Astrocyte growth, reactivity, and the target of the antiproliferative antibody, TAPA

Development of a Prodrug of Camptothecin for Enhanced Treatment of Glioblastoma Multiforme

A novel therapeutic approach for glioblastoma multiforme (GBM) therapy has been carried out through in vitro and in vivo testing by using the prodrug camptothecin-20-O-(5-aminolevulinate) (CPT-ALA). The incorporation of ALA to CPT may promote uptake of the cytotoxic molecule by glioblastoma cells where the heme synthesis pathway is active, improving the therapeutic action and reducing the side effects over healthy tissue. The antitumor properties of CPT-ALA have been tested on different GBM cell lines (U87, U251, and C6) as well as in an orthotopic GBM model in rat, where potential toxicity in central nervous system cells was analyzed. In vitro results indicated no significant differences in the cytotoxic effect over the different GBM cell lines for CPT and CPT-ALA, albeit cell mortality induced by CPT over normal cell lines was significantly higher than CPT-ALA. Moreover, intracranial GBM in rat was significantly reduced (30% volume) with 2 weeks of CPT-ALA treatment with no significant side effects or alterations to the well-being of the animals tested. 5-ALA moiety enhances CPT diffusion into tumors due to solubility improvement and its metabolic-based targeting, increasing the CPT cytotoxic effect on malignant cells while reducing CPT diffusion to other proliferative healthy tissue. We demonstrate that CPT-ALA blocks proliferation of GBM cells, reducing the infiltrative capacity of GBM and promoting the success of surgical removal, which improves life expectancy by reducing tumor recurrence.

Blockade of Cell Volume Regulatory Protein NKCC1 Increases TMZ-Induced Glioma Apoptosis and Reduces Astrogliosis

Glioma is one of the most common primary malignant tumors of the central nervous system accounting for approximately 40% of all intracranial tumors. Temozolomide is a conventional chemotherapy drug for adjuvant treatment of patients with high-risk gliomas, including grade II to grade IV. Our bioinformatic analysis of The Cancer Genome Atlas and Chinese Glioma Genome Atlas datasets and immunoblotting assay show that SLC12A2 gene and its encoded Na⁺-K⁺-2Cl^- cotransporter isoform 1 (NKCC1) protein are abundantly expressed in grade II-IV gliomas. NKCC1 regulates cell volume and intracellular Cl^- concentration, which promotes glioma cell migration, resistance to temozolomide, and tumor-related epilepsy in experimental glioma models. Using mouse syngeneic glioma models with intracranial transplantation of two different glioma cell lines (GL26 and SB28), we show that NKCC1 protein in glioma tumor cells as well as in tumor-associated reactive astrocytes was significantly upregulated in response to temozolomide monotherapy. Combination therapy of temozolomide with the potent NKCC1 inhibitor bumetanide reduced tumor proliferation, potentiated the cytotoxic effects of temozolomide, decreased tumor-associated reactive astrogliosis, and restored astrocytic GLT-1 and GLAST glutamate transporter expression. The combinatorial therapy also led to suppressed tumor growth and prolonged survival of mice bearing GL26 glioma cells. Taken together, these results demonstrate that NKCC1 protein plays multifaceted roles in the pathogenesis of glioma tumors and presents as a therapeutic target for reducing temozolomide-mediated resistance and tumor-associated astrogliosis.

Impact of Glutathione Modulation on Stability and Pharmacokinetic Profile of Redox-Sensitive Nanogels

Nanoparticles degradable upon external stimuli combine pharmacokinetic features of both small molecules as well as large nanoparticles. However, despite promising preclinical results, several redox responsive disulphide-linked nanoparticles failed in clinical translation, mainly due to their unexpected in vivo behavior. Glutathione (GSH) is one of the most evaluated antioxidants responsible for disulfide degradation. Herein, the impact of GSH on the in vivo behavior of redox-sensitive nanogels under physiological and modulated conditions is investigated. Labelling of nanogels with a DNA-intercalating dye and a radioisotope allows visualization of the redox responsiveness at the cellular and the systemic levels, respectively. In vitro, efficient cleavage of disulphide bonds of nanogels is achieved by manipulation of intracellular GSH concentration. While in vivo, the redox-sensitive nanogels undergo, to a certain extent, premature degradation in circulation leading to rapid renal elimination. This instability is modulated by transient inhibition of GSH synthesis with buthioninsulfoximin. Altered GSH concentration significantly changes the in vivo pharmacokinetics. Lower GSH results in higher elimination half-life and altered biodistribution of the nanogels with a different metabolite profile. These data provide strong evidence that decreased nanogel degradation in blood circulation can limit the risk of premature drug release and enhance circulation half-life of the nanogel.

Statistical study of biomechanics of living brain cells during growth and maturation on artificial substrates

There is increasing evidence that mechanical issues play a vital role in neuron growth and brain development. The importance of this grows as novel devices, whose material properties differ from cells, are increasingly implanted in the body. In this work, we studied the mechanical properties of rat brain cells over time and on different materials by using a high throughput magnetic tweezers system. It was found that the elastic moduli of both neurite and soma in networked neurons increased with growth. However, neurites at DIV4 exhibited a relatively high stiffness, which could be ascribed to the high outgrowth tension. The power-law exponents (viscoelasticity) of both neurites and somas of neurons decreased with culture time. On the other hand, the stiffness of glial cells also increased with maturity. Furthermore, both neurites and glia become softer when cultured on compliant substrates. Especially, the glial cells cultured on a soft substrate obviously showed a less dense and more porous actin and GFAP mesh. In addition, the viscoelasticity of both neurites and glia did not show a significant dependence on the substrates' stiffness.

Arsenic Exposure Induces Unscheduled Mitotic S Phase Entry Coupled with Cell Death in Mouse Cortical Astrocytes

There is serious concern about arsenic in the natural environment, which exhibits neurotoxicity and increases the risk of neurodevelopmental disorders. Adverse effects of arsenic have been demonstrated in neurons, but it is not fully understood how arsenic affects other cell types in the brain. In the current study, we examined whether sodium arsenite (NaAsO₂) affects the cell cycle, viability, and apoptosis of in vitro-cultured astrocytes isolated from the cerebral cortex of mice. Cultured astrocytes from transgenic mice expressing fluorescent ubiquitination-based cell cycle indicator (Fucci) were subjected to live imaging analysis to assess the effects of NaAsO₂ (0, 1, 2, and 4 μM) on the cell cycle and number of cells. Fucci was designed to express monomeric Kusabira Orange2 (mKO2) fused with the ubiquitylation domain of hCdt1, a marker of G1 phase, and monomeric Azami Green (mAG) fused with the ubiquitylation domain of hGem, a marker of S, G2, and M phases. NaAsO₂ concentration-dependently decreased the peak levels of the mAG/mKO2 emission ratio when the ratio had reached a peak in astrocytes without NaAsO₂ exposure, which was due to attenuating the increase in the mAG-expressing cell number. In contrast, the mAG/mKO2 emission ratio and number of mAG-expressing cells were concentration-dependently increased by NaAsO₂ before their peak levels, indicating unscheduled S phase entry. We further examined the fate of cells forced to enter S phase by NaAsO₂. We found that most of these cells died up to the end of live imaging. In addition, quantification of the copy number of the glial fibrillary acidic protein gene expressed specifically in astrocytes revealed a concentration-dependent decrease caused by NaAsO₂. However, NaAsO₂ did not increase the amount of nucleosomes generated from DNA fragmentation and failed to alter the gene expression of molecules relevant to unscheduled S phase entry-coupled apoptosis (p21, p53, E2F1, E2F4, and Gm36566). These findings suggest that NaAsO₂ adversely affects the cell cycle and viability of astrocytes by inducing unscheduled S phase entry coupled with cell death that may be caused by mechanisms other than apoptosis.

