Expression of glial fibrillary acidic protein and glutamine synthetase by Müller cells after optic nerve damage and intravitreal application of brain-derived neurotrophic factor

New insights into autoantibody profiles from immune privileged sites in the eye: a glaucoma study

Glaucoma is a chronic neurodegenerative disease and one of the leading causes of blindness. Autoantibody based immune processes are assumed to be involved in its pathogenesis. However, it is still unclear to what extent autoantibody patterns found in the eye (aqueous humor) are congruent to systemic autoantibodies (blood). Consistency would underline the specificity of known serum antibody markers for glaucoma. In this study we used antigen microarrays to analyze autoantibody reactivities in sera and corresponding aqueous humor samples of primary open-angle glaucoma patients (N=37) and non-glaucomatous controls (N=31). Compared to control subjects several divergent immunoreactivities were identified for the glaucoma group in both body fluids. Interestingly, 20% of the tested antigens revealed increased immunoreactivities (e.g., against HSP27, MBP, and α-1-antitrypsin) and 7.5% decreased immunoreactivities (e.g., against GFAP and β-L-crystallin), thus demonstrating a significant alteration of the autoantibody profiles in glaucoma patients. Using an artificial neural network in combination with a unique serum autoantibody pattern on prospective sera we were able to detect glaucoma with a specificity and sensitivity of approximately 93%. The intraindividual comparison revealed a strong correlation of detected immunoreactivities in sera and comparative aqueous humor samples in both study groups. These results emphasize the specificity of immunoreactions found in blood samples of glaucoma patients. Furthermore they indicate the necessity of analyzing not only up-regulated but also down-regulated antibody reactivities, which might be likewise relevant for the understanding of other diseases.

Gene expression changes in retinal Müller (glial) cells exposed to elevated pressure

PURPOSE

Retinal Müller (glial) cells undergo "reactive gliosis", a stress response that is accompanied by changes in their morphology and upregulation of various cellular markers. Reactive gliosis is seen in many retinal diseases and conditions; however, it is not known whether it is a common, stereotypic response or the nature of the response varies with the type of retinal stress. To address this question, we have examined gene expression changes in Müller cells exposed to elevated pressure.

MATERIALS AND METHODS

Rat Müller cells (rMC-1) were exposed to elevated pressure, and RNA was extracted and analyzed using Affymetrix GeneChip microarrays to identify pressure-responsive genes.

RESULTS

Analysis of microarray data showed that at 6 h, 186 genes had > 1.5-fold change with FDR < 0.01. Of these, 62 genes were up-regulated while 124 genes were down-regulated. At 24 h, 73 genes changed > 1.5-fold. Of these, 37 genes were up-regulated while 36 genes were down-regulated. Ingenuity canonical pathway analysis showed that several signaling and metabolic pathways were significantly changed in Müller cells under high pressure. In addition, among up- and down-regulated genes, we identified eight genes-areg, bmp4, cyp1b1, gpnmb, herc2, msh2, heph, and selenbp1, that have been directly or indirectly associated with elevated intraocular pressure. Two genes, areg and gpnmb, further showed time-dependent changes in mRNA and protein expression.

CONCLUSION

The results show that Müller cells in vitro respond to elevated pressure by differential regulation of expressed genes. The transcriptional profile is different from that seen with hypoxia, which indicates that Müller cells respond differentially to different microenvironmental changes in the retina.

Intravitreous interleukin-2 treatment and inflammation modulates glial cells activation and uncrossed retinotectal development

Interleukin-2 (IL-2) plays regulatory functions both in immune and nervous system. However, in the visual system, little is known about the cellular types which respond to IL-2 and its effects. Herein, we investigated the influence of IL-2 in the development of central visual pathways. Lister Hooded rats were submitted to multiple (at postnatal days [PND]7/10/13) or single (at PND10) intravitreous injections of phosphate-buffered saline (PBS) (vehicle), zymosan, or IL-2. IL-2 receptor α subunit was detected in the whole postnatal retina. Chronic treatment with either PBS or IL-2 increases retinal glial fibrillary acidic protein (GFAP) expression, induces intravitreous inflammation revealed by the presence of macrophages, and results in a slight rearrangement of retinotectal axons. Acute zymosan treatment disrupts retinotectal axons distribution, confirming the influence of inflammation on retinotectal pathway reordering. Furthermore, acute IL-2 treatment increases GFAP expression in the retina without inflammation and produces a robust sprouting of the intact uncrossed retinotectal pathway. No difference was observed in glial cells activity in superior colliculus. Taken together, these data suggest that inflammation and interleukin-2 modulate retinal ganglion cells development and the distribution of their axons within central targets.

