Evisceration of mouse vitreous and retina for proteomic analyses

5' Transgenes drive leaky expression of 3' transgenes in Cre-inducible bi-cistronic vectors

Molecular cloning techniques enabling contemporaneous expression of two or more protein-coding sequences provide an invaluable tool for understanding the molecular regulation of cellular functions. The Cre-lox system is used for inducing the expression of recombinant proteins encoded within a bi-/poly-cistronic cassette. However, leak expression of transgenes is often observed in the absence of Cre recombinase activity, compromising the utility of this approach. To investigate the mechanism of leak expression, we generated Cre-inducible bi-cistronic vectors to monitor the expression of transgenes positioned either 5' or 3' of a 2A peptide or internal ribosomal entry site (IRES) sequence. Cells transfected with these bi-cistronic vectors exhibited Cre-independent leak expression specifically of transgenes positioned 3' of the 2A peptide or IRES sequence. Similarly, AAV-FLEX vectors encoding bi-cistronic cassettes or fusion proteins revealed the selective Cre-independent leak expression of transgenes positioned at the 3' end of the open reading frame. Our data demonstrate that 5' transgenes confer promoter-like activity that drives the expression of 3' transgenes. An additional lox-STOP-lox cassette between the 2A sequence and 3' transgene dramatically decreased Cre-independent transgene expression. Our findings highlight the need for appropriate experimental controls when using Cre-inducible bi-/poly-cistronic constructs and inform improved design of vectors for more tightly regulated inducible transgene expression.

Investigation of Cas9 antibodies in the human eye

Preexisting immunity against Cas9 proteins in humans represents a safety risk for CRISPR–Cas9 technologies. However, it is unclear to what extent preexisting Cas9 immunity is relevant to the eye as it is targeted for early in vivo CRISPR–Cas9 clinical trials. While the eye lacks T-cells, it contains antibodies, cytokines, and resident immune cells. Although precise mechanisms are unclear, intraocular inflammation remains a major cause of vision loss. Here, we used immunoglobulin isotyping and ELISA platforms to profile antibodies in serum and vitreous fluid biopsies from human adult subjects and Cas9-immunized mice. We observed high prevalence of preexisting Cas9-reactive antibodies in serum but not in the eye. However, we detected intraocular antibodies reactive to S. pyogenes-derived Cas9 after S. pyogenes intraocular infection. Our data suggest that serum antibody concentration may determine whether specific intraocular antibodies develop, but preexisting immunity to Cas9 may represent a lower risk in human eyes than systemically.

Pre-existing antibodies against Cas9 proteins represent a potential issue for gene therapies, including those targeting the eye. Here the authors assess the presence of intraocular antibodies, and show that Cas9 antibodies were prevalent in human serum but not the eye, unless prior bacterial infection occurred.

Distinctive waves of innate immune response in the retina in experimental autoimmune encephalomyelitis

Neurodegeneration mediates neurological disability in inflammatory demyelinating diseases of the CNS. The role of innate immune cells in mediating this damage has remained controversial with evidence for destructive and protective effects. This has complicated efforts to develop treatment. The time sequence and dynamic evolution of the opposing functions are especially unclear. Given limits of in vivo monitoring in human diseases such as multiple sclerosis (MS), animal models are warranted to investigate the association and timing of innate immune activation with neurodegeneration. Using noninvasive in vivo retinal imaging of experimental autoimmune encephalitis (EAE) in CX3CR1^GFP/+–knock-in mice followed by transcriptional profiling, we are able to show 2 distinct waves separated by a marked reduction in the number of innate immune cells and change in cell morphology. The first wave is characterized by an inflammatory phagocytic phenotype preceding the onset of EAE, whereas the second wave is characterized by a regulatory, antiinflammatory phenotype during the chronic stage. Additionally, the magnitude of the first wave is associated with neuronal loss. Two transcripts identified — growth arrest–specific protein 6 (GAS6) and suppressor of cytokine signaling 3 (SOCS3) — might be promising targets for enhancing protective effects of microglia in the chronic phase after initial injury.

Diabetes Induced Alterations in Murine Vitreous Proteome Are Mitigated by IL-6 Trans-Signaling Inhibition

Purpose

Diabetic retinopathy (DR) is a microvascular complication caused by prolonged hyperglycemia and characterized by leaky retinal vasculature and ischemia-induced angiogenesis. Vitreous humor is a gel-like biofluid in the posterior segment of the eye between the lens and the retina. Disease-related changes are observed in the biochemical constituents of the vitreous, including proteins and macromolecules. Recently, we found that IL-6 trans-signaling plays a significant role in the vascular leakage and retinal pathology associated with DR. Therefore, in this study, comprehensive proteomic profiling of the murine vitreous was performed to identify diabetes-induced alterations and to determine effects of IL-6 trans-signaling inhibition on these changes.

Methods

Vitreous samples from mice were collected by evisceration, and proteomic analyses were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS).

Results

A total of 154 proteins were identified with high confidence in control mice and were considered to be characteristic of healthy murine vitreous fluid. The levels of 72 vitreous proteins were significantly altered in diabetic mice, including several members of heat shock proteins, 14-3-3 proteins, and tubulins. Alterations in 52 out of 72 proteins in diabetic mice were mitigated by IL-6 trans-signaling inhibition.

