Keratin expression by corneal and limbal stem cells during development

Ozone exposure affects corneal epithelial fate by promoting mtDNA leakage and cGAS/STING activation

Ozone is a common air pollutant associated with various human diseases. The human ocular surface is frequently exposed to ozone in the troposphere, but the mechanisms by which ozone affects the ocular surface health remain unclear. This study aimed to establish a mouse model to investigate the effects of ozone exposure on the ocular surface and the corneal epithelium. The findings revealed that ozone exposure disrupted corneal epithelial homeostasis and differentiation, resulting in corneal squamous metaplasia. Further, ozone exposure induced oxidative damage and cytoplasmic leakage of mitochondrial DNA (mtDNA), thereby activating the cGAS/STING signaling pathway. The activation of the cGAS/STING signaling pathway triggered the activation of downstream NF-κB and TRAF6 signaling pathways, causing corneal inflammation, thereby promoting corneal inflammation and squamous metaplasia. Finally, C-176, a selective STING inhibitor, effectively prevented and treated corneal inflammation and squamous metaplasia caused by ozone exposure. This study revealed the role of mtDNA leakage-mediated cGAS/STING activation in corneal squamous epithelial metaplasia caused by ozone exposure. It also depicted the abnormal expression pattern of corneal epithelial keratin using three-dimensional images, providing new targets and strategies for preventing and treating corneal squamous metaplasia and other ocular surface diseases.

Developmental toxicity assessment of neonicotinoids and organophosphate esters with a human embryonic stem cell- and metabolism-based fast-screening model

In recent years, neonicotinoids (NEOs) and organophosphate esters (OPEs) have been widely used as substitutes for traditional pesticides and brominated flame-retardants, respectively. Previous studies have shown that those compounds can be frequently detected in environmental and human samples, are able to penetrate the placental barrier, and are toxic to animals. Thus, it is reasonable to speculate that NEOs and OPEs may have potential adverse effects in humans, especially during development. We employed a human embryonic stem cell differentiation- and liver S9 fraction metabolism-based fast screening model to assess the potential embryonic toxicity of those two types of chemicals. We show that four NEO and five OPE prototypes targeted mostly ectoderm specification, as neural ectoderm and neural crest genes were down-regulated, and surface ectoderm and placode markers up-regulated. Human liver S9 fraction's treatment could generally reduce the effects of the chemicals, except in a few specific instances, indicating the liver may detoxify NEOs and OPEs. Our findings suggest that NEOs and OPEs interfere with human early embryonic development.

Sequence variants contributing to dysregulated inflammatory responses across keratoconic cone surface in adolescent patients with keratoconus

Background

Keratoconus (KTCN) is the most common corneal ectasia resulting in a conical shape of the cornea. Here, genomic variation in the corneal epithelium (CE) across the keratoconic cone surface in patients with KTCN and its relevance in the functioning of the immune system were assessed.

Methods

Samples from four unrelated adolescent patients with KTCN and two control individuals were obtained during the CXL and PRK procedures, respectively. Three topographic regions, central, middle, and peripheral, were separated towards the whole-genome sequencing (WGS) study embracing a total of 18 experimental samples. The coding and non-coding sequence variation, including structural variation, was assessed and then evaluated together with the previously reported transcriptomic outcomes for the same CE samples and full-thickness corneas.

Results

First, pathway enrichment analysis of genes with identified coding variants pointed to "Antigen presentation" and "Interferon alpha/beta signaling" as the most overrepresented pathways, indicating the involvement of inflammatory responses in KTCN. Both coding and non-coding sequence variants were found in genes (or in their close proximity) linked to the previously revealed KTCN-specific cellular components, namely, "Actin cytoskeleton", "Extracellular matrix", "Collagen-containing extracellular matrix", "Focal adhesion", "Hippo signaling pathway", and "Wnt signaling" pathways. No genomic heterogeneity across the corneal surface was found comparing the assessed topographic regions. Thirty-five chromosomal regions enriched in both coding and non-coding KTCN-specific sequence variants were revealed, with a most representative 5q locus previously recognized as involved in KTCN.

Conclusion

The identified genomic features indicate the involvement of innate and adaptive immune system responses in KTCN pathogenesis.

