It is widely accepted that long-term synaptic plasticity, which underlies long-term memory, depends on new gene transcription as well as new protein synthesis. Emerging evidence suggests that protein degradation also plays an important role. A major pathway for regulated protein degradation is the ubiquitin-proteasome pathway (UPP). Although less well characterized, the proteasome is also known to have other non-traditional roles in which it influences transcription. Several recent studies suggest that the proteasome enhances targeting of transcriptional co-activators to promoters of actively transcribed genes through epigenetic mechanisms, such as histone acetylation and methylation. Chemically induced long-term potentiation (cLTP) is a widely used model of long-term synaptic plasticity in the hippocampus. This application provides evidence that prior to cLTP induction, inhibition of the proteasome prevents upregulation of brain-derived neurotrophic factor (BDNF), a gene essential for synaptic plasticity and memory. BDNF mRNA is transcribed from several different promoters to produce a variety of transcript variants. This application describes a role of the proteasome in upregulation of transcriptional-promoting epigenetic modifications at specific BDNF promoters that drive the expression of BDNF transcripts after cLTP induction. The experimental goals of this project are to identify specific roles of the proteasome in histone acetylation, methylation, and ubiquitination at BDNF promoters and to investigate the interaction between the proteasome and transcription-modifying complexes, such as histone acetyltransferases and methyltransferases, in the nucleus after cLTP induction. Different proteasome inhibitors will be used to inhibit total or nuclear proteasome in acute hippocampal slices and chromatin immunoprecipitation studies will be performed to identify changes in epigenetic modifications at BDNF promoters in cLTP as compared to control. To identify nuclear binding partners of the proteasome, co- immunoprecipitation and mass spectrometry studies will be carried out after cLTP induction. Disregulation of both the UPP and epigenetics are associated with cognitive impairments in neurodegenerative diseases such as Alzheimer's. This project will help shed light on the proteasome-dependent epigenetic mechanisms behind gene expression in synaptic plasticity and will help find novel therapeutic targets and biomarkers for ameliorating memory impairment in neurodegenerative diseases.
Several diseases of the brain, such as Alzheimer's, Parkinson's, and Huntington's characterized by learning and memory impairments, have been linked to disruptions of a machinery, called the proteasome, that degrades proteins in the nerve cell. This project is aimed at understanding how the proteasome influences molecules that help change connections between nerve cells, called synapses. Because changes in synapses are important for memory formation, this research will help identify therapeutic targets for memory impairments that occur in many diseases of the brain.