Conclusions

Proteomic analysis of murine vitreous fluid performed in this study provides important information about the changes caused by diabetes in the ocular microenvironment. These diabetes-induced alterations in the murine vitreous proteome were mitigated by IL-6 trans-signaling inhibition. These findings further support that IL-6 trans-signaling may be an important therapeutic target for the treatment of DR.

Retrobulbar administration of purified anti-nerve growth factor in developing rats induces structural and biochemical changes in the retina and cornea

AIM

To develop an experimental model of endogenous nerve growth factor (NGF) deprivation by retrobulbar administration of purified neutralizing anti-NGF antibodies in young Sprague-Dawley rats and provide further information on NGF expression in the retina and cornea.

METHODS

Sixty old pathogen-free Sprague Dawley rats (p14, post-natal days) were treated with repeated retrobulbar injections of neutralizing anti-NGF (2 µL, 100 µg/mL, every 3d). After 2wk (p28), retinal and corneal tissues were investigated for morphological, biochemical, and molecular expression of trkA^NGFR by using Western blotting or immunofluorescence. Rhodopsin as well as protein profile expression were also investigated.

RESULTS

Chronic retrobulbar neutralizing anti-NGF antibodies changed the distribution of trkA^NGFR immunoreactivity at retinal level, while no changes were detected for global trkA^NGFR protein expression. By contrary, the treatment resulted in the increase of corneal trkA^NGFR expression. Retinal tissues showed a decreased rhodopsin expression as well as reduced number of both rhodopsin expressing and total retinal cells, as observed after single cell extraction. A decreased expression of ICAM-1, IL-17 and IL-13 as well as an increased expression of IL-21 typified retinal extracts. No significant changes were observed for corneal tissues.

CONCLUSION

The reduced availability of endogenous NGF, as produced by chronic retrobulbar anti-NGF administration, produce a quick response from retinal tissues, with respect to corneal ones, suggesting the presence of early compensatory mechanisms to protect retinal networking.

Intravitreal Injection of Liposomes Loaded with a Histone Deacetylase Inhibitor Promotes Retinal Ganglion Cell Survival in a Mouse Model of Optic Nerve Crush

Various neuroprotective agents have been studied for the treatment of retinal ganglion cell (RGC) diseases, but issues concerning the side effects of systemically administered drugs and the short retention time of intravitreally injected drugs limit their clinical applications. The current study aimed to evaluate the neuroprotective effects of intravitreally injected trichostatin A (TSA)-loaded liposomes in a mouse model of optic nerve crush (ONC) and determine whether TSA-loaded liposomes have therapeutic potential in RGC diseases. The histone deacetylase inhibitor, TSA, was incorporated into polyethylene glycolylated liposomes. C57BL/6J mice were treated with an intravitreal injection of TSA-loaded liposomes and liposomes loaded with a lipophilic fluorescent dye for tracking, immediately after ONC injury. The expression of macroglial and microglial cell markers (glial fibrillary acidic protein and ionized calcium binding adaptor molecule-1), RGC survival, and apoptosis were assessed. We found that the liposomes reached the inner retina. Their fluorescence was detected for up to 10 days after the intravitreal injection, with peak intensity at 3 days postinjection. Intravitreally administered TSA-loaded liposomes significantly decreased reactive gliosis and RGC apoptosis and increased RGC survival in a mouse model of ONC. Our results suggest that TSA-loaded liposomes may help in the treatment of various RGC diseases.

Metabolite therapy guided by liquid biopsy proteomics delays retinal neurodegeneration

Background

Neurodegenerative diseases are incurable disorders caused by progressive neuronal cell death. Retinitis pigmentosa (RP) is a blinding neurodegenerative disease that results in photoreceptor death and progresses to the loss of the entire retinal network. We previously found that proteomic analysis of the adjacent vitreous served as way to indirectly biopsy the retina and identify changes in the retinal proteome.

Methods

We analyzed protein expression in liquid vitreous biopsies from autosomal recessive (ar)RP patients with PDE6A mutations and arRP mice with Pde6ɑ mutations. Proteomic analysis of retina and vitreous samples identified molecular pathways affected at the onset of photoreceptor death. Based on affected molecular pathways, arRP mice were treated with a ketogenic diet or metabolites involved in fatty-acid synthesis, oxidative phosphorylation, and the tricarboxylic acid (TCA) cycle.

Findings

Dietary supplementation of a single metabolite, ɑ-ketoglutarate, increased docosahexaeonic acid levels, provided neuroprotection, and enhanced visual function in arRP mice. A ketogenic diet delayed photoreceptor cell loss, while vitamin B supplementation had a limited effect. Finally, desorption electrospray ionization mass spectrometry imaging (DESI-MSI) on ɑ-ketoglutarate-treated mice revealed restoration of metabolites that correlated with our proteomic findings: uridine, dihydrouridine, and thymidine (pyrimidine and purine metabolism), glutamine and glutamate (glutamine/glutamate conversion), and succinic and aconitic acid (TCA cycle).

Interpretation

This study demonstrates that replenishing TCA cycle metabolites via oral supplementation prolongs retinal function and provides a neuroprotective effect on the photoreceptor cells and inner retinal network.

Funding

NIH grants [R01EY026682, R01EY024665, R01EY025225, R01EY024698, R21AG050437, P30EY026877, 5P30EY019007, R01EY018213, F30EYE027986, T32GM007337, 5P30CA013696], NSF grant CHE-1734082.

