Glial fibrillary acidic protein (GFAP) immunoreactivity in rabbit retina: effect of fixation

Membranous nephropathy

Membranous nephropathy (MN) is a glomerular disease that can occur at all ages. In adults, it is the most frequent cause of nephrotic syndrome. In ~80% of patients, there is no underlying cause of MN (primary MN) and the remaining cases are associated with medications or other diseases such as systemic lupus erythematosus, hepatitis virus infection or malignancies. MN is an autoimmune disease characterized by a thickening of the glomerular capillary walls due to immune complex deposition. Identification of the phospholipase A2 receptor (PLA2R) as the major antigen in adults in 2009 induced a paradigm shift in disease diagnosis and monitoring and several other antigens have since been characterized. Disease outcome is difficult to predict and around one-third of patients will undergo spontaneous remission. In those at high risk of progression, immunosuppressive therapy with cyclophosphamide plus corticosteroids has substantially reduced the need for kidney replacement therapy. Owing to carcinogenic risk, other treatments (calcineurin inhibitors and CD20-targeted B cell depletion therapy (rituximab)) have been developed. However, disease relapses are frequent when calcineurin inhibitors are stopped and the remission rate with rituximab is lower than with cyclophosphamide, particularly in patients with high PLA2R antibody titres. Other new drugs are already available and antigen-specific immunotherapies are being developed.

Fixation strategies for retinal immunohistochemistry

Immunohistochemical and ex vivo anatomical studies have provided many glimpses of the variety, distribution, and signaling components of vertebrate retinal neurons. The beauty of numerous images published to date, and the qualitative and quantitative information they provide, indicate that these approaches are fundamentally useful. However, obtaining these images entailed tissue handling and exposure to chemical solutions that differ from normal extracellular fluid in composition, temperature, and osmolarity. Because the differences are large enough to alter intercellular and intracellular signaling in neurons, and because retinae are susceptible to crush, shear, and fray, it is natural to wonder if immunohistochemical and anatomical methods disturb or damage the cells they are designed to examine. Tissue fixation is typically incorporated to guard against this damage and is therefore critically important to the quality and significance of the harvested data. Here, we describe mechanisms of fixation; advantages and disadvantages of using formaldehyde and glutaraldehyde as fixatives during immunohistochemistry; and modifications of widely used protocols that have recently been found to improve cell shape preservation and immunostaining patterns, especially in proximal retinal neurons.

A common progenitor for retinal astrocytes and oligodendrocytes

Developing neural tissue undergoes a period of neurogenesis followed by a period of gliogenesis. The lineage relationships among glial cell types have not been defined for most areas of the nervous system. Here we use retroviruses to label clones of glial cells in the chick retina. We found that almost every clone had both astrocytes and oligodendrocytes. In addition, we discovered a novel glial cell type, with features intermediate between those of astrocytes and oligodendrocytes, which we have named the diacyte. Diacytes also share a progenitor cell with both astrocytes and oligodendrocytes.

NKCC1 does not accumulate chloride in developing retinal neurons

GABA excites immature neurons due to their relatively high intracellular chloride concentration. This initial high concentration is commonly attributed to the ubiquitous chloride cotransporter NKCC1, which uses a sodium gradient to accumulate chloride. Here we tested this hypothesis in immature retinal amacrine and ganglion cells. Western blotting detected NKCC1 at birth and its expression first increased, then decreased to the adult level. Immunocytochemistry confirmed this early expression of NKCC1 and localized it to all nuclear layers. In the ganglion cell layer, staining peaked at P4 and then decreased with age, becoming undetectable in adult. In comparison, KCC2, the chloride extruder, steadily increased with age localizing primarily to the synaptic layers. For functional tests, we used calcium imaging with fura-2 and chloride imaging with 6-methoxy-N-ethylquinolinium iodide. If NKCC1 accumulates chloride in ganglion and amacrine cells, deleting or blocking it should abolish the GABA-evoked calcium rise. However, at P0-5 GABA consistently evoked a calcium rise that was not abolished in the NKCC1-null retinas, nor by applying high concentrations of bumetanide (NKCC blocker) for long periods. Furthermore, intracellular chloride concentration in amacrine and ganglion cells of the NKCC1-null retinas was approximately 30 mM, same as in wild type at this age. This concentration was not lowered by applying bumetanide or by decreasing extracellular sodium concentration. Costaining for NKCC1 and cellular markers suggested that at P3, NKCC1 is restricted to Müller cells. We conclude that NKCC1 does not serve to accumulate chloride in immature retinal neurons, but it may enable Müller cells to buffer extracellular chloride.

