Role of misfolded prion protein in neurodegeneration

Chronic neurodegenerative diseases, such as Alzheimer’s disease, prion diseases and many others are unified by the aberrant folding of a host encoded protein to a disease-associated isoform and the predictable cell-to-cell spread of disease-associated misfolded proteins via a putative prion-like mechanism. Prion diseases, for example, are associated with the aberrant folding of host encoded prion protein (PrPC) to a disease-associated isoform, which acts as a seed for the further conversion of PrPC to misfolded protein species. The role of misfolded prion protein in neurodegeneration remains unclear. Accumulation and spread of misfolded prion protein is typically slow and progressive, correlating with neurodegeneration. A number of studies show that mice are susceptible to prion disease with characteristic hallmarks of prion pathology but in the presence of little detectable misfolded prion protein (e.g. the GSS/101LL model). In this thesis I test the hypothesis that detectable species of misfolded prion protein correlate with neurodegeneration and spreads in a predictable, progressive fashion from one anatomically distinct brain region to the next. Using the GSS/101LL model, misfolded prion protein was detected as mostly PK-sensitive isoforms (PrPsen). The progression and pathological presentation is comparable to other prion diseases with larger quantities of PK resistant prion isoforms. A highly sensitive in vitro assay system (the QuIC assay) was subsequently used to establish the extent that misfolded protein was present within the brain. Amyloidogenic prion seeds were found to be widespread throughout the brain from an early stage and spread rapidly throughout the brain. Absence of neurodegeneration in certain brain regions is not due to differing quantities of prion seeds between regions or time exposed to prion seeds, as unaffected regions are exposed to comparative quantities of prion seeds for the same time-period as regions of the brain which eventually succumb to neurodegeneration. These results indicate a clear dissociation between prion seeds and neurotoxicity. They highlight the need to understand regional host responses to prion seeds that may evoke neurodegeneration in some but resilience in others. To test this, transcriptomic analysis was carried out on brain samples from regions undergoing neurodegeneration and unaffected regions. A gene profile signature of hybrid pro-and anti-inflammatory response was observed in regions undergoing neurodegeneration. However, large cohorts of genes were down-regulated across all regions tested, including pro-inflammatory genes and a large proportion of genes involved within transcriptional and translational regulation and function. These results highlight the possible molecular pathways in response to the presence of misfolded protein. In summary, misfolded prion protein accumulates rapidly across the CNS but only specific brain regions undergo neurodegeneration. In the presence of the misfolded protein, the host elicits a robust molecular response. The additional activation of glial cells within regions undergoing neurodegeneration highlights their importance in disease. It is therefore proposed that misfolded prion protein, alone, is not sufficient to trigger neurodegeneration. This gives rise to a “multi-hit” hypothesis whereby two or more factors, for example the accumulation of misfolded protein and glial cell response, are required to trigger neurodegeneration

Human stem cell-derived astrocytes replicate human prions in a PRNP genotype-dependent manner.

Prions are infectious agents that cause neurodegenerative diseases such as Creutzfeldt-Jakob disease (CJD). The absence of a human cell culture model that replicates human prions has hampered prion disease research for decades. In this paper, we show that astrocytes derived from human induced pluripotent stem cells (iPSCs) support the replication of prions from brain samples of CJD patients. For experimental exposure of astrocytes to variant CJD (vCJD), the kinetics of prion replication occur in a prion protein codon 129 genotype-dependent manner, reflecting the genotype-dependent susceptibility to clinical vCJD found in patients. Furthermore, iPSC-derived astrocytes can replicate prions associated with the major sporadic CJD strains found in human patients. Lastly, we demonstrate the subpassage of prions from infected to naive astrocyte cultures, indicating the generation of prion infectivity in vitro. Our study addresses a long-standing gap in the repertoire of human prion disease research, providing a new in vitro system for accelerated mechanistic studies and drug discovery

Mechanisms of Cell Death in the Transmissible Spongiform Encephalopathies

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Insights into mechanisms of chronic neurodegeneration

Chronic neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and prion diseases are characterised by the accumulation of abnormal conformers of a host encoded protein in the central nervous system. The process leading to neurodegeneration is still poorly defined and thus development of early intervention strategies is challenging. Unique amongst these diseases are Transmissible Spongiform Encephalopathies (TSEs) or prion diseases, which have the ability to transmit between individuals. The infectious nature of these diseases has permitted in vivo and in vitro modelling of the time course of the disease process in a highly reproducible manner, thus early events can be defined. Recent evidence has demonstrated that the cell-to-cell spread of protein aggregates by a “prion-like mechanism” is common among the protein misfolding diseases. Thus, the TSE models may provide insights into disease mechanisms and testable hypotheses for disease intervention, applicable to a number of these chronic neurodegenerative diseases

Insights into Mechanisms of Chronic Neurodegeneration

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177Chronic neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and prion diseases are characterised by the accumulation of abnormal conformers of a host encoded protein in the central nervous system. The process leading to neurodegeneration is still poorly defined and thus development of early intervention strategies is challenging. Unique amongst these diseases are Transmissible Spongiform Encephalopathies (TSEs) or prion diseases, which have the ability to transmit between individuals. The infectious nature of these diseases has permitted in vivo and in vitro modelling of the time course of the disease process in a highly reproducible manner, thus early events can be defined. Recent evidence has demonstrated that the cell-to-cell spread of protein aggregates by a “prion-like mechanism” is common among the protein misfolding diseases. Thus, the TSE models may provide insights into disease mechanisms and testable hypotheses for disease intervention, applicable to a number of these chronic neurodegenerative diseases.https://doi.org/10.3390/ijms1701008217pubpub

Immunohistochemical Characterisation of GLUT1, MMP3 and NRF2 in Osteosarcoma.

Osteosarcoma (OSA) is an aggressive bone malignancy. Unlike many other malignancies, OSA outcomes have not improved in recent decades. One challenge to the development of better diagnostic and therapeutic methods for OSA has been the lack of well characterized experimental model systems. Spontaneous OSA in dogs provides a good model for the disease seen in people and also remains an important veterinary clinical challenge. We recently used RNA sequencing and qRT-PCR to provide a detailed molecular characterization of OSA relative to non-malignant bone in dogs. We identified differential mRNA expression of the solute carrier family 2 member 1 (SLC2A1/GLUT1), matrix metallopeptidase 3 (MMP3) and nuclear factor erythroid 2-related factor 2 (NFE2L2/NRF2) genes in canine OSA tissue in comparison to paired non-tumor tissue. Our present work characterizes protein expression of GLUT1, MMP3 and NRF2 using immunohistochemistry. As these proteins affect key processes such as Wnt activation, heme biosynthesis, glucose transport, understanding their expression and the enriched pathways and gene ontologies enables us to further understand the potential molecular pathways and mechanisms involved in OSA. This study further supports spontaneous OSA in dogs as a model system to inform the development of new methods to diagnose and treat OSA in both dogs and people