Altered glial gene expression, density, and architecture in the visual cortex upon retinal degeneration

Genes encoding the proteins of cytoskeletal intermediate filaments (IF) are tightly regulated, and they are important for establishing neural connections. However, it remains uncertain to what extent neurological disease alters IF gene expression or impacts cells that express IFs. In this study, we determined the onset of visual deficits in a mouse model of progressive retinal degeneration (Pde6b(-) mice; Pde6b(+) mice have normal vision) by observing murine responses to a visual task throughout development, from postnatal day (PND) 21 to adult (N=174 reliable observations). Using Q-PCR, we evaluated whether expression of the genes encoding two Type III IF proteins, glial fibrillary acidic protein (GFAP) and vimentin was altered in the visual cortex before, during, and after the onset of visual deficits. Using immunohistochemical techniques, we investigated the impact of vision loss on the density and morphology of astrocytes that expressed GFAP and vimentin in the visual cortex. We found that Pde6b(-) mice displayed 1) evidence of blindness at PND 49, with visual deficits detected at PND 35, 2) reduced GFAP mRNA expression in the visual cortex between PND 28 and PND 49, and 3) an increased ratio of vimentin:GFAP-labeled astrocytes at PND 49 with reduced GFAP cell body area. Together, these findings demonstrate that retinal degeneration modifies cellular and molecular indices of glial plasticity in a visual system with drastically reduced visual input. The functional consequences of these structural changes remain uncertain.

Down-regulation of CD81 tetraspanin in human cells producing retroviral-based particles: tailoring vector composition

Retroviral-derived biopharmaceuticals (RV) target numerous therapeutic applications, from gene therapy to virus-like particle (rVLP)-based vaccines. During particle formation, beside the pseudotyped envelope proteins, RV can incorporate proteins derived from the virus producer cells (VPC). This may be detrimental by reducing the amounts of the pseudotyped envelope and/or by incorporating protein capable of inducing immune responses when non-human VPC are used. Manipulating the repertoire of VPC proteins integrated onto the vector structure is an underexplored territory and should provide valuable insights on potential targets to improve vector pharmacokinetic and pharmacodynamic properties. In this work, human HEK 293 cells producing retrovirus-like particles (rVLPs) and infectious RV vectors were used to prove the concept of customizing RV composition by manipulating cellular protein content. The tetraspanin CD81 was chosen since it is significantly incorporated in the RV membrane, conferring to the vector significant immunogenicity when used in mice. RNA interference-mediated by shRNA lentiviral vector transduction was efficiently used to silence CD81 expression (up to 99%) and the rVLPs produced by knocked-down cells lack CD81. Silenced clones were analyzed for cell proliferation, morphological changes, susceptibility to oxidative stress conditions, and rVLP productivities. The results showed that the down-regulation of VPC proteins requires close monitoring for possible side effects on cellular production performance. Yet, they confirm that it is possible to change the composition of host-derived immunogens in RV by altering cellular protein content with no detriment for vector productivity and titers. This constitutes an important manipulation tool in vaccinology--by exploiting the potential adjuvant effect of VPC proteins or using them as fusion agents to other proteins of interest to be exposed on the vector membrane--and in gene therapy, by reducing the immunogenicity of RV-based vector and enhancing in vivo half-life. Such tools can also be applied to lentiviral or other enveloped viral vectors.

The effects of a CD81 null mutation on retinal pigment epithelium in mice

The present study examines the effects of Cd81-null mutation on the development of the retinal pigment epithelium (RPE), specifically cell size and number of cells with multiple nuclei. The outlines of RPE in retinal flat mounts were stained with rhodamine-labeled phalloidin and RPE nuclei with Hoechst stain. The RPE layer was sampled to define the number of cells, the size of the RPE cells and the number of nuclei within the cells. The Cd81-null mutation caused an increase in the number of cells within the RPE layer. The cells were smaller than those in the wild type mice. Furthermore there was an increase in the number of mono-nucleated cells. In the posterior portion of the eye there was a significant increase in the number of multi-nucleated cells. The data indicate that CD81 plays a significant role in the final stages of RPE development, controlling cell number and overall developmental pattern.

Male CD81 knockout genotype disrupts Mendelian distribution of offspring

CD81 is an integral membrane protein in the tetraspanin superfamily that serves as an adaptor protein. CD81 is also a maternally imprinted gene that is found in a regulated cluster of genes on mouse chromosome 7. Among offspring produced from heterozygous breeding pairs, CD81(null/null) mice grew at the same rate as CD81(+/+) and CD81(+/null) mice. Because of an inhibition in sperm-egg fusion, CD81(null/null) female mice are much less fertile than CD81(+/+) and CD81(+/null) mice. However, no published study has detailed the effect of the male CD81 genotype on the genotype and sex distribution of offspring. We set up breeding pairs of heterozygotic (C.129-Cd81(tm1) N7) female mice and male mice with CD81(+/null), CD81(+/+), or CD81(null/null) genotypes. The survival and development of CD81(+/null), CD81(+/+), and CD81(null/null) offspring were monitored and compared. Compared with those of heterozygous male breeders, CD81(null/null) pups were born at a less-than-expected ratio from CD81(null/null) males. Sex distribution did not differ among pups sired by CD81(null/null) compared with CD81(+/null) mice. The data suggest that the effect of the CD81(null/null) paternal genotype on offspring is manifested early in development or in utero.

