Expression of 3-fucosyl-N-acetyllactosamine on glia cells and its putative role in cell adhesion

Identification and validation of a Lewis x glycomimetic peptide

Glycans play important roles in regulating cell recognition and interactions to fine tune development, and synaptic plasticity and regeneration in the adult nervous system. The spatial and temporal expression pattern of Lewis(x) (a terminal trisaccharide epitope characterized by alpha1,3-fucosyl-N-acetyl-lactosamine) in the nervous system indicates an important role of this epitope in neurogenesis and brain development. Localization of Lewis(x) in the proliferative subventricular zone of the developing nervous system and also its expression on stem cells of the adult nervous system suggests a role in neurogenesis and hence regeneration. To provide an alternative tool to elucidate the functional roles of Lewis(x), we screened a random peptide phage library against a Lewis(x)-specific antibody to identify a Lewis(x) glycomimetic peptide. We identified a peptide that specifically bound to the Lewis(x)-specific antibody and this binding could be competed by the Lewis(x) glycan. Different aspects of the Lewis(x) glycomimetic peptide were investigated by introducing it in in vitro assays measuring neurite outgrowth and in in vivo assays to determine its efficacy in regeneration of peripheral nerve and spinal cord after injury in adult mice. In vitro, neurite outgrowth triggered by the Lewis(x-)carrying adhesion molecule CD24 was abolished alike by the Lewis(x) glycan and the glycomimetic peptide, while no influence of the glycomimetic peptide was seen in regeneration. Our results validate the use of Lewis(x) glycomimetic peptide as a functionally equivalent structure to the Lewis(x) glycan.

Impact of thyroid hormone deficiency on the developing CNS: cerebellar glial and neuronal protein expression in rat neonates exposed to antithyroid drug propylthiouracil

The developing rat cerebellum is vulnerable to thyroid hormone (TH) deficiency. The present study addresses the molecular mechanisms involved in this response. Specifically, the study focuses on the expression of selected cerebellar proteins that are known to be directly [protein expressing 3-fucosyl-N-acetyl-lactosamine antigen (CD15), neuronal cell adhesion molecule (L1)] or indirectly [glial fibrillary acidic protein (GFAP)], involved in glial-neuronal interactions and thus regulation of cell proliferation and granule cell migration. Cerebellar mass, structure, and protein expression in rat neonates exposed to antithyroid drug propylthiouracil (PTU) from the embryonic day (E) 16 to postnatal day (P) 21 were compared against rat neonates that received replacement of thyroxin (T4) starting on day P1 or untreated controls. Cerebellar proteins were analyzed by quantitative Western blots. PTU-treated rats lagged in growth and showed reduction in cerebellar mass and alterations in cerebellar structure on P15. Daily treatment of neonates with T4 restored normal cerebellum-to-body-mass ratio, cerebellar structure, and cerebellar protein expression. Densitometric analysis of Western blots revealed altered expression of selected proteins in the cerebella of hypothyroid neonates. A decrease of CD15 (46%, p = 0.031) was observed on P10 and was accompanied by a decrease in GFAP expression (64%, p = 0.039). Furthermore, a shift in the developmental GFAP profile was observed in the PTU-treated cerebellum. L1 expression was not significantly affected in the hypothyroid cerebellum. Altered expression of cerebellar proteins is likely to affect cell-cell interactions and consequently cell proliferation and migration and contribute to structural and functional alterations seen in the hypothyroid rat neonates.

Transient expression of stage-specific embryonic antigen-1 (CD15) in the developing dorsal rat spinal cord

The localization of CD15 (synonyms: stage-specific embryonic antigen-1 (SSEA-1), 3(alpha)-fucosyl-N-acetyl-lactosamine or FAL), which is implicated in neuronal differentiation, in the developing dorsal rat spinal cord was studied by immunocytochemistry. A embryonal day 9 (E9), SSEA-1 was detected in the neural ectoderm and, at E11, in cells near the ventricle of the matrix layer. This localization indicated that SSEA-1 is present in proliferating premigratory cells of the rat spinal cord. Between E12 and E16, cells of the alar plate expressed SSEA-1. Expression of the antigen was restricted to neuroblasts that will form the dorsal horn. SSEA-1, therefore, can be used at this stage as a marker for a subdivision of the matrix layer. At E14, the dorsal root entrance zone showed SSEA-1. This indicated that SSEA-1 is associated with ingrowing primary afferents. From E16 on, SSEA-1 was present in the dorsal raphe, which suggested a function for SSEA-1 in the guidance of developing fibres. After E17, the antigen was also found within the dorsal mantle layer. SSEA-1 was first present in Rexed's laminae II, IV and V. Later on in development the antigen was detected only in Rexed's laminae II (substantia gelatinosa). These distribution patterns indicated that SSEA-1 is present on migratory and/or postmigratory cells. In addition, SSEA-1 is associated with small-diameter dorsal root fibres, the C fibres and A(sigma) fibres, that terminate within the substantia gelatinosa. After birth, SSEA-1 was present throughout the dorsal horn, probably as a result of the myelination of the fibres.

