Restoration of Neuronal Metabolism and Memory in Alzheimer's Disease by Reprogramming the Exosomal microRNA Network.

Historically the development of amyloid-β plaques and tau neurofibrillary tangles have been used as the hallmarks of Alzheimer's disease (AD). However, there is increasing evidence suggests that these pathological hallmarks are secondary to deeper metabolic defect in the brain. AD is progressively being recognized as a metabolic synaptic disorder characterized by insulin resistance, impaired cellular energy homeostasis, mitochondrial dysfunction, and synaptic degeneration. Synaptic plasticity is closely linked to the insulin-sensitive system of glucose utilization, mitochondrial activity, and local protein synthesis that render the synapses highly sensitive to the malfunction of the metabolic system. Recent discoveries highlight the important role of exosomes in mediating communication between neural cells by transferring regulatory miRNAs across neuronal networks. Exosomal miRNAs regulate insulin signaling, synaptic gene expression, mitochondrial function, and neuroinflammation. In AD, exosomal miRNA profiles are significantly altered, with enrichment of miR-29, miR-34a, miR-146a, and miR-21, alongside depletion of synapse-supporting miR-132. These changes contribute to insulin resistance, impaired glucose transporter trafficking, dendritic spine destabilization, and reduced expression of synaptic proteins such as PSD-95 and synaptophysin, ultimately leading to cognitive decline. Importantly, neuron-derived exosomes can cross the blood-brain barrier, making their miRNA cargo promising biomarkers and therapeutic targets for early AD diagnosis and precision treatment.