Epidermal Growth Factor Receptor Expression in the Corneal Epithelium

A systematic review of the potential treatment effects of topical epidermal growth factor for ocular surface disorders

PURPOSE

This systematic review, evaluated the role of epidermal growth factor (EGF) in corneal wound healing and the pathogenesis of ocular surface disorders (OSDs).

METHODS

The clinical and experimental application of topical EGF therapy for OSDs was reviewed. This systematic research assessed articles published on PubMed/MEDLINE from 2000 to 2023 and summarized and discussed the findings of 38 experimental and 10 clinical studies. Reporting adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

The role of EGF and its receptor (EGFR) is indispensable in corneal wound healing after injury. The most important downstream molecular pathways are the MAPK/Erk and PI3K/Akt pathways, which lead to proliferation, migration, and differentiation of corneal epithelial cells. Other EGF-related pathways, such as Decorin and Erk signaling (decreasing Pax6), as well as upregulating VEGF, contribute to early and late remodeling after corneal healing. The effect of EGF on corneal wound healing is dose-dependent, and it interacts with other important pathways, such as TGF-β.

CONCLUSIONS

There are several studies on animals and humans that showed promise for topical EGF therapy in the form of drops, ointments, or loaded contact lenses for a variety of OSDs, such as dry eye disease, neurotrophic ulcers, and pterygium excision. The reported OSDs after using EGFR inhibitors for oncology patients, and their favorable response to topical EGF therapy, further support the significance of EGF in the pathogenesis and treatment of OSDs. However, current clinical evidence is scarce, and high-quality studies are warranted to confirm the therapeutic role of EGF topical treatment for a variety of OSDs and determine the most effective yet safe concentrations.

Diverse calcium signaling profiles regulate migratory behavior in avascular wound healing and aberrant signal hierarchy occurs early in diabetes

In avascular wound repair, calcium signaling events are the predominant mechanism cells use to transduce information about stressors in the environment into an effective and coordinated migratory response. Live cell imaging and computational analysis of corneal epithelial wound healing revealed that signal initiation and propagation at the wound edge are highly ordered, with groups of cells engaging in cyclical patterns of initiation and propagation. The cells in these groups exhibit a diverse range of signaling behavior, and dominant "conductor cells" drive activity in groups of lower-signaling neighbors. Ex vivo model systems reveal that conductor cells are present in wing cell layers of the corneal epithelium and that signaling propagates both within and between wing and basal layers. There are significant aberrations in conductor phenotype and interlayer propagation in type II diabetic murine models, indicating that signal hierarchy breakdown is an early indicator of disease. In vitro models reveal that signaling profile diversity and conductor cell phenotype is eliminated with P2X7 inhibition and is altered in Pannexin-1 or P2Y2 but not Connexin-43 inhibition. Conductor cells express significantly less P2X7 than their lower-signaling neighbors and exhibit significantly less migratory behavior after injury. Together, our results show that the postinjury calcium signaling cascade exhibits significantly more ordered and hierarchical behavior than previously thought, that proteins previously shown to be essential for regulating motility are also essential for determining signaling phenotype, and that loss of signal hierarchy integrity is an early indicator of disease state. NEW & NOTEWORTHY Calcium signaling in corneal epithelial cells after injury is highly ordered, with groups of cells engaged in cyclical patterns of event initiation and propagation driven by high-signaling cells. Signaling behavior is determined by P2X7, Pannexin-1, and P2Y2 and influences migratory behavior. Signal hierarchy is observed in healthy ex vivo models after injury and becomes aberrant in diabetes. This represents a paradigm shift, as signaling was thought to be random and determined by factors in the environment.

Efficacy of epidermal growth factor in suppressing inflammation and proliferation in pterygial fibroblasts through interactions with microenvironmental M1 macrophages