Investigations Into Bioenergetic Neuroprotection of Cone Photoreceptors: Relevance to Retinitis Pigmentosa

Recent studies suggest cone degeneration in retinitis pigmentosa (RP) may result from intracellular energy depletion. We tested the hypothesis that cones die when depleted of energy by examining the effect of two bioenergetic, nutraceutical agents on cone survival. The study had three specific aims: firstly, we, studied the neuroprotective efficacies of glucose and creatine in an in vitro model of RP. Next, we utilized a well-characterized mouse model of RP to examine whether surviving cones, devoid of their inner segments, continue to express genes vital for glucose, and creatine utilization. Finally, we analyzed the neuroprotective properties of glucose and creatine on cone photoreceptors in a mouse model of RP. Two different bioenergy-based therapies were tested in rd1 mice: repeated local delivery of glucose and systemic creatine. Optomotor responses were tested and cone density was quantified on retinal wholemounts. The results showed that glucose supplementation increased survival of cones in culture subjected to mitochondrial stress or oxidative insult. Despite losing their inner segments, surviving cones in the rd1 retina continued to express the various glycolytic enzymes. Following a single subconjunctival injection, the mean vitreous glucose concentration was significantly elevated at 1 and 8 h, but not at 16 h after injection; however, daily subconjunctival injection of glucose neither enhanced spatial visual performance nor slowed cone cell degeneration in rd1 mice relative to isotonic saline. Creatine dose-dependently increased survival of cones in culture subjected to mitochondrial dysfunction, but not to oxidative stress. Despite the loss of their mitochondrial-rich inner segments, cone somas and axonal terminals in the rd1 retina were strongly positive for both the mitochondrial and cytosolic forms of creatine kinase at each time point examined. Creatine-fed rd1 mice displayed enhanced optomotor responses compared to mice fed normal chow. Moreover, cone density was significantly greater in creatine-treated mice compared to controls. The overall results of this study provide tentative support for the hypothesis that creatine supplementation may delay secondary degeneration of cones in individuals with RP.

Interleukin 22 ameliorates neuropathology and protects from central nervous system autoimmunity

IL-22 has opposing effects in different tissues, from pro-inflammatory (skin, joints) to protective (liver, intestine) but little is known about its effects on neuroinflammation. We examined the effect of IL-22 on retinal tissue by using the model of experimental autoimmune uveitis (EAU) in IL-22-/- mice, as well as by intraocular injections of recombinant IL-22 or anti-IL-22 antibodies in wild type animals. During EAU, IL-22 was produced in the eye by CD4+ eye-infiltrating T cells. EAU-challenged IL-22-/- mice, as well as WT mice treated systemically or intraocularly with anti-IL-22 antibodies during the expression phase of disease, developed exacerbated retinal damage. Furthermore, IL-22-/- mice were more susceptible than WT controls to glutamate-induced neurotoxicity, whereas local IL-22 supplementation was protective, suggesting direct or indirect neuroprotective effects. Mechanistic studies revealed that retinal glial Müller cells express IL-22rα1 in vivo, and in vitro IL-22 enhanced their ability to suppress proliferation of effector T cells. Finally, IL-22 injected into the eye concurrently with IL-1, inhibited the (IL-1-induced) expression of multiple proinflammatory and proapoptotic genes in retinal tissue. These findings suggest that IL-22 can function locally within the retina to reduce inflammatory damage and provide neuroprotection by affecting multiple molecular and cellular pathways.

The obstacle course to the inner retina: Hyaluronic acid-coated lipoplexes cross the vitreous but fail to overcome the inner limiting membrane

Considerable research over the last few years has revealed dysregulation of growth factors in various retinal diseases, such as glaucoma, diabetic retinopathy and photoreceptor degenerations. The use of messengerRNA (mRNA) to transiently overexpress a specific factor could compensate for this imbalance. However, a critical challenge of this approach lies in the ability to efficiently deliver mRNA molecules to the retinal target cells. In this study we found that intravitreal (IVT) injection is an attractive approach to deliver mRNA to the retina, providing two critical barriers can be overcome: the vitreous and the inner limiting membrane (ILM). We demonstrated that the vitreous is indeed a major hurdle in the delivery of the cationic mRNA-complexes to retinal cells, both in terms of vitreal mobility and cellular uptake. To improve their intravitreal mobility and avoid unwanted extracellular interactions, we evaluated the use of hyaluronic acid (HA) as an electrostatic coating strategy. This HA-coating provided the complexes with a negative surface charge, markedly enhancing their mobility in the vitreous humor, without reducing their cellular internalization and transfection efficiency. However, although this coating strategy allows the mRNA-complexes to successfully overcome the vitreal barrier, the majority of the particles accumulated at the ILM. This study therefore underscores the crucial barrier function of the ILM toward non-viral retinal gene delivery and the need to smartly design mRNA-carriers able to surmount the vitreous as well as the ILM.

