| dc.description.abstract | Prion diseases (prionoses) are a group of fatal, neurodegenerative disorders, which affect humans and certain mammalian species. Underlaying the prion disease pathogenesis is accumulation of the disease-specific PrPSc (Sc-scrapie). PrPSc is an infectious and toxic conformer of the cellular prion protein PrPC. Key features of PrPSc include proteolytic resistance, susceptibility to oligomerization, and ability to self-replicate by binding to PrPC and altering its 𝛼�����-helix-rich conformation into the image of its own secondary structure, dominated by increased β-sheet content. Excessive accumulation of PrPSc on the cell surface and within the endolysosomal compartment leads to neurodegeneration and ultimately death of PrPSc-replicating neurons. Appearance and accumulation of PrPSc, followed by neuronal demise activates neuroinflammatory response from microglia and astrocytes, which contributes importantly to neurodegeneration in prionoses. Apolipoprotein (apo) E is a lipid transporting protein, which is implicated in the pathogenesis of several neurodegenerative disorders including Alzheimer’s disease, primary tauopathies, 𝛼�����-synucleinopathy, and age-related macular degeneration. In these entities the APOE allele polymorphism is a well-recognized factor affecting the risk of disease occurrence and (or) the rate of pathology progression. Three apoE isoforms encoded by respective APOE alleles 𝜀�����2, 𝜀�����3, and 𝜀�����4, differentially engage several biological mechanisms, which are critically involved in neurodegeneration. These include binding apoE receptors, influencing formation and trafficking of endolysosomal vesicles, synaptic plasticity and synaptic protein expression, modulating neuronal transcriptome, interacting with disease-specific misfolded proteins and regulating neuroinflammatory response. Although apoE has been established as a critical element in several neurodegenerative diseases its role in the pathobiology of prion diseases remains unknown. To elucidate contribution of apoE to prion pathogenesis a series of experiments were conducted in B6 wild type mice and apoE transgenic model mice, which were infected with 22L mouse adapted scrapie strain. B622L mice showed significantly increased brain apoE level compared to the B6 control mice and this increase was associated with marked cell-type shift in the apoE expression. B622L mice featured reduced apoE expression in reactive astrocytes, which under physiological conditions produce apoE-containing lipoparticles, while de-repression of the apoE expression was found in reactive microglia, which in resting (or surveilling) state do not express apoE. In the succeeding experiment Apoe-/- mice were infected with the 22L prion strain, resulting in significantly reduced disease incubation time, accelerated rate of neurological symptoms progression, and increased burden of brain pathology compared to B622L mice. Apoe-/-22L mice featured exacerbated neuroinflammatory response produced by reactive astrocytes and neurodegenerative phenotype microglia (MGnD), with the later additionally showing reduced ability to phagocyte damaged neurons and PrPSc. In the subsequent study mice with bi-allelic, targeted replacement (TR) of the murine Apoe gene for human APOE 𝜀�����2, 𝜀�����3, and 𝜀�����4 alleles were infected with prions. 𝜀�����4/𝜀�����422L mice showed the shortest disease incubation time, the fastest tempo of neurological symptoms progression, and the highest level of prion-specific neuropathological metrics. 𝜀�����2/𝜀�����222L mice were significantly less affected than 𝜀�����4/𝜀�����422L mice but nonetheless performed significantly worse compared to 𝜀�����3/𝜀�����322L mice. Two 𝜀�����4-allele attributable disease mechanisms, which explain exacerbated disease course in 𝜀�����4/𝜀�����422L mice were identified: increased conversion and accumulation of PrPSc and worsened prion-associated neuroinflammation. It also was determined that 𝜀�����2 allele independently increases prion-related inflammatory response, rendering the disease outcome worse relative to the 𝜀�����3 allele. Collectively, the work presented in this dissertation demonstrates involvement of apoE in several mechanisms related to prion pathology including conversion and accumulation of PrPSc, regulating inflammatory response of astrocytes and microglia, and modulating microglia phagocytosis of neuronal remnants and PrPSc. Furthermore, findings from APOE-TR mice suggests both 𝜀�����4 and 𝜀�����2 alleles can be disadvantageous determinants in prion pathology. | pl_PL |
