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SIGNAL TRANSDUCTION IN SYNAPTIC
TRANSMISSION AND PLASTICITY
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Kuo-Ping
Huang, PhD, Head, Section
on Metabolic Regulation Freesia L.
Huang, PhD, Staff Scientist Daniel E. Kolker,
PhD, Postdoctoral Fellow Pavan K. Shetty, PhD, Postdoctoral
Fellow Junfang Wu,
PhD, Postdoctoral Fellow |
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Enhancement of long-term potentiation and
learning by neurogranin/RC3 through calcium-mediated signaling Huang
K-P, Huang F, Lia; in collaboration with
Balschun, Jäger, Reymann Ng is localized in the neuronal soma and
dendrites and is present in high concentrations in the dendritic spines. It
has been suggested that Ng modulates synaptic responses through its capacity
to buffer and sequester CaM, thereby regulating the
level of free Ca2+ and Ca2+/ Huang K-P, Wu J, Huang K-P, Huang FL. Participation of NMDA-mediated
phosphorylation and oxidation of neurogranin in the
regulation of Ca2+- and Ca2+/calmodulin-dependent
neuronal signaling in the hippocampus. J Neurochem
2003;86:1524-1533. Wu J, Li J, Huang K-P, Huang FL. Attenuation
of protein kinase C and cAMP-dependent protein
kinase signal transduction in the neurogranin
knockout mice. J Biol Chem 2002;277:19498-19505. Effect of environmental
enrichment on the cognitive behaviors of neurogranin
knockout mice Huang
F, Huang K-P, Wu, Kolker Environmental enrichment and exercise can
alter neural plasticity and improve cognitive performances of rodents as a
result of increasing neurogenesis. Neurogranin
knockout mice exhibit severe deficits in learning and memory of spatial
tasks, induction and maintenance of LTP, and amplification of Ca2+-mediated
signaling in the hippocampus. To determine if increasing physical activities
of these mutant mice can improve performance in memory tasks, groups of
mutant mice and their wild-type littermates were housed
for three weeks in roomier cages, each with several toys and a running wheel
for voluntary exploration and exercise. The control groups were housed in the
regular home cages without any toys. Both Ng+/+ and Ng+/-
mice performed significantly better than their controls in the enriched
environment in both the hidden platform and probe trial versions of the
Morris water maze as well as in the step-down fear conditioning task.
However, environmental enrichment had minimal effect on the performances of Ng-/-
mice in these tasks. Hippocampal LTP in the CA1 region induced by
high-frequency stimulation was also higher in the enriched group than in the
controls among Ng+/+ and Ng+/- mice, whereas no
significant change was observed among Role of PKC gamma in the
phosphorylation of neurogranin: studies with PKC
gamma knockout mice Huang
K-P, Wu, Huang F PKC gamma is one of the major Ca2+/phospholipid/diacylglycerol-activated
isozymes expressed at a high level in the neurons of mammalian brain. The
kinase is localized in the cell bodies, axons, and dendrites, but not in the
presynaptic terminals. Of all the PKCs, PKC gamma
exhibits the closest relationship with Ng in its cellular localizations and
patterns of developmental expression. In the hippocampus, PKC gamma is
associated with the NMDA receptor–PSD-95 complexes and is believed to
participate in NMDA receptor–mediated signal transduction and
enhancement of synaptic plasticity. The brain-specific PKC gamma was believed
to be the kinase responsible for the phosphorylation of Ng, an event
implicated in signal amplification during synaptic transmission. However,
deletion of PKC gamma in mice caused only a minor modification of hippocampal
LTP induced by high-frequency stimulation and had no effect on synaptic
transmission, paired-pulse facilitation, long-term depression, or
phorbol-induced LTP. To resolve the issue concerning the specificity of the
various PKCs in the phosphorylation of Ng and the
role of Ng phosphorylation in signal transduction, we investigated the
phosphorylation of Ng by PKCs in vitro and
in hippocampal slices from the wild-type and PKC gamma null mutant mice. In
