The Nogo receptor, its ligands and axonal regeneration in the spinal cord; A review

At least three proteins present in CNS myelin, Nogo, MAG and OMgp are capable of causing growth cone collapse and inhibiting neurite outgrowth in vitro. Surprisingly, Nogo and OMgp are also strongly expressed by many neurons (including neocortical projection cells). Nogo expression is increased by some cells at the borders of CNS lesion sites and by cells in injured peripheral nerves, but Nogo and CNS myelin are largely absent from spinal cord injury sites, which are none the less strongly inhibitory to axonal regeneration. Nogo is found on growing axons during development, suggesting possible functions for neuronal Nogo in axon guidance. Although Nogo, MAG and OMgp lack sequence homologies, they all bind to the Nogo receptor (NgR), a GPI-linked cell surface molecule which, in turn, binds p75 to activate RhoA. NgR is strongly expressed by cerebral cortical neurons but many other neurons express NgR weakly or not at all. Some neurons, such as DRG cells, respond to Nogo and CNS myelin in vitro although they express little or no NgR in vivo which, with other data, indicates that other receptors are available for NgR ligands. NgR expression is unaffected by injury to the nervous system, and there is no clear correlation between NgR expression by neurons and lack of regenerative ability. In the injured spinal cord, interactions between NgR and its ligands are most likely to be important for limiting regeneration of corticospinal and some other descending tracts; other receptors may be more important for ascending tracts. Antibodies to Nogo, mainly the poorly-characterised IN-1 or its derivatives, have been shown to enhance recovery from partial transections of the spinal cord. They induce considerable plasticity from the axons of corticospinal neurons, including sprouting across the midline and, to a limited extent, regeneration around the lesion. Regeneration of corticospinal axons induced by Nogo antibodies has not yet been demonstrated after complete transections or contusion injuries of the spinal cord. It is not clear whether antibodies against Nogo act on oligodendrocytes/myelin or by binding to neuronal Nogo, or whether they can stimulate regeneration of ascending axons in the spinal cord, most of which express little or no NgR. Despite these uncertainties, however, NgR and its ligands offer important new targets for enhancing plasticity and regeneration in the nervous system.     

Genetic diversity of Streptomyces spp. causing common scab of potato in eastern Canada

Common scab is an important disease of potato caused by Streptomyces scabies and other closely related species. In this study, the genetic diversity of Streptomyces spp. causing common scab of potato in eastern Canada was for the first time investigated. Forty-one Streptomyces spp. isolates were retrieved from necrotic lesions of potato tubers harvested from different regions of the Canadian provinces New-Brunswick, Nova Scotia and Prince-Edward-Island. Most isolates were closely related to known pathogenic S. scabies strains on the basis of partial 16S ribosomal (r) RNA and rpoB gene sequence analyses. Two isolates were identified as pathogenic species of Streptomyces acidiscabies. To our knowledge, this species has never been previously isolated in these areas. Genome fingerprinting studies using repetitive elements (rep) polymerase chain reactions (PCR) revealed 10 distinct genetic groups in eastern Canada. The geographical distribution of the genetic groups was region-dependant. Pathogenicity- and virulence-related genes (txtA, txtC, and tomA) were PCR-amplified from each isolate, and nucleotide sequence analysis of partial gene fragments revealed slight polymorphisms in both txtA and txtC genes. No genetic variation was noted in the partial tomA gene sequences.     

Effects of Oxygenation on Hydrocarbon Biodegradation in a Hypoxic Environment

In 1984, an underground storage tank leaked approximately 41,000 L of gasoline into the ground water at the Naval Construction Battalion Command in Port Hueneme, CA (USA). Benzene, toluene, ethylbenzene, and xylenes (BTEX) contamination stimulated remedial action. In 1995, a ground water circulation well (GCW) and network of surrounding monitoring wells were installed. After year of operation, dissolved oxygen and nitrate concentrations remained low in all monitoring wells. Benzene utilization (the sum of respiration, uptake, and conversion to polar compounds) ranged from 0.03 to 4.6 µg L^-1 h^-1, and toluene utilization ranged from 0.01 to 5.2 µg L^-1 h^-1. Heterotrophic bacterial productivity (total carbon assimilation) increased dramatically in the GCW, although benzene and toluene utilization decreased markedly relative to surrounding wells. Benzene and toluene uptake accounted for a significant proportion (mean=22%) of the heterotrophic bacterial productivity except within the GCW, indicating other fuel contaminant or indigenous organic carbon and not BTEX compounds served as primary carbon source. The GCW effectively air-stripped BTEX compounds, but failed to stimulate benzene and toluene biodegradation and thus would not be effective for stimulating BTEX bioremediation under current deployment parameters. Air stripping was three orders of magnitude more effective than biodegradation for removing benzene and toluene in the GCW.     

