Genome-wide screening of mouse knockouts reveals novel genes required for normal integumentary and oculocutaneous structure and function

Oculocutaneous syndromes are often due to mutations in single genes. In some cases, mouse models for these diseases exist in spontaneously occurring mutations, or in mice resulting from forward mutatagenesis screens. Here we present novel genes that may be causative for oculocutaneous disease in humans, discovered as part of a genome-wide screen of knockout-mice in a targeted single-gene deletion project. The International Mouse Phenotyping Consortium (IMPC) database (data release 10.0) was interrogated for all mouse strains with integument abnormalities, which were then cross-referenced individually to identify knockouts with concomitant ocular abnormalities attributed to the same targeted gene deletion. The search yielded 307 knockout strains from unique genes with integument abnormalities, 226 of which have not been previously associated with oculocutaneous conditions. Of the 307 knockout strains with integument abnormalities, 52 were determined to have ocular changes attributed to the targeted deletion, 35 of which represent novel oculocutaneous genes. Some examples of various integument abnormalities are shown, as well as two examples of knockout strains with oculocutaneous phenotypes. Each of the novel genes provided here are potentially relevant to the pathophysiology of human integumentary, or oculocutaneous conditions, such as albinism, phakomatoses, or other multi-system syndromes. The novel genes reported here may implicate molecular pathways relevant to these human diseases and may contribute to the discovery of novel therapeutic targets.

Comparison of automated vs manual analysis of corneal endothelial cell density and morphology in normal and corneal endothelial dystrophy-affected dogs

OBJECTIVE

To determine the efficacy of automated imaging software of the Nidek ConfoScan 4 confocal biomicroscope at analyzing canine corneal endothelial cell density and morphology in health and disease, by comparing to a manual analysis method.

ANIMAL STUDIED

Nineteen eyes of 10 dogs were evaluated and include three Beagles, three Jack Russell Terriers, and four miscellaneous breeds. Twelve clinically normal and seven eyes affected with corneal endothelial dystrophy (CED) were scanned and analyzed.

PROCEDURES

Endothelial cell density (ECD), mean and standard deviation (SD) of cell area, percent polymegathism, mean and SD of the number of cell sides, and percent pleomorphism were calculated using automated and manual methods for each scan.

RESULTS

The automated analysis showed significantly greater ECD in comparison with the manual frame method due to misidentification of cell domains in CED-affected dogs. No significant differences in ECD were observed between normal and CED-affected dogs in automated analysis, while CED-affected dogs showed significantly lower ECD in manual frame method and planimetry. Using both automated and manual methods, CED-affected dogs showed greater variability of cell area or the number of cell sides than normal dogs.

CONCLUSION

The automated imaging software is unable to accurately identify cell borders in CED-affected dogs resulting in inaccurate estimates of ECD. Thus, manual analysis is recommended for use in clinical trials assessing adverse events associated with novel medical treatments and/or surgical procedures.

Prophylactic and therapeutic effects of twice-daily famciclovir administration on infectious upper respiratory disease in shelter-housed cats

OBJECTIVES

In humans with herpetic disease, early or pre-emptive famciclovir therapy reduces disease duration and severity. This prospective, masked, placebo-controlled study tested therapeutic and prophylactic effects of two famciclovir doses given to cats for 7 days following shelter entry.

METHODS

Cats were assigned to prophylactic or therapeutic study arms based on clinical evidence of herpetic disease at study entry. Cats in the therapeutic arm received no treatment (n = 19), placebo (lactose; n = 18) or famciclovir at ~30 (n = 21) or ~90 mg/kg (n = 20) PO q12h for 7 days. Cats in the prophylactic arm received no treatment (n = 25) or famciclovir at ~30 (n = 28) or ~90 mg/kg (n = 27) PO q12h for 7 days. Disease scores, body weight, conjunctival feline herpesvirus 1 (FHV-1) shedding, and adoption rates were recorded on days 1 (admission), 8 (end of therapy) and 15 (1 week after cessation of therapy).

RESULTS

No significant differences in clinical scores were observed among groups in the prophylactic or therapeutic arms at any of the three time points. However, within the therapeutic arm, viral shedding on day 8 was significantly higher in cats receiving no treatment than in those receiving ~30 or ~90 mg/kg famciclovir, and this effect persisted 1 week after famciclovir was stopped (day 15) only in cats receiving ~30 mg/kg, although this approached significance in cats receiving ~90 mg/kg. No significant differences in adoption rates were detected among groups in either arm throughout the study.

