Andrea Giani

Programmed necrosis, not apoptosis, is a key mediator of cell loss and DAMP-mediated inflammation in dsRNA-induced retinal degeneration

There is no known treatment for the dry form of an age-related macular degeneration (AMD). Cell death and inflammation are important biological processes thought to have central role in AMD. Here we show that receptor-interacting protein (RIP) kinase mediates necrosis and enhances inflammation in a mouse model of retinal degeneration induced by dsRNA, a component of drusen in AMD. In contrast to photoreceptor-induced apoptosis, subretinal injection of the dsRNA analog poly(I : C) caused necrosis of the retinal pigment epithelium (RPE), as well as macrophage infiltration into the outer retinas. In Rip3−/− mice, both necrosis and inflammation were prevented, providing substantial protection against poly(I : C)-induced retinal degeneration. Moreover, after poly(I : C) injection, Rip3−/− mice displayed decreased levels of pro-inflammatory cytokines (such as TNF-α and IL-6) in the retina, and attenuated intravitreal release of high-mobility group box-1 (HMGB1), a major damage-associated molecular pattern (DAMP). In vitro, poly(I : C)-induced necrosis were inhibited in Rip3-deficient RPE cells, which in turn suppressed HMGB1 release and dampened TNF-α and IL-6 induction evoked by necrotic supernatants. On the other hand, Rip3 deficiency did not modulate directly TNF-α and IL-6 production after poly(I : C) stimulation in RPE cells or macrophages. Therefore, programmed necrosis is crucial in dsRNA-induced retinal degeneration and may promote inflammation by regulating the release of intracellular DAMPs, suggesting novel therapeutic targets for diseases such as AMD.

Evaluation of Retinal Nerve Fiber Layer and Ganglion Cell Layer Thickness in Alzheimer's Disease Using Spectral-Domain Optical Coherence Tomography

PURPOSE To evaluate differences between the retinal nerve fiber layer (RNFL) thickness and RNFL + ganglion cell layer (GCL) thickness in patients affected by Alzheimers disease (AD) and healthy patients using spectral-domain optical coherence tomography (SD-OCT). METHODS This was a case-control prospective study. Twenty-one AD patients and 21 healthy subjects underwent neurological examination, clock-drawing test (CDT), Mini Mental State Examination (MMSE), and comprehensive ophthalmic evaluation with visual acuity. SD-OCT examination was performed using Spectralis and RTVue-100. An RNFL thickness map was obtained using the Spectralis volume protocol with 19 lines on the 30° field centered on the macula. On each B-scan, the outer RNFL limit was manually set. Statistical analysis was performed to assess interoperator RNFL evaluation thickness. An RNFL+GCL thickness map was obtained using the RTVue-100 MM6 protocol. Maps were divided into the nine ETDRS subfields and each map value in every area was evaluated. A single eye from each patient was randomly chosen to perform the analysis. Differences between AD and healthy subjects were assessed. RESULTS The two study groups were age and sex matched. MMSE results were 19.9 ± 3.1 and 27.9 ± 1.3, respectively (P < 0.001). There was good agreement in the manual delimitation of the RNFL layer. There was a significant difference in the thickness of both the RNFL and the RNFL+GCL in all examined fields. For example, in the inferior internal subfield, the RNFL thickness was 28.1 ± 3.1 μm for AD patients and 32.6 ± 3.8 μm for healthy subjects (P < 0.001). CONCLUSIONS These results indicate that RNFL and RNFL+GCL thickness measurements are reduced in AD patients compared with healthy subjects. This finding may represent a useful element for the diagnosis and follow-up of this pathology.

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.

Opposing Roles for Membrane Bound and Soluble Fas Ligand in Glaucoma-Associated Retinal Ganglion Cell Death

Glaucoma, the most frequent optic neuropathy, is a leading cause of blindness worldwide. Death of retinal ganglion cells (RGCs) occurs in all forms of glaucoma and accounts for the loss of vision, however the molecular mechanisms that cause RGC loss remain unclear. The pro-apoptotic molecule, Fas ligand, is a transmembrane protein that can be cleaved from the cell surface by metalloproteinases to release a soluble protein with antagonistic activity. Previous studies documented that constitutive ocular expression of FasL maintained immune privilege and prevented neoangeogenesis. We now show that FasL also plays a major role in retinal neurotoxicity. Importantly, in both TNFα triggered RGC death and a spontaneous model of glaucoma, gene-targeted mice that express only full-length FasL exhibit accelerated RGC death. By contrast, FasL-deficiency, or administration of soluble FasL, protected RGCs from cell death. These data identify membrane-bound FasL as a critical effector molecule and potential therapeutic target in glaucoma.

