Glial Fibrillary Acidic Protein Molecule Research Articles

Increase of glial fibrillary acidic protein fragments in the spinal cord of motor neuron degeneration mutant mouse

We analyzed protein fractions extracted from the spinal cord of the motor neuron degeneration ( Mnd) mouse, a mutant that exhibits progressive degeneration of lower spinal motor neurons, by one- and two-dimensional polyacrylamide gel electrophoresis (PAGE) after solubilization of the tissue with medium containing sodium dodecyl sulfate (SDS)-urea during growth of the animal, in comparison with those of age-matched controls (C57BL/6). Several protein spots were detected around a region of p I 5.6–6.0 and molecular mass of 35–50 kDa in Mnd spinal cord tissue on the two-dimensional PAGE separation profile with Coomassie brilliant blue staining, while only a few spots around the same region were found in the control spinal cord. These spots were all immunoreactive with an antibody against glial fibrillary acidic protein (GFAP), a cytoskeleton filamentous protein specific to astroglial cells. The protein spot with molecular mass of 50 kDa showed immunoreactivity with anti-GFAP antibody, had a blocked amino-terminus, and is assumed to be intact GFAP. Several protein spots with slightly smaller molecular masses of 35 to 48 kDa lacked the head domain of the GFAP molecule as a result of cleavage at the 29th and 56th residues from the amino terminus. In Mnd spinal cord tissue, the densities of the immunoreactive GFAP bands with smaller molecular masses increased with development, and became dominant at the time of the appearance of behavioral paralytic gait around 6 to 7 months of age. These results suggest that the increased GFAPs devoid of head domains are related to the degenerative loss of motor neurons in the Mnd spinal cord. Histopathological and GFAP immunohistochemical examination of Mnd spinal cord preparation demonstrated progressive degenerative loss of motor neurons, and considerable increases in number of GFAP-stained astrocytes in the ventral horn at 7 to 9 months of age. These processes of degenerative loss of motor neurons and proliferation of reactive astrocytes with increased levels of fragmented GFAP in the Mnd spinal cord during development seem to be characteristic and preceded the deterioration of motor activities in this animal model of amyotrophic lateral sclerosis.

Identification and characterization of an anti-glial fibrillary acidic protein antibody with a unique specificity in a demented patient with an autoimmune disorder

We detected an antibody to a 48 kd antigen of the central nervous system in the serum from a demented patient with an autoimmune disorder. To identify and characterize the antigen, we screened a human cerebral cDNA library and performed immunoblot analysis following two-dimensional gel electrophoresis (2-D blotting). The sequences of the isolated cDNA fragments were homologous to human glial fibrillary acidic protein (GFAP). Two-D blotting using patient serum revealed that the antibody reacted with a restricted subset of GFAP molecules which exhibited relatively high isoelectric points. Furthermore, to elucidate the importance of the anti-GFAP antibody in dementia, we screened for the presence of an anti-GFAP antibody in the sera of 46 demented patients: 26 with Alzheimer's disease and 20 with vascular dementia (VD). We found an anti-GFAP antibody in the serum of only one patient with VD. Two-D blotting revealed that the anti-GFAP antibody in the serum from the VD patient reacted with a more acidic subset of GFAP molecules compared with the anti-GFAP antibody from our patient. In conjunction with the fact that the GFAP molecule with high isoelectric point was insoluble and less degraded, these results suggested that the anti-GFAP antibody in the serum of our patient was not generated due to a secondary response to soluble and degraded GFAP which leaked through the damaged blood–brain barrier as found in the VD patient, but was generated actively on the basis of dysregulation of the immune system. Possible effects of the autoantibody on astrocytic function and the pathogenesis in dementia are discussed.

Two different protein kinases act on a different time schedule as glial filament kinases during mitosis.