CONCLUSIONS AND RELEVANCE

Although we did not demonstrate a statistically or clinically significant effect of famciclovir administration upon clinical signs of infectious upper respiratory disease or adoption, when it was administered at ~30 or ~90 mg/kg q12h for 1 week famciclovir reduced conjunctival FHV-1 shedding. This suggests a potential role in interrupting the infectious cycle within a shelter population; however, cost in time and resources, and stress and pathogen transmission induced by oral administration should be considered.

Medical management of deep ulcerative keratitis in cats: 13 cases

CASE SERIES SUMMARY

Described are 13 cats diagnosed with deep ulcerative keratitis and successfully managed medically without grafting procedures. Typical treatment involved frequent topical application of serum and antibiotics (usually a fluoroquinolone and a cephalosporin). Seven cats also received systemic antibiotics. Analgesia was achieved using various combinations of topical atropine and systemic buprenorphine, robenacoxib or corticosteroids. Six cats were hospitalized for a median (range) period of 2.5 (1-8) days, typically because of frequent medication administration. Median (range) follow-up time was 41.5 (9-103) days. Median (range) number of recheck examinations was 4 (2-6). Median (range) time to corneal re-epithelialization was 21 (9-103) days. Median (range) topical antibiotic course was 29.5 (16-103) days. Median (range) duration of Elizabethan collar use was 28 (13-73) days. At the time of writing, no further recheck examinations were recommended for 10 cats; median (range) time between initial to final examinations in these cats was 35 (20-103) days. All cats retained the affected globes and were apparently comfortable and visual at the latest recheck examination.

RELEVANCE AND NOVEL INFORMATION

These cases reveal that aggressive medical management is highly successful in select cats with deep ulcerative keratitis, and can result in a cosmetically acceptable, apparently comfortable and visual globe. However, therapy is intensive with frequent administration of multiple topical and sometimes systemic medications, and requires multiple veterinary visits over many weeks. Referral to a veterinary ophthalmologist for consideration of surgical stabilization is recommended, as not all cases may be amenable to the medical therapy described here.

Clinical findings and outcomes for dogs with uveodermatologic syndrome

OBJECTIVE To evaluate signalment, clinical signs, treatment, and factors affecting visual prognosis in dogs with uveodermatologic syndrome (UDS). DESIGN Retrospective case series and nested cohort study. ANIMALS 50 dogs (37 Akitas and 13 non-Akitas) with UDS evaluated at 4 ophthalmology practices. PROCEDURES Data were collected from the medical records regarding signalment, clinical signs, biopsy results, medications, adverse effects, vision and glaucoma status at initial and subsequent examinations, and duration of follow-up. Various factors were examined for associations with development of blindness or glaucoma following initial examination. RESULTS The most common ophthalmic signs included aqueous flare (n = 35 [70%]), iris abnormalities (29 [58%]), retinal detachment (23 [46%]), and choroidal depigmentation or chorioretinal infiltrates (10 [20%]). At initial examination, 36% (18/50) of dogs had glaucoma and 57% (26/46) were blind in both eyes. Twenty-five (50%) dogs had vision at their final visit, representing 78% of the 32 dogs that had vision at initial examination or regained vision during the follow-up period. In dogs that lost vision, median time to permanent blindness in both eyes was 13.5 months (range, 0.4 to 59 months) after initial examination. No significant associations with time to glaucoma or vision loss were identified for signalment variables, specific medications, or duration of clinical signs prior to initial examination. CONCLUSIONS AND CLINICAL RELEVANCE UDS commonly resulted in glaucoma, vision loss, or both in affected dogs. No evaluated factor was associated with visual prognosis; however, a subset of patients maintained vision through to the final recheck examination.

Evaluation of the major histocompatibility complex (MHC) class II as a candidate for sudden acquired retinal degeneration syndrome (SARDS) in Dachshunds

Objective

Sudden acquired retinal degeneration syndrome (SARDS) is one of the leading causes of acute blindness in dogs, with an unknown etiology and no effective treatment. Certain breeds such as Dachshunds are overrepresented among SARDS patients, and therefore, the syndrome is suspected to have a genetic component. The objective of this study was to determine if a genetic locus associated with SARDS in Dachshunds could be identified using a genome‐wide association study (GWAS).

