A role for mitochondrial AMPK signaling in neurons

Project Summary An early hallmark of Alzheimer’s Disease (AD) is a loss of neuronal connectivity reflected by decreased dendritic spine densities in the hippocampus and cortex. Coinciding with this synaptic loss, both human Alzheimer’s Disease patients and Alzheimer’s Disease animal models display a fragmented mitochondrial phenotype. Our recent work demonstrated that Alzheimer’s induced mitochondrial fragmentation occurs as a result of the overactivation of the CAMKK2-AMPK-MFF pathway. Excitingly, preventing AMPK-mediated activation of MFF not only blocked mitochondrial fragmentation but also ablated spine loss arguing for a casual link between mitochondrial loss and spine maintenance. Thus, the goal of this proposal is to determine how AMPK governs mitochondrial morphology and function to coordinate spine maintenance in vivo. This topic is especially relevant as repeated activation of AMPK, by drugs such as metformin, is being considered as an intervention for both normal aging and Alzheimer’s Disease. Interestingly, up to twelve unique AMPK complexes can exists, and recent work has shown that different complexes can have distinct activation kinetics, substrates and subcellular localizations including at the mitochondrial surface (mitoAMPK). Our overall hypotheses are that prolonged activation of mitoAMPK drives dendritic mitochondrial fragmentation and removal inducing spine loss, and that targeted ablation of AMPK at the mitochondrial surface is sufficient to rescue Aβ42-induced spine loss. The focus of Aim 1 is to determine the molecular composition and cellular dynamics of mitoAMPK in wildtype and AD neurons by using biochemical, Crispr/Cas9 knock-in and kinetic proteomics techniques. Aim 2 will establish the role of mitoAMPK activity for dendritic structure and function by using in vivo 2-photon microscopy and electrophysiology to determine mitoAMPK’s impact on dendrite branching, spine dynamics, calcium handling and neuronal activity in both wildtype and AD mouse models. Aim 3 will interrogate the cellular consequences of long-term AMPK activation in hippocampal neurons. While monitoring mitochondria and dendrite structure and function, we will genetically or pharmacologically activate AMPK in both wildtype and AD mouse models. The proposed work will provide a greater understanding of the mechanisms responsible for local AMPK activity in neurons, and potentially identify a distinct AMPK complex targetable in neurodegeneration.