Profile of biological characterizations and clinical application of corneal stem/progenitor cells

Corneal stem/progenitor cells are typical adult stem/progenitor cells. The human cornea covers the front of the eyeball, which protects the eye from the outside environment while allowing vision. The location and function demand the cornea to maintain its transparency and to continuously renew its epithelial surface by replacing injured or aged cells through a rapid turnover process in which corneal stem/progenitor cells play an important role. Corneal stem/progenitor cells include mainly corneal epithelial stem cells, corneal endothelial cell progenitors and corneal stromal stem cells. Since the discovery of corneal epithelial stem cells (also known as limbal stem cells) in 1971, an increasing number of markers for corneal stem/progenitor cells have been proposed, but there is no consensus regarding the definitive markers for them. Therefore, the identification, isolation and cultivation of these cells remain challenging without a unified approach. In this review, we systematically introduce the profile of biological characterizations, such as anatomy, characteristics, isolation, cultivation and molecular markers, and clinical applications of the three categories of corneal stem/progenitor cells.

Zebrafish cornea formation and homeostasis reveal a slow maturation process, similarly to terrestrial vertebrates' corneas

Corneal blindness is the fourth leading cause of blindness worldwide. The superficial position of cornea on the eye makes this tissue prone to environmental aggressions, which can have a strong impact on sight. While most corneal pathology studies utilize terrestrial models, the knowledge on zebrafish cornea is too scarce to comprehend its strategy for the maintenance of a clear sight in aquatic environment. In this study, we deciphered the cellular and molecular events during corneal formation and maturation in zebrafish. After describing the morphological changes taking place from 3 days post fertilization (dpf) to adulthood, we analyzed cell proliferation. We showed that label retaining cells appear around 14 to 21dpf. Our cell proliferation study, combined to the study of Pax6a and krtt1c19e expression, demonstrate a long maturation process, ending after 45dpf. This maturation ends with a solid patterning of corneal innervation. Finally, we demonstrated that corneal wounding leads to an intense dedifferentiation, leading to the recapitulation of corneal formation and maturation, via a plasticity period. Altogether, our study deciphers the maturation steps of an aquatic cornea. These findings demonstrate the conservation of corneal formation, maturation and wound healing process in aquatic and terrestrial organisms, and they will enhance the use of zebrafish as model for corneal physiology studies.

RDIVpSGP motif of ASPP2 binds to 14-3-3 and enhances ASPP2/k18/14-3-3 ternary complex formulation to promote BRAF/MEK/ERK signal inhibited cell proliferation in hepatocellular carcinoma

The Apoptosis Stimulating Protein of p53 2 (ASPP2) is a heterozygous insufficient tumor suppressor; however, its molecular mechanism(s) in tumor suppression is not completely understood. ASPP2 plays an essential role in cell growth, as shown by liver hepatocellular carcinoma (LIHC) RNA-seq assay using the Cancer Genome Atlas (TCGA) and High-Throughput-PCR assay using ASPP2 knockdown cells. These observations were further confirmed by in vivo and in vitro experiments. Mechanistically, N-terminus ASPP2 interacted with Keratin 18 (k18) in vivo and in vitro. Interestingly, the RDIVpSGP motif of ASPP2 associates with 14-3-3 and promotes ASPP2/k18/14-3-3 ternary-complex formation which promotes MEK/ERK signal activation by impairing 14-3-3 and BRAF association. Additionally, ASPP2-rAd injection promotes paclitaxel-suppressed tumor growth by suppressing cell proliferation in the BALB/c nude mice model. ASPP2 and k18 were preferentially downregulated in Hepatocellular Carcinoma (HCC), which predicted poor prognosis in HCC patients. Overall, these findings suggested that ASPP2 promoted BRAF/MEK/ERK signal activation by promoting the formation of an ASPP2/k18/14-3-3 ternary complex via the RDIVpSGP motif at the N terminus. Moreover, this study provides novel insights into the molecular mechanism of tumor suppression in HCC patients.

Single cell RNA-seq of human cornea organoids identifies cell fates of a developing immature cornea

The cornea is a protective and refractive barrier in the eye crucial for vision. Understanding the human cornea in health, disease, and cell-based treatments can be greatly advanced with cornea organoids developed in culture from induced pluripotent stem cells. While a limited number of studies have investigated the single-cell transcriptomic composition of the human cornea, its organoids have not been examined similarly. Here, we elucidated the transcriptomic cell fate map of 4-month-old human cornea organoids and human donor corneas. The organoids harbor cell clusters that resemble cells of the corneal epithelium, stroma, and endothelium, with subpopulations that capture signatures of early developmental states. Unlike the adult cornea where the largest cell population is stromal, the organoids contain large proportions of epithelial and endothelial-like cells. These corneal organoids offer a 3D model to study corneal diseases and integrated responses of different cell types.

