Brent A. Bell

This study characterizes a fluorescent Slc17a6 ‐tdTomato neuronal reporter mouse line with strong labeling of axons throughout the optic nerve, of retinal ganglion cell (RGC) soma in the ganglion cell layer (GCL), and of RGC dendrites in the inner plexiform layer (IPL). The model facilitated assessment of RGC loss in models of degeneration and of RGC detection in mixed neural/glial cultures. The tdTomato signal showed strong overlap with >98% cells immunolabeled with RGC markers RBPMS or BRN3A, consistent with the ubiquitous presence of the vesicular glutamate transporter 2 (VGUT2, SLC17A6) in all RGC subtypes. There was no cross‐labeling of ChAT‐positive displaced amacrine cells in the GCL, although some signal emanated from the outer plexiform layer, consistent with horizontal cells. The fluorescence allowed rapid screening of RGC loss following optic nerve crush and intraocular pressure (IOP) elevation. The bright fluorescence also enabled non‐invasive monitoring of extensive neurite networks and neuron/astrocyte interactions in culture. Robust Ca ²⁺ responses to P2X7R agonist BzATP were detected from fluorescent RGCs using Ca ²⁺ ‐indicator Fura‐2. Fluorescence from axons and soma was detected in vivo with a confocal scanning laser ophthalmoscope (cSLO); automatic RGC soma counts enhanced through machine learning approached the numbers found in retinal wholemounts. Controls indicated no impact of Slc17a6 ‐tdTomato expression on light‐dependent neuronal function as measured with a microelectrode array (MEA), or on retinal structure as measured with optical coherence tomography (OCT). In summary, the bright fluorescence in axons, dendrites and soma of ~all RGCs in the Slc17a6 ‐tdTomato reporter mouse may facilitate the study of RGCs.

Optical coherence tomography (OCT) is a non-invasive imaging technique that generates cross-sectional images of biological tissues at millimeter-level penetration depth with micron-level resolution. In this study, we developed a custom spectral-domain OCT system equipped with a flash stimulus module for dual-modality imaging of mouse retinal structure and function. The axial resolution of the system reached ∼2.7/2 μm in air/tissue following optimization and calibration. We deployed this system to conduct in vivo OCT structural imaging and optoretinography (ORG) functional assessment of mouse retina to investigate the effects of three anesthesia regimens. Statistical analysis of the results indicates that anesthesia results in a smaller relative intensity of inner/outer segment junction and external limiting membrane and a thickening of the outer segment compared to an awake state. Meanwhile, significant differences were observed in the effects on retinal structure and function between isoflurane and tribromoethanol anesthesia, while differences between isoflurane and esketamine+xylazine groups were small. These findings suggest that the type of anesthetic should be taken into account when comparing imaging results across studies reported in the literature.

Lipid processing by the retinal pigment epithelium (RPE) is necessary to maintain retinal health and function. Dysregulation of retinal lipid homeostasis due to normal aging or age‐related disease triggers lipid accumulation within the RPE, on Bruch's membrane (BrM), and in the subretinal space. In its role as a hub for lipid trafficking into and out of the neural retina, the RPE packages a significant amount of lipid into lipid droplets for storage and into apolipoprotein B (APOB)‐containing lipoproteins (Blps) for export. Microsomal triglyceride transfer protein (MTP), encoded by the MTTP gene, is essential for Blp assembly. Herein we test the hypothesis that MTP expression in the RPE is essential to maintain lipid balance and retinal function using the newly generated RPEΔMttp mouse model. Using non‐invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic depletion of Mttp from the RPE results in intracellular lipid accumulation, increased photoreceptor‐associated cholesterol deposits, and photoreceptor cell death, and loss of rod but not cone function. RPE‐specific reduction in Mttp had no significant effect on plasma lipids and lipoproteins. While APOB was decreased in the RPE, most ocular retinoids remained unchanged, with the exception of the storage form of retinoid, retinyl ester. Thus suggesting that RPE MTP is critical for Blp synthesis and assembly but is not directly involved in plasma lipoprotein metabolism. These studies demonstrate that RPE‐specific MTP expression is necessary to establish and maintain retinal lipid homeostasis and visual function.

