SLC4A11 depletion impairs NRF2 mediated antioxidant signaling and increases reactive oxygen species in human corneal endothelial cells during oxidative stress

Antioxidant MitoQ increases viability of human corneal endothelial cells with congenital hereditary endothelial dystrophy-associated SLC4A11 mutations

PURPOSE

To assess the impact of MitoQ, a mitochondria-targeted antioxidant, on viability of human corneal endothelial cell (hCEnC) lines expressing SLC4A11 mutations associated with congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy type 4 (FECD4).

METHODS

SLC4A11 wildtype (SLC4A11WT) and mutant (SLC4A11MU) hCEnC lines were created to express either SLC4A11 variant 2 (V2) or variant 3 (V3) by stable transduction of SLC4A11-/- hCEnC-21T with lentiviruses containing either SLC4A11WT or one of the following mutations: V2 (V3) mutants c.374 G>A (c.326 G>A) (CHED), c.1813C>T (c.1765C>T) (CHED), c.2263C>T (c.2215C>T) (CHED), or c.2224 G>A (c.2176 G>A) (FECD4). A SLC4A11-/- empty hCEnC line was created by stable transduction of SLC4A11-/- hCEnC-21T with an empty lentiviral plasmid. Cell viability was measured by exposing MitoQ treated and untreated cells to oxidative stress agent tert-butyl hydroperoxide (tBH) followed by performing XTT assays and spectrophotometry.

RESULTS

SLC4A11-/- empty, SLC4A11 V2WT, and SLC4A11 V3WT hCEnC exposed to ≤0.01 μM MitoQ retained over 90% of the viability of untreated SLC4A11-/- empty hCEnC. When treated with MitoQ, SLC4A11-/- empty was able to demonstrate partial restoration of cell viability. All CHED-associated mutant hCEnC lines treated with 0.01 μM MitoQ demonstrated increased viability compared to untreated following exposure to tBH. The FECD4-associated mutant hCEnC line treated with 0.01 μM MitoQ showed no significant increase in cell viability compared to untreated following exposure to tBH.

CONCLUSIONS

Media supplementation with antioxidant MitoQ has beneficial effects on cell viability in hCEnC harboring CHED-associated SLC4A11 mutations following exposure to tBH-induced oxidative stress.

Exploring single-cell RNA sequencing as a decision-making tool in the clinical management of Fuchs' endothelial corneal dystrophy

Single-cell RNA sequencing (scRNA-seq) has enabled the identification of novel gene signatures and cell heterogeneity in numerous tissues and diseases. Here we review the use of this technology for Fuchs' Endothelial Corneal Dystrophy (FECD). FECD is the most common indication for corneal endothelial transplantation worldwide. FECD is challenging to manage because it is genetically heterogenous, can be autosomal dominant or sporadic, and progress at different rates. Single-cell RNA sequencing has enabled the discovery of several FECD subtypes, each with associated gene signatures, and cell heterogeneity. Current FECD treatments are mainly surgical, with various Rho kinase (ROCK) inhibitors used to promote endothelial cell metabolism and proliferation following surgery. A range of emerging therapies for FECD including cell therapies, gene therapies, tissue engineered scaffolds, and pharmaceuticals are in preclinical and clinical trials. Unlike conventional disease management methods based on clinical presentations and family history, targeting FECD using scRNA-seq based precision-medicine has the potential to pinpoint the disease subtypes, mechanisms, stages, severities, and help clinicians in making the best decision for surgeries and the applications of therapeutics. In this review, we first discuss the feasibility and potential of using scRNA-seq in clinical diagnostics for FECD, highlight advances from the latest clinical treatments and emerging therapies for FECD, integrate scRNA-seq results and clinical notes from our FECD patients and discuss the potential of applying alternative therapies to manage these cases clinically.

Evidence for persistent UV-induced DNA damage and altered DNA damage response in xeroderma pigmentosa patient corneas

Xeroderma pigmentosum (XP) is a rare genetic disorder characterized by injury to the ocular surface due to exposure to ultraviolet (UV) radiation. UV-induced damage in the cells leads to the formation of cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidone photoproducts that are repaired by the NER (Nucleotide Excision Repair) pathway. Mutations in the genes coding for NER proteins, as reported in XP patients, would lead to sub-optimal damage repair resulting in clinical signs varying from photo-keratitis to cancerous lesions on the ocular surface. Here, we aimed to provide evidence for the accumulation of DNA damage and activation of DNA repair pathway proteins in the corneal cells of patients with XP. Corneal buttons of patients who underwent penetrating keratoplasty were stained to quantify DNA damage and the presence of activated DNA damage response proteins (DDR) using specific antibodies. Positive staining for pH2A.X and thymidine dimers confirmed the presence of DNA damage in the corneal cells. Positive cells were found in both control corneas and XP samples however, unlike normal tissues, positive cells were found in all cell layers of XP samples indicating that these cells were sensitive to very low levels of UV. pH2A.X-positive cells were significantly more in XP corneas (p < 0.05) indicating the presence of double strand breaks in these tissues. A positive expression of phosphorylated-forms of DDR proteins was noted in XP corneas (unlike controls) such as ataxia telangiectasia mutated/Rad-3 related proteins (ATM/ATR), breast cancer-1 and checkpoint kinases-1 and -2. Nuclear localization of XPA was noted in XP samples which co-localized (calculated using Pearson's correlation) with pATM (0.9 ± 0.007) and pATR (0.6 ± 0.053). The increased presence of these in the nucleus confirms that unresolved DNA damage was accumulating in these cells thereby leading to prolonged activation of the damage response proteins. An increase in pp53 and TUNEL positive cells in the XP corneas indicated cell death likely driven by the p53 pathway. For comparison, cultured normal corneal epithelial cells were exposed to UV-radiation and stained for DDR proteins at 3, 6 and 24 h after irradiation to quantify the time taken by cells with intact DDR pathway to repair damage. These cells, when exposed to UV showed nuclear translocation of DDR proteins at 3 and 6 h which reduced significantly by 24 h confirming that the damaged DNA was being actively repaired leading to cell survival. The persistent presence of the DDR proteins in XP corneas indicates that damage is being actively recognized and DNA replication is stalled, thereby causing accumulation of damaged DNA leading to cell death, which would explain the cancer incidence and cell loss reported in these patients.

Characterization of a Novel Mouse Model for Fuchs Endothelial Corneal Dystrophy

Purpose

Fuchs endothelial corneal dystrophy (FECD) is a progressive blinding disorder, characterized by increased corneal endothelial excrescences (guttae), corneal endothelial cell loss, and edema. These symptoms are hypothesized to be caused by changes in the extracellular matrix (ECM) and mitochondrial dysfunction in the corneal endothelium. Despite this clinical and biological relevance, a comprehensive animal model that recapitulates all the major disease characteristics is currently unavailable. In this study, we develop such a model to improve our understanding of the signaling pathways involved in the FECD progression and develop strategies for early intervention.

Method

To generate a comprehensive FECD model, we generated a double mutant mouse bearing tamoxifen-inducible knockdown of Slc4a11 and the Col8a2 (Q455K) mutation. We performed optical coherence tomography (OCT) and in vivo confocal microscopy using the Heidelberg Retinal Tomography 3 - Rostock Cornea module (HRT3-RCM) on the mice at 5 weeks of age before tamoxifen feeding to establish baseline values for corneal thickness, endothelial cell density, and test for the presence of guttae. We measured these parameters again post-tamoxifen treatment at 16 weeks of age. We collected corneas at 16 weeks to perform histopathology, immunofluorescence staining for tight junctions, adherens junctions, and oxidative stress. We evaluated endothelial pump function using a lactate assay.