Glial fibrillary acidic protein (GFAP) is a component of glial filaments specific to astroglia. We now report the spatial and temporal distributions of four phosphorylated sites in the GFAP molecule during mitosis of astroglial cells, determined by antibodies which can distinguish phosphorylated epitopes from non-phosphorylated-epitopes. Immunofluorescence microscopy showed that the Ser8 residues in the entire cytoplasmic glial filament system are initially phosphorylated when the cells enter mitosis. In cytokinesis, the phosphoSer8 residues become dephosphorylated, whereas Thr7, Ser13 and Ser34 in glial filaments at the cleavage furrow become the preferred sites of phosphorylation. The cdc2 kinase purified from mitotic cells can phosphorylate GFAP at Ser8 but not at Thr7, Ser13 or Ser34, in vitro. These results suggest that cdc2 kinase acts as a glial filament kinase only at the G2-M phase transition while other glial filament kinases are probably activated at the cleavage furrow before final separation of the daughter cells.

Microglial and astroglial reactions to inflammatory lesions of experimental autoimmune encephalomyelitis in the rat central nervous system

Gliosis is a repair process of lesions appearing in the central nervous system (CNS). Although gliosis by astrocytes (astrocytic gliosis) has been well documented, that by microglia (microglial gliosis) remains poorly understood. In the present study we induced experimental autoimmune encephalomyelitis (EAE) in Lewis rats and examined microglial and astroglial reactions to EAE lesions at various stages of the disease by immunohistochemistry. For the demonstration of microglia and astrocytes, antibodies against complement receptor type 3 (OX42) and glial fibrillary acidic protein (GFAP) were used, respectively. It was revealed that the whole course of microglial and astroglial reactions to EAE lesions is divisible into three stages, i.e., initial, peak and recovery stages. Microglial and astroglial reactions to EAE lesions at each stage correspond well with the clinical and histological stages of EAE. At the initial stage, rats showed mild clinical signs and a few inflammatory foci were found in the CNS. Microglia were increased in number in close association with inflammatory cell aggregates, whereas astrocytes showed no significant reaction in spite of the presence of inflammatory cells. At the peak stage, rats showed full-blown EAE and the number of inflammatory cells reached maximum. The most characteristic finding at this stage was ‘encasement’ of inflammatory lesions by astrocytic fibers. Microglia were increased in number, but association of microglia with lesions was prevented by astrocytes. Interestingly, however, such characteristic distribution of microglia and astrocytes was not observed at the recovery stage. Residual inflammatory cell aggregates were intermingled with dense microglial and astrocytic gliosis, forming ‘micro-astroglial scars’. Double immunofluorescence staining withe anti-GFAP and antibromodeoxyruridine (BrdU), or with OX42 and anti-BrdU revealed that BrdU-incorporated microglia, but not astrocytes, were present mainly at the initial and peak stages, suggesting that microglia would proliferate by cell division to create gliosis, whereas astrocytic gliosis would be a result of migration of astrocytes and/or up-regulation of expression of GFAP molecule. Taken together with previous in vitro findings that microglia, but not astrocytes, stimulate encephalitogenic T cell proliferation, these in vivo findings suggest that microglia augment, whereas astrocytes suppress, inflammatory processes in the CNS.

Expression in Escherichia coli of fragments of glial fibrillary acidic protein: characterization, assembly properties and paracrystal formation.

We have expressed in Escherichia coli a 1258 bp cDNA fragment corresponding to 97% of mouse glial fibrillary acidic protein (GFAP), the principal intermediate filament protein of astrocytes. High levels of expression were obtained, as a fusion protein with 32 residues of the bacteriophage lambda cII protein, using the pLcII expression vector system of K. Nagai and H.-C. Thogersen. Although removal of the cII protein fragment by proteolysis using factor X proved difficult, a protein corresponding to most of the cDNA fragment was obtained by cleaving at the endogenous thrombin site near the middle of the N-terminal non-helical domain of GFAP. A shorter 1047 bp fragment, in which the C-terminal non-helical domain of GFAP was deleted, was also produced using oligonucleotide-directed site-specific mutagenesis of the original cDNA clone. After proteolysis with thrombin, this material gave a fragment that corresponded to the alpha-helical coiled-coil rod region of the GFAP molecule, together with a portion of the non-helical N-terminal domain. The fragments produced were characterized both biochemically and ultrastructurally, and appeared to retain the conformation of native GFAP. Crosslinking showed that all fragments formed molecules containing two chains ('dimers') that associated to form four-chain molecular dimers ('tetramers') analogous to those formed by intact intermediate filament proteins. Shadowed preparations showed the presence of rod-like particles that closely resembled those observed for other intermediate filament proteins and proteolytically prepared rod domains. Remarkably, the fusion protein produced from the entire 1258 bp cDNA fragment and the cII peptide was able to form filaments that closely resembled those produced by native GFAP. However, fragments in which either the cII peptide or the C-terminal non-helical domain were removed, or in which both were removed, failed to form filaments under standard assembly conditions. Although preliminary in nature, these results suggest that both N- and C-terminal non-helical domains may have a role in intermediate filament formation. Moreover, the fragment corresponding approximately to the GFAP rod formed paracrystals similar to those observed with other coiled-coil proteins. The molecules in these paracrystals were arranged antiparallel with the two molecules in the unit cell, which may correspond to the four-chain molecular dimer (tetramer), overlapping by approximately two-thirds of their length.

