Anti-arrestin immunoreactivity in the human retina: difference between light- and dark-adaptation

Glaucoma related Proteomic Alterations in Human Retina Samples

Glaucoma related proteomic changes have been documented in cell and animal models. However, proteomic studies investigating on human retina samples are still rare. In the present work, retina samples of glaucoma and non-glaucoma control donors have been examined by a state-of-the-art mass spectrometry (MS) workflow to uncover glaucoma related proteomic changes. More than 600 proteins could be identified with high confidence (FDR < 1%) in human retina samples. Distinct proteomic changes have been observed in 10% of proteins encircling mitochondrial and nucleus species. Numerous proteins showed a significant glaucoma related level change (p < 0.05) or distinct tendency of alteration (p < 0.1). Candidates were documented to be involved in cellular development, stress and cell death. Increase of stress related proteins and decrease of new glaucoma related candidates, ADP/ATP translocase 3 (ANT3), PC4 and SRFS1-interacting protein 1 (DFS70) and methyl-CpG-binding protein 2 (MeCp2) could be documented by MS. Moreover, candidates could be validated by Accurate Inclusion Mass Screening (AIMS) and immunostaining and supported for the retinal ganglion cell layer (GCL) by laser capture microdissection (LCM) in porcine and human eye cryosections. The workflow allowed a detailed view into the human retina proteome highlighting new molecular players ANT3, DFS70 and MeCp2 associated to glaucoma.

Analysis of autoantibodies against human retinal antigens in sera of patients with glaucoma and ocular hypertension

PURPOSE

The aim of this study was to show that complex antibody patterns against retinal antigens in sera of patients with glaucoma, found in previous studies, are autoantibodies against human antigens.

METHODS

Sera of 179 patients were collected at the Department of Ophthalmology (University of Mainz, Germany): non-glaucomatous control patients (n=45), primary open-angle glaucoma (n=45), ocular hypertension (n=44), and normal tension glaucoma patients (n=45). The sera were tested against Western blots of human retinal antigens. IgG antibody patterns were analyzed by multivariate statistical techniques, and some significant antigens were identified by mass spectrometry.

RESULTS

All subjects, even healthy ones, showed different and complex banding patterns. Glaucoma groups showed up- and down-regulations of antibody reactivities compared to the control group. The multivariate analysis of discriminance found significant differences (p<0.05) in IgG antibody profiles between glaucoma groups, ocular hypertension, and healthy subjects against human retinal antigens. The antigen band at 12 kDa was identified as Histone H4 via mass spectrometry, the 29 kDa band as cellular retinaldehyde-binding protein, and one at 49 kDa as retinal S-antigen.

CONCLUSIONS

Using human retinal antigen, we demonstrated that complex autoantibody patterns exist in sera of patients with glaucoma. Large correlations with previous studies using bovine retinal antigens could be seen.

Arrestin migrates in photoreceptors in response to light: a study of arrestin localization using an arrestin-GFP fusion protein in transgenic frogs

Subcellular translocation of phototransduction proteins in response to light has previously been detected by immunocytochemistry. This movement is consistent with the hypothesis that migration is part of a basic cellular mechanism regulating photoreceptor sensitivity. In order to monitor the putative migration of arrestin in response to light, we expressed a functional fusion between the signal transduction protein arrestin and green fluorescent protein (GFP) in rod photoreceptors of transgenic Xenopus laevis. In addition to confirming reports that arrestin is translocated, this alternative approach generated unique observations, raising new questions regarding the nature and time scale of migration. Confocal fluorescence microscopy was performed on fixed frozen retinal sections from tadpoles exposed to three different lighting conditions. A consistent pattern of localization emerged in each case. During early light exposure, arrestin-GFP levels diminished in the inner segments (ISs) and simultaneously increased in the outer segments (OSs), initially at the base and eventually at the distal tips as time progressed. Arrestin-GFP reached the distal tips of the photoreceptors by 45-75 min at which time the ratio of arrestin-GFP fluorescence in the OSs compared to the ISs was maximal. When dark-adaptation was initiated after 45 min of light exposure, arrestin-GFP rapidly re-localized to the ISs and axoneme within 30 min. Curiously, prolonged periods of light exposure also resulted in re-localization of arrestin-GFP. Between 150 and 240 min of light adaptation the arrestin-GFP in the ROS gradually declined until the pattern of arrestin-GFP localization was indistinguishable from that of dark-adapted photoreceptors. This distribution pattern was observed over a wide range of lighting intensity (25-2700 lux). Immunocytochemical analysis of arrestin in wild-type Xenopus retinas gave similar results.

Photoreceptor function of retinal transplants implicated by light-dark shift of S-antigen and rod transducin

The aim was to demonstrate functional properties of transplanted histologically normal photoreceptors. Subretinal intact-sheet transplants of fetal E17-E20 rat retinas to light-damaged albino rat eyes were fixed in light or dark, 2 to 42 weeks after transplantation, and stained immunohistochemically for certain phototransduction proteins. In light adapted transplants, transducin was predominantly found in inner segments of parallel-organized photoreceptors. Transducin shifted to the outer segments with dark-adaptation. S-antigen distribution was opposite to transducin. Rhodopsin distribution did not change. The shift of signal transduction proteins correlated to the light conditions indicates that normal phototransduction processes were established in photoreceptors of transplanted retinal sheets.

Immunolocalization of ubiquitin and related enzymes in human retina and retinal pigment epithelium

PURPOSE

To examine the localization of ubiquitin (Ub) and related enzymes in human retina with emphasis on the retinal pigment epithelium (RPE)-Bruch's membrane complex.

METHODS

Thirty human eyes enucleated for various disease processes were examined. Immunohistochemistry was performed on paraffin sections using antibodies against Ub, Ub-conjugating enzyme (E2), Ub carboxyl-terminal hydrolase (PGP 9.5), and, for comparison, arrestin (Arr). Immunoreactivity (IR) was tested using the avidin-biotin method.

RESULTS

Ub was present throughout retina but was particularly prominent in ganglion cells and RPE. Most intriguing was the presence of Ub IR in age-related, sub-RPE deposits such as drusen and basal laminar deposits (BLD). RPE immunolabeling was more intense in older tissue, but otherwise no pattern of Ub IR could be linked to specific diseases. E2 IR colocalized with Ub, with one exception; E2 IR was not found in drusen or BLD. PGP 9.5 IR was intense in nerve fibers, ganglion cells, and the inner nuclear and plexiform layers. RPE staining was faint and patchy; sub-RPE deposits were not labeled. Arr IR was present in photoreceptors but not within or beneath RPE cells.

CONCLUSION

The ubiquitination process is important in human retina and particularly in ganglion cells. Ub-related processes are also active in RPE and may be involved in the degradation and disposal of proteins from these cells. The presence of Ub in sub-RPE deposits--without related Ub-processing enzymes--raises the possibility that certain proteins become ubiquitinated within RPE but that further degradation of the Ub-protein complexes does not occur.