Expression of CD15 in tumours of the nervous system

The expression of the CD15 epitope was investigated by immunohistochemistry, western blotting and immuno-thin-layer chromatography on a large series of human nervous system tumours and ethylnitrosourea-induced rat gliomas. Our results show that CD15 is expressed as a glycoprotein- or glycolipid-associated epitope in normal human and rat brain. In contrast, immunoreactivity for CD15 was absent in tumour cells of experimental rat gliomas. In human tumours we found a more complex expression pattern. While intra- and perivascular granulocytes as well as macrophages in necrotic areas of anaplastic tumours were always strongly CD15-positive, immunoreactive tumour cells were detectable only in a fraction of low-grade gliomas. Anaplastic gliomas and glioblastomas consistently did not express the epitope on their tumour cells. In addition to individual low-grade gliomas, we found CD15-positive cases among metastatic carcinomas, craniopharyngeomas, meningiomas, germinomas and malignant melanomas. Our results suggest that immunohistochemistry for CD15 is potentially useful in diagnostic neuropathology as a marker for granulocytes in paraffin sections, as a supplementary tool for the histopathological grading of gliomas, and as an aid for differentiation between anaplastic glioma cells and non-neoplastic glia. Furthermore, it can be speculated that the lack of CD15 expression on anaplastic glioma cells may potentially be responsible for some of their characteristics--such as altered cellular interaction and loss of contact inhibition.

Retinoic acid increases CD15 expression in immortalized rat astrocytes

We have studied the expression of the CD15 (3-fucosyl-N-acetyl-lactosamine) epitope on immortalized astroglial cells derived from embryonic (E 19/20) rat brain. Immortalization was achieved by pulse-treatment of primary culture with 5-azacytidine. Seventy-three permanent cell lines were established by repeated cell cloning. Clones expressing GFAP, A2B5, and vimentin were regarded as immature astrocytes. One of these clones expressing CD15 was selected for manipulation studies. Monoclonal antibody was used for immunocytochemical detection of CD15 epitope and in immunoblot analysis. CD15 expression was visible in about 20% of the cells and was associated with a special morphological appearance. In the presence of retinoic acid the proportion of CD15-positive cells increased in a time-dependent manner, reaching about 90% within four days. Again, this expression was associated with the formation of distinct morphological features, including immunoreactive perinuclear granula, tips of processes and contact sites. After treatment with neuraminidase, all cells showed CD15-positive immunoreaction, revealing the presence of the epitope masked by sialylation. Immunoblot patterns of glycoproteins from trypsinized and mechanically detached cell preparations suggest that proteins, carrying sialylated CD15, might represent intracellular precursors of extracellularly active molecules.

Age-related expression patterns of the CD15 epitope in the human lateral geniculate nucleus (LGN)

The age-related distribution of the trisaccharide epitope 3-fucosyl-N-acetyl-lactosamine (CD15) was evaluated in the human lateral geniculate nucleus (LGN). Coronal paraffin sections from individuals between the 12th week of gestation to 99 years of age were processed for immunohistochemistry using monoclonal antibodies against the CD15 epitope. CD15 immunoreactivity was present in the neuropil from the 14th week of gestation with a graded pattern along the anteroposterior and mediolateral axes of the LGN. Immunoreactivity then became preferentially located within the future cell layers, shortly before cellular segregation was visible in Cresyl Violet stained sections. Maximal CD15 expression occurred from the 22nd week of gestation until the beginning of visual experience (second week of postnatal life). During the subsequent period the spatial pattern of CD15 expression changed. Whereas immunoreactivity in the cell layers gradually disappeared, CD15 positive astrocytes became transiently concentrated in the intercellular layers. The staining within the interlaminar region was best developed at about one year of postnatal life. The adult pattern was found at around 10 years of age, when the LGN appeared almost unstained. Two stages of CD15 expression can thus be separated. The first is characterized by neuropil staining and is synchronized with the time profile of neuronal maturation and of formation of non-stabilized contacts. CD15 is at this time possibly correlated with structural instability and increased vulnerability but at the same time with a high degree of plasticity. The second, peri- and postnatal stage is characterized by CD15 positive astrocytes. These appeared when CD15 in the neuropil disappeared. This loss of CD15 expression in the neuropil occurs during the phase of experience-dependent establishment of the mature interconnectivity and probably heralds loss in plasticity. The time-related expression pattern of CD15 is therefore compatible with the idea that CD15 levels reflect different degrees of developmental determination of retino-geniculate interaction.

