The PolySialylated Neural Cell Adhesion Molecule Reaches Cell Surfaces Of HypoThalamic Neurons And Astrocytes Via The Constitutive Pathway
Pierre K, Bonhomme R, Dupouy B, Poulain DA, Theodosis DT
INSERM U 378, Institut Francois Magendie, Universite Victor Segalen Bordeaux II, 1 Rue Camille Saint Saens, F 33077 Bordeaux, France
Understanding how Neurons and Glia sort and deliver Cell Adhesion Molecules to their cell surface should provide important clues as to how such molecules participate in dynamic Neuronal functions in the developing and adult Brain.
The present study examines translocation of PolySialylated Neural Cell Adhesion Molecule (PSA-NCAM), a negative regulator of Cell Adhesion, in cells of the rat HypoThalamo-NeuroHypophysial System.
In which it is expressed throughout life and which undergo Morphological remodelling in response to stimulation.
PSA-NCAM expression in this system does not vary markedly in relation to different conditions of regulated NeuroSecretion, suggesting that the GlycoProtein reaches cell surfaces via the Constitutive Pathway.
To study this more directly, we here used ImmunoFluorescence for PSA on NCAM in live, unpermeabilized cells to monitor PSA-NCAM surface expression in organotypic slice cultures from postnatal rat HypoThalami.
Subsequent Immunolabelling for Oxytocin confirmed that the cultures included MagnoCellular OxytoCinergic Neurons displaying many properties of adult NeuroSecretory Neurons in situ.
In the cultures, ImmunoReaction for PSA-NCAM was visible on the surface of OxytoCinergic and Non-OxytoCinergic Axons.
This reaction disappeared after exposure of the cultures to EndoNeurAminidase, an Enzyme which specifically cleaves alpha-2-8-linked PSA from NCAM. PSA-NCAM reappeared on Axonal surfaces 4h after Enzyme washout.
Such re-expression was visibly not affected by Neuronal activity inhibition (blockade of Ca2+ channels with Mn2+), of Na+ channels with TetrodoToxin.
Or, of Glutamate Receptors with 6-Cyano-7-NitroQuinoxaline-2,3-Dione Or D-2-Amino-5-PhosphonoPentanoic Acid) or facilitation (K+ depolarization or GABA-A Receptor blockade with Bicuculline).
In contrast, PSA-NCAM surface translocation was inhibited reversibly by cooling the cultures at 20 degrees C.
A procedure which blocks constitutive secretion and which resulted in accumulation of PSA-NCAM in the Cytoplasm of OxytoCinergic and Non-OxytoCinergic Neurons.
This treatment also revealed PSA-NCAM in the Cytoplasm of underlying Astrocytes.
Our observations provide direct evidence that PSA-NCAM reaches the cell surface of HypoThalamic Neurons and Astrocytes via the Constitutive Pathway, independently of Ca2+ entry and enhanced Neuronal activity.
Thus, PSA-NCAM in the HypoThalamo-NeuroHypophysial System would be continuously available to permit its cells to undergo remodelling whenever the proper stimulus intervenes.
Immune function Of Astrocytes
Dong Y, Benveniste EN
Glia 2001 Nov;36(2):180-90
University of Alabama at Birmingham, Department of Cell Biology, Birmingham, Alabama 35294-0005, USA
Astrocytes are the major Glial Cell within the Central Nervous System (CNS) and have a number of important physiological properties related to CNS homeostasis.
The aspect of Astrocyte biology addressed in this review article is the Astrocyte as an ImmunoCompetent Cell within the Brain.
The capacity of Astrocytes to express Class II Major Histocompatibility Complex (MHC) Antigens and Costimulatory molecules (B7 and CD40) that are critical for Antigen Presentation and T-Cell activation are discussed.
The functional role of Astrocytes as Immune Effector Cells and how this may influence aspects of inflammation and Immune reactivity within the Brain follows, emphasizing the involvement of Astrocytes in promoting Th2 Responses.