Characterization and location of divalent cation binding sites in bovine glial fibrillary acidic protein.

In our previous work [Yang, Z. W., & Babitch, J. A. (1988) Biochemistry (preceding paper in this issue)] divalent cations were found to be more effective promoters of astroglial filament formation than were monovalent cations. To determine if one or more divalent cation binding sites were the basis for this difference, glial fibrillary acidic protein (GFAP) was attached to nitrocellulose membranes and bathed in 1 microM 45CaCl2 in 60 mM KCl, 0.5 mM MgCl2, and 10 mM imidazole hydrochloride, pH 7.4. After removal of unbound 45Ca2+, GFAP was observed to bind calcium. Flow dialysis experiments showed that GFAP, dissolved in 2 mM Tris-HCl, pH 7.5, contained three classes of binding sites and 0.61 +/- 0.08 (SD), 1.7 +/- 0.4, and 4.6 +/- 0.2 sites per GFAP molecule with dissociation constants of 0.66 +/- 0.01 microM, 6.6 +/- 0.3 microM, and 44 +/- 1 microM, respectively. After addition of 0.5 mM MgSO4 to the flow dialysis solution, the high- and low-affinity sites were not observed while the remaining sites (1.95 +/- 0.15 per GFAP molecule) had a Kd = 2.16 +/- 0.25 microM. This showed that the high- and low-affinity sites are "Ca2+-Mg2+" sites while sites with intermediate affinity are calcium specific. To locate the calcium-binding regions, GFAP peptides were examined for calcium binding by calcium-45 autoradiography. The calcium-specific binding areas were localized in coil I. Computer-assisted analysis of the GFAP sequence revealed several EF-hand-like areas which could be the calcium binding sites. We conclude that divalent cations may play both structural and regulatory roles in astroglial intermediate filaments.

Monoclonal antibodies to GFAP epitopes available in formaldehyde fixed tissue.

We have recently demonstrated that one of our monoclonal antibodies (MAB's) to glial fibrillary acidic protein (GFAP) recognizes an epitope on this molecule which is to a large degree blocked during fixation with formaldehyde or crosslinking with Dithiobis (Succinimidyl) Propionate (DTSP). This was shown to be due to the crossbinding of a single or a number of proteins to the GFAP and is not due to a change in the epitope on GFAP induced by the fixation itself. In an attempt to produce further MAB's capable of recognizing epitopes on the GFAP molecule available following formaldehyde fixation, we immunized BALB-C mice with cytoskeletal preparations of human glioma cells which contain GFAP where the blocking protein or proteins were crossbound by DTSP or formaldehyde to the GFAP. Following fusion of the spleen lymphocytes to Sp 2/0 myeloma cells we have cloned hybridomas which produce antibodies that recognize GFAP in formaldehyde fixed tissues. This method presents the antigen in its native "fixed" state for the mouse's immune system and avoids the production of MAB's which (although excellent for immunochemical studies) do not recognize any epitopes available on the molecule in question in formaldehyde fixed tissues. Antibodies so produced are of great interest in routine pathology where most tissues are still, unfortunately, undiscriminately fixed in formalin. The results also show that GFAP varies immunologically in different species (i.e. human v. rat/mouse) and confirm that the GFAP of the PNS is immunologically distinct and/or associated with different proteins from that found in the CNS.