Results

The double mutant tamoxifen-fed animals showed the presence of guttae, and displayed increased corneal thickness and decreased endothelial cell density. Endothelial cells showed altered morphology with disrupted adherens junctions and elevated reactive oxygen species (ROS). Finally, we found that stromal lactate concentrations were elevated in the double mutant mice, indicative of compromised endothelial pump function.

Conclusions

Overall, this mouse model recapitulates all the important phenotypic features associated with FECD.

Investigation of the functional impact of CHED- and FECD4-associated SLC4A11 mutations in human corneal endothelial cells

Mutations in the solute linked carrier family 4 member 11 (SLC4A11) gene are associated with congenital hereditary endothelial dystrophy (CHED) and Fuchs corneal endothelial dystrophy type 4 (FECD4), both characterized by corneal endothelial cell (CEnC) dysfunction and/or cell loss leading to corneal edema and visual impairment. In this study, we characterize the impact of CHED-/FECD4-associated SLC4A11 mutations on CEnC function and SLC4A11 protein localization by generating and comparing human CEnC (hCEnC) lines expressing wild type SLC4A11 (SLC4A11WT) or mutant SLC4A11 harboring CHED-/FECD4-associated SLC4A11 mutations (SLC4A11MU). SLC4A11WT and SLC4A11MU hCEnC lines were generated to express either SLC4A11 variant 2 (V2WT and V2MU) or variant 3 (V3WT and V3MU), the two major variants expressed in ex vivo hCEnC. Functional assays were performed to assess cell barrier, proliferation, viability, migration, and NH3-induced membrane conductance. We demonstrate SLC4A11-/- and SLC4A11MU hCEnC lines exhibited increased migration rates, altered proliferation and decreased cell viability compared to SLC4A11WT hCEnC. Additionally, SLC4A11-/- hCEnC demonstrated decreased cell-substrate adhesion and membrane capacitances compared to SLC4A11WT hCEnC. Induction with 10mM NH4Cl led SLC4A11WT hCEnC to depolarize; conversely, SLC4A11-/- hCEnC hyperpolarized and the majority of SLC4A11MU hCEnC either hyperpolarized or had minimal membrane potential changes following NH4Cl induction. Immunostaining of primary hCEnC and SLC4A11WT hCEnC lines for SLC4A11 demonstrated predominately plasma membrane staining with poor or partial colocalization with mitochondrial marker COX4 within a subset of punctate subcellular structures. Overall, our findings suggest CHED-associated SLC4A11 mutations likely lead to hCEnC dysfunction, and ultimately CHED, by interfering with cell migration, proliferation, viability, membrane conductance, barrier function, and/or cell surface localization of the SLC4A11 protein in hCEnC. Additionally, based on their similar subcellular localization and exhibiting similar cell functional profiles, protein isoforms encoded by SLC4A11 variant 2 and variant 3 likely have highly overlapping functional roles in hCEnC.

Potential Theranostic Roles of SLC4 Molecules in Human Diseases

The solute carrier family 4 (SLC4) is an important protein responsible for the transport of various ions across the cell membrane and mediating diverse physiological functions, such as the ion transporting function, protein-to-protein interactions, and molecular transduction. The deficiencies in SLC4 molecules may cause multisystem disease involving, particularly, the respiratory system, digestive, urinary, endocrine, hematopoietic, and central nervous systems. Currently, there are no effective strategies to treat these diseases. SLC4 proteins are also found to contribute to tumorigenesis and development, and some of them are regarded as therapeutic targets in quite a few clinical trials. This indicates that SLC4 proteins have potential clinical prospects. In view of their functional characteristics, there is a critical need to review the specific functions of bicarbonate transporters, their related diseases, and the involved pathological mechanisms. We summarize the diseases caused by the mutations in SLC4 family genes and briefly introduce the clinical manifestations of these diseases as well as the current treatment strategies. Additionally, we illustrate their roles in terms of the physiology and pathogenesis that has been currently researched, which might be the future therapeutic and diagnostic targets of diseases and a new direction for drug research and development.

Updates on congenital hereditary endothelial dystrophy

Congenital hereditary endothelial dystrophy (CHED) is a rare genetic corneal disorder causing progressive cornea clouding and significant visual impairment. CHED remains a leading indication for pediatric corneal transplantation despite its infrequency, particularly in regions with high consanguinity rates like Southeast Asia. Identifying the Solute Carrier Family 4 Member 11 (SLC4A11) gene as the genetic basis of CHED has led to the discovery of it's various genetic variations. However, a comprehensive understanding of its clinical-genetic correlation, pathophysiology, and optimal management is ongoing. This review aims to consolidate current knowledge about CHED, covering its genetic origins, pathophysiological mechanisms, clinical presentation, and management strategies. Surgical intervention, such as penetrating keratoplasty (PK), Descemet stripping automated endothelial keratoplasty (DSAEK), and Descemet membrane endothelial keratoplasty (DMEK), remains the primary treatment. DSAEK and DMEK offer advantages over PK, including quicker visual recovery, reduced complications, and longer graft survival, especially in the pediatric age group. The timing of surgical interventions depends on disease severity, age at presentation, comorbidities, and visual potential. Elevated oxidative stress in CHED corneal tissue suggests potential benefits from anti-inflammatory drugs to rescue mutated endothelial cells. Considering the limitations of corneal graft surgeries, exploring novel gene-based molecular therapies are essential for future management. Early diagnosis, appropriate surgical interventions, amblyopia control, and genetic counseling for predictive analysis are pivotal for optimizing CHED management. A multidisciplinary approach involving ophthalmologists, researchers, and genetic counselors is essential for precise diagnosis and optimal care for CHED patients.

Role of NADPH Oxidase 4 in Corneal Endothelial Cells Is Mediated by Endoplasmic Reticulum Stress and Autophagy

Human corneal-endothelial cells (hCEnCs) are located on the inner layer of the cornea. Injury to CEnCs leads to permanent corneal edema, requiring corneal transplantation. NADPH oxidase 4 (NOX4) has been reported to be implicated in the pathogenesis of CEnCs diseases. Thus, we investigated the role of NOX4 in CEnCs in this study. In an animal study, siRNA for NOX4 (siNOX4) or plasmid for NOX4 (pNOX4) was introduced into the corneal endothelium of rats by electroporation, using a square-wave electroporator (ECM830, Havard apparatus) to decrease or increase the expression of NOX4, respectively, and the rat corneas were cryoinjured through contact with a metal rod of 3 mm diameter frozen in liquid nitrogen for 10 min. The immunofluorescence staining of NOX4 and 8-OHdG showed that the levels of NOX4 and 8-OHdG were decreased in the siNOX4 group compared to the siControl, and increased in the pNOX4 group compared to the pControl at one week after treatment. Without cryoinjury, corneal opacity was more severe, and the density of CEnCs was lower, in pNOX4-treated rats compared to pControl. After cryoinjury, the corneas were more transparent, and the CEnC density was higher, in siNOX4-treated rats. The hCEnCs were cultured and transfected with siNOX4 and pNOX4. The silencing of NOX4 in hCEnCs resulted in a normal cell shape, higher viability, and higher proliferation rate than those transfected with the siControl, while NOX4 overexpression had the opposite effect. NOX4 overexpression increased the number of senescent cells and intracellular oxidative stress levels. NOX4 overexpression increased ATF4 and ATF6 levels, and nuclear translocation of XBP-1, which is the endoplasmic reticulum (ER) stress marker, while the silencing of NOX4 had the opposite effect. Additionally, the mitochondrial membrane potential was hyperpolarized by the silencing of NOX4, and depolarized by NOX4 overexpression. The LC3II levels, a marker of autophagy, were decreased by the silencing of NOX4, and increased by NOX4 overexpression. In conclusion, NOX4 plays a pivotal role in the wound-healing and senescence of hCEnCs, by modulating oxidative stress, ER stress, and autophagy. The regulation of NOX4 may be a potential therapeutic strategy for regulating the homeostasis of CEnCs, and treating corneal-endothelial diseases.

