Abstract:
Parkinson’s (PD) and Alzheimer’s disease (AD) are the two most common neurodegen- erative diseases and of growing importance for the rapidly aging population of indus- trialized countries. A common feature of both diseases is the progressive accumulation of proteins in insoluble aggregates, which are considered to play a fundamental role in the pathogeneses ultimately resulting in marked neuronal loss. The histopathological hallmark features of PD are called Lewy bodies (LBs) and Lewy neurites (LNs), both consisting predominantly of aggregated a-synuclein (aSyn), while neuropathological di- agnosis of AD relies on the presence of neurofibrillary tangles and senile plaques com- prised of hyperphosphorylated tau-protein or amyloid-b (Ab), respectively. However, the implicated pathological mechanisms and pathways contributing to these diseases are still not fully understood and numerous studies emphasize the need for early diagnosis before major neuron-loss occurs. Cerebrospinal fluid (CSF) is in close contact with the central nervous system and therefore a valuable source of biochemical markers reflecting pathological changes in the brain and spinal cord. For AD, three core CSF biomarkers (Ab, total-tau & phospho-tau) have been identified and extensively validated over the last years, while established biochemical markers are virtually absent for the diagnosis of PD. The aim of the thesis was to investigate proteome alteration in the presence of different types of protein aggregates and ultimately to identify novel biochemical markers of disease. Therefore, transgenic mouse models of a-synucleinopathy or b-amyloidosis, the hallmark neuropathological aspects of PD or AD, were used. These mice express mutated human genes initially identified in patients suffering from familial forms of PD or AD. The first set of experiments focused on the identification of proteins altered in the CSF of these models. This was done in an unbiased mass spectrometry-based shotgun approach, which led to the quantification of 636 and 665 CSF proteins in aged A30P- aSyn and APPPS1 cohorts, respectively. Both datasets contained transgene-related CSF protein changes that have already been associated with PD or AD, such as amy- loid precursor protein (APP)-derived peptides, TREM2, ApoE or neurofilament light (NfL), but also yielded novel insights in protein alterations, such as LAG-3, CART and lysosomal proteins. Next, both datasets generated from A30P-aSyn and APPPS1 CSF were compared and revealed a marked overlap of proteins deregulated in both models. The second part of the thesis focused on NfL, which plays a key role in axonal sta- bilization and gained attention as biomarker of axonal injury in multiple neurological disorders. A validated immunoassay was used for the quantification of NfL in CSF and plasma of A30P-aSyn, APPPS1 and a third mouse line expressing an A53T mutation in aSyn. Markedly elevated levels were found in CSF and plasma of the mice at the same age as the respective brain lesions became apparent. This demonstrates that CSF and blood NfL increases are not specific for aggregated aSyn or b-amyloid and emphasizes its potential as marker of axonal damage upon neurodegeneration. In conclusion, hundreds of proteins were quantified in the CSF of mouse models for a-synucleinopathy and b-amyloidosis. The datasets at hand provide novel and unbiased insights in pathological processes on molecular level and reveal common and distinct features of the respective pathology. The high proportion of hits related to PD, AD and other neurodegenerative diseases, as evaluated in human-based studies, substan- tiates the confidence in the high quality of the datasets and the translational value of the mouse models. Taken together, these findings provide a rich resource for the identification of novel biomarkers and their value concerning differential diagnosis.
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