The observation of retinal lesions in the posterior pole of laboratory mice has been found to occur for many reasons, some of which are due to native, developmental abnormalities and those that are influenced by environmental or experimental conditions. Herein, we investigated the rate and extent of retinal lesions as a result of prolonged ocular exposure following general anesthesia. Mice were housed under standard animal care conditions and transported to the laboratory for experimental preparation induction procedures (EPIP) involving general anesthesia, mydriasis/cycloplegia, and topical anesthesia to the cornea. Following EPIP, two ocular recovery conditions (protected and unprotected) were tested within two different animal recovery chambers (open or closed). During anesthesia recovery, and extending up to 2.5 months thereafter, the anterior and posterior poles were evaluated using digital color photography, scanning laser ophthalmoscopy, and spectral-domain optical coherence tomography to document the effects of eye protection and chamber recovery type on the development of retinal lesions. In some mice, electroretinograms and histological evaluations were performed to assess functional and structural changes that accompanied the retinal lesions detected by in vivo imaging. We found that the anterior segments of mice recovered in the open chamber with unprotected eyes showed substantial acute changes. At 1-hour post-EPIP, the anterior chamber exhibited corneal thinning, severe media opacities, a reduction in anterior chamber depth, and ocular lens prolapse. These changes largely resolved upon recovery. At 3- and 14-days post-EPIP, inspection of the posterior pole by fundus imaging revealed prominent lesions in the outer retina in a significant proportion of mice recovered in the open chamber. ERG testing conducted at 1-month post-EPIP revealed compromised functional responses in the eyes of affected vs. unaffected mice. Imaging at 14-days post-EPIP revealed that the outer retina lesions in affected mice almost wholly resolve over time to nearly insignificant levels. However, data collected at 80-days post-EPIP demonstrates that some lingering effects persist long-term and appear to be confined to the retinal pigment epithelium. In comparison, mice recovered in the closed chamber with unprotected eyes experienced only mild lens opacities at 1-hr post EPIP that cleared following a full recovery from the effects of sedation. Furthermore, protected eyes of mice recovered in either the open or closed chamber were completely devoid of any anterior or posterior pole complications. In sum, prolonged ocular surface exposure to circulating ambient room air leads to significant anterior and posterior segment ocular complications. We interpret these changes to be caused by dehydration and desiccation of the corneal surface of the eye. The most abundant, semi-reversible complication observed was the development of lesions in the outer retina, which had a 90% probability of occurring after 45 minutes of exposure. The lesions largely absolved short-term but some imaging evidence suggests that they may persist months after their initial appearance.Disclosures: B.A. Bell, none; V.L. Bonilha, none; S.A. Hagstrom, none; B.Anand-Apte, none; 14 J.G. Hollyfield, none; I.S. Samuels, none.Grant Information: Research reported in this publication was supported by the National Eye Institute of the National Institutes of Health under award numbers P30EY025585, R01EY016490, RO1EY026181, RO1EY027083, R01EY014240 and R01EY027750, US Dept. of Veterans Affairs Biomedical Laboratory Research and Development Service VA Merit Award I01BX002754, an unrestricted grant from the Research to Prevent Blindness to the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Foundation for Fighting Blindness Research Center Grant, The Wolf Family Foundation, the Llura and Gordon Gund Foundation and the Cleveland Clinic. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the US Dept. of Veterans Affairs.

The predominant function of the blood‐retinal barrier (BRB) is to maintain retinal homeostasis by regulating the influx and efflux between the blood and retina. Breakdown of the BRB occurs in a number of ocular diseases that result in vision loss. Understanding the molecular and cellular pathways involved in the development and maintenance of the BRB is critical to developing therapeutics for these conditions. To visualize the BRB in vivo , we used the transgenic Tg(l‐fabp:DBP‐EGFP:flk1:mCherry) zebrafish model that expresses vitamin D binding protein (a member of the albumin gene family) tagged to green fluorescent protein. Retinoic acid (RA) plays a number of important roles in vertebrate development and has been shown to play a protective role during inflammation‐induced blood‐brain barrier disruption. The role of RA in BRB development and maintenance remains unknown. To disrupt RA signaling, Tg(l‐fabp:DBP‐EGFP:flk1:mCherry) zebrafish were treated with N, N‐diethylaminobenzaldehyde and 4‐[(1E)‐2‐[5, 6‐dihydro‐5, 5‐dimethyl‐8‐(2‐phenylethynyl)‐2‐naphthalenyl]ethenyl] benzoic acid, which are antagonists of retinal dehydrogenase and the RA receptor, respectively. Treatment with either compound resulted in BRB disruption and reduced visual acuity, whereas cotreatment with all ‐ trans RA effectively rescued BRB integrity. Additionally, transgenic overexpression of Cyp26a1, which catalyzes RA degradation, resulted in breakdown of the BRB. Our results demonstrate that RA signaling is critical for maintenance of the BRB and could play a role in diseases such as diabetic macular edema.—Pollock, L. M., Xie, J., Bell, B. A., Anand‐Apte, B. Retinoic acid signaling is essential for maintenance of the blood‐retinal barrier. FASEB J. 32, 5674–5684 (2018). www.fasebj.org