CD81 inhibits the proliferation of astrocytes by inducing G(0)/G (1) arrest in vitro

Astrocytes play a major role in the reactive processes in response to neuronal injuries in the brain. Excessive gliosis is detrimental and can contribute to neuronal damage. CD81 (TAPA), a member of the tetraspanin family of proteins, is upregulated by astrocytes after traumatic injury to the rat central nervous system (CNS). To further understand the role of CD81 in the inhibition of astrocytes, we analyzed the effects of a CD81 antibody, on cultured rat astrocytes. The results indicated that the effect worked in a dose-dependent manner with certain dosage range. It, however, reached a dosage equilibrium at a high dosage. Furthermore, anti-CD81 antibody remarkably inhibited the proliferation of astrocytes after incubation with astrocytes for different periods of time and the effect presented a time-dependent fashion. However, anti-CD81 antibody substantially inhibited the proliferation of astrocytes at low density and middle density but slightly inhibited the proliferation of astrocytes at high density, suggesting that the effect was positively correlated with the proliferative ability of astrocytes. Finally, the cell cycle of astrocytes exposured to anti-CD81 antibody was arrested in S phase at the initial stage and at G(0)/G(1) phase over time. These findings indicated that CD81 exert significant inhibitory effect, dose-dependently and time-dependently, on the proliferation of astrocytes and the effect is positively correlated with the proliferative capability of astrocytes.

Engagement of CD81 induces ezrin tyrosine phosphorylation and its cellular redistribution with filamentous actin

CD81 is a tetraspanin family member involved in diverse cellular interactions in the immune and nervous systems and in cell fusion events. However, the mechanism of action of CD81 and of other tetraspanins has not been defined. We reasoned that identifying signaling molecules downstream of CD81 would provide mechanistic clues. We engaged CD81 on the surface of B-lymphocytes and identified the induced tyrosine-phosphorylated proteins by mass spectrometry. This analysis showed that the most prominent tyrosine phosphorylated protein was ezrin, an actin-binding protein and a member of the ezrin-radixin-moesin family. We also found that CD81 engagement induces spleen tyrosine kinase (Syk) and that Syk was involved in tyrosine phosphorylation of ezrin. After engagement of CD81, it colocalized with ezrin and F-actin, and this association was disrupted when Syk activation was blocked. Taken together, these studies suggest a model in which CD81 interfaces between the plasma membrane and the cytoskeleton by activating Syk, mobilizing ezrin, and recruiting F-actin to facilitate cytoskeletal reorganization and cell signaling. This mechanism might explain the pleiotropic effects induced in response to stimulation of cells by anti-CD81 antibodies or by the hepatitis C virus, which uses this molecule as its key receptor.

Lateral organization of membrane proteins: tetraspanins spin their web

Despite high expression levels at the plasma membrane or in intracellular vesicles, tetraspanins remain among the most mysterious transmembrane molecules 20 years after their discovery. Several genetic studies in mammals and invertebrates have demonstrated key physiological roles for some of these tetraspanins, in particular in the immune response, sperm-egg fusion, photoreceptor function and the normal function of certain epithelia. Other studies have highlighted their ability to modulate cell migration and metastasis formation. Their role in the propagation of infectious agents has drawn recent attention, with evidence for HIV budding in tetraspanin-enriched plasma membrane domains. Infection of hepatocytic cells by two major pathogens, the hepatitis C virus and the malaria parasite, also requires the tetraspanin CD81. The function of tetraspanins is thought to be linked to their ability to associate with one another and a wealth of other integral proteins, thereby building up an interacting network or 'tetraspanin web'. On the basis of the biochemical dissection of the tetraspanin web and recent analysis of the dynamics of some of its constituents, we propose that tetraspanins tightly regulate transient interactions between a variety of molecules and as such favour the efficient assembly of specialized structures upon proper stimulation.

Macrophage cell lines use CD81 in cell growth regulation

CD81 is an integral membrane protein belonging to the tetraspanin superfamily. It has two extracellular domains that interact with cell surface proteins and two intracellular tails that contribute to cellular processes. Although there are considerable data about how CD81 affects T- and B-cell function, not much is known about how it impacts macrophages. To address this, we established four cell lines from mouse bone marrow in the presence of macrophage colony-stimulating factor and transfection with SV40 large T antigen. Two were CD81(-/-) (ASD1 and ASD2) and two were CD81(+/-) (2ASD1.10 and 2BSD1.10). Cells were Mac-2-, PU.1-, and c-fms-positive and all the cell lines were phagocytic indicating that they were macrophage-like. In mixtures of the two cell types in tissue culture, CD81(-/-) cells out competed CD81(+/-) cells with CD81-bearing cells being undetectable after 50 cell culture passages. Although cell divisions during log-phase growth were not significantly different between CD81(+/-) macrophage cells and CD81(-/-) macrophage cells, we found that CD81(-/-) macrophage cells reached a higher density at confluency than CD81(+/-) macrophage cells. CD81 transcript levels increased as cultures became confluent, but transcript levels of other tetraspanin-related molecules remained relatively constant. Transfection of CD81 into ASD1 (CD81(-/-)) cells reduced the density of confluent cultures of transformants compared to cells transfected with vector alone. These data suggest that CD81 potentially plays a role in macrophage cell line growth regulation.

Targeting the tetraspanin CD81 blocks monocyte transmigration and ameliorates EAE

Leukocyte infiltration is a key step in the development of demyelinating lesions in multiple sclerosis (MS), and molecules mediating leukocyte-endothelial interactions represent prime candidates for the development of therapeutic strategies. Here we studied the effects of blocking the integrin-associated tetraspanin CD81 in in vitro and in vivo models for MS. In an in vitro setting mAb against CD81 significantly reduced monocyte transmigration across brain endothelial cell monolayers, both in rodent and human models. Interestingly, leukocyte as well as endothelial CD81 was involved in this inhibitory effect. To assess their therapeutic potential, CD81 mAb were administered to mice suffering from experimental autoimmune encephalomyelitis (EAE). We found that Eat2, but not 2F7 mAb directed against mouse CD81 significantly reduced the development of neurological symptoms of EAE when using a preventive approach. Concomitantly, Eat2 treated animals showed reduced inflammation in the spinal cord. We conclude that CD81 represents a potential therapeutic target to interfere with leukocyte infiltration and ameliorate inflammatory neurological damage in MS.

Genomic loci modulating the retinal transcriptome in wound healing

PURPOSE

The present study predicts and tests genetic networks that modulate gene expression during the retinal wound-healing response.

METHODS

Upstream modulators and target genes were defined using meta-analysis and bioinformatic approaches. Quantitative trait loci (QTLs) for retinal acute phase genes (Vazquez-Chona et al. 2005) were defined using QTL analysis of CNS gene expression (Chesler et al. 2005). Candidate modulators were defined using computational analysis of gene and motif sequences. The effect of candidate genes on wound healing was tested using animal models of gene expression.

RESULTS

A network of early wound-healing genes is modulated by a locus on chromosome 12. The genetic background of the locus altered the wound-healing response of the retina. The C57BL/6 allele conferred enhanced expression of neuronal marker Thy1 and heat-shock-like crystallins, whereas the DBA/2J allele correlated with greater levels of the classic marker of retinal stress, glial fibrillary acidic protein (GFAP). Id2 and Lpin1 are candidate upstream modulators as they strongly correlated with the segregation of DBA/2J and C57BL/6 alleles, and their dosage levels correlated with the enhanced expression of survival genes (Thy1 and crystallin genes).

