Mesenchymal stem cell-based adjunctive therapy for Pseudomonas aeruginosa-induced keratitis: A proof-of-concept in-vitro study.

PURPOSE: Pseudomonas aeruginosa-induced keratitis is one of the most severe and challenging forms of corneal infection, owing to its associated intense inflammatory reactions leading to corneal necrosis and dense corneal scar with loss of vision. Since mesenchymal stem cells (MSCs) are reported to possess antimicrobial and immunomodulatory properties, they can be tested as an adjuvant treatment along with the antibiotics which are the current standard of care. This study aims to investigate the anti-bacterial and immunomodulatory roles of human bone marrow MSC-derived conditioned medium (MSC-CM) in P. aeruginosa-infected human corneal epithelial cells (HCECs) in vitro. METHODS: The effect of MSC-CM on the growth of clinical isolates of P. aeruginosa was evaluated by colony-forming unit assay. The expression of inflammatory cytokines (IL-6 and TNF-α) and an antimicrobial peptide (Lipocalin 2) in lipopolysaccharide-treated MSCs and HCECs was analyzed through ELISA. Corneal epithelial repair following infection with P. aeruginosa was studied through scratch assay. RESULTS: Compared to control (P. aeruginosa (5*105) incubated in DMEM (1 ml) at 37 °C for 16 h), MSC-CM significantly: i) inhibits the growth of P. aeruginosa (159*109 vs. 104*109 CFU/ml), ii) accelerates corneal epithelial repair following infection with P. aeruginosa (9% vs. 24% closure of the wounded area after 12 h of infection), and iii) downregulates the lipopolysaccharide-induced expression of IL-6, TNF-α and Lipocalin 2 in HCECs. A combination of MSC-CM with an antibiotic, Ciprofloxacin moderately regulated the expression of IL-6, TNF-α, and Lipocalin 2. CONCLUSION: MSC-CM holds promise as an adjunctive therapeutic approach for P. aeruginosa-induced corneal epithelial damage.

Krupple-like factor 4 (KLF4) methylation signature in host cell in active viral keratitis with epithelial manifestation.

HSV1 presents as epithelial or stromal keratitis or keratouveitis and can lead to sight-threatening complications. KLF4, a critical transcription factor, and regulator of cell growth and differentiation, is essential in corneal epithelium stratification and homeostasis. Here, we want to understand the epigenetic modification specifically the methylation status of KLF4 in epithelium samples of HSV1 keratitis patients. After obtaining consent, epithelial scrapes were collected from 7 patients with clinically diagnosed HSV1 keratitis and 7 control samples (patients undergoing photorefractive keratectomy). Genomic DNA was isolated from the collected samples using the Qiagen DNeasy Kit. Subsequently, bisulfite modification was performed. The bisulphite-modified DNA was then subjected to PCR amplification using specific primers designed to target the KLF4, ACTB gene region, allowing for the amplification of methylated and unmethylated DNA sequences. The amplified DNA products were separated and visualized on a 3% agarose gel. KLF4 hypermethylation was found in 6 out of 7 (85.71%) eyes with viral keratitis, while 1 eye showed hypomethylation compared to PRK samples. Out of these 6, there were 2 each of epithelial dendritic keratitis, epithelial geographical keratitis, and neurotrophic keratitis. The patient with hypomethylated KLF4 had a recurrent case of HSV1 keratitis with multiple dendrites and associated vesicular lesions of the lip along with a history of fever. KLF4 hypermethylation in most viral keratitis cases indicated the under functioning of KLF4 and could indicate a potential association between KLF4 hypermethylation and the development or progression of HSV1 keratitis.

Short chain fatty acids inhibit corneal inflammatory responses to TLR ligands via the ocular G-protein coupled receptor 43.