Procedures

Genome‐wide association mapping was performed in 15 SARDS‐affected and 16 unaffected Dachshunds. Genotyping of three classical DLA class II genes (DLA‐DRB1, DLA‐DQA1, and DLA‐DQB1) was performed in 34 SARDS‐affected and 66 unaffected Dachshunds to evaluate for an association in this region.

Results

Although no single nucleotide polymorphisms (SNPs) were of genome‐wide statistical significance (P_Bonferroni < 0.05), 5 of the top 9 SNPs were in the major histocompatibility complex (MHC). Using DLA typing, the allele DLA‐DRB1*09401 was identified as a risk factor for the development of SARDS (P = 0.0032, OR = 4.0). The alleles DLA‐DQB1*00101 (P = 0.0050, OR = 0.31), DLA‐DQA1*00901 (P = 0.0087, OR = 0.33), and a previously identified DLA‐DRB1allele described as “DRB1‐T” (P = 0.0284, OR = 0.37) were identified as protective factors.

Conclusions

Although far from definitive, association of SARDS with alleles of immunologic importance further supports the hypothesis that autoimmunity may play a role in the pathogenesis of SARDS.

Ocular phenotypic consequences of a single copy deletion of the Yap1 gene (Yap1 +/-) in mice

PURPOSE

To identify the effects of a single copy deletion of Yap1 (Yap1 ^+/-) in the mouse eye, the ocular phenotypic consequences of Yap1 ^+/- were determined in detail.

METHODS

Complete ophthalmic examinations, as well as corneal esthesiometry, the phenol red thread test, intraocular pressure, and Fourier-domain optical coherence tomography were performed on Yap1 ^+/- and age-matched wild-type (WT) mice between eyelid opening (2 weeks after birth) and adulthood (2 months and 1 year after birth). Following euthanasia, enucleated eyes were characterized histologically.

RESULTS

Microphthalmia with small palpebral fissures, corneal fibrosis, and reduced corneal sensation were common findings in the Yap1 ^+/- mice. Generalized corneal fibrosis precluded clinical examination of the posterior structures. Histologically, thinning and keratinization of the corneal epithelium were observed in the Yap1 ^+/- mice in comparison with the WT mice. Distorted collagen fiber arrangement and hypercellularity of keratocytes were observed in the stroma. Descemet's membrane was extremely thin and lacked an endothelial layer in the Yap1 ^+/- mice. The iris was adherent to the posterior cornea along most of its surface creating a distorted contour. Most of the Yap1 ^+/- eyes were microphakic with swollen fibers and bladder cells. The retinas of the Yap1 ^+/- mice were normal at 2 weeks and 2 months of age, but the presence of retinal abnormalities, including retinoschisis and detachment, was markedly increased in the Yap1 ^+/- mice at 1 year of age.

CONCLUSIONS

The results show that the heterozygous deletion of the Yap1 gene in mice leads to complex ocular abnormalities, including microphthalmia, corneal fibrosis, anterior segment dysgenesis, and cataract.

A Population Study of Common Ocular Abnormalities in C57BL/6N rd8 Mice

Purpose

The purpose of this study was to quantify the frequency and severity of ocular abnormalities affecting wild-type C57BL/6N mice, the most common strain used worldwide for the creation of single-gene knockouts.

Methods

A total of 2773 animals (5546 eyes) were examined at one colony at UC Davis and in three more colonies at the Institut Clinique de la Souris in Strasbourg, France. Mice were examined at 15 to 16 weeks postnatal age by performing anterior segment biomicroscopy, posterior segment examination by indirect ophthalmoscopy, intraocular pressure measurement, and optical coherence tomography of anterior and posterior segment structures.

Results

Common ocular findings in the C57BL/6N strain included corneal deposits (3%), increased optical density of the anterior lens capsule (67%), punctate nuclear cataracts (98%), vitreous crystalline deposits (61%), hyaloid vascular remnant (6%), and retinal dysplasia attributed to the rd8 mutation (58%). Interestingly, retinal dysplasia was more common in male mice in all four breeding colonies evaluated in this study. The thickness of ocular tissues and compartments were measured by spectral-domain optical coherence tomography, including the central cornea, anterior chamber, vitreous, and retinal layers. Intraocular pressure was measured by rebound tonometry.

Conclusions

Ocular abnormalities are common in anterior and posterior segments of the C57BL/6N mouse, the most common background on which single-gene knockout mice have been made. It is important that vision scientists understand the extent and variability of ocular findings associated with this particular genetic background of mice.

