Multiplexed protein analysis in neurodegenerative diseases

QC 2024-05-07

Abstract

Proteins are essential biomolecules that perform a vast array of functions within the human body. The abundance of proteins within cells, tissues, and bodily fluids is dy- namic and can be associated with different physiological and disease states. As such, studying proteins and protein profiles in health and disease can provide insights into the mechanisms and pathological processes associated with different diseases as well as different disease stages. Furthermore, protein biomarkers identified in research have the potential to aid clinical diagnostics and therapeutic development, leading to im- provement of patient care and outcomes. 

The majority of the work included in this thesis, revolves around the analysis of protein profiles in the context of neurodegenerative diseases, with the main focus on demen- tias. In the studies, preselected protein panels were measured in cerebrospinal fluid (CSF) samples employing the multiplexed high-throughput antibody-based suspension bead array technology. 

In paper I, the potential of using protein pairs to reflect Alzheimer’s disease pathology and cognitive decline was explored, with the aim to identify biomarkers which could possibly aid in monitoring the efficacy of disease-modifying treatments in clinical tri- als. A number of protein pairs was identified providing significantly higher performance compared to single proteins, likely due to adjustment for inter-individual variability in general protein levels. 

Paper II built upon the findings from paper I, expanding the investigation of CSF protein patterns across multiple neurodegenerative diseases. This study demonstrated that the performance of single brain-derived proteins in disease prediction is affected by variability in general protein levels, accounting for 70 % of protein variability be- tween individuals irrespective of disease. Adjusting for the general protein levels directly or through combining proteins in pairs improved the performance of proteins as biomarkers. However, the majority of the proteins with altered levels in CSF were not specific for a single disease, suggesting their association to processes common for the diseases, and highlighting the need for disease comparisons in biomarker studies. 

While paper I and II established the presence of variability in general CSF levels of brain-derived proteins between individuals, the factors underlying this variability re- mained unclear. Paper III explored whether the levels of proteins in CSF are influenced by CSF volume in a cohort of healthy individuals. The findings revealed negative correlations of brain-derived proteins with brain ventricular volumes, sug- gesting a dilution effect of proteins in CSF potentially contributing to differences in CSF levels of brain-derived proteins between individuals. In summary, these three Abstract i Abstract studies shed light on CSF protein patterns and their relevance in neurodegenerative diseases, pushing the boundaries of our current knowledge a step forward. 

A specific group of proteins present in the human body; the antibodies, are involved in the defense mechanisms against pathogens. These large molecules are produced by our immune system upon infection (or vaccination), and provide protection against future reinfections. However, the amount of antibodies produced and their protective effect through virus neutralization varies between individuals. Paper IV included in this thesis involved the development of a cell-free and virus-free bead-based assay for assessment of the neutralization capability of antibodies produced against the SARS- COV-2 virus. While this study can be considered an outlier in the theme of this thesis, it represents our contribution to the global research efforts which necessitated other activities to be put on hold in favor of endeavors in response to the rise of the Covid- 19 pandemic. 

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