Sulfur mustard corneal injury is associated with alterations in the epithelial basement membrane and stromal extracellular matrix

Sulfur mustard (SM; bis(2-chloroethyl) sulfide) is a highly reactive bifunctional alkylating agent synthesized for chemical warfare. The eyes are particularly sensitive to SM where it causes irritation, pain, photophobia, and blepharitis, depending on the dose and duration of exposure. In these studies, we examined the effects of SM vapor on the corneas of New Zealand white male rabbits. Edema and hazing of the cornea, signs of acute injury, were observed within one day of exposure to SM, followed by neovascularization, a sign of chronic or late phase pathology, which persisted for at least 28 days. Significant epithelial-stromal separation ranging from ~8-17% of the epithelial surface was observed. In the stroma, there was a marked increase in CD45+ leukocytes and a decrease of keratocytes, along with areas of disorganization of collagen fibers. SM also disrupted the corneal basement membrane and altered the expression of perlecan, a heparan sulfate proteoglycan, and cellular fibronectin, an extracellular matrix glycoprotein. This was associated with an increase in basement membrane matrix metalloproteinases including ADAM17, which is important in remodeling of the basement membrane during wound healing. Tenascin-C, an extracellular matrix glycoprotein, was also upregulated in the stroma 14-28 d post SM, a finding consistent with its role in organizing structural components of the stroma necessary for corneal transparency. These data demonstrate that SM vapor causes persistent alterations in structural components of the cornea. Further characterization of SM-induced injury in rabbit cornea will be useful for the identification of targets for the development of ocular countermeasures.

Downregulation of p38 MAPK signaling pathway ameliorates tissue engineered corneal epithelium

Tissue engineered corneal epithelium transplantation is effective treatment for severe limbal stem cell deficiency (LSCD), while epithelial terminal differentiation, tans-differentiation and insufficient stem cell during construction affects the quality of tissue engineered corneal epithelium. In this study, we applied SB203580 in the culture medium to downregulate the P38 MAPK signaling pathway during construction of tissue engineered corneal epithelium. With application of SB203580, tissue engineered corneal epithelium showed enhanced strength and condensed structure. The expression of progenitor cell markers ABCG2, P63, K14, Wnt7a was increased, differentiation markers K12, Pax6, K10, K13, and trans-differentiation markers α-SMA and Snail1 was decreased, while cell junction markers Claudin-1 and E-cadherin was increased in the tissue engineered corneal epithelium. The wnt/β-catenin signaling pathway was upregulated in the epithelium after p38 MAPK inhibition. Transplantation of tissue engineered corneal epithelium treated with SB203580 to rabbit LSCD model showed faster wound healing and improved epithelial quality. We conclude that downregulation of p38 MAPK signaling pathway helps maintain the stemness, prevent terminal differentiation and abnormal differentiation of corneal epithelial cells during epithelium construction process, thus can improve the quality of tissue engineered corneal epithelium.

An efficient simplified method for the generation of corneal epithelial cells from human pluripotent stem cells

Corneal epithelial cells derived from human pluripotent stem cells (hPSCs) are an important cell source for preclinical models to test ophthalmic drugs. However, current differentiation protocols lack instructions regarding optimal culturing conditions, which hinders the quality of cells and limits scale-up. Here, we introduce a simplified small molecule-based corneal induction method (SSM-CI) to generate corneal epithelial cells from hPSCs. SSM-CI provides the advantage of minimizing cell-culturing time using two defined culturing media containing TGF-β, and Wnt/β-catenin pathway inhibitors, and bFGF growth factor over 25 days. Compared to the conventional human corneal epithelial cell line (HCE-T) and human primary corneal epithelial cells (hPCEpCs), corneal epithelial cells generated by SSM-CI are well differentiated and express relevant maturation markers, including PAX6 and CK12. RNA-seq analysis indicated the faithful differentiation of hPSCs into corneal epithelia, with significant upregulation of corneal progenitor and adult corneal epithelial phenotypes. Furthermore, despite the initial inhibition of TGF-β and Wnt/β-catenin, upregulation of these pathway-related transcripts was observed in the later stages, indicating their necessity in the generation of mature corneal epithelial cells. Moreover, we observed a shift in gene signatures associated with the metabolic characteristics of mature corneal epithelial cells, involving a decrease in glycolysis and an increase in fatty acid oxidation. This was also attributed to the overexpression of metabolic enzymes and transporter-related transcripts responsible for fatty acid metabolism. Thus, SSM-CI provides a comprehensive method for the generation of functional corneal epithelial cells for use in preclinical models.