Extracellular superoxide dismutase (SOD3) regulates oxidative stress at the vitreoretinal interface

Oxidative stress is a pathogenic feature in vitreoretinal disease. However, the ability of the inner retina to manage metabolic waste and oxidative stress is unknown. Proteomic analysis of antioxidants in the human vitreous, the extracellular matrix opposing the inner retina, identified superoxide dismutase-3 (SOD3) that localized to a unique matrix structure in the vitreous base and cortex. To determine the role of SOD3, Sod3^-/- mice underwent histological and clinical phenotyping. Although the eyes were structurally normal, at the vitreoretinal interface Sod3^-/- mice demonstrated higher levels of 3-nitrotyrosine, a key marker of oxidative stress. Pattern electroretinography also showed physiological signaling abnormalities within the inner retina. Vitreous biopsies and epiretinal membranes collected from patients with diabetic vitreoretinopathy (DVR) and a mouse model of DVR showed significantly higher levels of nitrates and/or 3-nitrotyrosine oxidative stress biomarkers suggestive of SOD3 dysfunction. This study analyzes the molecular pathways that regulate oxidative stress in human vitreous substructures. The absence or dysregulation of the SOD3 antioxidant at the vitreous base and cortex results in increased oxidative stress and tissue damage to the inner retina, which may underlie DVR pathogenesis and other vitreoretinal diseases.

Liquid Biopsy of Vitreous Reveals an Abundant Vesicle Population Consistent With the Size and Morphology of Exosomes

Purpose

To investigate the molecular components of the vitreous in order to better understand retinal physiology and disease.

Methods

Vitreous was acquired from patients undergoing vitrectomy for macular hole and/or epiretinal membrane, postmortem donors, and C57BL/6J mice. Unbiased proteomic analysis was performed via electrospray ionization tandem mass spectrometry (MS/MS). Gene ontology analysis was performed and results were confirmed with transmission electron microscopy, atomic force microscopy, and nanoparticle tracking analysis (NTA).

Results

Proteomic analysis of vitreous obtained prior to vitrectomy identified a total of 1121 unique proteins. Gene ontology analysis revealed that 62.6% of the vitreous proteins were associated with the gene ontology term “extracellular exosome.” Ultrastructural analyses, Western blot, and NTA confirmed the presence of an abundant population of vesicles consistent with the size and morphology of exosomes in human vitreous. The concentrations of vitreous vesicles in vitrectomy patients, postmortem donors, and mice were 1.3, 35, and 9 billion/mL, respectively.

Conclusions

Overall, these data strongly suggest that information-rich exosomes are a major constituent of the vitreous. The abundance of these vesicles and the presence of retinal proteins imply a dynamic interaction between the vitreous and retina. Future studies will be required to identify the cellular origin of vitreal exosomes as well as to assess the potential role of these vesicles in retinal disease and treatment.

Translational Relevance

The identification of vitreous exosomes lays the groundwork for a transformed understanding of pathophysiology and treatment mechanisms in retinal disease, and further validates the use of vitreous as a proximal biofluid of the retina.

Dissection of Human Retina and RPE-Choroid for Proteomic Analysis

The human retina is composed of the sensory neuroretina and the underlying retinal pigmented epithelium (RPE), which is firmly complexed to the vascular choroid layer. Different regions of the retina are anatomically and molecularly distinct, facilitating unique functions and demonstrating differential susceptibility to disease. Proteomic analysis of each of these regions and layers can provide vital insights into the molecular process of many diseases, including Age-Related Macular Degeneration (AMD), diabetes mellitus, and glaucoma. However, separation of retinal regions and layers is essential before quantitative proteomic analysis can be accomplished. Here, we describe a method for dissection and collection of the foveal, macular, and peripheral retinal regions and underlying RPE-choroid complex, involving regional punch biopsies and manual removal of tissue layers from a human eye.One-dimensional SDS-PAGE as well as downstream proteomic analysis, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS), can be used to identify proteins in each dissected retinal layer, revealing molecular biomarkers for retinal disease.

Evidence of Dual Mechanisms of Glutathione Uptake in the Rodent Lens: A Novel Role for Vitreous Humor in Lens Glutathione Homeostasis

Purpose

Lens glutathione synthesis knockout (LEGSKO) mouse lenses lack de novo glutathione (GSH) synthesis but still maintain >1 mM GSH. We sought to determine the source of this residual GSH and the mechanism by which it accumulates in the lens.

Methods

Levels of GSH, glutathione disulfide (GSSG), and GSH-related compounds were measured in vitro and in vivo using isotope standards and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

Results

Wild-type (WT) lenses could accumulate GSH from γ-glutamylcysteine and glycine or from intact GSH, but LEGSKO lenses could only accumulate GSH from intact GSH, indicating that LEGSKO lens GSH content is not due to synthesis by a salvage pathway. Uptake of GSH in cultured lenses occurred at the same rate for LEGSKO and WT lenses, could not be inhibited, and occurred primarily through cortical fiber cells. In contrast, uptake of GSH from aqueous humor could be competitively inhibited and showed an enhanced K_m in LEGSKO lenses. Mouse vitreous had >1 mM GSH, whereas aqueous had <20 μM GSH. Testing physiologically relevant GSH concentrations for uptake in vivo, we found that both LEGSKO and WT lenses could obtain GSH from the vitreous but not from the aqueous. Vitreous rapidly accumulated GSH from the circulation, and depletion of circulating GSH reduced vitreous but not aqueous GSH.

Conclusions

The above data provide, for the first time, evidence for the existence of dual mechanisms of GSH uptake into the lens, one mechanism being a passive, high-flux transport through the vitreous exposed side of the lens versus an active, carrier-mediated uptake mechanism at the anterior of the lens.