The protein epidermal growth factor (EGF), which plays a crucial role in promoting cell proliferation and survival, has recently demonstrated potential in reducing inflammation. In this study, we examined the impact of EGF on the anti-inflammatory and anti-proliferative properties of pterygium, a prevalent hypervascular proliferative disease affecting the ocular surface. In surgically excised tissues, markers for fibrotic and inflammatory signals, including VIM, ACTA2, FAP, MMP2, VCAM1, ICAM1, CD86, IL6, and IL1B were upregulated in the pterygium body stroma compared to the normal conjunctival stroma. EGF exerted anti-inflammatory and anti-vasculogenic effects on pterygial fibroblasts when co-cultured with M1 macrophages. Moreover, exosomes derived from EGF-preconditioned M1 macrophages suppressed the heightened inflammatory and vasculogenic signals in pterygial fibroblasts induced by exosomes from M1 macrophages. Paradoxically, the proliferation of pterygial fibroblasts was inhibited by EGF in the in vitro microenvironment with M1 macrophages, despite EGF being known as a growth factor. EGF-preconditioning of M1 macrophages rescued the increased proliferation of pterygial fibroblasts induced by exosomes from M1 macrophages. In conclusion, our findings demonstrate that EGF effectively mitigates inflammation and proliferation in pterygial fibroblasts within a microenvironment containing M1 macrophages.

Activation of limbal epithelial proliferation is partly controlled by the ACE2-LCN2 pathway

In response to corneal injury, an activation of corneal epithelial stem cells and their direct progeny the early transit amplifying (eTA) cells to rapidly proliferate is critical for proper re-epithelialization. Thus, it is important to understand how such stem/eTA cell activation is regulated. Angiotensin-converting enzyme 2 (ACE2) is predominantly expressed in the stem/eTA-enriched limbal epithelium but its role in the limbal epithelium was unclear. Single cell RNA sequencing (scRNA-seq) suggested that Ace2 involved the proliferation of the stem/eTA cells. Ace2 was reduced following corneal injury. Such reduction enhanced limbal epithelial proliferation and downregulated LCN2, a negative regulator of proliferation in a variety of tissues, via upregulating TGFA and consequently activating epidermal growth factor receptor (EGFR). Inhibition of EGFR or overexpression of LCN2 reversed the increased proliferation in limbal epithelial cells lacking ACE2. Our findings demonstrate that after corneal injury, ACE2 is downregulated, which activates limbal epithelial cell proliferation via a TGFA/EGFR/LCN2 pathway.

EGF-conditioned M1 macrophages Convey reduced inflammation into corneal endothelial cells through exosomes

Epidermal Growth Factor (EGF), a protein pivotal in cell proliferation and survival, has recently shown promise in alleviating inflammation. This study investigates EGF's impact on M1 macrophages, exploring its potential for anti-inflammatory and anti-vasculogenic interactions with corneal endothelial cells (CECs). Polarized M1 macrophages treated with EGF exhibited a suppression of gene expressions related to inflammatory and vasculogenic signals. The anti-inflammatory effects of EGF were observed in co-culture systems with human CECs (HCECs), showcasing its ability to alter macrophage phenotypes. Exosomes derived from EGF-treated M1 macrophages demonstrated enriched proteomic profiles related to immune system regulation and inflammation inhibition. When applied as eye drops in murine corneas, EGF-conditioned M1 macrophage-derived exosomes effectively reduced inflammation and increased M2-related ARG1 expression. This study highlights EGF's potential in mitigating inflammation in M1 macrophages and its delivery through exosomes to cultured HCECs and murine corneas, suggesting a novel therapeutic avenue for ocular surface anti-inflammatory treatments.

Ocular surface toxicities associated with modern anticancer therapies

Cancer treatments have recently shifted from broad-spectrum cytotoxic therapies to more focused treatments, maximizing anticancerous activity while reducing toxicity to healthy cells. These modern anticancer therapies (MATs) encompass a wide range of innovative molecules that include immune checkpoint inhibitors and other targeted anticancer therapies, comprising antibody drug conjugates and inhibitors of signal transduction. Some MATs are associated with ocular surface adverse events that can cause severe discomfort and even lead to loss of vision. While these complications remain rare, they are probably underreported. It is likely that both oncologists and ophthalmologists will come across MATs-associated ocular surface-adverse events in their practices, owing to the increasing number of patients being treated with MATs. Rapid identification of ocular surface-adverse events is crucial, as early intervention can manage these conditions to avoid vision loss and reduce negative impacts on quality of life. We discuss characteristics of ocular surface pathologies attributed to MATs, describe the suspected underlying pathophysiological mechanisms, and outline the main lines of treatment.