Bone marrow mononuclear cells increase retinal ganglion cell survival and axon regeneration in the adult rat

The central nervous system (CNS) of adult mammals generally does not regenerate, and many studies have attempted to identify factors that could increase neuroprotection and/or axonal outgrowth after CNS lesions. Using the optic nerve crush of rats as a model for CNS injury, we investigated the effect of intravitreal transplantation of syngeneic bone-marrow mononuclear cells (BMMCs) on the survival of retinal ganglion cells (RGC) and on the regeneration of optic axons. Control animals received intravitreal saline injections after lesion. Injections of BMMCs resulted in a 1.6-fold increase in the number of RGCs surviving 14 days after injury. The BMMC-treated animals also had increased numbers of axons, which grew up to 1.5 mm from the crush site, and also had reduced Müller glia activation. Analysis of mRNAs in all conditions revealed an increase in levels of fibroblast growth factor 2 (FGF-2) mRNA in treated animals 14 days after injury. To investigate whether the regenerated axons could reach the brain, we retrograde labeled the RGCs by injecting a lipophilic tracer into the superior colliculus. We also analyzed the expression of NGFI-A in the superficial layers of the superior colliculus as a possible marker of synaptic input from RGC axons. We found evidence that more RGCs were able to reach the brain after treatment and we showed that NGFI-A expression was higher in the treated animals 60 days after injury. These results demonstrate that transplant of BMMCs can increase neuroprotection and neuroregeneration after injury in a model of optic nerve crush, and these effects could be mediated by FGF-2.

Involvement of gp130-associated cytokine signaling in Müller cell activation following optic nerve lesion

Ciliary neurotrophic factor (CNTF) and the related cytokine leukemia inhibitory factor (LIF) have been implicated in regulating astrogliosis following CNS lesions. Application of the factors activates astrocytes in vivo and in vitro, and their expression as well as their receptors is upregulated after brain injury. Here, we investigated their function by studying Müller cell activation induced by optic nerve crush in CNTF- and LIF-deficient mice, and in animals with deficiencies in cytokine signaling pathways. In the retina of CNTF(-/-) mice, basal GFAP expression was reduced, but unexpectedly, injury-induced upregulation in activated Müller cells was increased during the first 3 days after lesion as compared to wild-type animals and this corresponded with higher phosphorylation level of STAT3, an indicator of cytokine signaling. The observation that LIF expression was strongly upregulated in CNTF(-/-) mice but not in wild-type animals following optic nerve lesion provided a possible explanation. In fact, additional ablation of the LIF gene in CNTF/LIF double knockout mice almost completely abolished early lesion-induced GFAP upregulation in Müller cells and STAT3 phosphorylation. Early Müller cell activation was also eliminated in LIF(-/-) mice, despite normal CNTF levels, as well as in mutants deficient in gp130/JAK/STAT signaling and in conditional STAT3 knockout mice. Our results demonstrate that LIF signaling via the gp130/JAK/STAT3 pathway is required for the initiation of the astrogliosis-like reaction of retinal Müller cells after optic nerve injury. A potential role of CNTF was possibly masked by a compensatory increase in LIF signaling in the absence of CNTF.

A conditional immortalized mouse muller glial cell line expressing glial and retinal stem cell genes

PURPOSE

Müller glia have multiple functions in the retina, including synthesis of neurotrophic factors, uptake and metabolism of neurotransmitters, spatial buffering of ions, maintenance of the blood-retinal barrier, and response to injury. A population of Müller glia has some stem cell-like characteristics both in vivo and in vitro. The purpose of this study was to generate and characterize novel Müller glial cell lines from the postnatal mouse retina.

METHODS

Cells were cultured from postnatal day (P) 10 double heterozygous transgenic (H-2K(b)-tsA58/+; HRhoGFP/+) or C57BL/6 mice after papain dissociation. Interferon gamma (IFNγ) induction of the SV40 T-antigen (TAg) was assayed by immunohistochemistry and Western blot analysis. Proliferation was assayed by BrdU uptake and cell counts of calcein AM/ethidium bromide-stained cells. Gene expression was analyzed by RT-PCR and immunohistochemistry.

RESULTS

Conditionally immortalized (ImM10 [Immortmouse Müller P10]) and spontaneously immortalized (C57M10 [C57BL/6 Müller P10]) Müller glial cell lines were selected by differential adherence to laminin; both consisted of adherent flat cells with large, diffusely staining nuclei and an epithelial morphology. TAg induction stimulated BrdU uptake by Müller glia in mixed retinal cultures from H-2K(b)-tsA58/+; HRhoGFP/+ mice and increased the proliferation of ImM10 cells. ImM10 and C57M10 cells expressed genes characteristic of Müller glia but not genes characteristic of differentiated retinal neurons. ImM10 cells also expressed retinal stem cell genes.