Retinal pigment epithelial cell necroptosis in response to sodium iodate

Age-related macular degeneration (AMD) is a degenerative disease of the retina and the leading cause of blindness in the elderly in developed countries. The late stage of dry AMD, or geographic atrophy (GA), is characterized by extensive retinal pigment epithelium (RPE) degeneration. The underlying molecular mechanism for RPE cell death in GA remains unclear. Our previous study has established that RPE cells die predominantly from necroptosis in response to oxidative stress in vitro. Here, we extend our study and aim to characterize the nature of RPE cell death in response to sodium iodate (NaIO₃) in vitro and in a NaIO₃-induced retina degeneration mouse model. We found that NaIO₃ induces RPE necroptosis in vitro by using a combination of molecular hallmarks. By using TUNEL assays, active caspase-3 and HMGB1 immunostaining, we confirmed that photoreceptor cells die mainly from apoptosis and RPE cells die mainly from necroptosis in response to NaIO₃in vivo. RPE necroptosis in this model is also supported by use of the RIPK1 inhibitor, Necrostatin-1. Furthermore, using novel RIPK3-GFP transgenic mouse lines, we detected RIPK3 aggregation, a hallmark of necroptosis, in the RPE cells in vivo after NaIO₃ injection. Our findings suggest the necessity of re-evaluating RPE cell death mechanism in AMD models and have the potential to influence therapeutic development for dry AMD, especially GA.

Gene delivery of a viral anti-inflammatory protein to combat ocular inflammation

Inflammation of the retina is a contributing factor in ocular diseases such as uveitis, diabetic retinopathy, and age-related macular degeneration (AMD). The M013 immunomodulatory protein from myxoma virus has been shown to interfere with the proinflammatory signaling pathways involving both the NLRP3 inflammasome and NF-κB. We have developed and characterized an adeno-associated viral (AAV) vector that delivers a secretable and cell-penetrating form of the M013 protein (TatM013). The expressed TatM013 protein was secreted and blocked the endotoxin-induced secretion of interleukin (IL)-1β in monocyte-derived cells and the reactive aldehyde-induced secretion of IL-1β in retinal pigment epithelium cells. The local anti-inflammatory effects of AAV-delivered TatM013 were evaluated in an endotoxin-induced uveitis (EIU) mouse model after intravitreal injection of mice with an AAV2-based vector carrying either TatM013 fused to a secreted green fluorescent protein (GFP) tag (sGFP-TatM013) or GFP. Expression of the sGFP-TatM013 transgene was demonstrated by fluorescence funduscopy in living mice. In EIU, the number of infiltrating cells and the concentration of IL-1β in the vitreous body were significantly lower in the eyes injected with AAV-sGFP-TatM013 compared with the eyes injected with control AAV-GFP. These results suggest that a virus-derived inhibitor of the innate immune response, when delivered via AAV, could be a generalized therapy for various inflammatory diseases of the eye.

Analytical platforms in vitreoretinal proteomics

Current proteomic technologies can effectively be used to study the proteins of the vitreous body and retina in health and disease. The use of appropriate samples, analytical platform and bioinformatic method are essential factors to consider when undertaking such studies. Certain proteins may hinder the detection and evaluation of more relevant proteins associated with pathological processes if not carefully considered, particularly in the sample preparation and data analysis stages. The utilization of more than one quantification technique and database search program to expand the level of proteome coverage and analysis will help to generate more robust and worthwhile results. This review discusses important aspects of sample processing and the use of label and label-free quantitative proteomics strategies applied to the vitreous and retina.

NGF Expression in Reelin-Deprived Retinal Cells: A Potential Neuroprotective Effect

We recently reported that increased NGF and p75(NTR) as well as decreased trkA(NGFR) characterized the Reelin-deprived (E-Reeler) retina, prospecting a potential contribution of NGF during E-Reeler retinogenesis. Herein, retinal ganglion cells (RGCs), glial cells and rod bipolar cells (RBCs) were isolated from E-Reeler retinas, and NGF, trkA(NGFR)/p75(NTR) expression and apoptosis were investigated. E-Reeler (n = 28) and E-control (n = 34) retinas were digested, and RGCs, glial cells and RBCs were isolated by the magnetic bead separation. Expression of NGF, trkA(NGFR), p75(NTR), Annexin V/PI and Bcl2/Bax was quantified by flow cytometry and validated by real-time PCR or WB. In E-Reeler retinas, NGF was significantly increased in RGCs and glial cells, p75(NTR) was increased in both RBCs and RGCs, and trkA(NGFR) was unchanged. In E-control retinas, NGF and p75(NTR) were expressed mainly in RBCs and RGCs and faintly in glial cells, while trkA(NGFR) was weakly expressed by RBCs and RGCs. In RBCs and RGCs, Annexin V expression was unchanged, while Bcl2 increased and Bax decreased selectively in E-Reeler RGCs. The data indicate that E-Reeler RBCs and RGCs overexpress NGF and p75(NTR) as a protective endogenous response to Reelin deprivation. The observation is strongly supported by the absence of apoptosis in both cell types.

