Julia Chrupek, “Examining 17β-Estradiol-Induced Regulation of Ubiquitin Proteasome System Activity in the Dorsal Hippocampus Following Object Training in Ovariectomized Female Mice”
Mentor: Karyn Frick, Psychology, Letters & Science (College of)
Poster #108
17β-estradiol (E2) enhances long-term memory formation and the function of the dorsal hippocampus (DH). E2 regulates hippocampus-dependent memory by activating cell-signaling cascades in the DH to promote the synthesis of proteins that help structural changes at DH synapses. Protein degradation regulated by the ubiquitin proteasome system is equally relevant in memory function. This project aims to understand how E2 regulates ubiquitin proteasome system activity during the consolidation window of object memory formation. Here, female mice were ovariectomized and implanted with bilateral guide cannula targeting the DH. Mice were assigned to homecage or train groups. Trained mice were given 20 min to accumulate 30s of exploration time with two identical objects in an open field. Immediately after training, mice received an intrahippocampal infusion of vehicle or E2. DH tissue was collected 5 min, 1h, and 4h later. These time points are chosen because data indicates that these time points represent points at which protein synthesis and degradation activity peak. DH tissue has been fractionated to obtain the cytoplasmic and synaptic fractions and protein degradation activity was measured through western blot and proteasome activity assays. Here, we find that trained vehicle-treated mice decrease proteasome activity 1h later which is then reinstated 4h later. However, post-training DH infusion of E2 prevents the training-induced reinstatement of proteasome activity 4h later, suggesting E2 decreases overall proteasomal protein degradation at DH synapses at 4h following object training. Furthermore, E2 increases levels of K48 polyubiquitination in the DH cytoplasm at 4h following training, which suggests that E2-induced reduction in proteasome activity at this timepoint may lead to an accumulation of K48-tagged proteins. Future work will examine the identity and number of proteins spared for degradation at this 4h timepoint via mass spectrometry.