Thursday, April 3, 2025
4/3/2025
Synaptic activity-driven Abeta generation and aggregation - PROJECT SUMMARY/ABSTRACT: Numerous biochemical and biophysical studies have demonstrated that amyloid-β (Aβ) aggregates into toxic oligomers and fibrils when the concentration of the peptide is elevated and the pH is low (Paredes-Rosan et al. 2019; Zhao et al. 2018). Aβ aggregates can be detected neuron throughout the endo-lysosomal pathway (Brewer et al. 2020) where pH ranges from 4.5-6.5 which are prime conditions for Aβ to aggregate. However, what physiological processes influence Aβ aggregation in vivo within this compartment remain unknown. Elevated synaptic activity increases the formation of Aβ within endosomes before it is secreted into the brain interstitial fluid (ISF) (Cirrito et al. 2005, 2008). We hypothesize that elevated synaptic activity not only causes formation of Aβ, but also directly drives formation and release of Aβ aggregates. We propose that low, physiological synaptic activity causes release of Aβ monomer, whereas high bursts of aberrant activity reach a threshold when the combination of low pH endosomes with sufficiently high Aβ levels induces aggregation. We have developed a novel electrochemical micro-immunoelectrode (MIE) technology to measure Aβ40, Aβ42, or Aβ oligomer levels every 60 seconds in an awake, moving mouse for up to 6 hours in order to tightly link the amount of synaptic activity with the level and conformation of Aβ. Furthermore, we will determine if glutamatergic or GABAergic neurons are primarily responsible for producing Aβ and if one type of neuron is more prone to generate aggregates. All studies will use the APPNLF/NLF knock-in mouse model of amyloidosis in order to preserve normal expression patterns of APP which is critical for these types of studies. Our preliminary data demonstrates the tight link between synaptic activity and Aβ generation, as well as the characterization and specificity of the MIE technology for real-time detection of Aβ levels and aggregates. Using the MIE, preliminary data suggest that only a slight increase in neuronal activity produces Aβ monomer but that higher levels of activity induce secretion of Aβ aggregates. Also, our data suggests that excitatory neurons produce more Aβ than inhibitory neurons. While we propose that synaptic activity is a potent regulator of Aβ oligomer and fibril formation, we acknowledge that there are several means that will induce and influence aggregation, such as chaperones like apoE, and that synaptic activity is just mechanism that can generate these toxic species. Aim 1 will determine the threshold of synaptic activity that causes Aβ to aggregate into soluble oligomers then get released into the brain ISF. Aim 2 will determine whether excitatory or inhibitory neurons release Aβ monomer or Aβ aggregates, and if that differs between wake and sleep states, since inhibitory tone is much greater during sleep. Aim 3 will determine if chronically modulating activity of excitatory or inhibitory neurons within the hippocampus alters development of Aβ plaques. How synaptic activity impacts Aβ species and aggregation state is unclear. The scientific premise of this proposal is to understand the mechanisms that contribute to Aβ generation and aggregation in vivo. The FDA recently approved a monoclonal antibody, Lecanemab, that targets Aβ oligomers and finally has clinical benefits to patients. Understanding the source of oligomers could inform on risk factors that influence aggregation and lead to new therapies targeting oligomers in the future or identifying novel biomarkers for disease development.
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