DSP missense variant in a Scottish Highland calf with congenital ichthyosis, alopecia, acantholysis of the tongue and corneal defects

BACKGROUND

Ichthyosis describes a localized or generalized hereditary cornification disorder caused by an impaired terminal keratinocyte differentiation resulting in excessive stratum corneum with the formation of more or less adherent scales. Ichthyosis affects humans and animals. Two rare bovine forms are reported, the severe harlequin ichthyosis and the less severe congenital ichthyosis, both characterized by a severe orthokeratotic lamellar hyperkeratosis.

RESULTS

A 2-weeks-old purebred Scottish Highland calf was referred because of a syndrome resembling congenital ichthyosis. The clinical phenotype included diffuse alopecia and a markedly lichenified skin covered with large and excessive scales. Additionally, conjunctivitis and ulceration of the cornea were noted. Post-mortem examination revealed deep fissures in the diffusely thickened tongue and histopathological findings in the skin confirmed the clinical diagnosis. Whole-genome sequencing of the affected calf and comparison of the data with control genomes was performed. A search for private variants in known candidate genes for skin phenotypes including genes related with erosive and hyperkeratotic lesions revealed a single homozygous protein-changing variant, DSP: c.6893 C>A, or p.Ala2298Asp. The variant is predicted to change a highly conserved residue in the C-terminal plakin domain of the desmoplakin protein, which represents a main intracellular component of desmosomes, important intercellular adhesion molecules in various tissues including epidermis. Sanger sequencing confirmed the variant was homozygous in the affected calf and heterozygous in both parents. Further genotyping of 257 Scottish Highland animals from Switzerland revealed an estimated allele frequency of 1.2%. The mutant allele was absent in more than 4800 controls from various other cattle breeds.

CONCLUSIONS

This study represents the first report of combined lesions compatible with congenital ichthyosis, alopecia, acantholysis of the tongue and corneal defects associated with a DSP missense variant as the most likely underlying cause. To the best of our knowledge, this study is also the first report of a DSP-related syndromic form of congenital ichthyosis in domestic animals. The results of our study enable genetic testing to avoid the unintentional occurrence of further affected cattle. The findings were added to the Online Mendelian Inheritance in Animals (OMIA) database (OMIA 002243-9913).

Transcriptome Analysis of Pterygium and Pinguecula Reveals Evidence of Genomic Instability Associated with Chronic Inflammation

Solar damage due to ultraviolet radiation (UVR) is implicated in the development of two proliferative lesions of the ocular surface: pterygium and pinguecula. Pterygium and pinguecula specimens were collected, along with adjacent healthy conjunctiva specimens. RNA was extracted and sequenced. Pairwise comparisons were made of differentially expressed genes (DEGs). Computational methods were used for analysis. Transcripts from 18,630 genes were identified. Comparison of two subgroups of pterygium specimens uncovered evidence of genomic instability associated with inflammation and the immune response; these changes were also observed in pinguecula, but to a lesser extent. Among the top DEGs were four genes encoding tumor suppressors that were downregulated in pterygium: C10orf90, RARRES1, DMBT1 and SCGB3A1; C10orf90 and RARRES1 were also downregulated in pinguecula. Ingenuity Pathway Analysis overwhelmingly linked DEGs to cancer for both lesions; however, both lesions are clearly still benign, as evidenced by the expression of other genes indicating their well-differentiated and non-invasive character. Pathways for epithelial cell proliferation were identified that distinguish the two lesions, as well as genes encoding specific pathway components. Upregulated DEGs common to both lesions, including KRT9 and TRPV3, provide a further insight into pathophysiology. Our findings suggest that pterygium and pinguecula, while benign lesions, are both on the pathological pathway towards neoplastic transformation.

