Genome-wide transcriptional analysis of differentially expressed genes in diabetic, healing corneal epithelial cells: hyperglycemia-suppressed TGFβ3 expression contributes to the delay of epithelial wound healing in diabetic corneas

Corneal injury repair and the potential involvement of ZEB1

The cornea, consisting of three cellular and two non-cellular layers, is the outermost part of the eyeball and frequently injured by external physical, chemical, and microbial insults. The epithelial-to-mesenchymal transition (EMT) plays a crucial role in the repair of corneal injuries. Zinc finger E-box binding homeobox 1 (ZEB1), an important transcription factor involved in EMT, is expressed in the corneal tissues. It regulates cell activities like migration, transformation, and proliferation, and thereby affects tissue inflammation, fibrosis, tumor metastasis, and necrosis by mediating various major signaling pathways, including transforming growth factor (TGF)-β. Dysfunction of ZEB1 would impair corneal tissue repair leading to epithelial healing delay, interstitial fibrosis, neovascularization, and squamous cell metaplasia. Understanding the mechanism underlying ZEB1 regulation of corneal injury repair will help us to formulate a therapeutic approach to enhance corneal injury repair.

Elucidating the mechanism of corneal epithelial cell repair: unraveling the impact of growth factors

The repair mechanism for corneal epithelial cell injuries encompasses migration, proliferation, and differentiation of corneal epithelial cells, and extracellular matrix remodeling of the stromal structural integrity. Furthermore, it involves the consequential impact of corneal limbal stem cells (LSCs). In recent years, as our comprehension of the mediating mechanisms underlying corneal epithelial injury repair has advanced, it has become increasingly apparent that growth factors play a pivotal role in this intricate process. These growth factors actively contribute to the restoration of corneal epithelial injuries by orchestrating responses and facilitating specific interactions at targeted sites. This article systematically summarizes the role of growth factors in corneal epithelial cell injury repair by searching relevant literature in recent years, and explores the limitations of current literature search, providing a certain scientific basis for subsequent basic research and clinical applications.

Lack of Elevated Expression of TGFβ3 Contributes to the Delay of Epithelial Wound Healing in Diabetic Corneas

Purpose

To investigate the mechanisms underlying the differential roles of TGFβ1 and TGFβ3 in accelerating corneal epithelial wound healing (CEWH) in diabetic (DM) corneas, with normoglycemia (NL) corneas as the control.

Methods

Two types of diabetic mice, human corneal organ cultures, mouse corneal epithelial progenitor cell lines, and bone marrow-derived macrophages (BMDMs) were employed to assess the effects of TGFβ1 and TGFβ3 on CEWH, utilizing quantitative PCR, western blotting, ELISA, and whole-mount confocal microscopy.

Results

Epithelial debridement led to an increased expression of TGFβ1 and TGFβ3 in cultured human NL corneas, but only TGFβ1 in DM corneas. TGFβ1 and TGFβ3 inhibition was significantly impeded, but exogenous TGFβ1 and, more potently, TGFβ3 promoted CEWH in cultured TKE2 cells and in NL and DM C57BL6 mouse corneas. Wounding induced similar levels of p-SMAD2/SMAD3 in NL and DM corneas but weaker ERK1/2, Akt, and EGFR phosphorylation in DM corneas compared to NL corneas. Whereas TGFβ1 augmented SMAD2/SMAD3 phosphorylation, TGFβ3 preferentially activated ERK, PI3K, and EGFR in healing DM corneas. Furthermore, TGFβ1 and TGFβ3 differentially regulated the expression of S100a9, PAI-1, uPA/tPA, and CCL3 in healing NL and DM corneas. Finally, TGFβ1 induced the expression of M1 macrophage markers iNOS, CD86, and CTGF, whereas TGFβ3 promoted the expression of M2 markers CD206 and NGF in BMDMs from db/db or db/+ mice.

Conclusions

Hyperglycemia disrupts the balanced expression of TGFβ3/TGFβ1, resulting in delayed CEWH, including impaired sensory nerve regeneration in the cornea. Supplementing TGFβ3 in DM wounds may hold therapeutic potential for accelerating delayed wound healing in diabetic patients.

Insights into the mechanisms of diabetic wounds: pathophysiology, molecular targets, and treatment strategies through conventional and alternative therapies

