2000 — 2010 |
Hegde, Ashok N |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Regulated Proteolysis and Long-Term Memory @ Wake Forest University Health Sciences
[unreadable] DESCRIPTION (provided by applicant): Project Summary: Elucidation of mechanisms underlying synaptic plasticity is likely to aid in understanding both normal and abnormal functions of the nervous system. A tractable model system for investigating synaptic plasticity is long-term presynaptic facilitation of sensory-to-motor neuron synapses in Aplysia, the cellular mechanism underlying a simple form of learning and memory. The overall goal of this proposal is to investigate how the ubiquitin-proteasome pathway contributes to long-term facilitation. Long-term facilitation requires signal transduction from the neurotransmitter 5-HT to the nucleus for activation of gene transcription by the cAMP-responsive element binding protein (CREB). Normally, gene transcription by CREB is inhibited by repressers. Previous studies revealed that in Aplysia neurons, the CREB represser CREBIb is degraded by the ubiquitin-proteasome pathway. Preliminary results indicate that CREBIb is phosphorylated by protein kinase C. The first aim is to investigate regulation of CREBIb ubiquitination by phosphorylation and to show that phosphorylation-mediated regulation of CREBIb ubiquitination and degradation is critical for induction of long-term facilitation. During induction of long-term facilitation, regulation of proteasome is likely to play a critical role as well. Preliminary data show that the proteasome activity in the synaptic terminals significantly differs from the proteasome activity in the nucleus. The second aim is to test the hypothesis that the proteasome is differentially regulated in the nucleus and in the synaptic terminals. These studies are likely to provide insights into the mechanisms by which precise spatial and temporal regulation of ubiquitin-proteasome-mediated proteolysis contribute to long-term synaptic plasticity. Relevance: Memory that lasts a long-period of time forms only with strong or repeated stimulation of the senses. A key protein that suppresses memory formation needs to be degraded before long-lasting memory can form. The suppressor protein is marked for degradation by attachment of a tag called ubiquitin and is degraded by a part of the cell named the proteasome. The protein degradation is abnormal in many brain diseases like Alzheimer's. This research could shed light on how impairment in protein degradation could lead to memory loss as well as brain diseases. [unreadable] [unreadable]
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0.958 |
2004 — 2005 |
Hegde, Ashok N |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
Novel Approaches to the Study of Single-Trial Learning @ Wake Forest University Health Sciences
DESCRIPTION (provided by applicant): A major endeavor in neuroscience is to elucidate the mechanisms by which the brain stores information acquired through learning. To make progress towards a complete understanding of memory formation, model systems that allow the experimenter to relate changes in specific synapses to specific behavior are essential. We propose to study a pheromone memory model that is ideally suited for integrating several levels of analysis: from molecules to behavior. Female mice form memory to the male's pheromones during mating through single-trial learning and retain the information for a significant period of their lifetime. The memory formation occurs only if two neurotransmitter inputs, glutamate and norepinephrine (NE), coincide in the accessory olfactory bulb (AOB), the locus of pheromone memory. Glutamate and NE somehow lead to structural and functional modifications of the AOB synapses. Our overall goal is to understand how coincidence of glutamate and NE is detected, and to elucidate the signaling mechanisms downstream of glutamate and NE that control formation of long-term pheromone memory. Our preliminary results suggest that protein kinase C (PKC) has a critical signaling role. Our first aim is to use a novel approach that uses specific activators and inhibitors of PKC isoforms in electrophysiological experiments in combination with biochemical experiments to identify the isoform of PKC that detects coincident glutamate and NE inputs in the AOB. Our second aim is to develop a method to knock down the expression of a specific PKC isoform via virally-mediated delivery of small interfering RNAs. The proposed experiments would launch a research program that has enormous potential to address unanswered questions pertaining to mammalian long-term memory. In the pheromone memory model the neural circuitry is well delineated, the behavioral output is unambiguous, and genetic manipulations can be readily done. Therefore, this model system has unparalleled advantages over other systems in linking molecular changes in a specific synapse to changes in a specific behavior. Clarification of the mechanisms governing synaptic plasticity would be beneficial for discovering the causes of memory deficits and cognitive dysfunctions that occur in abnormalities like posttraumatic stress disorder, schizophrenia and Alzheimer's disease, and for devising therapeutic strategies.
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0.958 |
2009 — 2012 |
Hegde, Ashok N |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Local Mechanisms Underlying Synaptic Plasticity @ Wake Forest University Health Sciences
Description (provided by applicant): Understanding mechanisms by which synapses are modified for long-term memory storage is crucial for explaining normal brain function as well as diseases and disorders of the brain. Many studies have established that new gene expression and new protein synthesis are critical for synaptic changes that underlie long-term memory. Recent studies indicate that proteolysis by the ubiquitin-proteasome pathway plays a critical role in long-term synaptic plasticity. The goal of this proposal is to elucidate the spatial and temporal roles of the proteasome and the interplay between protein synthesis and degradation in long-term synaptic plasticity We will use a highly suitable model system of mammalian long-term synaptic plasticity, late phase long-term potentiation (L-LTP) in the hippocampus. Our results show that inhibition of the proteasome enhances the early, translation-dependent induction part of L-LTP but inhibits the transcription-dependent maintenance phase of L-LTP. Proteasome-mediated enhancement of early part of L-LTP depends on NMDA receptor and cAMP-dependent protein kinase. Our data indicate that proteasome inhibition increases induction of L-LTP by stabilizing the locally synthesized proteins in the dendrites but interferes with local translation at later stages. Our results also show that inhibition of proteasome blocks transcription of brain-derived neurotrophic factor (BDNF), which is a cAMP-responsive element binding protein (CREB)-inducible gene. Furthermore, our results show that proteasome inhibitors block degradation of ATF4, a CREB repressor that is known to suppress L-LTP and memory. Thus, proteasome inhibition appears to block maintenance of L-LTP by hindering CREB-mediated transcription. Our first aim is to investigate the mechanism by which L-LTP induction is enhanced by proteasome inhibition and to identify the newly synthesized proteins stabilized by the proteasome. Under our second aim, we will test the idea that blockade of the proteasome impairs the maintenance of L-LTP by causing a buildup of negative regulators of plasticity such as translation repressors and by hindering transcription in the nucleus. Using a powerful combination of proteomic, molecular biological and electrophysiological studies the proposed experiments will address important, unanswered questions pertaining to the relationship between proteolysis and protein synthesis in long-term synaptic plasticity. PUBLIC HEALTH RELEVANCE: Memories form when connections between nerve cells called synapses change. Recent discoveries show that regulation of proteins in the nerve cells by degradation plays a role in memory. Proteins are degraded by a part of the cell named proteasome when they are tagged by a little molecule called ubiquitin. Protein degradation is abnormal in many diseases and disorders of the brain. This research could help explain the memory loss that occurs in brain diseases and memory loss that happens in old age.
