Allelic origin of protease-sensitive and protease-resistant prion protein isoforms in Gerstmann-Sträussler-Scheinker disease with the P102L mutation.

Salvatore Monaco,Sergio Ferrari,Bernardino Ghetti,Matteo Gelati,Pedro Piccardo,Gianluigi Zanusso,Alessia Farinazzo,Michele Fiorini,Noriyuki Nishida

doi:10.1371/journal.pone.0032382

Abstract

Gerstmann-Sträussler-Scheinker (GSS) disease is a dominantly inherited prion disease associated with point mutations in the Prion Protein gene. The most frequent mutation associated with GSS involves a proline-to-leucine substitution at residue 102 of the prion protein, and is characterized by marked variability at clinical, pathological and molecular levels. Previous investigations of GSS P102L have shown that disease-associated pathological prion protein, or PrPSc, consists of two main conformers, which under exogenous proteolysis generates a core fragment of 21 kDa and an internal fragment of 8 kDa. Both conformers are detected in subjects with spongiform degeneration, whereas only the 8 kDa fragment is recovered in cases lacking spongiosis. Several studies have reported an exclusive derivation of protease-resistant PrPSc isoforms from the mutated allele; however, more recently, the propagation of protease-resistant wild-type PrPSc has been described. Here we analyze the molecular and pathological phenotype of six GSS P102L cases characterized by the presence of 21 and 8 kDa PrP fragments and two subjects with only the 8 kDa PrP fragment. Using sensitive protein separation techniques and Western blots with antibodies differentially recognizing wild-type and mutant PrP we observed a range of PrPSc allelic conformers, either resistant or sensitive to protease treatment in all investigated subjects. Additionally, tissue deposition of protease-sensitive wild-type PrPSc molecules was seen by conventional PrP immunohistochemistry and paraffin-embedded tissue blot. Our findings enlarge the spectrum of conformational allelic PrPSc quasispecies propagating in GSS P102L thus providing a molecular support to the spectrum of disease phenotypes, and, in addition, impact the diagnostic role of PrP immunohistochemistry in prion diseases.

Highlights

Prion diseases are fatal neurodegenerative disorders of humans and animals, occurring as idiopathic, genetic, and iatrogenic conditions [1]
PrPSc conformers are classified on the basis of the glycosylation status and the molecular mass of their protease-resistant unglycosylated backbone, or PrP27-30 core fragment, migrating at 21 kDa in type 1 PrPSc and at 19 kDa in type 2 PrPSc [10], controversial results have been obtained by different authors who have proposed the classification of PrP27–30 into four types [11]
The results reported here show that the heterogeneity of PrPSc species associated with GSS P102L mutation is wider than previously reported and is characterized by different degree of involvement of PrPM and PrPWt (Fig. 7)

Summary

Introduction

Prion diseases are fatal neurodegenerative disorders of humans and animals, occurring as idiopathic, genetic, and iatrogenic conditions [1]. Human prion disorders include Creutzfeldt-Jakob disease (CJD), variant Creutzfeldt-Jakob disease, kuru, fatal familial insomnia, sporadic fatal insomnia, and GerstmannStraussler-Scheinker (GSS) disease [2]. In these disorders, the cellular prion protein, or PrPC, is converted to a protease-resistant conformer with abnormal sedimentation properties, or PrPSc [3]. Several prion strains, either in naturally occurring disorders or in experimentally-induced conditions, harbour protease-sensitive PrPSc (sPrPSc) quasispecies, in association or not with protease-resistant PrPSc (rPrPSc) [12,13,14]; importantly, sPrPSc molecules cause neurological dysfunction [15,16]. The neuropathological hallmarks of prion diseases are prion protein (PrP) deposition, spongiosis, astrogliosis, and neuronal death [17]; it is still unknown which molecular forms of PrPSc are detected by immunohistochemistry (IHC)

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Results

Conclusion