Equine eosinophilic keratoconjunctivitis in California: retrospective study of 47 eyes from 29 cases (1993-2017)

OBJECTIVE

(a) To evaluate the epidemiology of equine eosinophilic keratoconjunctivitis (EK) in the western United States, (b) to ascertain the efficacy of keratectomy and diamond burr debridement vs medical management alone, (c) to determine the efficacy of various medical therapies, and (d) to further characterize the histopathologic findings of the disease in horses.

ANIMALS STUDIED

Twenty-nine horses (47 eyes) diagnosed with EK from 1993 to 2017.

PROCEDURE

Retrospective medical record review; owner questionnaire.

RESULTS

Average age of presentation was 11 ± 4 years. Warmbloods were significantly overrepresented (P = 0.024). Twenty horses were treated with medical therapy alone, five were treated with superficial lamellar keratectomy, and four were treated with diamond burr debridement. Follow-up data were available for 38 eyes of 23 horses. Median time to resolution for horses treated with either superficial keratectomy or diamond burr debridement (62 days) was not statistically significantly different from those that underwent medical therapy alone (46 days; P = 0.33). Eyes treated with topical steroids had a statistically significant longer median time to resolution (61 days) compared to those that did not receive topical steroid (44 days; P = 0.023). Common histopathologic findings in keratectomy samples included the presence of eosinophils, vascularization, and an eosinophilic membrane spanning areas of ulceration.

CONCLUSION

In this population, time to EK resolution was similar for horses treated with medical and surgical management. The use of topical steroids was associated with a prolonged time to resolution. Keratectomy samples from horses with EK had similar findings to those reported in other species.

A nonhuman primate model of inherited retinal disease

Inherited retinal degenerations are a common cause of untreatable blindness worldwide, with retinitis pigmentosa and cone dystrophy affecting approximately 1 in 3500 and 1 in 10,000 individuals, respectively. A major limitation to the development of effective therapies is the lack of availability of animal models that fully replicate the human condition. Particularly for cone disorders, rodent, canine, and feline models with no true macula have substantive limitations. By contrast, the cone-rich macula of a nonhuman primate (NHP) closely mirrors that of the human retina. Consequently, well-defined NHP models of heritable retinal diseases, particularly cone disorders that are predictive of human conditions, are necessary to more efficiently advance new therapies for patients. We have identified 4 related NHPs at the California National Primate Research Center with visual impairment and findings from clinical ophthalmic examination, advanced retinal imaging, and electrophysiology consistent with achromatopsia. Genetic sequencing confirmed a homozygous R565Q missense mutation in the catalytic domain of PDE6C, a cone-specific phototransduction enzyme associated with achromatopsia in humans. Biochemical studies demonstrate that the mutant mRNA is translated into a stable protein that displays normal cellular localization but is unable to hydrolyze cyclic GMP (cGMP). This NHP model of a cone disorder will not only serve as a therapeutic testing ground for achromatopsia gene replacement, but also for optimization of gene editing in the macula and of cone cell replacement in general.

Identification of genes required for eye development by high-throughput screening of mouse knockouts

Despite advances in next generation sequencing technologies, determining the genetic basis of ocular disease remains a major challenge due to the limited access and prohibitive cost of human forward genetics. Thus, less than 4,000 genes currently have available phenotype information for any organ system. Here we report the ophthalmic findings from the International Mouse Phenotyping Consortium, a large-scale functional genetic screen with the goal of generating and phenotyping a null mutant for every mouse gene. Of 4364 genes evaluated, 347 were identified to influence ocular phenotypes, 75% of which are entirely novel in ocular pathology. This discovery greatly increases the current number of genes known to contribute to ophthalmic disease, and it is likely that many of the genes will subsequently prove to be important in human ocular development and disease.

Bret Moore et al. from the International Mouse Phenotyping Consortium report the identification of 347 mouse genes that influence ocular phenotypes when knocked out. 75% of the identified genes have not previously been associated with any ocular pathology.