Corneal Edema in Inducible Slc4a11 Knockout Is Initiated by Mitochondrial Superoxide Induced Src Kinase Activation

PURPOSE

Inducible Slc4a11 KO leads to corneal edema by disruption of the pump and barrier functions of the corneal endothelium (CE). The loss of Slc4a11 NH3-activated mitochondrial uncoupling leads to mitochondrial membrane potential hyperpolarization-induced oxidative stress. The goal of this study was to investigate the link between oxidative stress and the failure of pump and barrier functions and to test different approaches to revert the process.

METHODS

Mice which were homozygous for Slc4a11 Flox and Estrogen receptor -Cre Recombinase fusion protein alleles at 8 weeks of age were fed Tamoxifen (Tm)-enriched chow (0.4 g/Kg) for 2 weeks, and controls were fed normal chow. During the initial 14 days, Slc4a11 expression, corneal thickness (CT), stromal [lactate], Na+-K+ ATPase activity, mitochondrial superoxide levels, expression of lactate transporters, and activity of key kinases were assessed. In addition, barrier function was assessed by fluorescein permeability, ZO-1 tight junction integrity, and cortical cytoskeleton F-actin morphology.

RESULTS

Tm induced a rapid decay in Slc4a11 expression that was 84% complete at 7 days and 96% complete at 14 days of treatment. Superoxide levels increased significantly by day 7; CT and fluorescein permeability by day 14. Tight junction ZO-1 distribution and the cortical cytoskeleton were disrupted at day 14, concomitant with decreased expression of Cldn1, yet with increased tyrosine phosphorylation. Stromal lactate increased by 60%, Na+-K+ ATPase activity decreased by 40%, and expression of lactate transporters MCT2 and MCT4 significantly decreased, but MCT1 was unchanged at 14 days. Src kinase was activated, but not Rock, PKCα, JNK, or P38Mapk. Mitochondrial antioxidant Visomitin (SkQ1, mitochondrial targeted antioxidant) and Src kinase inhibitor eCF506 significantly slowed the increase in CT, with concomitant decreased stromal lactate retention, improved barrier function, reduced Src activation and Cldn1 phosphorylation, and rescued MCT2 and MCT4 expression.

CONCLUSIONS

Slc4a11 KO-induced CE oxidative stress triggered increased Src kinase activity that resulted in perturbation of the pump components and barrier function of the CE.

Alterations in cell viability, reactive oxygen species production, and modulation of gene expression involved in mitogen-activated protein kinase/extracellular regulating kinase signaling pathway by glyphosate and its commercial formulation in hepatocellular carcinoma cells

Glyphosate (N-phosphonomethyl glycine) is a non-selective, organophosphate herbicide widely used in agriculture and forestry. We investigated the possible toxic effects of the glyphosate active compound and its commercial formulation (Roundup Star^®) in the human hepatocellular carcinoma (HepG2) cell line, including their effects on the cytotoxicity, cell proliferation, reactive oxygen species (ROS) levels, and expression of oxidative stress-related genes such as HO-1, Hsp70 Nrf2, L-FABP, and Keap1. MTT and NRU tests indicated that the IC₅₀ values of Roundup Star^® were 219 and 140 μM, respectively, and because glyphosate failed to induce cell death at the studied concentrations, an IC₅₀ value could not be determined for this cell line. Roundup Star at concentrations of 50 and 100 μM significantly increased (39.58% and 52%, respectively) cell proliferation, which 200 μM of glyphosate increased by 35.38%. ROS levels increased by 27.97% and 44.77% for 25 and 100 μM of Roundup Star and 32.74% and 38.63% for 100 and 200 μM of glyphosate exposure. In conclusion, Roundup Star and glyphosate significantly increased expression levels of selected genes related to the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway. This suggests that ROS production and the MAPK/ERK signaling pathway may be key molecular mechanisms in the toxicity of glyphosate in liver cells.

Zhen-Wu decoction and lactiflorin, an ingredient predicted by in silico modelling, alleviate uremia induced cardiac endothelial injury via Nrf2 activation

ETHNOPHARMACOLOGICAL RELEVANCE

Cardiorenal syndrome type 4 (CRS type 4), with high rates of morbidity and mortality, has become a social and economic problem worldwide over the last few decades. Zhen-Wu decoction, a traditional medicine used in East Asia, has been widely used in the treatment of cardiovascular disease and kidney disease, and has shown potential therapeutic effects for the clinical treatment of CRS type 4. However, the underlying mechanism has not been extensively explored.

AIM OF THE STUDY

The purpose of this study was to investigate the effect and underlying mechanism of Zhen-Wu decoction on uremic cardiomyopathy, offering a potential target for clinical treatment of CRS type 4.

MATERIALS AND METHODS

Five/six nephrectomized mice were utilized for experiments in vivo. The cardioprotective effects of Zhen-Wu decoction were evaluated by echocardiography and tissue staining. RNA-Seq data were used to investigate the potential pharmacological mechanism. The prediction of targets and active components was based on our previous strategy. Subsequently, the protective effect of the selected compound was verified in experiments in vitro.

RESULTS

Zhen-Wu decoction alleviated cardiac dysfunction and endothelial injury in 5/6 nephrectomized mice, and the mechanism may involve the inflammatory process and oxidative stress. The activation of the Nrf2 signaling pathway was predicted to be a potential target of Zhen-Wu decoction in protecting endothelial cells. Through our machine learning strategy, we found that lactiflorin as an ingredient in Zhen-Wu decoction, alleviates IS-induced endothelial cell injury by blocking Keap1 and activating Nrf2.

CONCLUSIONS

The present study demonstrated that Zhen-Wu decoction and lactiflorin could protect endothelial cells against oxidative stress in mice after nephrectomy by activating the Nrf2 signaling pathway.

Mitochondrial ROS in Slc4a11 KO Corneal Endothelial Cells Lead to ER Stress

Recent studies from Slc4a11 -/- mice have identified glutamine-induced mitochondrial dysfunction as a significant contributor toward oxidative stress, impaired lysosomal function, aberrant autophagy, and cell death in this Congenital Hereditary Endothelial Dystrophy (CHED) model. Because lysosomes are derived from endoplasmic reticulum (ER)-Golgi, we asked whether ER function is affected by mitochondrial ROS in Slc4a11 KO corneal endothelial cells. In mouse Slc4a11 -/- corneal endothelial tissue, we observed the presence of dilated ER and elevated expression of ER stress markers BIP and CHOP. Slc4a11 KO mouse corneal endothelial cells incubated with glutamine showed increased aggresome formation, BIP and GADD153, as well as reduced ER Ca2+ release as compared to WT. Induction of mitoROS by ETC inhibition also led to ER stress in WT cells. Treatment with the mitochondrial ROS quencher MitoQ, restored ER Ca2+ release and relieved ER stress markers in Slc4a11 KO cells in vitro. Systemic MitoQ also reduced BIP expression in Slc4a11 KO endothelium. We conclude that mitochondrial ROS can induce ER stress in corneal endothelial cells.

Intracellular pH affects mitochondrial homeostasis in cultured human corneal endothelial cells prepared for cell injection therapy

This study aimed to uncover the mechanism responsible for the clinical efficacy of cell injection therapy with fully differentiated cultured cells. Analysis of polarized expression of ion transporters on cultured human corneal endothelial cells (CECs) subpopulations (SPs) was performed. The intracellular pH (pHi) between two CEC SPs, distinct in the proportion of differentiated cells, was measured, and the association with mitochondrial respiration homeostasis was investigated. The effects of the ion transporter inhibition by their selective inhibitors or siRNA transfection were also explored. Na⁺/K⁺-ATPase, Aquaporin 1, SLC4A11, NBCe1, NHE1 as transporters, and ZO-1, were all selectively expressed in differentiated SPs, but were almost null in the cell-state-transitioned SPs. We also confirmed that the pHi of CEC SPs affected their mitochondrial respiration by modulating the expression of these ion transporters via inhibitors or siRNA transfection. Ion and water transporters might participate in the maintenance of pHi and mitochondria homeostasis in differentiated SPs, which may contribute, combined with integral barrier functions, to efficient water efflux. The differences in intracellular pH between the two SPs is attributed to variations in the expression profile of specific ion transporters and mitochondrial functions, which may associate with the efficacy of the SPs in cell injection therapy.