CAPN5 mutation in hereditary uveitis: the R243L mutation increases calpain catalytic activity and triggers intraocular inflammation in a mouse model

A single amino acid mutation near the active site of the CAPN5 protease was linked to the inherited blinding disorder, autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). In homology modeling with other calpains, this R243L CAPN5 mutation was situated in a mobile loop that gates substrate access to the calcium-regulated active site. In in vitro activity assays, the mutation increased calpain protease activity and made it far more active at low concentrations of calcium. To test whether the disease allele could yield an animal model of ADNIV, we created transgenic mice expressing human (h) CAPN5(R243L) only in the retina. The resulting hCAPN5(R243L) transgenic mice developed a phenotype consistent with human uveitis and ADNIV, at the clinical, histological and molecular levels. The fundus of hCAPN5(R243L) mice showed enhanced autofluorescence (AF) and pigment changes indicative of reactive retinal pigment epithelial cells and photoreceptor degeneration. Electroretinography showed mutant mouse eyes had a selective loss of the b-wave indicating an inner-retina signaling defect. Histological analysis of mutant mouse eyes showed protein extravasation from dilated vessels into the anterior chamber and vitreous, vitreous inflammation, vitreous and retinal fibrosis and retinal degeneration. Analysis of gene expression changes in the hCAPN5(R243L) mouse retina showed upregulation of several markers, including members of the Toll-like receptor pathway, chemokines and cytokines, indicative of both an innate and adaptive immune response. Since many forms of uveitis share phenotypic characteristics of ADNIV, this mouse offers a model with therapeutic testing utility for ADNIV and uveitis patients.

Gene therapy with the caspase activation and recruitment domain reduces the ocular inflammatory response

Inflammation is a key component of chronic and acute diseases of the eye. Our goal is to test anti-inflammatory genes delivered by an adeno-associated virus (AAV) vector as potential treatments for retinal inflammation. We developed a secretable and cell penetrating form of the caspase activation and recruitment domain (CARD) from the apoptosis-associated speck-like protein containing a CARD (ASC) gene that binds caspase-1 and inhibits its activation by the inflammasome. The secretion and cell penetration characteristics of this construct were validated in vitro by measuring its effects on inflammasome signaling in a monocyte cell line and in an retinal pigmented epithelium (RPE) cell line. This vector was then packaged as AAV particles and tested in the endotoxin-induced uveitis mouse model. Gene expression was monitored one month after vector injection by fluorescence fundoscopy. Ocular inflammation was then induced by injecting lipopolysaccharide into the vitreous and was followed by enucleation 24 hours later. Eyes injected with the secretable and cell penetrating CARD AAV vector had both a significantly lower concentration of IL-1β as well as a 64% reduction in infiltrating cells detected in histological sections. These results suggest that anti-inflammatory genes such as the CARD could be used to treat recurring inflammatory diseases like uveitis or chronic subacute inflammations of the eye.

Pathogenicity of ocular isolates of Acinetobacter baumannii in a mouse model of bacterial endophthalmitis

PURPOSE

To determine the virulence properties of ocular isolates of Acinetobacter baumannii in causing endophthalmitis in a mouse model.

METHODS

Endophthalmitis was induced by intravitreal injections of the bacteria into C57BL/6 (B6) mouse eyes. The disease progression was monitored by ophthalmoscopic, electroretinography (ERG), histologic, cell death (TUNEL labeling), and microbiological parameters. The expression of cytokines/chemokines was checked by quantitative RT-PCR (qRT-PCR) and ELISA. Flow cytometry was used to determine cellular infiltration. The role of neutrophils was determined using neutropenic mice. The virulence traits (biofilm formation, adherence, and cytotoxicity) of the ocular isolates were tested using corneal epithelial cells.

RESULTS

Among the three clinical isolates and a standard ATCC 19606 strain tested, a biofilm producing multidrug resistant (MDR) strain of A. baumannii AB12 caused severe endophthalmitis (100% destruction of the eyes) leading to the loss of retinal function as assessed by ERG analysis. Elevated levels of inflammatory mediators (TNF-α, IL-1β, CXCL2, and IL-6) were detected in AB12-infected eyes. Histologic and TUNEL staining revealed increased retinal cell death and the flow cytometry data showed the presence of inflammatory cells, primarily neutrophils (CD45(+)/Ly6G(+)). Neutropenic mice showed an increased bacterial burden, reduced inflammatory response, and severe tissue destruction.

CONCLUSIONS

These results indicate that A. baumannii causes severe intraocular inflammation and retinal damage. Furthermore, neutrophils play an important role in the pathogenesis of A. baumannii endophthalmitis.

Functional validation of a human CAPN5 exome variant by lentiviral transduction into mouse retina

Exome sequencing indicated that the gene encoding the calpain-5 protease, CAPN5, is the likely cause of retinal degeneration and autoimmune uveitis in human patients with autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). To explore the mechanism of ADNIV, a human CAPN5 disease allele was expressed in mouse retinas with a lentiviral vector created to express either the wild-type human (h) CAPN5 or the ADNIV mutant hCAPN5-R243L allele under a rhodopsin promoter with tandem green fluorescent protein (GFP) expression. Vectors were injected into the subretinal space of perinatal mice. Mouse phenotypes were analyzed using electroretinography, histology and inflammatory gene expression profiling. Mouse calpain-5 showed high homology to its human ortholog with >98% sequence identity that includes the ADNIV mutant residue. Calpain-5 protein was expressed in the inner and outer segments of the photoreceptors and in the outer plexiform layer. Expression of the hCAPN5-R243L allele caused loss of the electroretinogram b-wave, photoreceptor degeneration and induction of immune cell infiltration and inflammatory genes in the retina, recapitulating major features of the ADNIV phenotype. Intraocular neovascularization and fibrosis were not observed during the study period. Our study shows that expression of the hCAPN5-R243L disease allele elicits an ADNIV-like disease in mice. It further suggests that ADNIV is due to CAPN5 gain-of-function rather than haploinsufficiency, and retinal expression may be sufficient to generate an autoimmune response. Genetic models of ADNIV in the mouse can be used to explore protease mechanisms in retinal degeneration and inflammation as well as preclinical therapeutic testing.

