Luminescent molecular recognition of pathognomonic and aging associated protein aggregates

University dissertation from Linköping : Linköping University Electronic Press

Abstract: Various protein inclusions have been recognized to be associated with aging and pathogenic conditions, such as in Alzheimer’s disease, Parkinson’s disease, Type 2 diabetes, and the prionoses Creutzfeldt-Jakob disease, Chronic wasting disease (CWD), and Mad cow disease. The causative transition of protein aggregation is the alteration in the conformation of the protein that renders the protein susceptible towards self-assembly. Variations in the physico-chemical ultrastructure of the protein deposit, i.e. the conformation and the chemical nature of the fibril constituent protein monomers, translate into specific structure-property phenotype, hence clinicopathology. Upon transmission and/or propagation this phenomenon gives rise to specific protein aggregate strains. Today most potential treatments of the protein conformational diseases have been a huge failure, effectively due to late diagnosis and subsequent therapeutic intervention. An imperative for efficient treatment is early detection and accurate identification for proper clinical diagnosis.The purpose of the studies in this thesis was to develop highly sensitive methods for detection and discrimination of age- and disease associated protein deposits both for in vitro and ex vivo utilization.Herein we have shown that, for in vitro usage, Nile red will bind to amyloid-like protein aggregates derived from a plethora of precursor proteins. It was also found that the fluorescence was insensitive to acidic assay conditions in contrast to the standard in vitro dye Thioflavin T (ThT). Further, Nile red was shown to discriminate between conformational isoforms thus enabling conformational typing of amyloid structures.For the development of ex vivo detection methods we employed luminescent conjugated oligothiophenes (LCOs) and utilized the structure-conformation induced optical properties of this class of protein aggregate ligands. The heptameric oligothiophene h-FTAA was successfully used to detect, with high sensitivity, protein deposits from various systemic amyloidoses (ATTR, AA, AL-λ/κ, and the local amyloidosis AIAPP) derived from biopsy specimens. Also aging-associated protein deposits were detected which was found promising for early detection of potentially pathogenic protein inclusions. Further, LCO staining of tissue sections was found compatible with immunolabeling enabling subtyping of involved proteins. Early detection of amyloidosis also requires relatively non-invasive methods, why h-FTAA staining was directed towards fine-needle-aspirated (FNA) abdominal fat tissue smears. Staining of protein deposits and detection with high sensitivity was also found in the fat tissue smears.In addition to the relatively rare prionoses it has lately been shown that Alzheimer’s, Parkinson’s diseases share similar properties as the prion pathologies. Hence the urgent need for ligands that will recognize specific disease specific strain aggregates. Using an established murine model for prion strain propagation we were able to discriminate two different prion strains, murine adapted Sheep Scrapie (mSS) and murine adapted Chronic wasting disease (mCWD) from each other by using multimodal fluorescence microscopy entailing emission/excitation spectral imaging and fluorescent lifetime imaging (FLIM).In conclusion we have shown that the LCOs will recognize protein aggregates with high sensitivity and selectivity. In addition we have shown that the LCOs detect protein aggregates that Congo red failed to recognize thus allowing potentially early diagnosis. Last, we show that the LCOs will recognize and discriminate between different protein aggregate strains which potentially will allow disease specific therapeutic targeting.

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