Diabetes mellitus is a prevalent cause of mortality worldwide and can lead to several secondary issues, including DWs, which are caused by hyperglycemia, diabetic neuropathy, anemia, and ischemia. Roughly 15% of diabetic patient's experience complications related to DWs, with 25% at risk of lower limb amputations. A conventional management protocol is currently used for treating diabetic foot syndrome, which involves therapy using various substances, such as bFGF, pDGF, VEGF, EGF, IGF-I, TGF-β, skin substitutes, cytokine stimulators, cytokine inhibitors, MMPs inhibitors, gene and stem cell therapies, ECM, and angiogenesis stimulators. The protocol also includes wound cleaning, laser therapy, antibiotics, skin substitutes, HOTC therapy, and removing dead tissue. It has been observed that treatment with numerous plants and their active constituents, including Globularia Arabica, Rhus coriaria L., Neolamarckia cadamba, Olea europaea, Salvia kronenburgii, Moringa oleifera, Syzygium aromaticum, Combretum molle, and Myrtus communis, has been found to promote wound healing, reduce inflammation, stimulate angiogenesis, and cytokines production, increase growth factors production, promote keratinocyte production, and encourage fibroblast proliferation. These therapies may also reduce the need for amputations. However, there is still limited information on how to prevent and manage DWs, and further research is needed to fully understand the role of alternative treatments in managing complications of DWs. The conventional management protocol for treating diabetic foot syndrome can be expensive and may cause adverse side effects. Alternative therapies, such as medicinal plants and green synthesis of nano-formulations, may provide efficient and affordable treatments for DWs.

Immune Fingerprint in Diabetes: Ocular Surface and Retinal Inflammation

Diabetes is a prevalent global health issue associated with significant morbidity and mortality. Diabetic retinopathy (DR) is a well-known inflammatory, neurovascular complication of diabetes and a leading cause of preventable blindness in developed countries among working-age adults. However, the ocular surface components of diabetic eyes are also at risk of damage due to uncontrolled diabetes, which is often overlooked. Inflammatory changes in the corneas of diabetic patients indicate that inflammation plays a significant role in diabetic complications, much like in DR. The eye's immune privilege restricts immune and inflammatory responses, and the cornea and retina have a complex network of innate immune cells that maintain immune homeostasis. Nevertheless, low-grade inflammation in diabetes contributes to immune dysregulation. This article aims to provide an overview and discussion of how diabetes affects the ocular immune system's main components, immune-competent cells, and inflammatory mediators. By understanding these effects, potential interventions and treatments may be developed to improve the ocular health of diabetic patients.

The impact of sensory neuropathy and inflammation on epithelial wound healing in diabetic corneas

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, with several underlying pathophysiological mechanisms, some of which are still uncertain. The cornea is an avascular tissue and sensitive to hyperglycemia, resulting in several diabetic corneal complications including delayed epithelial wound healing, recurrent erosions, neuropathy, loss of sensitivity, and tear film changes. The manifestation of DPN in the cornea is referred to as diabetic neurotrophic keratopathy (DNK). Recent studies have revealed that disturbed epithelial-neural-immune cell interactions are a major cause of DNK. The epithelium is supplied by a dense network of sensory nerve endings and dendritic cell processes, and it secretes growth/neurotrophic factors and cytokines to nourish these neighboring cells. In turn, sensory nerve endings release neuropeptides to suppress inflammation and promote epithelial wound healing, while resident immune cells provide neurotrophic and growth factors to support neuronal and epithelial cells, respectively. Diabetes greatly perturbs these interdependencies, resulting in suppressed epithelial proliferation, sensory neuropathy, and a decreased density of dendritic cells. Clinically, this results in a markedly delayed wound healing and impaired sensory nerve regeneration in response to insult and injury. Current treatments for DPN and DNK largely focus on managing the severe complications of the disease. Cell-based therapies hold promise for providing more effective treatment for diabetic keratopathy and corneal ulcers.

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.

Unilateral zebrafish corneal injury induces bilateral cell plasticity supporting wound closure

The cornea, transparent and outermost structure of camera-type eyes, is prone to environmental challenges, but has remarkable wound healing capabilities which enables to preserve vision. The manner in which cell plasticity impacts wound healing remains to be determined. In this study, we report rapid wound closure after zebrafish corneal epithelium abrasion. Furthermore, by investigating the cellular and molecular events taking place during corneal epithelial closure, we show the induction of a bilateral response to a unilateral wound. Our transcriptomic results, together with our TGF-beta receptor inhibition experiments, demonstrate conclusively the crucial role of TGF-beta signaling in corneal wound healing. Finally, our results on Pax6 expression and bilateral wound healing, demonstrate the decisive impact of epithelial cell plasticity on the pace of healing. Altogether, our study describes terminally differentiated cell competencies in the healing of an injured cornea. These findings will enhance the translation of research on cell plasticity to organ regeneration.

Mechanistic investigations of diabetic ocular surface diseases

With the global prevalence of diabetes mellitus over recent decades, more patients suffered from various diabetic complications, including diabetic ocular surface diseases that may seriously affect the quality of life and even vision sight. The major diabetic ocular surface diseases include diabetic keratopathy and dry eye. Diabetic keratopathy is characterized with the delayed corneal epithelial wound healing, reduced corneal nerve density, decreased corneal sensation and feeling of burning or dryness. Diabetic dry eye is manifested as the reduction of tear secretion accompanied with the ocular discomfort. The early clinical symptoms include dry eye and corneal nerve degeneration, suggesting the early diagnosis should be focused on the examination of confocal microscopy and dry eye symptoms. The pathogenesis of diabetic keratopathy involves the accumulation of advanced glycation end-products, impaired neurotrophic innervations and limbal stem cell function, and dysregulated growth factor signaling, and inflammation alterations. Diabetic dry eye may be associated with the abnormal mitochondrial metabolism of lacrimal gland caused by the overactivation of sympathetic nervous system. Considering the important roles of the dense innervations in the homeostatic maintenance of cornea and lacrimal gland, further studies on the neuroepithelial and neuroimmune interactions will reveal the predominant pathogenic mechanisms and develop the targeting intervention strategies of diabetic ocular surface complications.

