Mitochondrial Alterations in Neurons Derived from the Murine AppNL- F Knock-In Model of Alzheimer's Disease

Background: Alzheimer's disease (AD) research has relied on mouse models overexpressing human mutant A beta PP; however, newer generation knock-in models allow for physiological expression of amyloid-beta protein precursor (A beta PP) containing familial AD mutations where murine A beta PP is edited with a humanized amyloid-beta (A beta) sequence. The App(NL-F) mouse model has shown substantial similarities to AD brains developing late onset cognitive impairment. Objective: In this study, we aimed to characterize mature primary cortical neurons derived from homozygous App(NL-F) embryos, especially to identify early mitochondrial alterations in this model. Methods: Primary cultures of AppNL-F neurons kept in culture for 12-15 days were used to measure A beta levels, secretase activity, mitochondrial functions, mitochondrial-ER contacts, synaptic function, and cell death. Results: We detected higher levels of A beta(42) released from App(NL-F) neurons as compared to wild-type neurons. App(NL-F) neurons, also displayed an increased A beta(42)/A beta(40) ratio, similar to adult App(NL- F) mouse brain. Interestingly, we found an upregulation in mitochondrial oxygen consumption with concomitant downregulation in glycolytic reserve. Furthermore, App(NL- F) neurons were more susceptible to cell death triggered by mitochondrial electron transport chain inhibition. Juxtaposition between ER and mitochondria was found to be substantially upregulated, which may account for upregulated mitochondrial-derived ATP production. However, anterograde mitochondrial movement was severely impaired in this model along with loss in synaptic vesicle protein and impairment in pre- and post-synaptic function. Conclusion: We show that widespread mitochondrial alterations can be detected in App(NL- F) neurons in vitro, where amyloid plaque deposition does not occur, suggesting soluble and oligomeric A beta-species being responsible for these alterations.

Automated summary

This study characterizes mature primary cortical neurons derived from homozygous App(NL-F) embryos and identifies early mitochondrial alterations in this model. The results show that App(NL-F) neurons display overexpression of A beta, abnormal mitochondrial functions, and increased mitochondrial-ER contacts.