Expression of glial fibrillary acidic protein in primary cultures of human Müller cells

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein which is primarily found in astrocytes. However, in eye diseases or when eye injuries occur, GFAP is expressed in large quantities in retinal Müller cells. The mechanism for this altered expression is unknown, but presumably involves injury-dependent signaling. The purpose of this study was to investigate regulation of GFAP gene expression in human Müller cells in vitro. Immunofluorescence, western blot, RT-PCR and Northern blot analyses were used to demonstrate the expression of GFAP in cultured Müller cells. Plasmids bearing various segments of the human GFAP promoter fused to a CAT reporter gene were used to transfect primary cultures of human Müller cells as well as the non-glial cell lines 293T and HeLa. Transcription directed by the GFAP promoter was found to be more than 50-times stronger in the Müller cells than in either of the non-glial cell lines, consistent with the data for endogenous GFAP expression. To our knowledge, this is the first study demonstrating GFAP gene regulation in human Müller cells. By examining the transcriptional activity of various segments from the human GFAP promoter, it can be concluded that the GFAP gene is differently regulated in Müller cells compared to glioma cell lines from the central nervous system (CNS).

Effects of post-mortem delay and storage duration on the expression of GFAP in normal human adult retinae

Glial fibrillary acidic protein (GFAP) is an established marker of retinal glia and has been shown to be modulated by several cytokines and retinal pathology. The influence of a number of factors, including post-mortem delay, storage duration and retinal pathology, on the distribution and morphology of macroglia and GFAP antigenicity was examined in human retina. The effects of these parameters on GFAP expression were estimated using immunohistochemistry, confocal microscopy and image analysis. Changes in expression of antigenicity were analysed in human retinal cryosections at three levels: constitutive,aberrant and total. The results indicated that short-term and long-term storage duration had no significant effect on GFAP immunoreactivity at all three levels of expression (P > 0.2).However, a significant increase in GFAP immunoreactivity and distribution at all three levels of expression was associated with prolonged post-mortem delay (> 30 h) (P < 0.05). This study highlights the importance of rigorous matching of post-mortem delay between control specimens in histological studies of human retinae. The study further demonstrates the utility of Eye Bank retinae fixed and stored in 2% paraformaldehyde, provided that appropriate controls are applied.

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

Müller glia play an important role in maintaining retinal homeostasis, and brain-derived neurotrophic factor (BDNF) has proven to be an effective retinal ganglion cell (RGC) neuroprotectant following optic nerve injury. The goal of these studies was to investigate the relation between optic nerve injury and Müller cell activation, and to determine the extent to which BDNF affects the injury response of Müller cells. Using immunocytochemistry and Western blot analysis, temporal changes in the expression of glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) were examined in rats after optic nerve crush alone, or in conjunction with an intravitreal injection of BDNF (5 microg). GFAP protein levels were normal at 1 day post-crush, but increased approximately 9-fold by day 3 and remained elevated over the 2-week period studied. Müller cell GS expression remained stable after optic nerve crush, but the protein showed a transient shift in its cellular distribution; during the initial 24-h period post-crush the GS protein appeared to translocate from the cell body to the inner and outer glial processes, and particularly to the basal endfeet located in the ganglion cell layer. BDNF alone, or in combination with optic nerve crush, did not have a significant effect on the expression of either GFAP or GS compared with the normal retina, or after optic nerve crush alone, respectively. The data indicate that although BDNF is a potent neuroprotectant in the vertebrate retina, it does not appear to have a significant influence on Müller cell expression of either GS or GFAP in response to optic nerve injury.