CONCLUSIONS

The ImM10 cell line is a novel, conditionally immortalized Müller glial cell line isolated from the P10 mouse retina that expresses genes characteristic of Müller glial and retinal stem cells.

The transcription factor RBP-J is essential for retinal cell differentiation and lamination

Background

The highly ordered vertebrate retina is composed of seven cell types derived from a common pool of retinal progenitor cells (RPCs), and is a good model for the studies of cell differentiation and interaction during neural development. Notch signaling plays a pivotal role in retinogenesis in mammals, but the full scope of the functions of Notch pathway, and the underlying molecular mechanisms, remain unclear.

Results

In this study, we conditionally knocked out RBP-J, the critical transcription factor downstream to all four Notch receptors, in RPCs of mouse retina at different developmental stages. Disruption of RBP-J at early retinogenesis resulted in accelerated RPCs differentiation, but only photoreceptors and ganglion cells were overrepresented, with other neuronal populations diminished. Similarly, deletion of RBP-J at early postnatal days also led to overproduction of photoreceptors, suggesting that RBP-J governed RPCs specification and differentiation through retinogenesis. In all the RBP-J deletion models, the retinal laminar structures were distorted by the formation of numerous rosette-like structures, reminiscent of β-catenin deficient retina. Indeed, we found that these rosettes aligned with gaps in β-catenin expression at the apical surface of the retina. By in vivo electroporation-mediated transfection, we demonstrated that lamination defects in RBP-J deficient retinae were rescued by overexpressing β-catenin.

Conclusions

Our data indicate that RBP-J-mediated canonical Notch signaling governs retinal cell specification and differentiation, and maintains retinal lamination through the expression of β-catenin.

Optic nerve and vitreal inflammation are both RGC neuroprotective but only the latter is RGC axogenic

Intravitreal inflammation, induced by either lens injury, or intravitreal injection of zymosan (IVZ), protects RGC from apoptosis and stimulates axon regeneration after optic nerve transection. Here, we investigate the differential effects of intra-optic nerve zymosan (ONZ) and IVZ injections on RGC neuroprotection and axogenesis. After both IVZ and ONZ injection, zymosan-induced inflammation promoted a similar 4-/5-fold enhancement in RGC survival, compared to optic nerve transected controls, but only IVZ promoted RGC axon regeneration. IVZ was the most effective in activating retinal astrocyte/Müller cells while regulated intramembraneous proteolysis (RIP) of p75(NTR) and inactivation of Rho (key components of the axon growth inhibitory signalling cascade) occurred in both ONZ and IVZ, but only in the latter did RGC axons regenerate. We suggest that neuroprotective factors may be transported to RGC somata by retrograde transport after ONZ and diffuse into the retina after IVZ injection, but an axogenic agent is required to initiate and maintain disinhibited RGC axon regeneration that may be an exclusive property of a Müller cell-derived factor released after IVZ.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

AT1 receptor inhibition prevents astrocyte degeneration and restores vascular growth in oxygen-induced retinopathy

We investigated the effect of receptor blockade induced by an angiotensin II type-1 receptor antagonist (AT(1)-RB) on glial and vascular changes in oxygen-induced retinopathy (OIR), a model of retinopathy of prematurity (ROP). OIR was induced in Sprague-Dawley rats by exposure to 80% oxygen from postnatal (P) days 0-11, followed by 7 days in room air. Control animals were in room air for the entire duration. One cohort of OIR and control pups received the AT(1)-RB valsartan (40 mg/kg/day intraperitoneal) from P11 to P18. The vascular response was examined immunocytochemically using retinal wholemounts and vertical sections labeled with endothelial (Isolectin-B4) and pericyte (NG2, desmin) markers. Glial cell changes were assessed by measuring cell numbers and immunoreactivity (S100beta, connexin-26, and glial fibrillary acidic protein). OIR resulted in extensive intravitreal neovascularization and under-development of the outer vascular plexus. Pericyte numbers were not significantly affected in OIR, although pericyte-endothelial (desmin-IB4) interactions were impaired. Peripheral astrocyte degeneration occurred between P11 and P13 with prominent Müller cell reactivity at P18. Valsartan imparted a protective effect on glia and blood vessels in OIR. At P18, valsartan-treated OIR retinae showed significantly greater astrocyte survival, improved revascularization of the retina, and reduced preretinal neovascularization and Müller cell reactivity. This study identifies a glio-vascular protective effect with AT(1)-RB in OIR.

