Biomedical subjects

Charles L Howe

Publications and source records attributed to Charles L Howe.

23 records · Page 2Linked to original sources

PubMed2003

Depolarization of PC12 cells induces neurite outgrowth and enhances nerve growth factor-induced neurite outgrowth in rats.

Synaptic plasticity is clearly controlled by synaptic activity and by neurotrophin-dependent signaling. We have previously hypothesized that synaptic activity modulates concomitant neurotrophin receptor signaling, thereby integrating the activity state of a synapse with the state of neurotrophic support available at the synapse. Herein we present evidence in support of this hypothesis. Using PC12 cells as a model of the presynaptic element, we show that depolarization increases TrkA tyrosine phosphorylation in response to nerve growth factor (NGF). Moreover, we show that depolarization alone is sufficient to induce the tyrosine phosphorylation of TrkA. These findings are functionally relevant, as evidenced by our observation that depolarization alone induces neurite outgrowth, and that depolarization dramatically enhances neurite outgrowth in response to NGF, especially in primed PC12 cells. We conclude that normal synaptic function may depend upon the integration of synaptic activity and activity-dependent neurotrophin release and signaling, and that these findings have potential relevance to neural repair.

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PubMed2003

Interleukin-6 protects anterior horn neurons from lethal virus-induced injury.

We evaluated the role of interleukin-6 (IL-6) in neuronal injury after CNS infection. IL-6-/- and IL-6+/+ mice of resistant major histocompatibility complex (MHC) H-2b haplotype intracerebrally infected with Theiler's virus cleared the infection normally without development of viral persistence, lethal neuronal infection, or late phase demyelination. In contrast, infection of IL-6-/- mice on a susceptible H-2q haplotype resulted in frequent deaths and severe neurologic deficits within 2 weeks of infection as compared with infected IL-6+/+ H-2q littermate controls. Morphologic analysis demonstrated dramatic injury to anterior horn neurons of IL-6-/- H-2q mice at 12 d after infection. Infectious viral titers in the CNS (brain and spinal cord combined) were equivalent between IL-6-/- H-2q and IL-6+/+ H-2q mice. In contrast, more viral RNA was detected in the spinal cord of IL-6-/- mice compared with IL-6+/+ H-2q mice. Virus antigen was localized predominantly to anterior horn cells in infected IL-6-/- H-2q mice. IL-6 deletion did not affect the humoral response directed against virus, nor did it affect the expression of CD4, CD8, MHC class I, or MHC class II in the CNS. Importantly, IL-6 was expressed by astrocytes of infected IL-6+/+ mice but not in astrocytes of IL-6-/- mice or uninfected IL-6+/+ mice. Furthermore, expression of various chemokines was robust at 12 d after infection in both H-2b and H-2q IL-6-/- mice, indicating that intrinsic CNS inflammatory responses did not depend on the presence of IL-6. Finally, in vitro analysis of virus-induced death in neuroblastoma-spinal cord-34 motor neurons and primary anterior horn cell neurons showed that IL-6 exerted a neuroprotective effect. These data support the hypothesis that IL-6 plays a critical role in protecting specific populations of neurons from irreversible injury.

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PubMed2003

Human monoclonal IgM antibody promotes CNS myelin repair independent of Fc function.

The human monoclonal IgM antibody sHIgM22 and mouse IgM monoclonal antibody 94.03 bind to oligodendrocytes, induce calcium signals in cultured glial cells, and promote remyelination in mouse models of multiple sclerosis. In order to address the mechanisms employed by these antibodies to promote CNS repair, bivalent monomers, F(ab')2 fragments, and monovalent forms of these antibodies were investigated to determine whether they exhibit the same remyelinating potential as the intact IgMs. The two antibodies displayed different structural requirements for retention of function. Antibody sHIgM22 remained functional even when reduced to a bivalent F(ab')2 fragment, while disruption of the pentameric structure of antibody 94.03 destroyed its functional properties. Competition studies demonstrated that the two antibodies recognize different entities on the surface of glial cells. These results indicate that the constant region and pentameric structure of IgM is not always necessary for the stimulation of myelin repair, eliminating the requirement for IgM immune effector functions in this process. The ability of the antibodies to cross-link cell surface determinants on oligodendrocytes appears to be an essential aspect of the mechanism of cellular activation. The finding that two antibodies, which induce similar in vivo effects, bind to different structures, and have different cross-linking requirements suggests that activation of glial cells involves the rearrangement of a complex membrane compartment.

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PubMed2003

Gamma interferon is critical for neuronal viral clearance and protection in a susceptible mouse strain following early intracranial Theiler's murine encephalomyelitis virus infection.

We evaluated the role of gamma interferon (IFN-gamma) in protecting neurons from virus-induced injury following central nervous system infection. IFN-gamma(-/-) and IFN-gamma(+/+) mice of the resistant major histocompatibility complex (MHC) H-2(b) haplotype and intracerebrally infected with Theiler's murine encephalomyelitis virus (TMEV) cleared virus infection from anterior horn cell neurons. IFN-gamma(+/+) H-2(b) mice also cleared virus from the spinal cord white matter, whereas IFN-gamma(-/-) H-2(b) mice developed viral persistence in glial cells of the white matter and exhibited associated spinal cord demyelination. In contrast, infection of IFN-gamma(-/-) mice of the susceptible H-2(q) haplotype resulted in frequent deaths and severe neurologic deficits within 16 days of infection compared to the results obtained for controls. Morphologic analysis demonstrated severe injury to spinal cord neurons in IFN-gamma(-/-) H-2(q) mice during early infection. More virus RNA was detected in the brain and spinal cord of IFN-gamma(-/-) H-2(q) mice than in those of control mice at 14 and 21 days after TMEV infection. Virus antigen was localized predominantly to anterior horn cells in infected IFN-gamma(-/-) H-2(q) mice. IFN-gamma deletion did not affect the humoral response directed against the virus. However, the level of expression of CD4, CD8, class I MHC, or class II MHC in the central nervous system of IFN-gamma(-/-) H-2(q) mice was lower than those in IFN-gamma(+/+) H-2(q) mice. Finally, in vitro analysis of virus-induced death in NSC34 cells and spinal motor neurons showed that IFN-gamma exerted a neuroprotective effect in the absence of other aspects of the immune response. These data support the hypothesis that IFN-gamma plays a critical role in protecting spinal cord neurons from persistent infection and death.

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PubMed2002

Growth factor treatment of demyelinating disease: at last, a leap into the light.

Researchers seeking treatments for multiple sclerosis (MS) have long dreamed of using neurotrophic factors to enhance remyelination. Previous attempts to apply trophic support for oligodendrocytes in experimental demyelination uniformly produced complicated outcomes that reflected unexpected effects on immune or inflammatory responses and could be interpreted only with caution. Now, two recent publications have demonstrated convincingly that cytokines of the interleukin (IL)-6 superfamily can ameliorate experimental autoimmune encephalomyelitis and promote oligodendrocyte survival, without demonstrable effect on inflammation or immune responses.

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