Long Noncoding RNA 3632454L22Rik Contributes to Corneal Epithelial Wound Healing by Sponging miR-181a-5p in Diabetic Mice

Purpose

This work explores the abnormal expression of long noncoding RNAs (lncRNAs), microRNAs (miRNAs) and messenger RNAs (mRNAs) in diabetic corneal epithelial cells (CECs) and constructs an associated competitive endogenous RNA (ceRNA) network. Moreover, we revealed that Rik may exert advantageous effects on diabetic corneal epithelial wound closure by sponging miR-181a-5p.

Methods

We obtained the profiles of differentially expressed lncRNAs (DELs) of CECs of type 1 diabetic versus control corneas by microarray and summarized the differentially expressed miRNAs (DEmiRs) and differentially expressed genes (DEGs) data by published literature. Subsequently, the ceRNA network was constructed using bioinformatics analyses. The levels of lncRNA ENSMUST00000153610/3632454L22Rik (Rik) and miR-181a-5p were verified. The localization of Rik was identified with fluorescence in situ hybridization (FISH), and dual-luciferase assays proved the targeted relationship between Rik and miR-181a-5p. Furthermore, we validated the functional impact of Rik in vitro.

Results

Overall, 111 upregulated and 117 downregulated DELs were detected in diabetic versus control CECs. The level of Rik located in both the cytoplasm and the nucleus was clearly downregulated, whereas miR-181a-5p was upregulated in vitro and in vivo in the diabetic group versus the control group. Rik can act as a ceRNA to bind to miR-181a-5p, thus promoting diabetic corneal epithelial wound healing in vitro.

Conclusions

This work investigated the expression profile of DELs and constructed ceRNA networks of diabetic CECs for the first time. Furthermore, we revealed that Rik may positively impact diabetic corneal epithelial wound healing by sponging miR-181a-5p, providing a novel potential therapeutic target of diabetic keratopathy (DK).

The common YAP activation mediates corneal epithelial regeneration and repair with different-sized wounds

Regeneration/repair after injury can be endowed by adult stem cells (ASCs) or lineage restricted and even terminally differentiated cells. In corneal epithelium, regeneration after a large wound depends on ASCs (limbal epithelial stem cells, LESCs), whereas repair after a small wound is LESCs-independent. Here, using rat corneal epithelial wounds with different sizes, we show that YAP activation promotes the activation and expansion of LESCs after a large wound, as well as the reprogramming of local epithelial cells (repairing epithelial cells) after a small wound, which contributes to LESCs-dependent and -independent wound healing, respectively. Mechanically, we highlight that the reciprocal regulation of YAP activity and the assembly of cell junction and cortical F-actin cytoskeleton accelerates corneal epithelial healing with different-sized wounds. Together, the common YAP activation and the underlying regulatory mechanism are harnessed by LESCs and lineage-restricted epithelial cells to cope with corneal epithelial wounds with different sizes.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.

Genome wide analysis of gene expression changes in skin from patients with type 2 diabetes

Non-healing chronic ulcers are a serious complication of diabetes and are a major healthcare problem. While a host of treatments have been explored to heal or prevent these ulcers from forming, these treatments have not been found to be consistently effective in clinical trials. An understanding of the changes in gene expression in the skin of diabetic patients may provide insight into the processes and mechanisms that precede the formation of non-healing ulcers. In this study, we investigated genome wide changes in gene expression in skin between patients with type 2 diabetes and non-diabetic patients using next generation sequencing. We compared the gene expression in skin samples taken from 27 patients (13 with type 2 diabetes and 14 non-diabetic). This information may be useful in identifying the causal factors and potential therapeutic targets for the prevention and treatment of diabetic related diseases.

Identification of novel predictive factors for post surgical corneal haze

Molecular factors altered in corneas that develop haze post refractive surgery have been described, but pre-existing factors that predispose clinically normal corneas to aberrant fibrosis post surgery and the role of the corneal epithelium remains unknown. We analyzed the global gene expression in epithelium collected intraoperatively from subjects undergoing photorefractive keratectomy. Subjects were grouped into those that developed haze 12 months post surgery (n = 6 eyes; haze predisposed) and those that did not develop haze in a similar follow up duration (n = 11 eyes; controls). Ontological analysis of 1100 upregulated and 1780 downregulated genes in the haze predisposed group revealed alterations in pathways associated with inflammation, wnt signaling, oxidative stress, nerve functions and extra cellular matrix remodeling. Novel factors such as PREX1, WNT3A, SOX17, GABRA1and PXDN were found to be significantly altered in haze predisposed subjects and those with active haze(n = 3), indicating their pro-fibrotic role. PREX1 was significantly upregulated in haze predisposed subjects. Ectopic expression of PREX1 in cultured human corneal epithelial cells enhanced their rate of wound healing while its ablation using shRNA reduced healing compared to matched controls. Recombinant TGFβ treatment in PREX1 overexpressing corneal cells led to enhanced αSMA expression and Vimentin phosphorylation while the converse was true for shPREX1 expressing cells. Our data identify a few novel factors in the corneal epithelium that may define a patient’s risk to developing post refractive corneal haze.