Investigating the movement of intravitreal human serum albumin nanoparticles in the vitreous and retina

PURPOSE

To investigate the movement of intravitreally injected human serum albumin nanoparticles (HSA-NP) with respect to nanoparticle surface charge and retinal injury.

METHODS

HSA-NPs were developed by a desolvation technique. HSA-NPs were cationized by covalent coupling of hexamethylenediamine on the particle surface. Either anionic or cationic HSA-NPs were injected to determine the effect of surface charge on intravitreal nanoparticle movement. HSA-NPs were injected intravitreally into both normal and laser photocoagulated eyes to examine the effect of the integrity of retinal tissue on the retinal penetration. The retinal penetration of fluorescence labeled anionic HSA-NPs was investigated by confocal microscopy.

RESULTS

Anionic particles (-33.3+/-6.1 mV) more easily diffused through the 3-dimensional vitreal network of collagen fibrils than did their cationic counterparts (11.7+/-7.2 mV). In the laser photocoagulated retina, more HSA-NPs were detected in the choroidal space, compared to the normal retina. The immunohistochemical studies indicated that HSA-NPs were taken up into Müller cells.

CONCLUSIONS

The movement of intravitreal nanoparticles depended on both nanoparticles surface charge and retinal injury. The Müller cells might play an important role in the retinal penetration of nanoparticles. The anionic HSA-NP is a promising drug or gene delivery carrier to the sub-retinal space and RPE.

Exogenous application of persephin influences phosphatidylinositol-3 kinase and MAPK/ERK signalling and enhances proliferation during early development in retinospheres

Persephin (PSPN), a member of the glial cell line-derived neurotrophic factor family, and its implication in the retina is not well understood but might be an interesting therapeutic target for degenerative diseases. Although, PSPN is lost in the chicken during evolution, its target, the GDNF family receptor alpha 4 (GFRalpha4), is still expressed in a temporal and spatial pattern in the developing retina. We used this "knockout-precondition" to study the bioactivity and the effect of exogenous PSPN application and subsequent GFRalpha activation during retinal development in vitro without impairments of endogenous PSPN. Retinospheres, derived from dissociated chicken retina of embryonic day 6, were treated with PSPN and intracellular signalling was monitored. Additionally, PSPN was added during cultivation of the retinospheres and immunhistochemical stainings and Western blotting were performed to evaluate changes in proliferation, apoptosis and differentiation. Exogenous applied PSPN enhanced phosphatidylinositol-3-kinase (PI-3K) signalling and decreased signalling of mitogen-activated protein kinases (MAPK). Most importantly early retinal proliferation was enhanced and glutamine synthetase expression was decreased whereas differentiation of major retinal cell types was not changed. In contrast to GDNF, PSPN is exclusively influencing early progenitors whereas differentiation is not effected and seems to be regulated through PSPN-independent mechanisms. Since the binding site of PSPN and therefore the target of potential therapeuticals, is well conserved among species and is with high probability not able to bind other members of the GDNF-family, these results might be assigned to other species including mammals and humans.

Immunoproteasome responds to injury in the retina and brain

It is well known that immunoproteasome generates peptides for MHC Class I occupancy and recognition by cytotoxic T lymphocytes (CTL). The present study focused on evidence for alternative roles for immunoproteasome. Retina and brain were analyzed for expression of immunoproteasome subunits using immunohistochemistry and western blotting under normal conditions and after injury/stress induced by CTL attack on glia (brain) or neurons (retina). Normal retina expressed substantial levels of immunoproteasome in glia, neurons, and retinal pigment epithelium. The basal level of immunoproteasome in retina was two-fold higher than in brain; CTL-induced retinal injury further up-regulated immunoproteasome expression. Immunoproteasome up-regulation was also observed in injured brain and corresponded with expression in Purkinje cells, microglia, astrocytes, and oligodendrocytes. These results suggest that the normal environment of the retina is sufficiently challenging to require on-going expression of immunoproteasome. Further, immunoproteasome up-regulation with retinal and brain injury implies a role in neuronal protection and/or repair of damage.

Sera of glaucoma patients show autoantibodies against myelin basic protein and complex autoantibody profiles against human optic nerve antigens

BACKGROUND

The aim of this study was to gain more information about the possible immunological mechanisms in glaucoma. We analyzed the complex autoantibody patterns against human optic nerve antigens in sera of patients with glaucoma and tried to identify important antigens.