Differentiation of a unique macroglial cell type in the pecten oculi of the chicken

Glial cells in the CNS of vertebrates serve specialized functions in close interaction with surrounding neurons and blood vessels. In the avian eye, the neural tissue (retina) and the supporting vascular structure (pecten oculi) are spatially separated and comprise distinct glial cell types, i.e., the Müller glia and the pecteneal glia, respectively. In the present study we combined morphological and immunocytochemical investigations on the differentiation of the pecteneal glia in comparison to the retinal Müller glia, the retinal pigment epithelium, and the astrocytic cells of the optic nerve head in order to elucidate the nature, origin, and function of the pecteneal glia. Conventional transmission electron microscopy and freeze-fracture imaging revealed striking similarities between the pecteneal glia and retinal pigment epithelial cells at the transition zone to the optic nerve head. Immunofluorescence investigation identified specific labeling for vimentin and glutamine synthetase (GS) but not for glial fibrillary acidic protein (GFAP) in the mature pecteneal glia. Immunogold labeling confirmed the cellular specificity. GS labeling was weak during embryonic development but increasingly strong after hatching. Surprisingly, the intraneuroectodermal endothelial cells were highly immunopositive for GS throughout embryonic development and lost GS expression after hatching. GS expression in the pecteneal glia may participate in pH-regulation of the avian eye. Endothelial GS expression in the developing CNS may detoxify detrimental ammonium concentrations resulting from egg yolk degradation.

Rabbit retinal Müller cells undergo antigenic changes in response to experimentally induced proliferative vitreoretinopathy

Experimental proliferative vitreoretinopathy (PVR) was induced in the rabbit eye by injecting mitotically active Müller cells into the vitreal chamber. Two weeks after the initiation of PVR, the retina and the epiretinal membrane that formed were examined to ascertain the antigenic expression of Müller cells in the retina and in the epiretinal membrane. Examination of various regions of the retina from the experimental PVR eye demonstrated that vimentin, glial fibrillary acidic protein (GFAP), cellular retinaldehyde binding protein (CRALBP), and beta-amyloid precursor protein (beta-APP), which were present in the Müller cells of the retina from the control eye, increased their expression, while the antigenicity of glutamine synthetase (GS), did not change; these proteins were also present in the cells contained within the experimentally induced epiretinal membrane. Alpha smooth muscle actin (alpha-SMA), a cytoskeletal protein that is associated with migration and tractional forces in many cell types, was not only present in the cells embedded within the epiretinal membrane, but was also present in the Müller cells underlying the epiretinal membrane. However, Müller cells that were in the inferior portion of the retina, where epiretinal membrane pathology was absent, did not express alpha-SMA. Although this protein is not normally found in Müller cells, they do express it de novo when they are maintained in culture. This suggests that a localized mechanism associated with epiretinal membrane formation induces the expression of alpha-SMA in Müller cells while the increased expression of GFAP, beta-APP, vimentin, and CRALBP are probably regulated via a more general mechanism.

Monoclonal antibody, KK1, recognizes human retinal astrocytes and distinguishes a subtype of astrocytes in mouse brain

Astrocytes exhibit a diverse morphology and numerous functions in the central nervous system as well as in the retina. In order to obtain markers for the analysis of astrocytes, we prepared monoclonal antibodies that recognized antigens specific to astrocytes. Monoclonal antibody (mAb), designated KK1, reacted with the processes of astrocytes in the nerve fiber layer and the ganglion cell layer in the human retina as detected by indirect immunofluorescence. Normal Müller cells, whose processes are localized vertically in retina, were not labeled by KK1 mAb. In mouse brain, KK1 mAb reacted specifically with astrocytes in the white matter, but not with those in the gray matter. Studies employing a high-resolution confocal laser scanning microscope and double-labeling with KK1 mAb and commercially available anti-glial fibrillary acidic protein (GFAP) mAb (GA5) revealed that KK1 mAb visualized the processes that were not recognized by anti-GFAP mAb (GA5) in both human retina and mouse brain. In cultured mouse astrocytes, KK1 mAb reacted only with anti-GFAP mAb (GA5)-positive cells, but a small percentage of anti-GFAP mAb (GA5)-positive cells were labeled with KK1 mAb. In addition, the subcellular distribution of the KK1 antigen in cultured astrocytes apparently differed from that of GFAP labeled by anti-GFAP mAb (GA5). The antigen that was purified from the normal mouse brain by KK1 mAb-conjugated beads reacted with anti-GFAP mAb(GA5) in immunoblotting. No reactivity of KK1 mAb was observed in immunohistochemical analysis in GFAP -/- mutant mouse brain. These results demonstrate that KK1 mAb specifically recognized an epitope of GFAP that did not react with other anti-GFAP mAb (GA5). Retinal astrocytes and a subtype of astrocytes in the white matter of mouse brain shared the epitope that was recognized by KK1 mAb. KK1 mAb might be a powerful tool to investigate a subtype of astrocytes.