Rescue of the Congenital Hereditary Endothelial Dystrophy Mouse Model by Adeno-Associated Viruse-Mediated Slc4a11 Replacement

Purpose

Congenital hereditary endothelial dystrophy (CHED) is a rare condition that manifests at an early age showing corneal edema, increased oxidative stress, mitochondrial dysfunction, and eventually apoptosis of the endothelium due to loss of function of the membrane transport protein SLC4A11. This project tested whether replacing Slc4a11 into the Slc4a11 -/- CHED mouse model can reverse the disease-associated phenotypes.

Design

Experimental study.

Participants

Five-week-old or 11-week-old Slc4a11 -/- mice. Age- and gender-matched Slc4a11 +/+ animals were used as controls. A total of 124 animals (62 female, and 62 male) were used in this study. Fifty-three animals of the genotype Slc4a11 +/+ were used as age- and gender-matched noninjected controls. Seventy-one Slc4a11 -/- mice were administered anterior chamber injections of adeno-associated virus (AAV).

Methods

Anterior chambers of young (5 weeks old) or older (11 weeks old) Slc4a11 -/- mice were injected once with adeno-associated virus serotype 9 (AAV9) mouse Slc4a11 or AAV9-Null vectors. Corneal thickness was measured using OCT. End point analysis included corneal endothelial cell density, mitochondrial oxidative stress, and corneal lactate concentration.

Main Outcome Measures

Corneal thickness, endothelial cell loss, lactate levels, and mitochondrial oxidative stress.

Results

In the young animals, AAV9-Slc4a11 reversed corneal edema, endothelial cell loss, mitochondrial oxidative stress, lactate transporter expression, and corneal lactate concentration to the levels observed in wild-type animals. In the older animals, gene replacement did not reverse the phenotype but prevented progression.

Conclusions

Functional rescue of CHED phenotypes in the Slc4a11 -/- mouse is possible; however, early intervention is critical.

The H+ Transporter SLC4A11: Roles in Metabolism, Oxidative Stress and Mitochondrial Uncoupling

Solute-linked cotransporter, SLC4A11, a member of the bicarbonate transporter family, is an electrogenic H+ transporter activated by NH3 and alkaline pH. Although SLC4A11 does not transport bicarbonate, it shares many properties with other members of the SLC4 family. SLC4A11 mutations can lead to corneal endothelial dystrophy and hearing deficits that are recapitulated in SLC4A11 knock-out mice. SLC4A11, at the inner mitochondrial membrane, facilitates glutamine catabolism and suppresses the production of mitochondrial superoxide by providing ammonia-sensitive H+ uncoupling that reduces glutamine-driven mitochondrial membrane potential hyperpolarization. Mitochondrial oxidative stress in SLC4A11 KO also triggers dysfunctional autophagy and lysosomes, as well as ER stress. SLC4A11 expression is induced by oxidative stress through the transcription factor NRF2, the master regulator of antioxidant genes. Outside of the corneal endothelium, SLC4A11's function has been demonstrated in cochlear fibrocytes, salivary glands, and kidneys, but is largely unexplored overall. Increased SLC4A11 expression is a component of some "glutamine-addicted" cancers, and is possibly linked to cells and tissues that rely on glutamine catabolism.

RNA sequencing uncovers alterations in corneal endothelial metabolism, pump and barrier functions of Slc4a11 KO mice

Slc4a11 KO mice show significant corneal edema, altered endothelial morphology, and mitochondrial ROS at an early age without a decrease in endothelial cell density. We examined the differential gene expression profile between wild type (WT) and KO with the goal of finding pathways related to corneal endothelial metabolic, pump and barrier function that can explain the corneal edema. Freshly dissected Corneal Endothelium-Descemet's Membrane (CEDM) and cultured Mouse Corneal Endothelial Cells (MCEC) were obtained from WT and Slc4a11 KO mice. RNA sequencing Ingenuity Pathway Analysis (IPA) predicted activation, inhibition or differential regulation of several pathways. QPCR and Western analysis validated downregulation of Glycolytic enzymes, Mitochondrial complex components and Ion transporters. Functional testing revealed decreases in endothelial lactate production, Extracellular Acidification Rate (ECAR), glutaminolysis, and Oxygen Consumption Rate (OCR) of KO CEDM in the presence of Glutamine (Gln) that was not compensated by fatty acid oxidation. Stromal lactate was significantly elevated in KO along with decreased expression of MCT1 and MCT4 lactate transporters in endothelial cells. ATP levels were 2x higher in KO CEDM, concomitant with a 3-fold decrease in Na-K-ATPase activity and reduced basolateral membrane localization. Genes for cholesterol biosynthesis, glutathione metabolism and tight and adherens junctions were elevated. Alteration of tight junction structure and cortical cytoskeleton is evident in KO corneal endothelium with a significant increase in trans-endothelial fluorescein permeability. We conclude that Slc4a11 KO induces a coordinated decrease in glycolysis, glutaminolysis, lactate transport and Na-K-ATPase activity. These changes together with an altered barrier function cause an accumulation of stromal lactate in Slc4a11 KO mice leading to chronic corneal edema.

Oxidative Stress Induces a Breakdown of the Cytoskeleton and Tight Junctions of the Corneal Endothelial Cells

Purpose: To investigate the impact of oxidative stress, which is a hallmark of Fuchs dystrophy, on the barrier function of the corneal endothelial cells. Methods: Experiments were carried out with cultured bovine and porcine corneal endothelial cells. For oxidative stress, cells were supplemented with riboflavin (Rf) and exposed to UV-A (15-30 min) to induce Type-1 photochemical reactions that release H₂O₂. The effect of the stress on the barrier function was assayed by transendothelial electrical resistance (TER) measurement. In addition, the associated changes in the organization of the microtubules, perijunctional actomyosin ring (PAMR), and ZO-1 were evaluated by immunocytochemistry, which was also repeated after direct exposure to H₂O₂ (100 μM, 1 h). Results: Exposure to H₂O₂ led to the disassembly of microtubules and the destruction of PAMR. In parallel, the contiguous locus of ZO-1 was disrupted, marking a loss of barrier integrity. Accordingly, a sustained loss in TER was induced when cells in the Rf-supplemented medium were exposed to UV-A. However, the addition of catalase (7,000 U/mL) to rapidly decompose H₂O₂ limited the loss in TER. Furthermore, the adverse effects on microtubules, PAMR, and ZO-1 were suppressed by including catalase, ascorbic acid (1 mM; 30 min), or pretreatment with p38 MAP kinase inhibitor (SB-203580; 10 μM, 1 h). Conclusions: Acute oxidative stress induces microtubule disassembly by a p38 MAP kinase-dependent mechanism, leading to the destruction of PAMR and loss of barrier function. The response to oxidative stress is reminiscent of the (TNF-α)-induced breakdown of barrier failure in the corneal endothelium.

Mitochondrial ROS Induced Lysosomal Dysfunction and Autophagy Impairment in an Animal Model of Congenital Hereditary Endothelial Dystrophy

Purpose

The Slc4a11 knock out (KO) mouse model recapitulates the human disease phenotype associated with congenital hereditary endothelial dystrophy (CHED). Increased mitochondrial reactive oxygen species (ROS) in the Slc4a11 KO mouse model is a major cause of edema and endothelial cell loss. Here, we asked if autophagy was activated by ROS in the KO mice.