Artifacts in automatic retinal segmentation using different optical coherence tomography instruments.

Purpose: The purpose of this study was to compare and evaluate artifact errors in automatic inner and outer retinal boundary detection produced by different time-domain and spectral-domain optical coherence tomography (OCT) instruments. Methods: Normal and pathologic eyes were imaged by six different OCT devices. For each instrument, standard analysis protocols were used for macular thickness evaluation. Error frequencies, defined as the percentage of examinations affected by at least one error in retinal segmentation (EF-exam) and the percentage of total errors per total B-scans, were assessed for each instrument. In addition, inner versus outer retinal boundary delimitation and central (1,000 &mgr;m) versus noncentral location of errors were studied. Results: The study population of the EF-exam for all instruments was 25.8%. The EF-exam of normal eyes was 6.9%, whereas in all pathologic eyes, it was 32.7% (P < 0.0001). The EF-exam was highest in eyes with macular holes, 83.3%, followed by epiretinal membrane with cystoid macular edema, 66.6%, and neovascular age-related macular degeneration, 50.3%. The different OCT instruments produced different EF-exam values (P < 0.0001). The Zeiss Stratus produced the highest percentage of total errors per total B-scans compared with the other OCT systems, and this was statistically significant for all devices (P ≤ 0.005) except the Optovue RTvue-100 (P = 0.165). Conclusion: Spectral-domain OCT instruments reduce, but do not eliminate, errors in retinal segmentation. Moreover, accurate segmentation is lower in pathologic eyes compared with normal eyes for all instruments. The important differences in EF among the instruments studied are probably attributable to analysis algorithms used to set retinal inner and outer boundaries. Manual adjustments of retinal segmentations could reduce errors, but it will be important to evaluate interoperator variability.

Soluble Guanylate Cyclase α1–Deficient Mice: A Novel Murine Model for Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is a leading cause of blindness worldwide. The molecular signaling involved in the pathogenesis of POAG remains unknown. Here, we report that mice lacking the α1 subunit of the nitric oxide receptor soluble guanylate cyclase represent a novel and translatable animal model of POAG, characterized by thinning of the retinal nerve fiber layer and loss of optic nerve axons in the context of an open iridocorneal angle. The optic neuropathy associated with soluble guanylate cyclase α1–deficiency was accompanied by modestly increased intraocular pressure and retinal vascular dysfunction. Moreover, data from a candidate gene association study suggests that a variant in the locus containing the genes encoding for the α1 and β1 subunits of soluble guanylate cyclase is associated with POAG in patients presenting with initial paracentral vision loss, a disease subtype thought to be associated with vascular dysregulation. These findings provide new insights into the pathogenesis and genetics of POAG and suggest new therapeutic strategies for POAG.

Spectral-Domain Optical Coherence Tomography as an Indicator of Fluorescein Angiography Leakage from Choroidal Neovascularization

PURPOSE To evaluate spectral-domain optical coherence tomography (SD-OCT) findings that predict angiographic leakage in choroidal neovascularization (CNV). METHODS SD-OCT and fluorescein angiography (FA) images of 93 eyes of 93 patients were retrospectively analyzed. All patients were previously treated with anti-vascular endothelial growth factor agents for CNV from age-related macular degeneration. FA images were analyzed to assess the presence of leakage. SD-OCT images were analyzed to identify the overall presence of fluid, as well as specific patterns of fluid presentation, including intraretinal cystic spaces (ICS), retinal pigment epithelium detachment (PED), and neurosensory detachment (NSD). The presence of ultrastructural features such as intraretinal hyperreflective flecks and the inherent reflectivity and boundary definition of the subretinal material were evaluated. Both the association and the sensitivity, specificity, and both positive and negative predictive values of SD-OCT findings compared with FA leakage were calculated. RESULTS A statistically significant association between SD-OCT findings and FA leakage was found for eyes that displayed fluid, NSD, intraretinal flecks, and low reflectivity or undefined boundaries from subretinal material, and not for PED or ICS. Sensitivity and specificity for SD-OCT findings were, respectively: 94% and 27% for fluid; 68% and 88% for NSD; 81% and 83% for intraretinal flecks; 63% and 92% for undefined boundaries of subretinal material; and 94% and 87% for low reflectivity from subretinal material. CONCLUSIONS The evidence of fluid on SD-OCT is sensitive but nonspecific in identifying FA leaky CNV. The assessment of neurosensory detachment as well as other ultrastructural elements may increase the specificity of analysis.

