Glial fibrillary acid protein, an astrocytic-specific marker, maps to human chromosome 17

[An atypical presentation of Infantile Alexander disease lacking macrocephaly]

BACKGROUND

Alexander disease is a rare form of leukodystrophy that involves mainly astrocytes; it is inherited in an autosomal recessive manner and occurs by mutations in the GFAP gene, located on chromosome 17q21. It can occur at any age and its infantile form is characterized by macrocephaly, seizures, severe motor and cognitive delay, and progressive spasticity or ataxia.

CASE REPORT

An 8-month-old female was evaluated with a history of neurodevelopmental delay and unprovoked focal motor seizures. Physical examination showed normal head circumference, increased motor responses to tactile and noise stimuli, pyramidal signs and no visceromegalies. Widespread hypodense white matter was found on magnetic resonance and lumbar puncture showed hyperproteinorrachia. Krabbe disease was ruled out by enzymatic assay and gene sequencing of GALC. In the reassessment of the case, abnormalities in neuroimaging lead to suspicion of Alexander disease, and GFAP gene sequencing reported a pathogenic mutation in exon 4 c.716G>A, which caused a change of arginine to histidine at position 239 of the protein (p.Arg239His).

CONCLUSIONS

The radiographic signs observed in the resonance were decisive for the diagnosis, later confirmed by molecular study. It is important to consider that certain mutations are not associated with macrocephaly, which may cause delay in diagnosis.

Delirium from the gliocentric perspective

Delirium is an acute state marked by disturbances in cognition, attention, memory, perception, and sleep-wake cycle which is common in elderly. Others have shown an association between delirium and increased mortality, length of hospitalization, cost, and discharge to extended stay facilities. Until recently it was not known that after an episode of delirium in elderly, there is a 63% probability of developing dementia at 48 months compared to 8% in patients without delirium. Currently there are no preventive therapies for delirium, thus elucidation of cellular and molecular underpinnings of this condition may lead to the development of early interventions and thus prevent permanent cognitive damage. In this article we make the case for the role of glia in the pathophysiology of delirium and describe an astrocyte-dependent central and peripheral cholinergic anti-inflammatory shield which may be disabled by astrocytic pathology, leading to neuroinflammation and delirium. We also touch on the role of glia in information processing and neuroimaging.

Keratin expression in schwannoma; a study of 115 retroperitoneal and 22 peripheral schwannomas

Schwannomas have been variably observed to be glial fibrillary acid protein (GFAP) and occasionally keratin positive, with antibodies reacting with multiple keratins (pankeratins, keratin cocktail (CK), but specific keratin polypeptides (K) have not been examined for in schwannoma. Since we observed CK positivity in retroperitoneal schwannomas, we wanted to study a large group of retroperitoneal and peripheral schwannomas with GFAP, CK and Ks to explore the frequency and biologic background of this finding. We immunohistochemically evaluated a large number of retroperitoneal (n=115) and peripheral schwannomas (n=22) for GFAP, 16 individual K and AE1/AE3 keratin cocktail. The great majority (104/115, 90%) of retroperitoneal schwannomas were positive for GFAP, and 72/104 (69%) cases were positive for AE1/AE3, often extensively. Both markers highlighted the cellular Antoni A areas, particularly adjacent to the capsule, myxoid or degenerative areas, and perivascularly. Most cases 87/104 (84%) stained for both AE1/AE3 and GFAP at least focally. No tumors stained for keratins that were GFAP negative. None of the immunostains for individual K showed positivity comparable to that obtained with AE1/AE3 CK. However, 62% were focally positive for high molecular weight K1 and 8/61 (13%) for K7. None of the retroperitoneal schwannomas were positive for other keratins including K2, 4, 5, 8, 9, 10 and K14-20. Peripheral schwannomas showed GFAP-positivity in only three of 22 cases (14%), and all were negative for keratins, both cocktail and individual K. We conclude that crossreactivity of AE1/AE3 with other intermediate filament proteins, such as GFAP, as previously observed in brain and glioma tissue, probably accounts for the extensive keratin-positivity seen in some retroperitoneal schwannomas. However, focal expression of K1 and K7 cannot be ruled out. Keratin-positive schwannomas should not be confused with other keratin-positive tumors, such as sarcomatoid carcinoma, mesothelioma, and synovial sarcoma.

