A critical role for the protein tyrosine phosphatase receptor type Z in functional recovery from demyelinating lesions

Mice lacking leukocyte common antigen-related (LAR) protein tyrosine phosphatase domains demonstrate spatial learning impairment in the two-trial water maze and hyperactivity in multiple behavioural tests

Leukocyte common antigen-related (LAR) protein is a cell adhesion molecule-like receptor-type protein tyrosine phosphatase. We previously reported that in LAR tyrosine phosphatase-deficient (LAR-Delta P) mice the number and size of basal forebrain cholinergic neurons as well as their innervation of the hippocampal area was reduced. With the hippocampus being implicated in behavioural activity aspects, including learning and memory processes, we assessed possible phenotypic consequences of LAR phosphatase deficiency using a battery of rodent behaviour tests. Motor function and co-ordination tests as well as spatial learning ability assays did not reveal any performance differences between wildtype and LAR-Delta P mice. A spatial learning impairment was found in the difficult variant of the Morris water maze. Exploration, nestbuilding and activity tests indicated that LAR-Delta P mice were more active than wildtype littermates. The observed hyperactivity in LAR-Delta P mice could not be explained by altered anxiety or curiosity levels, and was found to be persistent throughout the nocturnal period. In conclusion, behavioural testing of the LAR-Delta P mice revealed a spatial learning impairment and a significant increase in activity.

Transgenic animals in inflammatory disease models

Inflammatory diseases affect a significant portion of the population worldwide and have been intensely studied for several decades. The advent of transgenic technology has allowed researchers to study individual gene contributions to the pathogenesis of these diseases. This has been done using standard inflammatory disease models in transgenic animals and by identifying novel models through the spontaneous generation of disease in the transgenic animal. Recent advances have been made in the understanding of rheumatoid arthritis, pulmonary inflammation, multiple sclerosis and inflammatory bowel disease through the use of transgenic animals in models of human inflammatory disease.

BACE (β-secretase) modulates the processing of APLP2 in vivo

BACE is an aspartyl protease that cleaves the amyloid precursor protein (APP) at the beta-secretase cleavage site and is involved in Alzheimer's disease. The aim of our study was to determine whether BACE affects the processing of the APP homolog APLP2. To this end, we developed BACE knockout mice with a targeted insertion of the gene for beta-galactosidase. BACE appeared to be exclusively expressed in neurons as determined by differential staining. BACE was expressed in specific areas in the cortex, hippocampus, cerebellum, pons, and spinal cord. APP processing was altered in the BACE knockouts with Abeta levels decreasing. The levels of APLP2 proteolytic products were decreased in BACE KO mice, but increased in BACE transgenic mice. Overexpression of BACE in cultured cells led to increased APLP2 processing. Our results strongly suggest that BACE is a neuronal protein that modulates the processing of both APP and APLP2.

Receptor tyrosine phosphatase zeta/beta in astrocyte progenitors in the developing chick spinal cord

We cloned a cDNA encoding the receptor-type protein tyrosine phosphatase zeta/beta (RPTPZ/beta) from embryonic chick spinal cord. RPTPZ/beta was expressed throughout the ventricular zone (VZ) of the developing spinal cord and in scattered cells outside the VZ. Platelet-derived growth factor receptor alpha (PDGFRa)-positive oligodendrocyte progenitors co-expressed RPTPZ/beta within the VZ but down-regulated RPTPZ/beta after leaving the VZ. Most RPTPZ/beta-positive cells outside the VZ co-expressed glutamine synthetase and fibroblast growth factor receptor-3, indicating that they are astrocyte progenitors. Northern blot analysis revealed a single approximately 9 kbp RPTPZ/beta transcript expressed in the embryonic chick spinal cord, indicating that the shorter alternative-splice products of RPTPZ/beta found in rodent spinal cord and brain--including the abundant extracellular proteoglycan known as phosphacan--are not present in the embryonic chick spinal cord.

Expression and Function of the Receptor Protein Tyrosine Phosphatase ζ and Its Ligand Pleiotrophin in Human Astrocytomas

Using subtractive cloning combined with cDNA array analysis, we previously identified the genes encoding for the protein tyrosine phosphatase zeta/receptor-type protein tyrosine phosphatase beta (PTPzeta/RPTPbeta) and its ligand pleiotrophin (PTN) as overexpressed in human glioblastomas compared to normal brain. Both molecules have been implicated in neuronal migration during central nervous system development, and PTN is known to be involved in tumor growth and angiogenesis. We confirm overexpression of both molecules at the protein level in astrocytic gliomas of different malignancy grades. PTPzeta/RPTPbeta immunoreactivity was associated with increasing malignancy grade and localized predominantly to the tumor cells. PTN immunoreactivity as determined by ELISA and immunohistochemistry analysis was increased in low-grade astrocytomas compared to normal brain. Further increase in malignant gliomas was marginal, and thus no correlation with malignancy grade or microvessel density was present. However, PTN levels were significantly associated with those of fibroblast growth factor-2, suggesting co-regulation of both factors. Functionally, PTN induced weak chemotactic and strong haptotactic migration of glioblastoma and cerebral microvascular endothelial cells. Haptotaxis of glioblastoma cells towards PTN was specifically inhibited by an anti-PTPzeta/RPTPbeta antibody. Our findings suggest that upregulated expression of PTN and PTPzeta/RPTPbeta in human astrocytic tumor cells can create an autocrine loop that is important for glioma cell migration. Although PTN is a secreted growth factor, it appears to exert its mitogenic effects mostly in a matrix-immobilized form, serving as a substrate for migrating tumor cells.