The impact of hyperglycemia on the corneal epithelium: Molecular mechanisms and insight

Type 2 Diabetes Mellitus (T2DM) is reaching epidemic levels worldwide and with it, there is a significant increase in complications associated with the disease. T2DM affects virtually all organ systems including the eye. While frequently overlooked, diabetic keratopathy is the most common ocular complication of diabetes and can manifest in mild to severe forms, the latter of which poses a major threat to vision. As the initial barrier between the environment and the eye, the corneal epithelium functions in innate immune defense. Compromise of this barrier may predispose the cornea to infection and can hinder the refractive capabilities of the eye. The clinical burden in patients with diabetic keratopathy lies primarily in the inability of the corneal epithelium to repair damage and maintain its tight barrier function. Current therapies for diabetic keratopathy are supportive, centering on the prevention of infection and promotion of an optimal healing environment. With no clear disease-modifying agent identified as of yet, a thorough understanding of the pathophysiology that underlies the development of diabetic keratopathy at the cellular level is critical to identify and develop potential therapeutic agents capable of promoting corneal re-epithelialization to accelerate the wound healing process. The focus of this review is to examine what is known regarding the cellular and molecular mechanisms needed to maintain epithelial homeostasis and how it goes awry in diabetes.

Opposing Effects of Neuropilin-1 and -2 on Sensory Nerve Regeneration in Wounded Corneas: Role of Sema3C in Ameliorating Diabetic Neurotrophic Keratopathy

The diabetic cornea exhibits pathological alterations, such as delayed epithelial wound healing and nerve regeneration. We investigated the role of semaphorin (SEMA) 3C in corneal wound healing and reinnervation in normal and diabetic B6 mice. Wounding induced the expression of SEMA3A, SEMA3C, and their receptor neuropilin-2 (NRP2), but not NRP1, in normal corneal epithelial cells; this upregulation was suppressed for SEMA3C and NRP2 in diabetic corneas. Injections of Sema3C-specific small interfering RNA and NRP2-neutralizing antibodies in wounded mice resulted in a decrease in the rate of wound healing and regenerating nerve fibers, whereas exogenous SEMA3C had opposing effects in diabetic corneas. NRP1 neutralization, on the other hand, decreased epithelial wound closure but increased sensory nerve regeneration in diabetic corneas, suggesting a detrimental role in nerve regeneration. Taken together, epithelium-expressed SEMA3C plays a role in corneal epithelial wound closure and sensory nerve regeneration. The hyperglycemia-suppressed SEMA3C/NRP2 signaling may contribute to the pathogenesis of diabetic neurotrophic keratopathy, and SEMA3C might be used as an adjunctive therapeutic for treating the disease.

Inhibition of Soluble Epoxide Hydrolase 2 Ameliorates Diabetic Keratopathy and Impaired Wound Healing in Mouse Corneas

EPHX2 (encoding soluble epoxide hydrolase [sEH]) converts biologically active epoxyeicosatrienoic acids (EETs), anti-inflammatory and profibrinolytic effectors, into the less biologically active metabolites, dihydroxyeicostrienoic acids. We sought to characterize the expression and the function of EPHX2 in diabetic corneas and during wound healing. The expression of EPHX2 at both mRNA and protein levels, as well as sEH enzymatic activity, was markedly upregulated in the tissues/cells, including corneal epithelial cells as well as the retina of human type 2 and mouse type 1 (streptozotocin [STZ] induced) and/or type 2 diabetes. Ephx2 depletion had no detectable effects on STZ-induced hyperglycemia but prevented the development of tear deficiency. Ephx2-/- mice showed an acceleration of hyperglycemia-delayed epithelium wound healing. Moreover, inhibition of sEH increased the rate of epithelium wound closure and restored hyperglycemia-suppressed STAT3 activation and heme oxygenase-1 (HO-1) expression in the diabetic corneas. Treatment of diabetic corneas with cobalt protoporphyrin, a well-known HO-1 inducer, restored wound-induced HO-1 upregulation and accelerated delayed wound healing. Finally, Ephx2 depletion enhanced sensory innervation and regeneration in diabetic corneas at 1 month after epithelial debridement. Our data suggest that increased sEH activity may be a contributing factor for diabetic corneal complications; targeting sEH pharmacologically or supplementing EETs may represent a new, adjunctive therapy for treating diabetic keratopathy.

Association of long-term glycaemic control on tear break-up times and dry eye symptoms in Chinese patients with type 2 diabetes

IMPORTANCE

Diabetes mellitus is known to be associated with dry eye syndrome (DES), but the effects of long-term glycaemic control on tear film metrics and dry eye symptoms are not known in the Chinese population.