Facilitation of acetylcholine release and improvement in cognition by a selective M2 muscarinic antagonist, SCH 72788

Current treatment of Alzheimer's Disease (AD) requires acetylcholinesterase inhibition to increase acetylcholine (ACh) concentrations in the synaptic cleft. Another mechanism by which ACh levels can be increased is blockade of presynaptic M2 muscarinic autoreceptors that regulate ACh release. An antagonist designed for this purpose must be highly selective for M2 receptors to avoid blocking postsynaptic M1 receptors, which mediate the cognitive effects of ACh. Structure-activity studies of substituted methylpiperadines led to the synthesis of 4-[4-[1(S)-[4-[(1,3-benzodioxol-5-yl)sulfonyl]phenyl]ethyl]-3(R)-methyl-1-piperazinyl]-4-methyl-1-(propylsulfonyl)piperidine. This compound, SCH 72788, binds to cloned human M2 receptors expressed in CHO cells with an affinity of 0.5 nM, and its affinity at M1 receptors is 84-fold lower. SCH 72788 is a functional M2 antagonist that competitively inhibits the ability of the agonist oxotremorine-M to inhibit adenylyl cyclase activity. In an in vivo microdialysis paradigm, SCH 72788 increases ACh release from the striatum of conscious rats. The compound is also active in a rodent model of cognition, the young rat passive avoidance response paradigm. The effects of SCH 72788 suggest that M2 receptor antagonists may be useful for treating the cognitive decline observed in AD and other dementias.     

Impaired osteoclast formation in bone marrow cultures of Fgf2 null mice in response to parathyroid hormone

Fibroblast growth factor (FGF)-2 and parathyroid hormone (PTH) are potent inducers of osteoclast (OCL) formation, and PTH increases FGF-2 mRNA and protein expression in osteoblasts. To elucidate the role of endogenous FGF-2 in PTH responses, we examined PTH-induced OCL formation in bone marrow cultures from wild type and mice with a disruption of the Fgf2 gene. FGF-2-induced OCL formation was similar in marrow culture from both genotypes. In contrast, PTH-stimulated OCL formation in bone marrow cultures or co-cultures of osteoblast-spleen cells from Fgf2-/mice was significantly impaired. PTH increased RANKL mRNA expression in osteoblasts cultures from both genotypes. After 6 days of treatment, osteoprotegerin protein in cell supernatants was 40-fold higher in vehicle-treated and 30-fold higher in PTH-treated co-cultures of osteoblast and spleen cells from Fgf2-/mice compared with Fgf2+/+ mice. However, a neutralizing antibody to osteoprotegerin did not rescue reduced OCL formation in response to PTH. Injection of PTH caused hypercalcemia in Fgf2+/+ but not Fgf2-/mice. We conclude that PTH stimulates OCL formation and bone resorption in mice in part by endogenous FGF-2 synthesis by osteoblasts. Because RANKL- and interleukin-11-induced OCL formation was also reduced in bone marrow cultures from Fgf2-/mice, we further conclude that endogenous FGF-2 is necessary for maximal OCL formation by multiple bone resorbing factors.     

Deletion of the virion host shutoff protein (vhs) from herpes simplex virus (HSV) relieves the viral block to dendritic cell activation: potential of vhs- HSV vectors for dendritic cell-mediated immunotherapy

