A-beta/APP signaling impairs CaMKII-dependent synaptic plasticity after ischemic brain injury

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Project Summary Long-term potentiation (LTP) and other forms of synaptic plasticity are cellular correlates of learning and memory. The Ca2+/CaM-dependent protein kinase II (CaMKII) facilitates LTP by translocating to stimulated synapses and phosphorylating local targets. LTP is impaired in global cerebral ischemia (GCI) and Alzheimer’s disease (AD), two neurological disorders that demand effective treatment. GCI has acute and chronic effects: initially, it triggers excitotoxic neuronal cell death; long-term, it impairs LTP within the surviving neurons. Together, the neuronal loss and compromised synaptic plasticity underlie cognitive decline observed after ischemia, and an ideal therapy would target both. My proposed research aims to determine whether GCI-induced LTP impairments utilize signaling pathways previously implicated in AD. The amyloid-β precursor protein (APP) is proteolytically cleaved to form amyloid-β peptide1-42 (Aβ). Exogenous application of Aβ impairs LTP and CaMKII synaptic enrichment in hippocampal neurons. How does Aβ signal to disrupt CaMKII? Recent published work suggests that APP acts not only upstream of Aβ (as the Aβ precursor) but also downstream (as the Aβ receptor): Aβ association with APP was found to be required for LTP and memory impairments, as APP knockout (KO) prevented exogenous Aβ-induced deficits. While increased APP and Aβ are well-studied in AD pathology, a potential function for Aβ/APP signaling in ischemia has not been fully elucidated. Studies from our lab indicate that GCI- and Aβ-induced reductions in LTP utilize a common mechanism through CaMKII. To test the hypothesis that APP mediates the GCI-induced LTP impairment by disrupting CaMKII signaling, I will test three specific aims: i) whether APP mediates Aβ-induced impairments in LTP and CaMKII synaptic translocation, ii) APP mediates GCI-induced LTP impairments, and iii) whether the therapeutic window for protecting synaptic plasticity after GCI shows an extended range (days), even if the window for protecting neuronal cell death is much shorter (hours). This project will utilize acute hippocampal slices and cultures hippocampal neurons for biochemistry, slice electrophysiology, and live confocal microscopy. Imaging will employ FingR intrabodies that are designed to label endogenous proteins, including CaMKIIα and post-synaptic markers. The mouse in vivo model of global cerebral ischemia (GCI) closely mimics the most prevalent human condition (cardiac arrest). These optimized approaches will allow me to investigate whether potential cross-talk between APP/Aβ and CaMKII underlies impaired LTP following ischemic brain injury. Results from this project will improve our understanding of neurological disorders that utilize Aβ/APP-dependent mechanisms to impair synaptic plasticity.