Distribution and cellular localization of insulin-regulated aminopeptidase in the rat central nervous system

Central infusions of angiotensin IV enhance spatial learning, memory retention and retrieval, neurotransmitter release, and long-term potentiation via interaction with a specific, high-affinity binding site. This site was recently purified and identified as the insulin-regulated aminopeptidase (IRAP). This enzyme was previously characterized as the marker protein of specialized insulin-responsive vesicles containing GLUT4 in muscle and adipose tissue. The present study provides the first comprehensive description of IRAP distribution in the adult rat brain. By using immunohistochemistry, IRAP was found to be highly expressed in selected olfactory regions, in septal and hypothalamic nuclei, throughout the hippocampal formation and cerebral cortex, and in motor and motor associated nuclei. IRAP was expressed exclusively in neurons in these regions. At the cellular level, IRAP was localized within cell bodies, excluding the nucleus, in a punctate vesicular pattern of expression. IRAP-positive immunoreactivity was also found in some proximal processes but was not detected in synaptic nerve terminals. The neurochemical composition of IRAP-containing neurons was further characterized by dual-label immunohistochemistry. IRAP was expressed in cholinergic cell bodies of the medial septum, a source of cholinergic projections to the hippocampus and cerebral cortex. The distribution of IRAP in motor and motor-associated nuclei; the colocalization of the enzyme with potential in vivo substrates, oxytocin and vasopressin in the hypothalamus; and the colocalization with GLUT4 in selected nuclei all suggest diverse physiological roles for IRAP in the rat central nervous system.

Glutamate transporter expression and function in human glial progenitors

Glutamate is the major neurotransmitter of the brain, whose extracellular levels are tightly controlled by glutamate transporters. Five glutamate transporters in the human brain (EAAT1-5) are present on both astroglia and neurons. We characterize the profile of three different human astroglial progenitors in vitro: human glial restricted precursors (HGRP), human astrocyte precursors (HAPC), and early-differentiated astrocytes. EAAT 1, EAAT3, and EAAT4 are all expressed in GRPs with a subsequent upregulation of EAAT1 following differentiation of GRPs into GRP-derived astrocytes in the presence of bone morphogenic protein (BMP-4). This corresponds to a significant increase in the glutamate transport capacity of these cells. EAAT2, the transporter responsible for the bulk of glutamate transport in the adult brain, is not expressed as a full-length protein, nor does it appear to have functional significance (as determined by the EAAT2 inhibitor dihydrokainate) in these precursors. A splice variant of EAAT2, termed EAAT2b, does appear to be present in low levels, however. EAAT3 and EAAT4 expression is reduced as glial maturation progresses both in astrocyte precursors and early-differentiated astrocytes and is consistent with their role in adult tissues as primarily neuronal glutamate transporters. These human glial precursors offer several advantages as tools for understanding glial biology because they can be passaged extensively in the presence of mitogens, afford the potential to study the temporal changes in glutamate transporter expression in a tightly controlled fashion, and are cultured in the absence of neuronal coculture, allowing for the independent study of astroglial biology.

Characterization of A2B5+ glial precursor cells from cryopreserved human fetal brain progenitor cells

The identification and characterization of human neural precursor cells are critical in extending our understanding of central nervous system development from model animal systems to our own species. Moreover, availability of well-characterized populations of human cells is of potential value in endeavors ranging from cell transplantation to drug screening. We have isolated a population of continuously dividing glial-restricted precursor cells from commercially available cryopreserved 18-20 weeks old fetal brain neural progenitor cells. These human glial-restricted precursor cells are A2B5(+) and do not express polysialylated E-NCAM (PSA-NCAM). They can be grown as purified populations in serum-free medium supplemented with basic fibroblast growth factor (bFGF) and can be induced to generate cells with the antigenic characteristics of oligodendrocytes and distinct astrocytic populations.

Conversion of taurine into N-chlorotaurine (taurine chloramine) and sulphoacetaldehyde in response to oxidative stress

N-Chlorotaurine (taurine chloramine), formed by treating taurine with hypochlorous acid, was shown to decompose to sulphoacetaldehyde with a first-order rate constant of 9.9+/-0.5 x 10(-4).h-1 at 37 degrees C in 0.1 M phosphate buffer, pH 7.4. Rat liver homogenates accelerated this decay in a process that was proportional to tissue-protein concentration and saturable, with maximum velocity (Vmax) and Km values of 0.28+/-0.01 nmol/min per mg of protein and 37+/-9 microM respectively. This activity was found to be lost on heat denaturation, but retained after dialysis. There was no detectable formation of sulphoacetaldehyde when taurine itself was incubated with the tissue homogenates under the same conditions. Activation of human neutrophils (1.67 x 10(6) cells/ml) with latex beads resulted in a respiratory burst of oxygen-radical production, the products of which were partially sequestered by 12.5 mM taurine. Under these conditions sulphoacetaldehyde was generated at a constant rate of 637+/-18 pmol/h per ml for over 7 h. A non-activated neutrophil suspension contained constant levels of 1.42+/-0.02 nmol/ml sulphoacetaldehyde, as did activated cells incubated in the absence of taurine, a basal level which may indicate a steady turnover of taurine in these cells. Such formation of chlorotaurine and its decay to the aldehyde may be the first steps in the metabolism of taurine to isethionate (2-hydroxyethanesulphonate) that has been demonstrated by various authors to occur in vivo.