Herpes simplex virus (HSV) infects dendritic cells (DC) efficiently but with minimal replication. HSV, therefore, appears to have evolved the ability to enter DC even though they are nonpermissive for virus growth. This provides a potential utility for HSV in delivering genes to DC for vaccination purposes and also suggests that the life cycle of HSV usually includes the infection of DC. However, DC infected with HSV usually lose the ability to become activated following infection (M. Salio, M. Cella, M. Suter, and A. Lanzavecchia, Eur. J. Immunol. 29:3245-3253, 1999; M. Kruse, O. Rosorius, F. Kratzer, G. Stelz, C. Kuhnt, G. Schuler, J. Hauber, and A. Steinkasserer, J. Virol. 74:7127-7136, 2000). We report that for DC to retain the ability to become activated following HSV infection, the virion host shutoff protein (vhs) must be deleted. vhs usually functions to destabilize mRNA in favor of the production of HSV proteins in permissive cells. We have found that it also plays a key role in the inactivation of DC and is therefore likely to be important for immune evasion by the virus. Here, vhs would be anticipated to prevent DC activation in the early stages of infection of an individual with HSV, reducing the induction of cellular immune responses and thus preventing virus clearance during repeated cycles of virus latency and reactivation. Based on this information, replication-incompetent HSV vectors with vhs deleted which allow activation of DC and the induction of specific T-cell responses to delivered antigens have been constructed. These responses are greater than if DC are loaded with antigen by incubation with recombinant protein.     

Unexpected absence of the Epstein-Barr virus (EBV) lyLMP-1 open reading frame in tumor virus isolates: lack of correlation between Met129 status and EBV strain identity

The lytic cycle-associated lytic latent membrane protein-1 (lyLMP-1) of Epstein-Barr virus (EBV) is an amino-terminally truncated form of the oncogenic LMP-1. Although lyLMP-1 shares none of LMP-1's transforming and signal transducing activities, we recently reported that lyLMP-1 can negatively regulate LMP-1-stimulated NF-kappaB activation. The lyLMP-1 protein encoded by the B95-8 strain of EBV initiates from methionine 129 (Met129) of the LMP-1 open reading frame (ORF). The recent report that Met129 in the B95-8 LMP-1 ORF is not conserved in the Akata strain of EBV prompted us to screen a panel of EBV-positive cell lines for conservation of Met129 and lyLMP-1 expression. We found that 15 out of 16 tumor-associated virus isolates sequenced encoded an ATT or ACC codon in place of ATG in the LMP-1 ORF at position 129, and tumor cell lines harboring isolates lacking an ATG at codon 129 did not express the lyLMP-1 protein. In contrast, we found that EBV DNA from 22 out of 37 healthy seropositive donors retained the Met129 codon. Finally, the lyLMP-1 initiator occurs variably within distinct EBV strains and its presence cannot be predicted by EBV strain identity. Thus, Met129 is not peculiar to the B95-8 strain of EBV, but rather can be found in the background of several evolutionarily distinct EBV strains. Its absence from EBV isolates from tumors raises the possibility of selective pressure on Met129 in EBV-dependent tumors.     

Herpes simplex virus type 1 induces CD83 degradation in mature dendritic cells with immediate-early kinetics via the cellular proteasome

Mature dendritic cells (DCs) are the most potent antigen-presenting cells within the human immune system. However, Herpes simplex virus type 1 (HSV-1) is able to interfere with DC biology and to establish latency in infected individuals. In this study, we provide new insights into the mechanism by which HSV-1 disarms DCs by the manipulation of CD83, a functionally important molecule for DC activation. Fluorescence-activated cell sorter (FACS) analyses revealed a rapid downmodulation of CD83 surface expression within 6 to 8 h after HSV-1 infection, in a manner strictly dependent on viral gene expression. Soluble CD83 enzyme-linked immunosorbent assays, together with Western blot analysis, demonstrated that CD83 rapidly disappears from the cell surface after contact with HSV-1 by a mechanism that involves protein degradation rather than shedding of CD83 from the cell surface into the medium. Infection experiments with an ICP0 deletion mutant demonstrated an important role for this viral immediate-early protein during CD83 degradation, since this particular mutant strain leads to strongly reduced CD83 degradation. This hypothesis was further strengthened by cotransfection of plasmids expressing CD83 and ICP0 into 293T cells, which led to significantly reduced accumulation of CD83. In strong contrast, transfection of plasmids expressing CD83 and a mutant ICP0 defective in its RING finger-mediated E3 ubiquitin ligase function did not reduce CD83 expression. Inhibition of the proteasome, the cellular protein degradation machinery, almost completely restored CD83 surface expression during HSV-1 infection, indicating that proteasome-mediated degradation and HSV-1 ICP0 play crucial roles in this novel viral immune escape mechanism.