Utilizing Targeted Gene Therapy with Nanoparticles Binding Alpha v Beta 3 for Imaging and Treating Choroidal Neovascularization

Purpose The integrin αvβ3 is differentially expressed on neovascular endothelial cells. We investigated whether a novel intravenously injectable αvβ3 integrin-ligand coupled nanoparticle (NP) can target choroidal neovascular membranes (CNV) for imaging and targeted gene therapy. Methods CNV lesions were induced in rats using laser photocoagulation. The utility of NP for in vivo imaging and gene delivery was evaluated by coupling the NP with a green fluorescing protein plasmid (NP-GFPg). Rhodamine labeling (Rd-NP) was used to localize NP in choroidal flatmounts. Rd-NP-GFPg particles were injected intravenously on weeks 1, 2, or 3. In the treatment arm, rats received NP containing a dominant negative Raf mutant gene (NP-ATPμ-Raf) on days 1, 3, and 5. The change in CNV size and leakage, and TUNEL positive cells were quantified. Results GFP plasmid expression was seen in vivo up to 3 days after injection of Rd-NP-GFPg. Choroidal flatmounts confirmed the localization of the NP and the expression of GFP plasmid in the CNV. Treating the CNV with NP-ATPμ-Raf decreased the CNV size by 42% (P<0.001). OCT analysis revealed that the reduction of CNV size started on day 5 and reached statistical significance by day 7. Fluorescein angiography grading showed significantly less leakage in the treated CNV (P<0.001). There were significantly more apoptotic (TUNEL-positive) nuclei in the treated CNV. Conclusion Systemic administration of αvβ3 targeted NP can be used to label the abnormal blood vessels of CNV for imaging. Targeted gene delivery with NP-ATPμ-Raf leads to a reduction in size and leakage of the CNV by induction of apoptosis in the CNV.

Evidence for baseline retinal pigment epithelium pathology in the Trp1-Cre mouse

The increasing popularity of the Cre/loxP recombination system has led to the generation of numerous transgenic mouse lines in which Cre recombinase is expressed under the control of organ- or cell-specific promoters. Alterations in retinal pigment epithelium (RPE), a multifunctional cell monolayer that separates the retinal photoreceptors from the choroid, are prevalent in the pathogenesis of a number of ocular disorders, including age-related macular degeneration. To date, six transgenic mouse lines have been developed that target Cre to the RPE under the control of various gene promoters. However, multiple lines of evidence indicate that high levels of Cre expression can be toxic to mammalian cells. In this study, we report that in the Trp1-Cre mouse, a commonly used transgenic Cre strain for RPE gene function studies, Cre recombinase expression alone leads to RPE dysfunction and concomitant disorganization of RPE layer morphology, large areas of RPE atrophy, retinal photoreceptor dysfunction, and microglial cell activation in the affected areas. The phenotype described herein is similar to previously published reports of conditional gene knockouts that used the Trp1-Cre mouse, suggesting that Cre toxicity alone could account for some of the reported phenotypes and highlighting the importance of the inclusion of Cre-expressing mice as controls in conditional gene targeting studies.

Enhanced depth imaging optical coherence tomography features of choroidal osteoma.

Purpose: To describe the choroidal findings in eyes affected by choroidal osteoma imaged by enhanced depth imaging optical coherence tomography. Methods: Retrospective case series. Results: Seven eyes from five patients with choroidal osteoma were included in the study. Patients mean age of presentation was 26 years (median, 34; range, 6–37 years) and mean best-corrected visual acuity was 20/32 (median, 20/20; range, 20/20–20/200). Enhanced depth imaging optical coherence tomography examination revealed normal inner retina in all the cases and normal outer retina in three eyes. Abnormalities included irregularities in external limiting membrane (n = 2), myoid zone (n = 1), ellipsoid junction (n = 4), cone outer segments of photoreceptors (n = 5), and retinal pigment epithelium (n = 3). Choroidal analysis revealed thinned (n = 4) or non visible (n = 2) choriocapillaris, thinned (n = 3) or non visible (n = 4) medium vessels, and thinned large vessels layer (n = 4). The osteoma showed multiple intralesional layers (n = 5), a sponge-like appearance (n = 7), and intralesional vessels (n = 7). The sclero-choroidal junction was visible in all cases. Choroidal neovascularization was found in four eyes. Conclusion: Analysis of eyes affected by choroidal osteoma revealed a characteristic sponge-like tumor appearance with the presence of multiple intralesional layers. The lesion showed a typical transparency with visibility of sclero-choroidal junction in all cases.