Retinal Vascular Abnormalities and Microglia Activation in Mice with Deficiency in Cytochrome P450 46A1-Mediated Cholesterol Removal.

CYP46A1 is the cytochrome P450 enzyme that converts cholesterol to 24-hydroxycholesterol, a cholesterol elimination product and a potent liver X receptor (LXR) ligand. We conducted retinal characterizations of Cyp46a1-/- mice that had normal fasting blood glucose levels but up to a 1.8-fold increase in retinal cholesterol. The retina of Cyp46a1-/- mice exhibited venous beading and tortuosity, microglia/macrophage activation, and increased vascular permeability, features commonly associated with diabetic retinopathy. The expression of Lxrα and Lxrß was increased in both the whole Cyp46a1-/- retina and retinal macroglia/macrophages. The LXR-target genes were affected as well, primarily in activated microglial cells and macrophages. In the latter, the LXR-transactivated genes (Abca1, Abcg1, Apod, Apoe, Mylip, and Arg2) were up-regulated; similarly, there was an up-regulation of the LXR-transrepressed genes (Ccl2, Ptgs2, Cxcl1, Il1b, Il6, Nos2, and Tnfa). For comparison, gene expression was investigated in bone marrow-derived macrophages from Cyp46a1-/- mice as well as retinal and bone marrow-derived macrophages from Cyp27a1-/- and Cyp27a1-/-Cyp46a1-/- mice. CYP46A1 expression was detected in retinal endothelial cells, and this expression was increased in the proinflammatory environment. Retinal Cyp46a1-/- phosphoproteome revealed altered phosphorylation of 30 different proteins, including tight junction protein zonula occludens 1 and aquaporin 4. Collectively, the data obtained establish metabolic and regulatory significance of CYP46A1 for the retina and suggest pharmacologic activation of CYP46A1 as a potential therapeutic approach to dyslipidemia-induced retinal damage.

Correlation of ultra-widefield fundus autofluorescence patterns with the underlying genotype in retinal dystrophies and retinitis pigmentosa.

PURPOSE: Ultra-widefield fundus autofluorescence (UW-FAF) allows the characterization of the peripheral retinal features of vitreoretinal diseases. The purpose of this study was to examine possible genotypic/phenotypic correlations of UW-FAF patterns in patients with a variety of retinal dystrophies and retinitis pigmentosa (RP). METHODS: An IRB-approved retrospective consecutive case series study was performed of genetically characterized retinal dystrophy or RP patients who underwent UW-FAF imaging. UW-FAF was performed with the Optos 200Tx system. Clinical variables, genotypic analysis, and phenotypic characteristics were reviewed. RESULTS: Seventeen patients were identified who had identified mutations in retinal dystrophy or RP genes and who also had undergone UW-FAF. Three patients had X-linked RP with RPGR mutations. Six patients had autosomal dominant RP (four with RHO mutations and one with a PRPF31 mutation, and one with RDS/PRPH2 mutation). Four patients had autosomal recessive RP (four with USH2A mutations). Three patients had Leber Congenital Amaurosis (LCA) with mutations including CRB1, CEP290, and RPGRIP1. Macular hyperautofluorescence was noted in all patients. A ring of hyperautofluorescence was clear in patients with RHO and USH2A mutations, and patients with USH2A mutations demonstrated a second ring of hyperautofluorescence. In the periphery, patients with RHO or RPGR mutations exhibited hyperautofluorescence with patchy areas of hypoautofluorescence. Patients with USH2A mutations had a distinctive pattern of diffuse and homogeneous peripheral hypoautofluorescence. CONCLUSION: UW-FAF may provide important information to facilitate diagnosis and further research is needed to better characterize this technology as an imaging biomarker for genotype association in retinal dystrophies and RP.

Wound construction.

Wound construction is critical in microincision vitrectomy surgery. The three main steps in constructing a proper wound include displacing the conjunctiva away from the sclera, flattening the sclera on insertion, and angling the incision. Each one of these steps helps create wounds that will not leak. Misaligning the conjunctiva from the scleral hole prevents a vitreous wick from extending external to the conjunctiva. Flattening the sclera on trocar insertion provides a longer wound cord length, which is less likely to leak, and angling the incision has been proven to seal better in both anterior and posterior segment incisions. When you make an angled incision, you initially insert the blade at a 30° angle (at least). This will make the wound more stable because it is less likely to cause internal disruption of the wound edges. These three basic steps are simple, but very important to follow when constructing a microincision wound in order to limit postoperative complications including wound leakage, gas leak, hypotony, and endophthalmitis.