vitro, Ng is a substrate of Ca2+-activated PKC alpha, beta,
and gamma but is poorly phosphorylated by the Ca2+-insensitive
delta, epsilon, zeta, and eta isoforms; the activities of the latter group of
PKCs were less than one-third of those of the
former. Both the glutamate- and NMDA-stimulated phosphorylations
of Ng in hippocampal
slices of PKC gamma knockout mice were lower than those of the wild-type
mice. In contrast, the phorbol ester– and high-frequency
tetanus–induced phosphorylations of Ng were
comparable in the PKC gamma knockout and wild-type mice. The findings suggest
that activation of PKC gamma is intimately coupled to the glutamate
receptors, whereas phorbol ester and high-frequency tetanic stimulation cause
a global activation of multiple PKCs to
phosphorylate Ng. The compensatory effects of other PKCs
provide a logical explanation for the mild deficits in synaptic plasticity
and cognitive behaviors observed in PKC gamma knockout mice. Thionylation of
protein by disulfide S-oxide and -dioxide generated from Fenton’s
reaction Huang
F, Huang K-P Redox regulation through modifications of
proteins has emerged as one of the major cellular responses to oxidative and nitrosative stresses. In the central nervous system,
neurotransmission under normal or pathological conditions generates a variety
of oxidants. Cellular sulfhydryl compounds are the major reductants operating
against oxidative stress, which can be detrimental to cell survival. Numerous
neural disorders, including Alzheimer’s and Parkinson’s diseases,
are believed to result in part from excessive damage to neurons by the
endogenous oxidants produced in the presence of iron. The pivotal role of
iron in pathogenesis has been hypothesized as attributable to its
participation in Fenton’s reaction, which
generates highly reactive and toxic hydroxyl radicals via reaction of Fe(II) and hydrogen peroxide. Oxidation of sulfhydryl
compounds by oxidants generated from Fenton’s
reaction is generally thought to form disulfides. Detailed analysis of the
oxidation products of thiols by hydrogen peroxide and iron revealed that, in
addition to each of their respective disulfides, both the disulfide
S-monoxides (DSO) and disulfide S-dioxides (DSDO) were formed. In vitro,
proteins can be effectively thionylated by
disulfide S-oxide (DSO) and -dioxide (DSDO). Formation of these S-oxides was
more effective in the presence of Fe(III) than that
of Fe(II). The same products were also generated by oxidation of thiols with methyltrioxorhenium (VII) (CH3ReO3).
Formation of DSO and DSDO by either Fenton’s
reagent or CH3ReO3 was more efficient with free thiols
than with their corresponding disulfides, suggesting that sulfenic and
sulfinic acids are the intermediates for the formation of these compounds. We
purified both DSO and DSDO by high-pressure liquid chromatography and
identified them by mass spectrometry; they were highly reactive toward thiol
to form mixed disulfides. The reaction rate of DSDO was at least an order of
magnitude higher than that of DSO when tested by reaction with
5-mercapto-2-nitro benzoate. Both oxides effectively modified neurogranin, which resulted in thionylation
of its four Cys residues, as verified by mass spectrometry. The oxides also
caused dose-dependent inactivation of PKC, whose glutathionylation
was detected by Western blots with a specific antibody. The results suggest
that such disulfide oxides are useful reagents for thionylation
of protein and may contribute to the modification of proteins by Fenton’s reaction under pathological conditions. Huang K-P, Huang FL. Glutathionylation
of proteins by glutathione disulfide S-oxide. Biochem
Pharmacol 2002;64:1049-1056. aJungfa Li,
MD, PhD, former Postdoctoral Fellow COLLABORATORs Detlef Balschun, PhD, Leibniz
Institute for Neurobiology, Tino Jäger, PhD, Leibniz Institut für Neurobiologie, Klaus Reigmann, PhD, Leibniz Institut für Neurobiologie, For
further information, contact huangk@mail.nih.gov |
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