CONCLUSION

We defined a genetic network associated with the retinal acute injury response. Using genetic linkage analysis of natural transcript variation, we identified regulatory loci and can didate modulators that control transcript levels of acute phase genes. Our results support the convergence of gene expression profiling, QTL analysis, and bioinformatics as a rational approach to discover molecular pathways controlling retinal wound healing.

CD81, a cell cycle regulator, is a novel target for histone deacetylase inhibition in glioma cells

Recent advances in cancer cell biology have focused on histone deacetylase inhibitors (HDACi's) because they target pathways critical to the development and progression of disease. In particular, HDACi's can induce expression of epigenetically silenced genes that promote growth arrest, differentiation and cell death. In glioma cells, one such repressed gene is the tetraspanin CD81, which regulates cytostasis in various cell lines and in astrocytes, the major cellular component of gliomas. Our studies show that HDACi's, trichostatin and sodium butyrate, promote growth arrest and differentiation with negligible cell death in glioma cells and induce expression of CD81 and cyclin-dependent kinase inhibitor 1A (p21(CIP/WAF-1)), another regulator of cytostasis in astrocytes. Interference RNA knock-down of CD81 abrogates cytostasis promoted by HDAC inhibition indicating that HDACi-induced CD81 is responsible for growth arrest. Induction of CD81 expression through HDAC inhibition is a novel strategy to promote growth arrest in glioma cells.

The developmental regulation of CD81 in the rat retina

PURPOSE

The tetraspanin CD81 is expressed in Müller glial cells and retinal pigment epithelium (RPE). CD81 and other members of the tetraspanin family link extracellular interactions of cells into intracellular cascades. This study examined the developmental expression of CD81 and protein-protein interactions linking CD81 to intracellular proteins.

METHODS

We used synthetic peptides of the C-terminal intracellular domains of CD81 to probe fusion proteins of PDZ domains blotted to nitrocellulose membranes, then confirmed the relationships between the PDZ proteins using immunoprecipitation methods. Colocalization of the associated proteins was analyzed across development, using double-label immunohistochemical methods in the retina of Sprague-Dawley rats.

RESULTS

The C-terminal intracellular sequences of CD81 bound to three putative PDZ domains that potentially represented domains on Sap97 and EBP50. In immunoprecipitation experiments using RPE cells, CD81 coprecipitated with both proteins, EBP50 and Sap97. Like CD81, EBP50 and Sap97 are expressed at low levels immediately after birth and upregulated during the first two postnatal weeks, reaching almost adult levels at postnatal day 20. In the RPE layer, synapse-associated protein 97 (Sap97) and CD81 were associated with the basolateral surface of the cells; ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) localizing with CD81 was found on microvilli at the inner surface of RPE cells.

CONCLUSIONS

These results support the hypothesis that CD81 is associated with the final stages of RPE cell maturation, establishing key molecular interactions linking the cell membrane proteins into macromolecular complexes containing PDZ protein scaffolds.

Genomic Loci Modulating the Retinal Transcriptome in Wound Healing

Purpose

The present study predicts and tests genetic networks that modulate gene expression during the retinal wound-healing response.

Methods

Upstream modulators and target genes were defined using meta-analysis and bioinformatic approaches. Quantitative trait loci (QTLs) for retinal acute phase genes (Vazquez-Chona et al. 2005) were defined using QTL analysis of CNS gene expression (Chesler et al. 2005). Candidate modulators were defined using computational analysis of gene and motif sequences. The effect of candidate genes on wound healing was tested using animal models of gene expression.

Results

A network of early wound-healing genes is modulated by a locus on chromosome 12. The genetic background of the locus altered the wound-healing response of the retina. The C57BL/6 allele conferred enhanced expression of neuronal marker Thy1 and heat-shock-like crystallins, whereas the DBA/2J allele correlated with greater levels of the classic marker of retinal stress, glial fibrillary acidic protein (GFAP). Id2 and Lpin1 are candidate upstream modulators as they strongly correlated with the segregation of DBA/2J and C57BL/6 alleles, and their dosage levels correlated with the enhanced expression of survival genes ( Thy1 and crystallin genes).

Conclusion

We defined a genetic network associated with the retinal acute injury response. Using genetic linkage analysis of natural transcript variation, we identified regulatory loci and candidate modulators that control transcript levels of acute phase genes. Our results support the convergence of gene expression profiling, QTL analysis, and bioinformatics as a rational approach to discover molecular pathways controlling retinal wound healing.

Discovery of antiglioma activity of biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues

Cultured rat astrocytes and C6 rat glioma were used as a differential screen for a variety of 1,2,3,4-tetrahydroisoquinoline (THI) derivatives. Compound 1 [1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride] selectively blocked the growth of C6 glioma leaving normal astrocytes relatively unaffected. The potential for clinical utility of 1 was further substantiated in human gliomas and other tumor cell lines. Preliminary SAR of this activity was characterized by synthesis and testing of several THI and conformationally flexible variants.

Neuronal expression of keratinocyte-associated transmembrane protein-4, KCT-4, in mouse brain and its up-regulation by neurite outgrowth of Neuro-2a cells

One group of proteins that regulates neurite outgrowth and maintains neuronal networks is the immunoglobulin superfamily (IgSF). We previously identified a new member of the IgSF, keratinocyte-associated transmembrane protein-4 (KCT-4), by the signal sequence-trap method from primary cultured human keratinocytes. The KCT-4 mRNA has been found to be highly expressed in the adult human brain, although it is also distributed in various tissues. In the present study, to gain insight into the role of KCT-4 in the nervous system, we examined the expression profile and localization of KCT-4 mRNA in mouse brain. We also evaluated changes in KCT-4 mRNA expression in the differentiation of the neuroblastoma cell line Neuro-2a as the in vitro model of neurite outgrowth. KCT-4 mRNA was detected broadly in various regions of the adult mouse brain by RT-PCR. In situ hybridization revealed that it was expressed highly selectively by neurons but not by glial cells. Moreover, expression of KCT-4 mRNA was induced by neurite outgrowth of Neuro-2a. These data suggest that KCT-4 participates in the regulation of neurite outgrowth and maintenance of the neural network in the adult brain.

Isolation of neural stem cells from the postnatal cerebellum

The cerebellum is critical for motor coordination and cognitive function and is the target of transformation in medulloblastoma, the most common malignant brain tumor in children. Although the development of granule cells, the most abundant neurons in the cerebellum, has been studied in detail, the origins of other cerebellar neurons and glia remain poorly understood. Here we show that the murine postnatal cerebellum contains multipotent neural stem cells (NSCs). These cells can be prospectively isolated based on their expression of the NSC marker prominin-1 (CD133) and their lack of markers of neuronal and glial lineages (lin-). Purified prominin+ lin- cells form self-renewing neurospheres and can differentiate into astrocytes, oligodendrocytes and neurons in vitro. Moreover, they can generate each of these lineages after transplantation into the cerebellum. Identification of cerebellar stem cells has important implications for the understanding of cerebellar development and the origins of medulloblastoma.

