent (from −4.70 D ± 3.86 to −3.75 D ± 3.49; P = 0.15). Three eyes of two patients with vernal keratoconjunctivitis (VKC) showed progression. There were no intra- or postoperative complications. Conclusion. In pediatric patients ACXL is an effective and safe procedure for the management of keratoconus. Optimal management of VKC is important to arrest the progression of keratoconus.

Tear film inflammatory mediators in patients with keratoconus

To determine the concentration of inflammatory mediators in the tear film of patients with keratoconus. Basal tears from patients with keratoconus and from normal controls were collected using a capillary tube. Patients with keratoconus were examined in a routine fashion, and keratometric readings were also taken from corneal topographic maps .The concentration of cytokines including Interleukin 6,10,1b and Interferon-γ was measured by enzyme-linked immunoadsorbent assay. Seventy-two subjects were enrolled in the study including 42 patients with keratoconus and 30 normals. Patients with keratoconus had significantly higher levels of Interlukin 6,1b and Interferon-γ (17.49 ± 1.92 pg/ml), (8.58 ± 1.15 pg/ml), and (33.33 ± 7.57 pg/ml) compared with control subjects (13.81 ± 1.71 pg/ml), (4.98 ± 0.52 pg/ml), and (22.99 ± 4.68 pg/ml), (P = 0.0001, P = 0.0001, and P = 0.0001). But the level of Interlukin-10 in keratoconus patients was significantly lower (6.07 ± 1.35 pg/ml) than controls (8.99 ± 0.70 pg/ml) (P = 0.0001). We realized that the proinflammatory markers (Interlukin-6,1-b and Interferon-γ) are over expressed, whereas the anti-inflammatory marker (Interlukin-10) is under expressed, indicating that the pathogenesis of keratoconus may involve complex chronic inflammatory events. Additional future studies will reveal the exact molecular and biochemical mechanisms that are required to better manage the disease and halt its progression.