PURPOSE: Short chain fatty acids (SCFAs) produced by gut microbiota are known to play primary roles in gut homeostasis by immunomodulation partially through G-protein coupled receptors (GPR) 43. Using mouse models of TLR ligand induced keratitis, we investigated whether SCFAs and GPR43 play any regulatory roles in the pathogenesis of inflammatory responses in the eye. METHODS: Both human and mouse eyes were labeled with a specific antibody for GPR43 and imaged by a laser scanning confocal microscope. Corneal cups from naïve C57BL/6J (B6) and GPR43 knockout (KO) mice were stimulated with TLR ligands in the presence or absence of sodium butyrate overnight and then processed for RT-PCR assay for expression of GPR43 and cytokines. Keratitis was induced by Poly I:C in wild type (WT) B6, GPR43KO and chimeric mice and the disease severity was evaluated by the corneal fluorescein staining test, and infiltrating cell staining and calculating in corneal whole mount. RESULTS: GPR43 is expressed in both human and mouse eyes and the expression is bidirectionally regulated by TLR ligands and butyrate. Butyrate significantly inhibited inflammation caused by several TLR ligands such as Poly I:C, Flagellin, and CpG-ODN (TLR-3, 5 and 9 agonists, respectively) in WT, but not GPR43KO, mice. Butyrate inhibition of TLR-induced keratitis is mediated by the GPR43 expressed in tissue but not hematopoietic, cells. CONCLUSIONS: This is the first report to demonstrate of the protective effect of SCFAs on microbial keratitis, and the dynamic expression and anti-inflammatory function of GPR43 in the eye. SCFAs can modulate inflammation and immunity in the eye through GPR43.

Preliminary observations on tear film interferometry performed in horses.

This retrospective study evaluated tear film (TF) interferometry on horses examined in Northern Italy in 2019-2021. The objectives were to evaluate horses affected by keratitis, and to describe TF values in horses with no evidence of ocular disease. All horses received a complete ophthalmic examination and were examined with the Ocular Surface Analyser, Veterinary-setting, prior to eye manipulation, staining and sample collection. Eighteen horses with no evidence of ocular disease were included in the comparison group. Additionally, 46 horses displaying signs of keratitis (neovascularization, corneal opacities, ulceration, epithelial and subepithelial infiltrates) were evaluated. These horses were divided into presumed non-infectious and infectious or presumed infectious keratitis groups (one with proven bacterial origin, and the others with diagnosed or presumptive keratomycosis) with the former including immune-mediated keratitis. From the observations of TF interferometry in the comparison population the authors concluded that for non-invasive break-up time (NIBUT), the estimated preliminary reference interval was 10.4-31.2s, and for tear meniscus height (TMH), it was 0.215-0.457mm. Moreover, within the keratitis population, from an interferometric point of view punctate lesions of the ocular surface were present in all cases of active diagnosed or presumptive subepithelial keratomycosis but not in any of the non-infectious cases, either non-ulcerative or ulcerative. Limitations of the study include a relatively low number of horses examined and the fact that the diagnosis of infectious keratitis was presumptive and based on clinical improvement after treatment in some cases. To the authors' knowledge, this is the first report of TF interferometry performed in horses.

A. castellanii and P. aeruginosa mutually exacerbate damage to corneal cells during coinfection.

IMPORTANCE: At the National Cheng Kung University Hospital, numerous cases of amoebic keratitis had been identified with concurrent bacterial infections. Among these bacterial coinfections, Pseudomonas aeruginosa accounted for 50% of the reported cases. However, the impact of pathogenic bacteria on amoeba-induced corneal damage remains unclear. In our study, we successfully demonstrated that P. aeruginosa accumulated on the Acanthamoeba castellanii surface and caused more severe corneal damage. We also indicated that the exposure of P. aeruginosa to amoeba-soluble antigens enhanced its adhesion ability, promoted biofilm formation, and led to more severe corneal cell damage. These findings significantly contributed to our understanding of the risk associated with P. aeruginosa coinfection in the progression of amoeba keratitis.

Endogenous TSG-6 modulates corneal inflammation following chemical injury.

PURPOSE: Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) is upregulated in various pathophysiological contexts, where it has a diverse repertoire of immunoregulatory functions. Herein, we investigated the expression and function of TSG-6 during corneal homeostasis and after injury. METHODS: Human corneas, eyeballs from BALB/c (TSG-6+/+), TSG-6+/- and TSG-6-/- mice, human immortalized corneal epithelial cells and murine corneal epithelial progenitor cells were prepared for immunostaining and real time PCR analysis of endogenous expression of TSG-6. Mice were subjected to unilateral corneal debridement or alkali burn (AB) injuries and wound healing assessed over time using fluorescein stain, in vivo confocal microscopy and histology. RESULTS: TSG-6 is endogenously expressed in the human and mouse cornea and established corneal epithelial cell lines and is upregulated after injury. A loss of TSG-6 has no structural and functional effect in the cornea during homeostasis. No differences were noted in the rate of corneal epithelial wound closure between BALB/c, TSG-6+/- and TSG-6-/- mice. TSG-6-/- mice presented decreased inflammatory response within the first 24 h of injury and accelerated corneal wound healing following AB when compared to control mice. CONCLUSION: TSG-6 is endogenously expressed in the cornea and upregulated after injury where it propagates the inflammatory response following chemical injury.

