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Amyloid β

Amyloid β is a 4 kD peptide formed by the sequential cleavage of the amyloid precursor protein. It ranges from 39-43 amino acids in length and exists primarily in two isoforms, Aβ40 and Aβ42. The normal physiological function of Aβ is not well understood, but the aggregation of Aβ42 is a pathological hallmark of Alzheimer’s disease, the most prevalent neurodegenerative disease affecting the elderly. Unravelling the molecular mechanisms through which peptide aggregation is initiated and proceeds is crucial for gaining a better understanding of the disease and designing new therapeutic strategies. Within our group we have probed the mechanisms of Aβ aggregation using various in vitro and in vivo techniques (Kaminski Schierle et al., 2011; Esbjörner et al., 2014). Abeta

Amyloid proteins such as Aβ develop an intrinsic fluorescence lifetime. Research from previous group members revealed that Aβ develops an intrinsic fluorescence upon amyloid formation. State-of-the-art ab initio molecular dynamic simulations performed by our collaborators at the ICTP in Trieste and fluorescence spectroscopy techniques showed that proton transfer across the dense network of hydrogen bonds that stabilise the β sheet structure is responsible for this phenomenon, which can be used to directly probe Aβ aggregation in a label free manner (Pinotsi et al., 2016; Grisanti et al., 2017). 

Intrinsic_Fluorescence

 

Fluorescence Lifetime Imaging (FLIM)-based sensor reports directly on amyloid aggregation state in vivo. The lifetime sensor reports on Aβ aggregation by monitoring the change in fluorescence lifetime of covalently attached labels. As the partially labelled peptide self-assembles the dye molecules are brought into close proximity. The increased local concentration of the dye causes increased self-quenching, which is accompanied with a decrease in the overall fluorescence lifetime (Chen et al., 2017). The lifetime sensor is a non-invasive and has been employed to measure the aggregation propensity of Aβ and alpha-synuclein (Kaminski Schierle et al., 2011) in live cells and in Caenorhabditis elegansAbeta_worms

A unified in vitro to in vivo fluorescence lifetime screening platform yields amyloid β aggregation inhibitors. Perturbing the process of amyloid aggregation is a key strategy for the development of therapeutic agents against the onset and progression of Alzheimer’s disease. A variety of issues with current screening methods, including lack of reproducibility and high reagent consumption, have limited the efficiency of identifying small molecule inhibitors. Furthermore, the lack of methods for monitoring the anti-aggregation activity of hit compounds in live cells and whole organism models has previously restricted attempts to validate the activity of such compounds in living systems. Through the implementation of the lifetime sensor and microfluidic techniques (in collaboration with Prof. Hollfelder) we have developed an assay to screen for small molecule inhibitors. Using this assay, we have identified novel inhibitory compounds (in collaboration with Prof. Spring) which have been validated to suppress Aβ aggregation in cellular and C. elegans disease models.

Technologies

Fluorescence Spectroscopy Techniques

Ab-initio Molecular Dynamics

Fluorescence Lifetime Imaging

Microdroplet fabrication

C. elegans