Methods

Immortalized cell lines and mouse corneal endothelia were used to measure autophagy and lysosome associated protein expressions using Protein Simple Wes immunoassay. Autophagy and lysosome functions were examined in wild type (WT) and KO cells as well as animals treated with the mitochondrial ROS quencher MitoQ.

Results

Even though autophagy activation was evident, autophagy flux was aberrant in Slc4a11 KO cells and corneal endothelium. Expression of lysosomal proteins and lysosomal mass were decreased along with reduced nuclear translocation of lysosomal master regulator, transcription factor EB (TFEB). MitoQ reversed aberrant lysosomal functions and TFEB nuclear localization in KO cells. MitoQ injections in KO animals reduced corneal edema and decreased the rate of endothelial cell loss.

Conclusions

Mitochondrial ROS disrupts TFEB signaling causing lysosomal dysfunction with impairment of autophagy in Slc4a11 KO corneal endothelium. Our study is the first to identify the presence as well as cause of lysosomal dysfunction in an animal model of CHED, and to identify a potential therapeutic approach.

Mitochondrial Targeting of the Ammonia-Sensitive Uncoupler SLC4A11 by the Chaperone-Mediated Carrier Pathway in Corneal Endothelium

Purpose

SLC4A11, an electrogenic H⁺ transporter, is found in the plasma membrane and mitochondria of corneal endothelium. However, the underlying mechanism of SLC4A11 targeting to mitochondria is unknown.

Methods

The presence of mitochondrial targeting sequences was examined using in silico mitochondrial proteomic analyses. Thiol crosslinked peptide binding to SLC4A11 was screened by untargeted liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis. Direct protein interactions between SLC4A11 and chaperones were examined using coimmunoprecipitation analysis and proximity ligation assay. Knockdown or pharmacologic inhibition of chaperones in human corneal endothelial cells (HCECs) or mouse corneal endothelial cells (MCECs), ex vivo kidney, or HA-SLC4A11–transfected fibroblasts was performed to investigate the functional consequences of interfering with mitochondrial SLC4A11 trafficking.

Results

SLC4A11 does not contain canonical N-terminal mitochondrial targeting sequences. LC-MS/MS analysis showed that HSC70 and/or HSP90 are bound to HA-SLC4A11–transfected PS120 fibroblast whole-cell lysates or isolated mitochondria, suggesting trafficking through the chaperone-mediated carrier pathway. SLC4A11 and either HSP90 or HSC70 complexes are directly bound to the mitochondrial surface receptor, TOM70. Interference with this trafficking leads to dysfunctional mitochondrial glutamine catabolism and increased reactive oxygen species production. In addition, glutamine (Gln) use upregulated SLC4A11, HSP70, and HSP90 expression in whole-cell lysates or purified mitochondria of HCECs and HA-SLC4A11–transfected fibroblasts.

Conclusions

HSP90 and HSC70 are critical in mediating mitochondrial SLC4A11 translocation in corneal endothelial cells and kidney. Gln promotes SLC4A11 import to the mitochondria, and the continuous oxidative stress derived from Gln catabolism induced HSP70 and HSP90, protecting cells against oxidative stress.

Whole exome sequencing identified FAM149A as a plausible causative gene for congenital hereditary endothelial dystrophy, affecting Nrf2-Antioxidant signaling upon oxidative stress

BACKGROUND

Congenital hereditary endothelial dystrophy (CHED) is a rare genetic disease of the corneal endothelium with a very early onset of bilateral corneal edema due to degeneration and dysfunction of the corneal endothelium. Currently SLC4A11 is the only established causative gene for CHED, but not all these reported CHED patients could be explained by SLC4A11 deficiency, indicating that the genetic predisposition of CHED still requires further exploration.

METHODS

Trio-based whole-exome sequencing was performed on a CHED patient and his unaffected parents. The GATK2 and an in-house bioinformatics pipeline were applied for variant analyses, following the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines. Potential pathogenic variants were further validated by Sanger sequencing. The expression profiles of FAM149A in cell line, murine tissues or human corneal endothelia were determined by RT-qPCR. Small interfering RNA was used to knock down the expression of FAM149A in vitro. Cell viability was detected by a CCK-8 assay. ROS and 8-OHdG were examined by fluorometric analysis. The nuclear translocation of NRF2 was determined by western blotting.

RESULTS

We identified a homozygous mutation (NM_015398.3: c.991A > G; p.R331G) in the FAM149A gene that related to the phenotype of CHED. FAM149A was found to be highly expressed in corneal endothelium, and up-regulated upon oxidative stress. Further functional investigations demonstrated that deficiency in FAM149A impaired Nrf2-antioxidant signaling, rendering cells more vulnerable to oxidative stress. Consistently, the expression of FAM149A was significantly reduced in patients with corneal endothelium dysfunction.

CONCLUSION

This study demonstrated, for the first time, FAM149A as a plausible causative gene for CHED etiology, offering new insight for future investigation targeting CHED.

SLC4A11 and MFSD3 Gene Expression Changes in Deoxynivalenol Treated IPEC-J2 Cells

Deoxynivalenol (DON) caused serious cytotoxicity for animal cells. However, genes involved in regulating DON toxicity and the underlying molecular mechanisms remain largely unknown. This study explored the role of SLC4A11 and MFSD3 in alleviating DON toxicity and analyzed the DNA methylation changes of these two genes. Viability and cell cycle analysis showed that DON exposure decreased the IPEC-J2 viability (P < 0.01), blocked the cell cycle in the G2/M phase (P < 0.01), and increased the rate of apoptosis (P < 0.05). Expression of the SLC4A11 and MFSD3 genes was significantly downregulated upon DON exposure (P < 0.01). Overexpression of SLC4A11 and MFSD3 can enhance the cell viability (P < 0.01). DNA methylation assays indicated that promoter methylation of SLC4A11 (mC-1 and mC-23) and MFSD3 (mC-1 and mC-12) were significantly higher compared with those in the controls and correlated negatively with mRNA expression (P < 0.05). Further analysis showed that mC-1 of SLC4A11 and MFSD3 was located in transcription factor binding sites for NF-1 and Sp1. Our findings revealed the novel biological functions of porcine SLC4A11 and MFSD3 genes in regulating the cytotoxic effects induced by DON, and may contribute to the detection of biomarkers and drug targets for predicting and eliminating the potential toxicity of DON.

Inducible Slc4a11 Knockout Triggers Corneal Edema Through Perturbation of Corneal Endothelial Pump

Purpose

The conventional Slc4a11 knockout (KO) shows significant corneal edema at eye opening, a fact that complicates the study of the initial events leading to edema. An inducible KO would provide opportunities to examine early events following loss of Slc4a11 activity.

Methods

Slc4a11 Flox (SF) mice were crossed with mice expressing the estrogen receptor Cre Recombinase fusion protein and fed tamoxifen (Tm) for two weeks. Corneal thickness (CT) was measured by OCT. At eight weeks endpoint, oxidative damage, tight junction integrity, stromal lactate concentration, endothelial permeability, differentially expressed transporters, and junction proteins were determined. Separately, a keratocyte only inducible Slc4a11 KO was also examined.

Results

At four weeks post-Tm induction Slc4a11 transcript levels were 2% of control. Corneal thickness increased gradually and was 50% greater than Wild Type (WT) after eight weeks with significantly altered endothelial morphology, increased nitrotyrosine staining, significantly higher stromal lactate, decreased expression of lactate transporters and Na-K ATPase activity, higher ATP, altered expression of tight and adherens junctions, and increased fluorescein permeability. No significant differences in CT were found between WT and keratocyte only Slc4a11 KO.