The ability of Astrocytes to produce a wide array of Chemokines and Cytokines is discussed, with an emphasis on the Immunological properties of these mediators.
The significance of Astrocytic Antigen Presentation and Chemokine/Cytokine production to Neurological Diseases with an Immunological component is described.
Copyright 2001 Wiley-Liss, Inc.
Liu JS, Zhao ML, Brosnan CF, Lee SC
Am J Pathol 2001 Jun;158(6):2057-66
Harvard Medical School, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
Nitric Oxide generated by the inducible form of Nitric Oxide Synthase (INOS) may contribute to the pathogenesis of Multiple Sclerosis (MS).
In this report, we studied postmortem tissues of MS patients for the expression of iNOS by in situ hybridization and ImmunoCytoChemistry.
ImmunoCytoChemistry for NitroTyrosine, a putative footprint for Peroxynitrite formation was also performed.
In acute MS lesions, intense reactivity for iNOS mRNA and protein was detected in reactive Astrocytes throughout the lesion and in adjacent Normal-Appearing White Matter.
Staining of Macrophages, inflammatory cell infiltrates, and Endothelial Cells was variable from case to case, but generally detected only in acute lesions.
In chronic MS lesions reactive Astrocytes at the lesion edge were positive for INOS whereas the lesion center was nonreactive.
Normal-Appearing White Matter demonstrated little reactivity, as did tissues from noninflamed control Brains.
Staining for NitroTyrosine was also detected in acute but not chronic MS lesions, and displayed a diffuse Parenchymal, membranous, and PeriVascular pattern of ImmunoReactivity.
These results support the conclusion that iNOS is induced in multiple cell types in MS lesions and that Astrocyte-derived Nitric Oxide could be important in orchestrating inflammatory responses in MS, particularly at the Blood-Brain Barrier.
Inactivation Of The Glial Fibrillary Acidic Protein Gene, But Not That Of Vimentin, Improves Neuronal Survival And Neurite Growth By Modifying Adhesion Molecule Expression
Menet V, Gimenez y Ribotta M, Chauvet N, Drian MJ, Lannoy J, Colucci-Guyon E, Privat A
J NeuroSci 2001 Aug 15;21(16):6147-58
Institut National de la Sante et de la Recherche Medicale U336, Universite Montpellier II, F-34095 Montpellier, France
Intermediate Filaments (IFs) are a major component of the CytoSkeleton in Astrocytes. Their role is far from being completely understood.
Immature Astrocytes play a major role in Neuronal migration and NeuritoGenesis, and their IFs are mainly composed of Vimentin. In mature differentiated Astrocytes, Vimentin is replaced by the IF protein Glial Fibrillary Acidic Protein (GFAP).
In response to injury of the CNS in the adult, Astrocytes become reactive, upregulate the expression of GFAP, and re-express Vimentin.
These modifications contribute to the formation of a Glial scar that is obstructive to Axonal regeneration. Nevertheless, Astrocytes in vitro are considered to be the ideal substratum for the growth of embryonic CNS Axons.
In the present study, we have examined the potential role of these two major IF proteins in both Neuronal survival and Neurite growth.
For this purpose, we cocultured wild-type Neurons on Astrocytes from three types of knock-out (KO) mice for GFAP or/and Vimentin in a Neuron-Astrocyte coculture model.
We show that the double KO Astrocytes present many features of immaturity and greatly improve survival and Neurite growth of cocultured Neurons by increasing cell-cell contact and secreting diffusible factors.
Moreover, our data suggest that the absence of Vimentin is not a key element in the permissivity of the mutant Astrocytes.
Finally, we show that only the absence of GFAP is associated with an increased expression of some ExtraCellular Matrix and Adhesion Molecules.
To conclude, our results suggest that GFAP expression is able to modulate key biochemical properties of Astrocytes that are implicated in their permissivity.