Whole genome variant association across 100 dogs identifies a frame shift mutation in DISHEVELLED 2 which contributes to Robinow-like syndrome in Bulldogs and related screw tail dog breeds

Domestic dog breeds exhibit remarkable morphological variations that result from centuries of artificial selection and breeding. Identifying the genetic changes that contribute to these variations could provide critical insights into the molecular basis of tissue and organismal morphogenesis. Bulldogs, French Bulldogs and Boston Terriers share many morphological and disease-predisposition traits, including brachycephalic skull morphology, widely set eyes and short stature. Unlike other brachycephalic dogs, these breeds also exhibit vertebral malformations that result in a truncated, kinked tail (screw tail). Whole genome sequencing of 100 dogs from 21 breeds identified 12.4 million bi-allelic variants that met inclusion criteria. Whole Genome Association of these variants with the breed defining phenotype of screw tail was performed using 10 cases and 84 controls and identified a frameshift mutation in the WNT pathway gene DISHEVELLED 2 (DVL2) (Chr5: 32195043_32195044del, p = 4.37 X 10-37) as the most strongly associated variant in the canine genome. This DVL2 variant was fixed in Bulldogs and French Bulldogs and had a high allele frequency (0.94) in Boston Terriers. The DVL2 variant segregated with thoracic and caudal vertebral column malformations in a recessive manner with incomplete and variable penetrance for thoracic vertebral malformations between different breeds. Importantly, analogous frameshift mutations in the human DVL1 and DVL3 genes cause Robinow syndrome, a congenital disorder characterized by similar craniofacial, limb and vertebral malformations. Analysis of the canine DVL2 variant protein showed that its ability to undergo WNT-induced phosphorylation is reduced, suggesting that altered WNT signaling may contribute to the Robinow-like syndrome in the screwtail breeds.

Biomechanical changes to Descemet's membrane precede endothelial cell loss in an early-onset murine model of Fuchs endothelial corneal dystrophy

Early-onset Fuchs endothelial corneal dystrophy (FECD) has been associated with nonsynonymous mutations in collagen VIII α2 (COL8A2), a key extracellular matrix (ECM) protein in Descemet's membrane (DM). Two knock-in strains of mice have been generated to each express a mutant COL8A2 protein (Col8a2^L450W/L450W and Col8a2^Q455K/Q455K) that recapitulate the clinical phenotype of early-onset FECD including endothelial cell loss, cellular polymegathism and pleomorphism, and guttae. Due to abnormalities in ECM protein composition and structure in FECD, the stiffness of DM in Col8a2 knock-in mice and wildtype (WT) controls was measured using atomic force microscopy at 5 and 10 months of age, coinciding with the onset of FECD phenotypic abnormalities. At 5 months, only sporadic guttae were identified via in vivo confocal microscopy (IVCM) in Col8a2^Q455K/Q455K mice, otherwise both strains of Col8a2 transgenic mice were indistinguishable from WT controls in terms of endothelial cell density and size. By 10 months of age, Col8a2^L450W/L450W and Col8a2^Q455K/Q455K mice developed reduced corneal endothelial density, increased endothelial cell area and guttae, with the Col8a2^Q455K/Q455K strain exhibiting a more severe phenotype. However, at 5 months of age, prior to the development endothelial cell abnormalities, Col8a2^L450W/L450W and Col8a2^Q455K/Q455K mice knock-in mice had reduced tissue stiffness of DM that was statistically significant in the Col8a2^Q455K/Q455K mice when compared with wildtype controls. These data indicate that alterations in the tissue compliance of DM precede phenotypic changes in endothelial cell count and morphology, and may play a role in onset and progression of FECD.

Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease

Several ultrasonic and Fourier-domain optical coherence tomography (FD-OCT) pachymeters are used to measure corneal thickness in canine patients and research subjects. This study assessed the reliability of and consistency between two ultrasonic pachymetry (USP) devices, Pachette 3 and Accupach VI, as well as automated and manual measurements obtained using FD-OCT in dogs with and without corneal disease. Corneal thickness measurements were compiled from 108 dogs and analyzed using mixed effects linear regression, with Bonferonni adjustments for post-hoc comparisons, to determine the effects of age, weight and disease state. Data are presented as predicted mean±standard error. Canine corneal disease can result in marked increases in thickness that frequently exceed the upper limits of measurement of some pachymetry devices developed for human use. In this study, the corneas of dogs with endothelial disease or injury frequently exceeded the upper limits of quantitation of 999 and 800μm for the Accupach VI and automated FD-OCT pachymeters, respectively. Using values <800μm, the Pachette 3 generated significantly greater values for central corneal thickness (CCT) than the Accupach VI, manual FD-OCT and automated FD-OCT at 625±7.0, 615±7.2, 613±7.2, and 606±7.4μm respectively (P<0.001). Of the two devices where measurements >1000μm were obtained, manual FD-OCT demonstrated less variability than the Pachette 3. Corneal thickness increased linearly with age and weight with an increase of 6.9±1.8μm/year and 1.6±0.8μm/kg body weight (P<0.005 and P=0.038, respectively).