Conclusions

The Slc4a11 inducible KO shows development of a similar phenotype as the conventional KO, thereby validating the model and providing a tool for further use in examining the sequence of cellular events by use of noninvasive in vivo physiological probes.

Enhanced expression of SLC4A11 by tert-Butylhydroquinone is mediated by direct binding of Nrf2 to the promoter of SLC4A11

BACKGROUND

SLC4A11, a Na + dependent OH^- transporter, is highly expressed in the epithelium and endothelium of the cornea. Mutations in SLC4A11 cause congenital hereditary endothelial dystrophy (CHED), a progressive disease with gradual loss of vision and characterized by degeneration and dysfunction of corneal endothelial cells. SLC4A11 expression is also responsive to oxidative stress. Thus, understanding of SLC4A11 gene regulation is of utmost importance for therapeutic interventions. However, it remains elusive how SLC4A11 is regulated at transcriptional and translational level.

METHODS

Bioinformatics analysis of the SLC4A11 promoter was performed using TRANSFAC. SLC4A11 promoter constructs were generated and exposed to tert-Butylhydroquinone (tBHQ) or cotransfected with Nuclear factor erythroid 2-related factor 2 (Nrf2) expression plasmid and promoter activity was determined. The expression of SLC4A11 was also determined by quantitative PCR and immunoblot analysis. The binding of Nrf2 to the promoter of SLC4A11 was validated by chromatin immunoprecipitation assay.

RESULTS

Induction of Nrf2 by tBHQ or overexpression of Nrf2 caused increased expression of SLC4A11 in HeLa and human corneal endothelial cells. A conserved Nrf2 binding sequence was found in the promoter of SLC4A11 of several mammalian species. Reporter gene assays showed transcriptional activation of the SLC4A11 promoter in response to tBHQ treatment and Nrf2 overexpression. ChIP analysis validated Nrf2 binding to the conserved sequence of the SLC4A11 promoter. Induction of the Nrf2 pathway also resulted in increased endogenous SLC4A11 protein abundance. On the other hand, depletion of Nrf2 inhibited both transcriptional and translational activities of SLC4A11.

CONCLUSION

In summary, we determined direct Nrf2 binding to antioxidant responsive element site within the SLC4A11 promoter, and observed increased expression of SLC4A11 by Nrf2 inducers. To the best of our knowledge, this is the first study showing Nrf2 exerts an important role in regulation of SLC4A11 gene expression.

COL8A2 Regulates the Fate of Corneal Endothelial Cells

Purpose

To investigate the effect of COL8A2 repression on corneal endothelial cells (CECs) in vitro and in vivo.

Methods

Cultured human CECs (hCECs) were transfected with COL8A2 siRNA (siCOL8A2), and the cell viability and proliferation rate were measured. The expression of cell proliferation–associated molecules was evaluated by Western blotting and real-time reverse transcription PCR. Cell shape, Wingless-INT (WNT) signaling, and mitochondrial oxidative stress were also measured. For in vivo experiments, siCOL8A2 was transfected into rat CECs (rCECs), and corneal opacity and corneal endothelium were evaluated.

Results

After transfection with siCOL8A2, COL8A2 expression was reduced (80%). Cell viability, cell proliferation rate, cyclin D1 expression, and the number of cells in the S-phase were reduced in siCOL8A2-treated cells. The cell attained a fibroblast-like shape, and SNAI1, pSMAD2, and β-catenin expression, along with mitochondrial mass and oxidative stress levels, were altered. Corneal opacity increased, and the CECs were changed in rats in the siCOL8A2 group.

Conclusions

COL8A2 is required to maintain normal wound healing and CEC function.

Diseases of the corneal endothelium

The corneal endothelial monolayer and associated Descemet's membrane (DM) complex is a unique structure that plays an essential role in corneal function. Endothelial cells are neural crest derived cells that rest on a special extracellular matrix and play a major role in maintaining stromal hydration within a narrow physiologic range necessary for clear vision. A number of diseases affect the endothelial cells and DM complex and can impair corneal function and vision. This review addresses different human corneal endothelial diseases characterized by loss of endothelial function including: Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), bullous keratopathy, iridocorneal endothelial (ICE) syndrome, post-traumatic fibrous downgrowth, glaucoma and diabetes mellitus.

Energy Shortage in Human and Mouse Models of SLC4A11-Associated Corneal Endothelial Dystrophies

Purpose

To elucidate the molecular events in solute carrier family 4 member 11 (SLC4A11)-deficient corneal endothelium that lead to the endothelial dysfunction that characterizes the dystrophies associated with SLC4A11 mutations, congenital hereditary endothelial dystrophy (CHED) and Fuchs endothelial corneal dystrophy 4.

Methods

Comparative transcriptomic analysis (CTA) was performed in primary human corneal endothelial cells (pHCEnC) and murine corneal endothelial cells (MCEnC) with normal and reduced levels of SLC4A11 (SLC4A11 KD pHCEnC) and Slc4a11 (Slc4a11^−/− MCEnC), respectively. Validation of differentially expressed genes was performed using immunofluorescence staining of CHED corneal endothelium, as well as western blot and quantitative PCR analysis of SLC4A11 KD pHCEnC and Slc4a11^−/− MCEnC. Functional analyses were performed to investigate potential functional changes associated with the observed transcriptomic alterations.

Results

CTA revealed inhibition of cell metabolism and ion transport function as well as mitochondrial dysfunction, leading to reduced adenosine triphosphate (ATP) production, in SLC4A11 KD pHCEnC and Slc4a11^−/− MCEnC. Co-localization of SNARE protein STX17 with mitochondria marker COX4 was observed in CHED corneal endothelium, as was activation of AMPK–p53/ULK1 in both SLC4A11 KD pHCEnC and Slc4a11^−/− MCEnC, providing additional evidence of mitochondrial dysfunction and mitophagy. Reduced Na⁺-dependent HCO₃⁻ transport activity and altered NH₄Cl-induced membrane potential changes were observed in Slc4a11^−/− MCEnC.

Conclusions

Reduced steady-state ATP levels and subsequent activation of the AMPK–p53 pathway provide a link between the metabolic functional deficit and transcriptome alterations, as well as evidence of insufficient ATP to maintain the Na⁺/K⁺-ATPase corneal endothelial pump as the cause of the edema that characterizes SLC4A11-associated corneal endothelial dystrophies.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

Determination of Oxidative Stress Markers in the Aqueous Humor and Corneal Tissues of Patients With Congenital Hereditary Endothelial Dystrophy

PURPOSE

The aim of this study is to determine the presence of oxidative stress markers in the aqueous humor (AH) and corneal tissues of patients with congenital hereditary endothelial dystrophy (CHED).

METHODS

Interventional prospective study was undertaken to quantify levels of ascorbic acid and glutathione in the AH of patients with CHED. AH was collected from patients undergoing keratoplasty and levels of ascorbic acid and glutathione were determined using biochemical assays and measured spectrophotometrically. AH collected from pediatric patients with cataract were used as control. Corneal sections of patients who underwent penetrating keratoplasty were obtained, and presence of glutathione peroxidase 1, catalase, and superoxide dismutase was determined by immunohistochemistry. Tissue sections obtained from cadaveric corneas unsuitable for clinical transplant were used as control.

RESULTS

Significantly increased ascorbic acid levels were determined in patients with CHED (605.6 ± 158.9 μM) compared with those in controls (190.5 ± 74.72 μM). However, a trend toward reduced level of glutathione was detected in patients with CHED compared with that in the controls. Increased glutathione peroxidase 1 staining and reduced expression of catalase was detected in corneal tissues of patients with CHED compared with those in control corneal tissues. There was no apparent changes observed in the expression of superoxide dismutase in the corneal sections obtained from patients with CHED.

CONCLUSIONS

To the best of our knowledge, this is the first study to determine the levels of ascorbic acid and glutathione in AH of patients with CHED. Our data suggest the presence of oxidative stress in CHED that might be responsible for the pathological changes in patients with CHED.

