Intracellular trafficking SNARE protein, syntaxin-6, modifies prion cellular phenotypes and risk of disease development in vivo.

Increased expression of syntaxin-6, a SNARE protein involved in intracellular protein trafficking, is a proposed genetic risk mechanism for sporadic prion disease and progressive supranuclear palsy, as well as being implicated in Alzheimer's disease. However, no study has validated its functional role in prion disease, its mechanism of action nor explored the disease stage at which it is acting. Here, we show that syntaxin-6 knockdown in cellular models increases cell-associated infectivity, whilst overexpression produces the opposite effect. This observation is broadly consistent across multiple cell types and prion strains. Furthermore, syntaxin-6 knockdown leads to an accumulation of perinuclear disease-related PrP, consistent with a trafficking mechanism, and alters the morphology of disease-related PrP. We demonstrate that syntaxin-6 knockdown reduces the secretion of prions from infected cells, which provides a mechanism for the prion-related cellular phenotypes observed. Complementary in vivo studies showed that syntaxin-6 influences early stages of prion disease in experimental mice, increasing transmission risk after inoculation with low prion doses. Conversely, syntaxin-6 does not affect prion propagation kinetics or toxicity during established disease. Taken together, our studies firmly establish syntaxin-6 as a modifier of prion pathogenesis with a role in prion trafficking and export. Our findings further suggest that syntaxin-6 modifies the risk of the establishment of disease in line with its genetic association in humans. Thus, this work provides important insights into the role of a pleiotropic prion/prion-like modifier, grounded in human genetics evidence, which may have wider relevance to other neurodegenerative diseases.