In Vitro Seeding Activity of Glycoform-Deficient Prions from Variably Protease-Sensitive Prionopathy and Familial CJD Associated with PrP Mutation.

Both sporadic variably protease-sensitive prionopathy (VPSPr) and familial Creutzfeldt-Jakob disease linked to the prion protein (PrP) V180I mutation (fCJD) have been found to share a unique pathological prion protein (PrP) that lacks the protease-resistant PrP glycosylated at residue 181 because two of four PrP glycoforms are apparently not converted into the PrP from their cellular PrP (PrP). To investigate the seeding activity of these unique PrP molecules, we conducted in vitro prion conversion experiments using serial protein misfolding cyclic amplification (sPMCA) and real-time quaking-induced conversion (RT-QuIC) assays with different PrP substrates. We observed that the seeding of PrP from VPSPr or fCJD in the sPMCA reaction containing normal human or humanized transgenic (Tg) mouse brain homogenates generated PrP molecules that unexpectedly exhibited a dominant diglycosylated PrP isoform along with PrP monoglycosylated at residue 181. The efficiency of PrP amplification was significantly higher in non-CJDMM than in non-CJDVV human brain homogenate, whereas it was higher in normal TgVV than in TgMM mouse brain homogenate. PrP from the mixture of normal TgMM and Tg mouse brain expressing PrP mutation (Tg180) but not TgV180I alone was converted into PrP by seeding with the VPSPr or fCJD. The RT-QuIC seeding activity of PrP from VPSPr and fCJD was significantly lower than that of sCJD. Our results suggest that the formation of glycoform-selective prions may be associated with an unidentified factor in the affected brain and the glycoform-deficiency of PrP does not affect the glycoforms of in vitro newly amplified PrP.