Nrf2: A unifying transcription factor in the pathogenesis of Fuchs' endothelial corneal dystrophy

Nuclear factor, erythroid 2 like 2 (Nrf2), is an oxidative stress induced transcription factor that regulates cytoprotective gene expression. Thus, Nrf2 is essential for cellular redox homeostasis. Loss or dysregulation of Nrf2 expression has been implicated in the pathogenesis of degenerative diseases, including diseases of the cornea. One of the most common diseases of the cornea in which Nrf2 is implicated is Fuchs' endothelial cornea dystrophy (FECD). FECD is the leading indication for corneal transplantation; and is associated with a loss of corneal endothelial cell (CEC) function. In this review, we propose that Nrf2 is an essential regulator of CEC function. Furthermore, we demonstrate that deficiency of Nrf2 function is a hallmark of FECD. In addition, we advocate that pharmacological targeting of Nrf2 as a possible therapy for FECD.

Polarized Expression of Ion Channels and Solute Carrier Family Transporters on Heterogeneous Cultured Human Corneal Endothelial Cells

Purpose

To clarify the expression profiles of ion channels and transporters of metabolic substrates among heterogeneous cultured human corneal endothelial cells (cHCECs) distinct in their effectiveness in reconstituting the corneal endothelium.

Methods

Integrated proteomics for cell lysates by liquid chromatography–tandem mass spectrometry was carried out from three aliquots of cHCECs enriched in either cluster of definition (CD)44^−/+ (mature) cHCECs or CD44^++/+++ cell-state transition (CST) cHCECs. The expression profiles of cations/anions, monocarboxylic acid transporters (MCTs), and solute carrier (SLC) family proteins, as well as carbonic anhydrases (CAs), were investigated.

Results

The polarized expression of cations/anions, MCTs, and SLC family proteins, as well as CAs, was clarified for mature and CST cHCECs. Most SLC4 family members, including SLC4A11 and SLC4A4 (NBCe1), were upregulated in the CST cHCECs, whereas SLC9A1 (Na⁺/H⁺ exchanger isoform one [NHE1]) and CA5B were detected only in the mature cHCECs. In addition, SLC25A42, catalyzing the entry of coenzyme A into the mitochondria, and SLC25A18, functioning as a mitochondrial glutamate carrier 2 (both relevant for providing the substrates for mitochondrial bioenergetics), were selectively expressed in the mature cHCECs.

Conclusions

Our findings may suggest the relevance of qualifying the polarized expression of these ion channels and transporter-like proteins to ensure not only the suitability but also the in vivo biological functionality of cHCECs selected for use in a cell-injection therapy.

Potential Protective and Therapeutic Roles of the Nrf2 Pathway in Ocular Diseases: An Update

Nuclear factor- (erythroid-derived 2-) like 2 (Nrf2) is a regulator of many processes of life, and it plays an important role in antioxidant, anti-inflammatory, and antifibrotic responses and in cancer. This review is focused on the potential mechanism of Nrf2 in the occurrence and development of ocular diseases. Also, several Nrf2 inducers, including noncoding RNAs and exogenous compounds, which control the expression of Nrf2 through different pathways, are discussed in ocular disease models and ocular cells, protecting them from dysfunctional changes. Therefore, Nrf2 might be a potential target of protecting ocular cells from various stresses and preventing ocular diseases.

Molecular Mechanisms of Fuchs and Congenital Hereditary Endothelial Corneal Dystrophies

The cornea, the eye's outermost layer, protects the eye from the environment. The cornea's innermost layer is an endothelium separating the stromal layer from the aqueous humor. A central role of the endothelium is to maintain stromal hydration state. Defects in maintaining this hydration can impair corneal clarity and thus visual acuity. Two endothelial corneal dystrophies, Fuchs Endothelial Corneal Dystrophy (FECD) and Congenital Hereditary Endothelial Dystrophy (CHED), are blinding corneal diseases with varied clinical presentation in patients across different age demographics. Recessive CHED with an early onset (typically age: 0-3 years) and dominantly inherited FECD with a late onset (age: 40-50 years) have similar phenotypes, although caused by defects in several different genes. A range of molecular mechanisms have been proposed to explain FECD and CHED pathology given the involvement of multiple causative genes. This critical review provides insight into the proposed molecular mechanisms underlying FECD and CHED pathology along with common pathways that may explain the link between the defective gene products and provide a new perspective to view these genetic blinding diseases.

IPSC-Derived Corneal Endothelial-like Cells Act as an Appropriate Model System to Assess the Impact of SLC4A11 Variants on Pre-mRNA Splicing

Purpose

To report molecular genetic findings in six probands with congenital hereditary endothelial dystrophy (CHED) variably associated with hearing loss (also known as Harboyan syndrome). Furthermore, we developed a cellular model to determine if disease-associated variants induce aberrant SLC4A11 pre-mRNA splicing.

Methods

Direct sequencing of the entire SLC4A11 coding region was performed in five probands. In one individual, whole genome sequencing was undertaken. The effect of c.2240+5G>A on pre-mRNA splicing was evaluated in a corneal endothelial-like (CE-like) cell model expressing SLC4A11. CE-like cells were derived from autologous induced pluripotent stem cells (iPSCs) via neural crest cells exposed to B27, PDGF-BB, and DKK-2. Total RNA was extracted, and RT-PCR was performed followed by Sanger and a targeted next generation sequencing (NGS) approach to identify and quantify the relative abundance of alternatively spliced transcripts.

Results

In total, 11 different mutations in SLC4A11 evaluated as pathogenic were identified; of these, c.1237G>A, c.2003T>C, c.1216+1G>A, and c.2240+5G>A were novel. The c.2240+5G>A variant was demonstrated to result in aberrant pre-mRNA splicing. A targeted NGS approach confirmed that the variant introduces a leaky cryptic splice donor site leading to the production of a transcript containing an insertion of six base pairs with the subsequent introduction of a premature stop codon (p.Thr747*). Furthermore, a subset of transcripts comprising full retention of intron 16 also were observed, leading to the same functionally null allele.

Conclusions

This proof-of-concept study highlights the potential of using CE-like cells to investigate the pathogenic consequences of SLC4A11 disease–associated variants.

Human Corneal Expression of SLC4A11, a Gene Mutated in Endothelial Corneal Dystrophies

Two blinding corneal dystrophies, pediatric-onset congenital hereditary endothelial dystrophy (CHED) and some cases of late-onset Fuchs endothelial corneal dystrophy (FECD), are caused by SLC4A11 mutations. Three N-terminal SLC4A11 variants: v1, v2 and v3 are expressed in humans. We set out to determine which of these transcripts and what translated products, are present in corneal endothelium as these would be most relevant for CHED and FECD studies. Reverse transcription PCR (RT-PCR) and quantitative RT-PCR revealed only v2 and v3 mRNA in human cornea, but v2 was most abundant. Immunoblots probed with variant-specific antibodies revealed that v2 protein is about four times more abundant than v3 in human corneal endothelium. Bioinformatics and protein analysis using variant-specific antibodies revealed that second methionine in the open reading frame (M36) acts as translation initiation site on SLC4A11 v2 in human cornea. The v2 variants starting at M1 (v2-M1) and M36 (v2-M36) were indistinguishable in their cell surface trafficking and transport function (water flux). Structural homology models of v2-M36 and v3 suggest structural differences but their significance remains unclear. A combination of bioinformatics, RNA quantification and isoform-specific antibodies allows us to conclude that SLC4A11 variant 2 with start site M36 is predominant in corneal endothelium.