Proteomic interactions in the mouse vitreous-retina complex

PURPOSE

Human vitreoretinal diseases are due to presumed abnormal mechanical interactions between the vitreous and retina, and translational models are limited. This study determined whether nonstructural proteins and potential retinal biomarkers were expressed by the normal mouse vitreous and retina.

METHODS

Vitreous and retina samples from mice were collected by evisceration and analyzed by liquid chromatography-tandem mass spectrometry. Identified proteins were further analyzed for differential expression and functional interactions using bioinformatic software.

RESULTS

We identified 1,680 unique proteins in the retina and 675 unique proteins in the vitreous. Unbiased clustering identified protein pathways that distinguish retina from vitreous including oxidative phosphorylation and neurofilament cytoskeletal remodeling, whereas the vitreous expressed oxidative stress and innate immunology pathways. Some intracellular protein pathways were found in both retina and vitreous, such as glycolysis and gluconeogenesis and neuronal signaling, suggesting proteins might be shuttled between the retina and vitreous. We also identified human disease biomarkers represented in the mouse vitreous and retina, including carbonic anhydrase-2 and 3, crystallins, macrophage inhibitory factor, glutathione peroxidase, peroxiredoxins, S100 precursors, and von Willebrand factor.

CONCLUSIONS

Our analysis suggests the vitreous expresses nonstructural proteins that functionally interact with the retina to manage oxidative stress, immune reactions, and intracellular proteins may be exchanged between the retina and vitreous. This novel proteomic dataset can be used for investigating human vitreoretinopathies in mouse models. Validation of vitreoretinal biomarkers for human ocular diseases will provide a critical tool for diagnostics and an avenue for therapeutics.

Translational vitreous proteomics

The vitreous is an extracellular matrix that is still poorly understood. Although many constituents and characteristics have been previously determined, there are many attributes still being discovered. Currently, using protein arrays, MS, and bioinformatics, the vitreous provides a wealth of knowledge regarding ocular diseases and potential targets for personalized therapeutics.

Loss of retinoschisin (RS1) cell surface protein in maturing mouse rod photoreceptors elevates the luminance threshold for light-driven translocation of transducin but not arrestin

Loss of retinoschisin (RS1) in Rs1 knock-out (Rs1-KO) retina produces a post-photoreceptor phenotype similar to X-linked retinoschisis in young males. However, Rs1 is expressed strongly in photoreceptors, and Rs1-KO mice have early reduction in the electroretinogram a-wave. We examined light-activated transducin and arrestin translocation in young Rs1-KO mice as a marker for functional abnormalities in maturing rod photoreceptors. We found a progressive reduction in luminance threshold for transducin translocation in wild-type (WT) retinas between postnatal days P18 and P60. At P21, the threshold in Rs1-KO retinas was 10-fold higher than WT, but it decreased to <2.5-fold higher by P60. Light-activated arrestin translocation and re-translocation of transducin in the dark were not affected. Rs1-KO rod outer segment (ROS) length was significantly shorter than WT at P21 but was comparable with WT at P60. These findings suggested a delay in the structural and functional maturation of Rs1-KO ROS. Consistent with this, transcription factors CRX and NRL, which are fundamental to maturation of rod protein expression, were reduced in ROS of Rs1-KO mice at P21 but not at P60. Expression of transducin was 15-30% lower in P21 Rs1-KO ROS and transducin GTPase hydrolysis was nearly twofold faster, reflecting a 1.7- to 2.5-fold increase in RGS9 (regulator of G-protein signaling) level. Transduction protein expression and activity levels were similar to WT at P60. Transducin translocation threshold elevation indicates photoreceptor functional abnormalities in young Rs1-KO mice. Rapid reduction in threshold coupled with age-related changes in transduction protein levels and transcription factor expression are consistent with delayed maturation of Rs1-KO photoreceptors.

Nucleofection of whole murine retinas

The mouse retina constitutes an important research model for studies aiming to unravel the cellular and molecular mechanisms underlying ocular diseases. The accessibility of this tissue and its feasibility to directly obtain neurons from it has increased the number of studies culturing mouse retina, mainly retinal cell suspensions. However, to address many questions concerning retinal diseases and protein function, the organotypic structure must be maintained, so it becomes important to devise methods to transfect and culture whole retinas without disturbing their cellular structure. Moreover, the postmitotic stage of retinal neurons makes them reluctant to commonly used transfection techniques. For this purpose some published methods employ in vivo virus-based transfection techniques or biolistics, methods that present some constraints. Here we report for the first time a method to transfect P15-P20 whole murine retinas via nucleofection, where nucleic acids are directly delivered to the cell nuclei, allowing in vitro transfection of postmitotic cells. A detailed protocol for successful retina extraction, organotypic culture, nucleofection, histological procedures and imaging is described. In our hands the A-33 nucleofector program shows the highest transfection efficiency. Whole flat-mount retinas and cryosections from transfected retinas were imaged by epifluorescence and confocal microscopy, showing that not only cells located in the outermost retinal layers, but also those in inner retinal layers are transfected. In conclusion, we present a novel method to successfully transfect postnatal whole murine retina via nucleofection, showing that retina can be successfully nucleofected after some optimization steps.