Modulation of human corneal stromal cell differentiation by hepatocyte growth factor and substratum compliance

Corneal wound healing is a complex process that consists of cellular integration of multiple soluble biochemical cues and cellular responses to biophysical attributes associated with the matrix of the wound space. Upon corneal stromal wounding, the transformation of corneal fibroblasts to myofibroblasts is promoted by transforming growth factor-β (TGFβ). This process is critical for wound healing; however, excessive persistence of myofibroblasts in the wound space has been associated with corneal fibrosis resulting in severe vision loss. The objective of this study was to determine the effect of hepatocyte growth factor (HGF), which can modulate TGFβ signaling, on corneal myofibroblast transformation by analyzing the expression of α-smooth muscle actin (αSMA) as a marker of myofibroblast phenotype particularly as it relates to biomechanical cues. Human corneal fibroblasts were cultured on tissue culture plastic (>1 GPa) or hydrogel substrates mimicking human normal or wounded corneal stiffness (25 and 75 kPa) in media containing TGFβ1 ± HGF. The expression of αSMA was analyzed by quantitative PCR, Western blot and immunocytochemistry. Cellular stiffness, which is correlated with cellular phenotype, was measured by atomic force microscopy (AFM). In primary human corneal fibroblasts, the mRNA expression of αSMA showed a clear dose response to TGFβ1. The expression was significantly suppressed when cells were incubated with 20 ng/ml HGF in the presence of 2 ng/ml of TGFβ1. The protein expression of αSMA induced by 5 ng/ml TGFβ1 was also decreased by 20 ng/ml of HGF. Cells cultured on hydrogels mimicking human normal (25 kPa) and fibrotic (75 kPa) cornea also showed an inhibitory effect of HGF on αSMA expression in the presence or absence of TGFβ1. Cellular stiffness was decreased by HGF in the presence of TGFβ1 as measured by AFM. In this study, we have demonstrated that HGF can suppress the myofibroblast phenotype promoted by TGFβ1 in human corneal stromal cells. These data suggest that HGF holds the potential as a therapeutic agent to improve wound healing outcomes by minimizing corneal fibrosis.

Effects of 5% sodium chloride ophthalmic ointment on thickness and morphology of the normal canine cornea

OBJECTIVE

To determine the effect of 5% sodium chloride ophthalmic ointment (5% NaCl) on thickness and morphology of the normal canine cornea using ultrasonic pachymetry (USP), in vivo confocal microscopy (IVCM), and Fourier-domain optical coherence tomography (FD-OCT).

METHODS

Five healthy laboratory Beagles received ophthalmic examinations including USP, IVCM, and FD-OCT prior to and at fixed intervals following treatment. The right and left eyes were treated with 5% NaCl and artificial tears ophthalmic ointment (AT), respectively, every 2 hours for 4 treatments/d (days 2-9), and then hourly for 7 treatments/d (day 10). Treatment groups were statistically compared using mixed-effects linear regression.

RESULTS

Treatment with 5% NaCl resulted in a 12 μm decrease in corneal thickness from baseline (P < .001), while there was no significant difference in corneal thickness between values obtained at baseline and following treatment with AT (P = .82). Epithelial cell density significantly increased from baseline (530 ± 52 cells/mm² ) to 577 ± 43 and 567 ± 15 cells/mm² with 5% NaCl and AT, respectively (P = .003 and .005, respectively). However, keratocyte cell density in the anterior and posterior stroma and endothelial cell density did not significantly differ following treatment with 5% NaCl or AT ointment (P > .05).

CONCLUSIONS

Short-term topical treatment with 5% NaCl decreased corneal thickness in normal dogs with no observable changes in corneal morphology or signs of ocular toxicity.

Genetic analysis of optic nerve head coloboma in the Nova Scotia Duck Tolling Retriever identifies discordance with the NHEJ1 intronic deletion (collie eye anomaly mutation)