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0.958 |
2012 — 2013 |
Hegde, Ashok N |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
A Novel Strategy For Treating Memory Impairment in An Alzheimer's Disease Model @ Wake Forest University Health Sciences
DESCRIPTION (provided by applicant): The proposed project plans to develop a new strategy to prevent memory loss in Alzheimer's disease (AD) model mice. The strategy is based on a novel concept that selective local inhibition of the proteasome, a proteolytic complex that degrades protein substrates marked by attachment of ubiquitin molecules, is beneficial and can prevent the harmful effects of amyloid ? (A?) on long-term synaptic plasticity. The conventional wisdom is that in AD, pathological changes brought about by A? peptide accumulation or other causes of AD impair the ubiquitin- proteasome pathway and defective proteolysis exacerbates AD. Our unconventional approach stems from our observation that the proteasome performs different and often opposite functions in different parts of the neuron. Using hippocampal late phase long-term potentiation (L-LTP) as a model system for long-term synaptic plasticity, we found that inhibition of the nuclear proteasome impairs synaptic plasticity, while inhibition of th dendritic proteasome improves it. Therefore, we believe that although inhibition of the proteasome neuron-wide or in the nucleus would certainly exacerbate AD pathology, selective inhibition of the dendritic proteasome would help ameliorate synaptic deficits and memory impairment in AD. To test this idea, we devised a novel strategy to target a recombinant proteasome inhibitor specifically to dendritic spines in neurons. This recombinant inhibitor has a protein transduction domain (PTD) that enables it to traverse across the plasma membrane and enter neurons. Our preliminary data show that selective inhibition of the proteasome in dendritic spines can prevent the adverse A? effects on L-LTP and can restore normal L-LTP. Because the PTD technique has limitations for use in behavioral studies, now we plan to develop adeno-associated virus-mediated delivery into the hippocampus to test whether selective inhibition of the proteasome in dendritic spines can rescue memory deficits in AD model mice. This exploratory project will lay the groundwork for translating our research on the role of the proteasome in synaptic plasticity towards development of a new therapeutic strategy for ameliorating memory loss in AD.
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0.958 |
2016 |
Hegde, Ashok N |
R15Activity Code Description: Supports small-scale research projects at educational institutions that provide baccalaureate or advanced degrees for a significant number of the Nation’s research scientists but that have not been major recipients of NIH support. The goals of the program are to (1) support meritorious research, (2) expose students to research, and (3) strengthen the research environment of the institution. Awards provide limited Direct Costs, plus applicable F&A costs, for periods not to exceed 36 months. This activity code uses multi-year funding authority; however, OER approval is NOT needed prior to an IC using this activity code. |
Nuclear Role of the Proteasome in Synaptic Plasticity @ Georgia College and State University
Elucidating the mechanisms by which synapses are altered for long-term memory storage is crucial for understanding both normal and abnormal functions of the nervous system. Investigations over the years have established that new gene transcription and translation of the newly transcribed genes is required for maintenance of long-term synaptic plasticity and consolidation of long-term memory. Research during the last two decades has revealed that proteolysis by the ubiquitin-proteasome pathway (UPP) has an essential role in synaptic plasticity and memory. Much of the work on the UPP has been focused on its traditional function, namely, degradation of substrate proteins. It is now becoming clear that the proteasome has other roles in the cell such as regulation of transcription. Studies carried out on non-neuronal cell types have shown that the proteasome binds to promoters of actively transcribed genes and assists in transcription. A part of the proteasome called the 19S regulatory complex contains several ATPases among which Rpt1 has been shown to play a critical role in transcription. We will investigate the role of the proteasome in transcription by focusing on Rpt1. We will use hippocampal late phase long-term potentiation (L-LTP) as a model system for our studies. Our preliminary data show that Rpt1 translocates to the nucleus in hippocampal slices in response to L-LTP- inducing stimuli. Also, our results show that Rpt1 binds to specific promoters of the brain-derived neurotrophic factor (BDNF) gene. Our first aim is to use a high-throughput sequencing method in combination with chromatin immunoprecipitation with Rpt1 antibodies to identify the transcriptional targets of Rpt1. Our second aim is to test the hypothesis that the function of nuclear Rpt1 is critical for transcription and L-LTP maintenance. This project will lay the groundwork for elucidating the unconventional roles of the proteasome in transcription required for long-term synaptic plasticity which will have significant implications for understanding normal long-term memory as well as loss of memory seen in many diseases and disorders of the brain. Furthermore, by providing hands-on research experience to undergraduate students, this project will significantly enhance the training of future biomedical scientists.
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0.901 |