Preservation of the structural integrity of a freshly lesioned or transplanted mouse neocortex and the immunoreactivity of cell-specific marker proteins in demineralized histological material

Analysis of superficially lesioned or grafted brains poses the problem that their removal from the skull prior to histological processing often causes damage to the operated area and may lead to loss of the graft. Here, we propose an original approach to this problem, developed on mice whose cortices have been surgically lesioned and some grafted with fetal neural tissue. The experimental animals were killed 1, 3 or 6 days after operation. Our procedure was based on the softening of skulls by demineralization in Gendre's picric solution, followed by solidification of the wounded region by embedding in polyester wax. This permitted the preparation of serial sections from brains together with neurocrania. To check their immunoreactivity, the sections were later reacted with specific antisera for glial fibrillary acidic protein (GFAP), microtubule-associated protein 2 (MAP2), calbindin, and the thermolabile cell-surface glycoprotein Thy-1. The histological material revealed excellent structural integrity and cytoarchitecture. In transplanted animals, the tiny graft, protected by the overlying bone, was found in the host cavity. Immunostaining showed typical localization of the chosen marker proteins. The anti-Thy-1 antibody enabled us to distinguish between graft and host tissues, which differed, in our experiments, in their expression of two distinct allelic forms of the Thy-1 molecule. The method lends itself perfectly to histochemical study of the earliest stages of freshly operated superficial brain regions in small laboratory animals, and should also be applicable to the evaluation of other brain structures which are difficult to gain access to without being damaged.

Müller cell survival and proliferation in response to medium conditioned by the retinal pigment epithelium

Müller cells have been implicated in the pathogenesis of proliferative vitreoretinopathy and subretinal scar formation; however, the source(s) and signal(s) responsible for their activation are unknown. This study was undertaken to determine if the retinal pigment epithelium (RPE) could be involved in this signaling process by studying its effects on Müller cell survival and division in vitro. A pure population of Müller cells isolated from 1-2 day Long-Evans rats was seeded at low density and treated with medium conditioned by neonatal rat RPE (RPE-CM) or a nonconditioned, defined medium. By day 3, Müller cells cultured in RPE-CM increased in number 2-fold. These cells survived up to 21 days, which was the longest time tested. In contrast, cell number decreased in control wells 75% by day 3, and 100% by day 4. The RPE-mediated survival and proliferation of the Müller cells occurred in a dose-dependent manner. The mitogenic response was specific for the RPE when compared with fibroblasts and non-retinal epithelial cells. Heat and trypsin treatment of the RPE-CM completely abolished its survival and mitogenic activity. These findings demonstrate the establishment of an in vitro model which can be used to investigate RPE-Müller cell interactions. This study also provides evidence for RPE involvement in Müller cell interactions. This study also provides evidence for RPE involvement in Müller cell survival and proliferation.

