Sporadic Creutzfeldt-Jakob disease VM1: phenotypic and molecular characterization of a novel subtype of human prion disease

Abstract

The methionine (M)-valine (V) polymorphic codon 129 of the prion protein gene (PRNP) plays a central role in both susceptibility and phenotypic expression of sporadic Creutzfeldt-Jakob diseases (sCJD). Experimental transmissions of sCJD in humanized transgenic mice led to the isolation of five prion strains, named M1, M2C, M2T, V2, and V1, based on two major conformations of the pathological prion protein (PrP^Sc, type 1 and type 2), and the codon 129 genotype determining susceptibility and propagation efficiency. While the most frequent sCJD strains have been described in codon 129 homozygosis (MM1, MM2C, VV2) and heterozygosis (MV1, MV2K, and MV2C), the V1 strain has only been found in patients carrying VV. We identified six sCJD cases, 4 in Catalonia and 2 in Italy, carrying MV at PRNP codon 129 in combination with PrP^Sc type 1 and a new clinical and neuropathological profile reminiscent of the VV1 sCJD subtype rather than typical MM1/MV1. All patients had a relatively long duration (mean of 20.5 vs. 3.5 months of MM1/MV1 patients) and lacked electroencephalographic periodic sharp-wave complexes at diagnosis. Distinctive histopathological features included the spongiform change with vacuoles of larger size than those seen in sCJD MM1/MV1, the lesion profile with prominent cortical and striatal involvement, and the pattern of PrP^Sc deposition characterized by a dissociation between florid spongiform change and mild synaptic deposits associated with coarse, patch-like deposits in the cerebellar molecular layer. Western blot analysis of brain homogenates revealed a PrP^Sc type 1 profile with physicochemical properties reminiscent of the type 1 protein linked to the VV1 sCJD subtype. In summary, we have identified a new subtype of sCJD with distinctive clinicopathological features significantly overlapping with those of the VV1 subtype, possibly representing the missing evidence of V1 sCJD strain propagation in the 129MV host genotype.

Keywords: CJD; Classification; Codon 129; Histotype; PRNP; PrP; Prion disease; Prion strains.

Fig. 1

Characteristic histopathological features in the reported sCJD cases. Prominent spongiform change is observed in HE-stained sections in the frontal cortex (A1, a1 higher magnification), striatum (B1, b1 higher magnification), parahippocampal region (C1, c1 higher magnification), and occipital cortex (E1, e3 higher magnification). Ballooned neurons are observed in severely affected brain areas (c1, arrow inset). There is a striking dissociation between the marked spongiform change and the very faint deposition of pathological prion protein (PrP) by immunohistochemistry (anti-PrP antibody 12F10) in the frontal cortex (A2, a2 higher magnification), striatum (B2, b2 higher magnification), parahippocampal region (C2, c2 higher magnification) and in most areas of the occipital cortex (E2, e4 higher magnification). There are focal areas (square in E2) with coarse patchy-like PrP deposits (e1, e2). In the cerebellum (D1), spongiform change is focally prominent in the molecular layer (d1), and also here, there is a dissociation between the rather severe spongiform change and the mild PrP deposits (D2, d2 left, higher magnification). Focally, deposits appear coarser and patchy (d2, right panel). Scale bars: 10 μm: c1 inset, a2, b2, c2, e3, e4; 20 μm: a1, b1, c1, d2, e2; 50 μm: d1, e1; 500 μm: A1, A2, B1, B2; 1,2 mm: C1, C2, D1, D2, E1, E2. Panels A1, A2, B1, B2, C1, C2, E1, E2 correspond to patient 1 and panels D1, D2 to patient 2

Fig. 2

Lesion profiles of spongiform change according to sCJD subtype. Regional profiles of spongiform change severity in sCJD MM1, MV1, VM1, and VV1. In each area, the degree of spongiform change was scored as absent, 0; mild, 1; moderate, 2; severe, 3; status spongiosus 4. Fc frontal cortex, Tc Temporal cortex, Pc Parietal cortex, Oc Occipital cortex, Hipp hippocampus, ParaHipp Parahippocampal region, Str striatum, Th thalamus, Bst brainstem, Ce cerebellum

Fig. 3

Immunoblot profiles of PK-resistant PrP^Sc fragments (PrP^res) in the reported sCJD cases. A Immunoblot analysis of PK-treated frontal cortex homogenates by standard SDS-PAGE gel electrophoresis (running gel of 6.5 cm). The six reported cases (#1–6) are compared with sCJD cases of the MM1, MV1, VV1, and VV2 groups. Note the slightly faster migration of unglycosylated PrP^res in cases 1–6 and the VV1 compared to the MM1 and MV1. B Immunoblot analysis of PK-treated frontal cortex homogenates by high-resolution SDS-PAGE gel electrophoresis (running gel of 15 cm). A sCJD MM1 and a sCJD VV1 are included for comparison with cases #1–4. The higher resolution of the gel shows that unglycosylated PrP^res in VM1 and VV1 cases comprises a doublet (i.e., two bands of 21 and 20 kDa), explaining the slightly faster migration compared to MM1 and MV1 cases (they show one band of 21 kDa) C Immunoblot profile of PrP^res comprising PrP^Sc type 1 and the 12–13 kDa C-terminal fragments. Note the higher proportion (i.e., relative amount) of C-terminal fragments in VM1 and VV1 cases compared to MM1 and MV1 (see Table 3 for the quantitative data). D Comparison of the electrophoretic mobility of PK-resistant PrP^Sc after digestion at pH 6.9 or 8.0 (see * labels). There is a more consistent shift in migration (i.e., faster) when PK digestion is performed at pH 8 in MM1 and MV1 cases compared to VM1 and VV1. The immunoblots shown in A, B, and C are labeled by the N-terminal mAb 3F4. In contrast, the immunoblot in panel C is stained with the C-terminal antiserum 2301. Approximate molecular masses are in kilodaltons

Fig. 4

Evidence of CJD V2 features in the brainstem of patient #5. Small plaque-like PrP deposits in the substantia nigra (A) and midbrain periacqueductal gray (B) (immunohistochemistry for PrP with the mAb 3F4). C Western blot (mAb 3F4) shows the co-occurrence of PrP^Sc type 1 (unglycosylated band migrating at 21 kDa) and 2 (at 19 kDa) in multiple brainstem areas (MDB, midbrain; PNS, pons; ME medulla). Ctrl = control