BACKGROUND

To evaluate tear film stability and dry eye symptoms and their associations with systemic risk factors in Chinese patients with type 2 diabetes mellitus (T2DM).

DESIGN

Cross-sectional study set at the Lo Fong Siu Po Eye Centre (Grantham Hospital), Hong Kong.

PARTICIPANTS

A total of 80 Chinese participants, aged 18 or above, with T2DM recruited from the specialist outpatient setting were included.

METHODS

The Oculus Keratograph 5M (Oculus Inc., Wetzlar, Germany) was used to measure the non-invasive tear break-up time (NITBUT). Ocular symptoms were evaluated using the Ocular Surface Disease Index (OSDI). The association between OSDI, NITBUT and metabolic parameters relating to diabetes were evaluated using multiple linear regression.

MAIN OUTCOME MEASURES

The associations between long-term glycaemic control and NITBUT and OSDI scores.

RESULTS

Stepwise multiple linear regression analysis revealed glycated haemoglobin to be the only significant independent variable for NITBUT (R² = 0.099, P = 0.014) and OSDI (R² = 0.062, P = 0.044) after controlling for potential confounders. The age-adjusted prevalence of DES was 20% (95% confidence interval: 11-30%) in the Chinese T2DM population. The odds of DES for increasing percentage of glycated haemoglobin was 1.49 (95% confidence interval: 1.03-2.17, P = 0.04).

CONCLUSIONS AND RELEVANCE

Our findings highlight the importance of good glycaemic control as a modifiable risk factor for both dry eye symptoms and tear film instability in patients with T2DM.

TGF-β and NF-κB signaling pathway crosstalk potentiates corneal epithelial senescence through an RNA stress response

The corneal epithelium plays important roles in the maintenance of corneal transparency for good vision, and acts as a protective barrier against foreign insults. Structural and functional changes with aging in the corneal epithelium have been documented. Here we found that transforming growth factor-β (TGF-β) is highly expressed in the elderly donor corneal epithelium, as are senescence-associated genes, such as p16 and p21. In human corneal epithelial cell (HCEC) models, TGF-β induces cellular senescence, characterized by increased SA-β-gal positive cells and elevated expression of p16 and p21. Pharmacological inhibition of TGF-β signaling alleviates TGF-β-induced cellular senescence. In addition, we determined that senescence-associated inflammation was significantly aggravated in TGF-β-induced cellular senescence by detecting the expression of interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha (TNFα). Both genetic and pharmacological approaches revealed that blocking nuclear factor-κB (NF-κB) signaling not only inhibited the production of inflammatory factors, but also rescued the senescent phenotype induced by TGF-β in HCECs. Mechanistically, TGF-β induced an atypical RNA stress responses, leading to accelerated mRNA degradation of IκBα, an inhibitor of NF-κB. Together, our data indicate that TGF-β-driven NF-κB activation contributes to corneal epithelial senescence via RNA metabolism and the inflammation blockade can attenuate TGF-β-induced senescence.

[Influence of TGF-β cytokine and a number of other biochemical factors on regenerative process]

Scarring is one of the main causes of surgical failure in a number of eye diseases, dacryologic conditions in particular. The process of wound healing, including postoperative wound healing, goes through several stages mediated by various biochemical factors, such as growth factors and pro- and anti-inflammatory cytokines. The balance between the latter directly influences the wound healing. However, current data on the effect of these factors on postoperative outcomes are few and contradictory. Thus, in dacryology as well as in other areas of ophthalmology, the role of cytokines and growth factors in healing of surgical wounds is being intensively researched.

Differentiation of human embryonic stem cells into corneal epithelial progenitor cells under defined conditions

The development of cell-based therapies using stem cells represents a significant breakthrough in the treatment of limbal stem cell deficiency (LSCD). The aim of this study was to develop a novel protocol to differentiate human embryonic stem cells (hESCs) into corneal epithelial progenitor cells (CEPCs), with similar features to primary cultured human limbal stem cells (LSCs), using a medium composed of DMEM/F12 and defined keratinocyte serum-free medium (KSFM) (1:1) under different carbon dioxide (CO₂) levels in culture. The differentiated cells exhibited a similar morphology to limbal stem cells under 5%, 7%, and 9% CO₂ and expressed the LSC markers ABCG-2 and p63; however, CK14 was only expressed in the cells cultured under 7% and 9% CO₂. Quantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis indicated that the ABCG2, p63, and CK14 levels in the 7% CO₂ and 9% CO₂ groups were higher than those in the 5% CO₂ group and in undifferentiated hESCs (p<0.05). The highest expression of ABCG2 and p63 was exhibited in the cells cultured under 7% CO₂ at day 6 of differentiation. Western blotting indicated that the ABCG2 and p63 levels were higher at day 6 than the other time points in the 7% CO₂ and 9% CO₂ groups. The highest protein expression of ABCG2 and p63 was identified in the 7% CO₂ group. The neural cell-specific marker tubulin β3 and the epidermal marker K1/10 were also detected in the differentiated cells via immunofluorescent staining; thus, cell sorting was performed via fluorescence-activated cell sorting (FACS), and ABCG2-positive cells were isolated as CEPCs. The sorted cells formed three to four layers of epithelioid cells by airlifting culture and expressed ABCG2, p63, CK14, and CK3. In conclusion, the novel induction system conditioned by 7% CO₂ in this study may be an effective and feasible method for CEPC differentiation.

