Alzheimer’s Disease (AD) is a progressive neurodegenerative disorder, which is characterized by cognitive deficit due to synaptic loss and neuronal death. Extracellular amyloid β plaques are one of the pathological hallmarks of AD. The autophagic lysosomal pathway is the essential mechanism to maintain cellular homeostasis by driving clearance of protein aggregates and is dysfunctional in AD. Here, we showed that inhibiting MEK/ERK signaling using a clinically available MEK1/2 inhibitor, trametinib (GSK1120212, SNR1611), induces the protection of neurons through autophagic lysosomal activation mediated by transcription factor EB (TFEB) in a model of AD. Orally administered trametinib recovered impaired neural structures, cognitive functions, and hippocampal long-term potentiation (LTP) in 5XFAD mice. Trametinib also reduced Aβ deposition via induction of autophagic lysosomal activation. RNA-sequencing analysis revealed upregulation of autophagic lysosomal genes by trametinib administration. In addition, trametinib inhibited TFEB phosphorylation at Ser142 and promoted its nuclear translocation, which in turn induced autophagic lysosomal related genes, indicating that trametinib activates the autophagic lysosomal process through TFEB activation. From these observations, we concluded that MEK inhibition provides neuronal protection from the Aβ burden by increasing autophagic lysosomal activity. Thus, MEK inhibition may be an effective therapeutic strategy for AD.

Alzheimer’s disease (AD) is a multifactorial disorder that affects cognitive functioning, behavior, and neuronal properties. The neuronal dysfunction is primarily responsible for cognitive decline in AD patients, with many causal factors including plaque accumulation of Aβ42. Neural hyperactivity induced by Aβ42 deposition causes abnormalities in neural networks, leading to alterations in synaptic activity and interneuron dysfunction. Even though neuroimaging techniques elucidated the underlying mechanism of neural connectivity, precise understanding at the cellular level is still elusive. Previous multielectrode array studies have examined the neuronal network modulation in in vitro cultures revealing the relevance of ion channels and the chemical modulators in the presence of Aβ42. In this study, we investigated neuronal connectivity and dynamic changes using a high-density multielectrode array, particularly looking at network-wide parameter changes over time. By comparing the neuronal network between normal and Aβ42treated neuronal cultures, it was possible to discover the direct pathological effect of the Aβ42 oligomer altering the network characteristics. The detrimental effects of the Aβ42 oligomer included not only a decline in spike activation but also a qualitative impairment in neural connectivity as well as a disorientation of dispersibility. As a result, this will improve our understanding of how neural networks are modified during AD progression.

Exosomes contain various intracellular biomarkers reflecting the condition of cells, organs, and subjects. Under neurodegenerative condition, they contrive in detrimental neuronal communications leading to the initiation and propagation of neurodegenerative symptoms. The exosomes in olfactory fluid are useful neurodegenerative biomarkers for the rich contents of neural biomarkers. They are also readily accessible to collect in ample amount noninvasively suggesting as a primary biomarker candidate as long as the validity of precise pathophysiological information is assured. In this study, we collected nasal lavage fluid (NLF) from 5XFAD mice from where intact exosomes are separated via microfluidic system in a high efficacy. To investigate the functional effect of the collected exosomes, they were applied to the primary cortical neurons and organotypic hippocampal slice cultures (OHSC). The neuronal activities were recorded with a high density microelectrode array system allowing observation of overall neuronal spikes and local field potential (LFP) properties. Interestingly, 5XFAD NLF exosomes increased the firing rate of neuronal spikes with augmentation of neuronal connectivity similar to the effect of pathological amyloid beta oligomer treatment. Additionally, LFP recordings in OHSC incubated with the exosomes revealed elevated local activity that was confirmed with current source density analysis. The results demonstrate that exosomes in 5XFAD NLF can effectively modify neuronal networks, which suggests it may serve as a functional biomarker for Alzheimer's disease.