CD81-induced behavioural changes during chronic cocaine administration: in vivo gene delivery with regulatable lentivirus

CD81, a tetraspanin transmembrane protein involved in cell adhesion, is up-regulated in the mesolimbic dopaminergic pathway 24 h following acute administration of high doses of cocaine [Brenz-Verca et al., (2001) Mol. Cell. Neurosci., 17, 303-316]. Further evidence consecutive with this observation and based on microarray analysis are presented here. In addition, a regulatable lentivirus was developed bearing the rat CD81 gene under the control of a tetracycline inducible system. This lentivirus vector was stereotaxically injected into the ventral tegmental area (VTA) of two groups of animals, one fed water (expressing CD81) and the other Doxycycline solution (which down-regulates CD81 expression) and locomotor activity after chronic cocaine administration (10 mg/kg daily) was monitored. After 2 weeks, the groups were inverted, animals receiving water were placed on Doxycycline and the second group was placed on water. In all cases highly a significant increase (3.2-fold) in locomotor activity was observed in animals expressing CD81 in the VTA vs. animals placed on Doxycycline. Similar studies where CD81 was delivered into the nucleus accumbens (NAcc) resulted in significantly higher effects (30%), in accordance with microarray data and our previous reports, yielding a 4.2-fold increase in locomotor activity. No change was observed under similar conditions in control animals, which were injected a regulatable lentivirus expressing GFP. These findings suggest that CD81 expression in the mesolimbic dopaminergic pathway contributes to behavioural changes associated with cocaine sensitization. This study provides a powerful approach for evaluating a gene function in vivo in a single animal under various paradigms, even on gene candidates, which display small changes of expression.

Tetraspanin proteins mediate cellular penetration, invasion, and fusion events and define a novel type of membrane microdomain

This review summarizes key aspects of tetraspanin proteins, with a focus on the functional relevance and structural features of these proteins and how they are organized into a novel type of membrane microdomain. Despite the size of the tetraspanin family and their abundance and wide distribution over many cell types, most have not been studied. However, from studies of prototype tetraspanins, information regarding functions, cell biology, and structural organization has begun to emerge. Genetic evidence points to critical roles for tetraspanins on oocytes during fertilization, in fungi during leaf invasion, in Drosophila embryos during neuromuscular synapse formation, during T and B lymphocyte activation, in brain function, and in retinal degeneration. From structure and mutagenesis studies, we are beginning to understand functional subregions within tetraspanins, as well as the levels of connections among tetraspanins and their many associated proteins. Tetraspanin-enriched microdomains (TEMs) are emerging as entities physically and functionally distinct from lipid rafts. These microdomains now provide a context in which to evaluate tetraspanins in the regulation of growth factor signaling and in the modulation of integrin-mediated post-cell adhesion events. Finally, the enrichment of tetraspanins within secreted vesicles called exosomes, coupled with hints that tetraspanins may regulate vesicle fusion and/or fission, suggests exciting new directions for future research.

Synthesis of 1-boraadamantaneamine derivatives with selective astrocyte vs C6 glioma antiproliferative activity. A novel class of anti-hepatitis C agents with potential to bind CD81

A variety of amine complexes with 1-boraadamatane were synthesized and subsequently evaluated for an antiproliferative effect on CD81-enriched cell lines to provide evidence for binding and activation of CD81. CD81 is a member of the tetraspanin family of membrane proteins found in all cell lineages in the liver. CD81 signals for antiproliferation when bound by antibodies. It is known that the HCV-E2 envelope glycoprotein binds to the CD81 protein. While it is unclear whether virus entry into host cells is directly linked to virus attachment via CD81 for HCV, this step in the viral life cycle has recently proven to be an effective point of attack for other viruses including HIV and rhinoviruses. The aim of the current study concerns the synthesis of amantidine analogues by appending primary amines to 1-boraadamantane to evaluate such compounds for CD81-dependent antiproliferation of CD81-enriched cell lines (astrocyte) vs CD81-deficient cell lines (C6 glioma). If the antiproliferative effect of these amantidine analogues proves to be an effect of binding and activating CD81, then these compounds may have the potential to prevent or treat HCV infections. Each compound's potential for preventive and therapeutic activity stems from the compound's potential to block viral attachment, virus-cell fusion, or virus entry into host cells or to counter potential mechanisms of HCV immune evasion. Out of a library of over 500 compounds, including randomly selected small molecules and rationally designed small molecules, only the 1-boraadamantaneamine compounds and structurally similar analogues display a significant antiproliferative effect on the CD81-enriched astrocytes relative to the CD81-deficient cell lines. In fact, 1-boraadamantane.l-phenylalanine methyl ester complex (5), 1-boraadamantane.ethanolamine complex (8), and (S)-2-[(adamantane-1-carbonyl)amino]-3-phenylpropionic acid (15) show a dose-dependent, astrocyte-selective antiproliferative activity in the concentration range 0.1-10 microM. This is consistent with the binding and activation of CD81 and represents a 2-fold improvement compared to the clinically prescribed anti-HCV agent, amantidine, in the same concentration range. Consequently, the 1-boraadamantaneamine derivatives present a promising lead in the development of small molecules with potential to bind to CD81 and treat HCV infections.

Slit and glypican-1 mRNAs are coexpressed in the reactive astrocytes of the injured adult brain

The slit family serves as a repellent for growing axons toward correct targets during neural development. A recent report describes slit mRNAs expressed in various brain regions in adult rats. However, their functions in the adult nervous system remain unknown. In the present study, we investigated whether slit mRNAs were expressed in the cryo-injured brain, using in situ hybridization. All slit family members were expressed at the lesion. Slit2 mRNA was the most intensely expressed in the cells surrounding the necrotic tissue. A double-labeling study showed that slit2 mRNA was expressed in the glial fibrillary acidic protein (GFAP)-positive reactive astrocytes. In addition, glypican-1, a heparan sulfate proteoglycan that serves as a high-affinity receptor for Slit protein, was coexpressed with slit2 mRNA in the reactive astrocytes. These findings suggested that slit2 might prevent regenerating axons from entering into the lesion in concert with glypican-1.

