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Protein misfolding diseases are linked by common principles of protein aggregation, plaque development and tissue damage. There is no adequate therapy for these highly debilitating diseases. This thesis aims to increase the understanding of protein misfolding diseases, which will hopefully lead to development of safe therapeutics. In protein misfolding disorders, increased levels of platelet reactivity was observed, although the underlying mechanisms are not entirely understood. Therefore, we tested platelet activating capacity of misfolded proteins. Our findings illustrate that unrelated misfolded proteins induce platelet aggregation, which is mediated by CD36 and GPIbα. These results reveal novel platelet stimulatory mechanisms. Since misfolding of cellular proteins occurs during apoptosis and infection, one intriguing option is that platelets aid in the clearance of misfolded proteins and maintain homeostasis. There are other blood-born substances that recognize misfolded proteins. Pooled healthy human intravenous immunoglobulins (IVIg) are applied in the therapy of numerous diseases. We found that IVIg binds to unrelated misfolded proteins and inhibits platelet aggregation induced by misfolded proteins. We studied whether misfolded proteins share epitopes for conformational antibodies. Antibodies raised in mice recognize misfolded proteins, although in contrast to human IgG, these antibodies are IgM, which implies a role of human antibodies in clearance and that tolerance against misfolded proteins was not broken in mice. Aggregation aspects of amyloid-β (Aβ) are crucial for the pathology of the peptide. Soluble, rather than fibrillar species are supposed to participate in the progression of Alzheimer's disease, although, the principal mechanisms are not completely understood. To investigate the relationship between amyloidogenic characteristics and platelet stimulatory capacity of Aβ, we used different Aβ fragments. We found that non-fibrillar Aβ1-42 induced platelet aggregation, though Aβ1-40 and small fragments did not stimulate platelets, which suggests that platelet stimulatory capacity resides in non-fibrillar fractions. Proteins acquire dissimilar properties after conformational changes. Previous studies suggest that native CRP does not activate endothelial cells, however its conformational variant mCRP up-regulates adhesion molecule expression, whereas others found the opposite. We illustrate that neither nCRP nor mCRP evoked pro-inflammatory changes in HUVEC and that CRP preparations have toxic properties at high doses. Modified CRP exhibited membrane binding to HUVECs, whereas no detectable binding of nCRP was observed. These results show differences between native and modified CRP in their binding capacity to diverse endothelial compartments. Endothelial disfunction is the early event of protein misfolding diseases and cancer, where levels of endothelial growth factors are increased, which accelerate angiogenesis. Therefore, suppression of tumor capillarization is beneficial. Receptor tyrosine kinase inhibitors are potent tools in tumor therapy; however, their cytotoxic effect has not been studied. We show that protein kinase inhibitors have cytotoxic effects. There is strong positive correlation between EGF receptor inhibition and cytotoxicity and negative correlation between PDGF inhibition and cytotoxicity. These data provide possible explanations for side-effects of medicines and highlight the importance of endothelial cell cytotoxicity measurements of drug-candidate compounds. |