The use of flow cytometry to assess neutrophil infiltration in the injured murine spinal cord

Inflammatory cells, including neutrophils, are likely candidates in promoting early cell death after spinal cord injury. We describe a simple and reliable method for obtaining neutrophils from the injured murine spinal cord for flow cytometric quantification. Mice were subjected to either a moderate or severe spinal cord contusion injury and euthanized 24 h later. The area of maximal damage, designated the epicenter, was prepared for assessment of myeloperoxidase (MPO) activity, quantitative immunocytochemistry, or quantification of immunolabeled neutrophils by flow cytometry. For flow cytometry, a cell suspension was prepared from the epicenter by gentle mechanical disruption. After centrifugation, the pellet was resuspended, immunolabeled for neutrophils, and analyzed. There was no detectable MPO activity in the injured spinal cord. In contrast, neutrophil infiltration was confirmed by immunocytochemistry and found to be significantly greater in the more severely injured group. Flow cytometry, using a standard neutrophil marker, revealed a similar significant increase in immunolabeled cells in the more severely injured group. However, when cell viability was determined in the neutrophil labeled population, no significant difference in the numbers of live neutrophils were noted between the two injured groups. Together, these findings demonstrate an effective method for the detection and quantification of viable neutrophils in the injured murine spinal cord.

Genetic programs and responses of neural stem/progenitor cells during demyelination: potential insights into repair mechanisms in multiple sclerosis

In recent years, it has become evident that the adult mammalian CNS contains a population of neural stem cells (NSCs) described as immature, undifferentiated, multipotent cells, that may be called upon for repair in neurodegenerative and demyelinating diseases. NSCs may give rise to oligodendrocyte progenitor cells (OPCs) and other myelinating cells. This article reviews recent progress in elucidating the genetic programs and dynamics of NSC and OPC proliferation, differentiation, and apoptosis, including the response to demyelination. Emerging knowledge of the molecules that may be involved in such responses may help in the design of future stem cell-based treatment of demyelinating diseases such as multiple sclerosis.

Receptor protein tyrosine phosphatase alpha is essential for hippocampal neuronal migration and long-term potentiation

Despite clear indications of their importance in lower organisms, the contributions of protein tyrosine phosphatases (PTPs) to development or function of the mammalian nervous system have been poorly explored. In vitro studies have indicated that receptor protein tyrosine phosphatase alpha (RPTPalpha) regulates SRC family kinases, potassium channels and NMDA receptors. Here, we report that absence of RPTPalpha compromises correct positioning of pyramidal neurons during development of mouse hippocampus. Thus, RPTPalpha is a novel member of the functional class of genes that control radial neuronal migration. The migratory abnormality likely results from a radial glial dysfunction rather than from a neuron-autonomous defect. In spite of this aberrant development, basic synaptic transmission from the Schaffer collateral pathway to CA1 pyramidal neurons remains intact in Ptpra(-/-) mice. However, these synapses are unable to undergo long-term potentiation. Mice lacking RPTPalpha also underperform in the radial-arm water-maze test. These studies identify RPTPalpha as a key mediator of neuronal migration and synaptic plasticity.

Phosphacan short isoform, a novel non-proteoglycan variant of phosphacan/receptor protein tyrosine phosphatase-beta, interacts with neuronal receptors and promotes neurite outgrowth

Phosphacan, one of the principal proteoglycans in the extracellular matrix of the central nervous system, is implicated in neuron-glia interactions associated with neuronal differentiation and myelination. We report here the identification of a novel truncated form of phosphacan, phosphacan short isoform (PSI), that corresponds to the N-terminal carbonic anhydrase- and fibronectin type III-like domains and half of the spacer region. The novel cDNA transcript was isolated by screening of a neonatal brain cDNA expression library using a polyclonal antibody raised against phosphacan. Expression of this transcript in vivo was confirmed by Northern blot hybridization. Analysis of brain protein extracts reveals the presence of a 90-kDa glycosylated protein in the phosphate-buffered saline-insoluble 100000 x g fraction that reacts with antisera against both phosphacan and a recombinant PSI protein and that has the predicted N-terminal sequence. This protein is post-translationally modified with oligosaccharides, including the HNK-1 epitope, but, unlike phosphacan, it is not a proteoglycan. The expression of the PSI protein varies during central nervous system development in a fashion similar to that observed for phosphacan, being first detected around embryonic day 16 and then showing a dramatic increase in expression to plateau around the second week post-natal. Both the native and recombinant PSI protein can interact with the Ig cell adhesion molecules, F3/contactin and L1, and in neurite outgrowth assays, the PSI protein can promote outgrowth of cortical neurons when used as a coated substrate. Hence, the identification of this novel isoform of phosphacan/receptor protein tyrosine phosphatase-beta provides a new component in cell-cell and cell-extracellular matrix signaling events in which these proteins have been implicated.