Diabetic complications in the cornea

Diabetic corneal alterations, such as delayed epithelial wound healing, edema, recurrent erosions, neuropathy/loss of sensitivity, and tear film changes are frequent but underdiagnosed complications of both type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes mellitus. The disease affects corneal epithelium, corneal nerves, tear film, and to a lesser extent, endothelium, and also conjunctiva. These abnormalities may appear or become exacerbated following trauma, as well as various surgeries including retinal, cataract or refractive. The focus of the review is on mechanisms of diabetic corneal abnormalities, available animal, tissue and organ culture models, and emerging treatments. Changes of basement membrane structure and wound healing rates, the role of various proteinases, advanced glycation end products (AGEs), abnormal growth and motility factors (including opioid, epidermal, and hepatocyte growth factors) are analyzed. Experimental therapeutics under development, including topical naltrexone, insulin, inhibitors of aldose reductase, and AGEs, as well as emerging gene and cell therapies are discussed in detail.

A systematic review on the impact of diabetes mellitus on the ocular surface

Diabetes mellitus is associated with extensive morbidity and mortality in any human community. It is well understood that the burden of diabetes is attributed to chronic progressive damage in major end-organs, but it is underappreciated that the most superficial and transparent organ affected by diabetes is the cornea. Different corneal components (epithelium, nerves, immune cells and endothelium) underpin specific systemic complications of diabetes. Just as diabetic retinopathy is a marker of more generalized microvascular disease, corneal nerve changes can predict peripheral and autonomic neuropathy, providing a window of opportunity for early treatment. In addition, alterations of immune cells in corneas suggest an inflammatory component in diabetic complications. Furthermore, impaired corneal epithelial wound healing may also imply more widespread disease. The non-invasiveness and improvement in imaging technology facilitates the emergence of new screening tools. Systemic control of diabetes can improve ocular surface health, possibly aided by anti-inflammatory and vasoprotective agents.

Diabetic cornea wounds produce significantly weaker electric signals that may contribute to impaired healing

Wounds naturally produce electric signals which serve as powerful cues that stimulate and guide cell migration during wound healing. In diabetic patients, impaired wound healing is one of the most challenging complications in diabetes management. A fundamental gap in knowledge is whether diabetic wounds have abnormal electric signaling. Here we used a vibrating probe to demonstrate that diabetic corneas produced significantly weaker wound electric signals than the normal cornea. This was confirmed in three independent animal models of diabetes: db/db, streptozotocin-induced and mice fed a high-fat diet. Spatial measurements illustrated that diabetic cornea wound currents at the wound edge but not wound center were significantly weaker than normal. Time lapse measurements revealed that the electric currents at diabetic corneas lost the normal rising and plateau phases. The abnormal electric signals correlated significantly with impaired wound healing. Immunostaining suggested lower expression of chloride channel 2 and cystic fibrosis transmembrane regulator in diabetic corneal epithelium. Acute high glucose exposure significantly (albeit moderately) reduced electrotaxis of human corneal epithelial cells in vitro, but did not affect the electric currents at cornea wounds. These data suggest that weaker wound electric signals and impaired electrotaxis may contribute to the impaired wound healing in diabetes.

Ciliary Neurotrophic Factor Promotes the Migration of Corneal Epithelial Stem/progenitor Cells by Up-regulation of MMPs through the Phosphorylation of Akt

The migration of limbal epithelial stem cells is important for the homeostasis and regeneration of corneal epithelium. Ciliary neurotrophic factor (CNTF) has been found to promote corneal epithelial wound healing by activating corneal epithelial stem/progenitor cells. However, the possible effect of CNTF on the migration of corneal epithelial stem/progenitor cells is not clear. This study found the expression of CNTF in mouse corneal epithelial stem/progenitor cells (TKE2) to be up-regulated after injury, on both gene and protein level. CNTF promoted migration of TKE2 in a dose-dependent manner and the peak was seen at 10 ng/ml. The phosphorylation level of Akt (p-Akt), and the expression of MMP3 and MMP14, were up-regulated after CNTF treatment both in vitro and in vivo. Akt and MMP3 inhibitor treatment delayed the migration effect by CNTF. Finally, a decreased expression of MMP3 and MMP14 was observed when Akt inhibitor was applied both in vitro and in vivo. This study provides new insights into the role of CNTF on the migration of corneal epithelial stem/progenitor cells and its inherent mechanism of Up-regulation of matrix metalloproteinases through the Akt signalling pathway.