A quantitative study of the lateral spread of Müller cell responses to retinal lesions in the rabbit

A wide variety of retinal pathology is associated with an increase in Müller glial cell expression of glial fibrillary acidic protein (GFAP). In this study the time course and spatial spread of the Müller cell GFAP response following argon laser photocoagulation lesions was examined in wholemounted rabbit retina. At 24 hours single focal lesions were surrounded by GFAP positive Müller cell end feet which declined in density with distance but extended as far as 2-3 mm from the lesion. The Müller cell reaction reached a maximal spread of 4-5 mm at 14 to 21 days and had started to contract by 30 days, leaving a core of GFAP positive processes immediately around the lesion site at 60 days. This zone of spread was much larger than the area of disrupted pigment epithelium. Isodensity plots did not reveal any correlation with the trajectory of retinal ganglion cell axons. The spread of reaction was more confined for lesions within the visual streak than in the dorsal or ventral retinal periphery. Multiple lesions within a focal region of retina resulted in a greater density of GFAP reactive end feet with a corresponding greater spread. However, when five to ten lesions were made in a horizontal row, the Müller cells over the entire retina became GFAP immunoreactive. This pan-retinal reaction took several days to spread, peaked at 7-14 days, and contracted back to the primary lesion sites by 2 months. This spread of Müller cell reactivity may be triggered by the diffusion of substances released by injury or it may be due to direct cellular communication. The extensive indirect effect on Müller cells of laser irradiation might be an important component of the clinical effect of laser photocoagulation and indicates a long distance communication mechanism between retinal glia which is poorly understood. This study also shows the importance of the time at which the Müller cell response is assessed.

Taurine, GABA and GFAP immunoreactivity in the developing and adult rat optic nerve

The localizations of taurine, gamma-aminobutyric acid (GABA) and glial fibrillary acidic protein (GFAP) within the developing rat optic nerve were determined using immunocytochemical techniques on tissues from animals ranging in age from embryonic day 20 to postnatal 28 days. Mature nerves from 3-4-month-old adults were also examined. At the younger ages, taurine immunoreactivity was intense and localized specifically to the optic nerve axons, but by postnatal day 15 and thereafter its predominant localization was in macroglia. Some of these glia were astrocytes as indicated by the specific marker, GFAP. GABA immunoreactivity was present at the same time as taurine but was found only in macroglia. In mature nerves the patterns of taurine, GABA and GFAP distribution (within glia) were highly similar.

Immunocytochemical localization of taurine and glial fibrillary acidic protein in human optic nerve

Taurine immunoreactivity (IR) in 1-microns sections of glutaraldehyde-fixed human optic nerve was observed using light microscopy and an antibody raised in rabbit to taurine conjugated to bovine serum albumin. Throughout the nerve, taurine-IR was prominent in glial cells, in their perinuclear regions, and in their numerous branching processes, some of which extended to the pial septa. The peripheral glial mantle (glia limitans) was densely stained, whereas axons and the pial septa showed relatively little or no taurine-IR. Immunoreactivity for glial fibrillary acidic protein (GFAP), and astrocyte-specific marker, was evaluated on adjacent sections. The pattern of GFAP-IR was highly similar to that for taurine, suggesting that a subset of taurine-immunoreactive glial cells are optic nerve astrocytes. To our knowledge, this is the first localization of taurine and GFAP in human optic nerve.

Intraorbital transection of the rabbit optic nerve: consequences for ganglion cells and neuroglia in the retina

Rabbit retinae were stained with antibodies to glial fibrillary acidic protein (GFAP) at various times up to 5 months after complete unilateral intraorbital optic nerve transection, which is known to induce degeneration of ganglion cell axons and perikarya in the retina. A transient immunoreactivity for GFAP was observed in Müller glial cells that normally lack this marker. Müller-cell GFAP immunoreactivity became detectable 4 days after the lesion, but Müller cells were no longer labeled 3 months later. GFAP-labeled astrocytes located in the nerve fiber layer showed no change in immunoreactivity at any stage after transection. Application of horseradish peroxidase to the left and right superior colliculus of a rabbit whose optic nerve had been transected unilaterally 2 years before confirmed the completeness of the transection. Yet electron microscopy showed the presence of some healthy-looking ganglion cell axons in the lesioned retina, although these cells were deprived of their target. Labeling retinal wholemounts with neurofilament antibodies confirmed the presence of some ganglion cell axons and perikarya in the retina more than 2 years after transection. The course of these axons suggested that they were remnants of axons. Using antibodies to galactocerebroside (GC) we found that, as in the normal rabbit, these persisting ganglion cell axons were myelinated in the medullary rays. Although many ganglion cell axons had disappeared after 2 years, the number of neuroglial cells (including astrocytes and oligodendrocytes) present in the medullary ray region was not altered. The cell bodies of some oligodendrocytes were covered with a myelin sheath, an aberrant feature not seen normally.

