LiLian Yuan - US grants

[unreadable] DESCRIPTION (provided by applicant): Long-term changes in synaptic responses and membrane excitability are different forms of neuronal plasticity thought to underlie memory. The nature of and mechanisms underlying the synaptic conductance changes have been extensively investigated. However, there are often changes in excitability and EPSP-spike coupling associated with synaptic plasticity. The mechanisms involved in intrinsic plasticity, the other component of neural plasticity, remain unknown. [unreadable] One mechanism through which plastic changes in membrane excitability can be achieved is via kinase dependent regulation of ion channel surface expression or trafficking. Kv4.2 subunits-mediated A-type K currents (IA) emerged as a key player controlling signal propagation and membrane excitability. We have recently made an unexpected finding that CaMKII activity increases the cell surface expression of Kv4.2 in COS cells. Furthermore, we demonstrated that Kv4.2 is a substrate for CaMKII, identified the exact sites of phosphorylation, and showed that direct phosphorylation of these sites is necessary for CaMKII-mediated upregulation of K channel expression. [unreadable] These results lead to the intriguing idea that synaptic activity and/or CaMKII phosphorylation drives new K channels into the plasma membrane of neurons, consequently regulating and establishing the dendritic distribution of A-type K channels. In concert with the potentiation of synaptic conductances, promotion of K channel surface expression may provide a homeostatic mechanism by reducing overall excitability of a neuron. For this proposal I will test experimentally the above hypotheses, and extend our studies to a mouse model for Angelman syndrome (AS). The implications of these studies are more general in that they can be applied as a molecular model for the trafficking and regulation of other ion channels by protein kinases during neuronal plasticity. Moreover, the studies proposed above represent our efforts to define the precise dendritic mechanisms involved in an animal model for human neurological diseases. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): With the ability to directly measure electrical signals from the neuronal dendrites, we have learned a great deal about the active properties of the dendrites over the past ten years. The most remarkable finding is that action potentials (b-APs) initiated at soma also actively propagate back into dendrites, reversing the conventional direction of information flow. Emerging evidence suggests that b-APs are involved in NMDA-receptor dependent plasticity by providing a large enough membrane depolarization to unblock NMDA receptors in synapses. Thus, factors determining b-AP back-propagation, b-AP amplitude and duration are likely to have an important impact on this signaling pathway. The fast activation kinetics, near-threshold activation profile, and a high current density in dendrites of CA1 pyramidal neurons have made A-type K+ channels the ideal determining factor of b-AP. The regulation, however, can be further complicated as A-type K+ channels themselves are subject to modulation by various protein kinases, neurotransmitters, and modulators, greatly extending the computational power of this system. Thus, A-type K+ channels represent a key regulatory component in hippocampal plasticity. Although quite some evidence suggests Kv4.2 is the major subunits underlying dendritic A-type K+ currents, this hypothesis has never been directly tested. We would like to know what mechanisms underlie the regulation and establishment of the unique dendritic gradient of A-type K+ channel distribution. Our recent work suggests the involvement of CaMKII activity in regulating surface expression of Kv4.2-mediated currents in the soma. These results formulate the intriguing hypotheses we wish to test: dendritic A-type K+ channels contribute to synaptic plasticity and neuronal activity helps to establish and maintain the characteristic dendritic distribution of this channel. Combining two unique techniques (dendritic recordings in mouse preparation and the use of a mutant form of sindbis virus that allows quick gene delivery in vivo with minimized neuronal toxicity), the studies proposed above should allow us to define the molecular mechanisms of A-type K+ channel mediated signal propagation and neuronal plasticity in dendrites. [unreadable] [unreadable] [unreadable]

? DESCRIPTION (provided by applicant): Accumulating evidence suggests that dysregulation of glutamatergic transmission in brain regions involved in mood regulation, such as prefrontal cortex (PFC), is linked with depressive disorders. In addition, applications of N-methyl-D-aspartate receptor (NMDAR) antagonists, such as ketamine, exhibit fast-acting and long-lasting antidepressants properties. However, despite these promising findings, limitations of ketamine use as an antidepressant treatment, particularly its dissociative/psychotomimetic effects and abuse potential, highlight the need for alternative glutamatergic agents. Our long-term research goal is to search for and characterize novel glutamatergic agents that exhibit fast-acting antidepressant effects. The objective for this application is to evaluate the antidepressant potential of D- serine, an endogenous NMDAR co-agonist that acts on glutamatergic synapses. The proposed ketamine treatment mechanisms pertain to rapidly enhanced glutamate transmission and synaptogenesis, possibly through inhibition of local GABAergic interneurons and postsynaptic activation of intracellular signaling cascades in the mTOR pathway. D-serine, as an endogenous NMDAR co-agonist, also boosts glutamate transmission and synaptogenesis. Our preliminary results along with previous studies lead to our central hypothesis that activation of NMDAR co-agonist site by D-serine results in fast-acting antidepressant effects. Moreover, D-serine may work cooperatively with ketamine to lower its therapeutic threshold, diminishing the likelihood of abuse. In aim 1, we will evaluate the therapeutic potential of D-serine as a fast-acting antidepressant in preclinical models of depression. Aim 2 is designed to examine the effectiveness of combining D-serine and ketamine at their therapeutic or sub-threshold doses. Finally, we will delineate the synaptic and neural circuitry mechanisms of D-serine and ketamine antidepressant actions, alone or in combination in aim 3. Upon completion, the studies proposed above are likely to generate mechanistic information on D-serine's fast-acting antidepressant potential as well as its feasibility of reducing adverse side effects of ketamine by lowering its therapeutic threshold.

Newly emerged, rapid acting antidepressant ketamine is able to achieve therapeutic improvement, in part, through stimulating activity of kinase-dependent signaling pathways. However, current investigations are limited to a single or small number of kinases and are unable to detect novel kinases. The goal of the proposed project is to uncover mechanisms underlying ketamine's antidepressant actions through a unique unbiased high-throughput screening. We propose to use a chemical proteomics approach that couples multiplexed inhibitor beads (MIBs) technology with quantitative mass spectrometry (MS) to capture kinases and their substrates that are activated by ketamine and its active metabolite HNK. This approach will open up a new realm of opportunities to link ketamine treatment with its underlying molecular mechanisms at the proteomics level. Kinases and pathways identified through the profiling approach will be subject for verification and in-depth examination. Preliminary application of this MIBs/MS approach replicated well-known molecular signature of ketamine action identified previously, including mTOR and ERK pathways. Furthermore, preliminary results suggest unchecked kinase activity and unappreciated pathways that mediate initial neural responses to ketamine as well as synaptogenesis induced by ketamine as a means of functional restoration. We expect our effort in identifying novel mechanisms underlying ketamine antidepressant actions to provide unmet therapeutic opportunities in treating depression and possibly other mood disorders.