Collie eye anomaly (CEA) encompasses a spectrum of different ophthalmic phenotypes from clinically inconsequential choroidal hypoplasia to blindness from coloboma of the optic nerve head (ONH). A previous study found a 7.8-kb deletion in intron 4 of the NHEJ1 gene to be associated with CEA. A genetic test based on this association is recommended for many breeds, including the Nova Scotia Duck Tolling Retriever (NSDTR). Collection of ONH coloboma-affected NSDTR showed lack of concordance of the NHEJ1 intronic deletion with ONH coloboma. Using genomewide single nucleotide polymorphism (SNP) genotyping in 7 ONH coloboma-affected NSDTR cases and 47 unaffected NSDTR controls with no ophthalmic signs, one SNP, located on chromosome 7, demonstrated genomewide significance. However, high genomic inflation may have confounded the results. Therefore, the genomewide association study was repeated using EMMAX to control for population structure in the cohort of 7 cases and 47 controls. However, no regions of the genome were significantly associated with ONH coloboma. These results failed to document significant association with the CEA locus. Due to the complex genetic etiology of ONH coloboma, the NHEJ1 intronic deletion test results should be carefully considered when making breeding decisions. If the goal is to select for visually competent dogs, our data suggest that eye examinations of puppies would be more effective as a guide in selection of breeding pairs than relying solely on currently available genetic tests.

Comparison of chorioretinal layers in rhesus macaques using spectral-domain optical coherence tomography and high-resolution histological sections

Nonhuman primates are important preclinical models of retinal diseases because they uniquely possess a macula similar to humans. Ocular imaging technologies such as spectral-domain optical coherence tomography (SD-OCT) allow noninvasive, in vivo measurements of chorioretinal layers with near-histological resolution. However, the boundaries are based on differences in reflectivity, and detailed correlations with histological tissue layers have not been explored in rhesus macaques, which are widely used for biomedical research. Here, we compare the macular anatomy and thickness measurements of chorioretinal layers in rhesus macaque eyes using SD-OCT and high-resolution histological sections. Images were obtained from methylmethacrylate-embedded histological sections of 6 healthy adult rhesus macaques, and compared with SD-OCT images from 6 age-matched animals. Thicknesses of chorioretinal layers were measured across the central 3 mm macular region using custom semi-automated or manual software segmentation, and compared between the two modalities. We found that histological sections provide better distinction between the ganglion cell layer (GCL) and inner plexiform layer (IPL) than SD-OCT imaging. The first hyperreflective band between the external limiting membrane (ELM) and retinal pigment epithelium (RPE) appears wider on SD-OCT than the junction between photoreceptor inner and outer segments seen on histology. SD-OCT poorly distinguishes Henle nerve fibers from the outer nuclear layer (ONL), while histology correctly identifies these fibers as part of the outer plexiform layer (OPL). Overall, the GCL, inner nuclear layer (INL), and OPL are significantly thicker on histology, especially at the fovea; while the ONL, choriocapillaris (CC), and outer choroid (OC) are thicker on SD-OCT. Our results show that both SD-OCT and high-resolution histological sections allow reliable measurements of chorioretinal layers in rhesus macaques, with distinct advantages for different sublayers. These findings demonstrate the effects of tissue processing on chorioretinal anatomy, and provide normative values for chorioretinal thickness measurements on SD-OCT for future studies of disease models in these nonhuman primates.

Latrunculin B and substratum stiffness regulate corneal fibroblast to myofibroblast transformation

The transformation of keratocytes and fibroblasts to myofibroblasts is important to corneal wound healing as well as formation of stromal haze. The purpose of this study was to determine the effect of latrunculin B, an actin cytoskeleton disruptor in conjunction with a fundamental biophysical cue, substrate stiffness, on myofibroblast transformation in vitro and in vivo. Rabbit corneal fibroblasts were cultured on substrates of differing compliance (1.5, 22, and 71 kPa) and tissue culture plastic (TCP; > 1 GPa) in media containing 0 or 10 ng/ml TGFβ1 for 72 h. Cells were treated with 0.4 μM Lat-B or DMSO for 30 min every 24 h for 72 h. RNA was collected from cells and expression of alpha-smooth muscle actin (α-SMA), keratocan, and ALDH1A1 determined using qPCR; immunocytochemistry was used to assess α-SMA protein expression. A rabbit phototherapeutic keratectomy (PTK) model was used to assess the impact of 0.1% Lat-B (n = 3) or 25% DMSO (vehicle control, n = 3) on corneal wound healing by assessment of epithelial wound size with fluorescein stain and semi-quantitative stromal haze scoring by an observer masked to treatment group as well as Fourier-domain optical coherence tomography (FD-OCT) at set time points. Statistical analysis was completed using one-way or two-way analysis of variance. Treatment with Lat-B versus DMSO resulted in significantly less αSMA mRNA (P ≤ 0.007) for RCF cells grown on 22 and 71 kPa substrates as well as TCP without or with TGFβ1, and significantly decreased α-SMA protein expression in RCFs cultured on the intermediate (22 kPa) stiffness in the absence (P = 0.028) or presence (P = 0.018) of TGFβ1. Treatment with Lat-B versus DMSO but did not significantly alter expression of keratocan or ALDH1A1 mRNA in RCFs (P > 0.05) in the absence or presence of TGFβ1, but RCFs grown on stiff hydrogels (71 kPa) had significantly more keratocan mRNA expression versus the 22 kPa hydrogel or TCP (P < 0.001) without TGFβ1. Administration of topical Lat-B BID was well tolerated by rabbits post-PTK but did not significantly alter epithelial wound closure, stromal haze score, stromal haze thickness as measured by FD-OCT in comparison to DMSO-treated rabbits. When corneal stromal cells are cultured on substrates possessing biologically relevant substratum stiffnesses, Lat-B modulates mRNA and protein expression of α-SMA and thus modulates myofibroblast transformation. At a dose and dose-frequency that reduced IOP in human glaucoma patients, Lat-B treatment did not substantially impact corneal epithelial or stromal wound healing in a rabbit PTK model. While a significant impact on wound healing was observed at the concentration and dose frequency reported here was not found, encouraging in vitro data support further investigations of topically applied Lat-B to determine if this compound can reduce stromal fibrosis.