Temporal regulation of CD81 following retinal injury in the rat

Following retinal injury, glial cells within the retina undergo a response that is characterized by the proliferation of astrocytes, Müller cells, and retinal pigment epithelial cells. CD81, a small membrane protein known to be involved in cell proliferation, is up-regulated after injury. This study focuses on the temporal regulation of CD81, relating the expression of this protein to glial fibrillary acidic protein (GFAP), the classic marker of gliosis. CD81 levels were elevated at 7 days after injury and remained elevated at 30 days after injury; GFAP was increased at 7 days and continued to increase until 30 days post injury. This association of CD81 with glial reactivity may provide a clue to the regulation of the proliferative response following retinal injury.

Increased brain size and glial cell number in CD81-null mice

A key issue in the development of the central nervous system (CNS) is understanding the molecular mechanisms regulating cell number. The present study examines the role of CD81 (previously known as TAPA, the target of the antiproliferative antibody) in the control of brain size and glial cell number. CD81 is a member of the tetraspanin family of proteins. This group of small membrane proteins is associated with the regulation of cell migration and mitotic activity. Glial cells express CD81, and antibodies directed against this protein suppress the mitotic activity of cultured cells. In this study, we examine the effects of the CD81 -/- mutation on the CNS of mature mice. These mice have extremely large brains, as much as 30% larger than the brains of wild-type (+/+) littermates. The increase in brain weight is accompanied by an increase in the number astrocytes and microglia, whereas the number of neurons and oligodendrocytes in the CD81 -/- animals appears to be normal. When the CD81 -/- mutation is placed on different genetic backgrounds, there is a remarkable range in the penetrance of the null allele phenotype, demonstrating that the mutation can be affected by modifier loci. This work provides support for the role of CD81 in the regulation of astrocyte and microglial number, perhaps by regulating cell proliferation by a contact inhibition-dependent mechanism.

Increased syndecan expression by pleiotrophin and FGF receptor-expressing astrocytes in injured brain tissue

Syndecan-1, -2, -3, and -4 are heparan sulfate proteoglycans that are differentially expressed during development and wound repair. To determine whether syndecans are also involved in brain injury, we examined the expression of syndecan core proteins genes in cryo-injured mouse brain, using in situ hybridization. All syndecan mRNA transcripts were similarly expressed in the region surrounding the necrotic tissue, exhibiting peak levels at day 7 after injury. Comparison with cellular markers showed that reactive astrocytes were the primary source of syndecans. Syndecans serve as co-receptors for fibroblast growth factor (FGF) and as a reservoir for another heparin-binding growth factor, pleiotrophin (PTN, or heparin-binding growth-associated molecule. In our model, FGF receptor1 (FGFR1) and PTN mRNA levels were upregulated in reactive astrocytes. The distribution patterns of FGFR1 and PTN overlapped considerably with those of syndecan-1 and -3 mRNAs, respectively. These results suggest that syndecans are expressed primarily in reactive astrocytes, and may provide a supportive environment for regenerating axons in concert with heparin-binding growth factors (e.g., FGF and PTN) in the injured brain.

Methods to examine molecular changes and behavioral effects of drug administration

Our laboratory has developed an integrative approach to study the molecular changes and behavioral effects of drug administration consisting of a combination of quantitative real-time reverse transcription polymerase chain reaction, RNA isolation and differential display, in situ hybridization, place preference conditioning and high-performance liquid chromatography. Although the techniques are not novel, this multi-systems approach allows for the examination of gene expression changes following the administration of drugs of abuse such as cocaine, and allows for an analysis of behavior and neurochemistry of gene knockout mice. As a result of this combination of techniques, we have been able to determine the expression, location and function of the CD81 protein. Specifically, CD81 was induced exclusively in the nucleus accumbens by cocaine treatment. Subsequent behavioral testing of CD81 knockout mice revealed these mice displayed altered sensitivity to cocaine.

Rapid morphological changes in astrocytes are accompanied by redistribution but not by quantitative changes of cytoskeletal proteins

Astrocytes have the potential to acquire very different morphologies, depending on their regional location in the CNS and on their functional interactions with other cell types. Morphological changes between a flat or a fibroblast-like and a stellate or process-bearing appearance, and vice versa, can occur rapidly, but very little is known as to whether morphological transformations are based on quantitative changes of cytoskeletal proteins in microfilaments, intermediate filaments, and/or microtubules. Using a cell culture of selective type 1 astrocytes, we compared the distribution and protein amounts of a number of cytoskeletal proteins both during primary process growth induced by specific media conditions and after secondary transformations induced by dBcAMP. Our data presented in this report support the idea that astrocytes can undergo dramatic changes in their morphology requiring subcellular redistribution of most cytoskeletal proteins but no quantitative modifications of the amount of the respective proteins. After pharmacological treatment with lysophosphatic acid and genistein we show that astrocytes can acquire intermediate morphologies reminiscent of both fibroblast and stellate-like cells. These experiments demonstrate that the recently described RhoA-mediated signaling cascade between the cell surface and cytoskeletal proteins is only one of several signaling pathways acting on the astrocytic cytoskeleton.

The molecular characterisation of mouse tspan-3

The Tetraspanin/Transmembrane-4 Superfamily of cell surface molecules is defined by their four highly conserved transmembrane domains and is found in a wide variety of species and cell types. A common function for these molecules has yet to be discovered, however their broad expression patterns and conservation over evolution suggests that they will have an important general function relevant to many cell lineages. Here we describe the cloning and characterisation of the murine homologue of a recently described member of this superfamily, tspan-3. Murine tspan-3 was remarkably similar to the human molecule showing 88% identity at the nucleic acid level and 98% homology on the amino acid level. Northern blot analyses of mouse tspan-3 show a very broad pattern of expression, with expression readily detected in most organs including neural and bone marrow derived tissues.

Altered sensitivity of CD81-deficient mice to neurobehavioral effects of cocaine

CD81, also known as target of the antiproliferative antibody, is known to be expressed in astrocytes and involved in cell adhesion and, recently, we demonstrated its induction exclusively in the accumbens following cocaine. In the present study, the sensitivity of CD81-deficient mice to behavioral effects of cocaine was evaluated. It was found that CD81-deficient mice exhibited altered sensitivity to cocaine as assessed in the place preference conditioning paradigm and locomotor activity. This deficit in place preference conditioning was not accompanied by a deficit in acquisition or retention of water maze behavior. In addition, CD81 knockout mice exhibited higher levels of nucleus accumbens dopamine as compared to their controls. These observations are discussed in the context of the role of CD81 in cocaine-mediated behaviors.

Lupus anti-DNA autoantibodies cross-react with a glomerular structural protein: a case for tissue injury by molecular mimicry

Anti-DNA autoantibodies are the hallmark of human and murine systemic lupus erythematosus (SLE), an autoimmune rheumatic disease of unknown etiology. Some of these antibodies are believed to be pathogenic for kidney tissue and to initiate immune glomerulonephritis. However, the mechanisms by which anti-DNA antibodies participate in tissue injury remain controversial. We have studied the in vivo pathogenicity of anti-DNA monoclonal antibodies in immune deficient mice, using a panel of murine B cell hybridomas. No consistent genetic or immunochemical differences were found between pathogenic and non-pathogenic anti-DNA antibodies. However, the two antibody populations differed in their cross-reaction with the acidic actin-binding protein, alpha-actinin, that is known to play a major role in the structural integrity of glomerular filtration components. These results suggest that kidney dysfunction in SLE may be facilitated by protein-nucleic acid antigenic mimicry.

