Rescuing neurons in prion disease

Longitudinal clinical, neuropsychological, and neuroimaging characterization of a kindred with a 12-octapeptide repeat insertion in PRNP: the next generation

BACKGROUND

Highly penetrant inherited mutations in the prion protein gene (PRNP) offer a window to study the pathobiology of prion disorders.

METHOD

Clinical, neuropsychological, and neuroimaging characterization of a kindred.

RESULTS

Three of four mutation carriers have progressed to a frontotemporal dementia phenotype. Declines in neuropsychological function coincided with changes in FDG-PET at the identified onset of cognitive impairment.

CONCLUSIONS AND RELEVANCE

Gene silencing treatments are on the horizon and when they become available, early detection will be crucial. Longitudinal studies involving familial mutation kindreds can offer important insights into the initial neuropsychological and neuroimaging changes necessary for early detection.

Gerstmann-Sträussler-Scheinker syndrome misdiagnosed as conversion disorder

Gerstmann-Sträussler-Scheinker syndrome (GSS) is a rare cause of genetic prion disease. Overlapping neurological, cognitive and psychiatric symptoms make GSS difficult to diagnose based on clinical features alone. We present a 40-year-old man without relevant medical or family history who developed progressive neurocognitive and behavioural symptoms over 3 years. Initial extensive diagnostic workup of his variable motor symptoms was unrevealing and he was diagnosed with conversion disorder. This diagnosis persisted for over 2 years, despite progressive neurocognitive symptoms. He eventually developed dementia and severe neurological impairment. Repeat brain MRI revealed generalised cortical volume loss, establishing the diagnosis of a rapidly progressive neurodegenerative process. He ultimately died from aspiration pneumonia at age 43. Postmortem neuropathological examination showed widespread multicentric prion protein amyloid plaques characteristic of GSS. Ultimately, genetic testing of brain tissue revealed a heterozygous A117V variant in the PNRP gene, confirming the diagnosis.

Oxytosis/Ferroptosis-(Re-) Emerging Roles for Oxidative Stress-Dependent Non-apoptotic Cell Death in Diseases of the Central Nervous System

Although nerve cell death is the hallmark of many neurological diseases, the processes underlying this death are still poorly defined. However, there is a general consensus that neuronal cell death predominantly proceeds by regulated processes. Almost 30 years ago, a cell death pathway eventually named oxytosis was described in neuronal cells that involved glutathione depletion, reactive oxygen species production, lipoxygenase activation, and calcium influx. More recently, a cell death pathway that involved many of the same steps was described in tumor cells and termed ferroptosis due to a dependence on iron. Since then there has been a great deal of discussion in the literature about whether these are two distinct pathways or cell type- and insult-dependent variations on the same pathway. In this review, we compare and contrast in detail the commonalities and distinctions between the two pathways concluding that the molecular pathways involved in the regulation of ferroptosis and oxytosis are highly similar if not identical. Thus, we suggest that oxytosis and ferroptosis should be regarded as two names for the same cell death pathway. In addition, we describe the potential physiological relevance of oxytosis/ferroptosis in multiple neurological diseases.

Vaccination strategies

Currently all prion diseases are without effective treatment and are universally fatal. It is increasingly being recognized that the pathogenesis of many neurodegenerative diseases, such as Alzheimer disease (AD), includes "prion-like" properties. Hence, any effective therapeutic intervention for prion disease could have significant implications for other neurodegenerative diseases. Conversely, therapies that are effective in AD might also be therapeutically beneficial for prion disease. AD-like prion disease has no effective therapy. However, various vaccine and immunomodulatory approaches have shown great success in animal models of AD, with numerous ongoing clinical trials of these potential immunotherapies. More limited evidence suggests that immunotherapies may be effective in prion models and in naturally occurring prion disease. In particular, experimental data suggest that mucosal vaccination against prions can be effective for protection against orally acquired prion infection. Many prion diseases, including natural sheep scrapie, bovine spongiform encephalopathy, chronic wasting disease, and variant Creutzfeldt-Jakob disease, are thought to be acquired peripherally, mainly by oral exposure. Mucosal vaccination would be most applicable to this form of transmission. In this chapter we review various immunologically based strategies which are under development for prion infection.

