Selective Vulnerability of Cholinergic Neurons in Alzheimer’s Disease - PROJECT SUMMARY / ABSTRACT Alzheimer's disease (AD) is a neurodegenerative condition that progressively destroys memory and cognition, exacting devastating personal and public health costs. Recent evidence indicates that soluble oligomeric Aβ42 (oAβ42) begins accumulating in the human brain one to two decades before clinical symptoms of AD emerge. Multiple studies suggest that elevated levels of soluble oAβ42, rather than insoluble Aβ plaques, drive the selective degeneration of vulnerable neurons and serve as the strongest predictors of cognitive decline in AD. Basal forebrain cholinergic neurons (BFCNs) are particularly vulnerable to functional modulation by oAβ42, and their dysfunction has been implicated in memory loss and cognitive impairment. In septo-hippocampal pathways, α7-containing nicotinic acetylcholine receptors mediate synaptic transmission and neuronal intrinsic excitability. Most α7-nAChR contain only α7 subunits. However, α7β2-containing nAChRs, are predominantly expressed on BFCNs. Our published research has demonstrated (i) α7β2-nAChRs are selectively sensitive to functional modulation by oAβ42, (ii) oAβ42/α7β2-nAChRs interactions lead to BFCN dysfunction by altering neuronal intrinsic excitability, and (iii) genetic deletion of the β2 nAChR subunit improves memory deficits observed in the APP/PS1 mouse model of AD. In this proposal, we provide direct evidence that oAβ42/α7β2- nAChRs interactions enhance BFCN excitability by altering large-conductance (BK-type), small-conductance (SK-type), and KCNQ/Kv7 (M-type) K+ channel subtypes on BFCNs. We will expand our published work to demonstrate how oAβ42/α7β2-nAChR interactions drive BFCN dysfunction by altering BK-, SK-, and M-type K+ activity in distinct forebrain cholinergic sub-regions. In Specific Aim 1, we will use whole-cell patch-clamp recordings to determine how α7β2-nAChRs contribute to oAβ42-induced alterations in BK-, SK-, and M-type K+ channel function and BFCN hyperexcitability by using our newly-developed α7β2-nAChR-selective antagonist, conotoxin α-CtxPnIC[L10Y]. Using next-generation RNA sequencing (RNAseq), we will investigate specific gene ontologies and associated signaling pathways implicated in (i) K+ channel functional regulation, (ii) neuronal intrinsic excitability, and (iii) AD-related neuronal dysfunction. In Specific Aim 2, we will use two experimentally- tractable mouse models of AD to determine whether knockdown of α7β2-nAChRs ameliorates AD-related spatial-reference and working memory deficits. Long-term AAV-mediated delivery of small inhibitory RNAs (siRNAs), targeting α7- and/or β2-nAChR subunit genes will be delivered in both young and mature adult male and female mice to capture disease progression and sex-dependent effects. We will perform ex vivo patch clamp recordings from the same animals to correlate the behavioral outcomes with BK-, SK-, and M-type K+ channel activity and BFCN intrinsic excitability. By integrating multidisciplinary approaches, we aim to identify novel drug targets for developing effective, long-term pharmacotherapies to prevent BFCN dysfunction and memory loss in AD, either by disrupting oAβ42/α7β2-nAChR interactions or by modulating the function of specific K+ channels.