Ammonia sensitive SLC4A11 mitochondrial uncoupling reduces glutamine induced oxidative stress

SLC4A11 is a NH₃ sensitive membrane transporter with H⁺ channel-like properties that facilitates Glutamine catabolism in Human and Mouse corneal endothelium (CE). Loss of SLC4A11 activity induces oxidative stress and cell death, resulting in Congenital Hereditary Endothelial Dystrophy (CHED) with corneal edema and vision loss. However, the mechanism by which SLC4A11 prevents ROS production and protects CE is unknown. Here we demonstrate that SLC4A11 is localized to the inner mitochondrial membrane of CE and SLC4A11 transfected PS120 fibroblasts, where it acts as an NH₃-sensitive mitochondrial uncoupler that enhances glutamine-dependent oxygen consumption, electron transport chain activity, and ATP levels by suppressing damaging Reactive Oxygen Species (ROS) production. In the presence of glutamine, Slc4a11^-/- (KO) mouse CE generate significantly greater mitochondrial superoxide, a greater proportion of damaged depolarized mitochondria, and more apoptotic cells than WT. KO CE can be rescued by MitoQ, reducing NH₃ production by GLS1 inhibition or dimethyl αKetoglutarate supplementation, or by BAM15 mitochondrial uncoupling. Slc4a11 KO mouse corneal edema can be partially reversed by αKetoglutarate eye drops. Moreover, we demonstrate that this role for SLC4A11 is not specific to CE cells, as SLC4A11 knockdown in glutamine-addicted colon carcinoma cells reduced glutamine catabolism, increased ROS production, and inhibited cell proliferation. Overall, our studies reveal a unique metabolic mechanism that reduces mitochondrial oxidative stress while promoting glutamine catabolism.

The Molecular Basis of Fuchs' Endothelial Corneal Dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is a common disease resulting from corneal endothelial cell dysfunction. It is inherited in an autosomal dominant fashion with incomplete penetrance, and with a female bias. Approximately half of cases occur sporadically, and the remainder are familial. Early and late-onset forms of the disease exist. A review of the literature has revealed more than 15 genes harbouring mutations and/or single nucleotide polymorphisms associated with FECD. The proteins encoded by these genes cover a wide range of endothelial function, including transcription regulation, DNA repair, mitochondrial DNA mutations, targeting of proteins to the cell membrane, deglutamylation of proteins, extracellular matrix secretion, formation of cell-cell and cell-extracellular matrix junctions, water pump, and apoptosis. These genetic variations will form the platform for the further understanding of the pathological basis of the disease, and the development of targeted treatments. This review aims to summarise known genetic variations associated with FECD, discuss any known molecular effects of the variations, how these provide opportunities for targeted therapies, and what therapies are currently in development.

REVIEW: Current understanding of the pathogenesis of Fuchs' endothelial corneal dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is the most prominent reason for corneal-endothelial transplantations across the globe. The disease pathophysiology manifests through a combination of various genetic and non-heritable factors. This review provides a comprehensive list of known genetic players that cause FECD, and discusses the prominent pathological features that participate in disease progression, such as channel dysfunction, abnormal extracellular matrix deposition, RNA toxicity, oxidative stress, and apoptosis. Although current practices to correct visual acuity involve surgical intervention, this review also discusses the scope of various non-surgical therapeutics to remedy FECD.

Differential Expression of Antimicrobial Peptides in Streptococcus pneumoniae Keratitis and STAT3-Dependent Expression of LL-37 by Streptococcus pneumoniae in Human Corneal Epithelial Cells

Streptococcus pneumoniae is the leading cause of bacterial keratitis in the developing world with a growing trend of acquiring resistance against various antibiotics. In the current study, we determined the expression of different antimicrobial peptides (AMPs) in response to S. pneumoniae in patients, as well as in primary and immortalized human corneal epithelial cells. We further focused on LL-37 and determined its expression in human cornea infected with S. pneumoniae and studied the killing ability of LL-37 against S. pneumoniae. The expression of AMPs was determined by quantitative PCR and the phosphorylation of signaling proteins was evaluated by immunoblot analysis. LL-37 expression was also determined by immunofluorescence and Western blot method and the killing ability of LL-37 against S. pneumoniae was determined by colony-forming units. Differential expression of antimicrobial peptides was observed in patients with S. pneumoniae keratitis. Although S. pneumoniae induced expression of the AMPs in human corneal epithelial cells (HCEC), it did not induce AMP expression in U937, a human monocyte cell line. S. pneumoniae also caused activation of nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB)and mitogen activated protein kinase (MAPK) pathways in corneal epithelial cells. LL-37 was found to be effective against both laboratory and clinical strains of S. pneumoniae. LL-37 induction by S. pneumoniae in human corneal epithelial cells was mediated by signal transducer and activator of transcription 3 (STAT3) activation, and inhibition of STAT3 activation significantly reduced LL-37 expression. Our study determines an extensive profile of AMPs expressed in the human cornea during S. pneumoniae infection, and suggests the potential of LL-37 to be developed as an alternative therapeutic intervention to fight increasing antibiotic resistance among bacteria.

Feeder-free differentiation of cells exhibiting characteristics of corneal endothelium from human induced pluripotent stem cells

The purpose of this study was to devise a strategy for the derivation of corneal endothelial cells (CEnCs) from adult fibroblast-derived induced pluripotent stem cells (iPSCs). IPSCs were generated from an adult human with normal ocular history via expression of OCT4, SOX2, KLF4 and c-MYC Neural crest cells (NCCs) were differentiated from iPSCs via addition of CHIR99021 and SB4315542. NCCs were driven toward a CEnC fate via addition of B27, PDGF-BB and DKK-2 to CEnC media. Differentiation of NCCs and CEnCs was evaluated via rt-PCR, morphological and immunocytochemical analysis. At 17 days post-NCC induction, there were notable changes in cell morphology and upregulation of the neural crest lineage transcripts PAX3, SOX9, TFAP2A, SOX10 and p75NTR and the proteins p75/NGFR and SOX10. Exposure of NCCs to B27, PDGF-BB and DKK-2 induced a shift in morphology from a spindle-shaped neural phenotype to a tightly-packed hexagonal appearance and increased expression of the transcripts ATP1A1, COL8A1, COL8A2, AQP1 and CDH2 and the proteins ZO-1, N-Cad, AQP-1 and Na+/K+ATPase. Replacement of NCC media with CEnC media on day 3, 5 or 8 reduced the differentiation time needed to yield CEnCs. IPSC-derived CEnCs could be used for evaluation of cornea endothelial disease pathophysiology and for testing of novel therapeutics.

Molecular phenotype of SLC4A11 missense mutants: Setting the stage for personalized medicine in corneal dystrophies

SLC4A11 mutations cause cases of congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (HS), and Fuchs endothelial corneal dystrophy (FECD). Defective water reabsorption from corneal stroma by corneal endothelial cells (CECs) leads to these corneal dystrophies. SLC4A11, in the CEC basolateral membrane, facilitates transmembrane movement of H₂ O, NH₃ , and H⁺ -equivalents. Some SLC4A11 disease mutants have impaired folding, leading to a failure to move to the cell surface, which in some cases can be corrected by the drug, glafenine. To identify SLC4A11 mutants that are targets for folding-correction therapy, we examined 54 SLC4A11 missense mutants. Cell-surface trafficking was assessed on immunoblots, by the level of mature, high molecular weight, cell surface-associated form, and using a bioluminescence resonance energy transfer assay. Low level of cell surface trafficking was found in four out of 18 (20%) of FECD mutants, 19/ out of 31 (61%) of CHED mutants, and three out of five (60%) of HS mutants. Amongst ER-retained mutants, 16 showed increased plasma membrane trafficking when grown at 30°C, suggesting that their defect has potential for rescue. CHED-causing point mutations mostly resulted in folding defects, whereas the majority of FECD missense mutations did not affect trafficking, implying functional impairment. We identified mutations that make patients candidates for folding correction of their corneal dystrophy.