METHODS

Sera of 133 patients were included: healthy control subjects (n = 44), primary open-angle glaucoma (n = 44), and normal tension glaucoma patients (n = 45). The sera were tested against Western blots of human optic nerve, and antibody bands were visualized with chloronaphthol. IgG antibody patterns were analyzed by multivariate statistical techniques, and the most significant antigens were identified by mass spectrometry (Maldi-TOFTOF).

RESULTS

All subjects, even healthy ones, showed different and complex antibody patterns. Glaucoma groups showed specific 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 against human optic nerve antigens between both glaucoma groups and healthy subjects. The identified antigens include: myelin basic protein (up-regulated in the POAG group), glial fibrillary acidic protein (down-regulated in the glaucoma groups), and vimentin (down-regulated in the glaucoma groups in comparison to controls).

CONCLUSIONS

Using human optic nerve antigen, we were able to demonstrate that complex IgG autoantibody patterns exist in sera of patients with glaucoma. Large correlations between the given and our previous studies using bovine optic nerve antigens could be seen. Furthermore, anti-myelin basic protein antibodies, which can also be detected in patients with multiple sclerosis, were found in sera of glaucoma patients.

Neuronal and glial cell changes are determined by retinal vascularization in retinopathy of prematurity

We have characterized the vascular, neuronal, and glial changes in oxygen-induced retinopathy, a model of retinopathy of prematurity (ROP). Newborn Sprague-Dawley rats were exposed to either 80% +/- 2% oxygen to postnatal day P11 and then room air until P18 (ROP) or room air for the entire duration (controls). Retinal structure was examined under the light microscope and following postembedding immunocytochemistry in central, midperipheral, and peripheral regions. Müller cells were evaluated immunocytochemically with glial fibrillary acidic protein. The extent of vascularization was established histologically. ROP caused significant thinning of the inner cellular and plexiform layers, which became more pronounced in the peripheral inner nuclear layer of ROP animals (11.3% loss vs. 25.4% loss). Amacrine cell amino acid levels were particularly vulnerable in the peripheral retina; bipolar cells showed similar but less prominent changes. Müller cells had elevated glutamine levels and were most gliotic in the periphery. The vasculature extended to peripheral retinal regions at P18 in controls but not in ROP rats. The most striking pattern of change was evident in the midperipheral "transition zone" of ROP animals. Areas close to blood vessels showed neurochemical properties that were similar to those of the central retina, indicating a local protective effect of the inner retinal blood supply. We find that ROP produces complex vascular, neural, and glial changes that relate to the proximity of inner retinal blood vessels.

Reactive changes of retinal astrocytes and Müller glial cells in kainate-induced neuroexcitotoxicity

The aim of this study was to investigate reactive changes of astrocytes and Müller glial cells in rats subjected to kainate treatment, which leads to neuronal degeneration in the ganglion cell layer and the inner border of the inner nuclear layer as confirmed by labelling with Fluoro-Jade B, a marker for degenerating neurons and fibres. Both the astrocytes and the Müller glial cells reacted vigorously to kainate injection as shown by their up-regulated expression of nestin, glial fibrillary acidic protein and glutamine synthetase. A major finding was the induced expression of nestin together with glial fibrillary acidic protein beginning at 1 day post-injection of kainate. The marked nestin expression appeared to be most intense at 1 day and was sustained till 2 weeks as compared with the untreated/normal retina. Western blotting analysis confirmed a marked increase in expression of nestin, glial fibrillary acidic protein and glutamine synthetase as compared with untreated/normal retina. Double labelling study revealed that astrocytes and Müller glial cells expressed the radial glia marker nestin, and incorporated bromodeoxyuridine to re-enter into their cell cycle. The induced expression of these proteins in astrocytes and Müller glial cells indicated an induction of gliotic responses and de-differentiation that may be associated with regenerative efforts after kainate-induced injury. Indeed, with the acquisition of an immature molecular profile as manifested by the induced expression of brain lipid-binding protein and doublecortin in astrocytes and Müller glial cells, the potential of these cells to de-differentiate in retinal neurodegeneration is greatly amplified.

Regeneration of inner retinal neurons after intravitreal injection of ouabain in zebrafish