Noninvasive ocular imaging platforms are undeniably useful in identifying retinal abnormalities. The purpose of this study was to investigate a novel method for integrating information acquired from two independent imaging platforms, AF-SLO and SDOCT, in order to demonstrate retinal perturbations as a result of genetic or pharmacological manipulation. Two cohorts of mice were investigated, Nyx ^nob and C57BL/6 J. In Nyx ^nob mice, SLO revealed an atypical but variable amount of autofluorescent foci (AFF); SDOCT showed altered photoreceptor outer segment architecture. Naïve Nyx ^nob had significantly more AFF than C57BL/6 J, suggesting that Nyx ^nob have some predisposition for developing AFF. Interestingly, both findings were significantly ameliorated in diabetic Nyx ^nob mice as compared to the controls. These data were incorporated into a novel analysis plot comparing AF-SLO and SDOCT results. The integration of the qualitative changes and accompanying quantitative analysis approach described herein provide a sensitive means for detecting whether a mouse model is susceptible to degeneration before other hallmark indicators are observed.

In addition to its conventional roles in the innate immune system, complement has been found to directly regulate T cells in the adaptive immune system. Complement components, including C3, C5, and factor D, are important in regulating T cell responses. However, whether complement component C4 is involved in regulating T cell responses remains unclear. In this study, we used a T cell-dependent model of autoimmunity, experimental autoimmune uveitis (EAU) to address this issue. We compared disease severity in wild-type (WT) and C4 knockout (KO) mice using indirect ophthalmoscopy, scanning laser ophthalmoscopy, spectral-domain optical coherence tomography, and histopathological analysis. We also explored the underlying mechanism by examining T cell responses in ex vivo antigen-specific recall assays and in in vitro T cell priming assays using bone marrow-derived dendritic cells, splenic dendritic cells, and T cells from WT or C4 KO mice. We found that C4 KO mice develop less severe retinal inflammation than WT mice in EAU and show reduced autoreactive T cell responses and decreased retinal T cell infiltration. We also found that T cells, but not dendritic cells, from C4 KO mice have impaired function. These results demonstrate a previously unknown role of C4 in regulating T cell responses, which affects the development of T cell-mediated autoimmunity, as exemplified by EAU. Our data could shed light on the pathogenesis of autoimmune uveitis in humans.

Purpose To evaluate the histopathology in donor eyes from patients with autosomal dominant retinitis pigmentosa (ADRP) caused by p.P23H, p.P347T and p.P347L rhodopsin ( RHO ) gene mutations. Methods Eyes from a 72-year-old male (donor 1), an 83-year-old female (donor 2), an 80-year-old female (donor 3), and three age-similar normal eyes were examined macroscopically, by scanning laser ophthalmoscopy and optical coherence tomography imaging. Perifoveal and peripheral pieces were processed for microscopy and immunocytochemistry with markers for photoreceptor cells. Results DNA analysis revealed RHO mutations c.68C>A (p.P23H) in donor 1, c.1040C>T (p.P347L) in donor 2 and c.1039C>A (p.P347T) in donor 3. Histology of the ADRP eyes showed retinas with little evidence of stratified nuclear layers in the periphery and a prominent inner nuclear layer present in the perifoveal region in the p.P23H and p.P347T eyes, while it was severely atrophic in the p.P347L eye. The p.P23H and p.P347T mutations cause a profound loss of rods in both the periphery and perifovea, while the p.P347L mutation displays near complete absence of rods in both regions. All three rhodopsin mutations caused a profound loss of cones in the periphery. The p.P23H and p.P347T mutations led to the presence of highly disorganized cones in the perifovea. However, the p.P347L mutation led to near complete absence of cones also in the perifovea. Conclusions Our results support clinical findings indicating that mutations affecting residue P347 develop more severe phenotypes than those affecting P23. Furthermore, our results indicate a more severe phenotype in the p.P347L retina as compared to the p.P347T retina.