Human prion diseases and neurodegeneration

Mouse models of chronic wasting disease: A review

Animal models are essential tools for investigating and understanding complex prion diseases like chronic wasting disease (CWD), an infectious prion disease of cervids (elk, deer, moose, and reindeer). Over the past several decades, numerous mouse models have been generated to aid in the advancement of CWD knowledge and comprehension. These models have facilitated the investigation of pathogenesis, transmission, and potential therapies for CWD. Findings have impacted CWD management and disease outcomes, though much remains unknown, and a cure has yet to be discovered. Studying wildlife for CWD effects is singularly difficult due to the long incubation time, subtle clinical signs at early stages, lack of convenient in-the-field live testing methods, and lack of reproducibility of a controlled laboratory setting. Mouse models in many cases is the first step to understanding the mechanisms of disease in a shortened time frame. Here, we provide a comprehensive review of studies with mouse models in CWD research. We begin by reviewing studies that examined the use of mouse models for bioassays for tissues, bodily fluids, and excreta that spread disease, then address routes of infectivity and infectious load. Next, we delve into studies of genetic factors that influence protein structure. We then move on to immune factors, possible transmission through environmental contamination, and species barriers and differing prion strains. We conclude with studies that make use of cervidized mouse models in the search for therapies for CWD.

The Conspicuous Link between Ear, Brain and Heart-Could Neurotrophin-Treatment of Age-Related Hearing Loss Help Prevent Alzheimer's Disease and Associated Amyloid Cardiomyopathy?

Alzheimer's disease (AD), the most common cause of dementia in the elderly, is a neurodegenerative disorder associated with neurovascular dysfunction and cognitive decline. While the deposition of amyloid β peptide (Aβ) and the formation of neurofibrillary tangles (NFTs) are the pathological hallmarks of AD-affected brains, the majority of cases exhibits a combination of comorbidities that ultimately lead to multi-organ failure. Of particular interest, it can be demonstrated that Aβ pathology is present in the hearts of patients with AD, while the formation of NFT in the auditory system can be detected much earlier than the onset of symptoms. Progressive hearing impairment may beget social isolation and accelerate cognitive decline and increase the risk of developing dementia. The current review discusses the concept of a brain-ear-heart axis by which Aβ and NFT inhibition could be achieved through targeted supplementation of neurotrophic factors to the cochlea and the brain. Such amyloid inhibition might also indirectly affect amyloid accumulation in the heart, thus reducing the risk of developing AD-associated amyloid cardiomyopathy and cardiovascular disease.

A structural overview of the vertebrate prion proteins

Among the diseases caused by protein misfolding is the family associated with the prion protein (PrP). This is a small extracellular membrane-anchored molecule of yet unknown function. Understanding how PrP folds both into its cellular and pathological forms is thought to be crucial for explaining protein misfolding in general and the specific role of PrP in disease. Since the first structure determination, an increasing number of structural studies of PrP have become available, showing that the protein is formed by a flexible N-terminal region and a highly conserved globular C-terminal domain. We review here the current knowledge on PrP structure. We focus on vertebrate PrPs and analyse in detail the similarities and the differences among the coordinates of the C-terminal domain of PrP from different species, in search for understanding the mechanism of disease-causing mutations and the molecular bases of species barrier.

Fibrillogenesis of tau: insights from tau missense mutations in FTDP-17

Frontotemporal dementia and Parkinsonism linked to chromosome 17 (FTDP-17) is a neurological disorder associated with tau pathology.Tau deposits in FTDP-17 brains consist of polymerized filaments of hyperphosphorylated tau, the morphology of which is determined by the nature of the tau gene mutation observed in each case. A number of mutations associated with FTDP-17 have been identified in the 5' splice site of exon 10 and in exons 9-13 of the tau gene. The exon 10 5' splice site mutations disrupt alternative splicing and thus alter the ratio of 4R and 3R Tau isoforms. The majority of Tau missense mutations decrease its ability to bind tubulin and promote microtubule assembly. The extent of reduction varies depending on the site and nature of the mutation. Some Tau missense mutations also have a direct effect on the rate and the extent of tau filament formation. In the presence of polymerization-inducing agents such as heparin or arachidonic acid, mutant tau forms polymers more efficiently than wild type tau in vitro. Tau mutations affect polymerization at both nucleation and elongation phases. One mutation (R406W) is also known to alter the susceptibility of tau to phosphorylation. Expression of mutant tau in cultured cells changes the cytoskeletal integrity of CHO and COS-7 cells, but none of the tau transfected cells display tau filament inclusions. These findings suggest involvement of at least two mechanisms in the pathogenesis of FTDP-17.

Vertical transmission of bovine spongiform encephalopathy prions evaluated in a transgenic mouse model

In this work we show evidence of mother-to-offspring transmission in a transgenic mouse line expressing bovine PrP (boTg) experimentally infected by intracerebral administration of bovine spongiform encephalopathy (BSE) prions. PrP(res) was detected in brains of newborns from infected mothers only when mating was allowed near to the clinical stage of disease, when brain PrP(res) deposition could be detected by Western blot analysis. Attempts to detect infectivity in milk after intracerebral inoculation in boTg mice were unsuccessful, suggesting the involvement of other tissues as carriers of prion dissemination. The results shown here prove the ability of BSE prions to spread centrifugally from the central nervous system to peripheral tissues and to offspring in a mouse model. Also, these results may complement previous epidemiological data supporting the occurrence of vertical BSE transmission in cattle.