IDO Regulates Macrophage Functions by Inhibiting the CCL2/CCR2 Signaling Pathway in Fungal Keratitis.

PURPOSE: The aim of this study was to investigate the effects of indoleamine 2,3-dioxygenase (IDO) on macrophage polarization, phagocytosis, and killing through regulation of the CCL2/CCR2 signaling pathway in Aspergillus fumigatus keratitis. METHODS: In vivo and in vitro experiments were conducted in mice and mouse peritoneal macrophages after infection with A. fumigatus . Clinical scoring, reverse transcription-polymerase chain reaction, and immunofluorescence staining were used to evaluate the fungal keratitis lesions, macrophage-related cytokines, and macrophage recruitment. The expression of CCL2 and CCR2 was detected by reverse transcription-polymerase chain reaction and western blot after pretreatment with or without an IDO inhibitor (1-MT). After pretreatment with 1-MT, a CCR2 antagonist, a CCL2 neutralizing antibody, an IDO agonist (IFNG), and recombinant CCL2 protein (CCL2), the flow cytometry and colony-forming unit counts were used to detect the polarization, phagocytosis, and killing function. RESULTS: Compared with the control group, the infected eyes showed increased clinical scores, macrophage-related cytokine expression, and macrophage recruitment. 1-MT pretreatment increased the expression of CCL2 and CCR2 and the proportion of CD206+/CD86+ macrophages; macrophages polarized toward the M2 type, with enhanced killing function. CCR2 antagonists and CCL2 neutralizing antibodies reversed the effects of 1-MT. Compared with the infected group, IFNG pretreatment decreased the proportion of CD206+/CD86+ macrophages, and macrophages polarized toward the M1 type, with decreased phagocytosis and impaired killing function. CCL2 reversed the effect of IFNG. CONCLUSIONS: IDO can promote the polarization of macrophages to the M1 type by blocking the CCL2/CCR2 signaling pathway, inhibiting the phagocytosis and killing function of macrophages, and mediating the protective immune role of A. fumigatus .

Immunity to pathogenic fungi in the eye.

Fusarium, Aspergillus and Candida are important fungal pathogens that cause visual impairment and blindness in the USA and worldwide. This review will summarize the epidemiology and clinical features of corneal infections and discuss the immune and inflammatory responses that play an important role in clinical disease. In addition, we describe fungal virulence factors that are required for survival in infected corneas, and the activities of neutrophils in fungal killing, tissue damage and cytokine production.

Antibody gene transfer treatment drastically improves epidermal pathology in a keratitis ichthyosis deafness syndrome model using male mice.

BACKGROUND: Keratitis ichthyosis deafness (KID) syndrome is a rare disorder caused by hemichannel (HC) activating gain-of-function mutations in the GJB2 gene encoding connexin (Cx) 26, for which there is no cure, or current treatments based upon the mechanism of disease causation. METHODS: We applied Adeno Associated Virus (AAV) mediated mAb gene transfer (AAVmAb) to treat the epidermal features of KID syndrome with a well-characterized HC blocking antibody using male mice of a murine model that replicates the skin pathology of the human disease. FINDINGS: We demonstrate that in vivo AAVmAb treatment significantly reduced the size and thickness of KID lesions, in addition to blocking activity of mutant HCs in the epidermis in vivo. We also show that AAVmAb treatment eliminated abnormal keratinocyte proliferation and enlarged cell size, decreased apoptosis, and restored the normal distribution of keratin expression. INTERPRETATION: Our findings reinforce the critical role played by increased HC activity in the skin pathology associated with KID syndrome. They also underscore the clinical potential of anti-HC mAbs coupled with genetic based delivery systems for treating the underlying mechanistic basis of this disorder. Inhibition of HC activity is an ideal therapeutic target in KID syndrome, and the genetic delivery of mAbs targeted against mutant HCs could form the basis of new therapeutic interventions to treat this incurable disease. FUNDING: Fondazione Telethon grant GGP19148 and University of Padova grant Prot. BIRD187130 to FM; Foundation for Ichthyosis and Related Skin Types (FIRST) and National Institutes of Health grant EY 026911 to TWW.

Resolvin D1 Inhibits Corneal Inflammation in Staphylococcus Aureus Keratitis.