CD81 and microglial activation in vitro: proliferation, phagocytosis and nitric oxide production

CD81 (TAPA), a member of the tetraspanin family of proteins, is upregulated by astrocytes and microglia after traumatic injury to the rat central nervous system (CNS). To further understand the role of CD81 in the microglial response to injury, we analysed the functional effects of a CD81 antibody, AMP1, on cultured rat microglia. We found that AMP1 suppressed microglial proliferation in a dose-dependent manner. Furthermore, AMP1 stimulated myelin phagocytosis, probably by opsonizing the myelin. The phagocytosis of latex beads, as well as the production of nitric oxide, were not significantly influenced by AMP1. These data indicate that CD81 is involved in an important subset of microglial effector functions after CNS injury.

CD81 regulates neuron-induced astrocyte cell-cycle exit

Astrocytes respond to contact with neurons by cell-cycle arrest and complex process formation. In our effort to discover the molecular mechanisms that underlie this phenomenon we have identified a known tetraspanin, CD81, as a critical component of astrocyte responses to neuronal differentiation signals. Here we show that CD81 is expressed on the surface of the astrocyte and that its expression level can be modulated by contact with neurons. Further, using three separate antibodies, 2F7, Eat1, and Eat2, which recognize unique epitopes in the extracellular domains of the CD81 protein, we show that there is a unique domain, recognized by Eat1, that is required for astrocyte cell-cycle withdrawal in response to neurons. This is likely due to conformational changes in the CD81 molecule, as inclusion of 2F7 actually augments neuron-induced astrocyte growth arrest. The critical nature of CD81 in normal astrocyte-neuron biology was confirmed by using mice in which CD81 had been deleted by homologous recombination. Astrocytes null at the CD81 locus were blind to the proliferative arrest encoded on the neuronal cell surface. Taken together, these data strongly suggest that CD81 is a critical regulator of neuron-induced astrocytic differentiation.

Cocaine-induced expression of the tetraspanin CD81 and its relation to hypothalamic function

CD81, a tetraspanin transmembrane protein involved in cell adhesion, was found by differential display to be upregulated in the nucleus accumbens of rat brain following acute cocaine treatment (four injections of 30 mg/kg every 2 h followed by 24 h withdrawal). Cocaine-induced expression of CD81 in adult rat brain was confirmed by quantitative real-time RT-PCR. Its expression in neurons and its function in the brain are unknown. In situ hybridization shows a neuron-specific expression pattern in brain regions functionally related to the regulation of cardiovascular function and fluid homeostasis. CD81 displays codistribution to galanin and, to a lesser extent, to vasopressin. These findings add to data that suggest a connection between the brain reward pathway and the centers regulating endocrine and autonomic functions, in relation to neurochemical, behavioral, and somatic consequences of drug abuse.

Up-regulation of CD81 (target of the antiproliferative antibody; TAPA) by reactive microglia and astrocytes after spinal cord injury in the rat

We examined the expression of CD81 (also known as TAPA, or target of the antiproliferative antibody) after traumatic spinal cord injury in the rat. CD81, a member of the tetraspanin family of proteins, is thought to be involved in reactive gliosis. This is based on the antiproliferative and antiadhesive effects of antibodies against CD81 on cultured astrocytes, as well as its up-regulation after penetrating brain injury. CD81 expression following dorsal hemisection of the spinal cord was determined immunohistochemically at time points ranging from 1 day to 2 months postlesion (p.l.). In the unlesioned cord a low background level of CD81 was observed, with the exception of the ependyma of the central canal and the pia mater, which were strongly CD81-positive. One day p.l., CD81 was diffusely up-regulated in the spinal cord parenchyma surrounding the lesion site. From 3 days onward, intensely CD81-positive round cells entered the lesion site, completely filling it by 7 days p.l. Staining with the microglial markers OX-42 and Iba1 revealed that these cells were reactive microglia/macrophages. At this time, no significant CD81 expression by GFAP-positive reactive astrocytes was noted. From the second week onward, CD81 was gradually down-regulated; i.e., its spatial distribution became more restricted. The CD81-positive microglia/macrophages disappeared from the lesion site, leaving behind large cavities. After 2 months, astrocytes that formed the wall of these cavities were strongly CD81-positive. In addition, CD81 was present on reactive astrocytes in the dorsal funiculus distal from the lesion in degenerated white matter tracts. In conclusion, the spatiotemporal expression pattern of CD81 by reactive microglia and astrocytes indicates that CD81 is involved in the glial response to spinal cord injury.

BERP, a novel ring finger protein, binds to alpha-actinin-4

We recently identified BERP as a novel RING finger protein belonging to the RBCC protein family. It contains an N-terminal RING finger, followed by a B-box zinc finger and a coiled-coil domain. BERP interacts with the tail domain of the class V myosins through a beta-propeller structure in the BERP C-terminal. To identify other proteins interacting with BERP, the yeast two-hybrid strategy was employed, using the RBCC domain as bait. Screening of a rat brain cDNA library identified alpha-actinin-4 as a specific binding partner for the N-terminus of BERP. This actinin isoform could be immunoprecipitated together with BERP from HEK 293 cells transfected with expression constructs for BERP and alpha-actinin-4. These proteins could also be colocalized immunohistochemically in the cytoplasm of differentiated PC12 cells. We suggest that BERP may anchor class V myosins to particular cell domains via its interaction with alpha-actinin-4.

The expression of TAPA (CD81) correlates with the reactive response of astrocytes in the developing rat CNS

During the development of the brain, astrocytes acquire the ability to become reactive and form a scar. This change in the astrocytes occurs at approximately the same time that there is a decrease in the regenerative capacity of the CNS. Previous work from our laboratory had revealed that TAPA (Target of Anti-Proliferative Antibody, also known as CD81) is associated with reactive gliosis and the glial scar. TAPA is a member of the tetraspan family of proteins that appears to be associated with the regulation of cellular behavior. In order to define the role of TAPA in relation to the developmentally regulated CNS response to injury, we examined the levels of TAPA and GFAP immunoreactivity in rat pups that received a penetrating cerebral cortical injury. All of the animals injured at postnatal day 9 (PND 9), PND 18, or as adults, exhibited reactive gliosis scar formation when they were sacrificed 10 days after the cortical injury. Of the nine animals injured at PND 2, only three displayed reactive gliosis and scar formation. The remaining six rat pups had either a modest gliotic response or no detectable gliosis. The level of TAPA at the site of injury mimicked the reactive gliosis as defined by GFAP immunoreactivity. In all of the rats with a glial scar, there was a dramatic upregulation of TAPA that is spatially restricted to the reactive astrocytes. These results suggest that the upregulation of TAPA is an integral component of glial scar formation.