Targeting Imbalance between IL-1β and IL-1 Receptor Antagonist Ameliorates Delayed Epithelium Wound Healing in Diabetic Mouse Corneas

Patients with diabetes mellitus often develop corneal complications and delayed wound healing. How diabetes might alter acute inflammatory responses to tissue injury, leading to delayed wound healing, remains mostly elusive. Using a streptozotocin-induced type I diabetes mellitus mice and corneal epithelium-debridement wound model, we discovered that although wounding induced marked expression of IL-1β and the secreted form of IL-1 receptor antagonist (sIL-1Ra), diabetes suppressed the expressions of sIL-1Ra but not IL-1β in healing epithelia and both in whole cornea. In normoglycemic mice, IL-1β or sIL-1Ra blockade delayed wound healing and influenced each other's expression. In diabetic mice, in addition to delayed reepithelization, diabetes weakened phosphatidylinositol 3-kinase-Akt signaling, caused cell apoptosis, diminished cell proliferation, suppressed neutrophil and natural killer cell infiltrations, and impaired sensory nerve reinnervation in healing mouse corneas. Local administration of recombinant IL-1Ra partially, but significantly, reversed these pathological changes in the diabetic corneas. CXCL10 was a downstream chemokine of IL-1β-IL-1Ra, and exogenous CXCL10 alleviated delayed wound healing in the diabetic, but attenuated it in the normal corneas. In conclusion, the suppressed early innate/inflammatory responses instigated by the imbalance between IL-1β and IL-1Ra is an underlying cause for delayed wound healing in the diabetic corneas. Local application of IL-1Ra accelerates reepithelialization and may be used to treat chronic corneal and potential skin wounds of diabetic patients.

Dendritic cell dysfunction and diabetic sensory neuropathy in the cornea

Diabetic peripheral neuropathy (DPN) often leads to neurotrophic ulcerations in the cornea and skin; however, the underlying cellular mechanisms of this complication are poorly understood. Here, we used post-wound corneal sensory degeneration and regeneration as a model and tested the hypothesis that diabetes adversely affects DC populations and infiltration, resulting in disrupted DC-nerve communication and DPN. In streptozotocin-induced type 1 diabetic mice, there was a substantial reduction in sensory nerve density and the number of intraepithelial DCs in unwounded (UW) corneas. In wounded corneas, diabetes markedly delayed sensory nerve regeneration and reduced the number of infiltrating DCs, which were a major source of ciliary neurotrophic factor (CNTF) in the cornea. While CNTF neutralization retarded reinnervation in normal corneas, exogenous CNTF accelerated nerve regeneration in the wounded corneas of diabetic mice and healthy animals, in which DCs had been locally depleted. Moreover, blockade of the CNTF-specific receptor CNTFRα induced sensory nerve degeneration and retarded regeneration in normal corneas. Soluble CNTFRα also partially restored the branching of diabetes-suppressed sensory nerve endings and regeneration in the diabetic corneas. Collectively, our data show that DCs mediate sensory nerve innervation and regeneration through CNTF and that diabetes reduces DC populations in UW and wounded corneas, resulting in decreased CNTF and impaired sensory nerve innervation and regeneration.

Hyperglycemia-suppressed expression of Serpine1 contributes to delayed epithelial wound healing in diabetic mouse corneas

PURPOSE

Patients with diabetes mellitus (DM) are at an increased risk for developing corneal complications, including delayed wound healing. The purpose of this study was to characterize the expression and the function of Serpine1 and other components of urokinase plasminogen activator (uPA)-proteolytic system in delayed epithelial wound healing in diabetic mouse corneas.

METHODS

Mice of the strain C57BL/6 were induced to develop diabetes by streptozotocin, and wound-healing assays were performed 10 weeks afterward. Gene expression and/or distribution were assessed by real-time PCR, Western blotting, and/or immunohistochemistry. The role of Serpine1 in mediating epithelial wound closure was determined by subconjunctival injections of neutralizing antibodies in either normal or recombinant protein in diabetic corneas. Enzyme assay for matrix metalloproteinase (MMP)-3 was also performed.

RESULTS

The expressions of Serpine1 (PAI-1), Plau (uPA), and Plaur (uPA receptor) were upregulated in response to wounding, and these upregulations were significantly suppressed by hyperglycemia. In healing epithelia, Plau and Serpine1 were abundantly expressed at the leading edge of the healing epithelia of normal and, to a lesser extent, diabetic corneas. Inhibition of Serpine1 delayed epithelial wound closure in normal corneas, whereas recombinant Serpine1 accelerated it in diabetic corneas. The Plau and MMP-3 mRNA levels and MMP-3 enzymatic activities were correlated to Serpine1 levels and/or the rates of epithelial wound closure.