PURPOSE: To investigate the role of lipid mediator, resolvin D1 (RvD1), in corneal inflammation. METHODS: The anti-inflammatory effect of RvD1 on stimulated human corneal epithelial cells (HCECs) was assessed. C57BL/6 mice corneas were abraded and treated with RvD1 after stimulation with Staphylococcus aureus. Cytokine levels in the corneas, cervical drainage lymph nodes (DLNs), and spleens were measured. Anterior segment photography and optical coherence tomography quantified the changes in corneal thickness and haziness. Neutrophil infiltration in the cornea was examined by haematoxylin and eosin (H&E) staining and immunohistochemistry. RESULTS: RvD1 significantly inhibited cytokine production in HCECs and mouse corneas, cervical DLNs, and spleens while stimulating interleukin-10 (IL-10) production. Corneal opacity development, thickening, and neutrophil infiltration significantly reduced in response to RvD1 stimulation in the S. aureus-infected mice corneas. CONCLUSION: RvD1 inhibited S. aureus-induced corneal inflammation. These results potentiate RvD1 as an anti-inflammatory therapy for patients with corneal inflammation induced by bacterial keratitis.

Assessment of Keratitis Severity Using Quantitative Image Analysis in an In Vivo Murine Model of Staphylococcus aureus Bacterial Keratitis.

Purpose: Bacterial keratitis (BK) severity in murine models has traditionally been measured by subjective clinical grading or quantification of ocular bacterial burden. This investigation explores an objective and repeatable quantification of slit lamp photography (SLP) images to measure BK severity. Methods: BALB/c strain mice underwent three parallel scratches of the right cornea with subsequent inoculation of 107Staphylococcus aureus cells. SLP imaging and clinical severity grading were performed at 48 hours post-infection. Stromal infiltrate (SI) area on SLP images were quantified. Bacterial burden was determined after enucleation and homogenization. Spearman rank correlations (rs) were used to estimate associations between SI area, clinical severity grades, and bacterial burden. Results: BALB/c strain mice (n = 14) were evaluated with an average SI area of 0.92 mm2 (standard deviation, SD = 0.65) and average bacterial burden of 3.16 × 105 colony forming units per milliliter (CFU/mL) (SD = 8.3 × 105). Clinical severity grade positively correlated with SI area (rs = 0.59, p = 0.0276) and bacterial burden (rs = 0.66, p = 0.0106). There was a trend towards positive association between SI area and bacterial burden (rs = 0.51, p = 0.0543). Conclusions: SLP annotation of SI area is correlated with clinical severity and may provide an objective, quantitative, and repeatable assessment of BK disease severity. Translational Relevance: SLP annotation of SI area is a novel quantitative method to evaluate bacterial keratitis severity longitudinally in mouse models which may be a powerful tool to better understand BK pathogenesis and response to treatments.

Diffuse lamellar keratitis as a rare complication of diamond burr superficial keratectomy for recurrent corneal erosion: a case report.

BACKGROUND: To present a case with a history of laser in situ keratomileusis (LASIK) developing diffuse lamellar keratitis (DLK) after diamond burr superficial keratectomy (DBSK) for recurrent corneal erosion (RCE). CASE PRESENTATION: A 25-year-old man presented with multiple episodes of RCE one year after femtosecond-assisted LASIK for myopia correction. Because conservative treatments failed to halt the repetitive attack of RCE, he underwent epithelial debridement and DBSK. However, severe foreign body sensation and blurred vision developed on postoperative day one. The next day, slit lamp biomicroscopy revealed DLK manifested as diffuse granular infiltrates at the flap interface. After topical corticosteroid treatment, the inflammation resolved gradually, and his vision recovered to 20/20. CONCLUSIONS: Diffuse lamellar keratitis is a rare post-LASIK complication that can be triggered by DBSK, which causes impairment of the corneal epithelial integrity and subsequent inflammation at the flap interface. For post-LASIK patients with RCE, alternative treatments, such as anterior stromal puncture, may be considered to avoid extensive disruption of corneal epithelium and DLK development depending on the size and the location of the lesions.

Galectin-3 Is a Crucial Immunological Disease Marker in Patients with Fungal Keratitis.

