Small Molecule-Induced Cytosolic Activation of Protein Kinase Akt Rescues Ischemia-Elicited Neuronal Death

Elevating Akt activation is an obvious clinical strategy to prevent progressive neuronal death in neurological diseases. However, this endeavor has been hindered because of the lack of specific Akt activators. Here, from a cell-based high-throughput chemical genetic screening, we identified a small molecule SC79 that inhibits Akt membrane translocation, but paradoxically activates Akt in the cytosol. SC79 specifically binds to the PH domain of Akt. SC79-bound Akt adopts a conformation favorable for phosphorylation by upstream protein kinases. In a hippocampal neuronal culture system and a mouse model for ischemic stroke, the cytosolic activation of Akt by SC79 is sufficient to recapitulate the primary cellular function of Akt signaling, resulting in augmented neuronal survival. Thus, SC79 is a unique specific Akt activator that may be used to enhance Akt activity in various physiological and pathological conditions

AMPA receptor trafficking and synaptic plasticity

grantor: University of TorontoAMPA receptors are a subtype of glutamate receptors which are responsible for most of the fast excitatory synaptic transmissions in the mammalian central nervous system. The redistribution of postsynaptic AMPA receptors has been proposed as a mechanism for synaptic plasticities, including long-term potentiation (LTP) and long-term depression (LTD), two cellular models for learning and memory. However, direct evidence to support this hypothesis is still lacking and the cellular mechanisms mediating AMPA receptor trafficking are poorly understood. We therefore set up to investigate the involvement of AMPA receptor trafficking in both LTD and LTP. We found that AMPA receptors undergo endocytosis via a clathrin-coated-pit pathway, and that the internalization can be accelerated by insulin in a GluR2 subunit-dependent manner. The insulin-stimulated endocytosis rapidly decreased the number of AMPA receptors in the plasma membrane, resulting in an LTD of AMPA receptor-mediated synaptic transmission in hippocampal CA1 neurons. Moreover, insulin-induced LTD and low-frequency-stimulation (LFS)-induced hippocampal CA1 homosynaptic LTD were found to mutually occlude each other and both were blocked by inhibiting postsynaptic clathrin-mediated endocytosis. These data indicate that controlling the number of postsynaptic receptors by endocytosis may be an important mechanism underlying LTD in the mammalian CNS. On the other hand, although AMPA receptor insertion is an attractive cellular model for LTP expression and is gaining increasing support in recent years, the underlying mechanisms for AMPA receptor translocation are still unknown. We found here that the phosphoinositide kinase PI3-kinase (PI3K) directly associates and co-localizes with AMPA receptors. Selective activation of synaptic NMDA receptors by the NMDA receptor co-agonist glycine activates the AMPA receptor-associated PI3K and induces long-term potentiation (LTP) of AMPA mini-EPSCs. Furthermore, brief glycine treatment induces increases in cell-surface expression of AMPA receptors and the increase is due to an enhancement in receptor plasma membrane insertion. Consistently, the glycine-induced LTP is blocked by inhibiting receptor insertion. Moreover, PI3K activation is also shown to be necessary in the expression of homosynaptic LTP in hippocampal CA1 neurons. These data provide evidence for an NMDA receptor-PI3K-AMPA receptor translocation mechanism in LTP generation.Ph.D

Phosphorylation of the AMPA receptor GluR1 subunit is required for synaptic plasticity and retention of spatial memory

1Department of Neuroscience Synaptic plasticity at excitatory synapses is thought to be critical for information processing in the brain and to underlie many complex behaviors such as learning and memory. The best-studied forms of synaptic plasticity in the central nervous system are long-term potentia-tion (LTP) and long-term depression (LTD) of excitator

Glycine Potentiates AMPA Receptor Function through Metabotropic Activation of GluN2A-containing NMDA Receptors

NMDA receptors are Ca2+-permeable ion channels. The activation of NMDA receptors requires agonist glutamate and co-agonist glycine. Recent evidence indicates that NMDA receptor also has metabotropic function. Here we report that in cultured mouse hippocampal neurons, glycine increases AMPA receptor-mediated currents independent of the channel activity of NMDA receptors and the activation of glycine receptors. The potentiation of AMPA receptor function by glycine is antagonized by the inhibition of ERK1/2. In the hippocampal neurons and in the HEK293 cells transfected with different combinations of NMDA receptors, glycine preferentially acts on GluN2A-containing NMDA receptors (GluN2ARs), but not GluN2B-containing NMDA receptors (GluN2BRs), to enhance ERK1/2 phosphorylation independent of the channel activity of GluN2ARs. Without requiring the channel activity of GluN2ARs, glycine increases AMPA receptor-mediated currents through GluN2ARs. Thus, these results reveal a metabotropic function of GluN2ARs in mediating glycine-induced potentiation of AMPA receptor function via ERK1/2 activation