CONCLUSIONS

Serpine1 plays a role in mediating epithelial wound healing and its impaired expression may contribute to delayed wound healing in DM corneas. Hence, modulating uPA proteolytic pathway may represent a new approach for treating diabetic keratopathy.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Myofibroblasts

Myofibroblasts are activated in response to tissue injury with the primary task to repair lost or damaged extracellular matrix. Enhanced collagen secretion and subsequent contraction - scarring - are part of the normal wound healing response and crucial to restore tissue integrity. Due to myofibroblasts ability to repair but not regenerate, accumulation of scar tissue is always associated with reduced organ performance. This is a fair price to pay by the body for not falling apart. Whereas myofibroblasts typically vanish after successful repair, dysregulation of the normal repair process can lead to persistent myofibroblast activation, for instance by chronic inflammation or mechanical stress in the tissue. Excessive repair leads to the accumulation of stiff collagenous ECM contractures - fibrosis - with dramatic consequences for organ function. The clinical need to terminate detrimental myofibroblast activities has stimulated researchers to answer a number of essential questions: where do myofibroblasts come from, what are the factors leading to their activation, how do we discriminate myofibroblasts from other cells, what is the molecular basis for their contractile activity, and how can we stop or at least control them? This article reviews the current state of the myofibroblast literature by emphasizing their role in ocular repair and fibrosis. It appears that although the eye is quite an extraordinary organ, ocular myofibroblasts behave or misbehave just like their siblings in other organs.

Bioinformatics analysis to identify the differentially expressed genes of glaucoma

The aim of the present study was to screen the differentially expressed genes (DEGs) associated with glaucoma and investigate the changing patterns of the expression of these genes. The GSE2378 gene microarray data of glaucoma was downloaded from the Gene Expression Omnibus database, which included seven normal samples and eight glaucoma astrocyte samples. Taking into account the corresponding associations between the probe ID and gene symbols, the DEGs were identified prior to and subsequent to the summation of probe level values using the Limma package in R language, followed by Gene Ontology (GO) and pathway enrichment analyses. Interaction networks of the DEGs were constructed using the Biomolecular Interaction Network Database, and cluster analysis of the genes in the networks was performed using ClusterONE. Subsequent to the summation of probe value, a total of 223 genes were identified as DEGs between the normal and glaucoma samples, including 74 downregulated and 149 upregulated genes. In addition, the DEGs were found to be associated with several functions, including response to wounding, extracellular region part and calcium ion binding. The most significantly enriched pathways were complement and coagulation cascades, arrhythmogenic right ventricular cardiomyopathy and extracellular matrix (ECM)-receptor interaction. Furthermore, interaction networks were constructed of the DEGs prior to and subsequent to the summation of probe values, and HNF4A and CEBPD were identified as hub genes. Additionally, 37 and 31 GO terms were identified to be enriched in the two DEGs of the networks prior to and subsequent to summation, respectively. The results indicated the identified genes associated with ECM as important, and the CEBPD gene was considered to be a critical gene in glaucoma. The findings of the present study offer a potential reference value in further investigations of glaucoma at the gene level.

Sensory nerve regeneration after epithelium wounding in normal and diabetic cornea

The cornea is the most densely innervated mammalian tissue. The sensory nerves are responsible for sensations of dryness, temperature, touch, and pain, and play important roles in the blink reflex, wound healing, and tear production. Many ocular and systemic diseases can adversely affect corneal sensory nerve and consequently impair their function. One of such systemic diseases is diabetes mellitus (DM) which causes sensory degeneration, neurotrophic keratopathy (DNK), and delayed wound healing. In this review, we summarize recent discoveries revealing mechanisms underlying the pathogenesis of DNK and the impairment of sensory nerve regeneration in post wound diabetic corneas in using animal model of human diabetes. Because it is generally believed that common mechanisms are operative in the pathogenesis of diabetic peripheral neuropathy in different tissues, the findings in the corneas have implications in in other tissues such as the skin, which often leads to foot ulceration and amputation in diabetic patients.

Convergence and divergence of genetic and modular networks between diabetes and breast cancer

Diabetes mellitus (DM) and breast cancer (BC) can simultaneously occur in the same patient populations, but the molecular relationship between them remains unknown. In this study, we constructed genetic networks and used modularized analysis approaches to investigate the multi-dimensional characteristics of two diseases and one disease subtype. A text search engine (Agilent Literature Search 2.71) and MCODE software were applied to validate potential subnetworks and to divide the modules, respectively. A total of 793 DM-related genes, 386 type 2 diabetes (T2DM) genes and 873 BC-related genes were identified from the Online Mendelian Inheritance in Man database. For DM and BC, a total of 99 overlapping genes, 9 modules, 29 biological processes and 7 pathways were identified. Meanwhile, for T2DM and BC, 56 overlapping genes, 5 modules, 20 biological processes and 12 pathways were identified. Based on the Gene Ontology functional enrichment analysis of the top 10 non-overlapping modules of the two diseases, 10 biological functions and 5 pathways overlapped between them. The glycosphingolipid and lysosome pathways verified molecular mechanisms of cell death related to both DM and BC. We also identified new biological functions of dopamine receptors and four signalling pathways (Parkinson's disease, Alzheimer's disease, Huntington's disease and long-term depression) related to both diseases; these warrant further investigation. Our results illustrate the landscape of the novel molecular substructures between DM and BC, which may support a new model for complex disease classification and rational therapies for multiple diseases.