Protease-sensitive prion species in neoplastic spleens of prion-infected mice with uncoupling of PrPSc and prion infectivity

Abstract

Prion diseases are fatal neurodegenerative disorders. An important step in disease pathophysiology is the conversion of cellular prion protein (PrPC) to disease-associated misfolded conformers (PrPSc). These misfolded PrP variants are a common component of prion infectivity and are detectable in diseased brain and lymphoreticular organs such as spleen. In the latter, PrPSc is thought to replicate mainly in follicular dendritic cells within spleen follicles. Although the presence of PrPSc is a hallmark for prion disease and serves as a main diagnostic criterion, in certain instances the amount of PrPSc does not correlate well with neurotoxicity or prion infectivity. Therefore, it has been proposed that prions might be a mixture of different conformers and aggregates with differing properties. This study investigated the impact of disruption of spleen architecture by neoplasia on the abundance of different PrP species in spleens of prion-infected mice. Although follicular integrity was completely disturbed, titres of prion infectivity in neoplastic spleens were not significantly altered, yet no protease-resistant PrPSc was detectable. Instead, unique protease-sensitive prion species could be detected in neoplastic spleens. These results indicate the dissociation of PrPSc and prion infectivity and showed the presence of non-PrPSc PrP species in spleen with divergent biochemical properties that become apparent after tissue architecture disruption.