Protective effect of pituitary adenylate cyclase activating polypeptide in diabetic keratopathy

Diabetic keratopathy (DK) is the major complication of the cornea characterizing diabetes-affected patients. This ocular pathology is correlated with the hyperglycemic state leading to delayed corneal wound healing and recurrent corneal ulcers. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with widespread distribution throughout the body, and exerting cytoprotective effects in the neural and non-neuronal parts of the eye, including the cornea. The purpose of the present study was to investigate whether changes in PACAP expression can concur for delayed epithelial wound healing in diabetic cornea and whether the protective effect of the peptide could be mediated through the activation of the EGFR signaling pathway, which has been reported to be impaired in DK. Expression and distribution of PACAP, PAC1R, and EGFR were investigated through immunohistochemistry analysis in the cornea of normal and diabetic rats. The role of the peptide on wound healing during DK was evaluated in an in vitro model represented by rabbit corneal epithelial cells grown in high glucose conditions. Western blotting and immunofluorescence analysis were used to examine the ability of PACAP to induce the activation of the EGFR/ERK1/2 signaling pathway. Our results showed that in diabetic cornea the expression of PACAP, PAC1R, and EGFR is drastically reduced. The treatment with PACAP via PAC1R activation enhanced cell viability and corneal epithelium wound healing in cells grown under high glucose conditions. Furthermore, both EGFR and ERK1/2 signaling was induced upon the peptide treatment. Overall, our results showed the trophic efficiency of PACAP for enhancing the corneal epithelium re-epithelialization suggesting that the peptide could be beneficially valuable as a treatment for DK.

Antibody-Drug Conjugates and Ocular Toxicity

Antibody-drug conjugates (ADCs) are a growing class of chemotherapeutic agents for the purpose of treating cancers that often have relapsed or failed first- and second-line treatments. ADCs are composed of extremely potent cytotoxins with a variety of side effects, one of the most significant being ocular toxicity. The available literature describes these toxicities as varying in severity and in incidence, although with disparate methods of evaluation and management. Some of the most common toxicities include microcyst-like epithelial keratopathy and dry eye. We discuss proposed mechanisms of ocular toxicity and describe the reports that mention these toxicities. We focus on ADCs with the most published literature and the most significant effects on ocular tissue. We propose areas for further investigation and possible ideas of future management. We provide a comprehensive look at the reports of ADCs in current literature to better inform clinicians on an expanding drug class.

Detection of pro-inflammatory cytokines in healthy canine tears using Canine Cytokine SpikeMix™ mass spectrometry via multiple reaction monitoring

PURPOSE

To evaluate the efficacy of the Canine Cytokine SpikeMix™ and MRM-MS for detecting pro-inflammatory cytokines in canine tears from healthy research Beagles.

METHODS

A complete ophthalmic examination was performed on 15 healthy research Beagles to verify no ophthalmic diseases. Tears were collected OU by placing a Weck-Cel® cellulose spear in the ventral conjunctival fornix for 1 min. The Weck-Cel® spear was placed in a 2.0 mL tube with a centrifuge filter forcing tears to flow through the filter into the bottom of the tube. The tears were analyzed using the Canine Cytokine SpikeMix™ and MRM-MS. Descriptive data from this study was reported as the normalized total peak area (nTPA) and median (range) using data imported from the online MRM-MS Skyline program.

RESULTS

The level of 16 pro-inflammatory cytokines was successfully detected in all 15 dogs. The four cytokines with the highest median amounts in the samples were IL-2 = 0.1243 (0.019-6.7289), IL-6 = 0.964 (0.0036-16.9365), TNFα = 0.1644 (0.0096-0.7138), and CSF-2 = 0.4022 (0.1475-2.6208).

CONCLUSIONS

This study revealed that 16 pro-inflammatory cytokines in canine tears from healthy dogs can be detected with Canine Cytokine SpikeMix™ and MRM-MS.

Single-Cell Transcriptomics Reveals Cellular Heterogeneity and Complex Cell-Cell Communication Networks in the Mouse Cornea

Purpose

To generate a single-cell RNA-sequencing (scRNA-seq) map and construct cell-cell communication networks of mouse corneas.

Methods

C57BL/6 mouse corneas were dissociated to single cells and subjected to scRNA-seq. Cell populations were clustered and annotated for bioinformatic analysis using the R package "Seurat." Differential expression patterns were validated and spatially mapped with whole-mount immunofluorescence staining. Global intercellular signaling networks were constructed using CellChat.