The molecular characterisation of a novel tetraspanin protein, TM4-B(1)

TM4-B is a novel member of the Tetraspanin superfamily and displays characteristics typical of the superfamily. It bears significant homology to other superfamily members and is most similar to Tspan-1. This molecule is broadly expressed in most human tissues and cell lines including neural and bone marrow derived tissues. TM4-B was mapped to the q34 region on human chromosome 9.

N-cadherin at the glial scar in the rat

Following injury to the central nervous system (CNS), astrocytes become reactive and in many cases form a glial scar. Very little is known about the adhesive interactions between astrocytes at the glial scar, even though reactive gliosis and scar formation are a central issue in CNS wound healing. In the present study, we examine the role of cadherin in the process of scar formation using immunohistochemistry and immunoblot methods. When a stab wound was made in the cerebral cortex of the rat, cadherins were consistently upregulated by the reactive astrocytes at the glial scar. Our immunoblot analysis demonstrates that the increase in cadherin immunoreactivity was due to a threefold upregulation of a single protein with a molecular weight of 135 kDa. The size (135 kDa) and location of the immunoreactive protein at regions of cell-cell contact in cultured astrocytes indicates that the immunoreactive protein is N-cadherin. These data are the first to demonstrate that N-cadherin plays a prominent role in the response of astrocytes to injury, including the formation and maintenance of the glial scar.

Identification of a novel gene, OASIS, which encodes for a putative CREB/ATF family transcription factor in the long-term cultured astrocytes and gliotic tissue

Gliosis is a characteristic response of astrocytes to inflammation and trauma of the central nervous system (CNS). To study the mechanisms underlying gliosis, we performed differential display screening for genes specifically induced in long-term cultured astrocytes used as an in vitro gliosis model. We identified and characterized a gene (named OASIS, for old astrocyte specifically-induced substance) expressed in long-term cultured mouse astrocytes, or 'old astrocytes (OA)'. The OASIS gene encoded a putative transcription factor belonging to the cyclic AMP responsive element binding protein/activating transcription factor (CREB/ATF) gene family, with homology to box B-binding factor-2 (BBF-2), a Drosophila transcription factor. Its expression was developmentally regulated; OASIS mRNA was primarily expressed in the salivary gland and cartilage in the mouse embryo and it was transiently upregulated in the brain during postnatal two weeks. The expression became weaker in the adult brain. We also demonstrated that an expression of the OASIS mRNA was induced in response to the cryo-injury of the mouse cerebral cortex. The distribution pattern of the OASIS-positive cells in the injured cortex was very similar to that of the glial fibrillary acidic protein (GFAP)-positive cells. These results suggest that OASIS protein may play a role in gliotic events.

Immunocytochemical characterization of reactive optic nerve astrocytes and meningeal cells

Regeneration in the adult central nervous system (CNS) is thought to be hampered by the lesion-induced activation of astrocytes and meningeal cells and the consecutive formation of a glial scar. The substrate properties of reactive astrocytes differ significantly from their neonatal counterparts, which promote axon growth, but in spite of intensive studies the underlying molecular changes are still not fully understood. We have used two cell culture systems to compare the expression of certain surface molecules on neonatal astrocytes, reactive astrocytes and meningeal cells in vitro. Both, neonatal and reactive adult astrocytes exhibited a very similar expression of growth promoting molecules (NCAM, L1, laminin, fibronectin, DSD-1 proteoglycan) and potential inhibitors (tenascinC, chondroitin sulfate, and NG2-proteoglycan), whereas we could not detect the inhibitory keratan sulfate on either astrocyte population. In contrast, meningeal cells expressed considerable levels of keratan sulfate, but only minimal amounts of NCAM. In addition, the much higher expression of extracellular fibronectin around meningeal cells implies an excess formation of extracellular matrix (ECM). In coculture experiments, embryonic retinal ganglion cell (RGC) axons clearly avoided meningeal cells and instead preferred even reactive adult astrocytes. Our results suggest that the expression of inhibitory keratan sulfate proteoglycans together with a lack of NCAM and an excess production of ECM may be responsible for the non-permissiveness of meningeal cells. Compared to reactive astrocytes, meningeal cells are even worse a substrate for growing axons. None of the molecules investigated, however, seems to account for the different substrate properties of neonatal and reactive adult astrocytes.

Binding of hepatitis C virus to CD81

Chronic hepatitis C virus (HCV) infection occurs in about 3 percent of the world's population and is a major cause of liver disease. HCV infection is also associated with cryoglobulinemia, a B lymphocyte proliferative disorder. Virus tropism is controversial, and the mechanisms of cell entry remain unknown. The HCV envelope protein E2 binds human CD81, a tetraspanin expressed on various cell types including hepatocytes and B lymphocytes. Binding of E2 was mapped to the major extracellular loop of CD81. Recombinant molecules containing this loop bound HCV and antibodies that neutralize HCV infection in vivo inhibited virus binding to CD81 in vitro.

CD81 (TAPA-1): a molecule involved in signal transduction and cell adhesion in the immune system

CD81 (TAPA-1) is a widely expressed cell-surface protein involved in an astonishing variety of biologic responses. It has been cloned independently several times for different functional effects and is reported to influence adhesion, morphology, activation, proliferation, and differentiation of B, T, and other cells. On B cells CD81 is part of a complex with CD21, CD19, and Leu13. This complex reduces the threshold for B cell activation via the B cell receptor by bridging Ag specific recognition and CD21-mediated complement recognition. Similarly on T cells CD81 associates with CD4 and CD8 and provides a costimulatory signal with CD3. In fetal thymic organ culture, mAb to CD81 block maturation of CD4-CD8- thymocytes, and expression of CD81 on CHO cells endows those cells with the ability to support T cell maturation. However, CD81-deficient mice express normal numbers and subsets of T cells. These mice do exhibit diminished antibody responses to protein antigens. CD81 is also physically and functionally associated with several integrins. Anti-CD81 can activate integrin alpha 4 beta 1 (VLA-4) on B cells, facilitating their adhesion to tonsilar interfollicular stroma. Similarly, anti-CD81 can activate alpha L beta 2 (LFA-1) on human thymocytes. CD81 can also affect cognate B-T cell interactions because anti-CD81 increases IL-4 synthesis by T cells responding to antigen presented by B cells but not by monocytes. The tetraspanin superfamily (or TM4SF) includes CD81, CD9, CD37, CD53, CD63, CD82, CD151, and an increasing number of additional proteins. Like CD81, several tetraspanins are involved in cell adhesion, motility, and metastasis, as well as cell activation and signal transduction.