Modulation of Glycosaminoglycans Affects PrPSc Metabolism but Does Not Block PrPSc Uptake

Abstract

Mammalian prions are unconventional infectious agents composed primarily of the misfolded aggregated host prion protein PrP, termed PrP(Sc). Prions propagate by the recruitment and conformational conversion of cellular prion protein into abnormal prion aggregates on the cell surface or along the endocytic pathway. Cellular glycosaminoglycans have been implicated as the first attachment sites for prions and cofactors for cellular prion replication. Glycosaminoglycan mimetics and obstruction of glycosaminoglycan sulfation affect prion replication, but the inhibitory effects on different strains and different stages of the cell infection have not been thoroughly addressed. We examined the effects of a glycosaminoglycan mimetic and undersulfation on cellular prion protein metabolism, prion uptake, and the establishment of productive infections in L929 cells by two mouse-adapted prion strains. Surprisingly, both treatments reduced endogenous sulfated glycosaminoglycans but had divergent effects on cellular PrP levels. Chemical or genetic manipulation of glycosaminoglycans did not prevent PrP(Sc) uptake, arguing against their roles as essential prion attachment sites. However, both treatments effectively antagonized de novo prion infection independently of the prion strain and reduced PrP(Sc) formation in chronically infected cells. Our results demonstrate that sulfated glycosaminoglycans are dispensable for prion internalization but play a pivotal role in persistently maintained PrP(Sc) formation independent of the prion strain.

Importance: Recently, glycosaminoglycans (GAGs) became the focus of neurodegenerative disease research as general attachment sites for cell invasion by pathogenic protein aggregates. GAGs influence amyloid formation in vitro. GAGs are also found in intra- and extracellular amyloid deposits. In light of the essential role GAGs play in proteinopathies, understanding the effects of GAGs on protein aggregation and aggregate dissemination is crucial for therapeutic intervention. Here, we show that GAGs are dispensable for prion uptake but play essential roles in downstream infection processes. GAG mimetics also affect cellular GAG levels and localization and thus might affect prion propagation by depleting intracellular cofactor pools.