Results

Unbiased clustering of scRNA-seq transcriptomes of 14,732 cells from 40 corneas revealed 17 cell clusters of six major cell types: nine epithelial cell, three keratocyte, two corneal endothelial cell, and one each of immune cell, vascular endothelial cell, and fibroblast clusters. The nine epithelial cell subtypes included quiescent limbal stem cells, transit-amplifying cells, and differentiated cells from corneas and two minor conjunctival epithelial clusters. CellChat analysis provided an atlas of the complex intercellular signaling communications among all cell types.

Conclusions

We constructed a complete single-cell transcriptomic map and the complex signaling cross-talk among all cell types of the cornea, which can be used as a foundation atlas for further research on the cornea. This study also deepens the understanding of the cellular heterogeneity and heterotypic cell-cell interaction within corneas.

Derivation of Limbal Stem Cells from Human Adult Mesenchymal Stem Cells for the Treatment of Limbal Stem Cell Deficiency

Approximately 10 million individuals have blindness due to limbal stem cell (LSCs) deficiency, one of the most challenging problems in ophthalmology. To replenish the LSC pool, an autologous extraocular cell source is appropriate, thereby avoiding the risk of immune rejection, the need for immunosuppression and the risk of damaging the contralateral eye. In recent years, adipose-derived mesenchymal stem cells (ADSCs) have been a key element in ocular regenerative medicine. In this study, we developed a protocol for deriving human LSCs from ADSCs compatible with the standard carrier human amniotic membrane, helping provide a stem cell pool capable of maintaining proper corneal epithelial homeostasis. The best protocol included an ectodermal induction step by culturing ADSCs with media containing fetal bovine serum, transforming growth factor-β inhibitor SB-505124, Wnt inhibitor IWP-2 and FGF2 for 7 days, followed by an LSC induction step of culture in modified supplemental hormonal epithelial medium supplemented with pigment epithelium-derived factor and keratinocyte growth factor for 10 additional days. The optimal differentiation efficiency was achieved when cells were cultured in this manner over vitronectin coating, resulting in up to 50% double-positive αp63/BMI-1 cells. The results of this project will benefit patients with LSC deficiency, aiding the restoration of vision.

Controlling the Nucleation and Growth of Au on a-Se Nanospheres to Enhance Their Cellular Uptake and Cytotoxicity

We report a method to experimentally control the heterogeneous nucleation and growth of Au nanoparticles on the surface of amorphous Se (a-Se) nanospheres. When a Au^III precursor is added into a colloidal suspension of a-Se nanospheres, galvanic replacement occurs between them and the resultant Au⁰ atoms then heterogeneously nucleate and grow from the surface of the a-Se nanospheres. As a unique feature of this system, the Au⁰ atoms can only be produced on the surface of the a-Se nanospheres in the nucleation stage. Once Au nuclei are formed on the surface at the very beginning of a synthesis, they will serve as the preferential sites for further deposition of Au⁰ atoms, making it possible to control the number of Au nanoparticles on each nanosphere and the morphology of the final product. The dependence of the initial reduction rate on the pH can be used to obtain Se-Au hybrid nanoparticles containing one, two, three, and multiple Au nanoparticles on the surface of each a-Se nanosphere. The presence of Au patches on the hybrid nanoparticles offers an experimental handle to optimize the ligand distribution for the achievement of enhanced cellular uptake and cytotoxicity for the a-Se nanospheres.

Tumor polyamines as guest cues attract host-functionalized liposomes for targeting and hunting via a bio-orthogonal supramolecular strategy

Inspired by the attractions of fruit flies to polyamines of rotten food, we developed a facile, bio-orthogonal, supramolecular homing and hunting strategy, relying on the elevated levels of polyamines in tumor as the natural guest cues to attract cucurbit [7] uril (CB[7]) functionalized liposomes to the tumor site, owing to the strong, bio-orthogonal host-guest interactions between CB[7] and polyamines. This supramolecular homing enabled a high targeting efficiency of CB[7] functionalized liposomes, and allowed better tissue penetration and retention in breast tumor. The employment of a receptor functionalized nanomedicine for direct tropism towards endogenous biomarkers as guest cues, reminiscent of natural chemotaxis but in a bio-orthogonal manner, has not been previously reported, offering new sights to the design and development of new nanoformulations that rely on bio-orthogonal interactions for chemotaxis-guided targeting.