Expression of glial fibrillary acidic protein by Müller cells in rd chick retina

Accumulation of glial fibrillary acidic protein (GFAP) in Müller cells has been observed in retinas of several mammalian species secondary to genetically induced degeneration and neuronal injury. In the present series of experiments, I have examined the effects of the rd (retinal degeneration) mutation on the expression of GFAP in retinas of chicks homozygous for the mutation (rd/rd) prior to and following the onset of photoreceptor degeneration, which first appears approximately 7 days posthatch (7 dph). Carrier (+/rd) and wild-type (+/+) retinas served as controls. Retinas taken from 1, 7, 21, and 33 dph rd/rd, +/rd, and +/+ chicks were analyzed for the presence of GFAP by immunocytochemical and SDS-PAGE/Western blot techniques. The following immunocytochemical observations were made: (1) GFAP immunostaining was limited to and located throughout the Müller cells. (2) The intensity of GFAP immunostaining increased with age in all three retina types in tissue sections, as well as on immunoblots. (3) The distribution of GFAP staining within rd/rd Müller cells following the onset of degeneration was slightly different from that observed in +/+ and +/rd retinas and was distinguished by increased staining of the cell bodies and the cell processes forming the outer limiting membrane. The results of these experiments show that Müller cells in chick retina contain GFAP. In addition, they suggest that, in contrast to Müller cells in degenerating mammalian retina, Müller cells in rd chick retina do not accumulate large amounts of GFAP in response to degeneration.

Glial and neuronal markers in bass retinal horizontal and Müller cells

Retinal horizontal cells (HCs) are second-order neurons that integrate information from photoreceptors over large retinal areas, mediating the lateral spread of visual signals in the distal retina. The 'glial' vs. 'neuronal' nature of the HC has been widely debated. For example, carbonic anhydrase (CA), glutamine synthetase (GS), and glial fibrillary acidic protein (GFAP) are considered 'glial' markers, yet both CA and GFAP have been previously reported in HCs of the teleost retina in species-specific patterns. In contrast, the neurofilament triplet (NFT) proteins are considered 'neuronal' markers; these proteins have been immunolocalized to a mammalian HC, but are absent from teleost HCs. We have studied these cytochemical characteristics in HCs from the white bass, by immunolabeling both cryosections of intact retina and freshly isolated, identified cells attached to coverslips. We found that both HCs (neurons) and Müller cells (MCs; glia) immunolabeled with antisera to CA. Both type 1 (external) HCs and MCs immunolabeled with an antibody to vimentin. Only MCs immunolabeled with antisera to GS and GFAP. Neither HC perikarya (and their major dendrites) nor MCs immunolabeled with an antibody to the 160-kDa subunit of NFT protein. Thus, bass HCs and MCs share the presence of CA and vimentin epitopes and absence of the NFT 160-kDa epitope. Moreover, retinal cell isolation, by itself, does not affect cell-type specific immunolabeling patterns in identified cells, except for what may be lost with the finer processes of the various cells. Isolated cell studies can aid in interpreting immunolabeling patterns observed in the intact retina, especially in retinal layers where several cell types may be present.

Immunocytochemical localization of taurine within glial cells in the optic nerve of adult albino rats

Taurine immunoreactivity in one micron sections of the adult rat optic nerve was observed using light microscopy. Prominent staining was seen in glial cell somata in the perinuclear region and in their processes throughout the nerve, particularly in endfeet on capillaries and in the peripheral basal lamina (glia limitans). Axons and blood vessels showed relatively little or no staining in the mature nerve. The pattern of glial fibrillary acidic protein immunoreactivity on subsequent sections was similar in many respects to that of taurine, suggesting that a sub-population of taurine immunoreactive glial cells are optic nerve astrocytes.