Activation of Neuronal Degradative Pathways to Ameliorate Prion Disease

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ABSTRACT Prionopathies are rare human neurodegenerative diseases characterized by spongiform change, gliosis, and by the deposition of misfolded prion protein (PrP) aggregates inside and outside of neurons across the brain. While cellular mechanisms remain largely undefined, evidence points toward a particular vulnerability of axons to the formation of misfolded protein aggregates, and their accumulation inside lysosome-like compartments suggests defective lysosomal degradative pathways in axons. Indeed, axonal dystrophies with enlarged endosomes occur early in disease in virtually all neurodegenerative diseases including Alzheimer’s Disease and Alzheimer’s Disease related dementias, where lysosomal dysfunction is well-recognized. Compelling evidence shows that PrP aggregates impair neuronal function by driving the accumulation of organelles/vesicles and cytoskeletal elements, thus poisoning axonal transport. This application builds on our previous findings that identified an endolysosomal pathway unique to axons, that promotes the initial stages of formation of misfolded mutant PrP aggregates inside enlarged endolysosome structures that do not acidify and thus fail to degrade misfolded and aggregated mutant PrP from axons, indicating impaired lysosomal degradation. We showed that in this axonal rapid endosomal sorting and transport-dependent aggregation (ARESTA) pathway, the molecular motor kinesin- 1C (KIF5C) transports vesicles carrying pathogenic and misfolded mutant PrP into axons resulting in neurotoxic axonal dystrophies filled with PrP aggregates inside endosomes that we term ‘endoggresomes’. Reducing the function of ARESTA genes, including kinesin-1, efficiently inhibits mutant PrP endoggresome formation and restores neuronal function. Furthermore, we have identified and tested a lysosomal flux activator (LFA) small molecule that efficiently inhibits and/or clears mutant PrP aggregate-containing endoggresomes from axons, restoring neuronal function. These findings form the premise of the central hypothesis of this grant that states that targeting neurotoxic axonal aggregates by genetic inhibition of ARESTA or by pharmacologic activation of lysosomal flux, prevents the formation of misfolded PrP aggregates and/or clears them, and ameliorates disease phenotypes in cellular and mouse models of prion disease. Our main LFA candidate molecule degrades PrP aggregates in the lower nanomolar range, does not show any overt signs of toxicity in mice, and has brain penetrance. The proposed aims will test the efficacy of LFAs in cellular (neuronal) and mouse models of familial and infectious prion disease. We will also identify the mechanisms of action (MoA) of LFAs. Our findings reveal a therapeutic strategy to treat prionopathies by genetic and pharmacological activation of macroautophagy. As lysosomal clearance is a common pathway impaired in Alzheimer’s Disease and Alzheimer’s Disease related dementias, our findings are expected to also be relevant to the treatment of these disorders.