2012 — 2013 |
Sultan, Faraz Ali |
F30Activity Code Description: Individual fellowships for predoctoral training which leads to the combined M.D./Ph.D. degrees. |
The Role of Dna Demethylation by Gadd45b in Memory and Synaptic Plasticity @ University of Alabama At Birmingham
DESCRIPTION (provided by applicant): Disorders of memory remain a major health care burden in the United States. As the population ages, the prevalence of aging-associated cognitive decline is expected to grow. Effective treatment of memory disorders is lacking, and novel pharmacological approaches are necessary. Despite a burgeoning body of research dedicated to the study of memory and its dysfunction in disease states, details behind the molecular regulation of memory remains elusive. Recent studies point to a novel function of epigenetic mechanisms in memory formation. Epigenetics has traditionally been described as a set of heritable molecular mechanisms that stably influence gene expression; these reports indicate the largely postmitotic brain has co-opted these processes for both dynamic and persistent regulation of transcription. Investigations into neuronal activity- dependent methylation of DNA at cytosine bases and covalent modification of histones, core chromatin constituents closely opposed to DNA, confirm functional roles of these mechanisms in memory formation. DNA methyltransferases catalyze active DNA methylation, but virtually no consistent evidence existed for a molecular regulator of the reverse reaction. Two recent studies, however, uncover the role of the Growth arrest and DNA damage-inducible protein 45 (Gadd45) family in DNA demethylation. Notably, the expression of the beta isoform responds to neuronal depolarization in the hippocampus, a brain region critical to memory processing. The function of Gadd45b as a mediator of DNA demethylation and as an immediate early gene suggests that it potentially induces DNA demethylation in memory formation. The purpose of this research proposal is to study the contribution of Gadd45b in hippocampus-dependent memory formation. A genetic approach using mice with engineered deletion of the gadd45b locus will be employed to address this question. To study the function of Gadd45b in memory formation, wildtype and mutant mice will be assessed in a behavioral battery designed to study memory and baseline behavior. Long-term memory consolidation is subserved by lasting changes in synaptic efficacy, a phenomenon known as synaptic plasticity. To study the function of Gadd45b in hippocampal long-term potentiation, hippocampal recordings from both genotypes will be taken. Further studies are designed to study the genetic targets of Gadd45b-mediated demethylation. Pharmacological induction of DNA demethylation in slices will be performed to gauge putative targets. Finally, an in vivo approach will be taken; animals will be trained in an associative memory task, and epigenetic regulation of gene expression in the hippocampus will be studied. Preliminary data indicate a suppressive function of Gadd45b in memory consolidation. This suggests DNA methylation and demethylation perform opposing functions not only in molecular processes but also in behavior. The proposed study is designed to investigate the breadth of the ethological, physiological and molecular role of DNA demethylation in further detail. PUBLIC HEALTH RELEVANCE: Burgeoning evidence points to the therapeutic benefits of inhibiting histone deacetylases in a number of neurodegenerative and cognitive disease states (21, 45, 48, 49, 67). No parallel target in the DNA methylation machinery, however, is currently known. Preliminary results from this study and further insights into the suppressive function of DNA demethylation in memory could uncover Gadd45b and other mediators of this molecular event as a second class of neuroepigenetic drug targets.
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2016 — 2018 |
Sultan, Faraz Ali |
F32Activity Code Description: To provide postdoctoral research training to individuals to broaden their scientific background and extend their potential for research in specified health-related areas. |
Striatal Modulation of Epigenetic Dna Demethylation in Reward Learning @ University of Alabama At Birmingham
Project Summary The neuroepigenetic model of learning and memory posits that a number of critical epigenetic changes in the active neuron regulate its firing properties in an acute or chronic manner and thereby provide the cell with a form of molecular memory. Driven in part by salient sensory experiences, these changes can potentially modulate behavior for the entire remaining lifespan of the animal. Because drug addiction is a state of chronic maladaptation dependent on broad molecular and physiological plasticity, the neuroepigenetic hypothesis of addiction is an emerging area of research. Psychostimulant reward in rodents has been shown to modulate the neuronal chromatin state. Dynamic DNA methylation in the nucleus accumbens, a central hub of reward processing that integrates drug-induced dopaminergic neurotransmission from the midbrain, was also shown to regulate cocaine sensitization and contextual reward memory. However, little is known about the role or mechanism of demethylation in the striatum. Recent evidence points to a sequential mechanism of demethylation involving oxidation of 5-methylcytosine and subsequent base-excision and repair to the default unmethylated base. This proposal will examine the breadth and functionality of DNA demethylation in the nucleus accumbens in reward learning and gene expression. A dissociated primary culture of striatal neurons will be used to examine the effect of dopamine on transcription and associated DNA methylation. Additionally, multiplex transcriptional control with CRISPR technologies will be used for global regulation of demethylation factors to determine the role of demethylation on learning-related gene expression and cocaine reward behavior. Finally, because the role of site-specific epigenetic dynamics in the brain is poorly understood, this study will utilize a novel fusion construct to direct single-locus demethylation in the striatum. The results of this proposal will expand the current understanding of molecular mechanisms by which drugs of abuse hijack the reward system and, in the long term, will offer novel insights into the potential effectiveness of epigenetic manipulation in addiction therapy.
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