Neuronal low-density lipoprotein receptor-related protein 1 binds and endocytoses prion fibrils via receptor cluster 4

Abstract

For infectious prion protein (designated PrPSc) to act as a template to convert normal cellular protein (PrPC) to its distinctive pathogenic conformation, the two forms of prion protein (PrP) must interact closely. The neuronal receptor that rapidly endocytoses PrPC is the low-density lipoprotein receptor-related protein 1 (LRP1). We show here that on sensory neurons LRP1 is also the receptor that binds and rapidly endocytoses smaller oligomeric forms of infectious prion fibrils, and recombinant PrP fibrils. Although LRP1 binds two molecules of most ligands independently to its receptor clusters 2 and 4, PrPC and PrPSc fibrils bind only to receptor cluster 4. PrPSc fibrils out-compete PrPC for internalization. When endocytosed, PrPSc fibrils are routed to lysosomes, rather than recycled to the cell surface with PrPC. Thus, although LRP1 binds both forms of PrP, it traffics them to separate fates within sensory neurons. The binding of both to ligand cluster 4 should enable genetic modification of PrP binding without disrupting other roles of LRP1 essential to neuronal viability and function, thereby enabling in vivo analysis of the role of this interaction in controlling both prion and LRP1 biology.

Alternative fates of newly formed PrPSc upon prion conversion on the plasma membrane

“…6A,E). Although our data cannot rule out the trafficking of a proportion of PrP Sc through the endolysosomal system, taken together our observations indicate that retrograde transport plays an important role in the lysosomal delivery and degradation of PrP Sc , and are consistent with previous work in sensory neurons, where purified PrP Sc was shown to accumulate in a perinuclear compartment prior to trafficking to the lysosome (Jen et al, 2010).…”

“…It is, however, important to acknowledge the possibility of cell type-specific differences in PrP Sc trafficking. For example, the endocytosis of PrP C and PrP Sc fibrils in sensory neurons appears to be dependent upon clathrin-coated pits (Jen et al, 2010;Parkyn et al, 2008). This apparent heterogeneity in PrP Sc trafficking in different cell types could also be explained by differences in the uptake of newly formed PrP Sc versus the more mature PrP Sc fibrils purified from end-stage prion-infected mouse brain that have been previously used to study endocytosis.…”

Targeting prion propagation using peptide constructs with signal sequence motifs

“…One such signal sequence is present in the Neural cell adhesion molecule-1 (NCAM1), a PrP C -interacting protein [50]. We constructed a chimeric peptide where the signal peptide NCAM1 1-19 was conjugated to mPrP [23][24][25][26][27][28] . The anti-prion effect from this construct was very potent in both RML-and 22L-infected cultures (Fig.…”

“…While membrane rafts control prion uptake [10], neuronal cell surfaces in BSE infected cattle exhibit abnormal coated pit formations associated with presence of misfolded PrP [24]. Membrane proteins interacting with PrP C / PrP Sc in both raft and non-raft membrane domains may promote their endocytosis [10,25] and possibly also their toxicity [26]. Pinocytosis of prions has also been reported [27,28].…”

Axonal and Transynaptic Spread of Prions

“…Although the best described examples are characterized by retrograde movement (e.g., neurotrophin trafficking), there are also examples of anterograde transcytosis within endosomes (e.g., L1/NgCAM, a neuron-glia cell adhesion molecule). Two extracellular receptors have been described for PrP Sc , the 37-kDa/67-kDa laminin receptor and neuronal low-density lipoprotein receptor-related protein 1 (LRP1), but neither has been implicated in transcytosis (58,59).…”