The role of hepatocyte growth factor in corneal wound healing

Hepatocyte growth factor (HGF) is a glycoprotein produced by mesenchymal cells and operates as a key molecule for tissue generation and renewal. During corneal injury, HGF is primarily secreted by stromal fibroblasts and promotes epithelial wound healing in a paracrine manner. While this mesenchymal-epithelial interaction is well characterized in various organs and the cornea, the role of HGF in corneal stromal and endothelial wound healing is understudied. In addition, HGF has been shown to play an anti-fibrotic role by inhibiting myofibroblast generation and subsequent production of a disorganized extracellular matrix and tissue fibrosis. Therefore, HGF represents a potential therapeutic tool in numerous organs in which myofibroblasts are responsible for tissue scarring. Corneal fibrosis can be a devastating sequela of injury and can result in corneal opacification and retrocorneal membrane formation leading to severe vision loss. In this article, we concisely review the available literature regarding the role of HGF in corneal wound healing. We highlight the influence of HGF on cellular behaviors in each corneal layer. Additionally, we suggest the possibility that HGF may represent a therapeutic tool for interrupting dysregulated corneal repair processes to improve patient outcomes.

Phenotypic Characterization of Corneal Endothelial Dystrophy in German Shorthaired and Wirehaired Pointers Using In Vivo Advanced Corneal Imaging and Histopathology

PURPOSE

To evaluate corneal morphology using ultrasonic pachymetry (USP), Fourier-domain optical coherence tomography (FD-OCT), and in vivo confocal microscopy (IVCM) in 2 related canine breeds-German shorthaired pointers (GSHPs) and German wirehaired pointers (GWHPs)-with and without corneal endothelial dystrophy (CED). This condition is characterized by premature endothelial cell degeneration leading to concomitant corneal edema and is similar to Fuchs endothelial corneal dystrophy.

METHODS

Corneas of 10 CED-affected (4 GSHP and 6 GWHP) and 19 unaffected, age-matched (15 GSHP and 4 GWHP) dogs were examined using USP, FD-OCT, and IVCM. A 2-sample t test or Mann-Whitney rank-sum test was used to statistically compare parameters between both groups. Data are presented as mean ± SD or median (range).

RESULTS

Central corneal thickness determined using USP was significantly greater in CED-affected than in unaffected dogs at 1179 (953-1959) and 646 (497-737) μm, respectively (P < 0.001). Central epithelial thickness was found to be significantly decreased in CED-affected versus unaffected dogs at 47 ± 7.1 and 55 ± 7.1 μm, respectively (P = 0.011), using FD-OCT. With IVCM, corneal endothelial density was significantly less (P < 0.001) in 5 dogs with CED versus 19 unaffected controls at 499 ± 315 versus 1805 ± 298 cells/mm, respectively. CED-affected dogs exhibited endothelial pleomorphism and polymegethism, whereas CED-unaffected dogs had regular hexagonal arrangement of cells.

CONCLUSIONS

GSHPs and GWHPs with CED exhibit marked differences in corneal morphology when compared with age-matched control dogs. These 2 CED-affected breeds represent spontaneous, large animal models for human Fuchs endothelial corneal dystrophy.