A simplified technique for in situ excision of cornea and evisceration of retinal tissue from human ocular globe

Enucleation is the process of retrieving the ocular globe from a cadaveric donor leaving the rest of the globe undisturbed. Excision refers to the retrieval of ocular tissues, especially cornea, by cutting it separate from the ocular globe. Evisceration is the process of removing the internal organs referred here as retina. The ocular globe consists of the cornea, the sclera, the vitreous body, the lens, the iris, the retina, the choroid, muscles etc (Suppl. Figure 1). When a patient is suffering from corneal damage, the cornea needs to be removed and a healthy one must be transplanted by keratoplastic surgeries. Genetic disorders or defects in retinal function can compromise vision. Human ocular globes can be used for various surgical procedures such as eye banking, transplantation of human cornea or sclera and research on ocular tissues. However, there is little information available on human corneal and retinal excision, probably due to the limited accessibility to human tissues. Most of the studies describing similar procedures are performed on animal models. Research scientists rely on the availability of properly dissected and well-conserved ocular tissues in order to extend the knowledge on human eye development, homeostasis and function. As we receive high amount of ocular globes out of which approximately 40% (Table 1) of them are used for research purposes, we are able to perform huge amount of experiments on these tissues, defining techniques to excise and preserve them regularly. The cornea is an avascular tissue which enables the transmission of light onto the retina and for this purpose should always maintain a good degree of transparency. Within the cornea, the limbus region, which is a reservoir of the stem cells, helps the reconstruction of epithelial cells and restricts the overgrowth of the conjunctiva maintaining corneal transparency and clarity. The size and thickness of the cornea are critical for clear vision, as changes in either of them could lead to distracted, unclear vision. The cornea comprises of 5 layers; a) epithelium, b) Bowman's layer, c) stroma, d) Descemet's membrane and e) endothelium. All layers should function properly to ensure clear vision(4,5,6). The choroid is the intermediate tunic between the sclera and retina, bounded on the interior by the Bruch's membrane and is responsible for blood flow in the eye. The choroid also helps to regulate the temperature and supplies nourishment to the outer layers of the retina(5,6). The retina is a layer of nervous tissue that covers the back of the ocular globe (Suppl. Figure 1) and consists of two parts: a photoreceptive part and a non-receptive part. The retina helps to receive the light from the cornea and lens and converts it into the chemical energy eventually transmitted to the brain with help of the optic nerve(5,6). The aim of this paper is to provide a protocol for the dissection of corneal and retinal tissues from human ocular globes. Avoiding cross-contamination with adjacent tissues and preserving RNA integrity is of fundamental importance as such tissues are indispensable for research purposes aimed at (i) characterizing the transcriptome of the ocular tissues, (ii) isolating stem cells for regenerative medicine projects, and (iii) evaluating histological differences between tissues from normal/affected subjects. In this paper we describe the technique we currently use to remove the cornea, the choroid and retinal tissues from an ocular globe. Here we provide a detailed protocol for the dissection of the human ocular globe and the excision of corneal and retinal tissues. The accompanying video will help researchers to learn an appropriate technique for the retrieval of precious human tissues which are difficult to find regularly.

Toll-like receptor 2 ligand pretreatment attenuates retinal microglial inflammatory response but enhances phagocytic activity toward Staphylococcus aureus

Staphylococcus aureus is a leading cause of severe endophthalmitis, which often results in vision loss in some patients. Previously, we showed that Toll-like receptor 2 (TLR2) ligand pretreatment prevented the development of staphylococcal endophthalmitis in mice and suggested that microglia might be involved in this protective effect (Kumar A, Singh CN, Glybina IV, Mahmoud TH, Yu FS. J. Infect. Dis. 201:255-263, 2010). The aim of the present study was to understand how microglial innate response is modulated by TLR2 ligand pretreatment. Here, we demonstrate that S. aureus infection increased the CD11b(+) CD45(+) microglial/macrophage population in the C57BL/6 mouse retina. Using cultured primary retinal microglia and a murine microglial cell line (BV-2), we found that these cells express TLR2 and that its expression is increased upon stimulation with bacteria or an exclusive TLR2 ligand, Pam3Cys. Furthermore, challenge of primary retinal microglia with S. aureus and its cell wall components peptidoglycan (PGN) and lipoteichoic acid (LTA) induced the secretion of proinflammatory mediators (tumor necrosis factor alpha [TNF-α] and MIP-2). This innate response was attenuated by a function-blocking anti-TLR2 antibody or by small interfering RNA (siRNA) knockdown of TLR2. In order to assess the modulation of the innate response, microglia were pretreated with a low dose (0.1 or 1 μg/ml) of Pam3Cys and then challenged with live S. aureus. Our data showed that S. aureus-induced production of proinflammatory mediators is dramatically reduced in pretreated microglia. Importantly, microglia pretreated with the TLR2 agonist phagocytosed significantly more bacteria than unstimulated cells. Together, our data suggest that TLR2 plays an important role in retinal microglial innate response to S. aureus, and its sensitization inhibits inflammatory response while enhancing phagocytic activity.