The failure of anti-amyloid-β immunotherapies to more than slightly slow the progression of Alzheimer's disease has not much dented the amyloid cascade hypothesis, just clarified that amyloid-β becomes unimportant to disease progression once at the stage of sizable tau aggregration, neuroinflammation, and loss of cognitive function. The consensus continues to be that amyloid aggregation is the originating cause of Alzheimer's disease, the pathology that sets the stage for what comes later. That hypothesis will be confirmed or disproven in the years ahead as anti-amyloid-β immunotherapies are deployed in ever earlier stages of the condition. There may be other approaches to obtaining useful data, however. Here, researchers note that an existing drug, levetiracetam, reduces amyloid-β production in the brain, which will in turn reduce misfolding and aggregation of amyloid-β. This suggests the potential for a trial to directly assess its ability to delay or prevent Alzheimer's disease.
Amyloid-β (Aβ) peptides are a defining feature of Alzheimer's disease (AD). These peptides are produced by the proteolytic processing of the amyloid precursor protein (APP), which can occur through the synaptic vesicle (SV) cycle. However, how amyloidogenic APP processing alters SV composition and presynaptic function is poorly understood. Using App knock-in mouse models of amyloid pathology, we found that proteins with impaired degradation accumulate at presynaptic sites together with Aβ42 in the SV lumen.
Levetiracetam (Lev) is a US Food and Drug Administration-approved antiepileptic that targets SVs and has shown therapeutic potential to reduce AD phenotypes through an undefined mechanism. We found that Lev lowers Aβ42 levels by reducing amyloidogenic APP processing in an SV-dependent manner. Lev modified SV cycling and increased APP cell surface expression, which promoted its preferential processing through the nonamyloidogenic pathway.
Stable isotope labeling combined with mass spectrometry confirmed that Lev prevents Aβ42 production in vivo. In transgenic mice with aggressive amyloid pathology, electrophysiology and immunofluorescence confirmed that Lev restores SV cycling abnormalities and reduces synapse loss. Brains from patients with Down syndrome also displayed presynaptic protein accumulation before the occurrence of substantial Aβ pathology, supporting the hypothesis that protein accumulation is a relevant pathogenic event in amyloid pathology. Together, these findings highlight the potential to prevent Aβ pathology before irreversible damage occurs.
Link: https://doi.org/10.1126/scitranslmed.adp3984
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