Fungal keratitis, one of the most common infectious eye diseases in China, often results in a poor prognosis due to a delayed diagnosis and the insufficiency of effective therapy. There is an urgent need to identify specific biomarkers for the disease. In this study, we screened out tear proteins in patients with fungal keratitis by microsphere-based immunoassay analysis. Levels of cytokine expression were determined in both human corneal epithelial cell models in vitro and the corneas of patients by western blot, quantitative polymerase chain reaction (qPCR), and immunofluorescence analysis. Neutrophil activation was examined by flow cytometry analysis. The relationship between the cytokine expression and neutrophils was evaluated by immunofluorescence costaining and correlation analysis. These results demonstrated that the galectin-3 expression level was increased in both cell model and patient samples at the early and late stages of fungal keratitis. The neutrophils were significantly activated during the disease course of fungal keratitis. Meanwhile, colocalization and a positive correlation between galectin-3 and neutrophils were observed, suggesting that galectin-3 may play a crucial role in the recruitment of neutrophils and immune regulation of fungal keratitis. In conclusion, galectin-3 could be a key disease marker implying a beneficial immune response in the pathogenesis of fungal keratitis, which might be a target of therapeutic strategy in the future.

Chlorhexidine in the treatment of microsporidial stromal keratitis and the effect of host immunity: A case series and literature review.

Microsporidial stromal keratitis is an increasingly well-known vision-threatening disease. A large proportion of cases are initially misdiagnosed as herpes simplex keratitis and treated with topical steroids. In most of such cases, medical treatment failed, and corneal transplantation was required. This study reported the results of 0.02% topical chlorhexidine used to treat three cases of microsporidial stromal keratitis and reviewed the literature on the outcomes of microsporidial stromal keratitis treatment. In the first case, histopathology of a specimen from penetrating keratoplasty (PK) revealed severe chronic inflammation involving the entire stromal layer but no microorganism activity after the application of topical chlorhexidine for 10 months. The second case exhibited complete resolution of keratitis after topical chlorhexidine. The patient in the third case did not respond to medical treatment, and therapeutic PK was performed. Histopathological examination revealed numerous microsporidial spores that had colonized in the mid and deep stroma, where few inflammatory cells were observed. These findings explain the variable microsporidial susceptibility to chlorhexidine, suggesting the crucial role of host immunity. In cases of host immunity, topical chlorhexidine may represent a promising option for the treatment of microsporidial stromal keratitis.

USP22 promotes pro­inflammatory responses in Pseudomonas aeruginosa­induced keratitis by targeting TRAF6.

Pseudomonas aeruginosa (PA)­induced keratitis is characterized by inflammatory epithelial edema, stromal infiltration, corneal ulceration and can lead to vision loss. The present study aimed to study the effect of ubiquitin­specific protease 22 (USP22) on PA­induced keratitis. Using RT­qPCR and western blotting, significantly increased expression of USP22 was identified in mouse corneas and cultured RAW264.7 cells following PA stimulation. In addition, the results of in vivo experiments, western blot assay and ELISA suggested that the silencing of USP22 attenuated disease progression, downregulated the NF­κB pathway and suppressed the expression of pro­inflammatory cytokines following PA stimulation. Notably, it was identified that the expression of tumor necrosis factor receptor­associated factor 6 (TRAF6) was decreased by silencing of USP22 and USP22 was found to remove lysine 48­linked poly­ubiquitination chains from TRAF6 to stabilize TRAF6 expression and these effects were clearly aggravated following PA infection.

Phenotypic spectrum of autosomal recessive Keratitis-Ichthyosis-Deafness Syndrome (KIDAR) due to mutations in AP1B1.

Inborn errors in copper metabolism result in a diverse set of abnormalities such as Wilson disease and MEDNIK syndrome. Homozygous pathogenic variants in AP1B1 lead to KIDAR (Keratitis-Ichthyosis-Deafness Syndrome). The main phenotypic features of KIDAR are ichthyosis, keratitis, erythroderma, and progressive hearing loss accompanied by developmental delay and failure to thrive. Herein, we describe a six-and-a-half-year-old boy with KIDAR caused by a novel pathogenic variant in AP1B1 (NM_001127.4:c.1263C > A, p.Tyr421*). The proband presented with ichthyosis, erythroderma, palmoplantar keratoderma, hearing loss, and corneal scarring. He also had hypotonia, global developmental delay, and photophobia. Lastly, we review all of the previously reported cases and the clinical features associated with KIDAR.

Secondary Amine Pendant ß-Peptide Polymers Displaying Potent Antibacterial Activity and Promising Therapeutic Potential in Treating MRSA-Induced Wound Infections and Keratitis.