Effects of intermediates on aggregation of native bovine serum albumin

Protein aggregation has been recognized to be a pathological indicator for several fatal diseases, such as Alzheimer's disease, transmissible spongiform encephalopathies, Creutzfeldt-Jacob disease, etc. Aggregation usually involves conformational changes of proteins that have acquired an intermediate beta-structure-rich conformation and can occur even at low protein concentration. Recent work in our laboratory has shown that bovine serum albumin (BSA), even at low-concentration, exhibits self-association properties related to conformational changes, so providing a very convenient model system to study this class of problems. Here we report data (obtained by different experimental techniques) on a mixture of BSA in native and intermediate (beta-structure-rich) form. Results show that the interaction between the two species is responsible for a decrease in the thermodynamic stability of the solution. This occurs without requiring noticeable conformational changes of the native protein. Results presented here can provide new insight on the "protein only" hypothesis proposed for the formation of plaques involved in several neurodegenerative diseases.

A Huntington disease-like neurodegenerative disorder maps to chromosome 20p

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor disturbance, cognitive loss, and psychiatric manifestations. The disease is associated with a CAG trinucleotide-repeat expansion in the Huntington gene (IT15) on chromosome 4p16.3. One family with a history of HD was referred to us initially for predictive testing using linkage analysis. However, the chromosome 4p region was completely excluded by polymorphic markers, and later no CAG-repeat expansion in the HD gene was detected. To map the disease trait segregating in this family, whole-genome screening with highly polymorphic dinucleotide-, trinucleotide-, and tetranucleotide-repeat DNA markers was performed. A positive LOD score of 3.01 was obtained for the marker D20S482 on chromosome 20p, by two-point LOD-score analysis with the MLINK program. Haplotype analysis indicated that the gene responsible for the disease is likely located in a 2.7-cM region between the markers D20S193 and D20S895. Candidate genes from the mapping region were screened for mutations.

Astrocyte-specific expression of hamster prion protein (PrP) renders PrP knockout mice susceptible to hamster scrapie

Transmissible spongiform encephalopathies are characterized by spongiosis, astrocytosis and accumulation of PrPSc, an isoform of the normal host protein PrPC. The exact cell types responsible for agent propagation and pathogenesis are still uncertain. To determine the possible role of astrocytes, we generated mice devoid of murine PrP but expressing hamster PrP transgenes driven by the astrocyte-specific GFAP promoter. After inoculation with hamster scrapie, these mice accumulated infectivity and PrPSc to high levels, developed severe disease after 227 +/- 5 days and died 7 +/- 4 days later. Therefore, astrocytes could play an important role in scrapie pathogenesis, possibly by an indirect toxic effect on neurons. Interestingly, mice expressing the same transgenes but also endogenous murine PrP genes propagated infectivity without developing disease.

Scrapie infection alters the membrane and synaptic properties of mouse hippocampal CA1 pyramidal neurones

1. Electrophysiological recordings using conventional intracellular and extracellular techniques were made from the CA1 region of the hippocampus of ME7 scrapie-infected mice in a brain slice preparation at specific stages during the incubation period of the disease and compared with data obtained from age-matched control animals. 2. Extracellular field EPSP recordings in the stratum radiatum showed a gradual increase in the effective stimulus threshold and a reduction in amplitude of the response 5 months after inoculation with scrapie. Terminal animals showed a complete loss of the field EPSP. 3. Intracellular recordings from CA1 pyramidal cells of scrapie-infected animals after 5 months showed that the Schaffer collateral-evoked EPSP was attenuated, the effective stimulus threshold was increased and the rise time was slower in slices from scrapie-infected mice than in age-matched control mice. Inhibitory potentials evoked by the same stimulus also appeared weaker in scrapie-infected mice at this time. 4. To determine if the mechanisms of transmitter release during low-frequency stimulation of the Schaffer collaterals were altered in scrapie-infected mice, paired-pulse experiments were performed, but failed to show any differences between cells from scrapie-infected and control animals. 5. Pyramidal cells from scrapie-infected mice showed depolarized resting potentials and an increased membrane resistance compared with age-matched control cells. 6. The majority of scrapie-infected cells were spontaneously active, showing both single spike and bursting activity. The observed bursting activity was abolished and the spontaneous discharge rate of infected cells was markedly reduced by removing the CA3 area from the slice. 7. The action potential of cells from scrapie-infected mice showed a faster falling phase and larger amplitude fast and medium after-hyperpolarizations (AHPs) than age-matched control cells. In response to depolarizing current pulses cells from infected tissue showed a loss of early spike frequency adaptation. 8. Morphological observations of biocytin-labelled neurones confirmed our recordings were from pyramidal cells and showed that CA1 cells from scrapie-infected mice after 5 months showed a marked loss of dendritic spines and an abnormal dendritic morphology that included the appearance of vacuolar swellings. 9. The data show that membrane and synaptic abnormalities of the CA1 pyramidal neurones develop around 5 months after intracerebral infection of the mouse hippocampus with ME7 scrapie.