Optical coherence tomography imaging of macular oedema.

Macular oedema (ME) occurs in a wide variety of pathological conditions and accounts for different degrees of vision loss. Early detection of ME is therefore critical for diagnosis and therapeutic management. Optical coherence tomography (OCT) is a non-contact, diagnostic method that uses infrared light, which allows the analysis of the retinal structure by means of high-resolution tomographic cross sections. The identification, localisation, quantification and long-term follow-up of fluid collections are the most important capabilities of OCT. Since the introduction of OCT in clinical practice, it has become an invaluable diagnostic tool and different patterns of ME have been reported. The purpose of this manuscript is to review OCT profiles of ME according to the aetiology and describe what has been reported regarding intraretinal features in vivo.

Inducing a visceral organ to protect a peripheral capillary bed: stabilizing hepatic HIF-1α prevents oxygen-induced retinopathy.

Activation of hypoxia-inducible factor (HIF) can prevent oxygen-induced retinopathy in rodents. Here we demonstrate that dimethyloxaloylglycine (DMOG)-induced retinovascular protection is dependent on hepatic HIF-1 because mice deficient in liver-specific HIF-1α experience hyperoxia-induced damage even with DMOG treatment, whereas DMOG-treated wild-type mice have 50% less avascular retina (P < 0.0001). Hepatic HIF stabilization protects retinal function because DMOG normalizes the b-wave on electroretinography in wild-type mice. The localization of DMOG action to the liver is further supported by evidence that i) mRNA and protein erythropoietin levels within liver and serum increased in DMOG-treated wild-type animals but are reduced by 60% in liver-specific HIF-1α knockout mice treated with DMOG, ii) triple-positive (Sca1/cKit/VEGFR2), bone-marrow-derived endothelial precursor cells increased twofold in DMOG-treated wild-type mice (P < 0.001) but are unchanged in hepatic HIF-1α knockout mice in response to DMOG, and iii) hepatic luminescence in the luciferase oxygen-dependent degradation domain mouse was induced by subcutaneous and intraperitoneal DMOG. These findings uncover a novel endocrine mechanism for retinovascular protection. Activating HIF in visceral organs such as the liver may be a simple strategy to protect capillary beds in the retina and in other peripheral tissues.

Prolyl hydroxylase inhibition during hyperoxia prevents oxygen-induced retinopathy in the rat 50/10 model.

PURPOSE: To study the effect of systemic hypoxia-inducible factor prolyl hydroxylase inhibition (HIF PHDi) in the rat 50/10 oxygen-induced retinopathy (OIR) model. METHODS: Oxygen-induced retinopathy was created with the rat 50/10 OIR model. OIR animals received intraperitoneal injections of dimethyloxalylglycine (DMOG, 200 µg/g), an antagonist of α-ketoglutarate cofactor and inhibitor for HIF PHD, on postnatal day (P)3, P5, and P7. Control animals received intraperitoneal injections of PBS. On P14 and P21, animals were humanely killed and the effect on vascular obliteration, tortuosity, and neovascularization quantified. To analyze HIF and erythropoietin, rats at P5 were injected with DMOG (200 µg/g). Western blot or ELISA measured the levels of HIF-1 and Epo protein. Epo mRNA was measured by quantitative PCR. RESULTS: Alternating hyperoxia and hypoxia in untreated rats led to peripheral vascular obliteration on day P14 and P21. Rats that were treated with systemic DMOG by intraperitoneal injections had 3 times less ischemia and greater peripheral vascularity (P = 0.001) than control animals treated with PBS injections. Neovascularization similarly decreased by a factor of 3 (P = 0.0002). Intraperitoneal DMOG administration increased the levels of HIF and Epo in the liver and brain. Serum Epo also increased 6-fold (P = 0.0016). Systemic DMOG had no adverse effect on growth of rats treated with oxygen. CONCLUSIONS: One of the many controversies in the study of retinopathy of prematurity is whether hyperoxia or alternating hyperoxia and hypoxia creates the disease phenotype in humans. We have previously demonstrated that PHDi prevents OIR in mice exposed to 5 days of sustained 75% oxygen followed by 5 days of 21% oxygen. The 50/10 rat experiments demonstrate that PHDi is also effective in a 24-hour alternating hyperoxia-hypoxia model. The rat OIR model further validates the therapeutic value of HIF PHDi to prevent retinopathy of prematurity because it reduces oxygen-induced vascular obliteration and retinovascular growth attenuation in prolonged and/or alternating hyperoxia.

Aflibercept for the treatment of age-related macular degeneration.

