HECTD2 is associated with susceptibility to mouse and human prion disease

Abstract

Prion diseases are fatal transmissible neurodegenerative disorders, which include Scrapie, Bovine Spongiform Encephalopathy (BSE), Creutzfeldt-Jakob Disease (CJD), and kuru. They are characterised by a prolonged clinically silent incubation period, variation in which is determined by many factors, including genetic background. We have used a heterogeneous stock of mice to identify Hectd2, an E3 ubiquitin ligase, as a quantitative trait gene for prion disease incubation time in mice. Further, we report an association between HECTD2 haplotypes and susceptibility to the acquired human prion diseases, vCJD and kuru. We report a genotype-associated differential expression of Hectd2 mRNA in mouse brains and human lymphocytes and a significant up-regulation of transcript in mice at the terminal stage of prion disease. Although the substrate of HECTD2 is unknown, these data highlight the importance of proteosome-directed protein degradation in neurodegeneration. This is the first demonstration of a mouse quantitative trait gene that also influences susceptibility to human prion diseases. Characterisation of such genes is key to understanding human risk and the molecular basis of incubation periods.

Figure 1. Quantitative RT-PCR of Hectd2I.

cDNA was prepared from whole brains of uninfected 8 week old male mice or mice at the terminal stages of disease following intracerebral inoculation with Chandler/RML mouse-adapted scrapie prions. All samples were duplexed for Hectd2 and GAPDH fluorogenic probes and run in triplicate with n = 6 for each mouse strain/group. Mean±s.e.m. Hectd2 mRNA expression level is expressed in arbitrary units as normalised by the quantity of GAPDH (y-axis). A, Inbred strains are grouped according to the major strain distribution pattern seen in Hectd2 (Group A = A, AKR, BALB; Group B = C3H, C57, CBA, DBA). Expression was ×2.4 greater in group A than group B (P = 2.85×10⁻⁹, unpaired t-test). B, Comparison of Hectd2 expression in normal and RML prion-infected C57BL6 mouse brains. Expression was ×5.0 greater in the brains of prion-infected mice, (P = 2.66×10⁻⁸, unpaired t-test). C, Expression of HECTD2 in cDNA prepared from lymphocytes of human blood donors (n = 140). Samples were duplexed for HECTD2 and β-actin fluorogenic probes and run four times. Mean±s.e.m. HECTD2 mRNA expression level is expressed in arbitrary units as normalised by the quantity of β-actin (y-axis). Data are grouped according to genotypes at rs12249854 as determined from genomic DNA. Expression was ×2.3 greater in the heterozygotes (TA) than for the major allele homozygotes (TT) (P = 0.0008 Mann-Whitney test).