Common therapeutic strategies for prion and Alzheimer's diseases

A number of unexpected pathophysiological connections linking different neurodegenerative diseases have emerged over the past decade. An example is provided by prion and Alzheimer's diseases. Despite being distinct pathologies, these disorders share several neurotoxic mechanisms, including accumulation of misfolded protein isoforms, stress of the protein synthesis machinery, and activation of a neurotoxic signaling mediated by the cellular prion protein. Here, in addition to reviewing these mechanisms, we will discuss the potential therapeutic interventions for prion and Alzheimer's diseases that are arising from the comprehension of their common neurodegenerative pathways.

Efficacy and mechanism of a glycoside compound inhibiting abnormal prion protein formation in prion-infected cells: implications of interferon and phosphodiesterase 4D-interacting protein

A new type of antiprion compound, Gly-9, was found to inhibit abnormal prion protein formation in prion-infected neuroblastoma cells, in a prion strain-independent manner, when the cells were treated for more than 1 day. It reduced the intracellular prion protein level and significantly modified mRNA expression levels of genes of two types: interferon-stimulated genes were downregulated after more than 2 days of treatment, and the phosphodiesterase 4D-interacting protein gene, a gene involved in microtubule growth, was upregulated after more than 1 day of treatment. A supplement of interferon given to the cells partly restored the abnormal prion protein level but did not alter the normal prion protein level. This interferon action was independent of the Janus activated kinase-signal transducer and activator of transcription signaling pathway. Therefore, the changes in interferon-stimulated genes might be a secondary effect of Gly-9 treatment. However, gene knockdown of phosphodiesterase 4D-interacting protein restored or increased both the abnormal prion protein level and the normal prion protein level, without transcriptional alteration of the prion protein gene. It also altered the localization of abnormal prion protein accumulation in the cells, indicating that phosphodiesterase 4D-interacting protein might affect prion protein levels by altering the trafficking of prion protein-containing structures. Interferon and phosphodiesterase 4D-interacting protein had no direct mutual link, demonstrating that they regulate abnormal prion protein levels independently. Although the in vivo efficacy of Gly-9 was limited, the findings for Gly-9 provide insights into the regulation of abnormal prion protein in cells and suggest new targets for antiprion compounds.

IMPORTANCE

This report describes our study of the efficacy and potential mechanism underlying the antiprion action of a new antiprion compound with a glycoside structure in prion-infected cells, as well as the efficacy of the compound in prion-infected animals. The study revealed involvements of two factors in the compound's mechanism of action: interferon and a microtubule nucleation activator, phosphodiesterase 4D-interacting protein. In particular, phosphodiesterase 4D-interacting protein was suggested to be important in regulating the trafficking or fusion of prion protein-containing vesicles or structures in cells. The findings of the study are expected to be useful not only for the elucidation of cellular regulatory mechanisms of prion protein but also for the implication of new targets for therapeutic development.

Gene therapy for misfolding protein diseases of the central nervous system

Protein aggregation as a result of misfolding is a common theme underlying neurodegenerative diseases. Accordingly, most recent studies aim to prevent protein misfolding and/or aggregation as a strategy to treat these pathologies. For instance, state-of-the-art approaches, such as silencing protein overexpression by means of RNA interference, are being tested with positive outcomes in preclinical models of animals overexpressing the corresponding protein. Therapies designed to treat central nervous system diseases should provide accurate delivery of the therapeutic agent and long-term or chronic expression by means of a nontoxic delivery vehicle. After several years of technical advances and optimization, gene therapy emerges as a promising approach able to fulfill those requirements. In this review we will summarize the latest improvements achieved in gene therapy for central nervous system diseases associated with protein misfolding (e.g., amyotrophic lateral sclerosis, Alzheimer's, Parkinson's, Huntington's, and prion diseases), as well as the most recent approaches in this field to treat these pathologies.