Aflibercept is a novel, recombinant, fusion protein that consists of portions of vascular endothelial growth factor (VEGF) receptor (R) 1 and VEGFR2 extracellular domains fused to the Fc portion of human immunoglobulin G1. It exhibits higher affinity for VEGF-A/-B and binds all the VEGF isoforms (VEGF-B and -C, placental growth factor). The efficacy of aflibercept was assessed in two randomized, double-masked, multicenter, active-controlled, clinical trials in patients with choroidal neovascularization due to exudative age-related macular degeneration (AMD) and compared it's efficacy to ranibizumab, which is already Food and Drug Administration (FDA)-approved for patients with wet AMD. In the two trials known as VIEW 1 and VIEW 2, aflibercept was as effective when dosed as 2 mg every 8 weeks after 3 monthly loading doses compared to monthly ranibizumab. Aflibercept was well tolerated with very rare systemic adverse events, including arterial thromboembolic events (ATEs). The incidence of ATEs was 1.8% during the first year of the clinical trials and included non-fatal strokes, non-fatal myocardial infarction, or death from vascular events or an unknown cause. In November 2011, aflibercept received FDA approval and is currently used in clinical practice for patients with wet AMD.

AMP-activated protein kinase suppresses matrix metalloproteinase-9 expression in mouse embryonic fibroblasts.

Matrix metalloproteinase-9 (MMP-9) plays a critical role in tissue remodeling under both physiological and pathological conditions. Although MMP-9 expression is low in most cells and is tightly controlled, the mechanism of its regulation is poorly understood. We utilized mouse embryonic fibroblasts (MEFs) that were nullizygous for the catalytic α subunit of AMP-activated protein kinase (AMPK), which is a key regulator of energy homeostasis, to identify AMPK as a suppressor of MMP-9 expression. Total AMPKα deletion significantly elevated MMP-9 expression compared with wild-type (WT) MEFs, whereas single knock-out of the isoforms AMPKα1 and AMPKα2 caused minimal change in the level of MMP-9 expression. The suppressive role of AMPK on MMP-9 expression was mediated through both its activity and presence. The AMPK activators 5-amino-4-imidazole carboxamide riboside and A769662 suppressed MMP-9 expression in WT MEFs, and AMPK inhibition by the overexpression of dominant negative (DN) AMPKα elevated MMP-9 expression. However, in AMPKα(-/-) MEFs transduced with DN AMPKα, MMP-9 expression was suppressed. AMPKα(-/-) MEFs showed increased phosphorylation of IκBα, expression of IκBα mRNA, nuclear localization of nuclear factor-κB (NF-κB), and DNA-binding activity of NF-κB compared with WT. Consistently, selective NF-κB inhibitors BMS345541 and SM7368 decreased MMP-9 expression in AMPKα(-/-) MEFs. Overall, our results suggest that both AMPKα isoforms suppress MMP-9 expression and that both the activity and presence of AMPKα contribute to its function as a regulator of MMP-9 expression by inhibiting the NF-κB pathway.

In vivo evaluation of laser-induced choroidal neovascularization using spectral-domain optical coherence tomography.

PURPOSE: To describe the in vivo evolution of laser-induced choroidal neovascularization (CNV) in mice using spectral domain optical coherence tomography (SD-OCT). METHODS: Laser photocoagulation was applied to the mouse fundus using a 532-nm diode laser (100, 150, and 200 mW; 100-µm diameter, 0.1-second duration). SD-OCT examination was performed immediately after laser application and at days 3, 5, 7, 14, 21, and 28 after laser. Fluorescein angiography (FA) was performed at day 5, 7, 14, and 28. Acquired SD-OCT images were analyzed to describe morphologic features, measure CNV size and retinal thickness, and assess the frequency of lesions resulting in fluid accumulation. Finally, SD-OCT images were compared to fluorescein angiograms and histologic sections with immunostaining at similar time points. RESULTS: SD-OCT allowed visualization of the initial laser damage and the subsequent stages of the injury response. CNV formation reached its maximum size at day 5. By day 7, significant size reduction was observed (P < 0.001), continuing through days 14 and 28. Exudation signs, such as fluid accumulation and increase in retinal thickness, followed the same time course, with a peak at day 5 and a decrease by day 7. Delivery of higher laser energy levels to the RPE/choroid complex resulted in a significant percentage of lesions demonstrating excessive chorioretinal damage without CNV formation. CONCLUSIONS: SD-OCT is a fast and reliable tool for the in vivo evaluation of laser-induced CNV, allowing quantification of lesion size and exudation parameters. Moreover, it provides morphologic information that correlates with histologic findings.

