The prion protein protease sensitivity, stability and seeding activity in variably protease sensitive prionopathy brain tissue suggests molecular overlaps with sporadic Creutzfeldt-Jakob disease

INTRODUCTION: Variably protease sensitive prionopathy (VPSPr) is a recently described, sporadic human prion disease that is pathologically and biochemically distinct from the currently recognised sporadic Creutzfeldt-Jakob disease (sCJD) subtypes. The defining biochemical features of the abnormal form of the prion protein (PrP(Sc)) in VPSPr are increased sensitivity to proteolysis and the presence of an N- and C-terminally cleaved ~8 kDa protease resistant PrP(Sc) (PrP(res)) fragment. The biochemical and neuropathological profile of VPSPr has been proposed to resemble either Gerstmann–Sträussler–Scheinker syndrome (GSS) or familial CJD with the PRNP-V180I mutation. However, in some cases of VPSPr two protease resistant bands have been observed in Western blots that co-migrate with those of type 2 PrP(res), suggesting that a proportion of the PrP(Sc) present in VPSPr has properties similar to those of sCJD. RESULTS: Here, we have used conformation dependent immunoassay to confirm the presence of PrP(Sc) in VPSPr that is more protease sensitive compared with sCJD. However, CDI also shows that a proportion of PrP(Sc) in VPSPr resists PK digestion of its C-terminus, distinguishing it from GSS associated with ~8 kDa PrP(res), and showing similarity to sCJD. Intensive investigation of a single VPSPr case with frozen tissue from multiple brain regions shows a broad, region-specific spectrum of protease sensitivity and differential stability of PrP(Sc) in the absence of PK treatment. Finally, using protein misfolding cyclic amplification and real-time quaking induced conversion, we show that VPSPr PrP(Sc) has the potential to seed conversion in vitro and that seeding activity is dispersed through a broad range of aggregate sizes. We further propose that seeding activity is associated with the ~19 and ~23 kDa PrP(res) rather than the ~8 kDa fragment. CONCLUSIONS: Therefore, PrP(Sc) in VPSPr is heterogeneous in terms of protease sensitivity and stability to denaturation with the chaotrope GdnHCl and includes a proportion with similar properties to that found in sCJD. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s40478-014-0152-4) contains supplementary material, which is available to authorized users.