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Co-Assembly and ion-channel formation of truncated Aβ isoforms in Alzheimer’s disease

  • Supervisor: Dr John Viles
  • Deadline: 31st January 2018
  • Funding: RCUK (UK students only)

About the Project

Background and Aims: Alzheimer’s disease (AD) has a profound impact on healthy ageing. It is characterized by the misfolding and self-assembly of a small (~40 residue) neuro-toxic amyloid-β-peptide (Aβ), which forms fibrous plaques within the brain. Toxic Aβ42 oligomers can form ion-channel pores which span the cellular membrane and are central to the amyloid cascade hypothesis of Alzheimer’s disease. At the synapse various forms of Aβ are released; with both N- and C-terminal truncations. N-terminally truncated forms, Aβ(11-40/42), constitute 20% of plaque load (Naslund et al 1994). We have recently shown that some Aβ isoforms will co-fibrilze nucleating the fibrillation of each other, while other isoforms combinations such as Aβ40 with Aβ42 will not, but rather frustrate fibre formation. (Barret and Viles: JBC 2015; Angewandte Chemie 2017). Recent progress has been made in identifying quite profound structural differences in the fibres of Aβ40 and Aβ42; these differences are caused by a salt bridge between Lys28 and the C-terminal carboxylate at Ala42. Furthermore, we have recently shown Aβ42 oligomers are capable of forming ion channels, but Aβ40 oligomers do not (Bode and Viles JBC 2017). 

You will probe the structural reasons behind co-fibrilization and ion-channel properties of Aβ42. You will use a large tool-kit of biophysical and electro-physiological techniques to probe the impact of the mixture of various lengths of Aβ on the kinetics of fibrilization, ion-channels formation and cellular membrane interactions. 

Objectives, Methodology and Training:
YEAR ONE. Kinetics of mixed Aβ fibre formation: The PhD student will use and gain expertise in a range of biophysical and spectroscopic techniques (TEM; NMR; AFM; CD and IR) to probe the kinetics of assembly in physiologically relevant Aβ mixtures. We are interested in how the C-terminal carboxylate in Aβ42 is directing Aβ42 assembly in amyloid fibre mixtures. You will building on our recent publication in Angewandte Chemie-2017. You will use ThT fluorescence and NMR to monitor fibre formation kinetics. Understanding the interplay between the Aβ42/40 isoforms is fundamental to the process by which Aβ triggers AD pathology. 

YEAR TWO. Ion-channel formation of N-terminally truncated Aβ: The mechanism by which Aβ might disrupt cellular homeostasis is believed to involve the formation of ion-channels (Bode and Viles JBC 2017). The PhD student will determine if physiologically relevant N-terminally truncated Aβ isoforms are capable of form ion-channels. Residues 1-10 might be important for directing positive ions to the channel with a number of acid sidechains in the N-terminus of Aβ. You will use excised membrane patched from HEK cells and investigate if oligomers of the of Aβ(11-40) and Aβ(11-42) are capable of forming cellular ion channels. Furthermore we have recently shown that Aβ42-oligomers are capable of forming ion channels while Aβ40-oligomers do not (Bode and Viles JBC 2017). The structural explanation for this is not understood. Aβ ion-channels may be crucial to neuro-toxicity and represent a promising therapeutic target for AD. 

YEAR THREE. Imaging lipid-bilayer/Aβ interactions by AFM and TEM-tomography: The structure of Aβ42 oligomers capable of forming ion channels will be probed by 3D single particale anylaysis using negitive-stain and cryo-EM. Furthormore oligomer interaction with the lipid bilayer will be probed by AFM and TEM-tomgraphy of lipid vesicals. We have promosing preliminary data and are set to take advantage of a newly purchased cryo-TEM within SBCS.

Training Support and Environment: The lab is currently well supported with BBSRC Project Grant (£433,000). I have an outstanding track record in PhD student supervision, with a 100% completion rate. I presently have a post-doc with considerable expertise to support the new PhD student. The Lab is well equipped to carry out the biophysical measurements outlined in this proposal with optical spectrometers (CD, fluorescence, UV-Vis, FTIR), and two microplate fluorescence well plate readers for fibre kinetic measurements. While within SBCS we have excellent TEM facilities, AFM and high-field 600 MHz NMR. A BBSRC funded cryo-TEM will arrive early in 2018 and will add to our capabilities.

References: (Barret and Viles: Angewandte Chemie 2017); (Bode and Viles JBC 2017); (Barret and Viles: JBC 2015) and also Naslund, J.; et al (1994) PNAS 91: 8378.  

Funding

The studentship will cover tuition fees and provide an annual tax-free maintenance allowance for 42 months at Research Councils UK rates (£16,553 in 2017/18).

Eligibility and Applying

This is an EPSRC funded studentship and only eligible students should apply. Find out more about EPSRC eligibility.

Applications are invited from outstanding candidates with or expecting to receive a first or upper-second class honours degree in an area relevant to the project. An masters degree is desirable, but not essential.

Informal enquiries can be sent to Dr John Viles (j.viles@qmul.ac.uk). For formal applications, please submit an online application before the stated deadline.

Apply Online

References

  • N‐Terminally Truncated Amyloid‐β (11‐40/42) Co‐Fibrillises with its Full‐Length Counterpart. JD Barritt, ND Younan JH Viles* (2017) Angewandte Chemie 129, 9948 –9951 
  • Ion Channel Formation by Amyloid-β42 Oligomers but not Amyloid-β40 in Cellular Membranes. 
    DC Bode, MD Baker, JH Viles (2017) J of Biol Chem 292, 1404-1413 
  • Amyloid-β (11-40/42) from Alzheimer's Disease Binds Copper2+ with a Femtomolar Affinity and Influences Fibre Assembly. J D Barritt, JH. Viles* (2015) J of Biol Chem, 290, 27791-27802 
  • Naslund, J.; et al (1994) PNAS 91: 8378.
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