Receptor interacting protein kinases mediate retinal detachment-induced photoreceptor necrosis and compensate for inhibition of apoptosis.

Apoptosis has been shown to be a significant form of cell loss in many diseases. Detachment of photoreceptors from the retinal pigment epithelium, as seen in various retinal disorders, causes photoreceptor loss and subsequent vision decline. Although caspase-dependent apoptotic pathways are activated after retinal detachment, caspase inhibition by the pan-caspase inhibitor Z-VAD fails to prevent photoreceptor death; thus, we investigated other pathways leading to cell loss. Here, we show that receptor interacting protein (RIP) kinase-mediated necrosis is a significant mode of photoreceptor cell loss in an experimental model of retinal detachment and when caspases are inhibited, RIP-mediated necrosis becomes the predominant form of death. RIP3 expression, a key activator of RIP1 kinase, increased more than 10-fold after retinal detachment. Morphological assessment of detached retinas treated with Z-VAD showed decreased apoptosis but significantly increased necrotic photoreceptor death. RIP1 kinase inhibitor necrostatin-1 or Rip3 deficiency substantially prevented those necrotic changes and reduced oxidative stress and mitochondrial release of apoptosis-inducing factor. Thus, RIP kinase-mediated programmed necrosis is a redundant mechanism of photoreceptor death in addition to apoptosis, and simultaneous inhibition of RIP kinases and caspases is essential for effective neuroprotection and may be a novel therapeutic strategy for treatment of retinal disorders.

Development of an efficiently cleaved, bioactive, highly pure FLAG-tagged recombinant human Mullerian Inhibiting Substance.

Mullerian Inhibiting Substance (MIS), a member of the TGF-beta family, causes regression of the Mullerian duct in male embryos, after binding to Mullerian Inhibiting Substance Receptor II (MISRII). It has also been extensively demonstrated that it can inhibit proliferation of various cancer cell lines such as ovarian, prostate, and breast cancer in vitro and in vivo. Hence, the availability of a recombinant, epitope tagged, bioactive MIS is important for the selection of patients for treatment and for probing novel molecular targets for MIS in various tissues. To this end, we have expressed a recombinant, internally FLAG-tagged form of hMIS with the tag (DYKDDDDK) immediately after the cleavage site (427-428) of MIS at the C-terminus with a modified dibasic cleavage motif sequence. We show that this construct results in a highly pure, endogenously processed (cleaved) FLAG MIS, that causes complete regression of the Mullerian Duct in an organ culture assay. In addition, purified FLAG MIS was able to bind and affinity purify both transfected and endogenous MIS type II receptor. The availability of this fully functional, epitope tagged form of MIS should facilitate scale-up for preclinical and clinical use and should also be used for the study of MIS binding proteins and for tracking in pharmacokinetic studies.

A novel nonradioactive method to evaluate vascular barrier breakdown and leakage.

PURPOSE: To identify a novel, sensitive, nonradioactive leakage assay that can be used in the assessment of retinal vascular permeability in rats and mice. METHODS: Breakdown of the vascular barrier was induced by vascular endothelial growth factor (VEGF), lipopolysaccharide (LPS), or diabetes. Biotinylated bovine serum albumin (bBSA) was administered as a tracer. After perfusion with lactated Ringer's solution, extravasated bBSA was detected with immunoprecipitation and Western blot analysis or sandwich ELISA. The results were then normalized against the final bBSA plasma concentration, the circulation time, and the protein concentration of the tissue. RESULTS: Six hours after VEGF injection, BRB breakdown was quantified in the injected eye and was 2.5-fold higher than in the contralateral phosphate-buffered saline (PBS)-injected eye (n = 6 rats, P < 0.01). Intravitreal LPS injection induced severe inflammation in the directly injected eye and moderate inflammation in the contralateral untreated eye. Leakage was six- and threefold higher, respectively, compared with that in the untreated control animals (n = 5 rats, P < 0.01). Nine-month diabetic rats had a threefold increase in vascular leakage compared with age-matched control animals (n = 6 retinas, P < 0.05). Twenty-four hours after intraperitoneal administration of LPS in mice, the animals showed increased vascular leakage in all tissue organs examined (retina, 1.7-fold; brain, 1.5-fold; and kidney, 1.3-fold). CONCLUSIONS: bBSA can serve as an effective alternative to the current methods used for quantitating vascular leakage and especially the blood-retinal barrier breakdown. It is reasonably easy to perform, low in cost, and adaptable to experiments in mice.