We examined the regenerative capacity of the adult zebrafish retina by intravitreal injection of a low ouabain concentration to rapidly damage the ganglion cell layer (GCL) and inner nuclear layer (INL) with minimal photoreceptor cell damage. By 24 h after ouabain injection, maximal numbers of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL)-positive cells were detected in the INL and GCL, with low numbers of TUNEL-positive cells in the outer nuclear layer. Immunolabeling revealed that approximately 85% of the HuC/D-positive amacrine and ganglion cells were lost by 7 d post-ouabain injection (dpi). This ganglion cell loss was consistent with the small, but statistically significant, decrease in the optic nerve diameter. The regeneration response began within 1 dpi with increased proliferating cell nuclear antigen (PCNA) expression in both the INL and GCL. By 3 dpi, PCNA expression is primarily restricted to the Müller glia. By 5 dpi, most of the PCNA expression was localized to neuronal progenitors expressing the olig2:egfp transgene rather than the Müller glia. By 7 dpi, the neuronal progenitors began committing to the ganglion cell fate based on the coexpression of the atoh7:EGFP transgene and the zn5 antigen. The regeneration of ganglion and amacrine cells continued until 60 dpi, when they reached 75% of their uninjected control number. This demonstrates that inner retinal damage, without extensive photoreceptor damage, is sufficient to induce a regeneration response that is marked by the Müller glial cells reentering the cell cycle to produce neuronal progenitor cells that regenerate INL and ganglion cells in the zebrafish retina.

Nestin expression in Müller glial cells in postnatal rat retina and its upregulation following optic nerve transection

This study examined the nestin immunoexpression and its specific cellular localization in the developing retina of rats and investigated its putative changes in an altered environment. At postnatal day 0, nestin immunoexpression was detected in radially oriented cells considered to be neural progenitors that were glutamine synthetase (GS) negative. With age, it was localized in differentiating and differentiated GS positive Müller glial cells. Nestin expression was down-regulated as maturation proceeded, so that by 12 weeks, it was almost completely diminished as confirmed also by real time-polymerase chain reaction analysis. Nestin expression along with that of glial fibrillary acidic protein (GFAP) was induced and upregulated in mature Müller glial cells following optic nerve transection. It is suggested that both nestin and GFAP may be useful biomarkers in retinal injuries. In view of their cytoskeletal nature, the marked expression of nestin and GFAP may provide a structural support for the framework of retina which would be disrupted as a result of loss of neurons in optic nerve lesion. It may also be neuronal protective taking into consideration the close spatial and functional links between Müller glial cells and the axotomized ganglion cells.

Analysis of IgG antibody patterns against retinal antigens and antibodies to alpha-crystallin, GFAP, and alpha-enolase in sera of patients with "wet" age-related macular degeneration

BACKGROUND

The aim of this study was to compare the IgG antibody patterns against retinal antigens in sera of patients with age-related macular degeneration (AMD) and healthy subjects to learn more about possible immunological aspects of this disease and to identify some of the most important antigens.

METHODS

Sera of 140 patients were analyzed: healthy volunteers (CO, n=101) and patients with "wet" age-related macular degeneration (AMD, n=39). The sera were tested against western blots of bovine retinal antigens. The IgG antibody patterns were analyzed by multivariate statistical techniques and some antigens were identified via LC-MS/MS.

RESULTS

All patients showed complex patterns of IgG antibodies against retinal antigens. The discriminant analysis revealed a statistical significant difference between the antibody profiles of the AMD and the CO group (P=0.000023). Not only up-regulations of antigen-antibody-reactivities in the AMD group at some molecular weight ranges, e.g. at 46 and 52 kDa, could be seen, but also down-regulations, e.g. at 18 and 36 kDa. The 18 kDa antigen band was identified as alphaB-crystallin, the band at 46 kDa as alpha-enolase, and one at 52 kDa as glial fibrillary acidic protein.

CONCLUSIONS

We could demonstrate that both groups (wet AMD and CO) show complex IgG antibody patterns against retinal antigens, which are highly specific for each group. This provides further hints for the immunological basis of the disease. These changes in the antibody profiles in "wet" AMD could represent a secondary response to retinal damage or can play a causative role in the disease.

Pals1/Mpp5 is required for correct localization of Crb1 at the subapical region in polarized Muller glia cells

Mutations in the human Crumbs homologue-1 (CRB1) gene cause retinal diseases including Leber's congenital amaurosis (LCA) and retinitis pigmentosa type 12. The CRB1 transmembrane protein localizes at a subapical region (SAR) above intercellular adherens junctions between photoreceptor and Müller glia (MG) cells. We demonstrate that the Crb1-/- phenotype, as shown in Crb1-/- mice, is accelerated and intensified in primary retina cultures. Immuno-electron microscopy showed strong Crb1 immunoreactivity at the SAR in MG cells but barely in photoreceptor cells, whereas Crb2, Crb3, Patj, Pals1 and Mupp1 were present in both cell types. Human CRB1, introduced in MG cells in Crb1-/- primary retinas, was targeted to the SAR. RNA interference-induced silencing of the Crb1-interacting-protein Pals1 (protein associated with Lin7; Mpp5) in MG cells resulted in loss of Crb1, Crb2, Mupp1 and Veli3 protein localization and partial loss of Crb3. We conclude that Pals1 is required for correct localization of Crb family members and its interactors at the SAR of polarized MG cells.

