Impaired transmissibility of atypical prions from genetic CJDG114V

Objective

To describe the clinicopathologic, molecular, and transmissible characteristics of genetic prion disease in a young man carrying the PRNP-G114V variant.

Methods

We performed genetic, histologic, and molecular studies, combined with in vivo transmission studies and in vitro replication studies, to characterize this genetic prion disease.

Results

A 24-year-old American man of Polish descent developed progressive dementia, aphasia, and ataxia, leading to his death 5 years later. Histologic features included widespread spongiform degeneration, gliosis, and infrequent PrP plaque-like deposits within the cerebellum and putamen, best classifying this as a Creutzfeldt-Jakob disease (CJD) subtype. Molecular typing of proteinase K-resistant PrP (resPrP^Sc) revealed a mixture of type 1 (∼21 kDa) and type 2 (∼19 kDa) conformations with only 2, rather than the usual 3, PrP^Sc glycoforms. Brain homogenates from the proband failed to transmit prion disease to transgenic Tg(HuPrP) mice that overexpress human PrP and are typically susceptible to sporadic and genetic forms of CJD. When subjected to protein misfolding cyclic amplification, the PrP^Sc type 2 (∼19 kDa) was selectively amplified.

Conclusions

The features of genetic CJD^G114V suggest that residue 114 within the highly conserved palindromic region (113-AGAAAAGA-120) plays an important role in prion conformation and propagation.

Metabolic processing of the amyloid precursor protein -- new pieces of the Alzheimer's puzzle

Alzheimer's disease (AD) continues to be a daunting and costly challenge for research, medicine, and society. AD pathologies point toward the involvement of metabolic fragments of the amyloid precursor protein (APP) in the pathogenesis of the disease. Through sequential enzymatic processing, APP is metabolized into several potential polypeptides, including the toxic amyloid-β (Aβ) peptide. Though great progress has been made in understanding the mechanism of conventional metabolic processing of APP to yield products such as Aβ, AD remains unpreventable and irreversible at any stage. Recent new reports provide data that add both complexity to the issue and new hope for potential avenues of therapeutic intervention. Novel metabolic processing events such as delta-secretase and eta-secretase have been revealed that generate previously uncharacterized APP metabolic fragments with the potential to participate in AD pathogenesis. Additionally, enzymes known to act in other metabolic pathways, such as meprin β, have been found to cleave APP to yield products known to participate in AD pathologies. This review provides an overview of current knowledge of conventional and novel APP processing.

Increased expression of endogenous biotin, but not BDNF, in telencephalic song regions during zebra finch vocal learning

Brain-derived neurotrophic factor (BDNF) is thought to regulate multiple aspects of brain development and neural plasticity in vertebrates. We have examined BDNF expression in two telencephalic nuclei (RA and HVC) in the zebra finch brain that control song learning by juvenile males and the production of already-learned song by adults. Using two different antibody-labeling techniques (avidin-biotin complex and horseradish peroxidase), we were unable to detect BDNF-like immunoreactivity in RA of juvenile or adult birds. BDNF-like immunoreactive labeling of somata was detected in HVC, but the density of labeled cells was not different between juvenile and adult birds. Immunocytochemical findings were confirmed by RT-PCR for BDNF mRNA. Thus, in contrast to a previous report (Akutagawa and Konishi, Proc. Natl. Acad. Sci. USA 95 (1998) 11429-11434), we did not observe elevated levels of BDNF immunoreactivity in RA and HVC of juvenile birds that were learning to sing. However, RA and HVC of juvenile birds were found to express elevated levels of endogenous biotin (as detected by avidin peroxidase), suggesting a possible role for biotin-regulated mechanisms in songbird vocal learning.