Neuronal AMP-activated protein kinase hyper-activation induces synaptic loss by an autophagy-mediated process.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by synaptic loss that leads to the development of cognitive deficits. Synapses are neuronal structures that play a crucial role in memory formation and are known to consume most of the energy used in the brain. Interestingly, AMP-activated protein kinase (AMPK), the main intracellular energy sensor, is hyper-activated in degenerating neurons in several neurodegenerative diseases, including AD. In this context, we asked whether AMPK hyper-activation could influence synapses' integrity and function. AMPK hyper-activation in differentiated primary neurons led to a time-dependent decrease in pre- and post-synaptic markers, which was accompanied by a reduction in synapses number and a loss of neuronal networks functionality. The loss of post-synaptic proteins was mediated by an AMPK-regulated autophagy-dependent pathway. Finally, this process was also observed in vivo, where AMPK hyper-activation primed synaptic loss. Overall, our data demonstrate that during energetic stress condition, AMPK might play a fundamental role in the maintenance of synaptic integrity, at least in part through the regulation of autophagy. Thus, AMPK might represent a potential link between energetic failure and synaptic integrity in neurodegenerative conditions such as AD.

AMP-Activated Protein Kinase Is Essential for the Maintenance of Energy Levels during Synaptic Activation.

Although the brain accounts for only 2% of the total body mass, it consumes the most energy. Neuronal metabolism is tightly controlled, but it remains poorly understood how neurons meet their energy demands to sustain synaptic transmission. Here we provide evidence that AMP-activated protein kinase (AMPK) is pivotal to sustain neuronal energy levels upon synaptic activation by adapting the rate of glycolysis and mitochondrial respiration. Furthermore, this metabolic plasticity is required for the expression of immediate-early genes, synaptic plasticity, and memory formation. Important in this context, in neurodegenerative disorders such as Alzheimer disease, dysregulation of AMPK impairs the metabolic response to synaptic activation and processes that are central to neuronal plasticity. Altogether, our data provide proof of concept that AMPK is an essential player in the regulation of neuroenergetic metabolic plasticity induced in response to synaptic activation and that its deregulation might lead to cognitive impairments.