Sustained upregulation of glial fibrillary acidic protein in Müller cells in pigeon retina following disruption of the parasympathetic control of choroidal blood flow

Choroidal blood flow in pigeon eyes is light driven and controlled by a parasympathetic input from ciliary ganglion (CG) neurons that receive input from the medial subdivision of the ipsilateral nucleus of Edinger-Westphal (EWM). EWM lesions diminish basal ChBF and irreversibly prevent ipsilateral light-evoked increases in ChBF, presumably rendering the retina mildly ischemic. To characterize the location, severity, and time course of the retinal abnormality caused by an EWM lesion, we quantitatively analyzed the cellular and regional extent of Müller cell glial fibrillary acidic protein (GFAP) immunolabeling up to nearly a year after an EWM lesion. We found that unilateral EWM lesions greatly increased Müller cell GFAP throughout the entire retinal depth and topographic extent of the affected eye, up to nearly a year post lesion. By contrast, destruction of the pupilloconstrictive pretectum or of the pupilloconstrictive part of lateral EW (EWL) did not appreciably increase Müller cell GFAP. Thus, the large increase in Müller cell GFAP following an EW lesion is attributable to an ongoing defect in choroidal vasodilatory function rather than to chronic pupil dilation. The Müller cell GFAP increase was greater ipsilateral than contralateral to the EWM destruction for the retinal territory deep to the heavily CG-innervated superior and temporal choroid, but not for the retinal territory deep to the poorly CG-innervated inferior and nasal choroid. The GFAP increase was light-dependent, since it did not occur in EW-lesioned birds housed in dim illumination. Our results show that the chronic vascular insufficiency caused by the loss of the EWM-mediated parasympathetic control of choroidal blood flow leads to a significant and sustained increase in retinal Müller cell GFAP. This increase could be a sign of a disturbance in retinal homeostasis that eventually leads to retinal injury and impaired visual function.

Long-term glial reactivity in rat retinas ipsilateral and contralateral to experimental glaucoma

Although glaucoma is known to alter glial reactivity, the long-term effect of elevated intraocular pressure (IOP) on glial change has not been fully elucidated. This study aimed to examine how chronically elevated IOP induced by episcleral vein cauterization (EVC) in unilateral eyes affect reactivities of astrocytes and Müller cells of rats in the treated as well as contralateral eyes over time. EVC in unilateral eyes of Sprague-Dawley rats were performed to produce chronically elevated IOP. Flat mounted retina preparations were made at several points until 6 months, which were subjected to immunostaining for glial fibrillary acidic protein (GFAP). Retinal homogenates were one- or two-dimensionally electrophoresed, followed by GFAP immunoblotting. EVC significantly increased IOPs up to 27.8 from 13.1 mmHg, which gradually decreased over time. In flat mounted retinas, astrocytes lost but Müller cells gained GFAP immunoreactivity at 3 days after cauterization. The glial changes were partially reversed over time but last even after IOP normalization. In the contralateral eyes, similar glial changes gradually appeared at 1 month after EVC and thereafter. Immunoblotting demonstrated not only molecular size shifts but also alteration of isoelectric focusing of GFAP both in treated and contralateral retina as compared with age-matched control retina. EVC led to opposite reactions in astrocytes and Müller cells in terms of GFAP immunoreactivity. Late-onset glial reactivity also occurred in the contralateral retina.

Crumbs homologue 1 is required for maintenance of photoreceptor cell polarization and adhesion during light exposure

Loss of Crumbs homologue 1 (CRB1) function causes either the eye disease Leber congenital amaurosis or progressive retinitis pigmentosa, depending on the amount of residual CRB1 activity and the genetic background. Crb1 localizes specifically to the sub-apical region adjacent to the adherens junction complex at the outer limiting membrane in the retina. We show that it is associated here with multiple PDZ protein 1 (Mupp1), protein associated with Lin-7 (Pals1 or Mpp5) and Mpp4. We have produced Crb1(-/-) mice completely lacking any functional Crb1. Although the retinas are initially normal, by 3-9 months the Crb1(-/-) retinas develop localized lesions where the integrity of the outer limiting membrane is lost and giant half rosettes are formed. After delamination of the photoreceptor layer, neuronal cell death occurs in the inner and outer nuclear layers of the retina. On moderate exposure to light for 3 days at 3 months of age, the number of severe focal retinal lesions significantly increases in the Crb1(-/-) retina. Crb2, Crb3 and Crb1 interacting proteins remain localized to the sub-apical region and therefore are not sufficient to maintain cell adhesion during light exposure in Crb1(-/-) retinas. Thus we propose that during light exposure Crb1 is essential to maintain, but not assemble, adherens junctions between photoreceptors and Müller glia cells and prevents retinal disorganization and dystrophy. Hence, light may be an influential factor in the development of the corresponding human diseases.