Recent Advancements in Molecular Therapeutics for Corneal Scar Treatment

The process of corneal wound healing is complex and induces scar formation. Corneal scarring is a leading cause of blindness worldwide. The fibrotic healing of a major ocular wound disrupts the highly organized fibrillar collagen arrangement of the corneal stroma, rendering it opaque. The process of regaining this organized extracellular matrix (ECM) arrangement of the stromal layer to restore corneal transparency is complicated. The surface retention capacity of ocular drugs is poor, and there is a large gap between suitable corneal donors and clinical requirements. Therefore, a more efficient way of treating corneal scarring is needed. The eight major classes of interventions targeted as therapeutic tools for healing scarred corneas include those based on exosomes, targeted gene therapy, microRNAs, recombinant viral vectors, histone deacetylase inhibitors, bioactive molecules, growth factors, and nanotechnology. This review highlights the recent advancements in molecular therapeutics to restore a cornea without scarring. It also provides a scope to overcome the limitations of present studies and perform robust clinical research using these strategies.

Hyperstable EGF-like bleogen derived from cactus accelerates corneal healing in rats

Corneal scarring reduces corneal transparency, compromises vision, and is a major cause of vision loss worldwide. Epidermal growth factor (EGF), which is the prototypic member of the EGF receptor (EGFR) agonists, is present in tears to provide repair and regeneration. Recently, we discovered bleogen pB1 in the cactus plant Pereskia bleo and showed that it is a non-canonical and hyperstable EGFR agonist with EGF-like wound healing properties for diabetic rats. Here, we apply bleogen pB1 to accelerate corneal wound healing in rats. To assess the corneal healing effects of bleogen pB1, we induced an acute alkali burn to the right eye of male Wistar rats. After five consecutive ophthalmic applications, fluorescein staining and opacity scores of the bleogen pB1-treated, and the positive control EGF-treated groups improved significantly compared to the saline control group. Immunohistochemical analyses revealed that infiltrated CD68+ macrophages and the expression of the myofibroblast marker alpha smooth muscle actin (α-SMA) were significantly decreased in the bleogen pB1- and the EGF-treated groups. By employing a differential gene expression analysis of bleogen pB1- and EGF-treated keratinocytes through RNA-seq, we demonstrated that bleogen pB1 or EGF treatments can affect the expression of genes associated with inflammatory responses and extracellular matrix remodeling. Taken together, our results indicate that the plant-derived EGFR agonist bleogen pB1 can produce similar effects to those of EGF in accelerating corneal wound healing as well as in reducing persistent inflammation and myofibroblast accumulation in the cornea.

The role of the PI3K/AKT signalling pathway in the corneal epithelium: recent updates

Phosphatidylinositol 3 kinase (PI3K)/AKT (also called protein kinase B, PKB) signalling regulates various cellular processes, such as apoptosis, cell proliferation, the cell cycle, protein synthesis, glucose metabolism, and telomere activity. Corneal epithelial cells (CECs) are the outermost cells of the cornea; they maintain good optical performance and act as a physical and immune barrier. Various growth factors, including epidermal growth factor receptor (EGFR) ligands, insulin-like growth factor 1 (IGF1), neurokinin 1 (NK-1), and insulin activate the PI3K/AKT signalling pathway by binding their receptors and promote antiapoptotic, anti-inflammatory, proliferative, and migratory functions and wound healing in the corneal epithelium (CE). Reactive oxygen species (ROS) regulate apoptosis and inflammation in CECs in a concentration-dependent manner. Extreme environments induce excess ROS accumulation, inhibit PI3K/AKT, and cause apoptosis and inflammation in CECs. However, at low or moderate levels, ROS activate PI3K/AKT signalling, inhibiting apoptosis and stimulating proliferation of healthy CECs. Diabetes-associated hyperglycaemia directly inhibit PI3K/AKT signalling by increasing ROS and endoplasmic reticulum (ER) stress levels or suppressing the expression of growth factors receptors and cause diabetic keratopathy (DK) in CECs. Similarly, hyperosmolarity and ROS accumulation suppress PI3K/AKT signalling in dry eye disease (DED). However, significant overactivation of the PI3K/AKT signalling pathway, which mediates inflammation in CECs, is observed in both infectious and noninfectious keratitis. Overall, upon activation by growth factors and NK-1, PI3K/AKT signalling promotes the proliferation, migration, and anti-apoptosis of CECs, and these processes can be regulated by ROS in a concentration-dependent manner. Moreover, PI3K/AKT signalling pathway is inhibited in CECs from individuals with DK and DED, but is overactivated by keratitis.