Evidence for subdivisions in the human suprachiasmatic nucleus

The human suprachiasmatic nucleus was analysed by immunohistochemical demonstration of various substances in combination with 3-dimensional computerized reconstruction and video overlay facilities. In the human, the suprachiasmatic nucleus is not as compact as in the rodent. Its boundaries are not easily delineated using conventional stains, and it shows no obvious cytoarchitectonic structure. However, based on its chemoarchitecture, the human suprachiasmatic nucleus can be apportioned into five major subdivisions: Dorsal, comprising a crescent shaped mass of densely packed neurophysin/vasopressin-neurons as well as neurotensin-neurons, and also containing 3-fucosyl-N-acetyl-lactosamine (FAL)-positive neurons in its medial part. Central, occupying the core of the nucleus and consisting precisely of a region devoid of neurophysin/vasopressin neurons but demarcated by calbindin, synaptophysin, and a circumscribed cluster of vasoactive intestinal polypeptide-neurons and containing neurotensin neurons as well. Anteroventrally this division also contains some intermingled neurons positive for neurotensin, neuropeptide Y, somatostatin, and FAL. Ventral, extending from the anterior extreme of the preoptic recess caudolaterally to a field between the optic chiasm and the anteroventral margin of the supraoptic nucleus. This subdivision is specified by synaptophysin, calbindin, and substance P immunoreactivity and is almost free of glial fibrillary acidic protein. From its rostral portion, fibers immunoreactive for calbindin, vasoactive intestinal polypeptide, synaptophysin, and substance P protrude deeply into the optic chiasm. Medial, comprising a thin band between the subependymal zone and the dorsal subdivision, containing scattered somatostatin neurons. External, extending as a band around the dorsal and lateral borders of the nucleus, containing astrocytes expressing the FAL-epitope and scattered neurophysin/vasopressin and neurotensin neurons. These findings indicate that the human suprachiasmatic nucleus contains well-defined subdivisions with different, chemically specific, connections and provides a basis for comparing these subdivisions with the structure and function of subdivisions previously described for the suprachiasmatic nucleus in experimental animals. In addition, the findings strengthen the concept that the human suprachiasmatic nucleus generates and expresses circadian rhythms in a manner similar to that documented for the suprachiasmatic nucleus in experimental animals, and suggest that different subdivisions may subserve specific functional roles.

Distribution of the 3-fucosyl-N-acetyl-lactosamine (FAL) epitope in the adult mouse brain

The distribution of the 3-fucosyl-N-acetyl-lactosamine (FAL) epitope within the adult mouse brain was studied by immunohistochemistry using the monoclonal antibody Leu-M1. Leu-M1-positive elements comprised astrocytes and neurons. FAL-positive astrocytes were particularly abundant in barrier structures of the brain, but were also prominent at the periphery of most medullated fiber tracts. Their intracerebral distribution led to a distinct pattern of organization, which in some locations, including the cerebral cortex, could be used for an extended regional architectonic description. Since only some FAL-positive astrocytes were also positive for glial fibrillary acid protein (GFAP), the emerging topography of the FAL-positive astrocytes often differed from the GFAP-distribution. In the cerebellum, Bergmann glia cells expressed the FAL epitope and, in the vermis, their arrangement had a band-like appearance. Positive oligodendrocytes could not be identified. The common ependymal cells were negative, whereas tanycytes were highly immunoreactive. The Leu-M1 antibody also stained some neurons. These occurred in selected neocortical regions, within the dorsal and ventral striatum, in the globus pallidus, the nucleus basalis of Meynert, the nucleus diagonalis and some hypothalamic areas. In some instances, their morphology and location indicated an association with neurochemically specified cell groups.

Changes in glial cell markers in recent and old demyelinated lesions in central pontine myelinolysis

An immunohistochemical study was performed to compare glial reactions in recent and old lesions of central pontine myelinolysis (CPM). Regions of demyelination and destruction of oligodendrocytes, showed reduced immunoreactivity of myelin basic protein (MBP), myelin-associated glycoprotein (MAG), transferrin, and carbonic anhydrase C (CA C). In addition, labeling of glial fibrillary acidic protein (GFAP) and S-100 protein revealed distinct dystrophic alterations of the astroglia. Remarkably, immunolabeling of GFAP was drastically reduced in astrocytic cytoplasm within freshly demyelinated lesions. Immunostaining of vimentin revealed a differential intracytoplasmic decoration of hypertrophic and dystrophic astrocytes in recent and old CPM lesions. Immunolabeling of desmin failed to stain glial cells. Monoclonal antibodies against HNK-1 exhibited greatly increased immunoreactivity both of persisting oligodendrocytes and of reactive fibrillary astrocytes in old CPM foci. In freshly demyelinated lesions, enhanced immunoreactivity of the X-hapten (3-fucosyl-N-acetyllactosamine) was prominent in astroglia and oligodendrocytes. Simultaneously, reactive astrocytes revealed intracytoplasmic labeling of laminin. Quantitation of GFAP+ astroglia in fresh CPM and control cases revealed an increase in the number of astrocytes within the demyelinated foci and in the surrounding non-demyelinated pontine tissue of CPM cases. The occurrence of astroglial alterations in the demyelinated foci of CPM could be interpreted as "astroglial dystrophy" which may represent a pathogenic factor in CPM. Furthermore, it is possible that changes of the glial microenvironment may influence the astroglia to revert transiently back to an immature phenotype as indicated by the enhanced expression of the X-hapten and HNK-1, and the de novo synthesis of vimentin and laminin.