Ciliary neurotrophic factor protects retinal ganglion cells from axotomy-induced apoptosis via modulation of retinal gliain vivo

Adenoviral-mediated transfer of ciliary neurotrophic factor (CNTF) to the retina rescued retinal ganglion cells (RGCs) from axotomy-induced apoptosis, presumably via activation of the high affinity CNTF receptor alpha (CNTFRalpha) expressed on RGCs. CNTF can also activate astrocytes, via its low affinity leukemia inhibitory receptor beta expressed on mature astrocytes, suggesting that CNTF may also protect injured neurons indirectly by modulating glia. Adenoviral-mediated overexpression of CNTF in normal and axotomized rat retinas was examined to determine if it could increase the expression of several glial markers previously demonstrated to have a neuroprotective function in the injured brain and retina. Using Western blotting, the expression of glial fibrillary acid protein (GFAP), glutamate/aspartate transporter-1 (GLAST-1), glutamine synthetase (GS), and connexin 43 (Cx43) was examined 7 days after intravitreal injections of Ad.CNTF or control Ad.LacZ. Compared to controls, intravitreal injection of Ad.CNTF led to significant changes in the expression of CNTFRalpha, pSTAT(3), GFAP, GLAST, GS, and Cx43 in normal and axotomized retinas. Taken together, these results suggest that the neuroprotective effects of CNTF may result from a shift of retinal glia cells to a more neuroprotective phenotype. Moreover, the modulation of astrocytes may buffer high concentrations of glutamate that have been shown to contribute to the death of RGCs after optic nerve transection.

Electrophysiological properties of retinal Müller glial cells from myelin mutant rat

The structural and functional similarities between Müller cells and oligodendrocytes prompted the present study of the electrophysiological properties of Müller (glia) cells obtained from the retinae of control and myelin mutant taiep rats during the postnatal developmental period (P12-P180). The whole-cell configuration of the patch-clamp technique was used to characterize the general properties and the K+ currents from dissociated Müller cells. During the first 3 weeks of life, a decrease of the membrane resistance and an increase of the membrane potential were observed in Müller cells from both control and taiep rats. However, Müller cells from taiep rats never achieved the very negative membrane potential (-50 mV vs -80 mV) and the low membrane resistance characteristic for control cells. Furthermore, Müller cells displayed increased inward and outward K+ currents during postnatal development up to P30/60 in controls; however, in taiep rats, this increase ceased at P20/30, and low-amplitude currents persisted into adulthood. These results provide first evidence of physiological changes in retinal Müller cells as a consequence of a myelin mutation causing a progressive deterioration of the central nervous system (CNS) due to a disturbance of the microtubule network of oligodendrocytes. We hypothesize that the progressive dysmyelination process of the optic nerve, accompanied by functional deficits of retinal neurons (e.g., ganglion cells), induces physiological alterations of Müller cells.

Up-Regulation of Glial Fibrillary Acidic Protein in Response to Retinal Injury: Its Potential Role in Glial Remodeling and a Comparison to Vimentin Expression

Intermediate filament proteins are a heterogeneous group of proteins that form 10-nm-diameter filaments, a highly stable cytoskeletal component occurring in various cell types. The up-regulation of one of these intermediate filament proteins, glial fibrillary acidic protein (GFAP), historically has been an indicator of "stress" in central nervous system (CNS) astrocytes. The retina also responds similarly to "stress" but the up-regulation of intermediate filaments occurs primarily in the Müller cells, the radial glia of the retina. This is a remarkably ubiquitous response in that a similar up-regulation can be observed in numerous forms of retinal degeneration. As a consequence of retinal detachment, a "mechanical" injury to the retina, GFAP, and another intermediate filament protein, vimentin, dramatically increase in Müller cells. Concomitant with this up-regulation is the hypertrophy of these cells both within the retina and onto the photoreceptor and vitreal surfaces of the retina. The function of this distinctive intermediate filament up-regulation in glial cells is unknown, but in the retina their expression is differentially regulated in a polarized manner as the Müller cells hypertrophy, suggesting that they play some role in this process. Moreover the response of intermediate filaments and the Müller cells differs depending on whether the retina has been detached or reattached to the retinal pigment epithelium. The differential expression of these proteins may give insight into their role in the formation of glial scars in the retina and elsewhere in the CNS.