Evaluating autophagy modulation as a therapeutic strategy for Alzheimer's Disease using human neuronal culture models

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ABSTRACT To date there is no effective treatment for Alzheimer’s disease that decreases cognitive decline. Although the available drugs are effective at reducing amyloid beta, a multi-target drug approach is more likely to succeed in impacting cognitive function. One potentially complementary treatment approach is modulation of the autophagic lysosomal pathway (ALP), which is responsible for protein turnover and has been shown to regulate degradation of misfolded proteins in the CNS. Autophagy activation normally helps clear protein aggregates and damaged organelles via sequestration into autophagosomes, these vesicles eventually fuse with lysosomes, which then degrade the autophagic cargo. This pathway is more complicated in long-lived, polarized neurons, where autophagy largely initiates in the distal axon and thus autophagic lysosomal intermediates must be removed from the axon via retrograde transport to the soma where proteolytically active lysosomes reside. Disruptions in the transport or maturation of ALP intermediates has long been implicated in AD pathogenesis, as they buildup in dystrophic neurites around Aβ aggregates and likely contribute to Aβ production in AD. Preliminary data in our AD model of iPSC-derived human i3Neurons shows that ALP intermediates that accumulate in axonal swellings are cleared upon treatment with a novel compound identified in a high throughput screen as an autophagy upregulator in Hela cells. Importantly, our data shows that this compound also reduces both intracellular and extracellular Aβ42 and increases neuronal autophagy (increased LC3II/LC3I) in our AD model i3Neurons. Exciting new data from the Aldrich lab has identified lysosomal membrane protein 1 (LAMP1) as a direct target of the compound. Given these preliminary studies, we hypothesize that the novel compound, through direct interaction with LAMP1 and potential stabilization of LAMP1 interactions with retrograde machinery, increases retrograde lysosomal transport and autophagosome maturation, and thus clears axonal ALP vesicles and ultimately lowers Aβ levels. We will test this hypothesis by determining the mechanism by which the novel compound alters ALP transport and ALP composition and function, as well as identify new potential targets in neurons (by an unbiased proteomics approach). Through these studies, we will also determine if the FDA-approved drug Rapamycin can alter axonal ALP buildup or Aβ42 levels in comparison to the novel compound, thus shedding new insight into the translational potential of both drugs. Lastly, we will determine if the novel compound can reduce Aβ42 in a familial AD model and how it alters ALP in these neurons. Given the strong evidence that this compound can modulate axonal ALP transport, Aβ42 and neuronal autophagy, the results from the proposed experiments could be relevant to therapeutic approaches in other neurodegenerative diseases that have ALP dysfunction as a contributing pathological feature, such as Parkinson’s disease, amyotrophic lateral sclerosis, and frontotemporal dementia.