Interest in developing antibacterial polymers as synthetic mimics of host defense peptides (HPDs) has accelerated in recent years to combat antibiotic-resistant bacterial infections. Positively charged moieties are critical in defining the antibacterial activity and eukaryotic toxicity of HDP mimics. Most examples have utilized primary amines or guanidines as the source of positively charged moieties, inspired by the lysine and arginine residues in HDPs. Here, we explore the impact of amine group variation (primary, secondary, or tertiary amine) on the antibacterial performance of HDP-mimicking ß-peptide polymers. Our studies show that a secondary ammonium is superior to either a primary ammonium or a tertiary ammonium as the cationic moiety in antibacterial ß-peptide polymers. The optimal polymer, a homopolymer bearing secondary amino groups, displays potent antibacterial activity and the highest selectivity (low hemolysis and cytotoxicity). The optimal polymer displays potent activity against antibiotic-resistant bacteria and high therapeutic efficacy in treating MRSA-induced wound infections and keratitis as well as low acute dermal toxicity and low corneal epithelial cytotoxicity. This work suggests that secondary amines may be broadly useful in the design of antibacterial polymers.

Sensory nerves promote corneal inflammation resolution via CGRP mediated transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway.

OBJECTIVES: To explore the role of the corneal sensory nerves in Pseudomonas aeruginosa (P. aeruginosa) keratitis, the synergistic effect between the sensory neurons and macrophages in calcitonin gene-related peptide (CGRP) release, and the functional mechanisms of CGRP-mediated transformation of macrophages to the M2 phenotype. METHODS: Corneal nerve loss, macrophage recruitment, and CGRP expression were evaluated. To explore the synergistic effect between the sensory neurons and macrophages, RAW 264.7 cells were challenged with lipopolysaccharide (LPS), then trigeminal ganglion (TG) sensory neurons were isolated and co-incubated with macrophages, and CGRP expression was tested. To investigate the biological function of cornea neuron-initiated immune responses mediated by CGRP, BIBN 4096BS was used to inhibit CGRP in vivo and α-CGRP was used to simulate CGRP in vitro. The expressions of inflammatory cytokines (IL-1ß, IL-6, TNF-α, and IL-10), M1 (CD80/CD86), M2 (CD163/CD206) macrophage markers, and signal transducers (PI3K/AKT) were detected. RESULTS: P. aeruginosa infection induced corneal nerve loss, macrophage recruitment, and CGRP up-expression. CGRP was co-localized with macrophages. Co-culture showed that sensory neurons and macrophages can mediate CGRP release. More CGRP was released when the two types of cells were combined to respond to LPS. BIBN 4096BS promoted pro-inflammatory cytokines and inhibited the anti-inflammatory cytokines and signal transducers, while, α-CGRP inhibited the pro-inflammatory cytokines and M1 markers and promoted the anti-inflammatory cytokine, M2 markers, and signal transducers. CONCLUSIONS: P. aeruginosa infection induces corneal sensory neuron activation, macrophage recruitment, and CGRP up-expression. The synergistic effect between the sensory neurons and macrophages promotes CGRP release. CGRP inhibits corneal inflammation and promotes the transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway.

Connexin hemichannel inhibition ameliorates epidermal pathology in a mouse model of keratitis ichthyosis deafness syndrome.

Mutations in five different genes encoding connexin channels cause eleven clinically defined human skin diseases. Keratitis ichthyosis deafness (KID) syndrome is caused by point mutations in the GJB2 gene encoding Connexin 26 (Cx26) which result in aberrant activation of connexin hemichannels. KID syndrome has no cure and is associated with bilateral hearing loss, blinding keratitis, palmoplantar keratoderma, ichthyosiform erythroderma and a high incidence of childhood mortality. Here, we have tested whether a topically applied hemichhanel inhibitor (flufenamic acid, FFA) could ameliorate the skin pathology associated with KID syndrome in a transgenic mouse model expressing the lethal Cx26-G45E mutation. We found that FFA blocked the hemichannel activity of Cx26-G45E in vitro, and substantially reduced epidermal pathology in vivo, compared to untreated, or vehicle treated control animals. FFA did not reduce the expression of mutant connexin hemichannel protein, and cessation of FFA treatment allowed disease progression to continue. These results suggested that aberrant hemichannel activity is a major driver of skin disease in KID syndrome, and that the inhibition of mutant hemichannel activity could provide an attractive target to develop novel therapeutic interventions to treat this incurable disease.