Medulla oblongata transcriptome changes during presymptomatic natural scrapie and their association with prion-related lesions

BACKGROUND

The pathogenesis of natural scrapie and other prion diseases is still poorly understood. Determining the variations in the transcriptome in the early phases of the disease might clarify some of the molecular mechanisms of the prion-induced pathology and allow for the development of new biomarkers for diagnosis and therapy. This study is the first to focus on the identification of genes regulated during the preclinical phases of natural scrapie in the ovine medulla oblongata (MO) and the association of these genes with prion deposition, astrocytosis and spongiosis.

RESULTS

A custom microarray platform revealed that 86 significant probes had expression changes greater than 2-fold. From these probes, we identified 32 genes with known function; the highest number of regulated genes was included in the phosphoprotein-encoding group. Genes encoding extracellular marker proteins and those involved in the immune response and apoptosis were also differentially expressed. In addition, we investigated the relationship between the gene expression profiles and the appearance of the main scrapie-associated brain lesions. Quantitative Real-time PCR was used to validate the expression of some of the regulated genes, thus showing the reliability of the microarray hybridization technology.

CONCLUSIONS

Genes involved in protein and metal binding and oxidoreductase activity were associated with prion deposition. The expression of glial fibrillary acidic protein (GFAP) was associated with changes in the expression of genes encoding proteins with oxidoreductase and phosphatase activity, and the expression of spongiosis was related to genes encoding extracellular matrix components or transmembrane transporters. This is the first genome-wide expression study performed in naturally infected sheep with preclinical scrapie. As in previous studies, our findings confirm the close relationship between scrapie and other neurodegenerative diseases.

Could immunomodulation be used to prevent prion diseases?

All prion diseases are currently without effective treatment and are universally fatal. The underlying pathogenesis of prion diseases (prionoses) is related to an autocatalytic conformational conversion of PrP(C) (C for cellular) to a pathological and infectious conformer known as PrP(Sc) (Sc for scrapie) or PrP(Res) (Res for proteinase K resistant). The past experience with variant Creutzfeldt-Jakob disease, which originated from bovine spongiform encephalopathy, as well as the ongoing epidemic of chronic wasting disease has highlighted the necessity for effective prophylactic and/or therapeutic approaches. Human prionoses are most commonly sporadic, and hence therapy is primarily directed to stop progression; however, in animals the majority of prionoses are infectious and, as a result, the emphasis is on prevention of transmission. These infectious prionoses are most commonly acquired via the alimentary tract as a major portal of infectious agent entry, making mucosal immunization a potentially attractive method to produce a local immune response that can partially or completely prevent prion entry across the gut barrier, while at the same time producing a modulated systemic immunity that is unlikely to be associated with toxicity. A critical factor in any immunomodulatory methodology that targets a self-antigen is the need to delicately balance an effective humoral immune response with potential autoimmune inflammatory toxicity. The ongoing epidemic of chronic wasting disease affecting the USA and Korea, with the potential to spread to human populations, highlights the need for such immunomodulatory approaches.

Heat shock transcription factor 1 as a therapeutic target in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and prion-based neurodegeneration are associated with the accumulation of misfolded proteins, resulting in neuronal dysfunction and cell death. However, current treatments for these diseases predominantly address disease symptoms, rather than the underlying protein misfolding and cell death, and are not able to halt or reverse the degenerative process. Studies in cell culture, fruitfly, worm and mouse models of protein misfolding-based neurodegenerative diseases indicate that enhancing the protein-folding capacity of cells, via elevated expression of chaperone proteins, has therapeutic potential. Here, we review advances in strategies to harness the power of the natural cellular protein-folding machinery through pharmacological activation of heat shock transcription factor 1--the master activator of chaperone protein gene expression--to treat neurodegenerative diseases.