Mapping of a disease locus for familial rapidly progressive frontotemporal dementia to chromosome 17q12-21

Familial frontotemporal dementia (FTD) is a complex disorder with lack of distinctive histopathological markers found in other types of dementia. Most of the linkage reports from FTD families map the disease loci to chromosome 17q21-22. However, FTD is genetically heterogeneous, as linkage also has been reported to chromosome 3. In the present study, we investigated the genetics of a Swedish family with an early-onset type of rapidly progressive FTD, associated with muscular rigidity and akinetic movements. Neuropathological features such as severe frontal lobe degeneration, spongy changes, and gliosis were present in affected family members. We here report probable linkage to chromosome 17q12-21 with a maximum two-point lod score of 2.76 at theta = 0 for marker D17S806, and a peak multipoint lod score of 2.86 for the same marker. Linkage to chromosome 3 was excluded, as two-point lod scores of -2.79, and -2.27 at theta = 0.01 for markers D3S1603 and D3S1552, respectively, were obtained. Sequencing of the translated exons of a strong candidate gene in the linked region of chromosome 17, the tau gene, failed to identify any mutations segregating with the disease.

Hereditary frontotemporal dementia is linked to chromosome 17q21-q22: a genetic and clinicopathological study of three Dutch families

Hereditary frontotemporal dementia (HFTD) is a rare autosomal dominant form of presenile dementia characterized by behavioral changes and reduced speech. Three multigeneration kindreds with this condition, in the Netherlands, were investigated for clinicopathological comparison and linkage analysis. Frontotemporal atrophy on computed tomographic scanning and/or magnetic resonance imaging was usually present. Single-photon emission computed tomography (SPECT) showed frontal hypoperfusion in the early phase of the disease. Brain tissue showed moderate to severe atrophy of frontal and temporal cortex with neuronal loss, gliosis, and spongiosis. Pick bodies were lacking in all cases of the 3 families. The mean age of onset varied significantly between families. We report here evidence for linkage to chromosome 17q21-q22 with a maximum lod score of 4.70 at theta = 0.05 with the marker D17S932. Recombination analysis positions the gene for HFTD in a region of approximately 5 cM between markers D17S946 and D17S791. Three other neurodegenerative disorders with a strong clinical and pathological resemblance have recently been mapped to the same chromosomal region, suggesting that a group of clinically related neurodegenerative disorders may originate from mutations in the same gene.

Structure and transcriptional regulation of the GFAP gene

Transcriptional regulation of the GFAP gene is intimately connected with astrocyte function: its initial activation marks the differentiation of astrocytes, and its up-regulation accompanies the reactive response to CNS injury. Studies of GFAP transcription should thus provide insights into multiple regulatory pathways operating in these cells. In addition, they should identify DNA elements that could be used to direct synthesis of other proteins to astrocytes in transgenic animals, permitting creation of disease models, and the testing of cause and effect relationships. This review describes several GFAP cDNA and genomic clones that have been isolated, including homology comparisons of the encoded RNAs and proteins. Cell transfection studies by several laboratories are summarized that have identified a DNA segment immediately upstream of the RNA start site that is essential for transcriptional activity, but which have yielded conflicting results concerning the importance of other segments located both further upstream and downstream of the RNA start site. Two procedures are recounted that have led to the successful expression of GFAP-transgenes in astrocytes in mice. One of these incorporates the transgene into the first exon of a fragment spanning the entire GFAP gene, while the other links it to a 2 kb 5'-flanking segment. Results already produced by GFAP-transgenic studies include demonstration of a neurotoxic effect of the HIV-1 gp120 coat protein, and creation of a hydrocephalic mouse model.

Assignment of 22 loci in the rat by somatic hybrid and linkage analysis

Twenty structural genes and two unique anonymous DNA fragments have been mapped in the rat (Rattus norvegicus) with a panel of mouse x rat hybrids and linkage analysis. Ten of the 20 autosomes are represented by at least one of these markers. A new syntenic relationship among rat Chromosome (Chr) 16, mouse Chr 14, and human Chr 10q was established. Results of this study further support the extensive conservation of synteny between the rat and mouse and, to a lesser degree, between rat and human.

Molecular cloning of mouse beta 2-glycoprotein I and mapping of the gene to chromosome 11

beta 2-Glycoprotein I (beta 2 GPI), a plasma protein that binds to anionic phospholipids, is composed of five repeating units called a short consensus repeat (SCR), which is found mostly in the regulatory proteins of the complement system. Recently the human beta 2 GPI gene has been assigned to chromosome 17, not to chromosome 1 where most of the genes of the SCR-containing proteins are clustered. In this report, we have isolated a full-length cDNA clone of mouse beta 2 GPI and determined the chromosomal localization of the gene. The amino acid sequence deduced from the nucleotide sequence of mouse beta 2 GPI revealed 76.1% identity with that of human beta 2 GPI. A genetic mapping by in situ hybridization and linkage analysis using 50 backcross mice has shown that the mouse beta 2 GPI gene (designated B2gp1) is located on the terminal portion of the D region of chromosome 11, closely linked to Gfap, and is 18 cM distal to Acrb, extending a conserved linkage group between mouse chromosome 11 and human chromosome 17. On the basis of these results, the evolutionary relationships among the SCR-containing proteins are discussed.