Wound healing of the corneal epithelium: a review

The corneal epithelium (CE) forms the outermost layer of the cornea. Despite its thickness of only 50 μm, the CE plays a key role as an initial barrier against any insults to the eye and contributes to the light refraction onto the retina required for clear vision. In the event of an injury, the cornea is equipped with many strategies contributing to competent wound healing, including angiogenic and immune privileges, and mechanotransduction. Various factors, including growth factors, keratin, cytokines, integrins, crystallins, basement membrane, and gap junction proteins are involved in CE wound healing and serve as markers in the healing process. Studies of CE wound healing are advancing rapidly in tandem with the rise of corneal bioengineering, which employs limbal epithelial stem cells as the primary source of cells utilizing various types of biomaterials as substrates.

Corneal Epithelial Stem Cells-Physiology, Pathophysiology and Therapeutic Options

In the human cornea, regeneration of the epithelium is regulated by the stem cell reservoir of the limbus, which is the marginal region of the cornea representing the anatomical and functional border between the corneal and conjunctival epithelium. In support of this concept, extensive limbal damage, e.g., by chemical or thermal injury, inflammation, or surgery, may induce limbal stem cell deficiency (LSCD) leading to vascularization and opacification of the cornea and eventually vision loss. These acquired forms of limbal stem cell deficiency may occur uni- or bilaterally, which is important for the choice of treatment. Moreover, a variety of inherited diseases, such as congenital aniridia or dyskeratosis congenita, are characterized by LSCD typically occurring bilaterally. Several techniques of autologous and allogenic stem cell transplantation have been established. The limbus can be restored by transplantation of whole limbal grafts, small limbal biopsies or by ex vivo-expanded limbal cells. In this review, the physiology of the corneal epithelium, the pathophysiology of LSCD, and the therapeutic options will be presented.

Novel Cell Culture Paradigm Prolongs Mouse Corneal Epithelial Cell Proliferative Activity in vitro and in vivo

It has been a long-standing challenge to obtain from cell cultures adequate amounts of mouse corneal epithelial cells (mCEC) to perform transplantation surgery. This limitation is attributable to the passage dependent declines in their proliferative activity. We describe here development of a novel 6C medium that contains six different modulators of different signaling pathways, which control proliferative mCEC activity. Its usage shortens the time and effort required to obtain epithelial sheets for hastening healing of an epithelial wound in an experimental animal model. This serum-free 6C medium contains:Y27632, forskolin, SB431542, DAPT, IWP-2, LDN-193189 and also DermaLife K keratinocyte calcium. Their inclusion inhibits rises in four specific markers of epithelial mesenchymal transdifferentiation:ZEB1/2, Snail, β-catenin and α-SMA. This medium is applied in a feeder-free air-lifted system to obtain sufficient populations of epithelial progenitor cells whose procurement is facilitated due to suppression of progenitor epithelial cell transdifferentiation into epithelial-mesenchymal cells. Diminution of this decline in transdifferentiation was confirmed based on the invariance of P63, K14, Pax6, and K12 gene expression levels. This cell culture technique is expected to facilitate ex vivo characterization of mechanisms underlying cell fate determination. Furthermore, its implementation will improve yields of progenitor mouse corneal epithelial cells, which increases the likelihood of using these cells as a source to generate epithelial sheets for performing transplantation surgery to treat limbal stem cell deficiency in a clinical setting. In addition, the novel insight obtainable from such studies is expected to improve the outcomes of corneal regenerative medicine.

Closing the Loop with Keratin-Rich Fibrous Materials

One of the agro-industry's side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.

Understanding cornea epithelial stem cells and stem cell deficiency: Lessons learned using vertebrate model systems

Animal models have contributed greatly to our understanding of human diseases. Here, we focus on cornea epithelial stem cell (CESC) deficiency (commonly called limbal stem cell deficiency, LSCD). Corneal development, homeostasis and wound healing are supported by specific stem cells, that include the CESCs. Damage to or loss of these cells results in blindness and other debilitating ocular conditions. Here we describe the contributions from several vertebrate models toward understanding CESCs and LSCD treatments. These include both mammalian models, as well as two aquatic models, Zebrafish and the amphibian, Xenopus. Pioneering developments have been made using stem cell transplants to restore normal vision in patients with LSCD, but questions still remain about the basic biology of CESCs, including their precise cell lineages and behavior in the cornea. We describe various cell lineage tracing studies to follow their patterns of division, and the fates of their progeny during development, homeostasis, and wound healing. In addition, we present some preliminary results using the Xenopus model system. Ultimately, a more thorough understanding of these cornea cells will advance our knowledge of stem cell biology and lead to better cornea disease therapeutics.